Abstract
Polyphosphate (polyP) is an essential chemical constituent of microbial cells, and is hypothesized to play important roles in the marine biogeochemistry of phosphorus. However, polyP has only rarely been measured in the oceans. Here, we present data on the distribution of polyP across a latitudinal transect in the tropical Indian Ocean. PolyP concentrations (quantified as molar equivalents of a synthetic polyP standard) and ratios of polyP to total particulate phosphorus (TPP) along the transect ranged between 3-7 nmol eq. L-1 (polyP concentration) and 0.2-0.4 nmol eq. nmol(-1) (polyP : TPP ratio), which is very similar to values reported from the North Pacific Subtropical Gyre. Yet unlike in the North Pacific, soluble reactive phosphorus was depleted to low concentrations (<= 0.03="" mu="" mol="" l-1),="" and="" alkaline="" phosphatase="" activity="" was="" relatively="" high="" (1-4="" nmol="" p="" l-1="" h(-1))="" along="" our="" cruise="" track.="" we="" attribute="" these="" results="" to="" the="" unique="" seasonal="" changes="" in="" iron="" and="" macronutrient="" supply="" in="" the="" indian="" ocean,="" which="" are="" caused="" by="" the="" monsoonal="" reversal="" in="" ocean="" currents.="" polyp="" concentrations="" and="" polyp="" :="" tpp="" ratios="" decreased="" sharply="" with="" depth="" down="" to="" 150="" m,="" suggesting="" that="" polyp="" was="" preferentially="" recycled="" relative="" to="" tpp,="" unlike="" in="" the="" north="" pacific="" subtropical="" gyre.="" we="" hypothesize="" that="" alkaline="" phosphatase="" exerts="" a="" significant="" control="" over="" marine="" polyp="">