A mass balance of chlorophyll degradation product accumulation in Black Sea sediments

Abstract

The distribution of chlorophyll degradation products was measured in Black Sea sediment trap and sediment samples. Chlorophyll degradation products were identified as free phorbins, phorbin steryl esters, high molecular weight chlorophyll degradation products, and acid extractable chlorophyll degradation products. When all these sinks are considered, an inventory of chlorophyll degradation products can be established which identifies four times more sedimentary phorbins than standard HPLC studies alone. The concentration of total chlorophyll degradation products in the sediment trap samples varies with season and, in the sediments, increases with depth from Unit I into Unit II. In Unit III sediments, the total phorbin concentration dramatically decreases. These trends are similar to those of the total organic carbon concentration. Variations in the ratio of total phorbin/total organic carbon with depth in the sediments appear to be related to previously suggested changes of oxygen concentrations over time in the Black Sea water column. This new data was combined with data from the literature to create a mass balance of chlorophyll flux, degradation, and accumulation in the Black Sea. It is concluded that once chlorophyll degradation products reach the anoxic water column, they survive to be deposited in the underlying sediments. Although a larger percentage of total organic carbon, compared to total phorbin, passes out of the photic zone. the phorbin macrocycle appears to be more stable under anoxic conditions than is total organic carbon.