Aquatic humic substances in pack ice-seawater-sediment system

Humic substances were isolated from samples of pack ice, sea water and sedi ments collected in the Gerlache Inlet and Wood Bay (Antarctica). The content and structures of the in-ice dissolved humic substances (DHS) a nd particulate humic substances (PHS) were determined in samples of cores, in the water column sampled under the pack ice, and in the water column and in sediments when sea ice was absent. The organic matter content of ice co res shows that the pack ice behaves as an organic matter "tank". The humifi cation process appears to proceed in the pack ice in which the phytoplankto nic material is trapped during its formation. The concentrations of humic s ubstances isolated from surface seawater sampled under the pack ice layer a nd when the ice is absent are constant in time. The absence of any increase in humic substance content in surface water and along the water column, wh en the ice has melted, may be explained by the different salinity values of the ice (from 6 to 20 parts per thousand) and of the seawater (34 parts pe r thousand), which determine an increase in the sedimentation process rate. This hypothesis is confirmed by fulvic acid/humic acid ratios in sediments that are higher than those found for sediments collected in Antarctic area s where the ice is always absent.