TERRAPUB Journal of Oceanography

Journal of Oceanography, Vol. 63 (No. 4), pp. 695-709, 2007

ENSO Related Variations in Biogeochemistry of AA and HA in Settling Particles along the Equatorial Pacific Ocean

Lallan P. Gupta1* and Hodaka Kawahata2

1SPD, CDEX, JAMSTEC, Yokohama Institute for Earth Sciences, Showamachi, Kanazawa-ku, Yokohama 236-0001, Japan
2Ocean Research Institute, University of Tokyo, Minamidai, Nakano-ku, Tokyo 164-8639, Japan

(Received 14 September 2006; in revised form 5 February 2007; accepted 15 March 2007)

Abstract: Four year-long time-series sediment trap experiments were conducted along the equatorial Pacific Ocean in order to understand the biogeochemistry of particulate organic matter (POM) on the basis of amino acid (AA) and hexosamine (HA) compositions of the settling particles. Total mass flux in the study area varied over 4 orders of magnitude without a common seasonality among all trap sites. Planktonic blooms were apparent in terms of total mass and AA fluxes at the easternmost end of the Niño-4 region. AA fluxes closely followed the total mass flux profiles, suggesting that increased particle flux delivered a greater amount of labile OM to the deep ocean. A labile OM index (LI)-based classification showed that during the El Niño conditions in 2002, the eastern side of the equatorial Pacific transported relatively more labile OM than the western equatorial Pacific. An overall change in AA and HA composition of settling particles could be revealed with the help of discriminant analysis, suggesting that settling particles during El Niño were compositionally different from those settling during La Niña condition in the equatorial Pacific.

*Corresponding author E-mail: gupta@jamstec.go.jp

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