Selenium (Se) is an essential trace element, which, with multiple oxidation states and six stable isotopes, has the potential to be a powerful paleo-environmental proxy. In this study, Se concentrations and isotopic compositions were analyzed in a suite of about 120 samples of fine-grained marine sedimentary rocks and sediments spanning the entire Phanerozoic. While the selenium concentrations vary greatly (0.22 to 72 ppm), the δ82/76Se values fall in a fairly narrow range from -1 to +1 , with the exception of laminated black shales from the New Albany Shale formation (Devonian), which have δ82/76Se values of up to +2.20 . Black Sea sediments (Holocene) and sedimentary rocks from the Alum Shale formation (Late Cambrian) have Se/TOC ratios and δ82/76Se values close to those found in modern marine plankton (1.72x10-6±1.55x10-7 mol/mol and 0.42±0.22 ). (Note: TOC = total organic carbon.) For the other sedimentary sequences, the Se/TOC ratios indicate enrichment in selenium relative to marine plankton. Additional input of isotopically light terrigenous Se (δ82/76Se ≈ -0.42 ) may explain the Se data measured in recent Arabian Sea sediments (Pleistocene). The very high Se concentrations in sedimentary sequences that include the Cenomanian-Turonian Ocean Anoxic Event (OAE) 2 possibly reflect a significantly enhanced input of volcanogenic Se to the oceans. As the latter has an isotopic composition (δ82/76Se ≈ 0 ) not greatly different from marine plankton, the volcanogenic source does not impart a distinct signature to the sedimentary Se isotope record. The lowest δ82/76Se values are observed in the OAE2 samples from Demerara Rise and Cape Verde Basin cores (δ82/76Se = -0.95 to 1.16 ) and are likely due to fractionation associated with microbial or chemical reduction of Se oxyanions in the euxinic water column. In contrast, a limiting availability of seawater Se during periods of increased organic matter burial is thought to be responsible for the elevated δ82/76Se values and low Se/TOC ratios in the black shales of the New Albany Shale formation. Overall, our results suggest that Se data may provide useful information on paleodepositional conditions, when included in a multi-proxy approach.

Thesis (Ph. D.)--Joint Program in Physical Oceanography (Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, and the Woods Hole Oceanographic Institution), 2003. / Includes bibliographical references (p. 145-148).

No description available.

We investigated the relationship between rhythms occurring at different time-scales, namely circadian and ultradian rhythms. Furthermore, we examined the potential role of the period (per) gene, a known clock gene initially isolated in Drosophila, for regulating these rhythms in the wild-type cricket, Teleogryllus oceanicus . Here we report a positive correlation between circadian and ultradian rhythms in crickets. Thus, crickets with a slow endogenous circadian rhythm also have a slow ultradian rhythm, and conversely, animals with a fast endogenous circadian rhythm have a fast ultradian rhythm. In addition to this correlation, we observed PER-like immunoreactivity in the regions of the cricket nervous system involved in regulating these rhythms, namely the brain, in particular the optic lobes, and the meso- and metathoracic ganglia. We thus conclude that different time-scale rhythms may be regulated by a common setting element, a role potentially played by the per gene.

The SST bias in the tropical Atlantic exists in the early to latest generation of coupled general circulation models. The maximum bias is not on the equator but at 16°S, the cause of which has not been thoroughly studied. Newly released CMIP5 models provide a useful tool to investigate the contributions of different physical processes to the SST bias in this area in the coupled system. We tested three existing mechanisms and found that: 1) there is no significant relationship between the SST bias and surface heat flux bias; 2) deficient coastal upwelling is a contributing but not the sole source of the bias; and 3) the SST bias is correlated with temperature biases in the upstream equatorial region. The Angola-Benguela front is displaced southward by more than 10° in latitude in many CIMP5 models. Due to the huge temperature contrasts on two sides of the front, such a frontal displacement generates a very strong SST bias. The correlation between the SST bias and frontal location error in this region is significant at the 99% level, demonstrating that the SST bias in coupled GCMs is attributable to the models’ inability to reproduce a realistic position of the front and the consequent erroneous advection by the southward Angola current. This is due to both errors in the simulated surface wind field and systematic errors in ocean models. Ocean reanalysis datasets and a high-resolution regional model simulation suffer a similar pattern of SST biases. Although they produce a more realistic ocean circulation than coarser resolution simulations and alleviate some of the severe SST bias near the front, a warm bias overlies on a northward current to the south of the front, which actually comes from the north of the front through a subsurface passage. We identify a strong subsurface temperature bias caused by a too-deep and diffused simulated thermocline along the coast of Angola, originating from the equatorial thermocline, advected by the Angola Current and an undercurrent beneath the Benguela current, and then brought to the surface by the coastal upwelling along the Benguela coast, contributing to the warm SST bias south of the front.

Thesis (Ph. D.)--University of Washington, 2002. / Vita. Includes bibliographical references (p. 136-145).

Thesis (Ph.D.)--University of Delaware, 2009. / Principal faculty advisor: A.D. Kirwan, College of Earth, Ocean, & Environment. Includes bibliographical references.

Thesis (M.Sc.)--Memorial University of Newfoundland, 1994. / Typescript. Bibliography: leaves 74-76. Also available online.

Thesis (D. Sc.)--Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 1980. / Vita. Grants: OCE 75-14056, OCE 76-82036 and OCE 77-28355." Includes bibliographical references (p. 315-325).

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