Effect of the nodal declination tide on the thermohaline water structure, sea surface heights and geostrophic currents in the southwestern Bering Sea

Satellite data on the sea level heights and data of Argo floats for the southwestern Bering Sea and adjacent area of the North Pacific are analyzed. Interannual variability of the thermohaline structure and water dynamics caused by the nodal (declination) tide with the period of 18.6 years is revealed. The tidal-induced 18.6-year variability is traced in variations of the sea level, water temperature and direction and velocity of the geostrophic currents. Extreme strengthening (in 2006) and weakening (in 1997 and 2015) of nodal tides led to lowering/rising of the sea level heights in the southwestern Bering Sea and in the areas southward from the Near Strait and Commander Islands. The sea level lowering was associated with increasing of salinity and water density in the layer of 50–400 m; as the result, the salinity and density at the depth of temperature minimum (~100 m) were higher in 2005–2006 than in 2015–2016 by 0.20 psu and 0.14 kg . m–3, respectively. This increasing can be explained by transformation of the Alaskan Stream waters due to intensified tidal mixing in the Aleutian Passes and in the Near Strait. No statistically significant correlation between the sea level and amplitude of the nodal tide was found in the areas remoted from the straits. Another consequence of the sea level lowering was an appearance of cyclonic circulation northward and southward from the Near Strait and weakening of the Alaskan Stream in spring of 2006, with cessation of the flow from the Near Strait to the mainland coast that caused SST decreasing in the southwestern Bering Sea. Intensification (weakening) of nodal tides was accompanied by decreasing (increasing) of sockeye salmon catches at East Kamchatka and Aleutian Islands.

ALEUTIAN EDDIES AND THEIR IMPACT ON TEMPERATURE AND DISSOLVED OXYGEN IN THE WESTERN SUBARCTIC PACIFIC

Aleutian eddies are anticyclonic vortices on scale of 100–200 kilometers that transport the Alaskan Stream warm water originating in the Gulf of Alaska to the western Subarctic Pacific (WSP). We present an analysis of satellite, Argo floats and ship borne observations of Aleutian eddies, revealing the influence of the wind forcing on the eddy formation and shedding. We demonstrate that the eastern winds promote the Aleutian eddy formation south of Near Islands. Positive (cyclonic) wind stress curl in late fall- winter results in the SSH decrease and the mesoscale cyclones formation at the Aleutian eddy boundaries and thereby leads to the eddy shedding from the Alaskan Stream. An appearance of the Aleutian eddies in the central part of the WSP is accompanied by the deepening of the isopycnals and an increase of the temperature and dissolved oxygen (DO) concentration in 150–400 m layer. The eddies decrease the DO concentration on 26.7σθ and 26.8σθ surfaces in the upper intermediate layer but enrich the 27.0σθ surface by DO. The extent to which eddies modulate the temperature and DO concentration in the WSP is related to the SSH amplitude of eddies.

Aggressive interactions affect foraging and use of space in a drift foraging salmonid, Salvelinus malma (Salmoniformes: Salmonidae)

Although intraspecific interactions likely affect habitat choice and foraging behaviour in animals, our knowledge regarding how these factors interact is frequently limited to either lab or field studies, but not both. We observed pairs of dominant and subordinate drift-foraging Dolly Varden char (Salvelinus malma) in an Alaskan stream, and quantified intraspecific interactions and foraging behaviour. Dominant individuals had higher foraging rates, occupied slower holding velocities and were displaced shorter distances during bouts compared to subordinate individuals. Individuals initiated bouts more frequently from the downstream position, than from lateral or upstream positions. Dominant individuals were more likely to occupy the upstream position after a bout than subordinates, which ensures that dominants have the first opportunity to capture drifting prey.

Alaskan Stream flow in the eastern subarctic Pacific and the eastern Bering Sea and its impact on biological productivity

We demonstrate the transport pathways of Alaskan Stream water in the eastern subarctic Pacific and the eastern Bering Sea from October 1, 1994 to September 12, 2016 with the help of altimetry-based Lagrangian maps. A mesoscale eddy activity along the shelf-deep basin boundaries in the Alaskan Stream region and the eastern Bering Sea is shown to be related with the wind stress curl in the northern North Pacific in winter. A significant correlation is found between the concentration of chlorophyll-a in the Alaskan Stream area and eastern Bering Sea in August–September and the wind stress curl in the northern North Pacific in November–March. The mesoscale dynamics, forced by the wind stress curl in winter, may determine not only lower-trophic-level organism biomass but also salmon abundance/catch in the study area.