2005 Funded Access to the Sea Proposals

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Field Testing of "Imaging FlowCytobot" at the Martha?s Vineyard Coastal Observatory (MVCO)
Robert J. Olson, Heidi M. Sosik

With the goal of better understanding how coastal plankton communities are regulated, we have begun a high-resolution, long-term plankton monitoring program at the Math’s Vineyard Coastal Observatory (MVCO).Our submersible flow cytometer, FlowCytobot (Olson et at. 2003), has been deployed for most of the past two years and is providing detailed information about the smallest phytoplankton cells (~1-10 μm),including daily estimates of Synechococcus cell division rates (Sosik et al. 2003).However, FlowCytobot’s success in observing very small cells is achieved by analyzing very small amounts of water, which means larger cells (> 10μm) which are much less numerous than the picoplankton, are not well sampled. This is an important limitation because phytoplankton in this size range, which includes many diatoms and dinoflagellates, can be especially important in coastal blooms. The > 10μm size range also includes many microzooplankton, such as ciliates, which exert strong grazing pressure on smaller phytoplankton and are critical to the diets of larger organisms such as copepods and larval fish.

To study these large phytoplankton and microzooplankton, we developed a new submersible imaging flow cytometer, based on a scaled-up version of FlowCytobot’s fluidics system but also capable of capturing a high-quality image (1 μm resolution) of each cell passing through the instrument. Images can be classified using an approach similar to that developed for the Video Plankton Recorder (Tang et al. 1998), while the measurements of chlorophyll fluorescence will allow us to discriminate heterotrophic from phototrophic cells; many dinoflagellate taxa, for example, have both heterotrophic and phototrophic members.

The detailed long-term data provided by Imaging FlowCytobot, which can identify many plankton cells to the genus or species level, will allow unprecedented studies of community dynamics in coastal waters.The purpose of this proposal is to obtain funds for the initial deployment of Imaging FlowCytobot at MVCO for field testing.

Reloadable Sampler with Verifiable Pickup (RSVP): A New Submergence Asset for Biological and Geological Sampling
Donald B. Peters, Timothy M. Shank, Robert A. Reves-Sohn

The deep-sea presents a formidable barrier to accessing biological and geological samples on the seafloor. Dredging is perhaps the most ubiquitously employed method for sampling in the deep ocean, but it is a very crude technique that is only suitable for large-scale investigations where the position and environmental context of the samples are largely irrelevant. Most geological studies, and essentially all biological studies of deep-sea species and their ecosystems, have progressed to the point where accurate information regarding the position and context of the samples are essential to the scientific objectives at hand. This has placed a strong demand on deep submergence assets such as submersibles and remotely operated vehicles (ROVs) that are capable of returning oriented samples with precise position and contextual information.

Development of Sensors for WHOI?s Buoy-Mounted Aerosol Sampler: Real-Time Measurements of Mineral Dust Deposition to the Oceans
Edward Sholkovitz, Sheri White, Norman Farr

The growth of phytoplankton in large areas of the ocean is limited by the supply of iron, an essential nutrient for marine productivity. The major source of iron (Fe) to the Atlantic and PacificOceans is the atmospheric transport and deposition of iron-containing mineral dust (aerosols) from the dusty regions of Africa and central Asia.The release of dissolved Fe from this mineral dust can be biologically metabolized in the upper ocean.Determining deposition rate of iron-bearing dust to the oceans is technically challenging. Sholkovitz and WHOI colleagues (Allsup, Hosom and Purcell) recently carried out a five-month maiden deployment of a buoy-mounted aerosol sampler on the Bermuda Testbed Mooring. This new instrument worked as designed and successfully captured the deposition of African dust onto the Sargasso Sea.This project demonstrates for the first time that buoys can be used as oceanic observatories to better quantify the temporal (weekly, monthly and seasonally) variability in the concentration and deposition of mineral dust, iron and other important trace elements to the oceans. Aerosol samples from this instrument were returned to WHOI for analysis. Our longer term objective is to measure the deposition of mineral dust and iron in real-time by adding a set of sensors to our aerosol sampler. Funding from this Access to the Sea award will be used to determine the applicability of adding three types of aerosol-sensing spectrometers to the aerosol sampling instrument. Two of the sensors have been developed by NASA engineers for the chemical analysis of planetary soil by the robotic MARS Rover. The third is commercially available. With White and Farr being recently added to the WHOI engineering staff, we now have in-house spectrometric expertise to make real progress on measuring the concentrations and deposition of mineral dust and Fe from ocean buoys.

Biogeochemistry of Nitrous Oxide Cycling
Karen L. Casciotti, James W. Moffett

The eastern tropical South Pacific (ETSP) is a hot spot for oceanic nitrogen cycling. This region of upwelling and high productivity fuels high rates of oxygen consumption below the mixed layer, nitrate regeneration from nitrification, and ultimately denitrification of nitrate to N2 gas. The climatically important trace gas nitrous oxide (N2O) also reaches extreme high concentrations in the oxycline and extreme low concentrations in the heart of the oxygen minimum zone (OMZ), indicating active cycling in this region.Despite many years of investigation, the mechanism of N2O production in this hot spot is ambiguous because of the potential overlap or coupling of nitrification and denitrification processes at low oxygen tensions. The work proposed here will employ novel isotopic techniques to identify processes involved with nitrous oxide production and consumption in the water column at multiple sites within the eastern tropical South Pacific. This work will be particularly effective in the context of a strong field program already in place to study trace metal and nitrogen cycle biogeochemistry on the R/V Knorr in October/November 2005.


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Last updated January 29, 2007
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