Sea ice drift near Bering Strait during 1982

Abstract

Six Argos ice stations were deployed in the northeastern Bering Sea in January and February 1982. Four moved north through Bering Strait and made between one and five passes through the strait before they sank or were crushed by the ice, and two remained in western Norton Sound and Shpanberg Strait. Net winds in the region were directed toward the southwest and were relatively uniform geographically. Net currents were northward, and both mean velocity and mean speed were greater at Bering Strait than at Shpanberg Strait. Norton Sound contributed ice northward through Bering Strait in the mean during winter and spring. There was also a net divergence of ice near Cap Lisburne. A theory for open-shelf shallow water ice drift is developed that adds terms for bottom drag and stress feedback from the water column. A stress analysis for a station that remained in western Norton Sound and Shpanberg Strait showed that bottom drag did not contribute significantly but that stress feedback from the accelerated shallow water current can be of the same order as the Coriolis force. However, the analysis contained a residual, possibly associated with internal ice stress, coastal setup, or unknown measurement error, which was of roughly the same order as the wind and current stress. INTRODUCTION Bering Strait connects the Bering and Chukchi seas. it is the only shipping lane for marine transportation to th e northslope of Alaska and is the only sire of mass exchange between th e Pacific and Arctic oceans. The strait is 83 km across between Cape DeZhneva on the Chukotsk Peninsula and Cape Prince of Wales on the Seward Peninsula (Figure 1). It is divided midway by two small islands called Big Diomede (Siberia) and Little Diomede (Alaska) and, slightly south, by Fairway Rock (Alaska). Bottom depths along the section range from 38 to 53 m with a slight depression between Little Diomede and the Seward Peninsula (Figure 2). The Bering and ChukChi shelves within 300 km of the strait are typically shallower than 50 in. There is a qualitative north-south symmetry between •h e Berin g and Chukchi seas with Norton Sound opening off the northeast Bering Sea and Kotzebue Sound. opening Off the southeast Chukchi Sea. The large noticeable exceptio n to the symmetry is St. Lawrence Island (Figur e 1), which partially blocks the entrance to the strait fro m the south. The Straits to the west and east of St. Lawrence are called Anadyr and Shpanberg straits, respectively. In the last decade, experimental studies of ice motion in the eastern Bering Sea indicated that ice floes are created along the western coast of Alaska, in Norton Sound, and along the south side of islands such as St. Lawrence Island and drift southwestward untier the primary influence of northeasterly winds until the floes melt at the ice edge [Muench and Ahlniis, 1976; Pease, 1980; McNutt, 1981]. Ice drift measurements taken during the winter and spring of 1982 do not confirm this simple conveyor belt picture of ice motion. Instead, they indicate that the Bering Sea actually con...

Polynya activity in the Arctic Ocean from 1958 to 1997

“…A drift angle of 37 ø was found by Thorndike and Colony [ 1982] for winter/spring conditions, and the 3% drift has been observed at several locations in the Arctic [e.g., Thorndike and Colony, 1982;Pease and Salo, 1987]. The polynya width, W, is a balance between advection and production of ice as dW PW --=ui---, (2) dt h i where P is the (area-averaged) ice production, hi is the effective collection thickness of frazil ice deposited at the ice edge (further discussed below), and u, is the ice velocity normal to the coast taken to be positive in the offshore direction.…”

Passive microwave remote sensing of thin sea ice using principal component analysis

“…Frazil formed in the polynyas is advected southward, eventually consolidating into a solid ice sheet within a few tens of kilometers of land. This ice is driven southward at rates as high as 3% of the wind speed [Pease and Salo, 1987;Pease and Overland, 1984]. As the process continues, ice is constantly generated in the polynyas and distributed downwind.…”

Modeling ice dynamics of coastal seas

“…For winds with an alongshore component the angle between the wind and ice drift will be less than the free drift angle. These predictions are confirreed for Alaskan shelves away from Bering Strait with an average ice/10-m wind speed ratio of 3.8% and drift angle of 21% for a January-February 1982 data set [Pease and Salo, 1987]. Pease and Salo [1987] also show a residual for a free drift force balance that is the same magnitude as the wind and current stress, which they attribute to coastal setup and internal ice stress.…”

“…Sea ice motion and concentration are influenced by the presence of coastlines (Figure 1). For example, wind-driven ice drift is coupled to changes in sea level and resulting coastal currents [Ikeda, 1985;Pease and Salo, 1987-]. The presence of coastlines contributes to large divergence and shear rates in the sea ice motion field, of the order of 12% per day compared to central Arctic rates of < 1% per day [Hibler et al, 1974].…”