LOCO-IRMINGER SEA
From the Gulfstream system warm and saline water enters the sub-arctic North Atlantic Ocean. There its properties change due to air-sea interaction. Sub-Arctic Mode Water (SAMW) is progressively formed in the cyclonic gyre of the North Atlantic Ocean by convective mixing in successive winters. One of the last stages of SAMW is found in the centre of the cyclonic sub-gyre in the Irminger Sea. Evidence is growing that in this ocean region occasionally deep convection occurs which homogenizes the water column to a depth of nearly 2000m. The heat, released to the atmosphere during the transformation of Gulfstream water to the much cooler SAMW is an important factor for the North Atlantic climate.
| Annual hydrographic surveys during the WOCE and CLIVAR programmes as well as satellite altimetry have shown that the inter-annual and seasonal variability of the hydrography in the Irminger Sea are of the same order of magnitude. Eddy variability is definitely smaller. How these different types of variability interact, and how convective mixing in winter depends on this variability is not well known. Therefore Royal NIOZ started a monitoring programme with moored sensors in the summer of 2003. At three positions in the Irminger Sea near the annual WOCE-CLIVAR section, moorings fitted with a profiling CTD and with ADCPs will monitor the varying hydrographic structure from 2003 until at least 2008. Together with two profiling moorings from Woods Hole Oceanographic Institution and a European ANIMATE mooring the LOCO moorings will contribute to a pre-operational monitoring programme in the Irminger Sea. |  |
| ADCP |
Near the central mooring site a sediment trap mooring has also been deployed to monitor the downward particle flux for 5 years. This will allow to determine the relation between climatic variability of the hydrography and the near bottom particle flux towards the sediment. from 2003 to 2004 additionally a internal wave array was deployed in the Irminger Sea.
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| Fig.1 The bathymetry of the Irminger Sea with depth contours every 500 m. The straight line shows the WOCE/CLIVAR section along which since 1990 until present nearly annually hydrographic surveys have been carried out. The red dots show the mooring locations and the four easternmost moorings form the internal wave array. |
LOCO-MOZAMBIQUE CHANNEL
A pilot-project with an array of current meter moorings in 2000-2001 showed that the meridional mass transport through the Mozambique Channel fluctuates remarkably regular with values between 20 Sv northwards and 60 Sv southwards. The mean value for this one year of observations is some 15 Sv southwards (Fig. 1).
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| Fig. 1 - Volume transport through the Mozambique Channel |
The spatial structure of the current field suggested that during the periods with a strong southward flow a current jet seperates from the African coast and forms a large anti-cyclonic eddy. These eddies migrate southward, interact with the Agulhas current and seem to initialize the meandering of the Agulhas current, thereby influence the formation of Agulhas rings. Thus the flow in Mozambique Channel is of importance not only for the tropical-subtropical transport in the Indian Ocean but also for the Indian-Atlantic ocean exchange.
At intermediate and deep levels against the African continental slope a northward flowing Mozambique Undercurrent was observed with a mean northward speed of 4.6 cms-1 (1500 m) and 4.5 cms-1 (2500 m). Hydrographic observations showed that the deepest flow consists of North Atlantic Deep Water.
As part of the LOCO program a new array of moorings, with much more current meters, ADCP’s and T-S sensors, was deployed at the narrowest section in the Mozambique Channel in November 2003 (Fig. 2 and 3). These sub-surface moorings will be serviced each 1.5 years and the observations will continue till 2008. The observations will be used mainly to quantify the variability of the meridional mass and heat transport, to relate this variability to Indian Ocean (or El Nino) climate modes and to study the relation between this variability and the ‘downstream’ formation of Agulhas Rings.
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| Fig. 2 - Mooring section Mozambique Channel |