Aarhus University Seal / Aarhus Universitets segl

No. 357: Identification of offshore hot spots

Møller EF, Juul-Pedersen T, Mohn C, Dalgaard MA, Holding J, Sejr M, Schultz M, Lemcke S, Ratcliffe N, Garbus SE, Clausen DS, Mosbech A. 2019. Identification of offshore hot spots. An integrated biological oceanographic survey focusing on biodiversity, productivity and food chain relations. Aarhus University, DCE – Danish Centre for Environment and Energy, 65 pp. Scientific Report No. 357. http://dce2.au.dk/pub/SR357.pdf

Summary

This study is part of the Strategic Environmental Study Plan for Northeast Greenland established to provide environmental information for planning and regulating oil exploration activities and oil spill response in the Green-land Sea and the shelf off Northeast Greenland. The aim is to provide information on the ecology and temporal and spatial sensitivity of this very little studied marine ecosystem. As a part of this, an interdisciplinary survey with R/V Dana was conducted in August/September 2017. 82 stations were sampled between 2° W and 20° W and 74.5° N and 79° N, primarily at stations on the shelf (100-400 m depth), but also at deeper stations at the shelf break and off shelf (up to 3.000 m depth).

During the survey, waters in the upper 100 m were dominated by Polar sur-face water, which is of Arctic origin and mainly associated with the East Greenland Current. Arctic Atlantic water, which is of Arctic origin with contributions from Atlantic waters therefore had higher salinity and dominated the water masses in the depth range 100-200 m. The warmest and most saline water was return Atlantic water or re-circulating Atlantic water, and was mainly found along the Greenland shelf break in the depth range 100-300 m. The coexistence of colder and less saline East Greenland Current waters and warmer and more saline waters from the Atlantic was clearly visible as a dynamic frontal system along the East Greenland shelf break during the cruise. A general trend in nutrient conditions throughout the study area was prevailing low concentrations in the surface waters (<20 m), particularly for nitrate at the shelf. The highest integrated levels of nitrate in the upper 50 m were recorded along the shelf break corresponding with deeper mixing of the water column.

The biology in the area was clearly associated with the physical-chemical environment. Depleted nitrate levels in the surface layer, which also has the most favourable light conditions, likely were a major factor controlling phytoplankton production. Integrated phytoplankton biomass and production within the 0-50 m depth strata across the study area revealed the highest values at or outside the East Greenland shelf break. Likewise, the mesozooplankton biomass and community composition were clearly associated with the oceanography and bathymetry of the area. The biomass was highest along the shelf break area, and species composition reflected the origin of the water. The North Atlantic Calanus finmarchicus was present at all stations, but much more abundant at the stations off the shelf in the Greenland Sea. The Arctic Calanus species C. glacialis and C. hyberboreus, on the other hand, had the opposite pat-terns, and were not found at all in the upper 50 m in the Greenland Sea. A large part of the dominant Calanus was still present in the surface water, which is important for visual predators and predators feeding from the sur-face, e.g. seabirds like little auk. The macrozooplankton like the mesozooplankton had elevated biomass in the shelf break area, but also at the stations near-shore. Acoustic measurements gave a high-resolution distribution of the density of organisms along the cruise track, and confirmed the pattern found by net sampling. 

As expected, the survey showed low diversity and abundance of seabirds and marine mammals. 22 bird species and 9 species of marine mammals were ob-served. Little auks were the most numerous seabird observed at the cruise with the highest densities observed along the shelf break, and lower densities on the shelf in the open pack ice. Fulmars (Fulmarus glacialis) and black-legged kittiwakes (Rissa tridactyla) were widespread in low numbers. Very few thick-billed murres (Uria lomvia) were observed during the Dana cruise. This is consistent with the records in the Greenland Seabirds at Sea database and SEA-TRACK data where thick-billed murres mainly have been observed further to the east.