Processes driving sea ice variability in the Bering Sea in an eddying ocean/sea ice model: Mean seasonal cycle

Abstract

a b s t r a c tThe seasonal cycle of sea ice variability in the Bering Sea, together with the thermodynamic and dynamic processes that control it, are examined in a fine resolution (1/10°) global coupled ocean/sea-ice model configured in the Community Earth System Model (CESM) framework. The ocean/sea-ice model consists of the Los Alamos National Laboratory Parallel Ocean Program (POP) and the Los Alamos Sea Ice Model (CICE). The model was forced with time-varying reanalysis atmospheric forcing for the time period [1970][1971][1972][1973][1974][1975][1976][1977][1978][1979][1980][1981][1982][1983][1984][1985][1986][1987][1988][1989]. This study focuses on the time period 1980-1989. The simulated seasonal-mean fields of sea ice concentration strongly resemble satellite-derived observations, as quantified by root-meansquare errors and pattern correlation coefficients. The sea ice energy budget reveals that the seasonal thermodynamic ice volume changes are dominated by the surface energy flux between the atmosphere and the ice in the northern region and by heat flux from the ocean to the ice along the southern ice edge, especially on the western side. The sea ice force balance analysis shows that sea ice motion is largely associated with wind stress. The force due to divergence of the internal ice stress tensor is large near the land boundaries in the north, and it is small in the central and southern ice-covered region. During winter, which dominates the annual mean, it is found that the simulated sea ice was mainly formed in the northern Bering Sea, with the maximum ice growth rate occurring along the coast due to cold air from northerly winds and ice motion away from the coast. South of St Lawrence Island, winds drive the model sea ice southwestward from the north to the southwestern part of the ice-covered region. Along the ice edge in the western Bering Sea, model sea ice is melted by warm ocean water, which is carried by the simulated Bering Slope Current flowing to the northwest, resulting in the S-shaped asymmetric ice edge. In spring and fall, similar thermodynamic and dynamic patterns occur in the model, but with typically smaller magnitudes and with season-specific geographical and directional differences.

The Oceanic Barrier Layer in the Eastern Indian Ocean as a Predictor for Rainfall Over Indonesia and Australia

“…In the ocean model, the vertical grid has 42 depth levels with variable thickness from 10 to 50 m in the upper 300 m. Sub‐grid scale horizontal mixing processes are parameterized via biharmonic operators (Maltrud et al., 2010) for both momentum and tracers, and the K‐Profile Parameterization (KPP) is used to represent vertical mixing (Large et al., 1994). The ocean and sea‐ice model components were initialized from a two‐year spun up state of a global 0.1° POP2/CICE4 simulation forced with interannually varying corrected Coordinated Ocean‐ice Reference Experiments phase II (Large & Yeager, 2009) surface atmospheric fluxes (Li et al., 2014). The preindustrial simulation was integrated for 131 years; our study used only the last 47 years (years 85–131) to exclude the initial model adjustment period.…”

The inhibition of warm advection on the southward expansion of sea ice during early winter in the Bering Sea

“…Generally, sea ice in the Bering Sea begins to form around the beginning of October and expands southward throughout the winter (Niebauer et al, 1999;Stabeno et al, 2012a;Li et al, 2014). In winter, sea ice forms mainly in the northern coastal area of the Bering Sea and the polynya areas on the southern coast of St. Lawrence Island and is then transported southward by north winds (Alexander and Niebauer, 1981;Niebauer, 1998;Stabeno et al, 2007;Ohshima et al, 2020).…”

“…With respect to the sea ice generation area, in December, sea ice often occurs north of St. Lawrence Island, while the January SIA increases are more likely to occur in the Bering Sea shelf area (Stabeno et al, 2012a). The large amount of warm water carried by the Bering Sea continental slope current in the southern waters causes a large amount of sea ice to melt, eventually leading to an S-shaped asymmetrical sea ice edge (Niebauer et al, 1999;Li et al, 2014).…”

“…Sea ice plays a key role in shaping the ecosystems of the Bering Sea (Kearney et al, 2021). Bering Sea waters contain one of the most productive marine ecosystems in the world and consequently support a large oceanic fishery that is critical for both commercial and subsistence use (Zhang et al, 2010;Hunt et al, 2011;Li et al, 2014;Hunt et al, 2020). Winter ice cover creates a pool of cold bottom water (<2℃) that is protected from summer mixing by the thermocline (Mueter and Litzow, 2008;Stabeno et al, 2012b).…”

“…A conveyor belt mechanism with a northern source, a southern sink, and an intermediate zone where ice is transported southward by northerly winds, has been proposed to explain the basic north-south SIA structure using observations alone (Pease, 1980;Niebauer et al, 1999;Li et al, 2014). In the northern Bering Sea, northerly or northeasterly wintertime winds promote ice growth and favor the southward transport of sea ice, while northward oceanic heat transport from the southern Bering Sea shelf can accelerate sea ice melting and inhibit southward sea ice expansion (Stabeno et al, 2007;Brown and Arrigo, 2012;Li et al, 2014). Simulation results have shown that from January to May, northeasterly winds transport 1.4×10 12 m 3 of sea ice to the south.…”