Changes in the distribution of carbon within the ocean are caused by a combination of physicochemical and biological processes. The solubility pump injects carbon into the deep sea through the sinking of cold waters at high latitudes where CO2 solubility is enhanced. The oceanic biological pump is highly dynamic and variable in space and time. This process consists in the production of organic carbon by organisms in the surface ocean and the subsequent sequestration of this material below the winter mixed layer. Significant effort has gone into understanding the controls of the biological pump and while the general function is understood, the details remain elusive. At present, processes in the surface euphotic zone are much better understood than those of the Twilight Zone (i.e. mesopelagic). It is within the poorly understood Twilight Zone that changes in C attenuation on sinking particles and the composition of sinking material occur, with important consequences for the rates of C uptake and exchange at the surface ocean with the atmosphere and for longer term C sequestration in the deep sea.
This proposal will develop improved particle flux collectors and use these to answer key science questions associated with C fluxes and exchange via sinking particles at the Bermuda Atlantic Time-series Study (BATS) site. Currently at BATS, the surface ocean C budgets are unbalanced, and production and community structure fail to predict particle export. At the same time, these questions are being addressed with an imperfect tool, the drifting sediment trap, a device that has not changed significantly since the early 1980's. This program includes the development and engineering of new tools while collecting time-series data. The project builds upon the recently developed neutrally buoyant sediment trap (NBST), which will be modified for continuous flux collection and swimmer free samples to a new design: the Twilight Zone EXplorer (TZEX).
In context of the C and Water in the Earth System Program, this proposal advances our understanding of the carbon cycle by combining the following multidisciplinary elements: (1) basic research in ocean biology obtained from ship based observations and remote sensing; (2) geochemistry of particles and waters and how these change with depth and time; (3) modeling of biological processes and particle transport in moving fluids; and (4) the engineering and application of novel observational equipment to capture sinking particles. These unique sediment trap devices will open up a new window to assess the ocean's role as a C sink and how marine export production will change in response to climate change.
Broader Impacts: By improving understanding of the carbon cycle in the mesopelagic twilight zone, this project will contribute to society's ability to anticipate the impacts of global climate change as well as to formulate remediation strategies. Educational and public outreach impact include berth space for high school, undergraduate and graduate students, journalists, an undergraduate student fellow and two graduate students. Finally, the significant instrumentation development and application component will likely bear significant fruit for the broader oceanographic community.
