Ellen E. Martin
University of Florida
Phone: 352-392-2141Fax: 352-392-9294
My research focuses on the use of radiogenic isotopes (Sr, Nd, and Pb) preserved marine sediments to address questions related to paleoceanography and paleoclimatology. I am particularly interested in reconstructing deep ocean circulation patterns on Cenozoic time scales in order to understand the relationship between circulation and climate.
An important aspect of this work is the development of new archives as recorders of seawater isotopic ratios. I have worked to evaluate and/or establish marine barite, fossil fish teeth and Fe-Mn oxide coatings on sediment as archives for seawater Nd isotopes, and fossil fish teeth, conodonts and Fe-Mn oxide coatings as archives for Pb isotopes.
Current Projects include:
Southern Ocean Paleocirculation: The Southern Ocean represents the “Great Mixmaster” (Broecker) of the oceans. As such, changes in circulation throughout the world’s oceans can be monitored from this location. In addition, the Drake Passage and Tasman Seaway represent critical gateways in ocean history. I have ongoing collaborative research with Howie Scher (ex-UF graduate student, currently at the University of Rochester) investigating the timing and consequences of the opening of Drake Passage. Research to date on Nd isotopes supports some of the earlier estimates for the opening, suggesting thermal isolation of Antarctica may have at least contributed to development of the southern cryosphere. Current work is investigating Pb isotopic variations in the Southern Ocean with particular focus on testing ideas of warm, saline, deep water formation in the Paleogene.
Late Cretaceous Circulation: The Late Cretaceous was the warmest interval of the last 150 Ma and it includes up to 6 intervals of widespread anoxia and organic carbon burial, referred to as Ocean Anoxic Events (OAE). These events represent major perturbations to the global carbon cycle, and some of the events have global distribution. Several ODP sites on Demerara Rise have relatively continuous sections through the Late Cretaceous and abundant fish debris. Initial results from a project in collaboration with Ken MacLeod (University of Missouri) and Susanna Blair (UF graduate student) illustrate that deep ocean circulation was involved in OAE2. We are currently using Nd isotopes to define the relationship between changes in surface and deep ocean circulation, as well as changes in the carbon cycle in the North Atlantic during this time.
Miocene Caribbean Carbonate Crash: Middle to late Miocene sediments in the Caribbean, equatorial Pacific, and western Atlantic all record intervals of enhanced carbonate dissolution referred to as “the carbonate crash.” Derrick Newkirk (UF graduate student) and I are compiling Nd isotopic records from several ODP sites in this region in order to determine what role deep ocean circulation played in these dissolution events. Results will also help us understand how the deep ocean responded to the closure of the Isthmus of Panama.
Indian Ocean Circulation: The conservative behavior of Nd isotopes is a critical element of their application to studies of paleocirculation. A Nd isotopic study of Cenozoic sediments from ODP site 757 on the Ninetyeast Ridge highlighted the fact that even intermediate depth sites are unaffected by weathering inputs from the Himalayas. In addition, the record preserves a history of flow through the Indonesian Seaway, another critical oceanic gateway. Additional work in this region might help to further constrain the closure history of this gateway.
Fluid Flow Through Peri-platform Sediments: Porewater geochemical data from the Miocene peri-platform sediment on Marion Plateau suggest subsurface fluid circulation. Steve Burns (University of Massachusetts- Amherst) and I are using Sr isotopic and elemental data, combined with other porewater chemical signatures, to try to understand the nature and timing of this flow.