Decadal scale signals in the Arctic's atmospheric and oceanic systems (Invited Presentation)

Significant variations are evident in the last century's records of the Arctic, which is considered the "canary" of climate change. They include a dramatic decrease in sea-ice area, a substantial redistribution and thinning of sea ice, a general increase in precipitation, glacier melting, and river discharge, rising sea level, alternating cyclonic and anticyclonic wind regimes with corresponding changes in the ice drift and ocean circulation patterns, warming and increased areal extent of the Arctic Ocean's Atlantic layer. The accepted hypothesis is that these changes relate to the Arctic Oscillation (AO) as the leading mode of Northern Hemisphere sea level pressure (SLP) variability. However, the AO describes only about 20% of the winter time SLP variability and frequently does not correlate well with changes in the central Arctic. Another index is the index of wind-driven circulation introduced by Proshutinsky and Johnson (1997) and is based on the results of numerical simulation of the Arctic Ocean wind-driven circulation. Anticyclonic wind-driven motion in the central Arctic appeared during 1946-1952, 1958-1963, 1972-1979, 1984-1988, 1997-2000, and cyclonic motion appeared during 1953-1957, 1964-1971, 1980-1983, 1989-1996, 2001-present. Shifts from one regime to another are forced by changes in the location and intensity of the Icelandic low and the Siberian high. These transformations from one regime to another occur quite rapidly and can be defined as climate shifts. This index describes more than 40% of ocean variability and correlates better with the central Arctic environmental parameters than AO but, similar to AO, it does not explain causes of the decadal variability of the Arctic system.

To understand the origin of arctic changes, they need to be placed in the perspective of the record for at least 100 years. Assembling these observations is not easy: Before 1943, most of the existing data do not cover the central Arctic area. Relatively good-quality but scarce observations are available following 1943, and there are much more data after 1948 when satellites and surface buoys began to proven information from the central Arctic. Though there are no data for the central Arctic until 1943, we reconstructed it for the earlier period using both a statistical technique and numerical modeling. Analyses of the atmospheric, cryospheric, oceanic, and terrestrial time-series allowed us to formulate a new hypothesis along with supporting evidence that the Beaufort Sea anticyclonic Gyre and the Greenland Sea cyclonic Gyre play a significant role in regulating the arctic climate variability. We propose and demonstrate that the Beaufort Gyre accumulates a significant amount of fresh water during one climate regime (anticyclonic) and releases this water to the Greenland Sea and North Atlantic during another climate regime (cyclonic). Depending on the circulation regime, the Greenland Sea Gyre regulates deep water formation and interactions of the Arctic with the North Atlantic. This hypothesis can explain the origin of the salinity anomaly periodically found in the North Atlantic as well as the role of the freshwater fluxes in the decadal variability in the Arctic region.