Söderkvist, J., Nielsen, T.G. & Jespersen, M. 2006. NERI Technical Report No. 581, 54 pp.
Summary
A hydrographic and plankton community description of the Disko Bay region has been made. The aim was to identify sensitive regions and time periods to oil spill. Analysis of historical observations of hydrography during the period April 1996 to August 1998 and spring 2005 showed that there was only polar water in Disko Bay, originating from the Arctic Ocean. In summer, the surface salinity is lower than in the polar water, which is an effect of ice melt from glaciers and sea ice. The observed hydrography at the Arctic Station, located 1 nautical mile south of Qeqertarsuaq, showed that the warming of the surface water in Disko Bay started in May and continued to late August. Ice melt during summer increased the strength of the stratification and intensified the heating rate in the upper layers. The summer mixed layer thickness was typically 10-20 m. Convection together with advection of water from outside the bay from early September 1996 to late January 1997 increased the sea surface salinity from 30.7 to 33.4. Satellite observations showed that the ice growth season exhibited large interannual variations. The ice growth season in 1996 and 1997 started in January, but in 2005 Disko Bay was nearly ice free throughout the winter season.
In contrast to the general believe that decreased surface density due to warming or decreased surface salinity triggers the spring bloom, the present study suggests that increased salinity below the surface layer initiated the spring blooms in Disko Bay in 1997 and 2005. The increase in vertical stratification might have been generated by upwelling or inflow of dense water in the deeper parts of Disko Bay. The spring bloom started around the 20th of April for both 1997 and 2005.
The horizontal mapping performed in June 1996 and 1997 in Disko Bay suggests that there was a clockwise circulation in the upper 100 m during early summer. The coastal current in the bay received warm and saline water from the West Greenland Current. A fraction of the water left the bay along the southern coast of Disko Island. Analysis of the easternmost area in June 1997 suggests that there was an inflow in the surface layer through the northern entrance of Disko Bay, the Vaigat.
The aim of the report is – based on an analysis of physical and biological oceanography with emphasis on shrimp and fish larvae distribution – to support the identification of potential hot spots in time and space where an oil spill will have the largest consequences on the marine ecosystem. The present report provides an overview of the hydrography and plankton dynamics and shrimp and fish larvae distribution in Disko Bay, and the waters along south west Greenland.
In this context, knowledge about the interaction between hydrography and the pelagic food web is essential. Therefore attention is drawn to the identification of hydrodynamic discontinuities, i.e. sites where water masses with different properties meet and enhanced biological activity can be expected. These sites are particularly sensitive and areas where pronounced ecological effects of a potential oil spill can be expected.
Full report in pdf-format (3,200 kB).
