Foraminifera are unicellular organisms with a wide marine distribution. Many species secrete carbonate tests whose physical and chemical nature reflect the seawater conditions in which they grow. Thus, fossil tests preserved on the sea floor represent an archive that may be used to investigate the composition of ancient seawater. With the aim of improving our understanding of past ocean-climate links, I have tested proxies for seawater composition in the modern ocean and applied them to a key period in Earth history. The ratio of boron to calcium (B/Ca) in the calcite tests of planktic foraminifers has previously been suggested as a proxy for past seawater carbonate chemistry, but controls on B incorporation are not yet clear. The theoretical basis for this proxy is rooted in the pH-dependent concentration of dissolved borate (B(OH)_4-) and its subsequent incorporation into foraminiferal calcite. In this thesis, I present: 1) new insights into the environmental controls on B/Ca revealed by culture experiments with living foraminifers, and 2) new reconstructions of past seawater chemistry during the last deglaciation based on B/Ca of fossil calcite from deep sea sediments. To test environmental controls on B incorporation, I performed several culture experiments that quantified the effects of pH, temperature, salinity, dissolved boron and inorganic carbon concentrations on the calcite tests of the planktic foraminifer species O. universa, G. sacculifer, and G. ruber (pink). In these experiments, B/Ca increases with pH (lower [HCO_3-], higher [CO2_3-] and [B(OH)_4-]) and salinity, but not with temperature. Thus, normalizing B/Ca data to a constant salinity (e.g., S=35) should improve our ability to isolate the carbonate chemistry signal in B/Ca paleo-records and samples from different ocean sites. In addition, B/Ca decreases with total dissolved inorganic carbon (DIC) at constant pH (higher [HCO_3-] and [CO2_3-], constant [B(OH)_4-]), which suggests competition between aqueous boron and carbon species for inclusion into the calcite lattice. While different cultured species exhibit similar B/Ca behavior in response to salinity, temperature, and pH changes, their absolute B/Ca values are offset under identical seawater conditions. Thus, B/Ca is both a function of environmental parameters that exert strong influence on test composition as well as biological processes that result in species offsets. To determine whether these culture calibrations are applicable in the open ocean, I used equations relating the B/Ca of cultured foraminifers with experimental seawater properties to predict B/Ca of wild specimens derived from sediment core-tops. Most measured core-top values for O. universal and G. sacculifer are similar to values predicted by culture calibrations (average offsets are 4 and 15 μmol mol^-1, respectively) but values predicted for coretop G. ruber deviate by up to 60 μmol mol^-1 from predicted values. The greater discrepancy observed for core-tops may suggest that our experiments still fall short of identifying all environmental controls on B/Ca and/or that we need to revisit the growth conditions assumed for planktic foraminifers, in particular the depth habitat of G. ruber. Further, an evaluation of planktic foraminiferal downcore data shows that B/Ca in planktic foraminifers is not sufficiently sensitive to surface ocean carbonate chemistry to permit reconstruction of Pleistocene atmospheric CO2 changes. However, B/Ca may serve as a useful proxy in environments that experienced large carbonate system changes, such as upwelling zones, or large events such as those during the Paleocene-Eocene. In contrast to planktic foraminifers, B/Ca of benthic foraminifer tests appears to respond to deep-water carbonate saturation state (ΔCO2_3-). B/Ca of the benthic species Cibicidoides wuellerstorfi increases linearly with ΔCO2_3- in all major ocean basins, as demonstrated in the modern core-top calibration of Yu and Elderfield (2007). To gain insight into carbon storage in the deep ocean across the last glacial termination, I investigated the B/Ca composition of C. wuellerstorfi in a sediment core from New Zealand's Bay of Plenty, located at a depth of 1,627 meters. The resulting reconstruction indicates that ΔCO2_3- changed up to 30 μmol kg^-1 across the deglaciation. Combined with benthic δ^13C and independent paleo-O_2 estimates, the [CO2_3-] record indicates increased storage of CO_2 in the deep ocean during the LGM, with major roles for the biologic pump and carbonate compensation.

Thesis (Ph. D.)--University of Wisconsin--Madison, 1972. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

Thesis (M.S.)--University of Wisconsin--Madison, 1984. / Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 96-101).

Thesis (Ph. D.)--Oregon State University, 1995. / Typescript (photocopy). Includes bibliographical references (leaves 211-225). Also available on the World Wide Web.

Thesis (Ph. D.)--University of Wisconsin--Madison, 1971. / Typescript. Vita. Description based on print version record. Includes bibliographical references.

Thesis (M.S.)--University of South Florida, 2003. / Title from PDF of title page. Document formatted into pages; contains 79 pages. Includes bibliographical references.

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The aim of this thesis is to model climate change in the Bolivian Andes through the last glacial-interglacial cycle, using glaciers and palaeolakes. This is important because the extent and timing of glacier and palaeolake fluctuations in this area are poorly understood. Furthermore, determining the synchrony of glaciers and palaeolakes has direct implications for understanding the nature of palaeoclimatic change in this high altitude sub-tropical region during the last glacial-interglacial transition. The results of this study are directly applicable to general circulation models (GCMs) attempting to simulate past and future global climate change. Glacier-fed delta depositional systems on massifs at the margin of the southern Altiplano, Bolivia, suggest a broadly coeval expansion of glaciers and palaeolake Tauca during the Late-glacial. This is shown by the succession of hummocky moraine, ice-contact fan sediment-landform associations that extend from within lateral moraines and connect with Hjulstrom and Gilbert-type deltas at Cerro Azanaques, Cerro Tunupa and Cerro Condor Iquina between altitudes of 3770 and 3720 m. Radiocarbon ages on peat underlying glacigenic debris flow and glacifluvial deposits reveal glaciers reached their maximum extent soon after 13,300-12,850 14C yr B.P. The delta-plain/delta-front contacts of the glacier-fed deltas confirm that this glacier advance broadly coincided with palaeolake Tauca radiometrically dated to the interval 13,500-11,500 14C yr B.P. Therefore these climatically sensitive systems in the Bolivian Andes attained their greatest extent during the Late-glacial and not during the Last Glacial Maximum (LGM). Independent modelling of the climatic controls required to produce the simultaneous lowering of Late-glacial glacier equilibrium line altitudes (ELAs) and volumetric changes in palaeolake water balance suggest the primary forcing mechanism was increased summer (wet season) precipitation, while overflow from the northern basin was also necessary to raise the level of palaeolake Tauca in the southern Altiplano. Palaeoclimatic simulations show that an increase in precipitation of 330-425 mm/yr above modern values, combined with greater cloud cover (10%) that depressed local temperatures (2-3 °C) and reduced evaporation rates (10%) could have generated the Stage 3 glaciers and a 3760 m palaeolake highstand in the southern Altiplano. The ELA of former glaciers rose towards the south and west, like the gradient of modem precipitation, which suggest that increased moisture during the Late-glacial was probably brought to the Altiplano by tropical circulation systems similar to those at present, but atmospheric conditions were cooler-and-cloudier than present.

Global climate is strongly influenced by fluctuations in atmospheric CO₂ concentrations. Weathering of silicate rocks consumes CO₂, transports cations to the oceans, and thus plays a critical role in both seawater chemistry and climate. A major product of silicate weathering is magnesium, which in the oceans is homogeneous in both concentration and isotopic composition (δ26Mg[subscript SW] = -0.82‰). This homogeneity reflects a balance between continental weathering input by rivers (δ26MgRiver ~ -1.09‰) and groundwaters, and removal by high-temperature hydrothermal oceanic crust alteration (δ²⁶Mg[subscript SW] - δ²⁶Mg[subscript HT] ~ 0.0‰), dolomite formation, and authigenic alumino-silicate clay formation during low-temperature alteration of the oceanic crust. Since the oceanic residence time of Mg is significantly longer than the ocean mixing time, temporal variations in Mg isotopic composition of seawater (δ²⁶Mg[subscript SW]) recorded by marine calcites, such as foraminifera, can reflect a global picture of Cenozoic climate that is driven by an imbalance between the source and sink. A review of previous geochemical proxies and the terrestrial processes of magnesium are discussed in Chapter 1. In Chapter 2, we present an improved method for trace level Mg measurements in natural carbonates. The method was developed for analysis of planktonic foraminifera samples in order to generate a Mg isotopic record for Cenozoic seawater, however it can also be applied to seawater and other natural samples with a high ionic strength sample matrix. There were three major analytical challenges that needed to be overcome: 1. Maintain a precision of ±0.1‰ with a mass consumption as low as ~10 ng of Mg; 2. Maintain minimal blanks (≤0.1 ng) on Mg and other matrix elements (Na, K, Ca, etc.); 3. Purify samples to have complete separation of Mg from matrix elements with 100% recovery. We achieved this through cation-exchange column chromatography and analysis on a Multi-Collector Inductively-Coupled Plasma Mass Spectrometer (Thermo-Scientific "Neptune" MC-ICP-MS). We quantified our precision and accuracy through measurements of CAM1, natural seawater, and the JCP-1 coral reference standard and compared with other published studies. In addition, elemental ratios were determined by Quadrupole-ICP-MS (Q-ICP-MS; Florida State University) or by Inductively Coupled Plasma-Atomic Emission Spectroscopy (ICP-AES; University of Cambridge) to verify that the sample had been properly chemically cleaned and that it had not undergone diagenesis that would alter the Mg isotope ratios. In chapter 3, we present data from 66 core-top planktonic foraminifera samples from the Holocene epoch to investigate the use of the Mg isotopic composition of foraminifera as a potential proxy for the Mg isotope record of Cenozoic seawater and to quantify the fractionation between seawater and foraminiferal calcite (Δ²⁶Mg[subscript Foram-Seawater]). The average δ²⁶Mg of the planktonic foraminifera in our samples is -4.79 ± 0.83‰ (2σ), which includes 10 species with varying size-fractions from 4 sampling sites. Our study demonstrates that there is limited inter-species variability in δ²⁶Mg. We also observed no differences between the δ²⁶Mg of foraminifera cleaned with and without the reductive cleaning step (hydrazine + citric acid). This suggests that the Mg isotopic composition of the high-Mg calcite bands, which are preferentially dissolved during reductive cleaning, is similar to that of the low-Mg bands. In addition, the discrimination against Mg is higher for foraminiferal calcite formation compared to precipitation of inorganic calcite, suggesting that biomineralization should induce additional fractionation of Mg isotopes. In chapter 4, we present a new record of planktonic foraminifera (n = 104) spanning the Cenozoic Era (0 to 70 Ma), which shows a ~1‰ decrease in δ²⁶Mg towards present day values. The significance of this decrease is challenged by the high variability in our core-top foraminifera calibration (δ²⁶Mg = -4.63±0.57‰ (n=48, 2σ)). However, box model scenarios demonstrate that such a decrease in δ²⁶Mg could be driven by a decrease in the dolomite formation flux from ~4.0 Tmol/yr to present-day values of 0.84 Tmol/yr. / A Dissertation submitted to the Department of Earth, Ocean, and Atmospheric Science in partial fulfillment of the requirements for the degree of Doctor of Philosophy. / Fall Semester 2016. / October 3, 2016. / cenozoic, foraminifera, isotopes, magnesium / Includes bibliographical references. / William M. Landing, Professor Co-Directing Dissertation; Vincent J. M. Salters, Professor Co-Directing Dissertation; John G. Dorsey, University Representative; Munir Humayun, Committee Member; Angela N. Knapp, Committee Member.

Thesis (Ph.D.)--McMaster University, 2003. / Advisor: H. P. Schwarcz. Includes bibliographical references. Also available via World Wide Web.