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Since funding for this award was received in February 2008, most of the proposed research has been accomplished, but the final data analysis and possible publications are still works in progress. Overall, the project attained stated goals by the end of August 2010.

This project has involved numerous students. Three Queens College undergraduates (Nathalie Diaz, Vadim Acosta, and Jennifer Nyirucz) who are all from under-represented groups in the sciences, as well as one graduate student, Yiyi Wong (Ph.D. anticipated 2013), have been involved in various aspects of this research. One of the undergraduates, Vadim Acosta, has decided to remain at Queens College to work on his M.A. with me on the subject of plankton community, suspended mineral material and carbon export in Long Island Sound. He has applied for national and CUNY-specific minority fellowships to help fund his project.

All the students involved have learned methods such as the rearing of zooplankton, culturing of phytoplankton, general experimental design, and the preparation and analysis of elemental composition of samples using both the Costech 1000 CHN analyzer and the Perkin-Elmer Optima 5300D ICP-OES. The students will also be involved with evaluating appropriate controls, performing statistical analyses, and interpreting results.

Besides the training of students, this project had three distinct goals: 1) conduct grazing experiments with various mineral material to investigate the assimilation of carbon by zooplankton 2) assess the change in sinking velocity and decomposition of the resultant fecal pellets and 3) identify the mineralogy and composition of mineral materials in order to determine which features of “dust” drive a response. Goals 1 and 3 have been accomplished but Goal 2 has proven more difficult than anticipated and will require further work.

Grazing experiments were conducted to assess the effect of different types and concentrations of mineral material on carbon assimilation by zooplankton (2 types of copepods) feeding on 4 species of phytoplankton.  In all control treatments, the phytoplankton (a diatom, a coccolithophorid, a dinoflagellate, and a chlorophyte) were cultured in local seawater before use as food particles for the copepods (either Centropages typicus or Tisbe sp.). In the experimental treatments, the phytoplankton were placed in a solution amended with three concentrations (between 1 and 5 mg/L) of pure diatom frustules (Vortex “Diatom Filter Powder”), Saharan dust collected in Monaco November 2002, pulverized Hudson River sediment, and volcanic ash collected in St. Thomas, USVI during the June 2008 Montserrat eruption.  Copepods were starved before grazing and then fed phytoplankton cells with or without suspended lithogenic particles in a slowly rotating “plankton wheel” which kept the food, grazers and mineral material suspended for two hours at room temperature. Phytoplankton cell concentration and suspended mineral particles were counted before and after feeding using a Beckman Coulter Multisizer III.  At the end of each experiment organic and inorganic carbon, nitrogen, and trace metals were measured in the food cells, the grazers, and the resulting fecal pellets. Following grazing, the copepods were removed from the feeding solution using a 100 mm mesh and then resuspended in filtered seawater.  Fecal pellets from the grazing and depurating animals were collected using a 20 mm mesh. We attempted to measure the sinking rates and the decomposition patterns of these fecal pellets containing various concentrations of different mineral materials, but without much success. We will pursue this aspect of the project in the future. Vadim and Yiyi will be conducting these experiments which should be completed by the end of 2009.

In addition to the lab experiments, we have conducted a single field test of the “Roughage Hypothesis” near the Canary Islands in the eastern tropical Atlantic. Grazers for these experiments were collected during the night using a 500um W2 (Bongo) net from 80m. Adult, non-pregnant copepods (Centropages typicus) were picked from the 20-200um fraction and placed in 0.2 um filtered ambient surface water. 100 copepods were starved for 12 hours until approximately 20mg (10L of 2mg/L) of a mixed natural phytoplankton assemblage from the Deep Chlorophyll Maximum (~60m) was added to each 200ml beaker. Before feeding, 3 cm² of a Supor filter with aerosol dust samples collected during the cruise (< 2mg total) were added to experimental beakers, while an equivalent area of blank filter was added to control beakers.  In both the control and experimental treatments the filter was removed after seawater leaching, and the copepods were allowed to graze for approximately two hours in the dark, at a constant temperature of 16 ºC.   Following grazing, the copepods and fecal pellets were separated using mesh as described above. Three replicates of the experiment were conducted in order to determine the reproducibility of the result. 

In all cases, adding mineral material to phytoplankton cultures appears to increase the organic carbon content of the fecal pellets produced by grazers.  In other words, grazers were less efficient at assimilating carbon in the presence of lithogenic and biogenic mineral material.  This is positive evidence for the validity of the “Roughage Hypothesis.” I expect at least one manuscript on these results to be submitted in 2010 (already 80% written) and another one, which will include the modeling sensitivity data, to be submitted in early 2011. I anticipate that the results from this project will provide enough evidence to justify the application for larger funding from the National Science Foundation, the National Oceanic and Atmospheric Administration, or the U.S. Department of Energy in 2011 or 2012 in order to pursue this avenue of research. I continue to believe that suspended mineral material in the surface ocean (which may increase due to climate change and land use practices) could have a relatively large impact on the sequestration of atmospheric carbon in the ocean via the biological pump. If so, this is an aspect of the marine carbon cycle which can no longer be ignored.