Convenors:
Curtis Deutsch (University of Washington, School of Oceanography, USA)
Nianzhi Jiao (Xiamen University, State Key Laboratory
          of Marine Environmental Science, China)
Louis Legendre (Pierre & Marie Curie University, Oceanography Laboratory, France)
Uta Passow (University of California Santa Barbara, Marine Science Institute, USA)

Invited Speakers:
Thorsten Dittmar (University of Oldenburg, Germany)
Marion Gehlen (Laboratoire des Sciences du Climat et de L'Environnement, France)
Phoebe Lam (University of California, Santa Cruz, USA)

The transfer of atmospheric CO₂ into the ocean is the largest carbon sink on Earth. The best known mechanisms for the sequestration of marine carbon are three vertical ocean carbon pumps, i.e. solubility, carbonate and soft-tissue or organic (“biological carbon pump”, BCP). The latter two pumps are biologically-driven. The carbonate pump consists in the precipitation of calcium carbonate in surface waters by calcifying organisms followed by sinking of the resulting bio-minerals to depth. The BCP is driven by primary production in the euphotic zone, followed by the transfer of carbon to depth by sinking of particulate organic carbon, by vertical migrations of zooplankton, and by vertical transport of dissolved organic carbon (DOC) by physical processes, like mixing and convection. An additional biological mechanism of ocean carbon sequestration was recently described under the name of microbial carbon pump (MCP). The vertical carbon pumps transport carbon from surface to depth, whereas the MCP transforms short-lived DOC into long-lived DOC. (Technically, the vertical carbon pumps maintain the gradient in total inorganic carbon between surface and deep waters, and the MCP maintains a concentration gradient between short- and long-lived DOC). Carbon is chemically sequestered in long-lived DOC at any depth in the water column. The MCP consists in the microbial transformation of labile organic carbon to refractory DOC (RDOC). In the deep ocean, the huge pool of RDOC accounts for >90% of the total marine organic carbon, and has an average residence time of ~5000 years. As the amount of carbon existing as RDOC is equivalent to the total inventory of atmospheric CO₂, changes in some of the processes that regulate the RDOC pool may be important factors in carbon cycling and climate change.

The quantitative roles played by the three biologically-driven ocean carbon pumps (i.e. carbonate pump, BCP, and MCP) is a subject of active research by field oceanographers, experimental biogeochemists, marine ecologists, and carbon-cycle modellers, but these research communities work largely independently. Hence, they often reach conclusions that are quite different. The proposed workshop intends to bring together specialists of field observations (including paleoceanographers), experimentalists and modellers who work on one or more of the three biologically-driven ocean carbon pumps. The objectives of the workshop address the possibility that the three biologically-driven ocean carbon pumps are highly responsive to climate change. Predicting these responses requires an understanding and quantification of the mechanisms that control the responses to environmental forcing.

The workshop will be comprised of four sessions. Sessions 1 to 3 will be dedicated to the three approaches (i.e. field-observational, experimental, and modelling, respectively) used to investigate the biologically driven ocean carbon pumps. Goals within each of these sessions include familiarizing all participants with the different perspectives, identifying the main stumbling blocks and challenges that presently exist, reviewing new results, and discussing developments and actions needed to make progress in coming years. Examples of processes to be discussed include: plankton community structure, stoichiometry, particle dynamics, bacterial remineralization, and production and removal of RDOC. Discussion periods will try to elucidate consensus views among the different approaches on the study of biologically-driven ocean carbon pumps. Session 4 will build on the results of the previous sessions to outline and draft a white paper. This paper will focus on multidisciplinary developments needed to address the responses of the biologically-driven ocean carbon pumps to climate change, and their feedbacks to the climate. The white paper will be submitted for publication in the peer-reviewed literature. Necessary studies to address responses and feedbacks of biologically-driven ocean carbon pumps will be identified, relevant approaches will be described; required national and international tools (e.g. research programs and infrastructures) will be identified; and strategies to achieve these goals will be proposed.