• Determining the relationship of subtropical ventilation to mode water and equatorial variability
• Lagrangian modeling of eel and other species in numerical models
• Generalizing ecosystem models to adaptively respond to environmental change
• Chesapeake Bay response to climate forcing
• Ocean response to acidification - calcification.

Relating microbial biodiversity to biological oceanographic processes (NSF)

There are some funds on this project for hiring an undergraduate student during summers, or for a graduate student for a short research project. Contact me for further details.

Despite great strides in our ability to evaluate the composition of marine microbial communities and even aspects of microbial function by molecular genetic techniques, we know very little about how community composition and function relate to biological oceanographic processes. This is largely due to the difficulty of integrating molecular biological-based community composition measurements into an oceanographic measurement program, even though recent data imply that microbial diversity should strongly affect many biogeochemical processes. However, new developments in whole-community molecular fingerprinting approaches and high throughput sequence analysis make such integration possible. Here we propose to evaluate microbial community diversity in the context of environmental data to provide a first step to linking structure, function, and relation to the environment. This is a critical first step to relating the potential of molecular genetic techniques to processes that may be represented in conceptual and numerical models of the ocean.

General : Can we better understand and predict functioning of marine food webs, including energy and material flow through them, if we have a greater and specific knowledge of microbial diversity?

•  Do certain taxa* associate with particular oceanographic conditions (see list below)?

•  Which taxa correlate strongly with each other and with physical/chemical/biological parameters, which negatively, and which have no significant correlation? Are relationships nonlinear?

•  Do any particular bacterial taxa tend to co-occur specifically with certain types of phytoplankton (e.g. as identified by HPLC pigment analysis)?

•  Do any taxa tend to correlate specifically with nitrogen fixation (may they indeed be the diazotrophs)?

•  Does the identity of taxa allow better prediction of bacterial secondary production from primary production or chlorophyll data than bulk parameters alone?

•  Are certain bacterial types found globally in certain environments (when assessed at the microdiversity level)?

•  What are the patterns of bacterial diversity in the sea?

•  Can we begin to discern the space and time scales of variability of bacterial community composition?

The image below shows the locations where we have samples on a map of mean surface chlorophyll, and with a range of Temperature and Salinity corresponding to the locations.

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Assessing the Impact and Variability of Coccolithophorid Blooms in the Ocean Carbon Cycle (NOAA)

There are some funds on this project for hiring a technician for a period of roughly 2 years. No modeling experience is necessary, but a high comfort level with computers is needed, so that the individual feels able to learn programming in a linux/unix environment.

Phytoplankton blooms of the coccolithophorid Emiliania huxleyi profoundly affect the biogeochemical and optical properties of the waters in which they grow.   They represent a regional inorganic carbon sink through coccolith export and a regional source through effects on upper ocean alkalinity. Their influence cascades to upper trophic levels and their subpolar and upper ocean distribution pattern suggest that they are prime candidates as sentinel or indicator species to detect climate change.   Here we propose to build a bridge between "environmental forcing" induced by climate change variability and biogeoechemical response through observations and modeling.   The establishment of quantitative biological - physical relationships will improve understanding of the factors that link climate variability to functional groups and subsequent ecosystem and carbon cycle response.   The overarching goal of this effort is to test two hypotheses; 1) Emiliani huxleyi blooms play an important role in the   ocean carbon cycle through calcification, export fluxes and feedbacks to their environment, and therefore directly impact the global distribution of ocean carbon sources and sinks; and 2) E. huxleyi blooms occur in mid- and high latitude regions that are sensitive to climate variability and change and they can be used as a sensitive n indicator species that integrates environmental changes into identifiable surface signals.

The specific objectives of this study are to: 1) document interannual and longer time-scale variability of the extent of Emiliania huxleyi blooms using satellite observations; 2) analyze the satellite-derived bloom variability with ocean and atmosphere reanalyses and other observations to quantify relationships between the observed climate variability and E. huxleyi distributions ; 3) mechanistically model the bloom variability and their physical and biogeochemical impacts in the North Atlantic; and 4) reconstruct coccolithophorid bloom variability back 50 years using a satellite derived empirical model based on ocean atmosphere reanalysis and our mechanistic model to assess the skill of the latter and to quantify errors in carbon cycle model projections.

My role in this project is to develop the numerical coupled ecosystem model, validate and run it. We have been working on a simple model described to the right conceptually, and the first results are also shown below. I am also developing an optical model based largely on work by Toby Tyrell and Barney Balch that allows the coccolith abundance to refract light and trap its energy in the upper model ocean, allowing for a positive feedback to the ecosystem by enhancing upper ocean stratification within a bloom.

Above are our first results of determining the distributions of coccolithophorid abundance on seasonal timescales. Some organisms are present in the tropics throughout much of the year, as expected, however the seasonal increase in abundance in the North Atlantic from June through September is the most significant pattern.

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The figure above shows a composite of all identified coccolithophorid blooms from Nov 1978-June 1986, from Brown and Yoder, 1994a

The above figure illustrates the connection between regions where temperature changes associated with global warming are expected to be large (top), coccolithophore distributions (middle), and ocean CO2 uptake (lower).

This schematic (above) shows the numerical model in a conceptual way. We find that phosphorus does not appear to be critical to the model distributions, but Iron and light availability/stratification may play a key role.

PIRANA - Potential Impacts of Riverine and Aeolian inputs on Atlantic Nitrogen fixation in the Atlantic (NSF)

This project is no longer funded, though I am still bootlegging some nitrogen fixation work.

This Biocomplexity project was aimed at understanding the interaction of riverine inflow, atmospheric dust deposition, and nitrogen fixation to the western tropical North Atlantic.

My component involved running a basin scale numerical model to determine what role Trichodesmium played in setting the basin scale biogeochemistry, as well as how the organism interacted with the riverine and dust components.

Several papers have come out of this work, and can be downloaded here. Most recently we have adapted the model to include the effects of nitrogen and phosphorus as well as iron deposition. This allows us to directly compare the model with the geochemical estimates of the rate of nitrogen fixation in the Atlantic. The model is generally consistent with the Gruber and Sarmiento 1997 estimates, though it is important that the model suggests that the subsurface distributions of excess nitrogen relative to phosphorus can be far removed from the location where nitrogen fixation occurs.

I have also run simulations using dust deposition scenarios from 2100, present day, and glacial conditions (provided by Natalie Mahowald at NCAR) to determine what the effects of iron deposition changes due to climate change might be on nitrogen fixation. The model suggests large decreases in carbon export associated with a reduction in dust deposition in the 2100 scenario. This is partially due to reductions in nitrogen fixation, but the larger effect is due to enhanced iron limitation of high latitude phytoplankton.

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This figure shows subsurface excess N (N*) on the 27.1 sigma-theta surface in the observations (top), and the model (bottom).

An adaptive food web model for the epipelagic and mesopelagic (NSF)

This project is just beginning. Opportunities for either a student or a technician exist.

In this project we seek tounderstand how export from the euphotic zone is affected by lateral advection, as well as temperature dependent remineralization. It is this export that oover long timescales sets the properties of the ocean biogeochemistry.

Currently I am working on upgrading the numerical scheme for export in the coupled model to improve its performance and conservation. Our next focus will be on temperature dependence in the remineralization, which can be validated against basin N* signatures.

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