Summary of Abstract Submission

Abstract Submission No. IO50-09-0051PresentationPoster

PARTICLE-REACTIVE RADIONUCLIDES (234TH, 210PB, 210PO) AS TRACERS FOR THE ESTIMATION OF POC EXPORT FLUXES IN THE NORTH INDIAN OCEAN: RESULTS FROM GEOTRACES STUDY

R. Rengarajan*1, S. Subha Anand1

1 Physical Research Laboratory, Ahmedabad, India

ABSTRACT :

As an interface for exchange of CO2 between the surface ocean and interior ocean, the euphotic zone plays a key role in the production, removal and cycling of biomass. Fluxes of carbon, nutrients and other associated elements within this zone involved in biogeochemical cycles are very important in the study of global CO2. Naturally-occurring particle-reactive radionuclides (234Th, 210Po, 210Pb) provide possible means for quantifying export flux of POC from the surface ocean at various time scales, because of their specific half-lives. 210Po is typically deficient relative to 210Pb in the surface ocean due to preferential removal by biota, while it is in near equilibrium or excess below the surface mixed layer due to rapid regeneration from sinking organic matter. To evaluate ocean POC export fluxes, seawater profiles for 210Po and 210Pb from surface to 800 m water depth were collected at several locations from the Indian Ocean during SK304, SK311 and SK312 cruises during 2013 and 2014 under GEOTRACES programme. The Arabian sea, being more productive zone, shows more deficit of 210Po relative to 210Pb indicating intense biological removal of 210Po. Removal flux of 210Po relative to 210Pb from 0-300 m depth from two transects along 87 E and 65 E between 18 N to 14 S ranged widely from 0.03 to 84.4 dpm m-2 d-1. The C/210Po ratio in particulates ranged between 239 and 717 M dpm-1. The derived export flux of POC using 210Po varied widely from 0.01 to 33.2 mmol m-2 d-1 due to the variable source of biogenic particles and spatial changes in the surface biogeochemical and physical conditions.