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This study investigates sea ice and ocean circulation using a 3‐D, 3.8 km CIOM (Coupled Ice‐Ocean Model) under daily atmospheric forcing for the period 1990–2008. The CIOM was validated using both in situ observations and satellite measurements.
The CIOM successfully reproduces some observed dynamical processes in the region, including the Bering‐inflow‐originated coastal current that splits into three branches: Alaska Coastal Water (ACW), Central Channel branch, and Herald Valley branch. In addition, the Beaufort Slope Current (BSC), the Beaufort Gyre, the East Siberian Current (ESC), mesoscale eddies, and seasonal landfast ice are well simulated. The CIOM also reproduces reasonable interannual variability in sea ice, such as landfast ice, and anomalous open water (less sea ice) during the positive Dipole Anomaly (DA) years, vice versa during the negative DA years.
Sensitivity experiments were conducted with regard to the impacts of the Bering Strait inflow (heat transport), onshore wind stress, and sea ice advection on sea ice change, in particular on the landfast ice. It is found that coastal landfast ice is controlled by the following processes: wind forcing, Bering Strait inflow, and sea ice dynamics. IntroductionThe Beaufort and Chukchi seas (Figure ) are located in an important region where North Pacific water via the Bering Strait encounters the Western Arctic water and seasonal ice in the Chukchi Sea, and both seasonal and perennial ice in the Beaufort Sea. The Chukchi Sea's main feature is a relatively wide continental shelf, while the Beaufort Sea is characterized by a relatively narrow continental shelf and a deep basin with a narrow, steep shelf slope. More importantly, the Beaufort Sea also features continuous landfast ice along the Alaskan Arctic coast, overlying the 20 m isobath Eicken et al. In comparison, the landfast ice along the western Alaska coast in the Chukchi Sea is discontinuous. The ocean circulation system in the Beaufort and Chukchi seas is very complex and consists of the Bering Strait inflow that separates into three branches: the Alaskan Coastal Water/Current (ACW/C), the Central Channel branch, and the Herald Valley branch (see Figure ).
The area also contains the anticyclonic Beaufort Gyre, the Beaufort Slope Current (BSC) Pickart, , and the East Siberian Current (ESC). The BSC has a cross‐slope spatial scale of about several dozen kilometers Weingartner et al.,; Pickart, , and the Barrow Canyon Current has a similar spatial scale of about 30 km to the BSC. Another important feature in the Beaufort Sea is the small mesoscale eddies of a few tens of kilometers in diameter Manley and Hunkins,; Muench et al.,; Chao and Shaw,; Mathis et al.,; Watanabe, , with anticyclones outnumbering the cyclones due to the negative sloping effect relative to the density front orientation Ikeda,; Wang and Ikeda,; Griffiths et al., , similar to the mesoscale eddies along the Bering Slope Current Mizobata et al.,. These small mesoscale features can be resolved only with high resolution observation arrays and models. A schematic diagram for coastal circulation in the Chukchi‐Beaufort Seas (light blue: Alaskan Coast Current with the origin of freshwater; median blue: Central Branch Current; dark blue: Herald Canyon Branch; red: Bering Slope Current; purple: Beaufort Gyre; green: East Siberian Current.) Depths are in meters (Courtesy of Tom Weingartner). Closed square denotes the mooring stations.The winter atmospheric wind pattern is mainly controlled by the anticyclonic (clockwise) Beaufort High, while the summer wind stress is relatively weak due to the weakened Beaufort High.
The northward propagating summer storms sometimes move to the Chukchi Sea via the Bering Strait Pickart et al., , producing strong wind and mixing. The winter anticyclonic wind stress associated with the Beaufort High has many important effects on (1) surface Ekman drift that advects the Beaufort coastal freshwater into the Beaufort Gyre Yang, , (2) subsurface upwelling that brings the warm, saline Arctic intermediate water (i.e., the Atlantic Water) into the Beaufort Sea shelf break, melting surface sea ice Melling,; Pickart et al., , and (3) formation of landfast ice Mahoney et al.,.An extensive review of ocean modeling in the Bering, Chukchi, and Beaufort Seas was given by Wang et al. Ocean only models have long been used to investigate ocean circulation in the absence of sea ice Nihoul et al.,. For example, an idealized ocean‐only modeling study was conducted by Winsor and Chapman to determine how wind stress, topography, and physical processes affect the Chukchi Sea current system in ice‐free conditions. However, without a sea‐ice model, ocean‐only models cannot reproduce the seasonal cycle of ocean circulation and thermohaline structure.There has been significant progress in understanding of large‐scale Arctic sea ice and ocean circulation through the Arctic Ocean Model Intercomparison Project (AOMIP) Proshutinsky et al.,; Holloway et al.,; Wang et al., and many others. Kowalik and Proshutinsky developed a 2‐D ocean tidal model in the Arctic Ocean.
applied a high resolution finite volume ocean model to simulate Arctic tides. In general, most sea‐ice models on basin scales use relatively simple thermodynamics and ice thickness distributions. These models can approximate sea ice as slabs of one to a few mean thicknesses as well as open water Hibler,.
While sufficient for simulating Arctic Ocean pack ice for climate study purposes, most present models lack the ability to sufficiently resolve the spectrum of ice thickness from thin, new ice to thick, ridged ice, or to resolve landfast ice anchored along the coast. developed a pan‐Arctic Coupled Ice‐Ocean Model (CIOM) with a resolution of 27.5 km, which, of course, is not sufficient to resolve coastal processes and dynamics.In recent years, eddy‐resolving models have been developed and are used to simulate ice and ocean dynamics in the Arctic seas Clement et al.,; Wang et al.,; Okkonen et al.,; Zhang et al.,; Watanabe,. Some important processes, including small mesoscale eddies, basin‐shelf interaction, and coastal currents, were studied in the Chukchi Sea. Nevertheless, there have been no 2‐D modeling studies of landfast ice in the coastal Chukchi and Beaufort Seas, although some field measurements studies were conducted Eicken et al.,; Mahoney et al.,; Yu et al., , and 1‐D thermodynamic only model was applied to the high Arctic Flato and Brown,.Landfast ice along the coastline of the Chukchi and Beaufort Seas plays an important role as a biologically productive habitat (such as walrus and polar bears) and transportation corridor. It also provides important protection to the shoreline and coastal installations Eicken et al.,. However, at the present time, it is not clear how the diminishing Arctic summer sea ice Wang et al.and the reduction in multiyear ice extent Maslanik et al.have impacted the seasonal cycle and distribution of landfast ice.
Thus, while the seasonal and interannual variability of the landfast ice in a diminishing sea ice scenario in the Chukchi and Beaufort Seas is an important emerging topic Wang et al., , evidence of such variability is somewhat limited. This is largely due to the temporally limited availability of synthetic aperture radar imagery required for accurate assessments of landfast ice extent Mahoney et al.,.Yu et al.
investigated interannual variability of Arctic landfast ice using observed.
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