Ice drift and regional meteorology in the southern Bering Sea: Results from MIZEX West

Abstract

In February 1983 a multifaceted study of the air‐ice‐ocean interaction was made in the southern Bering Sea. The study, MIZEX West, addressed a broad spectrum of physical problems related to the Bering Sea marginal ice zone (MIZ). As a part of that study an array of eight Argos‐tracked floes on a scale of 50 km provided information on the mesoscale behavior of the ice pack. Wind and current measuring platforms on two of the floes gave detailed information on the forces on individual floes which were compared with the larger‐scale motions. Under relatively steady northeast winds and with weak or negligible regional currents, the floes accelerated considerably as they crossed the MIZ. The array showed little distortion, even though it skirted around St. Matthew Island and changed trajectory direction by over 90° during the 12‐day study period. Similarly, individual floes remained within 20° of their original orientation, although their angular motions were erratic and often rapid. A baroclinicly forced acceleration of the wind over the MIZ contributed to floe acceleration. The relative currents at 2 and 6 m under the ice were highly variable and random in time, although well correlated in depth. One of the floes was much smoother than the other, and higher winds and currents were noted at the smoother floe. The motion of the floes reflect strong coupling to the currents at tidal and lower frequencies and low‐frequency (greater than 6 hours) response to the wind. Both floes drifted to the right of the mean wind by approximately 30° at about 4% of the wind speed at 3 m, and relative wind and current directions were within 20° of being colinear, traits that are consistent with free drift hypothesis. Using quadratic drag representations for wind and current stress, the near colinearity allowed calculation of the ratio of the air/ice to ice/water drag coefficients, Ca/Cw, relative to measurement heights of 3 m and −2 m. For the rough floe this ratio changed in mean from 0.06 to 0.2 in its movement to the MIZ. For the smooth floe the variation in the ratio was less, from 0.14 to 0.2. However, for the rough flow the angle between wind and current was generally less than 180°, and for the smooth flow it was greater. It is possible that another type of drag related to the bow effect of the floe pushing through the water can account for this observation. Finally, the motion of the ice floes and ice edge are compared by examination of satellite photos. Two regions of the ice pack—one thick with rafting and rubble, one thin and broken—showed a ratio of edge velocity to floe velocity of 0.64 and 0.43, respectively. Thinner ice overtakes the edge and melts more rapidly than the thicker ice. A simple thermodynamic model explains this observation.

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

“…This is consistent with other studies (Thorndike and Colony 1982;Reynolds et al 1985;Wakatsuchi 2000, 2001). Thorndike and Colony (1982) showed that the wind (estimated geostrophically from sea level pressure) explains a large fraction of the variance of ice velocity in the central Arctic on short timescales, while the long-term (several month) averaged ice motion has equal contributions from the geostrophic wind and the mean ocean circulation.…”

“…Thorndike and Colony (1982) showed that the wind (estimated geostrophically from sea level pressure) explains a large fraction of the variance of ice velocity in the central Arctic on short timescales, while the long-term (several month) averaged ice motion has equal contributions from the geostrophic wind and the mean ocean circulation. Reynolds et al (1985) show that in the open ocean, sea ice moves to the right of surface wind at an angle of 30°at approximate 4 % of the wind speed at 3 m. Wakatsuchi (2000, 2001) show a high correlation of sea ice motion and wind along the ice edge in the Bering Sea on daily timescales.…”

“…Here, we can also evaluate the free drift assumption for Bering Sea ice motion away from land (Pease and Overland 1984;Reynolds et al 1985;Connolley et al 2004). We ignore the ice acceleration term in the force balance since it was found above to be small.…”

Observation and simulation of a floe drift near the North Pole

“…There have been many observations of high-latitude sea ice motion based on drifting ice stations (Hunkins 1967;Khandekar 1980), buoys (Thorndike and Colony 1982), satellite remote sensing (Kwok et al 2003), Argos-tracked floes (Reynolds et al 1985), and mooring instruments (Fukamachi et al 2011). These observations are very useful for studying the sea ice drift characteristics.…”

Seasonally dependent interannual variability of sea ice in the Bering Sea and its relation to atmospheric fluctuations

“…The dynamic mechanism is wind drag of the sea ice. It is known that sea ice in the open ocean moves sea ice at an angle of 30° to the right of surface wind direction at about 4% of the wind speed at 3 m [ Reynolds et al , 1985]. Recently, Kimura and Wakatsuchi [2000, 2001] showed that ice motions are well explained by the wind drag in the Bering Sea, based on daily satellite observations.…”