气候变化领域集成服务门户

A portion of the freshwater transport through Fram Strait consists of low-salinity Pacific-derived Arctic water flowing southward along the east coast of Greenland. The pathways of this water are currently unclear. An Ice Tethered Profiler deployed over the southeastern Wandel Sea shelf (northeast Greenland) in May 2015 collected a profile every 3hr for a year recording conductivity-temperature-depth (CTD) and Colored Dissolved Organic Matter (CDOM) fluorescence. This was accompanied by velocity observations. The CTD data revealed that the subsurface water (similar to 15-85m depth) characterized by high CDOM resembles the cold Halostad in the Canada Basin formed by the injection of Pacific water. A coastal branch of the Pacific water outflow from the Arctic Ocean supplies the Wandel Sea halostad, which shows a clear seasonal pattern. From July to October-November, the halostad is shallow, more saline, warmer, and with less CDOM. Conversely, from November to April, the halostad deepens, cools, freshens and CDOM increases, likely indicating a higher fraction of Pacific winter water. The CTD surveys, wind and current data, and numerical simulations show that the seasonal variation of wind over the continental slope likely controls seasonal changes of this intermediate water layer. Over northeast Greenland, winter winds have a northerly component from November to April, favoring Ekman transport of the Pacific-derived water to the Wandel Sea shelf. In contrast, the prevailing southerly summer winds result in retreat of the Pacific-derived water off the shelf. The landfast ice off-slope extension modifies wind-forcing disrupting seasonal patterns.

Plain Language Summary Arctic climate change is manifested in increased freshening of the surface seawater over recent decades due to increased precipitation, river runoff, and sea-ice and glacier melt. Over the coastal domains of northern Greenland, contributions from glacial melt are superimposed on the low-salinity surface water comprised by river runoff and low-salinity water of Pacific origin, while intermediate water is primarily of Atlantic origin. The glacier meltwater fraction can be significant, but its quantification requires differentiation from the Pacific water, the second largest source of the fresh water in the Arctic Ocean. To date, the Pacific-derived Arctic water component over the Greenland shelves remains poorly studied. The ice-tethered oceanographic mooring deployed over the southeastern Wandel Sea shelf (northeast Greenland) in May 2015 collected oceanographic data for a year. The obtained data and model simulations suggest that the Wandel Sea subsurface layer down to about 80m depth is supplied by the coastal branch of the Pacific water outflow from the Arctic Ocean. This layer also shows a clear seasonal pattern likely indicating a higher fraction of the Pacific-derived water during winter. The seasonal variation of wind over the continental slope seems to control the Pacific water on-shelf inflow.