Phosphorus composition of sinking particles in the Guaymas Basin, Gulf of California

Abstract

Phosphorus (P) composition and fluxes were measured in samples collected using a moored sediment trap located at 500 m in depth in the center of Guaymas Basin, Gulf of California, from February 1991 through September 1997. P composition was measured using a sequential extraction technique that chemically separates the particulate inorganic P (PIP) pool into exchangeable, oxide‐bound, authigenic, and detrital phases. PIP comprised 69% ± 15% of the total particulate P pool, with significantly higher concentrations during the rainy summer. Strong relationships between authigenic and detrital P fluxes with lithogenic material (r2 ≥ 0.85) indicate that a significant component of PIP is terrestrially derived and varies with large‐scale changes in regional climate. Particulate organic P (POP) fluxes were significantly higher during the winter as a result of stimulation of biological production during upwelling. Average particulate organic carbon (POC) : POP ratios also varied seasonally, with higher ratios in the summer (221) vs. the winter (158). The fact that POC fluxes remained relatively constant throughout the year indicates that in winter, fresher, less degraded organic material was more effectively transported to depth. Strong correlations between POP and opal fluxes (r2 = 0.63) further support a ballast mechanism, whereby enhanced sinking rates reduce the time during which organic matter is subjected to water column degradation. Compared to trap concentrations, POP is preferentially remineralized over PIP, in concert with an increase in the authigenic P pool; this signifies rapid diagenetic transformations of sedimentary P between the sediment trap and underlying sediments.