Deep Sea Research Part I : Oceanographic Research

Volume 47, Issue 10, 01-October-2000

Deep Sea Research Part I : Oceanographic Research Vol. 47 (10) pp. 1937-1960
Copyright (c) 2000 Elsevier Science B.V. All rights reserved.

Amino acid and hexosamine composition and flux of sinking particulate matter in the equatorial Pacific at 175°E longitude

Lallan Prasad Gupta
Hodaka Kawahata

Marine Geology Department, Geological Survey of Japan, 1-1-3 Higashi, , Tsukuba-shi 305-8567, Japan
Graduate School of Science, Tohoku University, , Sendai 980-8578, Japan

Received 24 August 1998; Revised 10 August 1999; Accepted 4 January 2000

Abstract

Sinking matter collected by sediment traps, which were deployed in the equatorial Pacific Ocean at 175°E for about 11 months during 1992-1993, were analyzed for their flux and labile components in terms of amino acids and hexosamines. The samples provided a temporal resolution of 15 days and were collected from 1357 (shallow trap) and 4363 m (deep trap) depths where sea floor depth was 4880 m. Particle flux along with major components (carbonate, organic matter, biogenic opal and lithogenic material) and amino acid parameters showed distinct temporal variations, which were more pronounced in the shallow trap relative to deep trap. A coupling between the fluxes in the shallow and deep traps was more evident during the period of maximum particle flux, which seems to be connected with the short reappearance of non-El Nino conditions in equatorial Pacific during the 1991-1993 El Nino event. The biogeochemical indicators C/N, Asp/Bala, Glu/Gaba, Bala+Gaba mol%, THAA-C% and THAA-N% implied that the increase in sinking flux was associated with upwelling and enhanced surface production. Degradation of sinking particulate organic matter between the shallow and deep traps was also evident. Occasionally higher mass and major component fluxes in the deep trap relative to the shallow trap are attributed to contribution of resuspended particulates from sea floor (nepheloid layer) or to laterally advected particulates from nearby areas. Carbonate and opal composition of the sinking flux showed a predominance of calcareous plankton; however, Asp/Gly mol ratio and Ser+Thr mol% indicated enhanced occurrence of diatoms during the periods of higher flux.

Keyword(s): Organic carbon; Amino acids; Hexosamines; Particle flux; Sediment trap; Central equatorial Pacific