DCM - Report
Deep Chlorophyll Maximum 1996
Cruise Report
Dr. M.J.W. Veldhuis, Dr. Ir.
H.G. Fransz, Drs. T.F. de Bruin
The Deep Chlorophyll Maximum of the oceans:
persistence of the plankton community,
its biodiversity and its implication for carbon cycling
Hr. Ms. Tydeman
22 July to 31 August 1996
Contents
- Preface
- Introduction
- Summary review of the cruise
- Preliminary conclusions
- Scientific reports
- Technical highlights Lorendz
Boom, Eduard Bos and Ruud Groenewegen
- Appendix
- List of sampling dates, Julian day number and differences in local
and GMT
- Cruise plot with cruise track with Julian day indication (00:00)
- Cruise plot with cruise track of main stations with Julian day
indication (00:00)
- Station list, number, time and type of activity
- List of cast numbers and activities at main stations
- List of XBT files, position and dates
PREFACE
This cruise report
is a summary of a wealth of data and information collected during a nearly 7 weeks
cruise in the Atlantic Ocean. Although it may look like a long period the
cruise it self is only a brief moment of true seagoing activity. The whole
preparation of the DCM cruise took over 2 years. The idea of this project was
even much older. It also will take several of the participants probably an
other 2 years to analyse all collected samples and data.
The scientific
reports and data incorporated in this cruise report should be considered as
preliminary data and there will be an ongoing process of quality control. These
data will be the backbone of the final data report. We would urge each
participant to check and recheck your data before submitting them. Comments
concerning the bottle files should be addressed to Margriet Hiehle.
On a regular base we
will inquire about the status of your personal data set and the type of data
you want to submit to the data report. The final version of the data report
should be ready by the end of 1997.
When submitting data
to the data report please contact Margriet Hiehle beforehand to make sure that
the data are in the proper format. Essentially, the variables must be
accompanied by the station, cast and bottle number. So, the fourth parameter is
the variable of interest. e.g.
station cast bottle chlorophyll
100 01 24 0.2
Within the next months there
will be several small workshops with participants presenting data but there
will be also emphasis on the interdisciplinary character of this cruise.
As far as the Dutch participants
are concerned a hot-line is present. An email message for all can be mailed
using the connection DCM@NIOZ.nl. A list of separate addresses is
given in the Appendix.
Acknowledgements
We acknowledge a very good
co-operation with the commander KTZ L. ter Haar and the crew of the
Hydrographical Service of the Dutch Royal Navy. The service of the navy
included a mail dropping by aircraft on 19/8. Other social highlights are
described in the weekly reports (Appendix). The cruise and scientific program
were supported by the Netherlands Geosciences Foundation (GOA) with financial
aid from the Netherlands Organisation for Scientific Research (NWO) and
additional funding of the Netherlands Institute for Sea Research (NIOZ).
INTRODUCTION
(H.G. Fransz and M.J.W.
Veldhuis)
Scientific objectives of the
Deep Chlorophyll Maximum Study
The cruise with RV Tydeman
was devoted to study permanently stratified plankton systems in the
(sub)tropical ocean, which are characterised by a deep chlorophyll peak between
80 and 150 m. To minimise lateral effects by horizontal transport of nutrients
and organic matter from river outflow and upwelling regions, stations were
selected in the middle of the North Atlantic Ocean between the continents of
America and Africa. (5 - 35° N and 50 - 15° W). Here the vertical distributions
of light and nutrients control the abundance and growth of autotrophic algae in
the thermically stratified water column. This phytoplankton is numerically
dominated by the prokaryotic picoplankters Synechococcus spp. and
Prochlorococcus spp., which are smaller than 2 µm. The productivity of the 100
to 150 m deep euphotic zone can be high, because a high
heterotrophic/autotrophic biomass ratio induces a rapid regeneration of
nutrients and inorganic carbon. Primary grazers are mainly micro-organisms such
as heterotrophic nannoflagellates and ciliates, which feed on the small algae
and on bacteria. Heterotrophic bacteria can outnumber the autotrophic algae,
because their number is related to the substrate pools of dissolved and
particulate dead organic matter. These DOC and detritus pools reach equilibrium
at a concentration, where the rate of their production (proportional to algal
biomass) equals their mineralisation and sinking rate (proportional to the
concentration and weight of POC and detritus). At a relatively low value of the
weight-specific loss rates, the equilibrium concentration of these carbon pools
and their load of bacteria can be high. The bacterial productivity is
proportional to the mineralisation rate, which in a steady state can never be
higher than the rate of primary production. Hence the ratio in turnover rate of
bacteria and autotrophs tends to be reciprocally proportional to their biomass
ratio.
In a microbial food web
carbon and nutrients circulate between inorganic pools, autotrophs, bacteria,
DOC and detritus, and the grazing microzooplankton. In (sub)tropical ecosystems
changes in biomass tend to be small, but fluxes of carbon and nutrients between
the various components occur to be high. Bacteria can stimulate primary
production by mineralisation of DOC and detritus, but they also compete with
the primary producers for nutrients. The microzooplankton reduce the number of
algae and bacteria, but enhance their growth by regeneration of nutrients. This
component, however, induces instability because it can graze down the algae to
low levels and cause predator-prey oscillations.
The nutrient
-algae-POC/detritus/bacteria complex by itself can reach a steady state when
production and consumption of carbon and nutrients are in balance on a long
term. In general these components, and changes therein, are considered to be
mainly effected by the inverse light/nutrient (depth) gradient. However,
evidence is increasing that the microbial food web shows diel production cycles
as a consequence of diurnal fluctuations in light conditions (12light :12dark).
But in a system with only nutrient limitation of production there will be no
over-exploitation of resources. Where grazing keeps the algae below an
equilibrium level, the system is potentially unstable. Stability will be
improved when the grazing pressure on algae is released. This can be the case
when either the microzooplankton feeds mainly on bacteria and detritus, or when
it is kept low by larger predators in the mesozooplankton.
The mesozooplankton forms the
link towards macrozooplankton and large marine invertebrates and vertebrates
such as squids and fishes, which mainly at night rise to the euphotic zone to
harvest the secondary production. Mesozooplankton can feed on phytoplankton,
microzooplankton and the detritus/bacteria complex. Macro- and mesozooplankton
are the only plankton components capable of active vertical migration. By
predator-prey control at different trophic levels mesozooplankton can affect
the stability of the system.
The main question to be
answered is, why under rather stable environmental conditions in (sub)tropical
seas and oceans the typical DCM structure occurs world-wide as a system with
little temporal and spatial variation. What are the factors that prevent
(large) oscillations in this global ecosystem? Once we understand the reasons
for this stability, we are able to predict its response to global environmental
changes and the role it plays with respect to carbon cycling in the ocean. The
following aspects are studied:
1. What is the effect of the
vertical light and nutrient gradients on species diversity within the euphotic
zone?
2. What is the nature of the
ecosystem stability in the DCM, how does it depend on phytoplankton, micro- and
mesozooplankton and microbial trophic interactions, and how does it affect the
carbon and nitrogen mass balance?
3. How does the conversion of
phytoplankton-derived organic compounds by grazing activity of different size
classes of zooplankton, microbial activity and vertical transport affect the
export to the aphotic zone?
4. Is the diurnal rhythm in
light conditions (12l:12d) responsible for a phasing in biological
(growth/grazing) activity, and does this induce temporal variation in the
different components?
To find some answers, five
stations on a south-north transect were sampled to measure profiles of stocks
and activities of the different system components and physical/chemical
parameters of the environment to estimate state variables, transport rates and
conversion rates. With this data a 1-dimensional ecosystem model will be
implemented to study the consequences of adaptations and trophic interactions
for the equilibrium and the mass balance of carbon and nitrogen.
Summary review of the cruise
Hr. Ms. Tydeman left
Willemstad (Curaçao) on 22 July 1996 and, after conducting a test series for
seagoing instruments on 25 July, a transect of CTD casts was carried out on the
continental slope of Guyana on 26 and 27 July to study inorganic carbon
exchange between the southern and northern Atlantic ocean at different water
depths. A detailed study of the DCM was conducted at 5 main stations:
geographic date
position
station 100 12N, 48W 29/7-02/8
station 200 14N, 40W 05/8-09/8
station 300 23N, 38W 11/8-15/8
station 400 34N, 35W 18/8-22/8
station 500 34N, 23W 24/8-28/8
Between the main stations a
single CTD cast (400 m) and some optical measurements were made. The cruise track
and station list are presented in the Appendix, as well as a list of scientific
participants and the station programs.
Due to good weather
conditions and the skilful assistance of Navy crew the cruise was very
successful. All planned measurements and sampling schemes were carried out
without any loss of material, equipment or sampling time.
Preliminary conclusions
A pronounced DCM was found at
all 5 stations but each of them could be characterised by typical features
(physical, chemical or biological) not present at the others. The first three
stations (stations 100, 200 and 300) showed the DCM layer at a depth of 80, 100
and 130 m, respectively. Concurrently, the peak layer showed a decrease in the
fluorescence signal and a broadening of the peak. In the following two stations
(stations 400 and 500) sharp DCM peaks were found at a depth of 100 m.
With respect to the physical structure two processes were weakening the
stability of the upper water column. The first was double diffusion prominently
present at the first two stations. Internal waves, on the other hand, with an
amplitude of over 30 meters were also found. Both these processes will effect
the vertical flux of matter as well as the daily solar radiation of
phytoplankton growing in the area of the critical depth. The optical profiles
showed a pattern typical for open ocean water verifying the depth of the DCM.
The highest abundance of particles however, was found above the fluorescence
peak. Analysis of the particle distribution carried out with flow-cytometry
confirmed this observation. Below a depth of 200 m the water column was
extremely transparent indicating a low particle content.
As far as the nutrient distribution is concerned in the surface water layer,
till the peak of DCM, NO3 was depleted. At the same time PO4 and NH4 were
present in low but detectable concentrations. With depth the nutrient
concentrations increased but not in an identical pattern for every station.
Next to differences in absolute values also the N/P ratio varied. In the two
Western Atlantic stations (100 and 200) and station 500 the N/P ratio was
around 16. In the other two the ratio varied between 20 and 24. The
phytoplankton abundance, as examined with flow-cytometry showed a numerical
abundance of the prokaryotic phytoplankter Prochlorococcus in numbers up to
100,000 cells per ml. At all stations this species could be traced from the
surface till a depth of 180 m. As a result of the decreasing light intensity
pigmentation increased as could be derived from the increase in chlorophyll
fluorescence. Synechococcus spp. were only dominant in the surface water
layers. Typical populations of other pico-eukaryotes or larger phytoplankton
were found around the DCM but dominated only over a limited depth range. Some
of these algal groups were found below their critical depth since the
fluorescence signal showed a decrease after an increase. This suggests that
these cells have lost their ability to adapt to the prevailing light intensity
and cells are about to metabolise their structural components (photopigments).
A high frequent sampling program showed that the Prochlorococcus cell numbers
increased at the end of the day indicative of a diel rhythm. Phasing of the
physiological activity was not restricted to phytoplankton only. Also bacteria
showed daily changes in activity and growth characteristics. Time course
measurements of bacteria to which different mixtures of organic carbon and
nutrients (N and P) were added showed different growth characteristics. The
organic carbon source was stimulating in particular bacteria growth in samples
collected in the morning. This observation was supported by the fact that the
incorporation of thymidine (indicative of DNA synthesis in bacteria) was
pronounced in the early morning (04:00 AM to 07:30 AM). On the other hand the
highest protein synthesis rate (leucine incorporation) was around noon. The
different phasing of DNA and protein synthesis rates suggest an unbalance
between activity and growth in bacteria as well. In some incubations bacteria
stopped assimilating nutrient for several hours, but resumed this later. This
daily unbalance of growth and physiological activity seems indicative for
synchronisation of bacterial activity. A first impression of the grazing
experiments showed only moderate grazing activity of microzooplankton (<200
(m ) limited to the upper part of the DCM (range 0.1 to 0.2 per day). For the
prochlorophytes these rates were in the upper part of the DCM equal to the
growth rates of the species. At the peak and bottom of the DCM growth rates
were 0 and grazing resulted in decrease in cell abundance.
A inventory of the larger organisms present (>50 (m) showed low numbers of
net phytoplankton (few long diatom chains) but a relatively high number of
mesozooplankton (200 to 1000 (m size class). These large grazers were mainly
copepods in the upper 200 m (mean abundance about 0.2 per l). Next, also many
protozooplankters we present.
Based on the respiration rates and fact that incubation experiments showed no
significant grazing activity on picophytoplankton is must be concluded that the
dominant food source for this mesozooplankton had to be microzooplankton rather
than phytoplankton, although the exact nature of this source has to be
determined..
CTD-profiles and Physical
Oceanography
(C. Veth and M.A. Hiehle)
The CTD-rosette system is in
a number of aspects an essential part of the DCM expedition. In the first place
the CTD-rosette combination provides the water from different depths for
biological and chemical studies and, secondly, the physical profiles determined
with the CTD-system show the physical environment of the deep chlorophyll
maximum.
The sensors attached to the
CTD-system were for measuring conductivity, temperature and pressure (Seabird)
, from which salinity and density were derived, and sensors for fluorescence
(for the determination of chlorophyll concentration), for underwater PAR and
for turbidity. The standard CTD-sensors worked very well during the whole
cruise. It turned out, however, to be difficult to get enough samples for
calibration of the salinity, because most cast were surface casts, not deeper
than 400 m. The surface water is extremely inhomogeneous with strong vertical
gradients and small steps. To overcome this problem of getting water for
salinity calibration, a bottom cast was planned at each main station, but
technical problems with the winch (cogwheel wear) made it necessary to go not
too deep. Even at 2500 m most physical profiles were shown to be highly
irregular and in fact unsuitable for salinity calibrations. The marginal
salinity calibration, however, showed that the JGOFS recommendation for surface
water was met. The fluorometer (Chelsea) used at the beginning of the cruise
was replaced during the first main station, because of extremely bad
performance. The turbidity meter turned out to be sensitive to temperature
changes of the water and worked only well during the first 200 m of the
downcast. An oxygen sensor was incorporated in the system.
On the rosette NOEX sampling
bottles were used. These bottles are still an ergonomic disaster. Also
continuous care is necessary to keep the system with all those tubes and
balloons in good shape. Occasionally bottles seemed to have sampled the wrong
type of water, even when the reversing pressure meter has given the right
sample depth. Continuous determination of the macro-nutrient concentrations
(nitrate, phosphate and occasionally silicate) in the samples was the best way
to identify "wrong" bottles. It is clear that the NOEX bottles in the
present state are not the final answer to the hydrographic sampling of water.
The stepping motor of the rosette system also gave some problems that were
solved in a satisfactory way. In the first part of the cruise strategically
placed reversing thermometers and pressure meters offered the opportunity to
reconstruct the tripping sequence of bottles.
First impressions on the
Physical Oceanography during DCM
The DCM cruise started with a
hydrographic section off the continental Shelf near Surinam. The salinity
profiles showed very saline sub-surface water. Occasionally a salinity of
almost 38 was found. The surface layer of a thickness of 10 to 20 m had a
salinity that was much lower, even down to 32. This surface water apparently
had a high concentration of river run-off from the South-American continent.
The backbone of the cruise
were the five main stations in different biological provinces lasting 4 to 5
days with about 30 CTD casts per station. During the transfers between the
stations one cast per day was done. Figure 1 and 2 show the profiles of a
number of parameters of a, more or less representative, cast at each main
station. The stations show large differences. Stations 1 and 2 are in the
equatorial region with a clear rain surplus over the evaporation. In station 1
even some river water may be present. Although the surface salinity is high,
the salinity maximum is near 120 m in both stations. In particular at station
1, weaker in the other stations, the step structure caused by double-diffusion
processes was visible. The circumstances for these processes were clearly
present at depths where increasing density caused by the increasing salinity
towards the surface was compensated by the temperature distribution. Mixing
processes related to double-diffusion may play an important role in the flux of
nutrients from below the deep chlorophyll maximum. At station 3 the evaporation
is apparently stronger than the precipitation. Casts taken during one whole day
showed an enhancement of salinity in the upper meters in daytime that was mixed
downward during the night by convective overturning caused by surface cooling.
Stations 4 and 5 show gradually less saline profiles when going north. In the
deep casts of stations 4 and 5 Mediterranean water was visible near 1000 m. The
combination of all casts during the first one-and-a-half day at a station
presents the relation between the vertical motions of the DCM and the physical
structure of the water column showing internal waves (Figure 3). Amplitudes of
several tens of meters have been observed and, although the number of casts per
unit of time was not sufficient to resolve that, indications were found for
breaking of the internal waves. These breaking waves will stimulate the
vertical flux of matter.
Figures physical plots
Fig. 1 Typical temperature
and salinity profiles of 5 main stations of upper 400 m (numbers represent
station numbers)
Fig. 2 as fig. 1 but for
fluorescence and density.
Fig. 3 A-E. Collection of CTD
measurement (fluorescence, temperature, salinity and density) of first day of
the main station. Isolines fitted to CTD casts taken with a frequency of 1.5 h
over a period of 35 h. Dots indicate position of DCM peak.
Marine Optics en Remote
Sensing
(Marcel R. Wernand)
Measurement of Inherent
Optical Properties IOP's.
During all stations an
in-situ absorption/transmissometer (AC-9) was deployed for the vertical tracing
of i) pigmentlike matter and ii) all other particulate and dissolved matter.
The first day of a station down cast and up cast profiles were made every 1.5
hours during 24 hours. The 4 following day's a single down and up cast profile
was made. The instrument measures the absorption a in m-1 and the beam
attenuation coefficient c in m-1 in 9 spectral bands in agreement with SeaWiFS
(spaceborne ocean colour sensor) spectral bands. The instrument was recently developed
by Wetlabs, Oregon, USA. Before this cruise the AC-9 was thoroughly tested
during a 2 years program on the North Sea. For this cruise this instrument has
been upgraded with a pump system and a depth sensor. The instrument generates
direct in-situ profiles of a and c by means of a flow-through system. Profiles
were measured throughout the euphotic zone up to 250 meters depth. It could
clearly be seen that the chlorophyll maximum depth varied from 70 to 120
meters. The water mass below the depth of 200 meters was more transparent than
the purest water that can be made at the laboratory nowadays (milliQ).
Corrections for this phenomena will be applied in a later stage. Comparisons of
the IOP's profiles will be made with Salinity profiles and with particle
distribution determined with flow cytometry .
Fig. 4: Example of the down cast profile, station 304, of the AC9. The
profile shows the absorption coefficient and beam-attenuation coefficient at
440 nm and 675 nm.
Measurement of Apparent
Optical Properties AOP's.
During all stations from the
second day until the fifth day at 13.00 GMT the water column was measured at
different depth up to 200 meters with the Advanced Spectral IRradiance Meter
(ASIR, NIOZ). Simultaneously this radiometer measures the down and up welling
light (resp. Edown, Eup) between 400 and 720 nm in 22 spectral bands. Per depth
the spectral diffuse attenuation coefficients Kdown, Kup and the spectral
reflectance R- was then calculated. Underwater relationships between R and
particulate and dissolved matter will be established.
Fig.5: Example of the down and up welling irradiance, the calculated
Reflectance and the calculated diffuse attenuation coefficient by ASIR.
Above water ocean colour
measurements were performed from the bridge of the ship 3 times a day including
sailing days. Measurements of the down welling irradiance Ed+, upwelling
radiance Lu+ and in some cases sky radiance Ld+ with the PR650 radiometer. The
instrument measures between 380nm and 780 nm in 101 bands. The spectral R+ was
then calculated. These measurements were specially performed for the validation
of forthcoming ocean colour sensors. Together with the surface in situ values
of total suspended matter and total pigment concentration ocean colour
algorithms including primary production can be developed or given ones
validated.
Fig.6: Example of the down welling Irradiance, up welling radiance and the
calculated reflectance R= 5*Lu/Ed above the water surface at station 300, cast
45 (by PR650).
Ultraviolet radiation- its
evaluation and some potential effects on the marine microbial community and its
chemical environment
(Ingrid Obernosterer)
(1) - Evaluation of the underwater light regime with
special concern to ultraviolet radiation
(2) - Spatial and diurnal dynamics of hydrogen peroxide
(3) - Measurements of the photochemical oxygen demand
(4) - DNA damage in phytoplankton and bacteria
(5) - DNA dosimeter
(6) - Sampling for the molecular analysis of the bacterial
community above, in, and below the DCM
General
Introduction
The increase in ultraviolet
(UV)-radiation due to the depletion of stratospheric ozone has gained enormous
attention during the past decade. The alteration of the chemical environment
through the production of bioactive free radicals, such as hydrogen peroxide,
the photode-composition of organic matter and thus the change in the availability
of trace metals and inorganic nutrients can be regarded as processes affecting
indirectly the biology of marine organisms. Among the direct potential effects
of enhanced UV-B radiation on marine micro-organisms, DNA-damage through the
production of thymidine dimers has been quantified recently. The goal of this
cruise was to investigate the underwater irradiance spectrum with special
concern to UV-radiation and to relate specific chemical and biological
processes to the radiation environment.
(1) - Evaluation of the
underwater light regime with special concern to ultraviolet radiation
A Profiling Ultraviolet
Radiometer (PUV-500), consisting of a PUV-500 underwater unit and a PUV-510
surface reference sensor, has been used. The instrument measures the irradiance
at 4 distinct wavelengths in the UV-B (305 nm, 320 nm) and UV-A (340 nm, 380
nm) regions as well as the integrated irradiance of the photosynthetic active
radiation (PAR, 400 nm-700 nm).
(2) - Spatial and diurnal
dynamics of hydrogen peroxide
Hydrogen peroxide (H2O2) is
an important and seemingly ubiquitous photochemically generated compound. In
natural surface waters, H2O2 is formed by secondary photochemical reactions
involving light absorbing organic materials. Its stability relative to other
compounds formed by solar radiation makes it a useful indicator of overall
photochemical processes in the marine environment.
Variations in H2O2 concentrations result from a kinetic balance of formative,
destructive and input processes. Hydrogen peroxide has been measured most
extensively in the gas phase and in rain and cloud vapour largely due to its
role in atmospheric chemistry and in acid rain generation. Its distribution in
surface waters is also of great interest and has recently received significant
attention as an indicator of photochemical activity.
On this cruise, the spatial and temporal distribution of hydrogen peroxide was
examined and related to UV-profiles in order to investigate the role of
UV-radiation in the formation processes of H2O2. At each station, time series
and vertical profiles of H2O2 were collected at 10 different depths (0 m-120 m)
for 48 h every 1.5 h. Hydrogen peroxide concentrations were measured with a
Jasco spectrofluorometer using the enzyme catalysed dimerization of p-hydroxyphenylacetic
acid.
Preliminary results show that the average H2O2 concentration at noon is about
100 nM at 0 m, decreasing to 10 nM at 100 m depth. Time series have shown an
increase in H2O2 concentration of up to 180 nM at 3:00 p.m. at 0 m, while the
concentration increased from 40 nM at 7:30 a.m. to 70 nM at 3:00 p.m. at 40 m.
Figures 7A,B,C show typical
depth profiles taken at 8:30 p.m., 1:00 a.m. and 5:30 p.m. at station 400 on
August 19th.
(3) - Measurements of the
photochemical oxygen demand
Sunlight photolyzes organic
compounds in surface waters of the marine environment, destroying some substances
and synthesising others. Such reactions may proceed at high rates and have
biological, chemical and geological implications. The rates of photoreactivity
are determined by the sunlight spectrum and intensity, the absorption spectrum
of the chromophore and the efficiency with which chemical change results from
excitation of the chromophore (quantum yield). It is proposed that
photochemical processes have a net oxidative character in seawater, and that
such reactions may provide one sink for organic molecules in the marine
environment.
Quartz-glass bottles were filled with 0.2 'm-filtered seawater from 10 m depth.
In order to elucidate the role of UV-B versus UV-A radiation in photo-oxidation
processes, cut-off filters (Mylar-D, 320 nm) were wrapped around the
quartz-bottles. The incubation was done for 48 hours in an on-deck water bath
at in-situ temperature. Simultaneously, 0.8 'm-filtered water was incubated in
the dark.
Photochemical and biological oxygen consumption was then measured by the Winkler-method,
applying the spectrophotometrical method to determine the oxygen concentration.
(4) - DNA damage in
phytoplankton and bacteria
Intracellular absorption of
UV-B radiation can be detrimental to bacteria, phytoplankton and other marine
organisms. The goal of this experiment was to quantify UV-induced thymidine
dimers in DNA using fluorescently-labeled antibodies targeted against thymidine
dimers. Samples from two different fractions (bacteria: 0.2 - 1 (m,
phytoplankton 1 - 10 (m) have been taken at several depths and times of the
day. According to the UV-profiles, freshly collected seawater from 0, 5 and 15
m was filtered onto 10 (m, 1(m and 0.2 (m filters at 4:00 a.m., 1:00 p.m., 4:00
p.m. and 7:00 p.m. at each station. To avoid repair of the damaged DNA, the
filtration was done as quickly as possible with the three different filters 'in
line', followed by freezing the filters at -80 -C. The filters will be further
processed according to a protocol developed at the Department of Marine Biology,
University of Groningen.
(5) - DNA dosimeter
At each station, bare DNA was
incubated in quartz tubes at several depths from sunrise to sunset. The amount
of thymine dimers produced in the DNA correlates with the biologically
effective dose received. According to the ultraviolet radiation levels,
duplicate quartz tubes (10 cm) were incubated at 1, 2.5, 5, 15, 30 and 50 m
depth. The incubation was performed on the same day as experiment (4).
Experiments (4) and (5) were
conducted in co-operation with Anita Buma and Peter Boelen from the University
of Groningen, Dept. of Marine Biology.
(6) - Sampling for the
molecular analysis of the bacterial community above, in, and below the DCM
In order to determine
variations in the composition of the bacterial community at different depths of
the water column, samples were taken for PCR and RFLP analysis using a
newly-developed fluorometric HPLC-technique to quantify the DNA fragments.
At each station, samples from 20, 200 m and, according to the CTD-profiles,
from the deep chlorophyll maximum layer were taken.
The freshly collected water samples were immediately 0.8 'm-prefiltered, then
filtered onto 0.2 (m filters which were frozen at -80oC.
The filters will be processed by Markus M"seneder at the Department of
Marine Biology, University of Vienna.
Nutrient analysis:
(K. Bakker)
Some 3000 CTD samples were
taken for nutrient analysis. The CTD-NOEX bottles were first sampled for
nutrients before other samples were taken, because ammonia is sensitive for
contamination. The samples were directly poured into polyethylene bottles,
stored cool at 4º C and filtered within 6 hours over 0.2 µm pore size and
immediately capped with a sheet of parafilm. The samples were analysed within
24 hours after filtration for ammonia, phosphate nitrate and nitrite, the last
two in a medium and a high sensitive range (see statistics) because of
depletion above the deep chlorophyll maximum layer.
Furthermore some 1500 samples
were analysed from different bacteria experiments.
I want to thank Ruud
Groenewegen for assisting with filtering at least 50% off the samples.
Methods:
All nutrients were measured
on a Technicon Autoanalyzer system "TRAACS 800" using the following
colorimetric methods:
Phosphate:
Phosphate was measured, as
the blue colloid complex formed with ammonium molybdate using potassium
antimonylartrate as a catalyst and reduced with ascorbic acid, at 880 nm.
Ammonia:
Ammonia was measured during
the first part of the cruise (first two stations) by dialysing the NH3 as a gas,
by adding NaOH in citrate medium (to prevent precipitation of Ca and Mg salts),
through a dialysis-membrane to a second acidified-stream; where it is detected
by the classic phenol-hypochlorite method. The colour is measured at 630 nm.
During the second part of the cruise, problems with the dialysis necessitated
to measure the NH4 directly with the phenol-hypochlorite method.
Nitrite and
Nitrate:
Diazotation of nitrite with
sulfanilamide and-(1-naphtyl)-ethylene diammonium dichloride to form a pink coloured
dye measured at 550nm. Nitrate is first separately reduced in a copperized
Cd-coil using imidazole as a buffer and is measured as nitrite.
Silicate:
Silicate is measured as the blue
reduced silicomolybdenium complex at 810 nm. Ascorbic acid is used as the
reductant and oxalic acid is used to prevent interference of the phosphate
molybdenium complex.
Preliminary results:
Above the DCM, NO3 was
depleted (below detection limit) while PO4 was still present (ca. 0.02 (M ).
NH4 was still available at all stations at a level off 0.15(M. At the peak of
the DCM a NO2 peak was observed just 5 meters below this Below the DCM the
nutrient values of stations 100 and 500 differed from the other three. Other
changes were observed in the N/P ratio of the nutrient rich water below the
DCM. A "normal" Redfield ratio for P:N is about 16 and was observed
for the stations 100, 200 and 500 but 24 to 20 for station 300 and 400,
respectively.
Dissolved oxygen by Winkler
spectophotometry
(G.W.Kraay)
During this cruise 500
dissolved oxygen samples as duplicates or replicates have been taken in order
to calibrate the O2sensor of the CTD. At the 24 hours day-stations every CTD
have been sampled at two depths on the oxygen maximum and minimum. Further on
most CTD cast's on the transfer between the stations; every oxygen production
cast and also all the deep calibration cast. The analysing was according the
method from Su-Cheng Pai(1993) modified by G.W Kraay and J v Bennekom.
We have chosen for this
technique because of the analyse time (40 samples per hour) the precision; the
reliability, and also the more independence of the bottle volume. The only
thing you need is a high quality spectrophotometer equipped with a wide bore
volume flowcell. We used the Hitatchi U1000 spectrophotometer with on the
analog output a four digit voltmeter.
The calibration curve was made on the NIOZ lab and the empirical coefficients K
was 0.0005455 µmol-1cm-l for 456nm and 0.0126 µmol-1cm-l
for 355nm. The last one is used for measuring the seawater-blank and the
reagents-blank.
Calculation:
(O2)
µmol = mV*(1/(2*k*d))*(Vb+Vc)/(Vb-Vr)
mV = reading voltmeter.
K = empirical coefficient
Vb = bottle volume
Vc = volume sulphuric acid
Vr = volume Winkler reagents
Data recorded in the data
report are corrected by subtracting 1.05 (Mol/l for the oxygen in the pickling
reagents. No correction was made for the seawater and reagents-blanks.
Some results:
Reagents blank 0.32 µMol/l
Seawater blank 0.36±0.1 µMol/l for samples deeper then 100 m and 0.16±0.1
µMol/l for samples in the euphotic zone.
The reproducibility: 55% of the duplicates had a CV smaller than 0.1% and by
83% of all the samples was the CV smaller than 0.2%.
Fig. 8 comparison of CTD
oxygen sensor and bottle data of 5 main stations.
Regression lines and data included in the graphs
Dissolved and particulate organic
carbon
(Jan Hegeman)
On all the large stations,
samples were taken for DOC and POC on different days and times. The samples for
DOC were filtered over polycarbonate filters with a pore-size of 0.2 micron.
The POC-samples were filtered over Whatman glassfibre filters with a pore-size
of 0.7 micron. Initially the DOC-samples should be measured onboard the ship
using an automatic instrument, but because the instrument did not perform well,
possibly caused by power problems on the Tydeman, another method was used. The
samples were transferred in triple to sealed ampoules with phosphoric-acid and
persulphate, following the method of Menzel and Vaccaro, for later measurement
at the institute on Texel. Furthermore extra samples were sealed with only phosphoric-acid
for HTC-measurement. The filters of POC were also sealed in ampoules following
the same method of Menzel and Vaccaro. Samples were always taken at six depths.
Sediment-traps:
(Jan Hegeman)
On all large stations where POC
and DOC was sampled, free floating sediment-traps were released, suspending
from buoys on two depths. One set of traps was deployed at 300 m, the other set
just below the chlorophyll-maximum. After 24 hours the traps were taken on
board and the sediment was collected on filters, which were stored deep frozen
for analysis of organic carbon and nitrogen at the NIOZ on Texel. The traps
were released again for the next 24 hours. This was continued for every day on
the stations.
Phytoplankton pigments.
(G.W.Kraay, B. Kuipers and S
Oosterhuis)
In order to estimate the
algal pigments by HPLC large volumes (20 l were filtered over 47mm GF/F filters
by over-pressure. On every station at the first day the water column was
sampled from 180 to 10 m divided in about10 depths intervals.
The filters were immediately frozen by -80(C for analysis later at the
laboratory. The extraction and separation will by done by the method described
in Kraay et al. (J.Phycol.28:708-712)
Comparison of the
Fluorometers used for the Chlora extraction method
(G.W.Kraay and B. Irwin)
Since two fluorometers were
used on the cruise: one from the NIOZ and one from Bedford Institute both
calibrated independently. Comparison of both instruments was necessary. At two
occasions 1 litre and 0.1 litre of seawater was filtered and extracted in 10ml
90 % acetone and this solution was measured at the same time on both
fluorometers.
Results:
|
no
|
vol
|
chlora(NIOZ)
|
phaeo(NIOZ)
|
chlora(Bedford)
|
phaeo(Bedford)
|
|
|
(l)
|
(microg/l)
|
(microg/l)
|
(microg/l)
|
(microg/l)
|
|
1
|
1
|
0.191
|
0.261
|
0.189
|
0.196
|
|
2
|
1
|
0.126
|
0.208
|
0.122
|
0.164
|
|
3
|
0.1
|
0.113
|
0.288
|
0.138
|
0.193
|
|
4
|
0.1
|
0.153
|
0.205
|
0.174
|
0.131
|
Chlorophyll extraction.
(G.W.Kraay, H. Bouman, S.
Oosterhuis, H. Witte and B.R. Kuipers)
Samples for the chlorophyll a
extraction were taken of almost every CTD cast. Ten depths were chosen over the
water column from 10 to 200m. One litre was filtered over a 45mm GF/F filter by
low vacuum pressure. All the filters were stored in the min 800C freezer before
analysing on board. Except for the filters from station 5 those are analysed on
the lab two months later.
Extraction was done following
the procedure from Holm-Hansen, et al. (J.Conseil, Conseil perm. Intern.
Exploration Mer, 30: 3, 1965) and (Strickland and Parson: A practical handbook
of seawater analysis. Fisheries Research Board of Canada).
The filter was extracted in
10 ml 01% acetone and measured twice first Rb and after adding one drop 10% HCL
for the second time Ra.
Turner designs 10AU
fluorometer was calibrated with HPLC pure Chlor a.
Concentrations were
calculated by the following formula's:
(g chlorophyll a/l = Fd(af/af-1)(Rb-Ra)
(g phaeopigment/l =Fd(af/af-1)(af*Ra-Rb)
Where Fd is the calibration factor and af the acid factor.
Calibration February 1996: FD= 1.89
AF=2.31
Bacterial production,
microbial diversity, and methanogenesis in the deep-chlorophyll maximum
(M. J. E. C. van der Maarel)
During the 1996
Deep-Chlorophyll Maximum (DCM) research cruise on the central Atlantic Ocean
three different aspect of the microbiology of the DCM has been studied. The
first aspect was concerned with the bacterial production, based on the
incorporation of radiolabelled thymidine, which is incorporated into newly
synthesized DNA, and leucine, which is incorporated into newly synthesized
proteins. By using conversion factors reported in the literature the amount of
carbon produced by bacteria can be calculated. Samples from ten different
depths were taken at every major station. Preliminary results show that the
bacterial production ranged from 48.7 mg C/m2/day to 114.7 mg C/m2/day. At
station 200 and 400 samples were taken at four different times of the day (04:00;
07:30; 12:30; and 19:30 local time) to see whether the bacterial production
showed a diurnal cycle. Preliminary results indicate that thymidine
incorporation was the highest between 04:00 and 07:30. Leucine incorporation,
on the contrary, showed a maximum in the early afternoon. A similar experiment
was done by incubation of a water sample, which was taken from the chlorophyll
peak of the DCM, at a light intensity of 11% of the photosynthetic available
radiation in the deck incubator and measuring leucine incorporation every 2
hours during a 24 hour period. The leucine incorporation in this experiment
showed an increase starting at approximately 12:00 and was at its maximum at
22:00. A similar incubation in the dark did not show an increase in the leucine
incorporation.
The second aspect of the
microbiology of the DCM that was studied was the possible presence of a methane
maximum in the top of the DCM and the possible presence of methanogenic
archaei, the microorganisms responsible for the formation of methane. The
underlying thought is that in many oceans a supersaturation of methane can be
found at a certain depth that also shows a high concentration of oxygen. Since
methanogenesis is an obligately anaerobic process this phenomenon has been
called the oceanic methane paradox. To see whether active methanogenesis and a
methane maximum exists in the DCM of the central Atlantic Ocean samples were
taken to measure the concentration of methane and dimethylsulfide, a well known
precursor of methanogenesis that is derived from the algal osmolyte
dimethylsulfoniopropionate. These samples will be analyzed in the laboratory.
Also enrichment cultures using seawater samples supplemented with vitamins,
micro nutrient, and monomethylamine as a substrate were setup to look for the
presence of methanogens. The seawater samples were taken above, in, and below
the DCM at station 100, 300, and 500.
The third aspect is an
investigation into the microbial diversity of the DCM, compared to the
microbial diversity above and below the DCM. At every major station 200 l of
seawater was sampled and subsequently filtered over 8.0 mm and 0.8 mm and
finally concentrated using cross-flow filtration over a 0.1 mm filter
(Durapore, Millipore). From these samples DNA and RNA will be extracted for
further molecular analysis based of the microbial diversity with special
emphasis on methanogens and marine archaea, a recently discovered group of
microorganisms.
Fig. 9 Typical vertical
profiles of Thymidine and leucine incorporation in bacterial communities of the
5 main stations (left). In the right part temperature and nitrate profiles are
shown.
Microbial biomass and
activities at five stations in the Atlantic ocean during the Deep Chlorophyll
Maximum cruise
(G.J. van Noort in
co-operation with J.H. Vosjan)
Introduction
We studied the microbial
biomass and activities in the Deep Chlorophyll Maximum layers at the five main
stations in the Atlantic Ocean. The distribution of the bacteria and
flagellates were analysed at five depth in the water column. The bacterial
number in the upper water layers were estimated too.
We expected that the Deep
Chlorophyll Maximum is in a P and N limited condition. In this situation
bacteria, formerly thought to be mineralisers, can be N and P consumers if
there is enough dissolved organic C as energy and C source. In this way
bacteria could be competitors for P and N of phytoplankton. Only together with
bacteriovores (heterotrophic protozoa) the N and P, incorporated in the
bacteria, will be excreted to the environment and will become available again
to phytoplankton and bacteria. That's why also bacterial growth and nutrient
uptake have been studied at three depth (upper, middle and lower level) of the
Deep Chlorophyll Maximum layers.
Methods
The microbial biomass is
calculated from counted number of the micro-organisms and the measured volumes.
The bacteria and flagellates have been filtered on a 0.2 µm nuclepore filter.
They have been stained with acridine orange for bacteria and with proflavine
for flagellates, and fixed on slides and stored in a deep freeze. Later on they
will be counted and measured at the laboratory by the epifluorescence
microscope technique. Incubation experiments have been executed with water
samples from three depths at every station. The growth rate of bacteria and the
uptake rate of nutrients like, ammonia, nitrate and phosphate have been
measured in these experiments. The effect of additions of P, N and organic C is
followed in incubation experiments with unfiltered and over 0.6 µm filters prefiltered
seawater (to remove algae and protozoa). These bioassay experiments were
executed to follow the effect of nutrient additions on the bacterial growth and
uptake kinetics. Several hundreds of nutrient samples have been analysed by K.
Bakker.
Preliminary results
Experiments with water from
the D.C.M. layer (upper, middle and lower level) showed that addition of C,N
and P immediately increased the uptake of the C,N and P and did increase the
bacterial numbers. This occurred in the unfiltered and prefiltered (over 0.6 (m
filter) samples. This directly proved that there is a shortage of degradable
organic carbon and that the bacteria consume N and P. Sometimes a small
increase of ammonia was seen at the end of the experiment when nitrate and
phosphate had been consumed. Samples enriched with P and N showed only a small
uptake of N and P from the water. This means that bacteria were limited by
organic carbon in the water. This mostly happened only in the upper layer of
the D.C.M. and when the experiment was started at 12 o'clock in the morning.
When such an experiment at the same station was started at 6 o'clock in the
morning, there was no response at all on the N and P additions. Even after 48
hours, as long as the incubations lasted, no effect was seen. This probably
means that the organic carbon was almost taken up by the bacteria during the
night. This happened at several stations.
In some experiments bacteria
stopped taking up nutrients for several hours, but resumed this later. Perhaps
a rhythm in bacterial growth, synchronic divisions or a period of lysis which
submitted organic materials could be an explanation for this phenomenon. This
rhythm of nutrient consumption through the day could be triggered by the
limiting factor organic matter. This organic material is produced by the diel
rhythm of primary producers. Dividing rhythms in bacteria, if they grow
synchronously, can also cause periodic P and N uptake. These possibilities will
be studied when the bacterial numbers and biomasses in the preserved samples
have been analysed.
Phytoplankton dynamics
(Marcel J. W. Veldhuis & Gijsbert W. Kraay)
In order to study the
phytoplankton dynamics (in situ and during incubations) on 24 h light/dark
cycle different types of experiments were designed.
1) Tracing in situ cell
abundance. This was done by a high frequent sampling strategy (14 times over 24
h light/dark period) of the upper 300 m of the water column. CTD data were
collected to assay changes in the physical structure of the upper water column
(internal waves). Bottle samples were collect for chlorophyll and species
composition (flow cytometry). Since cell abundance is subject to drifting water
mass's and therefore patchy distribution of the phytoplankton samples were also
taken van DNA-cell-cycle analysis. The advantage of the DNA-cell-cycle method
is that this assay estimates the growth rate independent of the cell numbers
present and is therefore not sensitive to changing water masses.
2) Phytoplankton biomass (whole
and species selective) will be estimated using either the cell size
distribution, chlorophyll fluorescence or DNA cell concentration. These three
independent parameters will be compared with total POC and chemical measured
chlorophyll values. Besides phytoplankton bacterial biomass will be calculated
based on microscopically- and/or flow cytometrically counts.
3) In a different set of
experiments (deck incubator) changes in cell abundance (phyto- and
bacterioplankton) were traced over a light dark period experiments which ran
parallel to 14C primary productivity. These experiments are carried out at 7
depths mimicking the light regime of the whole euphotic zone. Primary
productivity will be compared with changes in cell biomass. A comparison of both
data sets will be used to estimate the carbon turnover rate and to calculate
the actual amount of primary production converted in plant biomass. Since
grazing activity in these small bottles (ca. 250 ml) is included this approach
only gives a net change in the plankton biomass. In combination with the
DNA-cell-cycle it is possible to calculate the gross growth rates. From these
two parameters the grazing activity can be derived.
4) Simultaneously, changes in
the cell fluorescence will be measured to trace adaptive response of the
phytoplankton cell to day to day and light/dark cycle. Selective changes in
light intensity (shift-up or shift down) of the samples is thought to give
insight in rates of adaptation on the level of the photosynthetic activity as well
as growth responses. Hence, changes in community structure within the time span
of a single day. The optical properties will be compared plant pigment
composition and spectral properties of the upper water column.
Fig. 10 Vertical profiles of
cell numbers of different groups of phytoplankton (Prochlorococcus,
Synechococcus, total eukaryotes (E), pico-eukaryotes (K) and larger
phytoplankton (J), all number per ml. Changes in Chlorophyll fluorescence
signal of phytoplankton with depth.
Flow-cytometry
(Marcel J.W. Veldhuis,
Gijsbert W. Kraay, Harry Witte)
Algal Flow-Cytometry (AFC)
was used as a technique for a rapid analysis of the phytoplankton composition
and numbers using small sample volumes (<1 ml). After calibration the
relative values for size, scatter and chlorophyll fluorescence can be
determined of selective groups of phytoplankton.
The instrument used was a
Coulter XL-MCL equipped with a carousel (32 vials). This standard bench top
flow cytometer is equipped with a 15mW air cooled laser 488nm. Cell properties
(scatter and autofluorescence) were measured with special detectors. Since the
instrument in its standard configuration is not sensitive enough, the hard ware
was upgraded. To enhance the sensitivity of the instrument the pressure of the
sheath fluid was lowered. Next, sidescatter (SS) was measured in PMT1. PMT2 was
used to detect the PE-fluorescence of Synechococcus type of cyanobacteria or
PE-containing eukaryotes (575 nm BP). PMT3 was used to collect the chlorophyll
fluorescence (>630 nm).
All parameter values were
transformed in a logarithmic scale (4 decades). The instrument was optimised
using monospherical beads (3.06 µm in diameter). The whole sample analysis was
stored as a listmode file for post-processing at NIOZ. Instrumental sample flow
rate was calibrated on a regular base but turned out to be remarkably constant
(ca. 120-130 µl/min). Accuracy of counting: replicate measurements showed that
variation in cell numbers was in the order of 2% (n=5)
The advantage of direct
analysis is that insight of the phytoplankton composition can be given within a
few minutes using whole untreated life samples. As a result set-ups for growth
or grazing experiments can be adapted or changed if desired. Furthermore, the
prokaryotic phytoplankter Prochlorococcus, in particular at surface waters, can
only be detected in life samples. Preservation negatively effects fluorescence
signals and causes cell rupture. Since this species was in particular abundant
(often >80% of total cell numbers), on-line analysis turned out to be a wise
decision.
Life samples were counted
usually within 1 hour after sampling and kept on melting ice in the dark to
prevent light damage or changes in cellular properties due to storage. Next to
life samples, small volumes (2 ml) were preserved with paraformaldehyde (0.5%
final solution) at -80º C for post-analysis of DNA of phytoplankton and
bacteria at NIOZ.
The instrument was used to
analyse phytoplankton samples of the CTD casts and experiments:
1) the continuous 24 hour CTD-rosette sampling (Day 1)
2) whole community incubations in the deck incubator
subject to different incident irradiances (Day 2)
3) grazing experiments of microzooplankton (Day2, 4,5)
4) grazing experiment of copepods (Day 2, 4 and 5)
Primary production
(G.W.Kraay and S Oosterhuis)
During this cruise samples
were taken for primary production at each station 3 times for the 14C production
and one to two times for the oxygen community production and respiration. On
the stations 4 and 5 additional samples were spiked with H2O18 to measure the
real gross production.
Sampling was done at the
first morning CTD cast at four o'clock, eight depths were sampled for the 14C
method and six depths for the oxygen light-dark method. These depths were
calculated from the optical PAR sensor measurements from the day before. The
PAR sensor was mounted on the rosette sampler. In the sampling strategy special
attention was given to the fluorescence peak
Duplicates of the acid
cleaned 250ml 14C polycarbonate bottles were spiked with 5 to 15 (Ci (14C)
bicarbonate, depending on expected production. For the oxygen method three to
four replicates were taken each for the initial the dark and the light values.
The H2O18 was done in 250ml oxygen glass bottles, two for the incubation and
two for the initial isotope ratio.
All these kind of bottles
were deployed on a free floating rig at about six o'clock local time, at the
same depth of sampling. coolbox. At six o'clock in the afternoon, just before
dark. The dark incubations and the night-time of the 24 hours incubations were
stored the in a coolbox. The 14C samples were filtered over 47mm GFF filters at
low overpressure. Overpressure was used because of the high depth of
incubations, this gives often gas oversaturation in the water and increases the
filtration time. Filters were fumed with damp of fuming HCL in order to remove
inorganic radioactive bicarbonate and the possible calcification of some algae
species. The filters were stored in scintilationflasks in the minus 80 freezer,
for analysing later in the lab.
The oxygen bottles were analysed on board by the Winkler spectro- photometry
method, described in an other paragraph. The samples for the H2O18 gross
production were conserved with a iodide solution and stored under water in a
coolbox for analysing later in the lab where the gases will be stripped from
the seawater and the 18/16 ratio of the dissolved O2 can be measured with a
isotope mass spectrometer.
The phytoplankton C14
production will be estimated using the following equation:
(Mol C/l= (((dpmL1+dpmL2)/2-dpmD)/added dpm)*1.05*2080.
Whereas dpmL1: radioactivity in terms of disintegration's per minute of light bottle 1
dpmL2: the same but for light bottle 2
dpmD: the same but for the dark bottle
1.05: the discrimination factor for C14/C12
2080: Concentration used for the total inorganic C in (Mol/l
For the oxygen community
production and respiration: Net O2 production = the difference in the measured
dissolved O2 concentration of seawater before and after the 12 hours
incubation. Gross production = The difference in the measured dissolved O2
concentration in the light and the dark bottles.
O-18 Gross O2 will by
calculated by the method M.L Bender et al.
Reference: The carbon balance
during the 1989 spring bloom in the North Atlantic Ocean, 47oN,20o. Deep sea
Research. Vol. 39, No 10. pp 1707-1725, 1992
Primary Production / New
Production
(Brian Irwin and Heather
Bouman)
PI Experiments
Discrete water samples were
collected at pre-selected depths in the euphotic zone by the rosette sampler.
At transit stations two depths in the mixed layer (10 m and 40 m) were sampled.
On day 1 of each of the long stations water from a single depth was collected
every 3 hours from 0400 to 1930 hours. Selected depths were 10m at station 100,
30m at station 200, 60m at station 300, 90 m (deep chlorophyll maximum) at
station 400 and 70 m at station 500. On subsequent days on the long stations
two samples at 10 m intervals were collected twice a day to get a complete
profile of the euphotic zone.
Primary production was
estimated by the 14C method. A total of 30 light bottles for each experiment were
incubated for 3 hours in a light gradient. At the end of the experiment the
phytoplankton was collected on GF/F glass fibre filters for later counting at
the Bedford Institute of Oceanography (BIO).
For each PI experiment
samples were also collected for chlorophyll, particulate carbon and nitrogen,
pigments by HPLC, absorption spectra and inorganic nutrients. All samples
except chlorophyll and nutrients will be analysed at BIO.
table of PI
Experiments
|
Date
|
Station #
|
Cast #
|
Depth
|
|
26/07
|
002
|
01
|
10, 40
|
|
|
004
|
01
|
10, 40
|
|
27/07
|
009
|
01
|
20, 50
|
|
|
010
|
01
|
20, 50
|
|
28/07
|
013
|
01
|
10, 40
|
|
29/07
|
100
|
01
|
10
|
|
|
100
|
06
|
10
|
|
|
100
|
11
|
10
|
|
|
100
|
15
|
10
|
|
|
100
|
19
|
10
|
|
|
100
|
23
|
10
|
|
30/07
|
100
|
33
|
5, 20
|
|
|
100
|
41
|
30, 40
|
|
31/07
|
100
|
46
|
50, 60
|
|
|
100
|
52
|
70, 80
|
|
01/08
|
100
|
59
|
90, 100
|
|
|
100
|
65
|
110, 120
|
|
02/08
|
100
|
72
|
40, 90
|
|
03/08
|
104
|
02
|
10, 40
|
|
04/08
|
113
|
01
|
10,40
|
|
05/08
|
200
|
01
|
30
|
|
|
200
|
06
|
30
|
|
05/08
|
200
|
11
|
30
|
|
|
200
|
17
|
30
|
|
|
200
|
21
|
30
|
|
|
200
|
26
|
30
|
|
06/08
|
200
|
35
|
5, 20
|
|
|
200
|
42
|
30,40
|
|
07/08
|
200
|
50
|
50, 60
|
|
|
200
|
55
|
70, 80
|
|
08/08
|
200
|
64
|
90, 100
|
|
|
200
|
66
|
110, 120
|
|
09/08
|
200
|
79
|
100, 130
|
|
10/08
|
202
|
02
|
10, 40
|
|
11/08
|
300
|
01
|
60
|
|
|
300
|
06
|
60
|
|
|
300
|
11
|
60
|
|
|
300
|
17
|
60
|
|
|
300
|
21
|
60
|
|
|
300
|
26
|
60
|
|
12/08
|
300
|
35
|
5, 20
|
|
|
300
|
43
|
30, 40
|
|
13/08
|
300
|
50
|
50, 60
|
|
|
300
|
56
|
70, 80
|
|
14/08
|
300
|
61
|
90, 100
|
|
|
300
|
69
|
120, 140
|
|
15/08
|
300
|
76
|
120, 160
|
|
16/08
|
304
|
02
|
10, 40
|
|
17/08
|
306
|
02
|
10, 40
|
|
18/08
|
400
|
01
|
90
|
|
|
400
|
06
|
90
|
|
|
400
|
10
|
90
|
|
|
400
|
16
|
90
|
|
|
400
|
20
|
90
|
|
|
400
|
24
|
90
|
|
19/08
|
400
|
33
|
5, 20
|
|
|
400
|
43
|
30, 40
|
|
20/08
|
400
|
52
|
50, 60
|
|
|
400
|
58
|
70, 80
|
|
21/08
|
400
|
63
|
90, 100
|
|
|
400
|
72
|
110, 120
|
|
22/08
|
400
|
81
|
70, 94
|
|
23/08
|
405
|
01
|
10, 40
|
|
24/08
|
500
|
01
|
70
|
|
|
500
|
06
|
70
|
|
|
500
|
10
|
70
|
|
|
500
|
16
|
70
|
|
24/08
|
500
|
20
|
70
|
|
|
500
|
24
|
70
|
|
25/08
|
500
|
32
|
5, 20
|
|
|
500
|
43
|
30,40
|
|
26/08
|
500
|
52
|
50,60
|
|
|
500
|
58
|
70,80
|
|
27/08
|
500
|
63
|
90, 100
|
|
|
500
|
72
|
110, 120
|
|
28/08
|
500
|
81
|
50, 83
|
In Situ Experiments
Water samples were collected
from 8 depths in the euphotic zone by the rosette sampler. Primary production
was estimated by the addition of 13CO3 to 1L aliquots from each depth in 1L
polycarbonate bottles. New production was estimated by the addition of 15NO3
and 15NH3 to each bottle. The bottles were incubated in situ at their
respective depths from dawn to dusk. Phytoplankton were then filtered onto GF/F
glass fibre filters for later analysis at BIO. These experiments were carried
out on days 2, 3 and 4 of each of the long stations.
Table of In
Situ Experiments
|
Date
|
Station #
|
Cast #
|
Depths
|
|
30/07
|
100
|
33
|
5, 10, 30, 45, 60, 75, 85, 95
|
|
31/07
|
100
|
46
|
5, 10, 30, 45, 60, 75, 85, 95
|
|
01/08
|
100
|
59
|
5, 15, 40, 55, 75, 85, 90, 105
|
|
06/08
|
200
|
35
|
10, 30, 60, 80, 100, 110, 120, 140
|
|
07/08
|
200
|
50
|
10, 30, 65, 82, 90, 100, 125, 135
|
|
08/08
|
200
|
64
|
10, 30, 65, 82, 90, 100, 125, 135
|
|
12/08
|
300
|
35
|
15, 35, 60, 80, 100, 115, 130, 150
|
|
13/08
|
300
|
50
|
15, 35, 60, 80, 100, 110, 120, 150
|
|
14/08
|
300
|
61
|
15, 35, 60, 80, 100, 110, 120, 150
|
|
19/08
|
400
|
33
|
10, 22, 43, 75, 88, 100, 120, 130
|
|
20/08
|
400
|
52
|
10, 22, 43, 75, 88, 100, 120, 130
|
|
21/08
|
400
|
63
|
10, 22, 43, 75, 88, 100, 120, 130
|
|
25/08
|
500
|
32
|
20, 40, 60, 70, 80, 90, 100, 110
|
|
26/08
|
500
|
52
|
20, 40, 60, 70, 80, 90, 110, 130
|
|
27/08
|
500
|
63
|
20, 40, 60, 70, 80, 90, 110, 130
|
Grazing of microzooplankton
on picophytoplankton, nano-flagellates and heterotrophic bacteria in the
tropical Atlantic DCM.
(B.R. Kuipers and H.J. Witte)
The chlorophyll-a maximum at low
light intensities just above the nutricline at 70-120 m depth in the tropical
Atlantic suggests a niche for a micrograzer community especially adapted to
life in this surrounding. The most obvious function of the protozoan grazers is
to effectuate (next to the heterotrophic bacteria) the local nutrient
regeneration which allows for ongoing regenerated production in the DCM. At the
same time the micrograzers function as the trophic link between the
predominantly picoplanktonic DCM autotrophs and mesozooplankton. This leads to
faecal pellet production and downward nutrient export from the DCM. Because
modelling of the dynamics of the plankton community in the DCM as a function of
light and nutrient availability along the vertical is one of the objectives of
the present project, special attention was given to a quantitative field study
of the DCM micrograzers. At all five stations of the tropical Atlantic DCM
cruise, microzooplankton abundance and composition were studied in the
vertical, whereas in situ and shipboard grazing measurements were made
including size fractionation of grazers as well as prey.
For a quantitative
description of the microscopic grazer population 100 ml microzooplankton
samples were collected at a series of depth and preserved in 1.5 % acid lugol
solution for later enumeration of the dominating 20 - 200 µm groups by inverted
settlement microscopy. 5 ml glutaraldehyde preserved and proflavine stained
samples were concentrated on Sudan black stained 0.2 or 0.4 µm polycarbonate
filters for epifluorescence microscopically counting of the HNAN's and
heterotrophic bacteria. 2 ml samples were preserved at -80oC in 4% paraformalin
for later (experimental) flowcytrometrical counting of heterotrophic bacteria
after staining (see Veldhuis and Kraay).
For the quantification of
grazing on different components of the phytoplankton and especially its pico
size-fraction, shipboard dilution series were incubated in fourfold in 300 ml
polycarbonate bottles, starting with natural water from just below / in / just
above the chlorophyll peak (as located during CTD downcast) and diluted with
the same water filtered through GF/F and 0.2 µm filters to 100, 70, 40, 20 and
10 % of the natural concentration. The incubations (slowly rotating bottles in
light and temperature conditions as naturally as possible) started at sunrise
with T=0 sampling of total chlorophyll, microzooplankton and HNAN density in
100% bottles, from which T=0 values for al other dilution's were calculated.
Flowcytometrical counting of cyanobacteria and prochlorophytes (quadruple) and
bacterial sampling was done in all 100, 70. 40, 20 and 10 % incubation bottles
at T=0.
Additional to this, a 100 and 40 % dilution experiment was done with natural
water very carefully sieved (by gravity) through 10 µm, 5µm, 3 µ and 1 µm
polycarbonate filters, in order to unravel the predator-prey size
relationships. In this size fractionated set T=0 measurements comprised
flow-cytometry, bacteria and HNAN's in all bottles and microzooplankton only in
100%. All measurements including the microzooplankton fixation were repeated at
the end of the 24 hr light period; at T=12 all bottles were sampled for
flow-cytometry. After analysis this set of data will provide estimates on gross
growth rates (minus autotrophs respiration) and grazing rates for all size
groups both for day and night.
Because estimation of in situ
gross- and net growth rates (the principle of the applied Landry & Hasset
dilution method) of the highly adapted picophytoplankton in the severely light
limited DCM is most sensitive for the experimental light-regime, in situ
incubations completed the grazing study. These were done in 80 ml polycarbonate
bottles attached to the 14C in situ incubation string at the original depth of
the water sample in order to ensure accurate low light conditions. These
incubations were lowered before sunrise and recovered after sunset. Duplo
incubations of 3, 2 and 1 µm sieved natural water diluted to 100, 50 and 20 %
were made; flow-cytometrical measurements and bacterial and HNAN sampling were
done at T=0 and T=24, flow-cytometry in all bottle at T=12.
Preliminary impressions of
microzooplankton grazing could till now only be obtained from the shipboard
flow-cytometry, which yielded prochlorophyte growth rates from the same
incubations. Grazing rates on prochlorophytes were in the order of µ= 0.1 - 0.2
per 24 hrs, whereas prochlorophyte growth rates were 0 below and also in the
chlorophyll peak, whereas they exceeded the grazing rates at the depth of
maximal primary production (Oxygen-maximum) just above the Chl-a peak.Dilution
had its most clear effect in the 3 µm filtered incubations; in the coarser
samples there were obviously more trophic levels present, whereas under 1 µm
only prochlorophytes and other prey remained. This means that the grazers
feeding on prochlorophytes must be sought in the 1-3 µm size range and are most
likely small heterotrophic flagellates (HNAN's). Grazing of microzooplankton on
larger phytoplankton, HNAN's, bacteria, cyanobacteria and prochlorophytes, and
grazing of HNAN's on bacteria and cyano's will be known after analysis of all
samples. Grazing of microzooplankton by mesozooplankton was studied by Fransz
and Gonzalez.
Mesozooplankton
(George Fransz and Santiago
Gonzalez)
The animal plankton in the
size range of 200 to 2000 µm can be separated from the usually smaller
bacteria, algae, microzooplankton and detritus particles by filtering with a
200 µm screen. These animals feed on algae, microzooplankton and POC and can be
important as participants in the food web and for the mineralisation and
sedimentation (in fecal pellets) of particulate matter. The work on board was
directed to obtain data on 1) abundance and vertical distribution of stocks and
2) on activities such as grazing, respiration and egg production in the
different depth layers related to the DCM.. Sampling and incubation experiments
were carried out at each of the 5 main stations around noon and around midnight
to be able to study effects of diurnal migration and activity patterns.
Stocks
Two series of depth
stratified samples were obtained per station with a Hydrobios multinet fitted
with 5 nets with 50 µm mesh width. The series were obtained by oblique haul of
the towed net. The first series started at 400 m depth and concerned the 5
discrete depth layers between 400 m - 300 m - 200 m - underside DCM - upper
side DCM - 50 m - surface. A second series of 5 layers with a more detailed
depth resolution in the biologically active zone started at the underside of
the DCM and covered three zones in the DCM (lower, peak and upper zone), and
two depth layers between upper side DCM - 25 m - surface. At each station both
series were obtained once at noon and once at midnight. Because the depth
sensor of the multinet did not function well, intervals of the temperature
output were used to indicate the depth layers according to temperature profiles
provided by the last CTD cast before the net tow. The CTD profiles of
chlorophyll were used to indicate the position of the DCM.
The net samples were split
with a Folsom plankton splitter. One half was preserved in 4% buffered
formaline for numerical and species analysis. This half also includes organisms
between 50 an 200 µm, mainly small sized cyclopoid copepods which can be
predominant in tropical waters, and eggs and juvenile stages which can indicate
the productivity of the species concerned. The other half was filtered over
2000 µm, 1000 µm and 200 µm screens to obtain the size classes 200 to 1000 and
1000 to 2000 µm. Both size classes were split into two halves. One of these
halves was filtered over a tared GF/C glass fibre filter to determine AFDW (ash
free dry weight), the other half was subsampled to adequate size and filtered
on a small GF-F filter to determine carbon and nitrogen weight with a CHN
analyser.
Throughout the cruise
photographs were made with a microscope or macroscope camera of remarkably
shaped organisms and predominant copepod species to prepare colour slides.
Activities
During each station a 200 l
water sample was collected in the morning with the rosette sampler in three
subzones of the DCM zone: at the chlorophyll peak, above the peak and below the
peak. Per day one subzone was sampled and at station 500 the lower subzone
could not be sampled due to lack of incubation time. Four 20 l glass jars were
filled with the water and connected in such a way, that two jars could be
sampled for oxygen with immediate replenishment with water from the other jars.
In this way two couples of jars formed two set-ups for respiration experiments.
To both jars of one of the couples the 200 to 2000 µm size fraction of
mesozooplankton from 60 l of water was added, carefully concentrated by
siphoning off through a 200 µm gauze. In this couple the mesozooplankton
concentration was 4x the natural concentration. Both set-ups were placed in a
container at ambient water temperature as controlled by air conditioning.
Samples were collected 0h, 6h, 12h and 24h after incubation to measure oxygen,
and 0h, 6h and 24h to measure chlorophyll, algal cell number and
microzooplankton concentration. Respiration and grazing rates can be estimated
from relative decreases of these variables in the jars with added zooplankton.
Oxygen was measured on board by a Winkler titration method developed by G.
Kraay (see ....). Algal cells were counted by flow cytometry. The
microzooplankton will be analysed later in the laboratory by methods used by B.
Kuipers and H. Witte (see ....), while the chlorophyll will be measured later
by spectroscopical methods. At the end of the experiments 5 to 10 l of water
was filtered to count the zooplankton (mainly copepods). This sample was
filtered subsequently on a GF-F filter for CHN analysis.
On each station the upper
layer from the underside of the DCM to the surface was sampled with a 200µm
WP-2 vertical net to collect alive zooplankton during 3 days at noon and at
midnight. Adult females of predominant copepod species were picked out and
placed in 1 l glass beakers to be incubated for 24 h. After incubation eggs and
fecal pellets were counted. Gauze bottoms in the beakers prevented ingestion of
eggs and pellets. Fecal pellets and females were filtered separately for CHN
analysis.
Preliminary results
Visual inspection of the
filters for dry weight gave an impression of mesozooplankton abundance. The
filters suggested that mesozooplankton was present at all stations with the
highest abundance in the water layer between the surface and the peak of the
DCM. Below the DCM the abundance was very low. Biomass seemed to be dominated
by the 200 to 1000 µm size class, mainly consisting of copepods in a high
species diversity. Quantitative data will be obtained by analysis of the
samples in the home laboratory. The 50 µm net samples contained mainly
zooplankton and only low numbers of net phytoplankton (mainly long diatom
chains).
In the grazing and
respiration experiments algal cell abundance was monitored on board with the
flow cytometer and dissolved oxygen was measured with the Winkler method. Two
clusters of algae were counted: small cells representing the predominant
prochlorophytes and (if present as a separate cluster) a cluster of somewhat
larger and more fluorescent cells (large cells). The following Figures present
the changes of relative algal cell concentration (the concentration divided by
the initial concentration in the untreated water) and dissolved oxygen
concentration for the 5 stations in the upper, middle and lower part of the
DCM. The variation in algal abundance was consistently similar in natural water
(blank) and water with 4x increased density of mesozooplankton (meso). Hence
there was no indication of increased grazing in the zooplankton enriched jars.
The simplest explanation of this result is that the cells counted by the flow
cytometer were not eaten by the mesozooplankton.
During most incubation
experiments the oxygen concentration decreased faster in the jars with added
zooplankton than in the control jars. This difference may be used to estimate
weight specific respiration rates. The following table gives estimates of the
oxygen consumption per day of the mesozooplankton.
Figures mesozooplankton
Fig. 11A,B,C Changes in cell numbers
of selected groups of phytoplankton in incubations with increased number of
mesozooplankton A: upper part of DCM, B: middle part of DCM (peak) and C: lower
part of DCM.
Fig. 12 A,B Time course
measurements of oxygen respiration in samples with natural and increased number
of mesozooplankton.
Flying fish observations
(Swier Oosterhuis)
During the DCM project 1996
flying fish was counted. Taxonomy was not performed since the fishes couldn't
be caught. It was noticed that there were different species. The counting was
done during a 15 minutes period on the days when the ship was in transit. The
area observed was an area in front and on the side of the bow in an angle of 45
degree.
|
Date
|
time
|
position
|
number
|
|
23 July
|
11:00 hr
|
11 25 14 N 62 42 17 W
|
0
|
|
24 July
|
11:00 hr
|
10 11 00 N 59 12 30 W
|
3
|
|
25 July
|
17:30 hr
|
08 19 47 N 55 28 09 W
|
33
|
|
26 July
|
10:30 hr
|
07 32 28 N 56 48 28 W
|
65
|
|
27 July
|
16:00 hr
|
08 40 10 N 53 04 28 W
|
116
|
|
28 July
|
16:15 hr
|
10 04 29 N 51 15 12 W
|
360
|
|
2 August
|
16:00 hr
|
11 22 26 N 48 48 53 W
|
5
|
|
3 August
|
16:30 hr
|
12 44 22 N 45 19 27 W
|
12
|
|
4 August
|
14:45 hr
|
13 52 54 N 42 33 54 W
|
18
|
|
9 August
|
12:45 hr
|
15 40 00 N 40 49 00 W
|
14
|
|
10 August
|
17:00 hr
|
20 24 01 N 39 02 01 W
|
2
|
|
15 August
|
15:45 hr
|
23 58 06 N 37 38 38 W
|
0
|
|
16 August
|
11:45 hr
|
27 08 12 N 36 11 28 W
|
2
|
|
17 August
|
16:30 hr
|
31 57 08 N 33 57 40 W
|
2
|
|
22 August
|
16:30 hr
|
33 39 00 N 30 06 00 W
|
0
|
|
23 August
|
15:45 hr
|
33 51 41 N 25 12 41 W
|
0
|
|
28 August
|
15:30 hr
|
33 18 42 N 20 10 18 W
|
0
|
|
29 August
|
12:30 hr
|
31 37 28 N 16 48 29 W
|
0
|
Technical highlights during
DCM96.
(NIOZ technicians Lorendz
Boom, Eduard Bos and Ruud Groenewegen
The expedition was
technically a success. The problems encountered were mainly minor and were well
spread out over the duration of the cruise. The majority were solved or an
appropriate alternative found. A brief selection:
CTD-winch: Due to excessive
wear on the non-metal gearwheels the intended full ocean depth CTD-cast on each
station was limited to 2000 meters only. Salt intrusion and human error led to
some electrical problems with the cable. Restriction of the coolant flow for
the hydraulic power packs diesel motor caused rapid overheating until cured.
In the last few days of the cruise the hydraulic brake system for the gantry
failed and had to be replaced by a rope and pulley system to fix its position.
The airconditioners of two
containers had broken down while on board when not being used. Both were
repaired by a technician of the Tydeman crew, at great effort, but one kept
losing its coolant and eventually had to be shut down.
A lot of equipment was having
problems with the severe brown-outs of the ships power supply, caused by heavy
machinery such as the active rudder. A spare motor-generator combination was
put into service to bridge these power gaps by using the inertia of their
rotors.
Use of the large volume water
sampler (waterchest) had to be abandoned because the ships winch could not
pay-out fast enough to ensure proper functioning of the chest.
A number of radio beacons got
their antennas broken but there were enough spare parts to last the cruise.
Given the antenna heights used, their practical range perfectly matched the
theoretical 10 nautical miles.
The pressure sensor of the
Multinet appeared unrepairable. This led to sampling based on the temperature
profile provided by the CTD.
The UV-sensor got its cable
entangled in the ships propeller and was rerouted through the cable used by
ASIR and AC-9. This appeared to be an improvement in both handling the
equipment and obtainable maximum depth.
