The Arctic OceanIntroductionBathymetryGuides bottom currents, influences mixing and Arctic sea ice formationMajor connection to oceans through Atlantic, 1700km wide opening along large oceanic sill (Greenland across to Iceland, Faroe Islands and Scotland)Denmark Strait – Greenland to Iceland (600m)Iceland to Faroe Islands (400m)Faroe Bank Channel (800m)Minor openings to Atlantic – Canadian ArchipelagoConnection to Pacific through Bering Strait (45m d, 85km w) little influence on circulation, large importance in global freshwater balanceWithin Arctic Med Sea are Greenland, Iceland and Norwegian Seas, and Arctic Sea Greenland, Iceland and Norwegian Seas communicate with Arctic Sea through Fram Strait (450km w, 3000 m d)Arctic Sea structured into four basins through ridges: Canadian basin (3600-3800m d), Makarov basin (3900 m d), Amundsen basin (4300-4500m d) and Nansen basin (3800-4000m d)Alpha and Mendeleyev Ridges (1200-1500m), Lomonossov ridge (850-1600m) and Artic Mid-Ocean ridge (2500m)Amundsen and Nansen basins and Arctic Mid-Ocean ridge combined as Earasian basinArctic Med Sea volume 17.10^6km^2 -1.3% of world oceanLow volume, but large expanse due to shelf area- Siberian shelf exceeds 800km in most places, shelf is also shallow 10-40m in Laptew Sea – 70% of surface area of arctic sea SalinityLow salinty -mediterranean sea Surface circulationDecided by windsWind regime controlled by high pressure in vicinity of north pole More prominent in winter, pressure gradients are reduced in summer, but pressure near the pole is still higher than over the continentsMost of Arctic seas under influence of Polar easterlies, so have anticyclonic surface circulationOver Greenland and Norwegian seas wind system is dominated by Icelandic atmospheric low, generates cyclonic water movementInflow and outflow both occur near the surfaceGreenland-Iceland-Faroe-Scotland Ridge allows Coriolis force to exert influence of currents, concentrates outflow of low salinity water in east Greenland current on western side, leaving room for inflow in Norwegian current on eastern side Inflowing water origins in temperate and subtropical gyres of North Atlantic Ocean -low density due to high temps in Gulf StreamGeneration of strong currents in polar anticyclonic gyre by wind inhibited by ice coverage Thomdike and Colony 1982 demonstrated that about 70% of the variance of the daily ice velocity was accounted for by the geostrophic winds and concluded that ocean currents were responsible for only about 15% of the ice motion.Deep circulationArctic bottom water formation from two sources: Greenland Sea Deep Water and water from Arctic Shelf regionsGreenland Sea Deep Water formed in winter where cooling of surface warer cause intense verticle convectionSinking occurs in events linked to passage of storm systemsAt beginning of cycle surface layer is quite freshIce formation causes incresed salinity, so density increases overcoming the barrier of the warm but saline water belowSinking is compensated by upwelling of warm water, which melts the ice – cycle can begins againLow salinity of arctic shelf regions, due to freshwater from rivers, facilitates ice formationWhen salinity below ice exceeds 35, the water is dense enough to sink to bottom of Arctic sea basins Norwegian sea does not cool enough for deep winter convectionMixing basinOutflow of 4sv of Arctic bottom water from Norwegian sea into Atlantic OceanDeepest passage is Faroe Bank Channel, av.
1 SvOverflow over Iceland-Faroe sill 1 SvDenmark Strait 2 Sv4Sv transported into eastern Atlantic OceanLabrador Sea is region of intense surface cooling and deep winter convectionMixes with Arctic bottom water, which has similar salinities but is cooler, creating North Atlantic Bottom WaterIce and precipitationThe thermodynamic growth and melt of Arctic seaice is controlled basically by (1) the net heat transferbetween the ice cover and atmosphere and (2) heat transferredfrom the ocean below. Heat transferred from theocean below originates from stored solar radiation in thenear-surface layer or heat advected into the Arctic Oceanthrough the major gateways of the Bering Strait or FramStrait.Low precipitation in polar estualies region but sig in subpolar regionsMost precip occurs over ice, which doesnt melt until its exported from arctic region, so this has little effect in oceanic mass budgetBiggest contribution comes from precip over siberia and resuting river runoff With evap over ice being comparatively low, the Arctic Med Sea is a dilution basinPrecip over Greenland feeds the galciers whivh produce the several thousand icebergs annually found in East Greenland, west Greenland and Labrador currentsIce pack the ArcticOcean ice pack at the end of the summer melt seasonusually assumes either of two different positions.
One ofthese, called the Siberian mode, is characterized by theice pack being separated from the Alaskan coastline,leaving extensive open water areas along its shoreline.The other, the Alaskan mode, is characterized by the icepack impinging on or being close to the Alaskan coastline.Fast iceClimate change mean sea-ice thickness declined from more than 3 m down to less than 2 m (Renner et al.
2014; Lindsay and Schweiger 2015), leading to a stark reduction in multiyear ice (Comiso 2012). Other Arctic sea-ice characteristics have also started to change and will likely continue to do so, like the length of the sea-ice-free season, earlier break up and later freeze up, the occurrence of melt ponds and the under ice topography (e.g., Hwang et al. 2015; Divine et al. 2016).
Recent episodes of unusually early spring rain in the Canadian Arctic have led to melting, collapse, and washout of subnivean birth lairs of ringed seals (Pusa hispida), leaving newborn pups exposed on bare ice, increasing their vulnerability to hypothermia and predation (15). Episodic melting may, however, also benefit some animal populations, depending on the degree of melting (ablation). For example, substantial ablation associated with winter warming resulted in reduced mortality, increased fecundity, and increased abundance of Svalbard reindeer (Rangifer tarandus platyrhynchus) (16) (Fig. 2B). Some of the most rapid ecological changes associated with warming have occurred in marine and freshwater environments, associated with changes in sea ice dynamics and external nutrient loading. Species most affected are those with limited distributions and specialized feeding habits that depend on ice for foraging, reproduction, and predator avoidance, including the ivory gull (Pagophila eburnean), Pacific walrus (Odobenus rosmarus divergens), ringed seal, hooded seal (Cystophora cristata), narwhal (Monodon monoceros), and polar bear (Ursus maritimus) (12, 17). Polar bears, in particular, are experiencing rapid declines in birth rates and survival due to loss of sea ice habitat