<p> The export of particulate carbon from the surface ocean into deeper water and to the seabed is a critical component of the carbon cycle. The concentrations and compositions of particulate pigments collected at different depths and sinking at different settling velocities can be used as a proxy for biologically mediated processes important to the early degradation of OM. By knowing what processes the compositional and quantitative changes in the particulate pigments represent, the POM cycle of the BaRFlux area can be better understood. It is important to understand the POM cycle because deposition of OM to the seabed is the only way that OM is sequestered. The removal of POM from the marine POM cycle is especially important to understand in subtropical gyre areas like the BaRFlux site because: 1. subtropical gyres are areas of downwelling, and therefore POM transport to the deep ocean and may increase as global warming continues. 2.the flux of CO₂ to the ocean is increasing from rising levels of atmospheric CO₂, and CO₂ removed by the biological pump will lessen processes like ocean acidification.</p><p> This thesis examines the early degradation of chloropigments in the sediment and water column in the Bermuda Rise area of the Sargasso Sea. Water column particulate samples were collected with in-situ pumps, Niskin bottles, and Indented Rotating Sphere (IRS) sediment traps, and sediment was collected by box cores during 2011-2013 to record seasonal patterns in quantity and quality of particulate pigments as a function of water column depth and particle size. Chl-a, Chl-b, and pheopigments were separated and quantified using reverse-phase High Performance Liquid Chromatography (HPLC).</p><p> The comparison of data from in-situ pumps and Niskin bottles indicates that collection method significantly affects particulate pigment data concentrations. Niskin bottle data showed total pigment concentrations 10 times greater than in-situ pump pigment concentrations at shallow depths. At depths below the euphotic zone, Niskin bottle and in-situ pump concentrations both appear similar because the particulate pigment concentrations were below the detection limit. For the BaRFlux study area, the differences in Niskin bottle and pump data are most likely from: 1. the biased particle distribution due to sampling a small volume of seawater with Niskin bottles in an area of dilute particle concentration; 2. the greater retention efficiency of picophytoplankton on Niskin GF/F filters than 1-<i>&micro;</i>m in-situ pump microquartz filters.</p><p> The compositional changes seen in small suspended particulate pigments over depth is consist with small suspended particles being consumed by shallow water zooplankton and then increasingly altered by microbial activity with increasing depth. The composition of small and large particulate pigments were compared to determine if aggregation-disaggregation was an important process. Larger suspended particulate pigments were nearly 100% Chl-a over depth and distinct from smaller suspended particulate pigments other than samples from May or June, during which particle exchange may be more important. The comparison of particulate pigment data to CTD beam transmissivity profiles suggests that the nepheloid layer consists of small suspended particulate matter rather than large particles.</p><p> Sediment trap samples were compositionally enriched in pheopigments relative to smaller bottle and pump samples, indicative of enrichment with more rapidly sinking larger zooplankton fecal pellets. The mole% of chlorophyll-a labile pigment increased with increasing settling velocity, suggesting aggregation may increase the settling velocity of particles enough to escape zooplankton feeding. The particulate pigment composition of seafloor sediment collected in August was compositionally distinct from that of suspended and sinking particulate pigments and was nearly 100% pheophorbide-a, indicating POM degradation by feeding macrobenthos.</p>

Thesis (Ph. D.)--University of Wisconsin--Madison, 1980. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

Lake sediment cores collected from four lakes (Upper Fly Lake 61.04&deg;N, 138.09&deg;W, 1326 m a.s.l.; Jenny Lake 61.04&deg;N, 138.36&deg;W, 817 m. a.s.l.; Donjek Kettle 61.69&deg;N, 139.76&deg;W, 732 m a.s.l.; Lake WP02 61.48&deg;N, 139.97&deg;W, 1463 m a.s.l.) in the southwest Yukon provide records of postglacial climatic variability in the region. A 13,000 year pollen record from Upper Fly Lake indicated that herbaceous tundra existed on the landscape from 13.6 to 11 ka, followed by birch shrub tundra until 10 ka, when Picea forests were established in the region. Pollen-, chironomid-, and ostracode-inferred paleoclimate reconstructions showed a long-term cooling with increasing moisture from the late glacial through the Holocene. The early and mid-Holocene were warm and dry, with cool, wet conditions after 4 ka, and warm, dry conditions over the last 100 years. Chironomid accumulation rates provided evidence of millennial-scale climate variability, and the chironomid community responded to rapid climate changes. Late Holocene environmental variability was investigated through the analysis of paleoproduction indices (sediment loss-on-ignition, biogenic silica) and chironomid and ostracode communities. Coherent trends were revealed among the four lakes and pairs of sites located closer together showed more similarities than more distant sites located in similar environments (alpine tundra or boreal forest). Chironomid-inferred paleotemperature estimates are inconsistent with other data from the region, however certain fluctuations in paleoproduction indices and changes in abundance and composition of the chironomid and ostracode communities compare well with interpretations based on independent paleoclimate records. The White River Ash event (1147 cal yrs BP and 1953 cal yrs BP) impacted three of the four aquatic ecosystems studied, with a greater impact occurring at sites with greater ash thickness. Interannual variability in the lake environment is of lesser concern when deriving inference models relating organisms to environmental variables, and the results presented here provide guarded optimism that the sampling methodology applied in paleolimnological studies is appropriate in this region.

abstract: Sedimentary basins in the Afar Depression, Ethiopia archive the progression of continental breakup, record regional changes in east African climate and volcanism, and host what are arguably the most important fossiliferous strata for studying early human evolution and innovation. Significant changes in rift tectonics, climate, and faunal assemblages occur between 3-2.5 million years ago (Ma), but sediments spanning this time period are sparse. In this dissertation, I present the results of a geologic investigation targeting sediments between 3-2.5 Ma in the central and eastern Ledi Geraru (CLG and ELG) field areas in the lower Awash Valley, using a combination of geologic mapping, stratigraphy, and tephra chemistry and dating. At Gulfaytu in CLG, I mapped the northern-most outcrops of the hominin-bearing Hadar Formation (3.8-2.9 Ma), a 20 m-thick section of flat-lying lacustrine sediments containing 8 new tephras that directly overlie the widespread BKT-2 marker beds (2.95 Ma). Paleolake Hadar persisted after 2.95 Ma, and the presence and characteristics of the Busidima Formation (2.7-0.016 Ma) indicates Gulfaytu was affected by a reversal in depositional basin polarity. Combined with regional and geophysical data, I show the Hadar Formation underlying CLG is >300 m thick, supporting the hypothesis that it was the lower Awash Pliocene depocenter. At ELG, I mapped >300 m of sediments spanning 3.0-2.45 Ma. These sediments coarsen upward and show a progression from fluctuating lake conditions to fluvial landscapes and widespread soil development. This is consistent with the temporal change in depositional environments observed elsewhere in the lower Awash Valley, and suggests that these strata are correlative with the Hadar Formation. Furthermore, the strata and basalts at ELG are highly faulted, and overprinted by shifting extension directions attributed to the northern migration of the Afar triple junction. The presence of fossiliferous beds and stone tools makes ELG a high-priority target for anthropological and archaeological research. This study provides a new temporally-calibrated and high-resolution record of deposition, volcanism, and faulting patterns during a period of significant change in the Afar. / Dissertation/Thesis / Ph.D. Geological Sciences 2013

No description available.

Lake deposits are widespread throughout the Phanerozoic rock record and have long intrigued geologists and paleobiologists in search of natural resources or fossil biota. Low-energy lacustrine depositional environments, characterized by relatively rapid sediment influx rates and shallow zones of bioturbation, likewise produce highly-resolved archives of climate and ecosystems evolution. This dissertation describes four studies that use lake sediments for Quaternary environmental analysis. In East Africa, many decades of prior study provided the critical framework necessary for in-depth paleoenvironmental research at Lake Tanganyika (3° - 9°S). Seismic stratigraphic analysis integrated with radiocarbon-dated sediment cores from the Kalya horst and platform document a dramatic lake level lowstand prior to ~106 ka and a minor, short-lived regression during the Last Glacial Maximum (32 - 14 ka). Paleobathymetric maps reveal that Lake Tanganyika remains a large, connected water body even during episodes of extreme drought, which has implications for local and regional fauna. Over shorter timescales, geochronological, taphonomic and sedimentological analyses of shell beds around Kigoma (central Lake Tanganyika) document three distinct facies-types that are time-averaged over the latest Holocene. Lake level fluctuations associated with the termination of the Little Ice Age (~ 16th century CE) and subsequent encrustation played a key role in shell bed formation and persistence along high-energy littoral platforms, which has implications for structuring specialized communities of benthic fauna. In central South America (18° - 22°S), we studied the limnogeology of small lakes in the Puna and the Pantanal. Analyses of these sites were undertaken to: 1) ascertain how the lakes act as depositional basins; 2) assess sedimentation rates; and 3) construct limnogeological databases to guide future interpretations of ancient sediment cores. At Laguna de los Pozuelos (Argentine Puna), linear sedimentation rates approach 0.14 cm*y⁻¹ in the playa-lake center, and litho- and organo-facies development are dominantly controlled by basin hydrology, climate and biological feedbacks (both nutrient cycling and bioturbation) from waterbirds. At Lagoas Gaíva, Mandioré and Vermelha (Brazilian Pantanal), short-lived radioisotopes indicate uninterrupted depositional rates of 0.11 - 0.24 cm*y⁻¹, and hydrochemical and depositional patterns respond sensitively to changes in the seasonal flooding cycle of the Upper Paraguay River.

A detailed record of the Late Holocene sea level rise and landscape evolution that has taken place on the Georgia coast is contained within the sedimentary stratigraphy of its salt marsh depositional basins. Global relative sea level (RSL) has risen during the Late Holocene, and the rate of rise has accelerated during the Anthropocene. Jones Narrows marsh stratigraphy and radiocarbon analysis indicate increasing rates of RSL rise for the late Holocene on the Northern Atlantic Coast of Georgia, while FPXRF analysis of the marsh sediments facilitates a chemostratigraphic study of Jones Narrows salt marsh deposition and landscape evolution. Sedimentation and hydrology at the site have been heavily influenced by recent local anthropogenic impacts, which are examined through stratigraphic and spatial methods.

The Monkton Formation of the western shelf stratigraphic sequence in Vermont (VT) is identified as a Lower Cambrian regressive sandstone unit containing parasequences recording tidal flat progradation. Previous workers identified cycles believed to represent parasequences in a portion of a 1034' deep geothermal well drilled at Champlain College in Burlington, Vermont. For this study, both outcrop and well geophysical surveys were completed to better identify gamma emission curves and relative values for parasequences and select lithologies that are indicators of bathymetry and sea level. After using physical stratigraphic techniques to assemble a composite stratigraphic section for the Monkton Formation, analysis of the gamma emission curve and relative gamma values resulted in the identification and characterization of parasequences and select lithologies within the Monkton. Interpretation of bathymetry-sensitive lithologies along with parasequence architecture and thickness trends reveals three distinctive intervals over the thickness of the Monkton. It is recognized that the succession of these intervals represents an overall decreasing rate in accommodation space generation through Monkton deposition. Previous workers have suggested that biostratigraphic relationships of the Monkton Formation to the Potsdam Group in New York (NY) suggest that that they would be at least partially correlative. To further refine age relationships and constrain and compare the provenance of the Vermont stratigraphy locally and regionally, zircon samples were collected from the Monkton and the overlying Danby Formations and radiometric age determinations were completed by laser ablation–inductively coupled plasma mass spectrometry (LA-ICPMS) at University of Arizona Laserchron Center. Zircon age probability distribution curves show two dominate age peaks between 1.05-1.09 Ga and 1.15-1.18 Ga for the Monkton and Danby suggesting either a continuity of provenance through the Cambrian or the cycling of the Monkton's sand. The 1.05-1.09 Ga age range corresponds to rocks generated during the Ottawan Orogeny while the 1.15-1.18 Ga range is associated with the Shawinigan Orogeny and anorthosite-mangerite-charnockite-granite (AMCG) plutonism. Dominant age peaks in the Vermont samples between 1.15-1.18 Ga are similar to the 1.16 Ga age peak reported by other workers from the Altona and Ausable Formations of the Potsdam Group of New York. The shared dominant age peak and close proximity of the Vermont and New York stratigraphy may suggest a primarily shared provenance.

Inaccessibility due to harsh weather conditions and perennial sea ice has left the Weddell Sea embayment (WSE) vastly under-studied in comparison to other regions of Antarctica. Yet understanding its deglacial history since the Last Glacial Maximum (LGM) is vital for understanding the dynamics and stability of the Antarctic ice sheet. Additionally, the debate continues as to the magnitude and timing of West Antarctic Ice Sheet (WAIS), Antarctic Peninsula Ice Sheet (APIS) and East Antarctic Ice Sheet (EAIS) advance during the LGM. Here we present geologic and geophysical evidence from the southern and eastern continental shelves of the WSE that show diachronous retreat by the WAIS and EMS. Detailed analysis of sediment cores display a retreat stratigraphy in the WSE with distal glacimarine sediments overlying proximal glacimarine deposits and till. These results, in combination with AMS radiocarbon ages, demonstrate that the grounding line of the EAIS was very near that of present day as early as 30,476 cal yr BP and indicate little, if any, advance of the EMS during the LGM. In contrast, multibeam swath bathymetry data show mega-scale glacial lineations, indicative of grounded, flowing ice in two troughs on the southern continental shelf, which drain ice from the WAIS. Although there are no radiocarbon ages to absolutely constrain the timing of this grounding event on the southern continental shelf, we interpret the lineations as LGM age based on their pristine nature. Further, there are similar geomorphic features on the western continental margin where the LGM timing of APIS advance has been demonstrated. Thus, during the LGM, the Antarctic ice sheets behaved independently in the WSE.

Thesis (M.Sc.) - Carleton University, 2005. / Includes bibliographical references (p. 43-45). Also available in electronic format on the Internet.