Collaborative Research: Using Geochemical Tracers to Characterize the Effects of Wintertime Episodic Nutrient Inputs on Biological Activity in the Sargasso Sea

Woods Hole Oceanographic Institution, Woods Hole MA

Investigators

Abstract

ABSTRACT OCE-0351651 / OCE 0351396 Recent data suggest that in the Sargasso Sea the weekly passage of weather fronts leads to increased deep convective mixing, nutrient inputs and new production during the winter mixing period. It has been hypothesized that these events lead to enhanced NO3 input into the euphotic zone, followed by a rapid biological response and accumulation of biomass, and an equally rapid export of that biomass to the waters below. Direct observation and quantification of these potentially important nutrient injection events is challenging, however, an even greater challenge is understanding the mechanisms that link this nutrient input ultimately to carbon export. To expand the work of M.W. Lomas, et al. ("Enhanced New Production During Winter Mixing A Missing Component of Current Estimates"), researchers at the Woods Hole Oceanographic Institution and the Bermuda Biological Station for Research Inc. will add 3He Flux Gauge Techniques (FGT) measurements to the previously funded NSF project. The addition of FGT will enable the researchers to more accurately determine and quantify the important linkages between convective nutrient supply, biological response, and large-scale flux estimates specifically during the period of winter mixing when bi-weekly weather fronts pass through the Sargasso Sea. It is during this period that episodic nutrient inputs associated with deep convection are followed by short periods of stratification. The injected nutrients are rapidly consumed resulting in biomass accumulation, which is exported during the subsequent convective mixing event. The overall result is enhanced export production supported by short-lived, but quantitatively important nutrient injections. To enable the team of researchers to link the timing and magnitude of these fluxes and the ecological response, the researchers will use 3He (and 3He:NO3 ratios) as a tracer of these events. The information from this study will offer further insight into primary production and subsurface nutrient remineralization in oligotrophic systems, which are a central component of the ocean carbon-cycle and an important part of climate change modeling.