Project: MedFlux collaborative research project

The MedFlux collaborative research project will
test two hypotheses of the influence of "ballast" on the flux of
particulate matter through the water column. It either 1)
acts as a physical shielding of the organic matter protecting it as it
falls through the water column, or 2) is the ratio of
mineral ballast to organic carbon that controls the sinking
velocity and consequently the organic carbon flux to the deep
sea. The project has two major objectives:

1. To assess the extent to which settling velocity separation techniques accurately and reliably measure in-situ settling velocities and to devise mechanical improvements and/or statistical correction procedures to overcome any deficiencies.
2. To develop perspectives and protocols that take advantage of the different sampling characteristics of in-situ pumps, sediment traps, and optical instruments, combined with radiochemical analysis, to assess the dependence of settling velocity and remineralization on particle size and the organic and inorganic composition of particles.

Project description from the NSF award page:

Collaborative Research: Mineral Ballast and Organic Matter Compositions as Determinants of Particle Settling Velocities and Fluxes in the Sea (MedFlux)

Sinking particulate matter is the major vehicle for exporting carbon from the sea surface to the ocean interior. During its transit towards the sea floor, most (>90%) particulate organic carbon (POC) is returned to inorganic form and redistributed in the water column. This redistribution determines the depth profile of dissolved CO ₂, which in turn determines the concentration of CO2 in the surface mixed layer, and hence the rate at which the ocean can absorb CO₂ from the atmosphere. It also determines the depth profile of nutrient regeneration, which determines the time scale of return of mineral nutrients to the photic zone. The ability to predict quantitatively and mechanistically the depth profile of remineralization is therefore critical to predicting the response of the global carbon cycle to environmental change.

Minerals typically constitute more than half the mass of particles sinking out of the ocean surface, and this fraction increases dramatically with depth. Marine plankton contribute biominerals, e.g., opal by diatoms and radiolarians, and CaCO₃ by coccolithophorids and foraminifera. Detrital minerals (largely quartz and aluminosilicates) introduced from land by rivers and wind also can become associated with marine plankton (or their remains) through sorption and aggregation processes. Minerals are important for making less dense organic matter (OM) sink, and may also protect OM from degradation, allowing it to penetrate deeper into the ocean.

Prior to the inception of MedFlux, investigators demonstrated that ratios of particulate organic carbon to mineral ballast converge to a nearly constant value (~3-7 wt% POC) at depths >1800 m (Armstrong et al. 2002), and Klaas & Archer (2002) demonstrated that the variability in the data can largely be explained by the chemical composition of the ballast (opal vs. carbonate vs. dust). The focus of MedFlux is to develop a better mechanistic understanding of this “ballast hypothesis”. In particular, given the many processes that could cause large deviations from this ratio, a fundamental goal is to understand why POC:mass ratios seem to be well-delimited, and to use this understanding to create, as fully as possible, a new mathematical description of remineralization to replace those currently in use. This last goal is of utmost significance if, for example, lowered pH causes carbonate minerals to dissolve preferentially, affecting both ballasting and the average remineralization depth of POC in the ocean.

MedFlux is a collaborative research project that includes investigators from the U.S. and Europe.
Robert Armstrong, Stony Brook University, Stony Brook, NY
Kirk Cochran, Stony Brook University, Stony Brook, NY
Anja Engel, Alfred Wegener Institute, Bremerhaven, Germany
Scott Fowler, Stony Brook University, Stony Brook, NY
Madeleine Goutx, CNRS/Université de la Mediterranee (aix-Marseille) Marine Microbiology Laboratory, France
Cindy Lee, Stony Brook University , Stony Brook, NY
Pere Masqué, Universitat Autonoma de Barcelona, Spain
Juan Carlos Miquel, IAEA Marine Environment Laboratories, Monaco
Michael Peterson, University of Washington, Seattle, WA
Olivier Rageneau, Institute Universitaire Europeen de la Mer, Brest, France
Richard Sempéré, CNRS/Université de la Mediterranee (aix-Marseille) Marine Microbiology Laboratory, France
Gillian Stewart, Queens College, NYC, NY
Christian Tamburini, CNRS/Université de la Mediterranee (aix-Marseille) Marine Microbiology Laboratory, France
Stuart Wakeham, Skidaway Institute of Oceanography, Savannah, GA

Publications:

Goutx, M., Wakeham, S.G., Lee, C., Duflos, M., Guigue, C., Liu, Z., Moriceau, B., Sempéré, R., Tedetti, M., and Xue, J.. "Composition and degradation of marine particles with different settling velocities in the northwest Mediterranean Sea," Limnology and Oceanography, v.52, 2007, p. 1645.

Liu, Z. and Lee, C.. "The role of organic matter in the sorption capacity of marine sediments," Marine Chemistry, v.105, 2007, p. 240.

Liu, ZF; Lee, C; Wakeham, SG. "Effects of mercuric chloride and protease inhibitors on degradation of particulate organic matter from the diatom Thalassiosira pseudonana," ORGANIC GEOCHEMISTRY, v.37, 2006, p. 1003-1018.

McCarthy, M.D., Benner, R., Lee, C., and Fogel, M.L.. "Amino acid nitrogen isotopic fractionation patterns as indicators of heterotrophy in plankton, particulate, and dissolved organic matter," Geochim. Cosmochim. Acta, v.71, 2007, p. 4727.

Rodriguez y Baena, A.M., Fowler, S.W., and Warnau, M. "Could krill schools significantly bias 234Th-based carbon flux models?," Limnology and Oceanography, v.53, 2008, p. 1186.

Rodriguez y Baena, A.M., S.W. Fowler and J.C. Miquel. "Particulate organic carbon: natural radionuclide ratios in zooplankton and their freshly produced fecal pellets from the NW Mediterranean (MedFlux 2005)," Limnology and Oceanography, v.52, 2007, p. 966.

Stewart, G., Cochran, J.K., Xue, J., Lee, C., Wakeham, S.G., Armstrong, R.A., Masqué, P., and J.C. Miquel. "Exploring the connection between 210Po and organic matter in the northwestern Mediterranean," Deep-Sea Research I, v.54, 2007, p. 415.

Stewart, G., J. K. Cochran, J.C. Miquel, P. Masqué, J. Szlosek, A.M. Rodriguez yBaena, S.W. Fowler, B. Gasser and D.J. Hirschberg. "Comparing POC export from 234Th/238U and 210Po/210Pb disequilibria with estimates from sediment traps in the northwest Mediterranean," Deep-Sea Research I, v.54, 2007, p. 154.