Natural isotopic composition of nitrogen in suspended particulate matter in the Bay of Bengal

S. Kumar (1) , R. Ramesh (1) , N. B. Bhosle (2) , S. Sardesai (2) , M. S. Sheshshayee (3)

1 PRL - Physical Research Laboratory [Ahmedabad]
2 NIO - CSIR National Institute of Oceanography [India]
3 University of Agricultural Sciences

We present the first measurement of nitrogen isotopic composition (?¹⁵N) in suspended particulate matter (SPM) of the surface Bay of Bengal (BOB) at 24 different locations during pre- (April?May 2003) and post- (September?October 2002) monsoon seasons. The ?¹⁵N of particulate organic nitrogen (PON) in surface suspended matter of coastal as well as northern open BOB shows signatures of a two end-member mixing between continental inputs and marine sources. Dilution by the organic and detrital continental material brought in by rivers leads to consistently lower ?¹⁵N, evident from the relationship between surface salinity and ?¹⁵N. ?¹⁵N of surface PON of open ocean locations during both seasons, and also at coastal locations during pre-monsoon suggest the nitrate from deeper waters as a predominant source of nutrient for planktons. The depth profiles of ?¹⁵N of SPM during pre-monsoon season at nine different locations are also presented. These indicate an increase in ?¹⁵N by a maximum of 2.8? between euphotic depth and 300 m, which is lower than that observed in the eastern Indian Ocean, indicating the role of higher sinking rates of particles ballasted by aggregates of organic and mineral matter in BOB.

Domaines: Cosmologie et astrophysique extra-galactique [astro-ph.CO]; Astrophysique [astro-ph]; Interfaces continentales, environnement; Océan, Atmosphère; Sciences de la Terre

S. Kumar, R. Ramesh, N. B. Bhosle, S. Sardesai, M. S. Sheshshayee. Natural isotopic composition of nitrogen in suspended particulate matter in the Bay of Bengal. Biogeosciences Discussions, 2004, 1 (1), pp.87-105. ⟨hal-00297728⟩