Ocean flux studies: A status report

Abstract

Marine biogenic cycles play a key role in controlling atmospheric CO 2 concentrations. To predict future atmospheric CO2 levels and to interpret past changes that may have been associated with global climatic events, it is necessary to determine on a global scale the rates at which carbon is cycled through the ocean and the factors that may alter the rates of transfer. Because of uncertainties and limitations in existing measurement techniques and the extreme spatial and temporal variability of ocean properties and processes, studies have not yet produced an accurate, comprehensive description of the marine carbon cycle. While some advances in the measurement of specific components of the carbon cycle have been made, the fundamental problem of undersampling an extremely heterogeneous ocean has remained. Recently, satellitedeployed sensors have provided large-scale, nearly synoptic images of ocean surface water properties, such as temperature and color, which have revealed mesoscale features not observed previously. In addition, moored and free-drifting observation systems are being developed to determine directly the temporal variability of surface and subsurface water characteristics. With these remotely sensed properties to provide the space and time framework by which individual measurements of ocean processes and material fluxes can be extrapolated throughout ocean basins and over decadal time scales, we are poised to make a fundamental improvement in our understanding of ocean elemental cycles. fraction of the biogenic material sinks or is actively transported out of the surface waters into deeper water masses where it is decomposed and oxidized back to CO•. This combination of processes, referred to as the "biological pump" [Longhurst and Harrison, 1989], tends to continually strip CO• from the surface ocean that is in contact with the atmosphere and sequester it in the deeper water masses where it cannot directly exchange with the atmosphere. Except for short-term perturbations such as that caused by anthropogenic CO2 release, gas exchange with the surface ocean controls atmospheric levels of CO•. Thus the biological pump maintains atmospheric CO• at a lower level than if the ocean were abiotic. Changes in the biological pump have been suggested as the cause of the increase in atmospheric CO• at the end of the last glacial period [Broecker, 1982; McElroy, 1983; Martin and Gordon, 1988]. The biological pump may also influence how the ocean responds to and takes up anthropogenic CO• released to the atmosphere. However, it is important to recognize that ocean productivity is limited by a variety of factors such as the availability of nutrients and/or light and not by the availability of CO2. Thus increased atmospheric levels of CO• may have little effect on ocean productivity. Under steady state conditions the biological pump may have a negligible influence on the ocean's response to anthropogenic CO• [Peng and Broecker, 1984; Wagener and Rebello, 1987]. However, rapid changes in the biological pump could hav...

Changes in buoyancy and chemical composition during growth of a coastal marine diatom:ecological and biogeochemical consequences

“…Suspension and sinking of marine phytoplankton have received considerable attention in recent years due to increased interest in the flux of organic material to the deep sea (Michaels & Silver 1988, Jahnke 1990. Since an organism's vertical position in the water column will ultimately determine its overall primary productivity and growth, an understanding of mechanisms of suspension and sinking is critical to accurate descriptions of marine ecosystems (Smayda 1970, Walsby & Reynolds 1980.…”

Deep-Sea Food Chains and the Global Carbon Cycle

“…The chemistry of Santa Monica Basin is controlled by water flowing over the sill to the adjacent San Pedro Basin and the San Diego Trough at 737 m. Because this depth is within the local oxygen minimum layer, water flowing into Santa Monica Basin is already low in oxygen before it is further depleted within the basin. Shows flux of oxidants and reductants (Jahnke 1990), sedimentation rates (Jackson 1989) and biomass estimates based on data from Thompson (per. There is sediment varYing in some regions.…”

“…The inverse technique that we used solves for the minimum length of flow vector x that satisfy Eq. The carbon redox state might vary between that in lipid (-2) to that in polysaccharides (0) (Jahnke, 1990). 5.…”

“…268 CASE 4: VARYING DATA EQUATIONS AND THE C:N RATIO OF BURIED MATERIAL Jahnke (1990) has estimated that 43% of sedimenting carbon in the Santa Monica Basin is buried. They also respired and lost fecal material within the benthos.…”

Biogenic sediments on the Eauripik Rise of the western equatorial Pacific during the late Pleistocene.

“…Recent studies suggest that bottom water oxy gen does not play a primary role in the preserva tion of organic matter (Jahnke, 1990;Calvert and Pedersen, 1992). In addition, the pattern of car bonate sedimentation in the West Caroline Basin indicates that glacial deep water was depleted in nutrients and enriched in dissolved 02 (Kawahata et al, 1994b;Kawahata and Suzuki, 1994).…”