Mesoscale variability in the metabolic balance of the Sargasso Sea

Net community production (NCP) experiments based on in vitro changes in dissolved oxygen were carried out in three mesoscale eddies investigated in the Sargasso Sea in the summer of 2004. NCP estimates ranged from negative to positive values, and the age and type of the sampled eddy were important factors responsible for this variability. Positive rates occurred in younger cyclones and in areas of eddy-eddy interactions, whereas negative NCP rates were observed in anticyclones and older cyclone features that were decaying. This information was combined with a nine-year data set from the BATS program and satellite altimeter data to assess the role of mesoscale eddies in the metabolic balance of the Sargasso Sea. Indirect NCP estimates (NCPe) were obtained by calculating the difference between 14C phytoplankton production and bacterial carbon demand rates. The results showed highly variable NCPe rates that spanned the range of direct NCP observations. The metabolic balance of the photic layer in the ocean is determined by net community production (NCP), the difference between gross primary production (GPP) and total respiration (R). An excess of production over respiration, referred to as net autotrophic metabolic balance, implies a net synthesis of organic carbon that can be exported either vertically to the deep ocean, laterally to other regions, or to higher trophic levels. A negative balance, referred to as net heterotrophic balance, represents a net demand for allochthonous supplies of organic carbon or the consumption of dissolved organic matter produced elsewhere. Thus, the determination of NCP constitutes an important step in understanding carbon budgets and global