Aquatic humic substances in pack ice-seawater-sediment system

Humic substances were isolated from samples of pack ice, sea water and sediments collected in the Gerlache Inlet and Wood Bay (Antarctica). The content and structures of the in-ice dissolved humic substances (DHS) and 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 cores shows that the pack ice behaves as an organic matter "tank". The humification process appears to proceed in the pack ice in which the phytoplanktonic material is trapped during its formation. The concentrations of humic substances isolated from surface seawater sampled under the pack ice layer and 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, when 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 per 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 areas where the ice is always absent.