Abstract. The major goal of this paper is to demonstrate the existence in the Arctic Ocean of two regimes of wind-forced circulation. We simulated the vertically averaged currents, sea level heights, and ice drift in the Arctic Ocean from 1946 to 1993 using a two-dimensional, wind-forced, barotropic model that includes frictional coupling between the ocean and ice. The model has a spatial resolution of 55.5 km and is driven by winds, river runoff, and an imposed but realistic sea level slope between the Pacific and the Atlantic Oceans. There is a good agreement between velocities from observed buoy motions and velocities of modeled ice drift even though the model lacks ocean baroclinicity and ice thermodynamics. The results indicate that wind-driven motion in the central Arctic alternates between anticyclonic and cyclonic circulation, with each regime persisting for 5-7 years, based upon our analysis of the modeled sea level and ice motion. Anticyclonic wind-driven motion in the central Arctic appeared during 1946-1952, 1958-1963, 1972-1979, and 1984-1988, and cyclonic motion appeared during 1953-1957, 1964-1971, 1980-1983, and 1989-1993. Shifts from one regime to another are forced by changes in the location and intensity of the Icelandic low and the Siberian high. The two regimes may help explain the significant, basin-scale changes in the Arctic's temperature and salinity structure observed recently, the Great Salinity Anomaly, and the variability of ice conditions in the Arctic Ocean. A series of two-dimensional (2-D) numerical model results [Fel'zenbaum, 1958;Campbell, 1965;Galt, 1973;Hart, 1975 Introduction This paper examines the role of wind-driven variations in the

This study was motivated by a strong warming signal seen in mooring‐based and oceanographic survey data collected in 2004 in the Eurasian Basin of the Arctic Ocean. The source of this and earlier Arctic Ocean changes lies in interactions between polar and sub‐polar basins. Evidence suggests such changes are abrupt, or pulse‐like, taking the form of propagating anomalies that can be traced to higher‐latitudes. For example, an anomaly found in 2004 in the eastern Eurasian Basin took ∼1.5 years to propagate from the Norwegian Sea to the Fram Strait region, and additional ∼4.5–5 years to reach the Laptev Sea slope. While the causes of the observed changes will require further investigation, our conclusions are consistent with prevailing ideas suggesting the Arctic Ocean is in transition towards a new, warmer state.

Arctic atmospheric variability during the industrial era (1875-2000) is assessed using spatially averaged surface air temperature (SAT) and sea level pressure (SLP) records. Air temperature and pressure display strong multidecadal variability on timescales of 50-80 yr [termed low-frequency oscillation (LFO)]. Associated with this variability, the Arctic SAT record shows two maxima: in the 1930s-40s and in recent decades, with two colder periods in between. In contrast to the global and hemispheric temperature, the maritime Arctic temperature was higher in the late 1930s through the early 1940s than in the 1990s. Incomplete sampling of large-amplitude multidecadal fluctuations results in oscillatory Arctic SAT trends. For example, the Arctic SAT trend since 1875 is 0.09 Ϯ 0.03ЊC decade Ϫ1 , with stronger spring-and wintertime warming; during the twentieth century (when positive and negative phases of the LFO nearly offset each other) the Arctic temperature increase is 0.05 Ϯ 0.04ЊC decade Ϫ1 , similar to the Northern Hemispheric trend (0.06ЊC decade Ϫ1). Thus, the large-amplitude multidecadal climate variability impacting the maritime Arctic may confound the detection of the true underlying climate trend over the past century. LFO-modulated trends for short records are not indicative of the long-term behavior of the Arctic climate system. The accelerated warming and a shift of the atmospheric pressure pattern from anticyclonic to cyclonic in recent decades can be attributed to a positive LFO phase. It is speculated that this LFO-driven shift was crucial to the recent reduction in Arctic ice cover. Joint examination of air temperature and pressure records suggests that peaks in temperature associated with the LFO follow pressure minima after 5-15 yr. Elucidating the mechanisms behind this relationship will be critical to understanding the complex nature of low-frequency variability.

[1] Arctic variability is dominated by multi-decadal fluctuations. Incomplete sampling of these fluctuations results in highly variable arctic surface-air temperature (SAT) trends. Modulated by multi-decadal variability, SAT trends are often amplified relative to northern-hemispheric trends, but over the 125-year record we identify periods when arctic SAT trends were smaller or of opposite sign than northern-hemispheric trends. Arctic and northernhemispheric air-temperature trends during the 20th century (when multi-decadal variablity had little net effect on computed trends) are similar, and do not support the predicted polar amplification of global warming. The possible moderating role of sea ice cannot be conclusively identified with existing data. If long-term trends are accepted as a valid measure of climate change, then the SAT and ice data do not support the proposed polar amplification of global warming. Intrinsic arctic variability obscures long-term changes, limiting our ability to identify complex feedbacks in the arctic climate system.

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