Total organic nutrients in Drake Passage

Sanders, R. and Jickells, T. (2000) Total organic nutrients in Drake Passage. Deep Sea Research Part I: Oceanographic Research Papers, 47 (6), 997-1014. (doi:10.1016/S0967-0637(99)00079-5).

Abstract

Approximately 400 paired measurements of total organic nitrogen (TON) and total organic phosphorus (TOP) were made on a hydrographic transect across Drake Passage by a uv photooxidation technique. Latitudinal variations in TON and TOP concentrations were observed, with the continental margins having surface-water concentrations approximately 50% greater than those in the centre of Drake Passage. This may be due to enhanced primary production on the continental shelves leading to increased production of organic nutrients. The vertical distributions of TON and TOP were characterised by surface maxima, declining to approximately constant levels of about 2.5 ?M TON and levels of TOP below detection by about 800 m. TON and TOP can be related by the equation TON=(15.7±1.7)TOP+(2.48±0.17), r2=0.44, n=397. This is interpreted as reflecting two weakly connected pools of organic material, the first a substantial refractory pool containing about 2.5 ?M TON and undetectable levels of TOP, which dominates in deep water, and the second a surface labile pool containing TON and TOP in quasi-Redfield stoichiometry. This relationship between TON and TOP is not significantly different from a similar regression of data from the HOTS site in the central Pacific, implying that the composition of organic material, and hence the processes controlling its formation, are not substantially different in these two biogeochemically very different environments. Our postulation of two different pools of organic material with different chemical compositions and residence times leads us to suggest that the cycles of TON and TOP are more strongly coupled than is often thought.

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