central Labrador Sea
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Zooplankton are sampled once a year during spring or early summer (May-July) at up to 28 stations along a section across the Labrador Sea between Hamilton Bank on the Labrador Shelf and Cape Desolation on the Greenland Shelf. This section, the AR7W section (Atlantic Repeat Hydrography Line 7), was first sampled during the World Ocean Circulation Experiment (WOCE) in 1990, when measurements of temperature, salinity, and a comprehensive suite of chemical variables were made. In 1994, sampling of biological variables including bacteria, phytoplankton, and zooplankton was added.
The AR7W section includes the broad Labrador Shelf and narrow Greenland Shelf, which are both roughly 100 m in depth. Both are influenced by arctic inflows: from the north on the Labrador Shelf via the inshore branch of the Labrador Current, and from the south on the Greenland Shelf, via the West Greenland Current, which is formed as the East Greenland Current turns around the tip of Greenland. There are strong boundary currents beyond the shelf-break, which include inputs of arctic water from the north along the Labrador slope in the offshore branch of the Labrador Current, and of Atlantic water from the south into the eastern region of the Labrador Sea in the Irminger Current. The central basin exceeds 3500 m at its deepest point and is composed of a mixture of waters of Atlantic and Arctic origin. Most of the annual occupations of the AR7W section have been during late May (1996, 1997, 2000, 2004-2011). In some years the Labrador Shelf is still covered with pack ice at this time, which prevents sampling at some or all of the stations there. Farther east the section is ice-free, except for a few icebergs on or near the Greenland Shelf, which can also interfere with sampling at some stations.
Zooplankton sampling is by means of 202 ?m mesh ring nets, towed vertically between 100 m and the surface. Zooplankton are preserved in formalin, identified and enumerated, and the abundance data are analysed using a Multi-dimensional scaling method that groups stations according to community structure. The stations generally fall into five groups, which correspond geographically to the Labrador Shelf, the Labrador Slope, western and eastern regions of the central basin and the Greenland Shelf (Head et al. 2003). The boundaries between the three central groups are flexible, while the shelf stations are defined by bathymetry.
Head, E.J.H., Harris, L.R., Yashayaev, I. (2003) Distributions of Calanus spp. and other mesozooplankton in the Labrador Sea in relation to hydrography in spring and early summer (1995-2000). Prog. Oceanogr. 59: 1-30
Licandro, P., Head, E., Gislason, A., Benfield, M.C., Harvey, M., Margonski, P., Silke, J. (2011) Overview of trends in plankton communities. Chapter 7. pp103-122, in Reid, P.C. and Valdes, I. ICES Status Report on Climate Change in the North Atlantic. ICES Cooperative Research Report No. 310.