Quantification of new production during a winter Noctiluca scintillans bloom in the Arabian Sea

Abstract

We present new data on the nitrate (new production), ammonium, urea uptake rates and f-ratios for the eastern Arabian Sea (10° to 22°N) during the late winter (northeast) monsoon, 2004, including regions of green Noctiluca scintillans bloom. A comparison of N-uptake rates of the Noctiluca dominated northern zone to the southern non-bloom zone indicates the presence of two biogeochemical regimes during the late winter monsoon: highly productive north and less productive south. The conservative estimates of photic zone-integrated total N-uptake and f-ratio are high in the north (~19 mmolNm^-2d^-1 and 0.82, respectively) during the bloom and low (~5.5 mmolNm^-2d^-1 and 0.38 respectively) in the south. The present and earlier data imply persistence of high N-uptake and f-ratio during blooms year after year. This quantification of the enhanced seasonal sequestration of carbon is an important input to global biogeochemical models.