Spatial and Temporal Distribution of Particulate Organic Matter in the Ross Sea

Abstract

Spatial distribution and biochemical composition of particulate organic matter (POM) were studied in relation to ice melting of the Ross Sea (Antarctica) during the austral spring and summer 1994 (from 14 Nov to 15 Dec 1994). POM distribution, characterized by areas with different amounts and biochemical composition of organic particles, was strongly influenced by ice melting. POM, mostly of phytoplankton origin, showed a large detrital component. On average, proteins accounted for the largest fraction of POM (40–80%), followed by carbohydrates (10–40%) and lipids (5–35%). POM vertical distribution was characterised by a concentration decrease between 20- and 60-m depth. Particulate organic matter in the surface layer and in the deep layer differed in quantitative and qualitative biochemical composition. POC and PON concentrations ranged, in the surface layer, between 36–256 and 3–41 µg |-1, respectively, and in the deep layer between 16–50 and 1–7 μg |-1, respectively. Changes in chemical composition were related to microbial ectoenzymatic activity. Degradation processes lead to a strong decrease in the protein fraction, as a result of the activity of protein degrading ectoenzymes, mainly leucine aminopeptidase, which showed the highest activities (>30 nmol |−1h-1) in the surface layer.The Ross Sea system acts as a retentive system since a large part of the organic matter is remineralized within the water column. POM spatial variation is considered within the frame of biochemical composition changes induced by ice-melting processes and compared with previous observations in the Ross Sea.