Variations Of Opal,Organic Carbon,Total Nitrogen And Iron Burial In The Eastern Arabian Sea Since The Oligocene

Diatoms play a significant role in the marine primary productivity,which strongly influence global biogeochemical cycling of silicon and carbon in oceanic ecosystems.They are responsible for around forty percent of the marine primary production with a specific contribution to the biological pump of CO2 and involved in the export and burial of carbon in the deep ocean.Therefore,biogenic silica(BSi,or also called as opal)content in sediments has been used as a potential proxy for the reconstruction of paleoproductivity and paleoclimate of Earth at various timescales,millennial to tectonic.In general,variations of opal mass accumulation rate(opal MAR)in marine sediments from the continental margins can be used to reconstruct the primary productivity of diatoms during the past through time in these regional settings.Similarly,total organic carbon mass accumulation rate(TOC MAR)is used to assess the overall productivity in the upper ocean.In this study,a long drilled sediment core NGHP-01-01A,collected from the Eastern Arabian Sea during the Indian National Gas Hydrate Program(NGHP)Expedition 01,was analyzed for the contents of BSi,total iron(TFe),along with TOC and total nitrogen(TN),to estimate their burial rates.By calculating and comparing the mass accumulation rates of these parameters,this study explores the intimate links between opal and organic matter burial with the total iron in this region over the last?37 Ma.Based on the contents and mass accumulation rates of opal,TOC,TN and TFe,the following four intervals are distinguished from the results:(1)from?25 to?16.5 Ma:opal and total Fe slightly increased with relatively lower organic matter(TOC and TN)content;and this interval shows a relatively low mass accumulation rates;(2)from?16.5 to?10 Ma:organic matter content increased along with opal and total Fe.Besides,there are synchronous crashes in opal and total Fe records during this period;the mass accumulation rates increased slowly;(3)from?10 to?5.5 Ma:both the contents and mass accumulation rates of opal,TOC,TN and TFe show significant increase,but with fluctuations in this interval;(4)from?5.5 Ma to 2 Ma:a remarkable increase of these parameters exists during?4 to?2 Ma and after that rapidly decreased between?5.5 Ma and?4 Ma.The general trends of these parameters at the core location at million year time scale are discussed here based on the coarse resolution due to the wide sampling interval.It shows significant links between the mass accumulation rates of four proxies(opal,TOC,TN and TFe)at site NGHP-01-01A and the Neogene relative sea level curves,and the oxygen isotope data and the mean terrigenous flux delivered from the Himalayas to the northern Indian Ocean during the late Oligocene to Pleistocene(around the last 25 Ma).Enhanced biosiliceous sedimentation exists during the late Miocene to late Pliocene(from?10 to?2 Ma)with fluctuations,corresponding to the well-known"biogenic bloom" event in the world ocean.The opal content decreased between?97 Ma and this change seems to be linked to the gradually decreasing strength of upwelling in the northern Indian Ocean after?9 Ma.From?4 Ma to?2 Ma,the percentage of opal and MAR increased,coinciding with the high sediment flux from land to the northern Indian Ocean,and most likely can be associated with the erosion of Himalayas due to intensified South Asian monsoon.