Composition and flux of particulate amino acids and chloropigments in equatorial Pacific seawater and sediments

Compositions and fluxes of amino acids and major chloropigments were measur ed in the central equatorial Pacific Ocean as part of the US JGOFS EqPac pr ogram, Fluxes decreased by several orders of magnitude, from 400 to 0.03 mg amino acid m(-2) d(-1) and from 9 mg to 0.0004 mu g chloropigment m(-2) d( -1), between production in the surface waters and accumulation at the sea B oor, Most rapid losses were in surface waters and at the sediment interface . Losses from the mid-water column were as great as those in surface waters or at the sediment interface, but occurred over a much greater depth range , Export flux estimates based on Boating sediment traps were higher near th e equator and decreased poleward, similar to primary production. Little meridional difference was apparent in composition of either amino ac ids or pigments in exported material over the 24 degrees of latitude sample d in spite of the large (factor of 5-6) difference in fluxes. However, pigm ent composition changed dramatically with depth in the water column, and co nsiderable diagenesis occurred before particles reached the sediment. Pigme nt compositions suggest that suspended particles were more degraded in the northern than in the southern hemisphere, possibly due to differences in fo od chain structure. Compositional changes in amino acids occurred in the wa ter column, but were most noticeable at the sediment-seawater interface. In creases in the relative proportions of aspartic acid and glycine with depth were more consistent with preferential preservation within the particulate matrix than with any inherent stability of these compounds to heterotrophi c consumption, The contribution of amino acids and pigments to total organi c carbon clearly shows that selective degradation of organic matter occurs with depth; this is not evident from total organic carbon data alone. Amino acids contributed about a quarter of the total organic carbon (OC) in surf ace waters and 16% of the OC in sediment; pigments decreased from 1% of tot al OC in surface waters to < 0.001% in sediments. Decreases in the contribu tion of amino acids to total organic carbon map be due to transformation in to uncharacterizeable material as well as to respiration. (C) 2000 Elsevier Science Ltd. All rights reserved.