sea ice extent

Last Glacial Maximum (21 000 yrs BP; LGM) and Greenland Stadial 12 (44 000 yrs BP; GS12) climate has been simulated with the National Centre for Atmospheric Research (NCAR) Community Climate System Model version 3 (CCSM3). Although the simulations were initiated from simulated glacial climates, both simulations required 1500 years of additional integration to reach equilibrium under the imposed boundary conditions and forcings.

Identifying terrigenous sources in deep-sea sediments may reveal temporal trends in paleocirculation and the relative role of eolian, upwelled, and hemipelagic Fe sources to surface waters. Bulk elemental and isotopic geochemistry of deep-sea sediments recovered during Ocean Drilling Program Leg 177 in the southeastern Atlantic sector of the Southern Ocean reveal several important aspects of paleocirculation and terrigenous provenance. The sites studied span 43° 53° S and represent different oceanographic settings relative to regional hydrography and sediment type. Bulk sediment geochemistry indicates that terrigenous provenance varied over the past 600 k.y. Site 1089, the northernmost site, exhibits clear glacial-interglacial variability in provenance, while provenance appears to vary regardless of climate state at the more southerly sites (Site 1093 and 1094). Nd and Sr isotopes and Sm/Nd ratios of the terrigenous fraction indicate that study sites have geochemically distinguishable provenance. Nd and Sr isotopes further suggest that Sites 1089 and 1094 both contain detrital components that originated in South America over the past 30 k.y.; however, Site 1089 is also influenced by southern African sources and the strength of the Agulhas Current. The ɛNd data support a more hemipelagic source for the terrigenous material rather than an eolian source based on comparisons with Antarctic ice core data and known sea-ice extent.

Arctic winter, spring and autumn surface air temperature (SAT) anomalies and associated sea level pressure (SLP) fields have decidedly different spatial patterns at the beginning of the 21st century (2000–2007) compared to most of the 20th century; we suggest calling this recent interval the Arctic warm period. For example, spring melt date as measured at the North Pole Environmental Observatory (2002–2007) is 7 d earlier than the records from the Russian North Pole stations (1937–1987) and statistically different at the 0.05 level. The 20th century was dominated by the two main climate patterns, the Arctic Oscillation/Northern Annular Mode (AO/NAM) and the Pacific North American-like (PNA*) pattern. The predominately zonal winds associated with the positive phases of these patterns contribute to warm anomalies in the Arctic primarily over their respective Eastern and Western Hemisphere land areas, as in 1989–1995 and 1977–1987. In contrast, SAT in winter (DJF) and spring (MAM) for 2000–2007 show an Arctic-wide SAT anomaly of greater than +1.0°C and regional hot spots over the central Arctic of greater than +3.0°C. Unlike the AO and PNA*, anomalous geostrophic winds for 2000–2007 often tended to blow toward the central Arctic, a meridional wind circulation pattern. In spring 2000–2005, these winds were from the Bering Sea toward the North Pole, whereas in 2006–2007 they were mostly from the eastern Barents Sea. A meridional pattern was also seen in the late 1930s with anomalous winter (DJFM) SAT, at Spitzbergen, of greater than +4°C. Both periods suggest natural atmospheric advective contributions to the hot spots with regional loss of sea ice. Recent warm SAT anomalies in autumn are consistent with climate model projections in response to summer reductions in sea ice extent. The recent dramatic loss of Arctic sea ice appears to be due to a combination of a global warming signal and fortuitous phasing of intrinsic climate patterns.

Seasonal fast ice thickness at the island of Hopen (Barents Sea) was monitored over 40 years. Sea ice thickness variability as a climate indicator provides more quantitative information on the state of the ice cover than solely sea ice extent. Usually, starting to form just before December Hopen fast ice reaches maximum thickness in May (on average 0.99 m), before

The presence or absence of sea-ice over the Bering Sea influences the productivity of its waters as well as the regional climate of Beringia. Not only is the extent and distribution of sea-ice an important climate system feedback because of changes in albedo, it also has the potential to impact oceanographic and atmospheric circulation patterns by altering ocean stratification and

In this study, we present grain-size distributions of the terrigenous fraction of two deep-sea sediment cores from the SE Atlantic (offshore Namibia) and from the SE Pacific (offshore northern Chile), which we 'unmix'into subpopulations and which are interpreted as coarse ...

The Arctic lower troposphere represents a sensitive balance between surface, Arctic boundary layer, and cloud processes, forming a cloud-ABL-surface (CAS) system. The CAS system must be considered as a coupled system, since clouds, boundary layer, and ...

The extent of Arctic sea ice is a fundamental parameter of Arctic climate variability. In the context of climate change, the area covered by ice in the Arctic is a particularly useful indicator of recent changes in the Arctic environment. Climate models are in near universal agreement that Arctic sea ice extent will decline through the 21st century as a consequence of global warming and many studies predict a ice free Arctic as soon as 2012.

Circum-Antarctic coastal environmental shifts during the Late ... PAUL A. BERKMAN', JOHN T. ANDREWS', SVANTE BJORCK3, ERIC A. COLHOUN4, STEVEN D. EMSLIE5, IAN D. GOODWIN6, BRENDA L. HALL', CHARLES P. HART, KAZUOMI HIRAKAWA", ATSUO ...

Determining how climate fluctuations affect ocean ecosystems requires an understanding of how biological and physical processes interact across a wide range of scales. Here we examine the role of physical and biological processes in generating fluctuations in the ecosystem around South Georgia in the South Atlantic sector of the Southern Ocean. Anomalies in sea surface temperature (SST) in the South Pacific sector of the Southern Ocean have previously been shown to be generated through atmospheric teleconnections with El Niño Southern Oscillation (ENSO)-related processes. These SST anomalies are propagated via the Antarctic Circumpolar Current into the South Atlantic (on time scales of more than 1 year), where ENSO and Southern Annular Mode-related atmospheric processes have a direct influence on short (less than six months) time scales. We find that across the South Atlantic sector, these changes in SST, and related fluctuations in winter sea ice extent, affect the recruitment and ...