OREGON STATE UNIVERSITY
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Summer Research Internships for Undergraduates
Stratification and currents in the channel of Yaquina BayUsing current meter measurements, estuarine processes are examined in the channel of Yaquina Bay. Inquiries are made into the relationship between stratification in the water column and freshwater discharge in the estuary of Yaquina Bay. These estuarine processes affect currents in Yaquina Bay. Measurements of salinity and current velocity throughout the water column made with two conductivity, temperature, depth sensors (CTD) at the surface and base of the water column, as well as an Acoustic Doppler Current Profiler (ADCP) at the bottom, are compared to the tidal record and freshwater discharge. As freshwater discharge increases, stratification becomes stronger in the channel. Periods of low and medium discharge show a relationship between spring-neap cycles and stratification, with spring tides producing weaker stratification while neap tides produce stronger stratification, and the relationship is reversed during the period of highest discharge. Within single tidal cycles during spring and neap cycles of each period of low, medium or high discharge, distinct patterns in along and cross-channel currents and stratification were found.
Microphysical Retrieval and Rain Rates of Drizzling Stratocumulus in the Southeast Pacific OceanStratocumulus clouds play an important role in the radiation budget of the Earth. Climate models do a poor job modeling stratocumulus clouds, underestimating their radiative cooling effect, and resulting in large sea surface temperature discrepancies, the most noticeable of which is located in the southeast tropical Pacific Ocean. An understanding of the microphysical processes within clouds can provide vital insight into how to better model these stratocumulus clouds, resulting in more realistic model simulations. In 2008, the NOAA 94-GHz cloud radar measured reflectivity, Doppler velocity, and Doppler width data aboard the Ronald H. Brown on the VOCALS research cruise in the southeast Pacific Ocean. Profiles with maximum reflectivity at least 100 m below cloud base are identified as drizzling. The drop size distribution, modal radius, liquid water content, and rain rates for the drizzling stratocumulus clouds in this region were computed with the microphysical retrieval of Frisch et al. (1995). Comparing the cloud-base rain rates from the microphysical retrieval to the cloud-base Comstock et al. (2004) Z-R relationship, we find the cloud-base rain rates from the microphysical retrieval span a wider range than the rain rate predicted by the Z-R relationship. Drop size distributions with the same modal radius follow the relationship Z=aR^b with coefficient a (1184).
Microbial community distribution in methane-bearing sediments from the Ulleung BasinMicrobial communities present in methane-bearing sediments from the Ulleung Basin were examined using terminal-restriction fragment length polymorphism (T-RFLP) and PhyloChip microarray analyses. Non-metric multidimensional scaling (NMS) was used to compare microbial community compositions and to correlate communities with geochemical features of the sediment. Statistical analysis by multi-response permutation procedures (MRPP) revealed that microbial communities in hydrate and non-hydrate layers of methane-bearing sediments are not significantly different, while communities in the methane-poor sulfate-methane transition zone (SMTZ) are significantly different from the methane-bearing sediments below. It is likely that the presence or concentration of methane, hydrogen sulfide, or sulfate in sediments plays a role in determining microbial community distribution in methane-bearing and overlying sediments.
A Geochemical Model for the Petrogenesis of the Curaçao Lava FormationThe Curaçao Lava Formation (CLF), a remnant of the Caribbean plateau, serves as a record of the magmatic and tectonic processes involved in the formation of the Caribbean Large Igneous Province (CLIP). Here we present a model of the petrogenesis of the CLF developed using petrographic, geochemical, and geochronological data. These data include whole rock major and minor element chemistry obtained using X-ray fluorescence spectroscopy (XRF), mineral major and trace element chemistry obtained using electron microprobe analysis (EMPA), and ages obtained using 40Ar-39Ar dating. The wide range of 40Ar-39Ar ages (62.26 ± 0.81 Ma to 83.88 ± 1.61 Ma) obtained for the Curaçao lavas contradicts previous models suggesting that the CLF formed over a relatively short time period (1-2 m.y.). Crystallization modeling indicates that the sills and tholeiites of the CLF could potentially have formed by fractional crystallization of high-MgO parental magmas with similar compositions during at least three separate melting events.
A Foray into the Paleomagnetic Properties of Bering Sea SedimentsLack of understanding concerning the role of Bering Sea climate variability on global atmospheric and oceanic circulation patterns imposes a limit on our understanding of the causes of large-scale climate variability. This little studied region also has significant potential to inform our knowledge of the behavior of the earth's magnetic field over geological time scales due to the lack of high quality paleomagnetic data in the North Pacific. The paleomagnetic properties of sediments collected from Integrated Ocean Drilling Project (IODP) sites 1343, 1344, and 1345 were evaluated for their potential to refine the paleomagnetic record and further the understanding of environmental processes in the Bering. In addition to information collected by IODP scientists, a u-channel magnetometer was used to measure the NRM and ARM of the upper 7-10 meters of sediment at the sites. Significant magnetic mineral dissolution occurs at sites 1343 and 1345 during the Holocene. It is hypothesized that this results in a reduction and in remanence magnetism during periods of low clastic flux. During periods of high clastic flux, acquisition of magnetic remanence is acquired primarily after the sulfide-methane transition zone due to metastable greigite formation. If this hypothesis is true, then this would create an apparent offset of the age of a sediment's paleomagnetic record from the age of the sediment. Site 1344 does not display this delayed magnetic acquisition. This would result in an apparent age offset on the order of 5-10kyr between the paleomagnetic records of site 1344 and sites 1343/1345.
Compositional Characteristics of Plagioclase Crystal Size Distributions (CSDs) from the 2000 B.P. Eruption of El Misti Volcano, Southern PeruThe most recent significant explosive eruption of El Misti in southern Peru occurred 2000 yr B.P., producing considerable pyroclastic deposits and extensive lahars. Juvenile blocks from the 2000 B.P. eruption reveal the mixing of two magmas: a plagioclase rhyolite and amphibole-plagioclase andesite. To better understand the evolution of these magmas and the exchange of material during mixing, crystal size distributions (CSDs) of plagioclase were determined on five samples across the compositional spectrum to assess and quantify both the mixing relationship and cooling history of each magma. CSDs were determined via high-resolution Al Kα x-ray maps to allow for measurement of a large range of crystal sizes. Individual crystals were outlined and processed through Photoshop and ImageJ, crystal aspect ratios of plagioclase were determined through CSDSlice5, and crystal distributions were determined through CSDCorrections. CSDs for each sample are defined by two distinct slopes. CSD slopes for phenocrysts are shallow with low intercepts, reflecting low nucleation rates and low degrees of undercooling. CSD slopes for microphenocrysts and microlites are steep with high intercepts, reflecting both higher nucleation rates and cooling rates than for the phenocrysts. Kinked CSDs are associated with magma mixing, based on the assumption that different magmas have different crystal growth and compositional histories that, upon mixing, are reflected in the CSD curves. In the El Misti case, a test of composition versus crystal size yields no correlation. Both rhyolite and andesite microphenocryst and microlite CSD patterns exhibit almost identical trends, implying concurrent crystallization post-magma interaction during eruption withdrawal.
Effects of Upwelling on Salinity, Temperature, and Available Potential Energy on the Newport Hydrographic Line as Measured by Cumulative Wind Stress PeriodsObservations of salinity and temperature on the Newport Hydrographic line (NH-line, 44.65°N west of Newport, Oregon) during the upwelling season have not previously been analyzed by cumulative wind stress periods, though wind stress causes upwelling. Additionally, available potential energy evolution during upwelling on the NH-line, or the anomalous upwelling season of 2006 have not been studied in great detail. CTD data were collected by Slocum gliders and Seagliders from 2006-2010 and provide resolution greater than former data collected by research vessels. Findings include salinity and temperature evolving as supported by past findings and literature. Pre-upwelling profiles of temperature and salinity show evidence of upwelling before the official start of the upwelling season. Available potential energy increased with cumulative wind stress, and peaked at either the cumulative wind stress period between 1-2 or 2-3 N/m2 days during upwelling season. The results support the current upwelling model concerning temperature and salinity, however, the pre-upwelling profiles need further work to determine what is causing the differences between years, and wind work needs to be calculated to discover a possible connection with available potential energy and kinetic energy to complete the energy description of the shelf.
The Use of Magnetotelluric Methods to Image the Earth's InteriorMagnetotellurics (MT) is a geophysical imaging method that can be used to image the Earth's interior through measurement of natural or artificially induced variations in its magnetic and electric fields. Equipment used for MT measurements, such as the Narod Intelligent Magnetotelluric System (NIMS), produces reliable long-period MT data useful for imaging the electrical resistivity structure of the Earth to great depths. By collecting data from one site, we can use one dimensional inversion methods to determine the electrical conductivity structure of the Earth as it varies with depth beneath an OSU field site.
Satellite-guided research and prediction of river plume circulationLarge river plumes, such as the Columbia River plume, have important implications to coastal ocean dynamics because they provide a source of buoyant and nutrient-rich waters, which are distinct from surrounding ocean water in properties such as temperature, salinity, and turbidity. The plume can affect circulation, air-ocean gas exchange, and biological productivity on seasonal and inter-annual temporal scales. The density of the plume, which is dependent on salinity and temperature can affect sea surface height (SSH) thus potentially modifying both currents and eddies over the shelf. For reasons as these, it is important to fully understand river plume dynamics. In this project two dimensional ocean modeling will be used in conjunction with satellite and in-situ data to determine if the river signal can located via satellite derived sea surface temperature (SST) and sea surface height (SSH). This knowledge, combined with a better understanding of plume dynamics such as mixing and its interaction with coastal upwelling will ideally provide a more accurate assimilation of data for better modeling and forecasting of the coastal ocean.
Chemical Composition of Organic Matter in Surface Sediments of the Eel River Shelf DepocenterSmall mountainous river systems (SMRS) export large amounts of sediment from the continents to the ocean, where they typically accumulate in shelf depocenters. These depositional environments have the potential to provide high resolution records of past conditions in both land and coastal ocean because they sequester OM derived from both terrigenous as well as marine sources. In this study we investigate the distribution and composition of OM in surface sediments from shelf depocenter associated with the Eel River, a high-sediment yield SMRS in Northern California. To characterize OM in these samples a combination of elemental (e.g., %OC, C/N), isotopic (e.g., d13C, d15N, D14C) and biomarker (e.g., lignin and non-lignin derived CuO products) analyses were used. Marked contrast in the overall contents of OC and both terrigenous and marine biomarkers were found as a function of depth, reflecting well established cross-shelf trends in grain size and accumulation rates. Source indicators show terrigenous sources make up a major fraction of the OM in surface sediments with peak contributions in the highest accumulation region of the depocenter. The composition of the terrigenous OM in shelf sediments is distinct from the compositions previously determined for the suspended load of the Eel River, including higher lignin yields and a more conifer-like signature. Possible reasons include biologic (e.g., preferential degradation) and physical (e.g., hydrodynamic sorting) alteration of the river suspended load during transport to its ultimate accumulation site. Additionally, it is also likely that the signatures measured in the depocenter reflect the input of material during large floods, which have not been characterized by the river sampling to date. We discuss the implications of these findings from the point of view of reconstructing watershed conditions and processes using depocenter sediment records.
Lipid content and composition of juvenile English sole Parophrys vetulus in relation to dissolved oxygen and estuarine versus coastal habitatsThe body condition of juvenile English sole, Parophrys vetulus, is determined by the quality of the nursery location where they settle after the pelagic larval stage. Habitat quality is the result of many interacting variables, including dissolved oxygen concentration and temperature. The body condition of juvenile English sole was compared between nearshore coastal and estuarine nursery habitats, and in relation to the seasonal progression of temperature and hypoxic conditions along the central Oregon coast. Absolute total lipid content, determined gravimetrically (dry and wet weight basis), and relative triacylglycerol (TAG) to sterol composition, determined using thin-layer chromatography with flame ionization detection (Iatroscan), were taken as a measure of body condition for collected juvenile sole. ANOVA and regression analysis of resulting data revealed that changes in total extractable lipids (TEL) and TAG:sterol ratio of juvenile English sole are correlated with seasonal timing. In addition, samples which had not yet fully metamorphosed, collected early in the season from the nearshore coastal habitat, yielded much higher values of TEL than other samples. This data suggests that the value of TEL in juvenile English sole decreases significantly after metamorphosis and settlement, which is common for other flatfish species. In conclusion, a seasonal timing component was found in the relative comparison of data for total lipid content and class composition. This effect may be caused by several factors, such as development of hypoxia, differences in prey community, and progression through life cycle. Through the methodologies developed, these potential mechanisms can be more clearly resolved with further observations.