Summer Research Internships for Undergraduates
Last Glacial Maximum ocean circulation simulated by PMIP3 climate models
Melissa Breeden, Atmospheric and Oceanic Science major, University of Wisconsin
CEOAS mentor: Andreas Schmittner
Presented at 2012 Fall Meeting, American Geophysical Union, San Francisco, CA, December 3-7
The ocean circulation during the Last Glacial Maximum (LGM; 21,000 before present) may have been much different from today as suggested by various geochemical proxy records, with possible implications for climate and the carbon cycle. The Paleoclimate Modeling Intercomparion Project 2 (PMIP2) showed that climate models produced widely varying results concerning the Atlantic Meridional Overturning Circulation (AMOC) strength and structure. Here we analyze data from new model simulations that have recently been performed as part of PMIP3. In contrast to PMIP2, the five models that have so far been analyzed all show a strengthening in the flow of the North Atlantic Deep Water current. The models are less consistent with respect to the Antarctic Bottom Water in the Atlantic, however; three models simulate an increase whereas two simulate a decrease. Inflow of Circumpolar Deep Water into the Indian and Pacific oceans is either increased or not changed much. The barotropic circulation does not change much in the models except in the North Atlantic, where the subtropical gyre is stronger in all models. The Antarctic Circumpolar Current is enhanced in one model but not in the others. In the future we will explore different mechanisms that have been proposed to control the MOC, such as changes in winds, sea ice, and surface buoyancy fluxes in order to understand the reasons for the model responses.
Deoxygenation of Oregon shelf waters: a modeling study
Rachel Danielson, Earth and Environmental Science major, University of California-Irvine
CEOAS mentors: Hal Batchelder and Yvette Spitz
Hypoxia is a natural occurrence off the Oregon coast, but over the last decade or so, there have been several anomalous cases (including the summers of 2002 and 2006) of severe, sustained hypoxia and anoxia in the near-bottom water on the Oregon shelf. Because of the uncertainty of the root cause of these events, it is important to determine how remote forcing influence severe hypoxic events, and also to predict summer conditions along the coast based on the start-of-season conditions. These questions are significant because of the substantial mortality of marine life, particularly benthic species, that occurred in 2002 and 2006 due to severe hypoxia, and because these anomalous events may be indicators of a regional shift in coastal conditions in response to global climate change. The accuracy and reliability of a model to help answer these uncertainties are crucial, so the results of model simulations must be compared with field collected data. Here we have compared the output of five biological variables of several cases of a biological model coupled with a ROMS circulation model. Our results show the model has reasonable skill in predicting both nitrate and oxygen concentrations, but poor or no skill in predicting ammonium concentration and phytoplankton and zooplankton abundance.
Assessment of lipid content and classes in juvenile settled flatfish
Kathryn Doering, Marine Science and Biology major, University of Miami
CEOAS mentor: Lorenzo Ciannelli
English sole, Parophrys vetulus, is a species of flatfish found off the northwest coast of North America with commercial and ecological value. After pelagic egg and larval stages, English sole metamorphose and settle as juveniles in both nearshore coastal and estuarine nursery environments. The lipid content and composition of juvenile English sole collected off of Moolack Beach, a nearshore coastal nursery environment, and in Yaquina Bay, an estuarine nursery environment, will be compared through use of gas chromatography with flame ionization detection (GC/FID). The total extractable lipids (TEL) and triacylglycerol to sterol (TAG:ST) ratios will be quantified for individual fish samples in order to assess fish body condition. These data will then be compared between the two nursery habitats and over the progression of the summer season in order to determine habitat quality and the effects of different environmental conditions such as dissolved oxygen and temperature on the body condition of the juvenile English sole. Warmer temperatures can cause higher metabolism and growth rates in flatfish, and lower DO concentration stresses fish; these factors can lower body condition. Ultimately this information can be used to manage the English sole fishery appropriately.
Observing diagenesis on the Oregon Margin through a paleomagnetic lens
Alejandra Dominguez, Environmental Science major, Columbia University
CEOAS mentor: Joe Stoner
Four cores from the Oregon Margin at water depths ranging from 120 m to 450 m were studied by progressive AF demagnetization of u-channel samples. This highly productive location, well known for reductive diagenesis and magnetic dissolution, contains sediments with high accumulation rates that could provide important paleomagnetic archives. The magnetic properties of all sites are consistent with each other, revealing dramatic decreases in magnetic concentration within the top 50 cm of all cores. Unlike the conventional diagenetic model, however, these cores exhibit a magnetic dissolution that occurs at two fronts, indicating a migration in the sulfate-methane transition (SMT). This new magnetic diagenetic model also suggests that pyritization during early diagenesis leads to the progressive down-core growth of the ferrimagnetic iron sulfide greigite at the inferred position of the SMT. Future work will focus on assessing the difference between the age of the sediment by comparing these greigite recorded and radiocarbon-dated paleomagnetic records with regional paleomagnetic secular variation (PSV) templates, thereby temporally constraining this chemical remanent magnetization process in a range of environments.
Characterization of the microbial community of a hydrothermal vent system at the Chilean triple junction
Erick Dowell, Biology major, University of North Carolina
CEOAS mentor: Rick Colwell
Since the discovery of hydrothermal vents in 1977 and methane-rich cold-seeps in 1984, research has demonstrated them both to be biodiversity "hot-spots" sharing evolutionary histories and certain taxa within the relatively barren deep-sea benthos. Hydrothermal vent and cold-seep ecosystems are both dominated and regulated predominantly by methane concentrations and sulfide concentrations contained in the escaping fluid. Vents and seeps differ in temperature, fluid flow, substrates, and available geochemical nutrients that reflect in different dominant metabolisms (hydrogen oxidation, sulfide oxidation, and anaerobic oxidation of methane (AOM) in vents and AOM/ sulfate reduction (SR), aerobic methanotrophy, and sulfide oxidation in seeps) and ecosystem biodiversity (lower in vents and higher in seeps). A similar environment on Costa Rica Margin exhibits characteristic of both environments forming a "hydrothermal seep." The Chilean triple junction (CTJ) presents a similar contexture to the reducing habitat on the Costa Rica margin where regions that exhibit vent and seep characteristics exist in close proximity. These habitats likely represent that these environments exist on a biogeochemical continuum. If the unique mix of biogeochemical factors of several distinct ecosystems at the CTJ has created a novel, hybrid environment, then we predict the local microbial biodiversity should increase and the bacterial and archaeal endemics should coexist in the same area. A 16S rRNA amplicon approach was used to analyze the microbial diversity down a 35-cm sediment column from a recently discovered warm mud area in the CTJ. We will then ask whether the biological communities structure and diversity may be driven or explained by geochemical and physical factors also measured on the core using multidimensional statistical analysis based on covariance. Further phylogenetic analyses will be done as needed. Finally, analyses of core top-water and water-column samples will test whether the resident biodiversity is a mixture of vent and seep communities representing microbial dispersal or show the average water-column assemblages. If the biodiversity reflects the heterogeneity of the CTJ's unique biogeochemistry then we propose that diversity should be higher than vent or seep communities alone and include taxa from both vent and seep ecosystems.
Spatial and temporal structure of fluxes between a lateral embayment and the Columbia River estuary channel
Samuel Haugland, Physics major, Kansas State University
CEOAS mentor: Jim Lerczak
Estuary channels are often bordered by lateral bays and intertidal flats, which have shallow water depths but large surface areas compared to the neighboring estuary channel. Lateral bays play an important role in production of biogeochemicals in costal margins, and large biogeochemical fluxes are believed to be exchanged between lateral bays, estuary channels, and ultimately the coastal ocean. Due to seasonal weather variation, quantification of biogeochemical production is difficult. To quantify the spatial and temporal structure of water mass and biogeochemical fluxes between an intertidal lateral bay (Cathlamet Bay) and the main channel of the Columbia River estuary, surveys were conducted over semidiurnal tidal cycles during high river flow (May/June) 2012. A shipboard downward facing ADCP was used to take continuous measurements on current velocity while at three to five sampling stations along the transect a profiling package measured conductivity, temperature, water depth, dissolved oxygen concentration, chlorophyll fluorescence and optical backscatter. By comparing data from the wet and dry season, we study the influence of salt stratification and buoyancy forcing on the spatial and temporal structure of water mass exchange at the bay/estuary interface as well as gain an understanding of the role of lateral bays in biogeochemical production.
Holocene variations in paleoproductivity and hypoxia along the Oregon Margin
Conor Maginn, Geology major, Bates College
CEOAS mentor: Jennifer McKay
Presented at Northeastern Section Annual Meeting, Geological Society of America, Bretton Woods, NH, March 18-20, 2013
Recent hypoxic events off the Oregon coast within the last decade have been considered especially severe as they occupied a large area (3000 km2) and resulted in mass mortalities throughout the marine ecosystem. To determine whether these occurrences are part of a naturally variable system or due to anthropogenic influences, this study examined a sediment core collected off the Oregon coast. Trace metal (Mo, Re) and minor element (Mn, Al) geochemical analyses were conducted on the core and revealed a likely upwelling-induced hypoxic event in the last few thousand years (2-4 ka), although the age model is not well constrained. The data suggest a hypoxic event occurred in the past due to natural climate variability, and is thus likely susceptible to anthropogenic climate change.
Magnetotelluric investigation of Newberry Volcano and implications for enhanced geothermal systems
Thomas Martin, Earth Sciences major, University of California, San Diego
CEOAS mentor: Adam Schultz
To understand the subsurface structure at the Newberry Caldera, Oregon, a 2-D inverse model will be applied to the magnetotelluric (MT) data set. The data will be collected by two long period (1 Hz sampling) Narod Geophysics NIMS instruments in late July 2012, along with previously collected EarthScope data. Using programs Occam and MatLab, it is possible to visualize the data. Utilizing the visualizations, it is feasible to determine the variations in the electrical resistivity in the mid to lower crust beneath the western flank of the caldera. This study will reveal the deep structure of the Newberry site where a proposed Enhanced Geothermal System (EGS) power plant would be located. Later in the year, six ultra-wideband MT units will be deployed. With continuous monitoring at the site will reveal the shallow temporal changes in resistivity structure, it becomes possible to monitor how pressurized fluids intrude the rock formations following a process of hydroshearing or stimulation of the EGS, which will begin in September-October 2012. This study will be deep, baseline data to provide better geologic background for further MT studies at the proposed EGS site.
Active fault mapping at the northwestern end of a growing right-lateral strike-slip fault, Klamath Basin, Oregon
Thomas Martin, Earth Sciences major, University of California, San Diego
CEOAS mentor: Andrew Meigs
We use newly-acquired LiDAR topographic data to characterize the active tectonics of the Klamath Basin in southern Oregon. Three key tectonic domains present on the western edge of the North American plate, the Walker Lane Fault Zone (WLFZ), the northwestern Basin and Range extensional province (NWBR), and the Cascade arc, intersect in the region of the Klamath Basin. Right-oblique shear across the WLFZ accommodates ~15-30% of motion between the North America and Pacific plates in eastern California and western Nevada. Geologic data indicate that the WLFZ has been growing to the northwest since its inception after ~13 Ma. The northwestern tip of the WLFZ extends northwest through eastern California into southern Oregon where it intersects the Klamath Basin and Cascade arc. The Klamath Basin is a graben and marks the western-most extent of the Basin and Range extensional province at the latitude of the California-Oregon border. Due to the intersection between the WLFZ, the western margin of Basin and Range, and the Cascade arc, it is unclear whether the Klamath Basin opened in response to northwest propagation of the WLFZ or whether the WLFZ overprints a pre-existing arc-related graben on the edge of the Basin and Range. Faults in the Klamath Basin region fall into two groups. Group 1 faults bound the Klamath Graben, are north striking, and are marked by topographic escarpments with more than 600m local relief. Quaternary alluvial deposits bury the fault traces. Fault scarps mark the traces of Group 2 faults. Group 2 faults occur within the basin and include segments that strike north and northwest, creating a complex stair-step map pattern. A systematic overprinting of relatively more eastern faults by faults to the west characterizes the Group 2 faults. Moreover, Group 2 faults cut tilt blocks associated with Group 1 faults. Topographic relief across Group 2 faults is less than ~350m. Fault scarps in unconsolidated alluvium have as much as ~2 m of vertical and ~40 m of strike slip separation. Right-oblique slip active faulting in the graben center either (A) overprints tilt blocks formed due to earlier Basin and Range extension or (B) opened the Klamath Basin and is now localized along the basin axis. Regardless, these new data reveal a previously unrecognized seismic hazard. An earthquake sequence in 1993, the Klamath Falls earthquakes, consisted of two M6 events, neither of which ruptured to the surface. The longest continuous group 2 fault, which has a ~320m vertical separation, is ~25 km long. Earthquake scaling relationships and the length and size of the scarp on this fault indicate that at least one M7 event has occurred in the Klamath Falls area, larger than any historic earthquake.