Cariaco Trench: Oxidation of Organic Matter and Residence Time of Anoxic Water

Abstract

THE Cariaco Trench is located on the Caribbean shelf of Venezuela and has a maximum depth of 1,400 m. The surrounding shelf is nowhere deeper than 150 m, thus separating the deep water of the trench from that of the Caribbean. The deep water of the trench is devoid of dissolved oxygen¹. Between the sill depth and 500 m both temperature and salinity decrease, resulting in a slight increase in density which stabilizes the water column somewhat precariously. Below 500 m the water is uniform and well mixed. Such anoxic basins are critically dependent on the balance between supply of organic matter and renewal of the deep water. Although the sediments indicate that at least the deep part of the basin has been permanently anoxic for thousands of years² the relatively small density gradient may facilitate renewal of the deep water on a much shorter time scale. Estimates of the residence time vary between 100 and 2,000 yr (refs. 1,3). Data resulting from a cruise of RV Atlantis II in July 1971 provide a way of assessing the origin and oxidation of organic matter in the trench and the renewal rate of the deep water.