Biogeochemistry of trace elements and isotopes in the ...€¦ · by trace elements as they serve...
Transcript of Biogeochemistry of trace elements and isotopes in the ...€¦ · by trace elements as they serve...
Biogeochemistry of trace elements and isotopes in the Indian Ocean
Sunil Kumar Singh
2 July 2016
Geosciences DivisionPhysical Research LaboratoryAhmedabad 380009
Ministry of Earth SciencesGovernment 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 cycleThey 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 severelyaffects 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
ArabianSea
Bay ofBengal
Arabian Sea and Bay of Bengal are unique ocean basinsHigh productivity in the Arabian Sea Arabian Sea is a major denitrification / suboxic ocean basinBay of Bengal is a natural laboratory of river-ocean interactions
(water + particulate)Hydrothermal activityDust InputDistribution of trace elements will be impacted
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GEOTRACES - India
Technological DevelopmentScience
GEOTRACES - INDIA
ONLY 5-6 Labs worldwide have capability to measure seawater Fe
DFe In SeawaterFlow Injection System for determination of Dissolved Fe at ppt level
SK - 311
SK - 312
OMZ
Remineralisationin OMZ
SK - 304
Sub marine volcanism
Fe input from Kaireiand Edmond vent
fields
SK – 32405-18
SK – 32401-04
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
Bayof
Bengal
ArabianSea
Estuary: Chemical Reactor• REE & Nd: Role of Particulates
0 5 10 15 20 25 30 35Salinity
0
6
12
18
Riv
er-n
orm
aliz
ed N
d
1
4
0.5
Hooghly
Krishna
Godavari
Mahanadi
Dissolved Nd flux : 500 MgDust dissolution : 400 MgModel 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 PacificOceanITF transports ~10 million m3/s water from Pacific to Indian OceanHeat Transport of the ITF is 1.09 x1015 WattIt impacts Indian Ocean Dipole, ENSO and hence the monsoonLimited knowledge of transport of water from Pacific to Indian OceanTracking ITF using Nd isotope composition of seawaterWater 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 NdImpact of ITF on paleo-monsoon can be assessed using Nd in forams from sediments and corals
Eastern Indian Ocean
fij 1i 1
n
fij xii 1
n
x j
fijNdi Ndjexcess
i 1
n
Ndj
fijNdi NdiNdj
excessNd j
excess
i 1
n
Ndj Ndj
: excess fraction of dissolved Nd in ‘jth’ sample over Ndcontribution 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 massand ‘jth’ sample, and
excessjNd
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