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The interior shelves of the Arctic Mediterranean are the shelves of the Kara Sea, Laptev Sea, East Siberian Sea and Beaufort Sea. They comprise approximately 40% of the total arctic shelf area (∼2.5 × 10 6 km 2 ) and are distinguished from inflow and outflow shelves by their principal forcing dynamics. Along their southern (continental) boundary the interior shelves are dominated by the major arctic rivers, receiving over 80% of the total freshwater input to the Arctic Ocean. In the mid-shelf region wind and ice motion surface stresses dominate mixing and circulation, resulting in high variability. Along, their northern (seaward) boundary they are forced by upwelling- and downwelling-favourable surface stresses which drive shelf-basin exchanges with Atlantic- and Pacific-origin cyclonic boundary currents over the upper slope. Shelf-basin exchange is further modified by shelf-break morphometry (e.g. canyons, valleys, headlands and bottom slope). Here we review the physical oceanographic settings and forcing of the interior shelves and then focus on shelfbreak exchange and supply of nutrients for new primary production due to upwelling across the shelfbreak. As a proxy for this nutrient supply, we show seasonal and annual time series of along-shelfbreak surface-stress due to wind and ice motion from 1979 to 2011. We apply this analysis to the shallow shelves from the Kara Sea to the Beaufort Sea and comment on recent increases due to atmospheric changes and sea-ice retreat. [ABSTRACT FROM AUTHOR]

A comparison of the annual thermal histories in seven deep, intermontane lakes in western Canada along a north-south transect from 49.67° to 61.25° N reveals latitudinal trends in thermal structure; specifically: 1) summer maximum and winter minimum mean temperatures decrease ~ 0.2°C per degree latitude, 2) the dates of maximum and minimum heat content lag ~ 1 and ~ 6 days per degree latitude, respectively, 3) the lengths of summer and winter stratification lag ~ 8 days per degree latitude, 4) the timing of the spring and autumn turnovers lags ~ 4 days per degree latitude, 5) the timing of the onset and break-up of ice cover lags ~ 6 days per degree latitude, and 6) the rate of response to atmospheric heating and cooling is ~1MJm-2 day-1 per degree latitude. We propose that insight into the response of a lake at a specific latitude to climate change can be acquired by examining the present conditions of a morphologically and dynamically similar lake at an appropriate latitude and altitude further south. Of interest is the potential transition of a lake from one mictic state to another, with consequences to the resupply of nutrients to the euphotic zone and to the phenology of spring and fall phytoplankton blooms. The absence or presence of ice cover and timing of freeze-up and break-up also affect a lake's heat budget and thermal history. The full interpretation of climate signals in lake systems requires an understanding of lake-specific physical forcing and response mechanisms. [ABSTRACT FROM AUTHOR]

Abstract: Field data obtained in 2003–2004 are used to describe the influence of atmospheric and riverine forcing on the thermal history of fjord-type lakes using Quesnel Lake, British Columbia, Canada as an example. Typical of fjord-type lakes, Quesnel Lake is narrow, long (>100km total thalweg), multi-armed (three arms of comparable size), deep (maximum depth>500m), and has multiple basins separated by sills. The lake''s annual thermal history responds to the joint forcing of surface heat exchange, river inputs, and wind stress. The lake''s annual heat budget is dominated by surface radiative fluxes, and riverine input of heat is insignificant in this medium residence time lake (10years). Despite being insignificant to the annual heat budget, the three major rivers that feed the three arms of the lake contribute to the overall lake circulation pattern. Since these rivers have differing salinities, it is possible to identify, using temperature/salinity correlation diagrams, patterns of riverine circulation interflowing in the lake. Data from a 1-year thermistor-chain record suggests exchange between surface and intermediate waters occurs twice annually, but deep-waters below 150–250m are mainly renewed during autumn, by strong and episodic atmospheric forcing. This is because wind-forced turbulent diffusion and gravitational convection triggered by wind forced displacement of isotherms (initiating thermobaric instability) are required for full overturn and deep-water renewal. [Copyright &y& Elsevier]

Abstract: Academy Bay in the Sea of Okhotsk is an important summertime feeding ground for pelagic-feeding Bowhead whales (Balaena mysticetus) in the western subarctic North Pacific. The present work combines satellite observations with physical (CTD, currents, tides) and biological (zooplankton sampling) measurements. Data obtained aboard the RV Lugovoe in August–September 2003 and July–August 2004 show dense populations of zooplankton (such as copepods Calanus glacialis, Pseudocalanus sp., pteropods Limacina helicina, and chaetognaths Sagitta sp.) that are concentrated by physical mechanisms within this critically important ecosystem. We show that near-bottom, cold water intrusions from the northern Sea of Okhotsk associated with the estuarine circulation advect arctic herbivorous calanoids (Calanus glacialis) and mollusks Limacina helicina into the region. Satellite and in situ observations that include conductivity–temperature–depth (CTD) data and measurements of tidal currents are used to study the nature of the estuarine circulation. Results show an anticyclonic circulation, associated with the effect of earth''s rotation. An analytical model shows horizontally convergent flows in the lower layer toward the western coast of the bay that push water upward along the steep slope. This together with zooplankton vertical migration leads to aggregation. Thus the combination of the residual eddy formation and swimming behavior act to concentrate zooplankton near the cape and to provide the necessary densities of planktonic food supply for Bowhead whales. [Copyright &y& Elsevier]

Observations and modeling results are presented to explore the response of a multi-basin, fjord-type lake to episodic wind forcing. Field observations show that abrupt cooling and warming events (magnitude greater than 5°C d-I) lasting 3-6 days in a large, salmon-bearing river (Quesnel River) are due to upwelling in its upstream lake (Quesnel Lake) during the summer, stratified season. Within the lake, vertical displacement of isotherms in the vicinity of the river mouth associated with this upwelling is shown to be forced by wind events longer than one quarter of the fundamental seiche period and of sufficient magnitude that the Wedderburn number approaches one. Upwelling occurs nearly-simultaneously throughout a smaller basin adjacent to the outflow (West Basin) that is separated from the Main Basin of Quesnel Lake by a sill and contraction. Wind-driven water fluxes across the sill are estimated using a conceptual model based on volume and heat budgets. These estimates provide an upper bound for flow across the sill and suggest that exchange flow may at times be internally hydraulically controlled, with epilimnetic velocities of up to ~25 cm/s. Computed fluxes suggest the West Basin hypolimnion has a residence time of 6-8 weeks during the summer stratified period with each upwelling episode irreversibly exchanging 25-30% of the hypolimnetic volume with the rest of the lake. Implications of such events are profound for salmon bearing rivers wherein the thermal habitat is critical to migration success. [ABSTRACT FROM AUTHOR]

Abstract: Stratification is perhaps the most important attribute of oceans with regards to climate and biology. Two simple aspects of the ocean''s climate system appear to have a surprisingly important role in transforming waters that feed the global thermohaline circulation, dominating patterns of biogeochemical flux and establishing macroecological domains. First, largely because of meridional distillation (mainly due to the atmospheric transport of freshwater across the Isthmus of Panama) the North Pacific is fresher than the North Atlantic. Second, largely because of zonal distillation (e.g., warming and evaporation at low latitudes and poleward transport of latent heat and moisture by the atmosphere) the upper layers of subtropical seas are permanently stratified by temperature (N T 2=gαdT/dz>0; here called alpha oceans), while the upper layers of high-latitude seas are permanently stratified by salinity (N S 2=gβdS/dz>0; here called beta oceans). The physical basis for the boundary separating alpha and beta oceans is unclear, but may lie in the thermodynamical equations published by Fofonoff [1961. Energy transformations in the sea. Fisheries Research Board of Canada, Report Series 109, 82pp]. Nevertheless, it is clear that the resulting thermohaline distributions establish a ‘downhill journey’ of low-salinity (and nutrient-rich) waters from the North Pacific to the Arctic and then into the North Atlantic. The Arctic Ocean—itself—acts a double estuary, whereby waters entering from the North Atlantic become either denser through cooling (negative estuary) or lighter by freshening (positive estuary) as they circulate within the basin and then return to the North Atlantic as a variety of components of the ocean''s conveyor. Intermediate and deep waters generally form within cyclonic beta oceans in close proximity to alphas systems. Similar patterns of stratification, nutrients and biogeographical boundaries persist in the Southern Hemisphere. It is thus argued that this simple distinction—alpha versus beta oceans—provides a broad, conceptual framework for simple interpretation of key physical and biological processes and rates, including the impacts of climate variability. [Copyright &y& Elsevier]

Abstract: Mackenzie Trough, a cross shelf canyon in the Beaufort Sea shelf, is shown to be a site of enhanced shelf-break exchange via upwelling caused by wind- and ice-driven ocean surface-stresses. To characterize flow within the Trough, we analyze current meter mooring data and concurrent wind and ice velocity data from 1993 to 1996, and show CTD/ADCP sections from 2002. Mackenzie Trough is approximately 400m deep and 60km wide, but dynamically it is only 2–3 times the baroclinic Rossby radius at its mouth, and patterns of upwelling and downwelling flow within the canyon are similar to dynamically ‘narrow’ canyons. Large upwelling events within the canyon are associated with wind in the short ice-free summer season and with ice motion in winter. Ice motion does not necessarily reflect the wind-stress because of internal ice stresses that differentially block downwelling-causing ice motion. The asymmetry between upwelling and downwelling flow within the canyon combined with the predominance of upwelling-causing ice motion, suggests that Mackenzie Trough is a conduit for deeper, nutrient-rich water to the shelf. [Copyright &y& Elsevier]

The North Water is a large recurring polynya in northern Baffin Bay. Over 400 hydrographic CTD profiles taken over a grid of stations between April and July 1998 were analysed to understand the water-column structures underlying the polynya during spring transition. In the North Water, imported and dissimilar water masses converge over a complex bathymetry: Northern assembly (NA) waters are derived from inflows through Nares Strait and Jones Sound; Southern assembly (SA) waters are derived from a northern-moving branch of the West Greenland Current (WGC). NA and SA waters mix primarily over the north-south Smith Sound Canyon, between 76.5°N and 77°N latitude, to form a distinct, relatively thick halocline layer (termed 'North Water assembly', NWA), characterised by densitycompensating thermohaline intrusions. In the southern portion of the North Water, a sharp front between NWA waters and SA waters roughly aligns with the 500-m isobath. Flow patterns, deduced from potential temperature vs. salinity (θ -S) diagrams and from minima in stability frequency (N) profiles, indicate that this front results from the convergence of NWA waters and a branch of the WGC that is cyclonically re-directed as it approaches Smith Sound Canyon. Not all SA waters are immediately re-directed south towards the front, as a second branch follows the Greenland coast toward Smith Sound. While θ -S signatures show some evidence of upwelling along the Greenland coast (e.g. outcropping of isopycnal surfaces), no surfacing of warm Atlantic-derived water was observed during the sampling period (1998), suggesting that mechanical removal of ice by winds and currents is the primary mechanism by which the North Water forms. Some sensible heat exchange associated with brine rejection and penetrative convection may occur, but only during periods of active ice formation. [ABSTRACT FROM AUTHOR]

Provides information on a study conducted to determine the factors which contributes to changes in temperature and tracer properties in the Arctic Ocean. Factors which contributes to changes in the salinity of North Atlantic waters; Methodology used; Mechanisms involved in thermohaline transitions which appeared in Nansen, Amunsden and Makarov basins; Other findings obtained in the study.

Abstract: Semidiurnal tidal currents on the outer shelf of the Mackenzie Shelf in the Beaufort Sea were found to be strongly influenced by the locally generated baroclinic tide. Two primary factors are involved in this process: (1) the sharp shelf break along the northeastern Mackenzie Shelf, promoting the generation of vigorous internal tidal waves; and (2) the proximity to critical latitudes for M2 and N2 motions locking these waves and preventing them from leaving the source region. As a result, internal tides are resonantly trapped between the shelf and critical latitudes. The physical properties and temporal variations of tidal motions were examined using current meter measurements obtained from 1987–1988 at four sites (SS1, SS2, SS3, and SS4) offshore of the shelf break at depths of ∼200m. Each mooring had Aanderaa RCM4s positioned at ∼35m below the surface and ∼50m above the bottom. Complex demodulation was used to compute the envelopes (amplitude modulation) of these components. A striking difference in the variability of clockwise (CW) and counterclockwise (CCW) tidal currents was found. The CW tides are highly variable, have greater amplitude, exhibit a burst-like character associated with wind events and contain about 80% of the total energy of the semidiurnal tidal currents. In contrast, the CCW components have a more regular temporal regime with distinct monthly, fortnightly and 10-day modulation at astronomical periodicities associated with frequency differences M2–N2 (0.03629cpd), S2–M2 (0.06773cpd), and S2–N2 (0.10402cpd). Significant horizontal correlation of the CW current envelopes was found only between stations near the northeast Mackenzie Shelf, indicating this to be the main area of baroclinic internal wave generation. [Copyright &y& Elsevier]

Abstract: The nearshore shelf of the Beaufort Sea is defined by extreme physical and biological gradients that have a distinctive influence on its productivity and trophic structure. Massive freshwater discharge from the Mackenzie River, along with numerous smaller rivers and streams elsewhere along the coast, produce an environment that is decidedly estuarine in character, especially in late spring and summer. Consequently, the Beaufort coast provides a critical habitat for several species of amphidromous fishes, some of which are essential to the subsistence lifestyle of arctic native populations. Because of its low in situ productivity, allochthonous inputs of organic carbon, identifiable on the basis of isotopic composition, are important to the functioning of this arctic estuarine system. Coastal erosion and river discharge are largely responsible for introducing high concentrations of suspended sediment from upland regions into the nearshore zone. The depletion in the 13C content of invertebrate and vertebrate consumers, which drops about 4–5‰ eastward along the eastern Alaskan Beaufort Sea coast, may reflect the assimilation of this terrestrial organic matter into local food webs. In addition, the large range in 13C values of fauna collected in the eastern Beaufort (nearly 8‰) compared to the same species in the northeastern Chukchi (3‰), indicate a lower efficiency of carbon transfer between trophic levels in the eastern Beaufort. The wider spread in stable isotope values in the eastern Beaufort may also reflect a decoupling between benthic and pelagic components. Isotopic tracer studies of amphidromous fishes in the Simpson Island barrier island lagoon revealed that terrestrial (peat) carbon may contribute as much as 30–50% of their total dietary requirements. On the eastern Alaska Beaufort Sea coast, the δ 13C values of arctic cod collected in semi-enclosed lagoons were more depleted, by 3–4‰, compared to fish collected in the coastal Beaufort Sea. Calculations from isotopic mixing equations indicate cod from lagoons may derive 70% of their carbon from terrestrial sources. The δ 15N values of lagoon fish were also 4‰ lower than coastal specimens, reflective of the lower δ 15N values of terrestrially derived nitrogen (0–1.5‰ compared to 5–7‰ for phytoplankton). The role of terrestrial carbon in arctic estuarine food webs is especially important in view of the current warming trend in the arctic environment and the role of advective processes that transport carbon along the nearshore shelf. Biogeochemical studies of the arctic coastal estuarine environment may provide more insights into the function of these biologically complex ecosystems. [Copyright &y& Elsevier]