Introduction

R/V Pelagia Cruise BSIK/CAMP/LOCO/CIS

INTRODUCTION

As the large number of acronyms suggests, this is a programme that combines a lot of different projects. Writing out all participating programmes should even make the name much longer. The different programmes share that they all deal with climate variability in the Northern Atlantic Ocean and in particular the Irminger Sea near Greenland.

The CAMP (=Clivarnet Atlantic Monitoring Programme) project

The goal of the research carried out during the cruise is to establish the hydrography along a section between Ireland and Greenland. This section is the former A1E/AR7E section of the WOCE Hydrographic Programme, which has been surveyed annually since 1990. The re-surveying of this section is carried out in order to identify climate related inter-annual changes of the hydrographic structure in the North Atlantic Ocean. This survey is carried out in co-operation with Dr. K. P. Koltermann (BSH, Hamburg) who is in charge of similar surveys along sections located further to the south. The main instrument used is the so-called CTD-rosette. The CTD is an instrument package that measures a lot of physical parameters and the rosette is a series of 22 remotely closable bottles to collect water from different depths. The CTD-rosette frame is lowered with a velocity of about 1 m/s. During the de-/ascent a number of parameters is measured, in particular T (temperature), C (conductivity), p (pressure), oxygen concentration, turbidity and fluorescence. From these quantities several new parameters are derived such as salinity and density of the water. During the up-cast water samples are taken at prescribed depths. After each cast the CTD/rosette frame is placed on deck. Subsequently water samples are drawn for the determination of dissolved oxygen, dissolved carbon dioxide, nutrients, and salinity. The readings of the reversing electronic temperature and pressure sensors are recorded for calibration.

The LOCO (=Long-term Ocean Climate Observations) project

Satellite altimetry shows strong inter-annual changes in the sea surface level (SSL). These changes seem to be correlated with the NAO index (North Atlantic Oscillation). The near-annual survey of the AR7E section (see CAMP project) shows that these changes are correlated with water mass properties in the Irminger Sea. This survey, however, does not resolve the mechanism behind the changes in the water masses from year to year. In order to obtain a better resolution of the underlying processes, such as convection caused by strong surface cooling in winter or by changes in the advection caused by wind driven currents, measurements are done during the whole year. Within the framework of the Dutch Long-term Ocean Climate Observations (LOCO) programme two profiling CTD moorings have been deployed in 2003 in the Irminger Sea for a period of 5 years at least. During this cruise these moorings will be recovered, serviced and re-deployed. The moorings contain ADCP's to determine water velocity profiles, a CTD-profiler that moves up and down along a cable yielding one profile of physical parameters per day.

VAMOC (Variability of Atlantic Meridional Overturning Circulation) programme

This is a programme within the framework of RAPID (together with Norwegian and British colleagues). The Dutch contribution comes from the Royal NIOZ and Free University of Amsterdam (VU).The main question is: How did the Atlantic Meridional Overturning Circulation (AMOC) change on glacial-interglacial timescales and did the change take place in the same way every time? These changes can be derived from the bottom sediments. Within this project the Royal NIOZ is mainly studying the present on-going sedimentation in relation to the present water circulation. Others base their research on sediment cores from the area and the modeling of the underlying processes. An important aspect of the VAMOC project is the study of drift deposits. These are deposits with extremely high sedimentation rates of sediments that arrive more or less horizontally. On this cruise a mooring with two sediment traps will be recovered, serviced and re-deployed. The sediment traps contain 24 bottles that collect settling particles in intervals of two weeks over a period of one year. Thus seasonal cycles and short-lasting pulses of sediment resuspension can be observed. Having started in 2003, the mooring is planned for 5 years with refreshing every year. The traps are near the bottom (at about 3000 m) and 250 m above the bottom. Next year additional measurements will be done with a bottom lander with sensors to determine how drift deposits are actually formed. Detailed high-resolution information will be obtained to study the rapid change between the last glacial to the present interglacial. This period is very accurately dated by two well-known ash layers from Icelandic volcanic eruptions.

Animate CIS (=Central Irminger Sea)

Scientific rationale.

Physical:

The site of the CIS project is located in the centre of the Irminger Sea gyre. It is a region of minimum stratification. Deep convection is expected to reach maximum depth here, but the inter-annual variability of deep mixing and water mass formation is poorly known at present. The site is expected to be representative of the eastern part of the subpolar gyre. This position is an excellent place to study the relationship with the NAO index.

(Bio/geo)chemical:

The subpolar gyre is one of the most important regions of CO2 uptake of the oceans, and time-series observations in this area are important for quantifying the sequestration and its variability. This is possible by combined measurements of physical variables and CO2 partial pressure.

Biological:

The subpolar gyre is one of the ocean regions with a rather simple food chain, and the zooplankton community is dominated by a single species (Calanus Finmarchicus). There are interesting research questions about this important species and its relevance for the fisheries in the region (redfish), as well as about physical/climatic forcing. Being in the middle of a gyre, away from boundaries, the hope is that the system is reasonably 1-D and mooring time series can be more easily interpreted.

During this cruise the huge CIS-mooring will be recovered, serviced and re-deployed.

CARBOOCEAN

The CARBOOCEAN project consists of a huge number of subprojects. See the previous cruise 64PE239 for more information. One of the main aims of the project is to determine the ocean's uptake of atmospheric carbon dioxide (CO2), the most important manageable driving agent for climate change. The ocean has the most significant overall potential as a sink for anthropogenic CO2. The correct quantification of this sink is a fundamental necessary condition for all realistic prognostic climate simulations. During this cruise a study is made of how the atmospheric CO2 that enters the ocean surface finds its way to deeper layers in the ocean.

ARGO floats

At several positions along the AR7E section ARGO floats, from 3 different institutes, will be deployed. These floats stay at a pre-set depth for several days and subsequently measure a vertical profile of mainly physical parameters that they send to a central station via satellite during a short surface interval. Thereafter the float returns to the parking depth. The floats are supposed to stay working for several years.