After having reached the northernmost point of the expedition at the end of last week, we moved southeastward across the East Greenland Current toward the continental shelf of Northeast Greenland, that we reached at the outlet of Westwind Trough.
Underneath the surface layer of cold polar water, this deep shelf depression is filled with relatively warm water of Atlantic Ocean origin that can be traced up to the coast of Greenland. Subsequently we followed the trough axis far inshore toward the east across this particularly wide stretch of continental shelf, interrupted by two hydrographic sections across the trough and the deployment of a mooring. After that the cruise track turned toward the south across the shallow Belgica bank until reaching the latitude of the traditional zonal hydrographic section across Fram Strait at 78°50’N. From there we then headed back westward toward the shelf edge. Meanwhile we have reached the East Greenland Current in the deep part of Fram Strait again. The foci our work have been to observe the circulation, hydrographic properties and turbulent mixing both in Westwind Trough and close to the shelf edge, the geochemical and biochemical mapping of this region, and helicopter-based geodetic work on the Greenland coast. A special focus was on marine biology, as will be explained in the following.
Marine biological research during the expedition PS 100 addresses the question how climate change, the retreat of the Arctic sea ice and the inflow of warmer Atlantic water masses into the Arctic affect zooplankton and marine food chains. Zooplankton are small critters drifting with the ocean currents. They include a wide variety of different animal taxa. 60 to 80% of the total biomass is comprised by copepods (tiny crustaceans) as the most dominant zooplankton group.
Do warm-water species of Atlantic origin replace polar cold-water species? What is the fate of Arctic organisms living in or under the sea ice, when the sea ice melts and they loose their habitat? What effects do shifts in plankton composition have for the marine food chain and higher trophic levels including fish, seabirds and marine mammals?
To answer these questions, a team of six biologists and geneticists from the University of Bremen, from AWI and from the University of the Algarve in Portugal sample a large study area in Fram Strait between 79 and 80.5°N and from 12 to 0°W. The East Greenland Current transports zooplankton and sea ice from the central Arctic Ocean into this area, where the sea ice melts. First preliminary results of this cruise show that ice algae, which are released into the water column, when the sea ice melts, sink relatively quickly to great depths of more than 1000 m. On their way down, they are grazed upon by copepods and amphipods.
In temperature-controlled lab containers on board, experimental studies are conducted regarding the energy budget and temperature tolerance of polar vs. Atlantic zooplankton species in order to assess at which temperature ranges polar or Atlantic species prevail. Molecular analyses in the home lab will show which genes are most important for temperature acclimation and whether gene expression differs between polar and Atlantic congeners. Since polar species are usually far bigger and more lipid-rich than their Atlantic counterparts, a shift in the community composition towards more warm-water species will negatively affect food quality for predators such as fish or seabirds.
Plankton studies are supplemented by sea-ice sampling to collect ice algae and by helicopter flights to assess the habitat use and possibly stock size of seals and other marine mammals in the study area.
During the last week we were able to catch some spectacular sites of the coast of Greenland, several icebergs and polar bears. In a couple of days we will leave this working area, only to return to the shelf of Northeast Greenland about 200 km further to the south at Norske Trough
Many greetings from
Torsten Kanzow, Holger Auel on behalf of the entire biology team
