WHAT I DO
My research interests focus on using bio-optical techniques to study biogeochemical processes in the ocean. I am interested in time-scales that vary from less than a second, through seasonal, to multi-year and length-scales that vary from less than the size of a single phytoplankton cell(<5?m), through regional (10-100s km), to global. My research can be divided into two main categories that are not mutually exclusive: (1) the study of the temporal and spatial variability of optically important constituents and (2) phytoplankton photophysiology and ecology. To answer questions within these research categories I use both in-water optical measurements and ocean color remote sensing.
One of my main goals is to determine which physical, chemical, and biological processes must be considered to understand variations in optically important constituent concentrations. In conjunction with colleagues from the Woods Hole Oceanographic Institution and other institutions, I have used both traditional boat sampling methods and novel technology to collect an extensive optical dataset over the last three years. Optical property studies have included the effects of coastal fronts at the mouth of Long Island sound, the effects of internal waves in Massachusetts Bay, estuarine dynamics in the Delaware River, basin scale variations in the Gulf of Maine, and open ocean properties in the Sargasso Sea. One of the novel technologies I am using is the Autonomous Vertically Profiling Plankton Observatory (AVPPO), a profiling mooring. Profiles of physical and optical properties telemetered to shore at up to hourly intervals have demonstrated variations in optical properties due to tidal movement of fronts, internal waves, resuspension of benthic matter, and diel growth patterns in phytoplankton. These data are being used to examine the sources of both in-water optical property and ocean color variability and to verify and develop inversion algorithms for satellites (currently MODIS and SeaWiFS). Much of the funding for this work has been from a NASA SIMBIOS grant on which I am the lead investigator.
A better understanding of phytoplankton photophysiology is another one of my goals. Whilst I am generally interested in primary production and its modeling, I am especially fascinated by solar stimulated fluorescence of chlorophyll a and induction of UV sunscreening pigments. Solar stimulated fluorescence is detectable, both in-water and by satellites, as a peak in the red upwelling light. As a graduate student I developed a new algorithm to quantify this fluorescence from standard radiometric measurements. The quantum yield of fluorescence, the ratio of light absorbed to that emitted, is one of the major determinants of the fluorescence signal. I am currently investigating variations in the quantum yield using the above mentioned dataset and from space using MODIS data. This is of interest as fluorescence may be able to give insights into photosynthesis as fluorescence is derived from photosystem II, part of the photosynthetic apparatus.
Ultraviolet (UV) sunscreening pigments are ubiquitous in many taxa and are thought to have been important in early development of life on earth. The recent depletion in stratospheric ozone has stimulated study into these UV pigments, especially mycosporine-like amino acids (MAAs), with most of the work performed in Antarctica. Interestingly, the UV flux increases significantly towards the Equator. Recently I have demonstrated a seasonal cycle of induction of UV screening pigments in surface-water phytoplankton of the Sargasso Sea. This is the first time this has been documented and suggests that UV pigments may be of great importance in the majority of the world's oceans. MAAs are interesting as they are bio-accumulated and potentially offer UV protection to zooplankton and higher organisms. They also are potentially a source of highly colored dissolved organic matter (CDOM) in open oceans. Recent work suggests that CDOM in the open ocean may be the primary optical constituent, but its sources remain unclear.