Temporal studies of biogeochemical dynamics in oligotrophic oceans

A. F. Michaels, D. M. Karl and A. H. Knap

Keywords: time-series stations, carbon dynamics, nitrogen fixation, dissolved organic carbon, dissolved organic nitrogen, carbon dioxide, nitrate, phosphate

Introduction

The joint Global Ocean Flux Study (JGOFS) includes three major field components: time-series studies, process studies and a global survey. In the United States, the time-series component is represented by two open-ocean stations, one near Bermuda (Bermuda Atlantic Time-series Study; BATS) and one near Hawaii (Hawaii Ocean Time-series; HOT). The (goal of the research at both sites is to achieve an improved understanding of the time-varying fluxes of carbon and other biogenic elements within the ocean and the exchanges with the atmosphere, usually divided into three specific science questions and one technology-related objective:

to understand the seasonal and interannual variations in ocean physics, chemistry and biology;
to understand the relationships between the external physical forcings and the biological rate processes;
to understand the processes that determine sea-surface pCO₂, including thermodynamics, particle export and gas exchange;
to provide a test bed for the introduction and validation of new oceanographic instruments and technologies.

These goals are supplemented by more specific research objectives that are related to regional biogeochemical dynamics at each site and, to some extent, the interests and backgrounds of the scientists who are involved. These more specific goals include the need to understand the cycling of nitrogen as a control on the carbon cycle, the role of dissolved organic materials in both the elemental cycles and the net exports from the surface waters, and the role of community structure in affecting the cycling of elements. More recently, nitrogen fixation has been under increased study at both sites as this process appears to be crucial to understanding the seasonal and inter-annual patterns in the cycling of carbon, nitrogen and phosphorus in the sea.