"U.S. JGOFS Southern Ocean Process Study: Zooplankton Processes"

Abstract:

This research project is part of the U.S. Joint Global Ocean Flux Study (JGOFS) Southern Ocean Program aimed at (1) a better understanding of the fluxes of carbon, both organic and inorganic, in the Southern Ocean, (2) identifying the physical, ecological and biogeochemical factors and processes which regulate the magnitude and variability of these fluxes, and (3) placing these fluxes into the context of the contemporary global carbon cycle. The work is one of forty-four projects that are collaborating in the Southern Ocean Experiment, a three-year effort south of the Antarctic Polar Frontal Zone to track the flow of carbon through its organic and inorganic pathways from the air-ocean interface through the entire water column into the bottom sediment. The experiment will make use of the RVIB Nathaniel B. Palmer and the R/V Thompson. This specific project is a seasonal study of the mesoscale spatial distribution of the carbon utilization by zooplankton in the Antarctic Polar Frontal Zone and the Ross Sea. There is strong evidence to indicate that the egestion of pellets by zooplankton can contribute significantly to a highly variable and episodic biogenic carbon flux in the Southern Ocean. The research approach used will quantify the rate of total fecal production by the meso- and macrozooplankton community at scales that dominate the variability -- eddy-resolving spatial scales and seasonal time scales -- in both the Antarctic Polar Frontal Zone and the Ross Sea study regions. The process of quantification will depend upon measurements of zooplankton abundance and distribution using a SeaSoar-mounted Optical Plankton Counter (OPC) in the Polar Frontal Zone, a net-mounted OPC in the Ross Sea study area, and underway acoustic current measurements in both regions. Experimental measurements of ingestion rate will be directed at developing empirical relationships to body weight, food availability, and diel periodicity for the principal species of Antarctic zooplankton grazers. These relationships will then be combined with measurements of biomass and distribution to compute the rate of total fecal production. The approach addresses those factors that are most likely to give rise to the greatest variability in zooplankton-produced biogenic flux: (1) variability in zooplankton biomass, and the food available to that biomass, on scales of ten kilometers in the horizontal and ten meters in the vertical, (2) seasonal variability, and (3) variability that is attributable to the size-frequency distribution of the zooplankton themselves. The results will quantify the role of zooplankton in carbon flux processes of the Southern Ocean, leading to a better understanding of the Southern Ocean carbon cycle.