Abstract

New and primary production, measured using 15N and 13C tracers, integrated over the euphotic zone (mostly upper 80–100 m) varied from 7.5 to 14.1 mmol N m–2d–1(average 10.8 mmol N m–2d–1) and 2.7 to 17.7 mmol C m–2d–1 (average 11.3 mmol C m–2d–1), respectively, in the tropical India Ocean (TIO). Shoaling of thermocline in the thermocline ridge located in the tropical Indian Ocean (TR) influences new and total productivity by supplying nutrients to the upper layers. At the same time, N-limited conditions prevail to the north of the TR region reducing biological productivity. While higher surface light intensity reduces the surface productivity, it enhances the overall depth-integrated productivity. Productivity at different locations within the region is primarily controlled by the supply of N-nutrients from below. In contrast, at a given location with the available nutrient pool, productivity at different depths is determined by light availability. The region has potential for moderate export production, as do the other parts of the Indian Ocean; the maximum possible f-ratio is found to be 0.56, suggesting that it is capable of exporting a significant part of the total production to the deep, under favorable conditions (i.e., availability of N-nutrients). A comparison with earlier data suggests no significant temporal trend in the productivity here over the past three decades.

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