Geochemistry of benthic foraminifera as an enviornmental indicator:a study from multiple hydrographic regimes.

The geochemistry(stable isotopes and trace elements) of living(stained)calcareous benthic foraminifera was compared with ambient bottom water stable isotope values to provide modern analog conditions and calibrations for enviornmental and paleoenvironmental assessments.Stable isotope values of live(stained)benthic foraminifera were investigated from push core and multicorer samples from the North Pacific(on the Aleutian margin,water depth 1988m)and the South Australian Bight(water depth 2476m and 1634m).Living benthic foraminifera specimens collected from contaminated sites in the Venice Lagoon were analysed for trace elements.Both the isotopic and the trace element study involved interpretation of modern live foraminiferal chemical reponses to different enviornments.The isotope analyses of living foraminifera from the North Pacific and the South Australian Bight provide calibration information for the evaluation of bottom water temperature and circulation of ancient oceans based on fossil foraminiferal geochemistry.Trace elements concentrations of Venice Lagoon foraminifera were used to assess the possibility of using foraminiferal geochemistry as a pollution indicator.Consistent with previous studies,shallow infaunal benthic foraminifera from the Aleutian and Australian argins were depleted in δ13 C with respect to bottom water dissolved inorganic carbon(DIC),and the deep infaunal foraminifera showed greater difference in values between foraminiferal carbon isotope values and DIC.The deep infaunal,Globobulimina pacifica,had δ18 O values that were in equilibrium with oxygen isotopic values at equilibrium calcite(δ18 Occ).Based on a few specimens that were divided in half,there was only minor isotopic heterogeneity in the test composition of benthic foraminifera genus Globobulimina.Differential foraminiferal uptake of Zn as indicated in initial laser ablation analyses showed marked differences between contaminated and less polluted sites in the Venice Lagoon.Higher incorporation of zinc in foraminiferal calcite from the more contaminated site was possibly the result of greater bioavailability of zinc in this environment.Differences also exist between the uptake of other trace metals such as Al,Mg and Mn by different foraminiferal genera.Differences in metal sequestration by benthic foraminifera suggest that the trace metal geochemistry of some foraminiferal taxa may be useful as a pollution indicator.Chandranath BasakRathburn, Anthony EBrake, SandraLatimer, JenniferMaster of ScienceDepartment of Geography, Geology, and AnthropologyCunningham Memorial library, Terre Haute,Indiana State UniversityILL-ETD-034MastersTitle from document title page. Document formatted into pages: contains 92 p.: ill. Includes abstract and appendix

Pb isotopes in Cenozoic sediments of ODP Site 177-1090

Nd and Pb isotopic compositions extracted from bulk deep sea sediments have been shown to be robust proxies for deep water circulation as well as weathering provenance and intensity over geologically young time scales. In this study we evaluated ten deep sea samples from Ocean Drilling Program (ODP) site 1090 ranging in age from mid Eocene to early-Miocene to test whether Pb isotopic compositions extracted from geologically older sediments record reliable seawater isotopic ratios and to evaluate the source of the extracted Pb. The sequential extraction protocol used in this study is similar to protocols reported for previous studies and produces acetic acid, hydroxylamine hydrochloride (HH) and residue fractions. Each extracted fraction was analyzed for Pb isotopes, rare earth elements (REEs), and a suite of major elements. Similar 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb ratios are recorded from the acetic acid and HH fractions for ~70-80% of the samples, suggesting that either the acetic acid dissolves Fe-Mn oxides or multiple phases are recording the same seawater isotopic value. Several indirect tests, such as Al mass balance, comparison of Sr isotopes in HH extracts to contemporaneous seawater Sr isotopes, and comparison of Nd isotopic compositions in HH extracts to published fossil fish teeth values, provide evidence that Pb isotopic compositions measured in our bulk HH extracts record bottom water values. The relationship between Pb, Mn and Ca concentrations in HH fractions indicates that Fe-Mn oxides and a Mn-bearing carbonate are the dominant phases contributing seawater Pb. Comparison of REE patterns derived from the HH fraction and total digestions of Fe-Mn nodule standards reveals that the trivalent REEs exhibit patterns consistent with the parent archive, but Ce can be fractionated during extraction. Ratios of REEs also produce unique fields for each fraction and can be used to test the purity of the seawater signal of the extraction protocol. Finally, an initial evaluation of Pb isotopic compositions in fossil fish indicates that this archive is not suitable for bottom water Pb isotope studies

Neodymium isotopic characterization of Ross Sea Bottom Water and its advection through the southern South Pacific

Since the inception of the international GEOTRACES program, studies investigating the distribution of trace elements and their isotopes in the global ocean have significantly increased. In spite of this large-scale effort, the distribution of neodymium isotopes (143Nd/144Nd, εNd) and concentrations ([Nd]) in the high latitude South Pacific is still understudied, specifically north of the Antarctic Polar Front (APF). Here we report dissolved Nd isotopes and concentrations from 11 vertical water column profiles from the South Pacific between South America and New Zealand and across the Antarctic frontal system. Results confirm that Ross Sea Bottom Water (RSBW) is represented by an εNdvalue of ∼−7, and for the first time show that these Nd characteristics can be traced into the Southeast Pacific until progressive mixing with ambient Lower Circumpolar Deep Water (LCDW) dilutes this signal north of the APF. That is, εNdbehaves conservatively in RSBW, opening a path for studies of past RSBW behavior. Neodymium concentrations show low surface concentrations and a linear increase with depth north of the APF. South of the APF, surface [Nd] is high and increases with depth but remains almost constant below ∼1000m. This vertical and spatial [Nd] pattern follows the southward shoaling density surfaces of the Southern Ocean and hence suggests supply of Nd to the upper ocean through upwelling of Nd-rich deep water. Low particle abundance due to reduced opal production and seasonal sea ice cover likely contributes to the maintenance of the high upper ocean [Nd] south of the APF. This suggests a dominant lateral transport component on [Nd] and a reduced vertical control on Nd concentrations in the South Pacific south of the APF