SEMINAR: MGG Student Seminar: Tomorrow (WEDNESDAY) @ Noon

[David Weinstein <dweinstein@rsmas.miami.edu>]

MGG STUDENT SEMINAR

WEDNESDAY, May 2, 2012

12:00 - 1:00 PM

SLAB SEMINAR ROOM

Microbial and Geochemical Characterization of Carbonate Sediments from Florida Bay

Presenter: Alan Piggot

      Florida Bay is a modern carbonate depositional environment undergoing very early stages of diagenesis.Porewater geochemistry of mudbanks in Florida Bay reveals changes in the concentration of SO₄^-2,Ca²⁺and alkalinity, indicating carbonate dissolution and recrystallization are occurring. Numerous bacterial species have been assumed to play a role in the precipitation and dissolution of calcium carbonate in diverse environments.Previous studies have shown sulphate-reducing bacteria can induce the precipitation ofprimary dolomite in shallow marine and freshwater lake sediments. In this study, the interstitial water chemistry, sediment chemistry and bacterial community profiles of Florida Bay sediment cores were analyzed to discover how bacterial communities change along geochemical gradients in relation to carbonate mineralogy. Geochemical analyses of porewaters include alkalinity and chloride titrations, and trace elements such as calcium, magnesium and strontium were measured using standard ICP-OES methods. The inorganicd¹³C and d¹⁸O compositions were measured on the sediments, while the organic d¹³C and d¹⁵N values were analyzed on the co-occurring organic material throughout the cores. Carbonate mineralogy was determined using x-ray diffraction, which quantitatively tracked changes in aragonite, calcite and dolomite down core. Genomic DNA was extracted and the 16S rRNA gene was amplified using polymerase chain reaction (PCR) with universal bacterial primers. Terminal restriction fragment length polymorphism (T-RFLP) analysis of 16S rRNA gene was used track changes in the bacterial communities with sediment depth along the cores and between mud bank locations. Clone libraries were made and the 16S rRNA gene was sequenced to identify dominant populations within the mud cores. We hope to better understand how microbes can alter the chemical environment of shallow marine sediments, their resulting geochemical signatures, and the potential to recognize these processes in the geologic record.   

Using isotopic tools to assess and understand influence of elevated nutrients on zooxanthellate corals

Presenter: Quinn B. Devlin

    Previous studies have measured the signature of corals as an indicator of nutrient inputs to a reef environment. The interpretation of the δ¹⁵N signature, however, is complex, especially in zooxanthellate corals. Experiments are carried out to understand controls on the δ¹⁵N of coral host and symbiotic zooxanthellae. In addition, we investigate the influence of elevated levels of dissolved inorganic nitrogen on the health of zooxanthellate corals. Coral incubations are being conducted to elucidate the mechanism through which elevated NO₃^-, NH₄⁺ and PO₄^2- influence zooxanthellate corals. Stable isotopes are utilized as a tool to understand the sources and fates of carbon and nitrogen within the coral – dinoflagellate symbiosis in Acropora cervicornis and Pocillopora damicornis, while several parameters are measured to assess responses of coral health to elevated stressors (calcification, linear extension, photosynthesis, C/N ratios, symbiont density and diversity). Preliminary data suggest that elevated levels of inorganic nitrogen degrade corals directly through alteration of the symbiotic relationship between coral host and dinoflagellate algae. The δ¹⁵N signature of corals and zooxanthellae is found to be complex and is influenced by several factors including fractionation of ¹⁵N during uptake and assimilation of DIN, uptake rates, heterotrophic feeding and phosphate availability.