The distribution of DOC and POC in the water column and brines of the Tyro and Bannock Basins

Abstract

Dissolved organic carbon (DOC) and particulate organic carbon (POC) have been measured in the Tyro and Bannock Basins in the eastern Mediterranean Sea. These basins contain an anoxic brine with the interface at 3383 and 3330 dbar respectively. In the oxic water column, DOC is at its maximum at 70–100 m depth (∼2.5 mg Cl−1). Below this layer the DOC value is constant around 1.5 mg Cl−1 down to the depth at which the seawater/brine interface occurs. In the oxic water column POC values gradually decrease from 20 to 5 μg Cl−1 with increasing depth. POC and DOC show a sharp increase at the seawater/brine interface, where values of 150 μg Cl−1 and ∼ 4.0 mg Cl−1 respectively have been observed. Within the brine the POC values are about 10 times higher (∼ 50 μg Cl−1) than in the overlying oxic seawater. The DOC content in the brine is about 2–2.5 times higher (4–4.5 mg Cl−1) than in the oxic seawater. The accumulation of POC at the interface and the presence of a high POC and DOC concentration in the brine favour bacterial activity at the interface.