My graduate students are working on paleoclimate problems on time scales of one thousand to one million years, focused on the tropical and sub-tropical regions of the oceans.The main tools we are using are elemental (e.g., Mg/Ca) and isotopic proxies (e.g., oxygen isotopes) in planktonic (surface) and benthic (bottom) foraminifera. The goal of these studies is three-fold: 1) to establish the climate history of the tropical oceans; 2) to determine the climate impact of the tropics on both orbital (i.e., glacial - interglacial) and millennial time scales; and 3) to use the response of the tropics to past greenhouse forcing to determine the earth's climate sensitivity under different boundary conditions, work which is critical in future estimates of global warming.

I expect students to develop a firm background in the quantitative skills required for paleoclimate and earth system research. Much of my direct work with graduate students involves the development and application of new and novel proxy climate techniques which allow us to uncover the complex paleoclimate and paleoceanographic signals encoded in marine deposits. Students working in my group are encouraged to publish as they make discoveries so that they already have a solid publication record when they complete their studies.

All of the graduate students working with me in recent years have been in the interdepartmental Marine Science Graduate Program. Students from the Ecology, Evolution and Marin Biology (EEMB) department also work in my laboratory to utilize geochemical methods for tracking larval migration.

My teaching includes undergraduate courses in oceanography, earth systems, and global warming, and graduate courses in chemical oceanography, paleoceanography and paleoclimatology. Students in my group also benefit from classes and interaction with the many other scholars doing marine, climate and earth systems research at UCSB.

Graduate Studies in Paleoclimate Research, starting Fall 2006

I anticipate having one opening in my research group for a graduate student entering in Fall 2006. Potential projects are focused on tropical climate evolution in the Pacific and Indian Oceans, in particular testing the tropical greenhouse forcing hypothesis. There is also the possibility of participating in an NSF LTER program monitoring Tahitian (Moorea) coral reefs, focusing on potential paleoclimatic records from reef corals as well as geochemical proxy calibration. Please email me for details.

Current and Past Graduate Students

EAR = Earth Science; IDMS = Interdepartmental Program in Marine Science; EEMB = Ecology, Evolution and Marine Biology; GS = Geological Sciences (name changed to Earth Science, July 2005)

Martin Medina (IDMS)
Winner: UC MEXUS Fellowship

Current student: Martin is studying the history of tropical sea surface temperatures on time scales of one thousand to one million years. He has just published the first results from his thesis as a featured report in the Oct. 13th issue of Science Express (pdf). We argue in this paper that the shift in climate periodicities at the mid-Pleistocene transition was related to a shift in the periodicity of raditiave forcing due to atmospheric carbon dioxide. Martin is also studying speleothems (stalagmites) from cave deposits in the Yucatan to document climate history in this region during the last two millennia.

Mary Jane Coombs (IDMS)

Current student: Mary Jane is studying rapid climate change using a high sedimentation rate site from the Baja Margin.This site has an accumulation rate of over 1 mm per year, enabling near annual resolution reconstruction of climate variability. Mary Jane is focusing on the last 5000 years of Holocene history.

Sarah Medley (IDMS)

Current student: Sarah is studying the marine isotope stage 5 (77-130 kyr B. P.) sediment section from the Caraico Basin. She hopes to relate tropical to high latitude climate changes during the last interglacial, and in particular to explore the degree to which tropical climate can be implicated in the partial deglacition of the Greenland Ice Sheet that occurred during the Eemian, the peak of the last interglacial.

Benjamin Ruttenberg (EEMB)

Current student: Geochemical tracers of larval dispersal among tropical fish in the Galapagos Islands and other locales.

Danielle Zacherl (EEMB)

"Dispersal of larval invertebrates: use of natural tags to identify natal origins." Ph.D. awarded 2002. Present position: Assistant Professor, Department of Biological Sciences, Cal State Fullerton, CA.

Petra Dekens (IDMS)

Optimal use of Mg/Ca as a paleo-temperature proxy requires establishing calibrations for different species of foraminifera and quantifying the influence of dissolution. To achieve this goal, we have measured Mg/Ca and oxygen isotopes in a series of tropical and subtropical core-tops, including 4 depth transects: the Ceara Rise, the Sierra Leone Rise, and the Rio Grande Plateau in the Atlantic, and the Ontong Java Plateau in the Pacific, focusing on spinose mixed layer dwelling species Globigerinoides ruber and Globigerinoides sacculifer, and non-spinose thermocline dwelling Neogloboquadrina dutertrei. Shell Mg/Ca in G. sacculifer is 5-15% lower than in G. ruber, while N. dutertrei Mg/Ca is 49-55% lower than in G. ruber. This statistically significant offset has allowed us to establish different calibrations for each species. Multilinear regression analysis was used to develop calibration equations that include a correction term for the dissolution effect on Mg/Ca in foraminiferal calcite. Presented in this paper are 2 sets of calibrations; one set using core depth as a dissolution correction and another using delta-carbonate as a dissolution parameter. The calibrations suggest that G. ruber is the most accurate recorder of surface temperature, while G. sacculifer records temperatures below the surface at 20-30m. The depth habitat of N. dutertrei is more uncertain, owing to the wide range in habitat depths depending on hydrographic conditions, but on average Mg/Ca and oxygen isotope data suggest it is at ~50m. Of the three species, N dutertrei is the most sensitive to dissolution (up to 23% decrease in shell Mg/Ca per km), while G. sacculifer is the most resistant.

"Core Top Calibration of Mg/Ca in Tropical Foraminifera: Refining Paleo-temperature Estimation." M. S. awarded Summer 2001
Present position: Ph.D. student, Department of Ocean Sciences, UCSC, Santa Cruz, CA.

Peter von Langen (IDMS)

My research interests include trying to understand what controls there are on the chemical composition of shells from marine phytoplankton (foraminifera) which are used by geologists and oceanographers to reconstruct past ocean and atmospheric changes.

"Non spinose Planktonic Foraminifera (Neogloboquadrina pachyderma) Cultured for Geochemical and Paleoceanographic Applications" Ph.D. awarded Winter 2001. Present position: Environmental Scientist, California Regional Water Quality Control Board, San Luis Obispo, CA.

Apurva Davé (GS)

"Reconstructing Climate-based Hydrographic Variations in the eastern north Atlantic over the last 37,0000 Years using foraminiferal Magnesium." M. S. awarded 2000. Present position: Teacher, Tampa, FL.

Pamela Martin (GS)

"Reconstructions of Deep Ocean Climate Variability from Foraminiferal Geochemistry." Ph.D. awarded December 2000. Present position: Assistant Professor, Department of Geophysical Sciences, University of Chicago, IL.

Stephen Swearer (EEMB)

My doctoral research has focused on the dynamics of larval dispersal and its influence on spatial and temporal variation in recruitment of marine fishes. Specifically, I've developed analytical approaches using environmental markers recorded in fish otoliths(both trace element signatures and growth histories) as tools for reconstructing the dispersal history of recruiting larval coral reef fishes. I've applied this approach to determine the relative importance of local vs. non-local sources of recruitment to the maintenance of island populations. Through a combination of fish otolith environmental signature, nearshore oceanography (coastal circulation, primary and secondary productivity, and seawater chemistry) and recruitment surveys, I've been able to evaluate the importance of local retention and the mechanisms which facilitate self-recruitment. Ph.D. awarded 2000.
Present position: Lecturer (Assistant Professor), Department of Zoology, University of Melbourne, Melbourne, Australia.

Tracy Mashiotta (GS)

"The Trace Element Geochemistry of Planktonic Foraminifera." Ph.D. awarded March 1998. Present position: Researcher, Byrd Polar Center, Ohio State University, OH.

EAR = Earth Science; IDMS = Interdepartmental Program in Marine Science; EEMB = Ecology, Evolution and Marine Biology