Chemistry of surface sediment along a north-south transect across the equator in the Central Indian Basin: An assessment of biogenic and detrital influences on elemental burial on the seafloor

Abstract

The detailed chemistry of the surface sediment collected along a north-south transect across the equator in the Central Indian Ocean suggest that: biogenic sedimentation north of equator is dominated by carbonate ooze and the south of equator is dominated by siliceous ooze deposition. The carbonate compensation depth and the carbonate lysocline are located in a narrow depth zone of around 300 m thickness. The equatorial biogenic sediment domain is inturrupted by a detrital clay zone between 0~' and 3~'S latitudes due to combined effect of reduced dilution of distal Bengal fan sediment below the CCD and focussing of suspended detritus south of equator. The latitudinal trends of the detrital unsupported element (Element@dexcess@@) and inter-elemental correlations yield four main carrier phases responsible for burial of several elements; a) Carbonate phase, b) detrital phase, c) Oxide phase, and d) Biogenic phase. Elemental Ba exhibits latitudinal similarity and strong positive association with Mn, Co and Cu in both Element@dbulk@@ and Element@dexcess@@ correlation matices. The proportion of excess Ba, Mn, Co and Cu is > 80% of their respective bulk content in all three sediment zones. These observations suggest a close link between elemental-Ba and oxide fraction of the sediment. The close association of elemental-Ba with oxide suggests a complexity involved if the Ba is used as paleo-productivity indicator and the relationship appears not straight forward as was thought. Excess Al appears to be a potential indicator of productivity as it has shown a close relationship with carbonate north of equator and opal south of the equator, and its similar proportion in the bulk Al along the transect is comparable with nearly similar primary productivity in the region. Though the Rare Earth Elements (REE) exhibit a mutual coherence in the sediment, they display an increasing affinity towards Mn and decreasing affinity towards Ti with increasing atomic number. Such a subtle but systematic variation within the REE group suggests preferential burial of Heavy-REE by Mn-oxide phase and Light-REE by detrital phase