Outflow of Arctic ocean sea ice into the Greenland and Barents Seas: 1979-2007.

摘要

Twenty-nine years of Arctic sea ice outflow into the Greenland and Barents Seas are summarized. Outflow is computed at three passages: Fram Strait, between Svalbard and Franz Josef Land (S-FJL), and between Franz Josef Land and Severnaya Zemlya (FJL-SZ). Ice drift at the flux gates has been reprocessed using a consistent and updated time series of passive microwave brightness temperature and ice concentration (IC) fields. Over the record, the mean annual area outflow at the Fram Strait is 706(113) x 103 km2; it was highest in 1994/95 (1002x103 km2) when the North Atlantic Oscillation (NAO) index was near its 29-yr peak. The strength of the "Transpolar Drift Stream" (TDS) was high during the late 1980s through the mid-1990s. There is no statistically significant trend in the Fram Strait area flux. Even though there is a positive trend in the gradient of cross-strait sea level pressure, the outflow has not increased because of a negative trend in IC. Seasonally, the area outflow during recent summers (in 2005 and 2007) has been higher (>2 sigma from the mean) than average, contributing to the decline of summer ice coverage. Without updated ice thickness estimates, the best estimate of mean annual volume flux (between 1991 and 1999) stands at ~2200 km3 yr-1 (~0.07 Sv: Sv identical-to 106 m3 s-1). Net annual outflow at the S-FJL passage is 37(39) x10 3 km2; the large outflow of multiyear ice in 2002-03, marked by an area and volume outflow of 141x103 km2 and ~300 km3, was unusual over the record. At the FJL-SZ passage, there is a mean annual inflow of 103(93) x 103 km2 of seasonal ice into the Arctic. While the recent pattern of winter Arctic circulation and sea level pressure (SLP) has nearly reverted to its conditions typical of the 1980s, the summer has not. Compared to the 1980s, the recent summer SLP distributions show much lower SLPs (2-3 hPa) over much of the Arctic. Overall, there is a strengthening of the summer TDS. Examination of the exchanges between the Pacific and Atlantic sectors shows a long-term trend that favors the summer advection of sea ice toward the Atlantic associated with a shift in the mean summer circulation patterns.