Arctic Ocean sea ice volume: What explains its recent depletion?

Abstract

[1] Various observations and model results point to an arctic sea ice cover that was extraordinarily thin in the 1990s. This thin ice cover was caused by a strengthened cyclonic circulation of wind and ice and by unusual warmth of springtime air temperatures. Here modeled sea ice volume is decomposed into two components: first, a dynamic or wind-forced response to interannually varying winds but a fixed annual cycle of air temperature and second, a thermally forced solution responding only to interannually varying temperatures. Over the 52-year simulation from 1948 to 1999 these two components have a similar range and variance; the wind-forced component has no substantial trend, but the temperature-forced component has a significant downward trend of À3% per decade. Total ice volume shows a trend of À4% per decade. Export slightly exceeds production over the simulation. Annual export and production can differ from each other and from year to year by ±30%. This behavior seems to characterize an ice cover highly constrained by interannual variations in forcing and not in balance. The bulk (two thirds) of volume loss from the 1960s to the 1990s is a result of a striking thinning of undeformed ice. The remainder of the volume loss is due to thinning of ridged ice and reduced concentrations. The central Arctic Ocean and particularly the East Siberian Sea suffer the greatest losses (of up to 2 m); the ice north of the Canadian archipelago also thinned since the 1960s by $0.5 m.

Current estimates of freshwater flux through Arctic and subarctic seas

“…comm. 2004), similar to the annual losses of ice-volume ($2.8 mSv) estimated by Rothrock and Zhang (2005) for the past half-century . It has to be stated, however, that sea-ice parameters like thickness, extent and representation of the seasonal cycle from presently published coupled climate models differ greatly between themselves and in comparison with observations (Flato et al, 2004;Hu et al, 2004), as do atmospheric parameters such as air temperature (Holland and Bitz, 2003) and sea-level pressure.…”

“…It has to be stated, however, that sea-ice parameters like thickness, extent and representation of the seasonal cycle from presently published coupled climate models differ greatly between themselves and in comparison with observations (Flato et al, 2004;Hu et al, 2004), as do atmospheric parameters such as air temperature (Holland and Bitz, 2003) and sea-level pressure. In their 52-year simulation, Rothrock and Zhang (2005) find that the wind-forced component of sea-ice volume has no substantial trend but the temperature-forced component has a significant downward trend of À3% per decade. An additional uncertainty is the change to be expected in the separation of water into sea-ice and brine in the Arctic Ocean at times of low ice volume.…”

The Arctic Amplification Debate

“…Using a coupled ice-ocean model driven by winds and temperatures from the NCEP reanalysis, Rothrock and Zhang (2004) simulated sea ice thickness and volume changes over the period 1948-1999. They find that although wind forcing caused much of the rapid decline in thickness from the late 1980s through the mid 1990s, the overall downward trend in thickness is better explained by a general rise in temperatures.…”

“…Ice extent in September (the month of the seasonal minimum) has decreased by at least twice this rate (Parkinson et al, 1999;Comiso, 2000Comiso, , 2001Cavalieri et al, 2003;Stroeve et al, 2005) and the past four Septembers (2002Septembers ( through 2005 have seen extreme minima (Serreze et al, 2003;Stroeve et al, 2005; http://www.nsidc.org/data/seaice index/). There are also indications of decreased sea ice thickness and volume (Rothrock et al, 2003;Rothrock and Zhang, 2004;Lindsay and Zhang, 2005), warming of soils and permafrost (Osterkamp and Romanovsky, 1999), increased precipitation (Groves and Francis, 2002), and rising discharge from Arctic-draining rivers in Siberia (Peterson et al, 2002). Northern Hemisphere snow cover has exhibited modest negative anomalies since the late 1980s, largely owing to spring and summer deficits, but with large interannual and spatial variability (e.g., Robinson and Frei, 2000;Armstrong and Brodzick, 2001).…”

An Arctic and antarctic perspective on recent climate change

“…Of particular note are the extreme September ice minima of 2002(Stroeve et al, 2005. Rothrock and Zhang (2004) discuss a decrease in ice thickness. Part of the general downward trend in ice thickness and extent may be attributable to altered wind fields associated with the upward trend in the AO up to the mid-1990s (Rigor et al, 2002).…”