Research Interests in Tabular Form:
Research Interests in Conversational Form: My ultimate goal is to understand the basic controls of climate variability on glacial to interglacial timescales--commonly referred to as the "ice ages". The crucial question I (and other climate scientists) seek an answer to is, how does Earth's climate vary from warm periods such as we are enjoying today to glacial times where icesheets covered most of North America? And why does this dramatic climate variability vary on a ~100,000 year timescale? Understanding these basic underpinnings of "natural" climate variability is essential to predicting what human-induced climate change has in store for our future. The short answer for the question of, "what is your thesis project?" is this: I am currently studying tropical Pacific nutrient dynamics from the present-day through the past 2,000,000 years using the stable isotope geochemistry of deep sea sediments and modern day nitrate. With these studies, I hope to constrain the evolution of nitrate utilization and denitrification in the tropical Pacific. Now, here is the explanation for "why"? Why the tropical Pacific? Modern day El Nino Southern Oscillation (ENSO) events--resulting from changes in the distribution of tropical Pacific sea surface temperature--demonstrate the profound influence the tropical Pacific has over global climate. Modeling studies (Clement et al. 1999) have shown that precession (the 23 kyr variation in seasonal solar irradiance) may regulate the number of El Nino / La Nina events over geologic timescales. Despite the possible presence or absence of El Nino events over geological timescales, our pursuit of the mechanisms underlying glacial to interglacial climate variability must include climatically-critical regions such as the tropical Pacific. My role: In the tropical Pacific, nitrate utilization and denitrification are closely linked with specific physical conditions. By determining how these biologically-influenced processes varied over time we will be able to understand what the physical state of the tropical Pacific was at that time. Specifically, I am analyzing the nitrogen isotope ratio (d15N) in sediments across the tropical Pacific. Downcore bulk sediment d15N records from the equatorial Pacific reveal both the history of eastern tropical Pacific denitrification (the largest region in the world) and changes in nitrate utilization by photosynthesizers. However, several authors have suggested "bulk sediment d15N" is affected by diagenesis. To better understand what effects diagenesis has on sediment d15N records, I am analyzing the d15N of different sedimentary components including "diatom-bound d15N" with the help of Becky Robinson (formerly at Princeton--now at URI). Finally, the crucial element of this study is the isotopic ratio of N in equatorial Pacific nitrate. Luckily, I have been able to collect water samples from along the equatorial Pacific thanks to the people at NOAA's Pacific Marine Environmental Laboratory (especially Mike McPhaden and Brian Lake) and the crews of the R/V Ka'imimoana and R/V Ronald Brown. I am analyzing the d15N of nitrate in these water samples in Danny Sigman's lab at Princeton University. I am also collaborating with Julie Granger on the d18O of nitrate for Equatorial Pacific water. -------------------------------------------------------------------------------------------------- Patrick A. Rafter ::: Curriculum Vitae Mailing Address: SIO – UCSD 9500 Gilman Dr. Dept 0208 La Jolla, CA 92093 Phone: 858 534 4717 email: prafter (at) ucsd.edu
Education:
(Sept 2002 – Present) Graduate Student Researcher, Scripps Institution of Oceanography. Analysis of deep sea sediment using a variety of geochemical proxies such as alkenone unsaturation, as well as oxygen, carbon, and nitrogen stable isotopes to infer changes in ocean chemistry over glacial to interglacial cycles. (Sept 2000 – Sept 2002) Supervisor, Quality Painting. Responsible for 5 workers and equipment for indoor and outdoor painting contractor. (June – August 2000) National Network of Environmental Management Studies Fellow, US EPA National Health and Environmental Effects Lab Atlantic Ecology Division. Acquired and analyzed estuarine nutrient data to determine trends in seasonal variations of fixed nitrogen--applied to estuarine nitrogen export model (supervised by Edward Dettmann). (Sept 1999 – May 2000) Research Assistant: Dr. John Trefry Sediment Geochemistry Lab. Analysis of sediment grain size (using Folk’s settling tube technique) and trace metal concentrations (using a Perkin-Elmer model 4000 atomic absorption spectrometer in the flame mode). Basic maintenance of lab and sampling equipment. (May – August 1998) Research Intern: Wetlands Institute, Stone Harbor, NJ. Studies of local brackish water turtle population, migration, and egg incubation. Public speaking and education concerning wetland environments.
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