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  • Biogeochemistry of trace elements and isotopes in the Indian Ocean

    Sunil Kumar Singh

    2 July 2016

    Geosciences Division Physical Research Laboratory Ahmedabad 380009

    Ministry of Earth Sciences Government of India

  • One of the major discoveries of last decade was the presence of HNLC (High Nutrient Low Chlorophyll) region in world Ocean.

    The low productivity was found to be a result of deficiency of key trace elements, e.g.: Fe

    Trace elements serve as micronutrients and regulates marine ecosystem dynamics and carbon cycle They serve as paleo-oceanographic tracers

    High Nutrient Low Chlorophyll region of the Arabian Sea

    HNLC

  • Marine ecosystem dynamics and carbon cycling are regulated by trace elements as they serve as micronutrients. For example, Iron is a well known micronutrient, deficiency of which severely affects photosynthesis and nitrogen fixation.

    The biogeochemical cycling of trace elements, therefore has direct implications to marine carbon cycle, which in turn influences ocean ecosystem dynamics and climate change.

    The distribution of TEs in the oceans and their depositional fluxes hold clues to productivity variations / climate change.

    Similarly the abundances and isotope composition (e.g., Nd, Pb, U-Th) of water masses are unique and their records in authigenic deposits can serve as paleo-oceanographic tracers.

    Trace Elements and Isotopes (TEIs) in the Oceans

    GEO-SCIENCES

  • Important biogeochemical processes in the ocean and the trace metals thought to be fundamental to their action.

  • DataLimited for Fe

    Existing deep ocean Fe data

    Stations with Fe concentrations at depths > 2000 m in 2003 (taken from GEOTRACES Science Plan 2006)

    Fe data is scarce, particularly in the deep ocean, limited understanding of the Fe cycle

  • Indian Ocean

    Arabian Sea

    Bay of Bengal

    Arabian Sea and Bay of Bengal are unique ocean basins High productivity in the Arabian Sea Arabian Sea is a major denitrification / suboxic ocean basin Bay of Bengal is a natural laboratory of river-ocean interactions

    (water + particulate) Hydrothermal activity Dust Input Distribution of trace elements will be impacted

  • 8

    GEOTRACES - India

    Technological Development Science

  • GEOTRACES - INDIA

  • ONLY 5-6 Labs worldwide have capability to measure seawater Fe

    DFe In Seawater Flow Injection System for determination of Dissolved Fe at ppt level

  • SK - 311

    SK - 312

    OMZ

    Remineralisation in OMZ

    SK - 304

    Sub marine volcanism

    Fe input from Kairei and Edmond vent

    fields

    SK – 324 05-18

    SK – 324 01-04

    SK - 311

    Sources of Dissolved Fe in the Indian Ocean and productivity

    Fe from Hydrothermal source

    Fe from Shelf

  • Narmada

    Tapi

    Mandovi

    Ganga

    Mahanadi

    Godavari

    Krishna

    Ba y o

    f B eng

    al

    Arabian Sea

    Estuary: Chemical Reactor • REE & Nd: Role of Particulates

  • 0 5 10 15 20 25 30 35 Salinity

    0

    6

    12

    18

    R iv

    er -n

    or m

    al iz

    ed N

    d

    1

    4

    0.5

    Hooghly

    Krishna

    Godavari

    Mahanadi

    Dissolved Nd flux : 500 Mg Dust dissolution : 400 Mg Model Estimated Missing Nd: 5500 – 11000 Mg

    Nd Flux from particles : 5700±2600 Mg

  • Nd as tracer of ocean circulation

  • The Indonesian Throughflow (ITF) and Indian Ocean Dipole (IOD) North eastern Indian acts as conduit between the Indian and the Pacific Ocean ITF transports ~10 million m3/s water from Pacific to Indian Ocean Heat Transport of the ITF is 1.09 x1015 Watt It impacts Indian Ocean Dipole, ENSO and hence the monsoon Limited knowledge of transport of water from Pacific to Indian Ocean Tracking ITF using Nd isotope composition of seawater Water masses in the Andaman Sea

  • GEOTRACES - INDIA

  • Bay of Bengal

  • Arabian Sea

  • Eastern Indian Ocean

  • Indonesian Throghflow

    Results indicate that Nd (Nd isotope composition) of water can be used to track Indonesian Throughflow (ITF) as the pacific waters have higher Nd Impact of ITF on paleo-monsoon can be assessed using Nd in forams from sediments and corals

    Eastern Indian Ocean

  • fij 1 i 1

    n

    fij xi i 1

    n

    x j

    fijNdi Ndj excess

    i 1

    n

    Ndj

    fijNdi Ndi Ndj excess

    Nd j excess

    i 1

    n

    Ndj Ndj

    : excess fraction of dissolved Nd in ‘jth’ sample over Nd contribution from different water masses, respectively.

    where,

    ijf : the fraction of the ‘ith’ water mass in ‘jth’ sample, : either potential temperature or salinity of the ‘ith’ water mass and ‘jth’ sample, and

    excess jNd

    ix jx&

    Inverse Model Calculation

  • Excess Nd is derived from sinking detrital material or slope sediments

    Excess Nd and their isotope composition

  • Dust Flux : 7 g m-2 y-1

    Excess Nd and their isotope composition

  • Excess Nd and their isotope composition

  • Thanks

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