Varved, anoxic sediments in Saanich Inlet, British Columbia, are formed by the annual cycle of summer deposition of diatom frustules and winter inputs of terrigenous material derived from land runoff. The objective of this study was to sample the varve record in order to develop a palaeoceanographic history of the Inlet. Box-cores of varved sediments were collected from Finlayson Arm, Saanich Inlet. The cores were quick, frozen upon recovery, to preserve the laminae, were subsequently sectioned and X-radiographs of the sections prepared. The varves were individually sampled and analysed for their diatom assemblages together with carbon, carbonate, major and minor element concentrations and ²¹⁰Pb activity. The chronology of a representative core determined by ²¹⁰Pb was inconsistent with that determined by varve counting. The geochemical data indicated that the upper 15cm of the core had a distinct elemental composition and a lower porosity that indicated a changed sedimentation rate. It also appeared that around 20 years of sediment had been lost from the core-top. The upper sediment contains a carbonate increase linked to a dust dump from a local cement plant which occurred between 1960-1963. In the lower section of the core, both the diatom and the geochemical data indicate seasonal variation expected from the formation of annual varves. However, a well constrained chronology cannot be obtained for this core because of the non-steady state sedimentation. This makes the interpretation of inter-varve variations in the light of regional climatic records impossible. Nevertheless, a change in production on a cycle of approximately 10-15 years is evident and this study provides conclusions that will be useful to future palaeoceanographic investigations on longer cores from a part of the Inlet where sedimentation is more constant. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

Bibliography: pages 45-55. / Eleven gravity cores from the continental margin off Eire and Land's End (SW England) were examined and found to document the major trends of the Late Pleistocene climate. Several stratigraphic indicators; - carbonate content, sediment texture, grain size, composition, nature of terrigenous components, ice-rafted debris and foraminiferal diversity were examined and show that the glacial history of the study area can be closely correlated with the palaeoclimatic evolution of the adjacent European shelf. Sediments deposited during Late Pleistocene glacial conditions show the following characteristics when compared to the surface sediments deposited under Holocene interglacial conditions: an increase in the quantity of ice-rafted debris and percentage of mica, and a notable increase in the degree of frosting and pitting of the quartz grains. Overall grain size was finer resulting in a silty sediment package. Sedimentologically the cores fall into two groups (1 and 2). The major difference being that Group 1 (located on the Pendragon Escarpment) received increased quantities of fine silts from a 'shelf spill-over' mechanism operating on the Fastnet and Western Approaches Basins, during glacial regressions. All sediment samples displayed polymodal characteristics reflecting the interaction of several different physical processes e.g. ice-rafting, contour currents etc. Striking variations in the populations of planktonic foraminifera were noted, alternating between Arctic and Sub-Arctic assemblages, reflecting the waxing and waning of glacial activity. The coccolith-carbonate minima correlate with the Arctic-fauna maxima and the ¹⁸O/¹⁶O maxima of the oxygen-isotope curves. Foraminiferal-test analysis (ratio of whole foraminifera fragmented foraminifera) revealed that no correlation existed with any of the other parameters analysed. However, the cores were severely affected by the presence of bottom currents which were strong enough to remove the fragmented tests. Parallellaminated contourites and evidence of erosion were noted in all cores. Ten cores penetrated sediments deposited during the last glacial maximum of 20,000 B.P - 18,000 B.P. near the 75cm depth mark (Core 1865 was too short to reach such sediments). However sediments reflecting the 11,000 B.P glacial readvance, detected at around the 25cm mark, were not as clearly represented. Bioturbation has smoothed the climatic record throughout the lengths of these cores and has also suppressed the high-frequency oscillations (<10³ B.P).

Thesis (Ph. D.)--Joint Program in Oceanography (Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), 2006. / This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections. / Includes bibliographical references (leaves 117-126). / In this thesis, I present high-resolution stable-isotope and planktonic-fauna records from Bering Sea sediment cores, spanning the time period from 50,000 years ago to the present. During Marine Isotope Stage 3 (MIS3) at 30-20 ky BP (kiloyears before present) in a core from 1467m water depth near Umnak Plateau, there were episodic occurrences of diagenetic carbonate minerals with very low 13C (-22.4%), high 18O (6.5%), and high [Mg]/[Ca], which seem associated with sulfate reduction of organic matter and possibly anaerobic oxidation of methane. The episodes lasted less than 1000 years and were spaced about 1000 years apart. During MIS3 at 55-20 ky BP in a core from 2209m water depth on Bowers Ridge, N. pachyderma (s.) and Uvigerina 18O and 13C show no coherent variability on millennial time scales. Bering Sea sediments are dysoxic or laminated during the deglaciation. A high sedimentationrate core (200 cm/ky) from 1132m on the Bering Slope is laminated during the Blling warm phase, Allerd warm phase, and early Holocene, where the ages of lithological transitions agree with the ages of those climate events in Greenland (GISP2) to well within the uncertainty of the age models. The subsurface distribution of radiocarbon was estimated from a compilation of published and unpublished North Pacic benthic-planktonic 14C measurements (475{2700 m water depth). There was no consistent change in 14C probles between the present and the Last Glacial Maximum, Blling-Allerd, or the Younger Dryas cold phase. N. pachyderma (s.) 18O in the Bering Slope core decreases rapidly (in less than 220 y) by 0.7-0.8h at the onset of the Blling and the end of the Younger Dryas. These isotopic shifts are accompanied by transient decreases in the relative abundance of N. pachyderma (s.), suggesting that the isotopic events are transient warnings and sustained freshenings. / by Mea S. Cook. / Ph.D.

Thesis (Ph. D.)--Joint Program in Oceanography (Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), 2006. / Includes bibliographical references. / To provide a new perspective on the fate of both natural organic matter and hydrophobic organic contaminants (HOCs) in marine sediments, we have investigated the relationship between radiocarbon (14C) age and the different modes of association in aquatic sediments and soils. Radiocarbon is a sensitive tracer of OM provenance, with variations in its natural abundance reflecting the age and origin of material. The main objective has been to determine the significance of these associations, and to assess how they affect the transport, bioavailability, preservation and residence times of organic compounds in the environment. Our results indicate that the majority of HOCs that persist in marine sediments are solvent-extractable and incorporation into insoluble sediment residues is not quantitatively significant. For pristine sediments, systematic variations in 14C content are observed between different chemically defined sedimentary organic fractions. These variations are dependent on organic matter inputs and/or the affects of diagenesis. Our observations also provide evidence for the protection of labile marine carbon by chemical binding. / (cont.) Finally, the persistence of n-alkanes from biogenic sources compared to those derived from petroleum indicates that protective matrix association can play a crucial role in determining the long-term fate of a compound. Overall, it is clear that both natural organic compounds and HOCs can undergo very different fates depending on their mode of introduction to, and physical disposition in environmental matrices. / by Helen K. White. / Ph.D.

Thesis (Ph. D.)--Joint Program in Oceanography (Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), 2005. / Includes bibliographical references (p. 229-238). / The fate of trace metals in contaminated coastal sediments is poorly understood, yet critical for effective coastal management. The aim of this thesis is to investigate and quantify the mechanisms leading to the release of silver, lead and copper across the sediment-water interface. Two contrasting sites were investigated, a heavily contaminated site in Boston Harbor and a less impacted, offshore site in Massachusetts Bay. High-resolution porewater and solid phase samples were collected in each season to determine the diagenetic cycles and chemistry controlling the fate of these metals. The trace metals are scavenged by iron oxyhydroxides and released to the porewaters when these oxides are reduced. At the strongly reducing site in Boston Harbor, there is seasonal transfer of trace metals from oxide phases in winter, to sulfides phase in summer. At the Massachusetts Bay site, due to the lack of sulfide, the metals are focused into the surface oxide layer, giving a solid phase enrichment. There is a diffusive flux of copper to the water column throughout the year, while silver is released only in winter. Lead is strongly scavenged and is rarely released to the overlying waters. / (cont.) Analysis of reduced sulfur compounds in the porewaters has shown that there is also a significant flux of these strong ligands to the overlying waters. Polysulfide species enhance the solubility of copper within the porewaters. Sediment resuspension fluxes were quantified using an erosion chamber. Sediment resuspension leads to enhanced release of dissolved metals and is especially important in redistributing contaminants as the first particles to be eroded are enriched in trace metals. The total release of dissolved metals from the sediments by diffusion and sediment resuspension is estimated to be 60% and 10% of the riverine flux for copper and lead respectively. With continued pollution control reducing the discharge of metals from other sources, the benthic release of metals will become increasingly important terms in the metal budget of Boston Harbor. / by Linda H. Kalnejais. / Ph.D.

Thesis: Ph. D., Joint Program in Chemical Oceanography (Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), 2017. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 169-190). / Terrestrial organic carbon (OC) erosion, remineralization, transport through river networks, and burial in marine sediments is a major pathway of the global carbon cycle. However, our ability to constrain these processes and fluxes is largely limited by (i) analytical capability and (ii) temporal sampling resolution. To address issue (i), here I discuss methodological advancements and data analysis techniques for the Ramped PyrOx serial oxidation isotope method developed at WHOI. Ramped-temperature pyrolysis/oxidation coupled with the stable carbon (¹²C, ¹³C) and radiocarbon (¹⁴C) analysis of evolved CO₂ is a promising tool for understanding and separating complex OC mixtures. To quantitatively investigate distributions of OC source, reservoir age, and chemical structure contained within a single sample, I developed a kinetic model linking RPO-derived activation energy, ¹³C composition, and radiocarbon content. This tool provides a novel method to fundamentally address the unknown relationship between OC remineralization rates and chemical structure in various environmental settings. To address issue (ii), I additionally present results from time-series sample sets collected on two end-member systems: the Congo River (Central Africa) and the LiWu River (Taiwan). For the Congo River, bulk and plant-wax-lipid ¹³C compositions indicate that a majority of particulate OC is consistently derived from downstream, C₃-dominated rainforest ecosystems. Furthermore, bulk radiocarbon content and microbial lipid molecular distributions are strongly correlated with discharge, suggesting that pre-aged, swamp-forest-derived soils are preferentially exported when northern hemisphere discharge is highest. Combined, these results provide insight into the relationship between hydrological processes and fluvial carbon export. Lastly, I examined the processes controlling carbon source and flux in a set of soils and time-series fluvial sediments from the LiWu River catchment located in Taiwan. A comparison between bedrock and soil OC content reveals that soils can contain significantly less carbon than the underlying bedrock, suggesting that this material is remineralized to CO₂ prior to soil formation. Both the presence of bacterial lipids and a shift toward lower activation energy of ¹⁴C-free OC contained in soil saprolite layers indicate that this process is microbially mediated and that microbial respiration of rock-derived OC likely represents a larger geochemical flux than previously thought. The results presented in this thesis therefore provide novel insight into the role of rivers in the global carbon cycle as well as their response to environmental perturbations. / by Jordon Dennis Hemingway / Ph. D.

Thesis (Ph. D.)--Joint Program in Oceanography (Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), 2005. / Includes bibliographical references (p. 131-149). / This thesis evaluates the nature and magnitude of tropical climate variability from the Last Glacial Maximum to the present. The temporal variability of two specific tropical climate phenomena is examined. The first is the position of the Intertropical Convergence Zone (ITCZ) in the Atlantic basin, which affects sea surface temperature (SST) and precipitation patterns throughout the tropical Atlantic. The second is the strength of the Indian Monsoon, an important component of both tropical and global climate. Long-term variations in the position of the ITCZ in the Atlantic region are determined using both organic geochemical techniques and climate modeling. Upwelling in Cariaco Basin is reconstructed using chlorin steryl esters as proxies for phytoplankton community structure. We find that the diatom population was larger during the Younger Dryas cold event, indicating that upwelling was enhanced and the mean position of the ITCZ was farther south during the Younger Dryas than it is today. A climate simulation using an ocean-atmosphere general circulation model confirms these results by demonstrating that the ITCZ shifts southward in response to high-latitude cooling. The climate of the Arabian Sea region is dominated by the Indian Monsoon. / (cont.) Results from modern sediments from a suite of cores located throughout the Arabian Sea suggest that wind strength is well represented by the accumulation rate and carbon isotopic composition of terrestrially-derived plant waxes in sediments. Arabian Sea SST patterns, reconstructed from a suite of sediment cores representing four time slices utilizing the Mg/Ca SST proxy, suggest that both the summer and winter monsoons were enhanced 8,000 yr BP relative to today while the summer monsoon was weaker and the winter monsoon stronger at 15,000 and 20,000 yr. These results are confirmed by a time-series reconstruction of SST on the Oman Margin that reveals that SST at this site is sensitive to both regional and global climate processes. The results of this thesis demonstrate that tropical climate, as evaluated by a number of different proxies as well as climate models, has varied substantially over the past 20,000 years and is closely coupled to climate at high-latitudes. / by Kristina Ariel Dahl. / Ph.D.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences, 2016. / Ph. D. Joint Program in Oceanography (Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), 2012 / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 179-192). / Since the Last Glacial Maximum (LGM, ~ 20,000 years ago) air temperatures warmed, sea level rose roughly 130 meters, and atmospheric concentrations of carbon dioxide increased. This thesis combines global models and paleoceanographic observations to constrain the ocean's role in storing and transporting heat, salt, and other tracers during this time, with implications for understanding how the modem ocean works and how it might change in the future. -- By combining a kinematic ocean model with "upstream" and "downstream" deglacial oxygen isotope time series from benthic and planktonic foraminifera, I show that the data are in agreement with the modem circulation, quantify their power to infer circulation changes, and propose new data locations. -- An ocean general circulation model (the MITgcm) constrained to fit LGM sea surface temperature proxy observations reveals colder ocean temperatures, greater sea ice extent, and changes in ocean mixed layer depth, and suggests that some features in the data are not robust. -- A sensitivity analysis in the MITgcm demonstrates that changes in winds or in ocean turbulent transport can explain the hypothesis that the boundary between deep Atlantic waters originating from Northern and Southern Hemispheres was shallower at the LGM than it is today. / by Daniel Edward Amrhein. / Ph. D.

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