Carbon dioxide exchange in the coastal ocean-sea ice-atmosphere system

The Arctic Ocean and coastal tundra zone are significant sources and sinks for radiatively active trace gases. These gases could play a key role in forcing global and Arctic climate change. Measurements along the coast of the Arctic Ocean and at Barrow, Alaska, show that the concentrations of carbon dioxide, methane, and other important greenhouse gases have increased substantially over the past several decades (Dlugokency et al. 1995; Conway et al. 1994). At the same time, however, the role of CO2 transport across the sea ice in the regional carbon budget has not been evaluated because there are scanty experimental data, except for the pioneering measurement of Gosink et al. (1976) in the 1960-70s. These show the high permeability of sea ice for CO2 for temperatures above -15oC.

In this report, we present preliminary results obtained in an IARC/UAF pilot project performed in cooperation with CRREL. Using eddy-correlation techniques, we measured the carbon dioxide flux on fast ice near Point Barrow using a LICOR 7500 open-path CO2/H2O analyzer and a 3-D sonic anemometer/thermometer installed on a tower 5.5 m high. Additionally, to evaluate the CO2 concentration and to obtain rough estimates of CO2 fluxes through different parts of the sea ice cover (melt ponds, dry snow, bare ice), we used a chamber technique. For these latter measurements, we used small (1-2 gallons) and large (25 gallons) chambers and a closed cell LICOR 800 gas analyzer. The same technique was used for estimating pCO2 in sub-ice water samples taken just beneath the ice and at depths below the sharp halocline.

Our observations (located about 5 miles from the NOAA Base Observatory) show that, in June, absorption of atmospheric CO2 by sea ice and water beneath the ice decrease the near-surface atmospheric CO2 content compared with the atmospheric CO2 content over the coastal tundra.