Deep Greenland Sea Research Articles

Demersal fish assemblages in the boreo-Arctic shelf waters around Svalbard during the warm period 2007–2014

The temporal and spatial resilience of abundance patterns of assemblages of organisms inhabiting transition zones between Arctic and boreal regions is an issue of concern in relation to climate change. The recognition that baseline information spanning such transition zones is required to facilitate future monitoring and assessments of temporal dynamics provided the motivation for the present study. One such transition area is the Svalbard archipelago of the Northeast Atlantic, located between the Arctic and the boreal Atlantic, where significant climate changes occur. The study aimed to utilize an existing data series from Svalbard to analyse and describe demersal fish assemblage structure and distributions. Norwegian bottom trawl surveys sampled the area annually in August–September 2007–2014, and the dataset is the first from this area which is sufficiently comprehensive to carry out assemblage analyses. The survey years analysed represent the recent unprecedented warm period in the Barents Sea–Svalbard region which started around 2004. The new baseline information improves the basis for future studies of resilience under changing environmental conditions. A key finding was that the major transition in species composition is that between deep Greenland Sea and Arctic Ocean assemblages (upper slope assemblages) and the shelf assemblages. In shallower shelf areas (<500 m depth) structuring is weaker with assemblages having many species in common. The expected association of fish assemblages with regional bathymetric and hydrographic features was confirmed. The observed patterns probably reflect a comparatively extensive Atlantic influence during the warm period.

Exchange of warming deep waters across Fram Strait

Current meters measured temperature and velocity on 12 moorings from 1997 to 2014 in the deep Fram Strait between Svalbard and Greenland at the only deep passage from the Nordic Seas to the Arctic Ocean. The sill depth in Fram Strait is 2545m. The observed temperatures vary between the colder Greenland Sea Deep Water and the warmer Eurasian Basin Deep Water. Both end members show a linear warming trend of 0.11±0.02°C/decade (GSDW) and 0.05±0.01°C/decade (EBDW) in agreement with the deep water warming observed in the basins to the north and south. At the current warming rates, GSDW and EBDW will reach the same temperature of −0.71°C in 2020. The deep water on the approximately 40km wide plateau near the sill in Fram Strait is a mixture of the two end members with both contributing similar amounts. This water mass is continuously formed by mixing in Fram Strait and subsequently exported out of Fram Strait. Individual measurements are approximately normally distributed around the average of the two end members. Meridionally, the mixing is confined to the plateau region. Measurements less than 20km to the north and south have properties much closer to the properties in the respective basins (Eurasian Basin and Greenland Sea) than to the mixed water on the plateau. The temperature distribution around Fram Strait indicates that the mean flow cannot be responsible for the deep water exchange across the sill. Rather, a coherence analysis shows that energetic mesoscale flows with periods of approximately 1–2 weeks advect the deep water masses across Fram Strait. These flows appear to be barotropically forced by upper ocean mesoscale variability. We conclude that these mesoscale flows make Fram Strait a hot spot of deep water mixing in the Arctic Mediterranean. The fate of the mixed water is not clear, but after the 1990s, it does not reflect the properties of Norwegian Sea Deep Water. We propose that it currently mostly fills the deep Greenland Sea.

Increasing amount of Arctic Ocean deep waters in the Greenland Sea

In the last three decades, deep convection has come to a halt in the Greenland Sea. Hydrographic data reveal that during this period, temperature and salinity in the deep Greenland Sea have increased at mean rates without precedent in the last 100 years, and these trends are among the highest in the global deep ocean. The origin of these changes is identified as the advection of Arctic Ocean deep waters and the necessary transports to explain them are calculated (0.44±0.09 Sv). Despite the fact that the deep Greenland Sea hardly covers 0.05% of the global surface, the resulting trends constitute 0.3% of the World Ocean heat content increase per unit area of earth's surface and 0.1% of the global sea level rise. These results suggest that changes of the deep Arctic Mediterranean and their contribution to the global budgets need to be addressed.

The East Greenland Current and its impacts on the Nordic Seas: observed trends in the past decade

Abstract Rudels, B., Korhonen, M., Budéus, G., Beszczynska-Möller, A., Schauer, U., Nummelin, A., Quadfasel, D., and Valdimarsson, H. 2012. The East Greenland Current and its impacts on the Nordic Seas: observed trends in the past decade. – ICES Journal of Marine Science, 69: 841–851. For the past 30 years, it has been known that dense waters are created in the Arctic Ocean. However, before the late 1980s, observations indicated that Arctic Ocean deep waters only modified the deep water in the Greenland Sea, which was still thought of as the major source of dense water. In the mid-1990s, this picture began to fade. The deep convection in the Greenland Sea weakened and only Arctic Intermediate Water was formed. A deep salinity maximum was reinforced and a temperature maximum emerged at mid-depth. The densities of the salinity and temperature maxima were those of the deep waters in the Arctic Ocean, and one possibility was that waters below the convection were ventilated by Arctic Ocean deep waters from the East Greenland Current. Between 1998 and 2010, the salinity and temperature of the deep water in the Greenland Sea increased, implying continuous input from the East Greenland Current. Water from the Greenland Sea advected to Fram Strait now has almost Arctic Ocean characteristics and cannot significantly change the outflowing Arctic Ocean waters by mixing in the East Greenland Current, leading to a more-rapid transformation of the deep Greenland Sea water column.

Colonisation of hard substrata along a channel system in the deep Greenland Sea

The colonisation of hard substrata (HS) by epibenthic megafauna was studied by photographic surveys along the Ardencaple Canyon in the deep western Greenland Sea in 2000. Seven transects at 2,700–3,200 m water depth showed generally low densities of dropstones, sunken wood, and other substrata including anthropogenic material (range: 2–11 HS km−1). Overall, 30 different taxa and morphotypes were found on or associated with HS. While the sea anemone Bathyphellia margaritacea and the pantopod Ascorhynchus abyssi dominated the fauna on the substrate surfaces, a ball-shaped morphotype of uncertain taxonomic origin characterised assemblages marginally associated with HS. Community analysis revealed differences in faunal patterns near the continental rise and towards the deep sea, but diversity and evenness did not differ significantly between the various regions. However, we conclude that dropstones and other hard substrata at the seafloor serve as colonisation islands and thereby generally increase small-scale habitat diversity in polar deep-sea environments.

Flux of anthropogenic carbon into the deep Greenland Sea

Measurements of the carbonate system and the transient tracers, CFC‐11 and carbon tetrachloride (CCl4), in the Greenland Sea and western Eurasian Basin are used to deduce the sources and magnitude of excess dissolved inorganic carbon in the deep Greenland Sea. The salinity in the deep Greenland Sea has increased during the past 20 years as a result of Arctic Ocean water advecting into the area. From salinity and temperature data the relative amount of advective water below 1500 m is estimated to ∼2% yr−1 between 1982 and 1994. Data from the western Eurasian Basin, collected during the Oden 91 cruise, are used as the advective source waters. A mixing box model is applied to estimate the evolution of CFCs and anthropogenic total dissolved inorganic carbon in the deep waters of the Greenland Sea since preindustrial times. The source functions are the surface water concentrations of CFC‐11, CCl4, and total dissolved inorganic carbon CT, which are the result of anthropogenic emission. In order to explain the measured CFC data in the Greenland Sea an annual percent renewal by deep water formation of between 0.5 and 1.2% is needed below 1500 m, corresponding to a mean ventilation of 0.17±0.05 Sv, considering realistic uncertainties in the calculations. This ventilation gives a sequestering of anthropogenic carbon dioxide, which in 1994 equaled 2.4±0.7×1012 g C yr−1.

Metabolism of deep-sea sponges in the Greenland-Norwegian Sea

During two cruises with RV “Meteor” in 1991 and 1992 to the Norwegian and Greenland Sea, sponges were collected by either box corer or Agassiz trawl at a depth of > 2000m, in order to assess the role of deep-sea sponges for energy fluxes through the deep-sea benthic community. Heat production was measured via direct microcalorimetry and adenosine nucleotide levels were determined. Energy charge ranged between 0.5-0.8 for most individuals and was thus comparable to values for normally active shallow water organisms. Oxygen consumption calculated from heat production measurements was about 20 μmol O 2 · h −1 · g −1 ash-free dry weight (AFDW) for all species studied. From the combination of body mass values with individual respiration rates, sponge community oxygen demand, ranging from 20–140 μmol O 2 · m −2 · h −1, could be determined. A comparison with sediment oxygen demand (SOD) measurements (Graf et al., 1995) showed that sponges contribute up to 22% of SOD to benthic oxygen consumption and thus in the deep Greenland Sea belong to the primary organisms involved in the turnover of organic carbon at the deep-sea floor.

Late Quaternary paleoceanography of the Eurasian Basin, Arctic Ocean

We reconstructed late Quaternary deep (3000–4100 m) and intermediate depth (1000–2500 m) paleoceanographic history of the Eurasian Basin, Arctic Ocean from ostracode assemblages in cores from the Lomonosov Ridge, Gakkel Ridge, Yermak Plateau, Morris Jesup Rise, and Amundsen and Makarov Basins obtained during the 1991 Polarstern cruise. Modern assemblages on ridges and plateaus between 1000 and 1500 m are characterized by abundant, relatively species‐rich benthic ostracode assemblages, in part, reflecting the influence of high organic productivity and inflowing Atlantic water. In contrast, deep Arctic Eurasian basin assemblages have low abundance and low diversity and are dominated by Krithe and Cytheropteron reflecting faunal exchange with the Greenland Sea via the Fram Strait. Major faunal changes occurred in the Arctic during the last glacial/interglacial transition and the Holocene. Low‐abundance, low‐diversity assemblages from the Lomonosov and Gakkel Ridges in the Eurasian Basin from the last glacial period have modern analogs in cold, low‐salinity, low‐nutrient Greenland Sea deep water; glacial assemblages from the deep Nansen and Amundsen Basins have modern analogs in the deep Canada Basin. During Termination 1 at intermediate depths, diversity and abundance increased coincident with increased biogenic sediment, reflecting increased organic productivity, reduced sea‐ice, and enhanced inflowing North Atlantic water. During deglaciation deep Nansen Basin assemblages were similar to those living today in the deep Greenland Sea, perhaps reflecting deepwater exchange via the Fram Strait. In the central Arctic, early Holocene faunas indicate weaker North Atlantic water inflow at middepths immediately following Termination 1, about 8500–7000 year B.P., followed by a period of strong Canada Basin water overflow across the Lomonosov Ridge into the Morris Jesup Rise area and central Arctic Ocean. Modern perennial sea‐ice cover evolved over the last 4000–5000 years. Late Quaternary faunal changes reflect benthic habitat changes most likely caused by changes in the import of cold, deepwater of Greenland Sea origin and warmer and middepth Atlantic water to the Eurasian Basin through the Fram Strait, and export of Arctic Ocean deepwater.Appendix Tables Al‐A4 are available on microfiche. Orderfrom the American Geophysical Union, 2000 Florida Avenue,N.W., Washington, DC 20009. Document P94‐002; $2.50.Payment must accompany order.

Chlorofluoromethanes in the Arctic mediterranean seas: evidence for formation of bottom water in the Eurasian Basin and deep-water exchange through Fram Strait

During July–August of 1984, the polar research vessel R.V. Polarstern occupied sections of oceanographic stations in and north of Fram Strait and across the Greenland Sea (Boreas Basin) south of Fram Strait. The temperature, salinity and chlorofluoromethane (CFM) data for the Polarstern stations within the Eurasian Basin reveal two deep-water masses, Eurasian Basin Bottom Water (EBBW) which lies below the σ 2 = 37.46 density surface and Eurasian Basin Deep Water (EBDW) which lies above this surface. The depth of this surface is close to the 2600 m sill depth of Fram Strait. The CFM, temperature and salinity distributions suggest that EBBW is partially composed of dense, high salinity shelf water advected into the deep Eurasian Basin, where it probably circulates around the basin in a deep cyclonic boundary current. An upper limit of about 0.1 Sv was estimated from the CFM data for the transport of pure high salinity shelf water into the Eurasian Basin below 3000 m. These data together with data collected on previous cruises to the Norwegian and Greenland seas reveal that EBDW exchanges with water masses south of Fram Strait, first flowing through Fram Strait in a narrow (<10 km) deep boundary current, then mixing with Greenland Sea Deep Water in the periphery of the Greenland Gyre to form new Norwegian Sea Deep Water (NSDW). Some of this new NSDW flows southeastward into the Norwegian Sea and a mixture of old and new NSDW flows northward on the eastern side of Fram Strait, returning to the Eurasian Basin. We estimate the volume transport of EBDW southwrd through Fram Strait to be 0.80–0.93 Sv. Volume transports between the deep Greenland and deep Norwegian seas and between the surface and deep Greenland Sea were also estimated with respective values of 0.80–0.93 Sv and 0.50 –0.52 Sv.

Ventilation of the deep Greenland and Norwegian seas: evidence from krypton-85, tritium, carbon-14 and argon-39

On leg 5 of the TTO expedition, the distributions of 85Kr, tritium, 14C, 39Ar, temperature, salinity, oxygen, carbon dioxide and nutrients were measured in the Greenland and Norwegian seas. These observations support previous observations that Greenland Sea Deep Water is formed by a deep convective process within the Greenland gyre. They also support Aagaard et al.'s (1985, Journal of Geophysical Research, 90, 4833–4846) new hypothesis that Norwegian Sea Deep Water forms from a mixture of Greenland Sea Deep Water and Eurasian Basin Deep Water. Volume transports estimated from the distributions of 85Kr, tritium, 14C and 39Ar range from 0.53 to 0.74 Sv for exchange between the surface and deep Greenland Sea and from 0.9 to 1.47 Sv for exchange between the deep Greenland and deep Norwegian seas. The residence time of water in the deep Greenland Sea with respect to exchange with surface water ranges from 24 to 34 years compared to 26–31 years reported by Peterson and Rooth (1976, Deep-Sea Research, 23, 273–283) and 35–42 years reported by Bullister and Weisss (1983, Science, 221, 265–268). The residence time of water in the deep Norwegian Sea with respect to exchange with the deep Greenland Sea ranges from 19 to 30 years compared to 97–107 years reported by Peterson and Rooth (1976) and 10–28 years reported by Bullister and Weiss (1983). The oxygen consumption rate was estimated to be at most 1.04 μM kg −1 y −1 for the deep Greenland Sea and to be between 0.47 and 0.79 μM kg −1 y −1 for the deep Norwegian Sea.

Anthropogenic Chlorofluoromethanes in the Greenland and Norwegian Seas

The concentrations of two industrially produced chlorofluoromethanes, CCl(3)F(F-11) and CCl(2)F(2)(F-12), have been measured in the water column and in the marine atmosphere of the Greenland and Norwegian seas. Measurable concentrations of these two chlorofluoromethanes have penetrated to the deep basins of both of these regions, and the general characteristics of their vertical distributions are similar to those of the bomb-produced radioisotopes injected into the atmosphere on a similar time scale. The data have been fitted to a time-dependent box model based on deep convective mixing in the Greenland Sea and lateral exchange between the deep basins. The model calculations for the two chlorofluoromethanes in the Greenland Sea give similar results, with a time scale for deep convection of about 40 years. The time scale for lateral mixing between the deep Greenland Sea and the deep Norwegian Sea is estimated to be 20 to 30 years, although the agreement between the calculations for the two chlorofluoromethanes is limited by analytical uncertainties at the low concentrations found in the deep Norwegian Sea and by uncertainties in the model assumptions.

Formation and exchange of deep water in the Greenland and Norwegian seas

The formation and exchange of deep water in the Greenland and Norwegian seas are modeled by a time-dependent box model. Using tritium and radiocarbon data, primarily from the Geochemical Sections (GEOSECS) 1972 operation, the time scale for deep convective mixing in the Greenland Sea is estimated to be about 30 years, which implies that about 100 m of surface water are mixed down annually. The time scale for exchange between the deep Greenland Sea and the deep Norwegian Sea is estimated to be at least 100 years. It appears, on the basis of tritium data, that the formation and exchange of deep water in the Greenland and Norwegian seas are essentially isolated from the formation of the dense overflow waters of the Denmark Strait and the Iceland-Faroe Passage.