Annual Graduate Dissertation Topic List

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SHAHLA ALI

Date Orals Passed: 03/06

Advisory Committee: B. Anderson, Stute, Winckler

Helium isotope and rare gas concentrations in rcoks.

My thesis work applies the principles of Noble Gas Isotope Chemistry to two different topics, namely Helium isotope concentrations found in the marine record as a proxy for freshwater input from melting icebergs to the Southern Ocean and the distribution of rare gas concentrations in matrix fluids recovered from cores obtained at depth in the San Andreas Fault.

1. Freshwater budgets at sites of deep water formation influence the strength of the thermohaline circulation, which provides an important ocean atmosphere link to millennial scale climate change.  Melting icebergs can be an important source of freshwater in Polar Regions.  Ice rafted debris layers in marine sediment are used as indicators of melting icebergs, but they offer little information about the volume of ice involved.  In this project, I am exploring the use of 3-He as a tracer for the volume of freshwater released by melting icebergs.  3-He is contained in Interplanetary Dust Particles (IDPs) which are accumulated in ice and marine sediments at a known rate.  Because they are incorporated throughout the ice sheet, IDPs are released wherever icebergs melt.
2. The presence of superhydrostatic fluid pressures is used to explain the low friction slip along the San Andreas Fault Zone.  We are testing this hypothesis by direct sampling of cores obtained at depth in the San Andreas Fault and measuring the distribution of rare gas concentrations in matrix fluids. U/Th decay-series-elements and K  decay in rock produce 4-He and 40-Ar as well as nucleogenic (21,22Ne) and fissiogenic (132,134,136Xe) rare gases. The entire suite of measured noble gas isotopes (3,4He, 20, 21, 22Ne, 36, 38,40Ar, 84,86Kr, and 129,131, 132, 134, 136Xe) are used to separate the non-atmospheric (produced and accumulated) from the atmospheric noble gas components. Rare gas concentrations in the matrix fluids are used to investigate fluid flow and constrain mechanics of earthquake rupture in the San Andreas Fault.

PETER ALMASI

Date Orals Passed: 03/03

Advisory Committee: deMenocal, Fairbanks, Cane

North Atlantic Holocene paleoceanography and millennial climate cycles.

North Atlantic climate has varied on centennial to millennial time scales throughout the Holocene. To assess the magnitude and spatial pattern of sea surface temperature (SST) changes during the Holocene, the feasibility of paired planktonic δ18O and Mg/Ca is assessed. Reconstructions are generated for three sub-polar sediment cores at 40-60 year time resolution from 0-14000 BP

1. Assessing paired δ18O and Mg/Ca in the Holocene North Atlantic

The potential of paired Mg/Ca and δ18O measurements to resolve 1-2 °C SST variability in the Holocene North Atlantic was evaluated in G. bulloides and N. pachyderma (d.) foraminifera. Individual components of external (calibration) and internal (measurement) errors were derived from existing calibrations, core tops from this study, and tests of cleaning procedures and laboratory reproducibility. To test the sensitivity of Mg/Ca in G. bulloides and N. pachyderma (d.) across a sub-polar North Atlantic SST gradient, paired Mg/Ca and δ18O were measured in 7 core top samples containing post-1950 radiocarbon. An exponential curve fit to Mg/Ca vs. δ18O-derived calcification temperature yielded the relation Mg/Ca=0.931±0.148*e^(0.072±0.014*T). Mg/Ca from N. pachyderma (d.) does not appear sensitive to calcification temperature in these samples, an unexpected result that may reflect sample dissolution during intense cleaning procedures

2. Holocene climate from d18O and Mg/Ca in G. bulloides down-core records

   Surface water proxy reconstructions of temperature and salinity can provide insight into mechanisms of centennial-millennial Holocene climate change by the magnitude and spatial pattern of their variability. Foraminiferal δ18O and Mg/Ca from cores in the central and eastern North Atlantic suggest that temperature and salinity varied up to 3°C during centennial to millennial cycles throughout the Holocene. Modern gradients in foraminiferal δ18O and Mg/Ca were maintained between coring sites on the Björn Drift (Reykjanes Ridge) and Feni Drift (eastern Rockall Plateau) within sample replicate error throughout the Holocene. This suggests climate change in the spatial pattern representing southward movement of the sub-polar front during centennial to millennial scale cooling. Shifts in millennial-scale reconstructed δ18O and Mg/Ca are more consistent between the central and eastern North Atlantic cores than with petrologic tracer indicators of drift ice or cosmogenic proxies for solar variability.

ZAHID AZIZ

Date Orals Passed: 11/05

Advisory Committee: Stute, Schlosser, van Geen

Local hydrology and arsenic (As) concentrations in shallow aquifers of Araihazar, Bangladesh.

Arsenic is highly toxic but a common element found in the atmosphere, soils and rocks, natural waters and organisms. However, As in drinking water probably poses the greatest threat to human health - cardiovascular disease, skin lesions; skin, lung and bladder cancers, hinders child intellectual development. WHO and US-EPA limit for As is 10 µg/L. In Bangladesh 30% of wells have elevated concentrations of As considering the Bangladesh standard 50 µg/L, which put approximately 35 millions people at risk. If we follow the WHO guideline, 46% exceed the limit and 57 million people are exposed. Scenario is worse at shallow depth (<30m) where 55% of wells are unsafe. However, aquifers are hydrogeologically and geochemically dynamic at this depth, which made me interested to take a closer look at shallow aquifers of Araihazar, Bangladesh to understand subsurface processes that control As concentrations in groundwater. 6000 private wells in Araihazar tested for As concentrations show a wide range of variability (1-1000 µg/L) both spatially and seasonally where about 60% of shallow wells have elevated dissolved As.

In my first chapter, we compared dissolved As concentrations in 5200 shallow wells with the nature of surface soils mapped with EM31 conductivity meter (a hand held geophysical instrument). Our study showed that electromagnetic (EM) conductivity reading reflects the clay percentage and the recharge capability of surface soils. We also found that low dissolved As corresponds to areas where EM conductivities of surface soils are also low and vice versa. Based on these observations we concluded that local recharge inhibits As concentrations from rising in shallow aquifers.

In second chapter, we tracked both physical and chemical processes that control dissolved As in shallow aquifers by installing a series of very shallow multilevel (depths range from 3 to 9m) monitoring wells. A time series analysis of dissolved As demonstrated a variation in concentration seasonally. This variation was explainable by simple mixing between two water masses with different chemical compositions at two depths. This mixing process was attributed to the seasonal changes in vertical and horizontal hydraulic gradients (recharge processes).

The final chapter includes a numerical groundwater model where we made an attempt to explain the observations and processes discussed in the second chapter. The groundwater flow model was simulated using the computer code known as “modflow” through a commercial interface GMS 6.0.

Over all, these works suggest that local hydrology plays an important role in the distribution of dissolved As in shallow aquifers.

DALIA BACH

Date Orals Passed: 03/07

Advisory Committee: Lerner-Lam, Kushnir, Weissel

Risk assessment and mapping of rainfall-triggered landsliding in the Caribbean Basin.

AMY BALANOFF

Date Orals Passed: 04/07

Advisory Committee: Norell, Flynn, Olsen

The evolutionary history of Oviraptorosaur.

Oviraptorosaurs are an unusual group theropod dinosaurs who possess an array of avian-like features.  These morphological similarities between birds and oviraptorosaurs are used in some phylogenetic analyses to propose a close relationship between the two groups.  Other analyses, however, suggest that this clade, along with therizinosaurs, is most closely related to Paraves (Deinonychosaurs + Avialae).  In order to more fully understand the placement oviraptorosaurs within Theropoda the relationships within this less inclusive clade need to be resolved, yet most trees for Oviraptorosauria conflict with one another.  Therefore, I propose to perform a phylogenetic analysis of the relationships within oviraptorosaur dinosaurs to help place this important group within a larger evolutionary context.

JONATHAN BARBOUR

Date Orals Passed: 03/05

Advisory Committee: Scholz, Stark, Weissel

I am focusing on the channel and hillslope processes that link extreme hydrologic events, such as tropical cyclones, to the evolution of mountain landscapes. Using a variety of data sources, including satellite imagery, digital elevation models, mesoscale atmospheric models, meteorological and river gauging station data, and field observations, I have found a remarkable link between storm frequency and emergent sinuosity along incising bedrock rivers.

Although some incised meanders may inherit their form from a past alluvial phase by strictly vertical incision, emergent incised meanders exhibit a suite of features which can only result from a simultaneous process of lateral erosion. In the western North Pacific Ocean, lateral erosion along bedrock rivers is most rapid on typhoon-prone islands such as southern Honshu, Taiwan, and northern Luzon. For geologically similar terrain, mountain river sinuosity increases linearly with the frequency of typhoon strikes, and with rainfall and discharge variability. Mean discharge and runoff, however, do not appear to exert any control on the planform morphology of these rivers. I believe that extreme rain rates, such as those associated with tropical cyclones, accelerate lateral erosion in mountain rivers by driving extreme discharges, extreme sediment loads, and extreme valley wall pore fluid pressures.

But hydrology is only half of the story. Horizontal erosion rates are also accelerated along channels cutting weaker lithologies such as the trench sediments of Shikoku, Japan and the Coastal Mountain Range of Taiwan. I am using a variety of field and laboratory measurements to quantify the effect of rock strength on mountain river meander development. Treatments of bedrock river incision and models of landscape evolution have largely neglected these processes of lateral erosion, so I am also building a theoretical framework to explain my observations.

ROB BIALAS

Date Orals Passed: 04/07

Advisory Committee: Lerner-Lam, Weissel, Buck

The Effects of Temperature, Sedimentation, and Erosion on Extensional Systems.

The rifting of continental lithosphere can be accommodated in different ways, including narrow rifts, wide rifts, and core complexes.  Many different factors can influence the style of extension expressed at a rift.  Using numerical and analytical techniques, I will explore the effects of different temperature regimes, sedimentation, and erosion on extensional systems.  These results are compared with gravity, seismic, topography, and geological data from different rifted systems, both active and ancient, to gain insight into these systems.  My current work has focused on the West Antarctic Rift System and the Gulf of California.

LOUISA BRADTMILLER

Date Orals Passed: 03/06

Advisory Committee: B. Anderson, Burckle, Martinson

Testing the Silicic Acid Leakage Hypothesis: Records of Opal Burial and ²³¹Pa/²³⁰Th from the Equatorial and Southern Oceans.

Ice core records show that atmospheric pCO₂ levels have fluctuated throughout the past 700,000 years in approximately 100,000-year cycles. These cycles also correspond to glacial-interglacial cycles, but the mechanism linking lower pCO₂ and glaciations (and vice verse) is unclear. The deep sea represents the largest reservoir of (relatively quickly exchangeable) carbon on earth, and is therefore thought to play a major role in linking these phenomena.

The Silicic Acid Leakage Hypothesis (SALH) proposed that changes in the cycling of silica in the ocean could provide an explanation for lowered pCO₂ during glaciations. Silica is a nutrient utilized primarily by diatoms, which have the potential to export a large amount of carbon to the seafloor if allowed to thrive in the presence of excess silica. The SALH suggests that during the last glacial maximum (20,000 years ago), excess silica escaped the Southern Ocean and was transported through mode waters to the major upwelling areas of the equatorial ocean off of Peru and West Africa, as well as the equatorial divergence. Here the excess silica would have fertilized diatom productivity, changing the balance of carbon export between carbonate (cocolithophorid) and silicate (diatom) producers, and therefore ocean carbon chemistry and eventually atmospheric pCO₂.

My research seeks to test this hypothesis by examining downcore records of opal burial in deep-sea cores from across the equatorial Pacific, Atlantic and Indian oceans, as well as from the Southern Ocean.  Opal is produced by diatoms as a shell, and is often well preserved in areas of high upwelling.  In addition to opal fluxes, I will measure ²³¹Pa/²³⁰Th ratios of bulk sediment as a crosscheck to detect possible periods of opal dissolution in the record.  Pa preferentially adsorbs to opal in the water column, while Th is removed as a function of total particle rain, so the ratio of the two is a good proxy for the relative amount of opal in a downcore record.  Using these two proxies I hope to quantitatively evaluate the hypothesis and provide new data and ideas to the ongoing debate surrounding the links between glaciations, ocean circulation, pCO₂ and climate.

MERRY CAI

Date Orals Passed: 10/04

Advisory Committee: Goldstein, Spiegelman, Ryan

My thesis includes two different topics. The first topic is about magma generation and differentiation at convergent margins. The approach is to study the geochemistry of arc volcanic located on thick continental crust at the Eastern Mexican Volcanic Belt (EMVB). Previous geochemical study suggested that primitive lavas erupted in this region record signature of contamination from subducted pelagic and terrigenous sediments (LaGatta, 2001, Ph.D. thesis). Using previously studied samples, I have been analyzing Hf isotope compositions of volcanic from the EMVB and sediments on the downgoing slab from deep-sea core DSDP 487 located on the oceanic crust near the trench. Hf isotopes and Nd isotopes are positively correlated in most mantle and crustal silicate rocks. However, weathering processes fractionate the parent/daughter ratios among different reservoirs so that seawater Nd-Hf isotope compositions fall out of the mantle-crust correlation trend. The pelagic sediments record the Nd-Hf isotope composition of ambient seawater. Therefore we can use Hf isotopes as a tracer to test the contamination of pelagic sediments transported into the mantle from the subducted slab. Another benefit of using Hf isotopes comes from the low mobility of Hf in fluids. Transportation of Hf from the subducting slab to the melting regime requires silicate melt phases. This then allow us to confine the physical condition of the subducting slab.

The second topic is to study the magma generation at divergent margins, focused on the Gakkel ridge. Gakkel ridge is a largely unstudied slow-spreading ridge covered by sea-ice all-year-round in the Arctic Ocean. It was long believed to produce little or no active volcanism due to its extremely slow spreading rate. Recently, geological surveys revealed that abundant volcanism are present at Gakkel ridge. Furthermore, our data suggest that a major mantle domain boundary is present along the ridge. The spreading rate decreases eastwards as the overlying lithosphere thickens. This would allow us to examine two major questions related to formation of the oceanic crust. One is the relative importance of lithosphere thickness and mantle temperature on the genesis of ocean ridge basalts. The other is the “veined mantle” hypothesis, which argues that small extent of melting preferentially sample the enriched components in the mantle and therefore produces higher heterogeneity in mid-ocean-ridge basalts. I will carry out a comprehensive isotope geochemistry study, which involves Hf, Nd, Sr Pb isotopes on basaltic lavas erupted on the Gakkel Ridge. By combining isotope data with the trace element data from other sources, we will model the trace element and isotope evolution of the region

LI CAO

Date Orals Passed: 03/05

Advisory Committee: Fairbanks, Goldstein, B. Anderson

The radiocarbon reservoir age of surface ocean water (the difference between the ¹⁴C age of the ocean surface and that of the atmosphere) reflects the balance among ¹⁴C production, the spatial variability and magnitude of ¹⁴CO₂ flux across the air-sea interface, oceanic circulation, and mixing with ¹⁴C-depleted intermediate and deep waters. For the pre-anthropogenic ocean the sea surface ¹⁴C reservoir age is about 300 - 400 years in tropical oceans and increases to 1200 years at higher latitudes in the Southern Ocean and the North Pacific. By contrast, there is little surface reservoir age gradient in the North Atlantic Ocean between 40°N and 70°N. The radiocarbon reservoir age of these surface waters is almost constant, at about 400-500 years.

The radiocarbon reservoir age of the ocean surface water is essential for linking the continental and marine climate records. I aim to measure the surface water reservoir age using fossil corals.

ANN COOK

Date Orals Passed: 03/07

Advisory Committee: Ryan, Goldberg, Malinverno

Distribution of gas hydrate on India’s eastern continental margin.

I propose to study the distribution and composition of natural gas hydrate in sub-seafloor sediments on India's eastern continental margin using direct in situ measurements, primarily well logs and borehole images, from the National Gas Hydrate Program (NGHP) in India. These data will be integrated with data from pressure cores, sediment cores and seismic surveys to evaluate the distribution of gas hydrate in its natural environment.

Borehole resistivity images from NGHP-India show high resistivity fractures, which are likely filled with natural gas hydrate; pressure cores from NGHP-India confirm gas hydrate forms in fracture veins. These gas-hydrate filled fractures on borehole images will be analyzed by picking the strike and dip of the fractures to determine the stress state at the time of fracturing.  The stress state will be related to local or regional stress and geologic history of the margin.  

Hydrate saturation will be determined from the in situ logs using the Archie's saturation equation, and as well from the decrease in bulk density in hydrate-filled fracture intervals.  Both the Archie's equation and the density-derived technique will be compared to hydrate saturation from pressure cores and any other saturation estimates.

Preliminary analysis of the data from NGHP-India is very similar to the results from the Chevron-DOE Joint Industry Project hole in Keathley Canyon, Gulf of Mexico.  Thus, the results of this study may directly affect search for gas hydrates here on the continental margins of the United States.

MARTIN COLLIER

Date Orals Passed: 03/07

Advisory Committee: Spiegelman, Kelemen, Goldstein

The message of chemical systematics in basalts revisited.

My research is generally focused on constraining the physical conditions and dynamics involved in the formation and evolution of basaltic magmas. My current projects include 1) attempting to determine the degree to which Mid-Ocean Ridge Basalt (MORB) magmas chemically may react with surrounding mantle rocks as they rise to the surface; 2) constructing dynamic Mid-Ocean Ridge simulations that calculate both solid and (reactive) fluid flow. This allows prediction of observable geochemical consequences from various melt transport mechanisms; 3) creating and exploring a new MORB database allowing the effect of 'sampling length scale' as well as geological parameters to be quantified.

GREG DOWNING

Date Orals Passed: 03/05

Advisory Committee: Hemming, Broecker, Kent

Since the onset of large-scale northern hemisphere glaciation 2.6 million years ago, the earth’s climate system has been dominated by orbitally forced glacial-to-interglacial variations. Superimposed on these variations are shorter lived, millennial-scale climate events. These include the Dansgaard-Oeschger events initially observed in the Greenland ice cores and later in North Atlantic sediment cores, and the Heinrich events, also recorded in North Atlantic sediment. Most of the evidence we have of these suborbital variations comes from the last glacial-interglacial cycle (i.e., the last 125 ky).

I am interested in characterizing these variations back through time, including 1) the last several glacial-interglacial cycles (i.e., the 100k world) 2) the Early to Mid Pleistocene (the 40k world) and 3) the Middle Pleistocene Transition, when the dominant glacial-interglacial pacing switched from 40ky to 100ky, and the magnitude of ice volume changes dramatically increased. I have begun by looking for Heinrich-like events during the penultimate glaciation using several proxies, including counts of ice rafted detritus grains, magnetic susceptibility, oxygen isotopes, and uranium-thorium sediment flux estimates. The ultimate goal of my thesis is to better understand the relationship between glacial cycles and millennial-scale climate events, and the influence of global ice volume and distribution on abrupt climate change.

CHRISTY FIELD

Date Orals Passed: 03/03

Advisory Committee: Rind, Schmidt, Hemming

Modeling climate and production-related impacts on Ice-core Beryllium-10.

In order to better understand contemporary climate change and anthropogenic climate forcings, it is necessary to quantify solar forcing, the most significant natural forcing on centennial timescales. One way to learn more about past solar changes, particularly those on multi-decadal to centennial timescales, is to study the ice-bound archives of cosmogenic isotopes: substances that are produces by collisions between galactic cosmic rays (GCR) and atmospheric oxygen and nitrogen. Examples of cosmogenic isotopes include beryllium-10 (Be10, half-life of 1.5 My), Be7 (half-life 53 days) and C14 (half-life 5730 years). Cosmogenic isotope production is related to solar magnetic activity, which modulates Earth's exposure to GCR flux. Changes in solar magnetic activity, in turn, have historically been positively correlated with changes in solar irradiance, particularly over the course of the 11-year sunspot cycle. This relationship between cosmogenic isotopes, solar magnetic activity and solar irradiance is the basis for the potential use of substances like Be10 as proxies for solar activity.

Beryllium-10 is particularly well suited for this purpose for two reasons: its long half life (compared to Be7) means that it lasts long enough to record changes over glacial-interglacial timescales, and its short atmospheric residence time (compared to C14) means that it can provide high-resolution time series in well-dated polar ice core records.

However, it is possible for climate changes -- which may or may not be related to changes in solar irradiance -- to confound solar signals in the Be10 record. Processes that affect the distribution of Be10 in the troposphere -- such as changes in stratosphere-troposphere exchange (STE) or aerosol scavenging efficiency, both of which may change with climate -- could distort the degree to which ice core records reflect production changes. Similarly, because a more or less active hydrologic cycle may dilute or exaggerate Be10 snow concentrations, any process that affects precipitation could also obscure a production-rate signal.  If Be10 is to be unambiguously used to infer solar variation, we first need a way to account for the effects of climate as they appear in the ice core record. My thesis will approach this issue in three different ways:

1. One set of modeling experiments will broadly examine how production- and climate-related changes impact Be10 deposition by separately looking at how changes in production and changes in climate (doubled CO2, reduced NADW production, volcanic eruptions) affect Be10, particularly over Greenland and Antarctica (the main sources of the ice core data).
2. A second set of experiments will address the ways in which solar-related changes in both climate and production affect Be10 over the course of the 11-year sunspot cycle. Production and climate changes resembling those that might have characterized the Maunder Minimum will also be considered.
3. Finally, a set of transient 20th-century simulations will be performed to calibrate the ways in which which Be10 is recorded differently in Greenland as opposed to Antarctica. The results of this experiment will have implications on understanding the degree to which solar activity over the past century is unusually high with respect to the past several millenia.

ALLISON FRANZESE

Date Orals Passed: 04/04

Advisory Committee: Hemming, Broecker, B. Anderson

My dissertation research applies the radiogenic and trace element geochemistry of deep-sea sediments to paleoceanography of the South Atlantic at the Last Glacial Maximum (LGM, 20,000 years ago).  I am using the long-lived radiogenic isotopes of strontium and neodymium (87Sr/86Sr and eNd) in detrital sediments as tracers of provenance (source regions) and initial excess 230Th as a constant-flux proxy, to quantify particle flux and sediment redistribution.  My research goals are to use sediment provenance and flux measurements to reconstruct the transport pathways of terrigenous sediments, and thereby understand past changes in ocean circulation patterns.  My study area is the South Atlantic Ocean, and my main focus is the region south of Africa, where waters are exchanged between the Indian, Atlantic and Southern Oceans.

In chapter 1, I demonstrate the importance of long-distance transport of particles in surface and intermediate water in the South Atlantic and show the value in the combination of sediment provenance and flux tracers.  I use these tracers to evaluate the ocean circulation changes that caused observed variability in sediment provenance south of Africa, and demonstrate that the Indian to Atlantic exchange was probably reduced at the LGM.

In chapter 2, I focus on the region of the Agulhas Retroflection, the dynamic and turbulent region south of Africa where the inter-ocean exchange occurs.  By using sediment provenance tracers, I can map the location of the retroflection, and will determine whether it was different at the LGM.
In the final chapter, I will “ground-truth” the strontium isotope tracer by combining core top analyses with analyses of water column particulates.  This project involves the application of new sediment processing techniques, as it is the first of its kind.  These combined measurements should give me greater insight into the sediment sources and transport mechanisms in the Agulhas Current, even allowing me to determine how far suspended particles travel in the Agulhas Current before settling to the sea floor.

This thesis will provide new insights about the Agulhas Current system both today and at the LGM, from the unique perspective of the terrigenous sediments.  It will also serve as an example of what we can learn from the combination of several terrigenous sediment proxies, hopefully furthering their application to other oceanographic regions and other periods in Earth’s history.

ANDRES GIALLOMBARDO

Date Orals Passed: 04/06

Advisory Committee: Flynn, Norell, Christie-Blick

New cretaceous mammals from Mongolia and the early diversification of eutheria.

For their great diversity, complete (in comparative terms) fossil record, and well-studied life history, mammals (and particularly fossil mammals) have played a major role in our understanding of evolution. Many key concepts and ideas originated on the study of mammals were later applied to the more general theory of evolution.

The initial part of my research will consist on describing two newly discovered and fairly complete Cretaceous eutherians from the Gobi desert. Mesozoic eutherians are rare and usually fragmentary, and any addition has a potential large impact on our understanding of early eutherian diversification. Moreover, the two new taxa seem to be related to two of the most controversial groups in mammalian systematics, Zalambdalestidae and Zhelestidae. I will add these two new taxa and 20 other genera of eutherians to a recently published data matrix (63 taxa, 408 characters) (Wible et al. 2007), and perform a cladistic analysis based on morphology, using parsimony as the optimality criterion.

Currently, there are three competing general hypotheses about the timing of mammalian evolution: long fuse, short fuse and explosive radiation models. I expect the outcome of my phylogenetic analysis to support one model more than the other two. Constraining the time of origin of the more successful group of living mammals  (Placentalia) would allow a better idea of the context in which that process took place. In turn, this will make possible to address questions such as the role that continental fragmentation, climate change, the K-T mass extinction, etc. played in driving eutherian and placental mammalian evolution.

DAVID GRASS

Date Orals Passed: 03/04

Advisory Committee: Cane, Chillrud, Rosenzweig, Kinney

Modelling the Impacts of Global Warming on Biometeorological Conditions, Air Pollution, and Human Health in the Urban Environment.

One of the greatest challenges in modern epidemiology has been quantifying the impact on human health of prolonged exposure to air pollution. Meanwhile, growing concern over the health consequences of climate change has led to numerous studies of weather and health. Yet most studies only speculate as to the combined impacts of both weather and air pollution. These impacts are often claimed to be "synergistic" or "interactive", but few studies have measured whether the combined effects are antagonistic, additive, or non-linear. The present study aims to refine our understanding of the basic atmospheric processes that influence the transport and deposition of atmospheric pollutants, evaluate the relative and absolute importance of weather and pollution to human mortality rates, and examine the role of climate variability and climate change in modifying the relationships between pollution, weather, and health.

The first phase of this project uses a synoptic climatological approach to identify regional weather patterns associated with poor air quality and elevated cardiopulmonary, respiratory, and all-cause mortality in the Central Valley of Chile. The second phase considers the implications of trends in weather patterns over New York City and Santiago for air pollution conditions and human health. Lastly, the health risks of air pollution and biometeorological conditions are evaluated for the shared indoor space where the greatest number of people spend the greatest amount of time: the subway system. This microenvironment is characterized in terms its response to climate change forecasts for the 2020s, the 2050s, and the 2080s, and in terms of occupational exposures to air-borne metal particulates.

AMY GUAN

Date Orals Passed: 03/06

Advisory Committee: Ou, Gordon, Chen

Shear dispersion: its role in formation of the Antarctic Bottom Water and coastal seasonal thermocline.

R. CHADWICK HOLMES

Date Orals Passed: 04/05

Advisory Committee: Webb, Menke, Tolstoy

Oceanic Crustal Structure in Unique Mid-Ocean Ridge Environments.

Advances in ocean bottom instrumentation and techniques for seismic data analysis have given marine scientists a clearer picture of oceanic crustal structure.  Yet with clarity comes complication; studies now indicate oceanic crust can vary significantly from the basic 6-7 km thick 3-layer model where velocity gradients are linear and the Moho is a sharp discontinuity.  Much of this variability occurs near plate boundaries, particularly in close proximity to mid-ocean ridge systems where new crust is continuously created.  Does this reflect local stress differences changing the thickness of young lithosphere, inhomogeneities in the upper asthenosphere leading to non-uniform melting and underplating, or more regional differences at the whole plate level?  What controls thickness differences between individual seismic "layers," and can this vertically-stratified velocity model truly describe the physical structure of oceanic crust?

In my thesis, I will examine these issues by studying crustal velocity structure within several different tectonic settings.  With data captured primarily by ocean bottom instruments, I will explore:

1. The structure of young (~6 Ma) oceanic crust in the southern East Pacific Rise region with a 2D seismic refraction line that crosses non-hotspot ridge systems seemingly unrelated to normal mid-ocean ridge processes.
2. The variation in crustal thickness both on and off-axis from seismic refraction experiments conducted along several segments of the Southeast Indian Ridge where the character of the mid-ocean ridge system progressively changes from the classic slow-spreading to fast-spreading morphology but the spreading rate remains ~75 mm/yr.
3. The crustal structure of the Australian Antarctic Discordance zone and its implications on the geodynamics of this anomalous region.

KEVIN JONES

Date Orals Passed: 03/06

Advisory Committee: Goldstein, Hemming, B. Anderson

Exploring Neodymium Isotopes of Seawater in the Modern and Ancient Oceans.

My dissertation focuses on the study neodymium (Nd) isotopes in seawater and in ferro-manganese (Fe-Mn) oxy-hydroxide sediments to further explore their usefulness as a paleoceanographic tracer. I am using an ocean general circulation model to better understand Nd isotopes in the modern ocean and to identify the importance of internal sources in different ocean basins. Additionally, I am analyzing seawater collected near the coast of South Africa to test for the existence of internal sources of Nd in this region. In the same study area I will also compare the Nd isotope composition of proximal Holocene Fe-Mn oxy-hydroxide sediments from the same depths to determine their ability to record the Nd isotopes of modern seawater. If I find that the sediments do accurately record the Nd isotopes of seawater in this region and that internal sources of Nd are absent, then I will analyze sediments dating back to the Last Glacial Maximum (~18,000 years ago) to determine whether or not ocean circulation was different during this period of drastically different climate.

MIRIAM JONES

Date Orals Passed: 03/06

Advisory Committee: Peteet, Griffin, J. Hays

Vegetation response to climate change in subarctic Alaska through the Holocene and Late-glacial.

DAN KSEPKA

Date Orals Passed: 04/05

Advisory Committee: Norell, Meng, Olsen

The phylogeny, histology and functional morphology of fossil penguins (Sphenisciformes).

The shift from aerial to underwater flight is one of the most radical transitions in avian evolution. Penguins, archetypical wing-propelled divers, possess a rich fossil record and yield insight into this transition. Here, data from comparative osteology, dissections, CT imaging and bone microstructure are combined in a phylogenetic framework to explore penguin evolution, emphasizing assembly of the underwater flight apparatus.

Taxonomic revision grounded in quantifying intraspecific variation results in invalidation of 4 species and erection of 2 new species. Phylogenetic analysis of 60 penguin taxa utilizing 221 morphological characters and 5 genes yields a well-resolved consensus tree that exhibits strong fit to stratigraphy and indicates numerous Tertiary dispersal events.
Synapomorphies of the forelimb are spread throughout the cladogram.  Dissection of 5 penguins guides identification of osteological correlates of muscles and retia mirabilia, illuminating key soft tissue transitions. The basal penguin Waimanu lacks features related to downstroke efficiency (hyperelongate coracoids) and transfer of thrust from wing to body (paddle-like scapula for expanded scapulohumeralis caudalis) seen in all other penguins.  Crownward, proximal displacement of the latissimus dorsi insertion (more efficient thrust transfer), and reduction of intrinsic muscles and joints (immobilizing the wing during the thrust-producing upstroke) occur.

Histological sections document significantly lower bone density in basal penguins, demonstrating osteosclerosis progressed in the clade via increased remodeling of peripheral medullary trabeculae into compact bone.  Reticulate vascular canals and absence of LAGs imply rapid attainment of adult size in giant (>60kg) fossil taxa. CT-rendered endocasts reveal stem penguins possessed a hypertrophied flocculus and sagittal eminence (suggesting complex diving capability) but retained cranial sinuses lost in extant penguins.

This study provides a context to explore whether forelimb reorganization, osteosclerosis and neuroanatomy evolve along a similar or alternate trajectory in other clades of underwater fliers (i.e., Plotopteridae and Alcidae).

KATIE LEONARD

Date Orals Passed: 03/06

Advisory Committee: Christie-Blick, Tremblay, Weissel

Antarctic Snow Drift Processes.

My research combines numerical modeling, field observations, and remote sensing to study the redistribution of snow by the wind, with particular emphases on the role of drift in reshaping the Antarctic ice sheet surface and fresh water input to the southern ocean.  Aeolian transport of snow is important in many environments due to climatic and fresh water budget implications, but is principally studied at the interface between snowy regions and society, e.g. in relation to avalanching, or road management and construction.  Snow drift is also a potentially significant but poorly understood component of the mass balance of the Antarctic ice sheet.  The redistribution of snow by the wind can lead to substantial errors in local estimates of ice sheet mass balance as determined from stratigraphic methods.  Such point measurements are used as checks for mass balance and ice sheet models, and understanding drift processes should provide better estimates of the error of such measurements. Additionally, the amount of snow blown off the edges of the continent into the Southern Ocean is very poorly constrained, and may be as much as 10% of the total annual snowfall over Antarctica. When this snow leaves the ice sheet it plays a role in sea ice and polynya formation as well as air-sea interaction over open water.

JINBAO LI

Date Orals Passed: 04/05

Advisory Committee: Griffin, Cook, Peteet

Moisture Variability across China and Mongolia from Instrumental Data and Tree-ring Records.

China and Mongolia (CM) are located in a region characterized by complex topography and climate. Due to the varying effects of multiple climate forcings, moisture availability within the CM varies dramatically. Understanding on the occurrence of droughts/floods over this diverse area is limited, partly due to the shortness of instrumental data. In order to recover long-term moisture changes, tree-ring analysis is essential, as growth rings of trees provide the exactly-dated, annually resolved estimates of past climate. My research is focused on developing a large tree-ring network over China. Along with the available data from Mongolia, we can reconstruct moisture variability during the last several hundred years for much of CM. With such a more complete record we are able to understand how moisture has varied and what are the forcings of its variability. This knowledge will help to improve the prediction of moisture variations on annual to decadal and longer time scales.

ANDREW MADOF

Date Orals Passed: 03/07

Advisory Committee: Christie-Blick, Anders, Martinson

The non-eustatic mechanisms modulating sedimentation in salt-withdrawal intraslope mini-basins, north-central Green Canyon, Gulf of Mexico.

OUSMANE NDIAYE

Date Orals Passed: 11/05

Advisory Committee: Sobel, Ward, Martinson

Predictability of Sahelian Climate Characteristics and Impacts.

My thesis focuses on understanding and predicting rainfall variability and its impacts (year to year and within the season) over the Sahelian region of West Africa. The Sahel region is a transition zone between desert to the North (Sahara desert) and tropical forest to the South. Rainfall in this region strongly influences many aspects of society, including agriculture (crop production and livestock), water resources, and vector born disease outbreaks (malaria is the by far the first cause of mortality). Many studies, both statistical and dynamical, have related Sahelian rainfall variability to patterns of Sea Surface Temperature (SST), and a degree of predictability of the large-scale circulation patterns and associated seasonal rainfall totals in the region is well established.

A key issue concerns the changes in SST anomalies that take place in boreal spring and that currently limit the lead-time of seasonal predictions for the June-September rainfall season. One aim of the study is to provide a definitive analysis of this limitation, along with its reasons and possible ways to increase the lead-time of predictions beyond that currently achieved in models. A comparison of statistical and dynamical methods will be made.

Less is also known about how the large-scale predictability translates into ability to provide information on small spatial scales, and on the statistics of weather events through the season. These issues relate to how predictions can be made for variables like crop yield and vegetation greenness, and environmentally influenced diseases such as malaria. Through analysis of datasets and model outputs, key space and timescale prediction issues will be addressed, along with some key impact variables. The work will include more focused and detailed analyses on Senegal, comprising the westernmost zone of the Sahel, bordering the Atlantic Ocean.

STERLING NESBITT

Date Orals Passed: 10/06

Advisory Committee: Olsen, Norell, Christie-Blick

The relationships and rise of the archosaurs.

KORI NEWMAN

Date Orals Passed: 04/06

Advisory Committee: Menke, Cormier, Nedimovic

Application of new geophysics techniques on margins and ridges.

PHILIP ORTON

Date Orals Passed: 03/06

Advisory Committee: Martinson, McGillis, Sobel

Coastal Ocean Turbulent Mixing and Air-Sea CO₂ Fluxes.

A major uncertainty in global carbon budgets and predictions of future climate is the role of the tidal rivers, estuaries and the coastal ocean.  My Ph.D. research examines the physical controls on air-water transfer of carbon dioxide in these systems, primarily the role and sources of turbulent mixing near the sea surface. The overriding goal is to address how numerical models can most efficiently replicate this gas transfer, facilitating the inclusion of coastal ocean CO2 fluxes in global carbon budgets and climate models. Possible components include:

Variability of internally generated turbulence in an estuary, from 100 days of continuous observations. In press, Continental Shelf Research. (with M. Visbeck): Recent publications have developed a methodology called the “variance method” for remotely quantifying turbulence through the water column using Acoustic Doppler Current Profilers (ADCPs). We present detailed ADCP observations of internally generated turbulence in a sheared, stratified natural flow, as well as an analysis of the external factors leading to its generation and temporal variability.

Turbulence and stratification in the Hudson River estuary (with M. Visbeck, W. McGillis): This is the first comprehensive summary of stratification and turbulence in the Hudson River estuary, including measurements from a wide range of along-estuary locations, riverflow, and semi-diurnal tidal range.

Physical controls on air-water transfer of carbon dioxide in a partially mixed estuary (with W. McGillis, C. Zappa): I have been anchoring a small catamaran in the Hudson to make measurements of currents, turbulence, water column density structure, CO2 fluxes, and wind. I will analyze CO2 flux data against ambient forcing variables and compare the observations against a series of theories and models of increasing complexity.

Physical controls on continental shelf air-sea CO2 fluxes: Autonomous in situ observations (with W. McGillis, J. Moisan): I was awarded a 2007 summer fellowship to utilize NASA's autonomous 20' boat called OASIS (Ocean-Atmosphere Sensor Integration System) to study the physical controls on continental shelf air-sea CO2 fluxes. An additional goal is to evaluate the potential for using multiple OASIS platforms, satellite remote sensing data, and model assimilation for a larger-scale study that covers multiple shelf provinces and quantifies the global role of continental shelves in the carbon cycle.

RAN QIN

Date Orals Passed: 03/05

Advisory Committee: Buck, Keleman, Carbotte

Consequences of faulting and diking processes at Mid-Oceanic Ridges: Insights from modeling.

Plate spreading at Mid-Oceanic Ridges is accommodated by both magmatic and amagmatic activities. Dike intrusion is the main magmatic component, through which magma is injected into the ridge axis and forms new oceanic crust. Normal faulting presents the amagmatic component that offsets the oceanic crust and lifts the gabbro or mantle into the oceanic crust. Across Mid-oceanic Ridges under sea, we see that magmatic activities decreases with ridge spreading rate and the ridge topography changes from axial highes (e.g., East Pacific Rise, 300~400 meter above the background) to rift valleys (e.g, Mid-Atlantic Ridge, 1~2 km deep), along with the changes of tectonic features. This apparent correlation leads to the question how faulting and diking activities may have collaborated to shape the mid-oceanic ridges as they look like today.

My thesis research will use analytical and numerical modeling based on continuum mechanics to show: (1) the basic mechanism of rift valley formation through normal faulting, typical at slow spreading ridges; (2) the physics behind dike intrusions: the width and shape of a dike, when and why dike intrudes,  and the corresponding instantaneous and post-diking seafloor deformations; (3) In geological time scale, when the dike intrusions are coupled with faulting process, how they will shape the ridge topography, tectonic features (e.g., oceanic core complexes), and how they are related to magma budget.

BYRDIE RENIK

Date Orals Passed: 03/06

Advisory Committee: Christie-Blick, Anders, Keleman

A critical assessment of evidence for extreme crustal extension across the Death Valley region, California-Nevada.

JOY ROMANSKI

Date Orals Passed: 05/03

Advisory Committee: Del Genio, Rossow, Sobel

Investigating the Role of Diabatic Heating in Global Atmospheric Circulation and Climate Sensitivity:  An Energetics Approach.

The circulation of the atmosphere is driven by the equator-to-pole temperature gradient.  Exactly how this takes place, however, is the result of complex interactions among the various components of the climate system.  One way to look at these interactions is via the Lorenz energy cycle, which describes the response of the atmosphere to different sources of energy.

This study focuses on the generation of the energy available to drive atmospheric circulation.  Contributions to the zonal mean and eddy available potential energy from latent heating from precipitation, surface sensible heat fluxes and radiative flux convergence are examined to elucidate how the various processes responsible for diabatic heating affect the atmospheric energetics.

The energy cycle is characteristic of a particular climate.  The extent to which it varies under different climates is investigated using model output generated for the Intergovernmental Panel on Climate Change's Fourth Assessment Report.  Output from models exhibiting large and small sensitivity to doubled carbon dioxide is examined to determine how the energy cycle might change in a warmer climate, and how these changes relate to the models' climate sensitivity.

PAUL SCHMIEDER

Date Orals Passed: 04/06

Advisory Committee: Schlosser, Ho, Simpson

Investigations of Estuarine Mixing Using Deliberate Tracers.

My research investigates the small scale mixing dynamics and transport mechanisms associated with estuaries.  Many coastal waterways currently suffer from the effects of urbanization and industrialization in the form of polluted and contaminated water.  To understand the impact of contamination, the hydrodynamics of these water bodies must be quantified.  Through the use of deliberate tracers such as SF6 (sulfur hexafluoride), we can gain insight on how mixing is affected by water stratification, river geometry, and tides.  We can also use our tracer technique to quantify advection, dispersion, gas exchange, and residence times for these water bodies.

KYLA SIMONS

Date Orals Passed: 08/02

Advisory Committee: Goldstein, Langmuir, G. Hemming

Lithium isotope variability: new constriants on mantle heterogeneity.

ABBY SPIELER

Date Orals Passed: 03/05

Advisory Committee: Schlosser, Smethie, Martinson

Transient tracer studies of ocean circulation in the Arctic Ocean and Nordic Seas.

SANPISA SRITRAIRAT

Date Orals Passed: 03/07

Advisory Committee: Peteet, Griffin, deMenocal

Multiproxies analyses of past vegetation, climate, and sediment dynamics in Hudson River wetlands.

DEBRA TILLINGER

Date Orals Passed: 03/07

Advisory Committee: Gordon, Ou, Thurnherr

The Indonesian throughflow and its variability.

The Indonesian Seas are only low latitude conduit in the world ocean. Through their complex set of straits, the Indonesian Throughflow carries 10 million cubic meters of water per second from the Pacific Ocean to the Indian Ocean, altering the heat and freshwater budgets of both. This flow is variable on multiple temporal and spatial scales.

The objective of my research is to investigate the interannual time variability of the ITF transport and along channel speed with respect to El Nino-Southern Oscillation and the Indian Ocean Dipole Mode. The research will also include a broader examination of the role of the ITF in global heat transport. It will include observational in situ data from moorings in the Makassar Strait, the main route of the Indonesian Throughflow. The work will also incorporate historical hydrographic data and model output into a framework of geophysical fluid dynamics.

CHRIS WALKER

Date Orals Passed: 03/03

Advisory Committee: Anders, Scholz, Christie-Blick

A gravity slide origin for the Mormon Peak detachment.

The Mormon Peak detachment is an enigmatic, low-angle surface that cuts almost all other structures in the Mormon Mountains of southeast Nevada.  It has been described both as a large-magnitude offset, low-angle normal fault and as a rootless gravity slide.  The predictions of each of these models were tested and the gravity slide model was found to explain the geology exposed in the range, while the extreme extension model could not.  Specifically, kinematic indicators on the detachment showed down-dip motion, structure contours delimited discrete domains, exhumed structures indicated no large-magnitude offset, thermochronological modeling indicated basin-wide uplift at  ~ 20Ma, field mapping indicated pervasive and long-lived high-angle normal faults with spatially and temporally restricted detachment formation events, and measurements of the volume of rock contained in the hanging wall show it required only a small source area with respect to the size of the range.

The regional extension from the Meadow Valley Mountains to the Beaver Dam Mountains was found to be around 25%, an order of magnitude less than previously interpreted.  The lessons learned from the Mormon Mountains were applied to several interpreted detachment faults elsewhere and a set of –criteria proposed to help future workers distinguish between low-angle normal faults and other structures.

DAVID WANG

Date Orals Passed: 03/05

Advisory Committee: Cane, Seager, Chen

Thermocline Structure in the Eastern Tropical Pacific: the Roles of Upwelling, Turbulent Mixing and Meridional Overturning Circulation.

Under normal conditions, the trade winds blow from east to west over the tropical Pacific, driving the surface water to pile up in the western Pacific "warm pool" and causing a shoaling of the thermocline in the east. This mean thermocline slope provides a stage on which El Nino–Southern Oscillation (ENSO) phenomena are able to perform. Achieving a realistic thermocline structure is therefore crucial for ENSO modeling and forecasting. However modern coupled general circulation models (CGCMs) still have substantial biases in simulating ENSO variability, which can be partly attributed to the diffuse mean thermocline in the Eastern equatorial Pacific in various CGCMs. Intermediate anomaly models for ENSO simulation (e.g., Zebiak and Cane 1987) using a prescribed mean thermocline derived from observations often outperform more sophisticated CGCMs. Here we propose a research plan to tackle this problem by examining the roles of equatorial upwelling, turbulent mixing and shallow meridional overturning circulation in the maintenance of thermocline structure in the eastern equatorial Pacific, with emphasis on equatorial upwelling. We would start from the argument that the heat balance in the equatorial thermocline at the eastern Pacific is to the first approximation maintained by upwelling (cooling) and turbulent mixing (heating), and vertical motions, not well simulated in GCMs, pull the thermocline apart. Equatorial upwelling is the ascending limb of the shallow meridional overturning circulation that connects poleward surface Ekman flow, subduction in the subtropics, equatorward return flow within the thermocline and equatorial upwelling into a closed circuit. Therefore this shallow circulation system, which itself is steered by surface momentum, heat and buoyancy fluxes, imposes a dynamical constraint on the thermal structure of the equatorial thermocline.

KAREN WOVKULICH

Date Orals Passed: 04/07

Advisory Committee: Simpson, Chillrud, Stute, Mailloux

Mobilization of Arsenic from Contaminated Sediments.

My research focuses on arsenic cycling in the environment and specifically on the mobilization of arsenic from sediments at the highly contaminated Vineland Chemical Company Superfund site in southern New Jersey.  Arsenic is the second most common contaminant of concern at U.S. Superfund sites, and contaminated groundwater is often remediated using pump and treat technology.  However, arsenic can sorb to iron and aluminum oxyhydroxides in the sediments making pump and treat remediation less effective and thus slower to reach the desired level of clean up, as has been the case at Vineland.  Therefore, my current research aims to improve the efficiency of pump and treat by increasing the mobilization of arsenic from the sediment into the groundwater.  This project involves laboratory experiments in which I make chemical amendments to soil columns and monitor their effect on arsenic mobility as well as hydrological modeling.  These experiments will lead toward in situ field testing of the most promising chemical amendments. The information gained from these laboratory and field studies should be applicable to numerous arsenic contaminated sites where pump and treat remediation is currently being used or where it may be used in the future.  Additionally, what we learn in this work about factors that influence arsenic mobility may also help us understand arsenic cycling and mobilization in areas of the world where naturally occurring arsenic is contaminating groundwaters that are being used for drinking water supplies.

PENG XIAN

Date Orals Passed: 04/03

Advisory Committee: Del Genio, Miller, Kushnir

The interaction of Dust Aerosol Heating with the Hadley Circulation.

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