Geochemistry of calcareous sediments from the SW Carlsberg Ridge: Evidence for deeper carbonate compensation depth

Abstract

Concentration of Mn, Fe, Ni, Co, Zn, Ca, Mg, K, Al, Si, Ti, P and CaCO sub(3) show wide range for the calcareous sediments from SW Carlsberg Ridge (CR). Compared with the average pelagic clays, the CR sediments are enriched by Mg, Ni, Co, and Zn trace metals and are depleted in the other. Variation with respect to depth is significant for CaCO sub(3) (8.5-79.8%) and benthic ratios (1.5-32.5) whereas P sub(2)O sub(5) (0.28-0.38%) and organic carbon (0.18-0.46%) is low and constant. Correlation matrix on moisture, organic carbon (C) and CaCO sub(3) (MOC) free basis suggest three main processes responsible for the incorporation of various elements. It appears that biogenic process is most dominant among the others for the supply of Ca, Si, Mg, P, Cu, Ni and Zn elements due to high surface biological (calcareous) productivity. Mn and Fe are hydrogenous and Al, K and Ti are either terrigenous or in situ due to alteration of basalts. Occurrence of deeper lysocline (4700 m) and deeper carbonate compensation depth (CCD) (>5100 m) in the region is evident from the CaCO sub(3)-depth relationship which is different than that reported earlier. Inverse relationship between benthic ratio and CaCO sub(3) also supports high surface biological productivity, whereas increase in the benthic ratio point towards increase in the degree of dissolution with depth