Earth Sciences Commons^™

Geology Of The Western Llano Uplift, Fredericksburg To Mason, Texas, R. Larell Nielson, Chris Barker

Faculty Publications

This year's Texas Academy of Science Geology Field Trip will visit six interesting locations in the Texas Hill Country (Figure 01). At Bear Mountain quarry, former location of Balanced Rock, the contact between the Precambrian Bear Mountain Pluton and surrounding Cretaceous Edwards Group will be examined. Along Crab Apple Creek, south of Enchanted Rock, excellent exposures of the Hickory Sandstone provide the opportunity to study sedimentary structures and cross-bedding that represent the Sauk sequence deposited during the Cambrian Period (Figure 02). Next we will look at a Gypsum Mine and deposits of evaporites from the Cretaceous Kirschberg Lagoon (Figure 03 …

Biogenic Nitrogen Gas Production At The Oxic–Anoxic Interface In The Cariaco Basin, Venezuela, E. Montes, M. A. Altabet, F. E. Muller-Karger, M. I. Scranton, R. C. Thunell, Claudia R. Benitez-Nelson, L. Lorenzoni, Y. M. Astor

Faculty Publications

Excess nitrogen gas (N2xs) was measured in samples collected at six locations in the eastern and western sub-basins of the Cariaco Basin, Venezuela, in September 2008 (non-upwelling conditions) and March 2009 (upwelling conditions). During both sampling periods, N2xs concentrations were below detection in surface waters, increasing to ~ 22 μmol N kg−1 at the oxic–anoxic interface ([O2] < ~ 4 μmol kg−1, ~ 250 m). Below the oxic–anoxic interface (300–400 m), the average concentration of N2xs was 24.7 ± 1.9 μmol N kg−1 in September 2008 and 27.5 ± 2.0 μmol N kg−1 in March 2009, i.e., N2xs concentrations within this depth interval were ~ 3 μmol N kg−1 higher (p < 0.001) during the upwelling season compared to the non-upwelling period. These results suggest that N-loss in the Cariaco Basin may vary seasonally in response to changes in the flux of sinking particulate organic matter. We attribute the increase in N2xs concentrations, or N-loss, observed during upwelling to: (1) higher availability of fixed nitrogen derived from suspended and sinking particles at the oxic–anoxic interface and/or (2) enhanced ventilation at the oxic–anoxic interface during upwelling.

Delineation And Classification Of Karst Depressions Using Lidar: Fort Hood Military Installation, Texas, Melinda G. Shaw-Faulkner, Kevin W. Stafford, Aaron W. Bryant

Faculty Publications

The Fort Hood Military Installation is a karst landscape characterized by Cretaceous-age limestone plateaus and canyons in Bell and Coryell Counties, Texas. The area is located in the Lampasas Cut Plain region of the Edwards Plateau and is stratigraphically defined by exposures of the Fredericksburg Group. Spatial interpolation of 105 km2 of the Fort Hood Military Installation provided depression data that were delineated and classified using geoanalytical methods. Most of the karst features within the study area are predominantly surficial expressions of collapse features, creating windows into karst conduits with surficial exposures of epikarst spatially limited.

The increasing capabilities of …

Evaporite Karst And Hydrogeology Of The Castile Formation: Culberson County, Texas And Eddy County, New Mexico, Kevin W. Stafford

Faculty Publications

Karst development in Permian Castile evaporites has resulted in complex speleogenetic evolution with multiple phases of diagenetic overprinting. More than 10,000 surficial features, primarily sinkholes, occur throughout Culberson County, Texas, and Eddy County, New Mexico, based on GIS-analyses where laminated Castile sulfates crop out. Cave development is largely the result of hypogene processes, where ascending fluids from the underlying Bell Canyon Formation migrate near vertically through the Castile Formation, creating caves up to 100 meters deep and over 500 meters long, which have been breached through a combination of collapse and surface denudation. Numerous small and laterally limited epigene features …

Clastic Sinkhole And Pseudokarst Development In East Texas, Kevin W. Stafford, Melinda G. Shaw-Faulkner, Wesley A. Brown

Faculty Publications

Pseudokarst development in East Texas is controlled primarily by a combination of suffosion and preferential flow paths, often creating small ephemeral sinkholes but occasionally persistent features develop in more indurated facies. Pseudokarst occurs in Claiborne (Eocene) strata in Angelina, Cherokee, Nacogdoches, Panola, Rusk, San Augustine and Shelby counties. Strata consist of interbedded fine- and coarse-grained clastics with variable cementation and associated permeabilities.

Caves And Karst Hydrology Of The Mariana Islands (Abstract), Kevin W. Stafford

Faculty Publications

Abstract Attached

Dissolved Organic Matter Composition And Bioavailability Reflect Ecosystem Productivity In The Western Arctic Ocean, Yuan Shen, Cedric Fichot, Ronald Benner

Faculty Publications

Dissolved organic carbon (DOC) and total dissolved amino acids (TDAA) were measured in high (Chukchi Sea) and low (Beaufort Sea) productivity regions of the western Arctic Ocean to investigate the composition and bioavailability of dissolved organic matter (DOM). Concentrations and DOC-normalized yields of TDAA in Chukchi surface waters were relatively high, indicating an accumulation of bioavailable DOM. High concentrations and yields of TDAA were also observed in the upper halocline of slope and basin waters, indicating off-shelf transport of bioavailable DOM from the Chukchi Sea. In contrast, concentrations and yields of TDAA in Beaufort surface waters were relatively low, indicting …

Using Marine Snails To Teach Biogeography And Macroevolution: The Role Of Larvae And Dispersal Ability In The Evolution And Persistence Of Species, Jonathan R. Hendricks

Faculty Publications

While some marine animals are capable of traveling great distances, many have limited mobility as adults and spend the majority of their lifetimes in a small geographical area or may even be cemented to a single place. While it might be expected that species with limited mobility would have small geographic distributions, some nevertheless occur over very large areas. This is the case for some marine snails (gastropods). A key factor that impacts the geographic distribution of marine snails is the type of larvae they have during the phase of their life history that follows hatching from an egg. Because …

Atmospheric Organic Material And The Nutrients Nitrogen And Phosphorus It Carries To The Ocean, Maria Kanakidou, Robert A. Duce, Joseph M. Prospero, Alex R. Baker, Claudia R. Benitez-Nelson, Frank J. Dentener, Keith A. Hunter, Peter S. Liss, Natalie Mahowald, Gregory S. Okin, Manmohan Sarin, Kostas Tsigaridis, Mitsuo Uematsu, Lauren M. Zamora, Tong Zhu

Faculty Publications

[1] The global tropospheric budget of gaseous and particulate non‐methane organic matter (OM) is re‐examined to provide a holistic view of the role that OM plays in transporting the essential nutrients nitrogen and phosphorus to the ocean. A global 3‐dimensional chemistry‐transport model was used to construct the first global picture of atmospheric transport and deposition of the organic nitrogen (ON) and organic phosphorus (OP) that are associated with OM, focusing on the soluble fractions of these nutrients. Model simulations agree with observations within an order of magnitude. Depending on location, the observed water soluble ON fraction ranges from ∼3% to …

Bioactive Trace Metal Distributions And Biogeochemical Controls In The Southern Ocean, Christopher Measures, Mariko Hatta, Maxime Grand

Faculty Publications

Extensive sampling in many regions of the Southern Ocean has demonstrated that surface water concentrations of dissolved Fe are low enough to limit phytoplankton growth. In contrast, there is currently no evidence that other bioactive elements (e.g., Mn, Zn, Co) are similarly limiting. Although atmospheric input of dissolved Fe to Southern Ocean surface waters appears to be low, resuspension of sediments from shallow regions around islands and the Antarctic coastline can inject significant amounts of Fe into the surrounding waters, stimulating primary production and providing a natural laboratory for studying the response of biological systems to natural Fe fertilization processes. …

Predicting Decadal Trends And Transient Responses Of Radiocarbon Storage And Fluxes In A Temperate Forest Soil, C. A. Sierra, S. E. Trumbore, E. A. Davidson, Serita D. Frey, K. E. Savage, F. M. Hopkins

Faculty Publications

Representing the response of soil carbon dynamics to global environmental change requires the incorporation of multiple tools in the development of predictive models. An important tool to construct and test models is the incorporation of bomb radiocarbon in soil organic matter during the past decades. In this manuscript, we combined radiocarbon data and a previously developed empirical model to explore decade-scale soil carbon dynamics in a temperate forest ecosystem at the Harvard Forest, Massachusetts, USA. We evaluated the contribution of different soil C fractions to both total soil CO2 efflux and microbially respired C. We tested the performance of the …

Potential Role Of Inorganic Polyphosphate In The Cycling Of Phosphorus Within The Hypoxic Water Column Of Effingham Inlet, British Columbia, Julia M. Diaz, Ellery D. Ingall, Samuel D. Snow, Claudia R. Benitez-Nelson, Martial Taillefert, Jay A. Brandes

Faculty Publications

[1] The upper basin of Effingham Inlet possesses permanently anoxic bottom waters, with a water column redox transition zone typically occurring at least 40 m above the sediment‐water interface. During our sampling campaign in April and July 2007, this redox transition zone was associated with sharp peaks in a variety of parameters, including soluble reactive phosphorus (SRP) and total particulate phosphorus (TPP). Based on sequential extraction results, TPP maxima exhibited preferential accumulation of an operationally defined class of loosely adsorbed organic phosphorus (P), which may contain a substantial fraction of polyphosphate (poly‐P). This poly‐P may furthermore be involved in the …

Magnitude And Composition Of Sinking Particulate Phosphorus Fluxes In Santa Barbara Basin, California, Emily Sekula‐Wood, Claudia R. Benitez-Nelson, Melissa A. Bennett, Robert Thunell

Faculty Publications

[1] The composition and bioavailability of particulate P influence marine biological community production on both modern and geologic time‐scales, and continental margins play a critical role in the supply, modification, and storage of particulate P. This study examined particulate P cycling in the Santa Barbara Basin (SBB) off the coast of southern California using a ∼520 m deep‐moored sediment trap deployed from 1993–2006 and a sediment core collected in 2005 directly beneath the sediment trap at 590 m. Total particulate P (TPP), particulate inorganic P (PIP), and particulate organic P (POP) were quantified using a 5‐step sequential extraction method (SEDEX) …

The Transcriptome And Proteome Of The Diatom Thalassiosira Pseudonana Reveal A Diverse Phosphorus Stress Response, Sonya T. Dyhrman, Bethany D. Jenkins, Tatiana A. Rynearson, Mak A. Saito, Melissa L. Mercier, Harriet Alexander, Leann P. Whitney, Andrea Drzewianowski, Vladimir V. Bulygin, Erin M. Bertrand, Zhijin Wu, Claudia R. Benitez-Nelson, Abigail Heithoff

Faculty Publications

Phosphorus (P) is a critical driver of phytoplankton growth and ecosystem function in the ocean. Diatoms are an abundant class of marine phytoplankton that are responsible for significant amounts of primary production. With the control they exert on the oceanic carbon cycle, there have been a number of studies focused on how diatoms respond to limiting macro and micronutrients such as iron and nitrogen. However, diatom physiological responses to P deficiency are poorly understood. Here, we couple deep sequencing of transcript tags and quantitative proteomics to analyze the diatom Thalassiosira pseudonana grown under P-replete and P-deficient conditions. A total of …

Mean Atlantic Meridional Overturning Circulation Across 26.5° N From Eddy-Resolving Simulations Compared To Observations, Xiaobiao Xu, William J. Schmitz Jr., Harley E. Hurlburt, Patrick J. Hogan

Faculty Publications

Observations along 26.5 degrees N are used to examine the time mean structure of the Atlantic meridional overturning circulation (AMOC) in eddy-resolving simulations with the Hybrid Coordinate Ocean Model (HYCOM). The model results yield a 5 year mean AMOC transport of 18.2 Sv, compared to 18.4 Sv based on data. The modeled northward limb of the AMOC has a vertical structure similar to observations. The southward limb is shallower than observed but deeper than other ocean general circulation models and includes a secondary transport maximum near 4000 m corresponding to Nordic Seas Overflow Water. The modeled flow through the Florida …

Permanganate Oxidizable Carbon Reflects A Processed Soil Fraction That Is Sensitive To Management, Steven W. Culman, Sieglinde S. Snapp, Mark A. Freeman, Meagan E. Schipanksi, Josh Beniston, Rattan Lal, Laurie E. Drinkwater, Alan J. Franzluebbers, Jerry D. Glover, A. Stuart Grandy, Juhwan Lee, Johan Six, Jude E. Maul, Steven B. Mirsky, John T. Spargo, Michelle M. Wander

Faculty Publications

Permanganate oxidizable C (POXC; i.e., active C) is a relatively new method that can quantify labile soil C rapidly and inexpensively. Despite limited reports of positive correlations with particulate organic C (POC), microbial biomass C (MBC), and other soil C fractions, little is known about what soil fractions POXC most closely reflects. We measured POXC across a wide range of soil types, ecosystems, and geographic areas (12 studies, 53 total sites, n = 1379) to: (i) determine the relationship between POXC and POC, MBC and soil organic C (SOC) fractions, and (ii) determine the relative sensitivity of POXC as a …

Particle Transport Over Rough Hillslope Surfaces By Dry Ravel: Experiments And Simulations With Implications For Nonlocal Sediment Flux, Emmanuel Gabet, Morgan Mendoza

Faculty Publications

Past studies of hillslope evolution have typically assumed that soil creep processes are governed by a linear relationship between local hillslope angle and transport distance. The assumption of “linear diffusion” has fallen out of favor because, when coupled with an expression of mass continuity, it yields unrealistic hillslope profiles. As a consequence, a better understanding of the mechanics of sediment transport is needed. Here we report results from a series of flume experiments performed to investigate sediment transport by dry ravel, a common soil creep process in arid and semiarid environments. We find that, at gentle slopes, transport distances follow …

Mapview And Cross Section Animations, Jason Luke

Faculty Publications

Movie 1: A series of time slices animated through the amplitude volume. Movie 2: A series of time slices animated through the semblance volume. Movie 3: Cross section animation from SW-NE through the amplitude volume. Movie 4: Cross section animation from SW-NE through the semblance volume.

H2/Ch4 Ratios Cannot Reliably Distinguish Abiotic Vs. Biotic Methane In Natural Hydrothermal Systems, Susan Q. Lang, G. L. Früh-Green, D. S. Kelley, M. D. Lilley, G. Proskurowski, E. P. Reeves

Faculty Publications

No abstract provided.

New Science, Synthesis, Scholarship, And Strategic Vision For Society, David R. Foster, Emery Boose, Elizabeth A. Colburn, Elizabeth E. Crone, Aaron M. Ellison, Clarisse Hart, Kathy Fallon Lambert, David A. Orwig, Julie Pallant, Pamela M. Snow, Kristina A. Stinson, Dianna L. Doucette, Paul R. Moorcroft, Andrew D. Richardson, J. William Munger, Adrien C. Finzi, Lucy Hutyra, Anne Short, Brian Donahue, Christopher A. Williams, William V. Sobczak, W. Wyatt Oswald, Edward K. Faison, Jerry M. Melillo, Jonathan R. Thompson, Jeffrey L. Blanchard, Elizabeth S. Chilton, Kristen M. Deangelis, Stephen Destefano, David B. Kittredge, Serita D. Frey, Scott V. Ollinger, Eric A. Davidson

Faculty Publications

Harvard Forest LTER (HFR) is a two decade-strong, integrated research and educational program investigating responses of forest dynamics to natural and human disturbances and environmental changes over broad spatial and temporal scales. HFR engages >30 researchers, >200 graduate and undergraduate students, and dozens of institutions in research into fundamental and applied ecological questions of national and international relevance. Through LTER I–IV, HFR has added historical perspectives, expanded its scope to the New England region, integrated social, biological, and physical sciences, and developed education and outreach programs for K-12, undergraduate, and graduate students, along with managers, decision-makers, and media professionals.

No-Net-Loss Not Met For Nutrient Function In Freshwater Marshes: Recommendations For Wetland Mitigation Policies, Katie Hossler, Virginie Bouchard, M. Siobhan Fennessy, Serita D. Frey, Evelyn Anemaet, Ellen Herbert

Faculty Publications

Wetlands provide many important services throughout the world, with an estimated economic value that, in comparison to other ecosystems, far exceeds their relatively small global extent. In recognition of their importance, both national and international regulations exist to protect the world's remaining wetlands. Of growing interest is the “no-net-loss” policy which permits unavoidable destruction of wetlands if compensated by restoration of degraded wetlands or creation of new wetlands. The fundamental assumption of no-net-loss is that wetlands can be created which function equivalently to natural wetlands. One integral function that wetlands perform is cycling of carbon, nitrogen and phosphorus. Here we …

Spring Hydrology Of Colorado Bend State Park, Central Texas, Kevin W. Stafford, Melinda G. Shaw-Faulkner, Jessica L. Deleon

Faculty Publications

Karst development in Ellenburger carbonates near Colorado Bend State Park in central Texas exhibits complex polygenetic origins, with porosity development dominated by an early hypogene phase that has subsequently been overprinted to varying degrees by epigene processes. Quarterly physicochemical and continuous thermal monitoring analyses of eight springs in the study area indicate that modern groundwater flow paths are highly variable. Springs exhibit patterns that range from shallow, distributed recharge into diffuse-flow dominated systems, to focused recharge into well-connected conduit systems, to deep-circulation systems that equilibrate with bedrock. All springs, except Sulphur Spring, exhibit physicochemical characteristics indicative of proximal epigenic groundwater …

Measurements And Three-Dimensional Modeling Of Nearshore Circulation On A South Carolina Beach, Nirnimesh Kumar, George Voulgaris, John C. Warner

Faculty Publications

A numerical modeling system for simulating nearshore surf zone conditions and tidal processes is presented and evaluated with in situ data. The modeling system is comprised of the Regional Ocean Modeling System (ROMS v 3.0), a three-dimensional numerical ocean model, coupled with Simulating Waves Nearshore (SWAN), a spectral wave propagation model. The system has been modified with a new vertical distribution of radiation stress terms for applications in very shallow waters. The model performance is evaluated by comparing simulations to hydrodynamic data (wave height, direction, longshore and cross-shore currents) collected in the surf zone in northern South Carolina, U.S. Model …

Two-Stepping Into The Icehouse: East Antarctic Weathering During Progressive Ice-Sheet Expansion At The Eocene–Oligocene Transition, Howie Scher, Steven M. Bohaty, James C. Zachos, Margaret L. Delaney

Faculty Publications

In conjunction with increasing benthic foraminiferal 18O values at the Eocene–Oligocenetransition (EOT; ca. 34 Ma), coarse-grained ice-rafted debris (IRD; >425 μm) appearsabruptly alongside fossil fi sh teeth with continentally derived neodymium (Nd) isotope ratios( Nd) in Kerguelen Plateau (Southern Ocean) sediments. Increased Antarctic weathering fl ux,as inferred from two steps to less radiogenic Nd values, coincides with two steps in benthicforaminiferal 18O values. These results indicate that two distinct surges of weathering weregenerated by East Antarctic ice growth during the EOT. Weathering by ice sheets during aprecursor glaciation at 33.9 Ma did not produce signifi cant IRD accumulation during the …

Detecting Toxic Diatom Blooms From Ocean Color And A Regional Ocean Model, Clarissa R. Anderson, Raphael M. Kudela, Claudia R. Benitez-Nelson, Emily Sekula-Wood, Christopher T. Burrell, Yi Chao, Gregg Langlois, Jo Goodman, David A. Siegel

Faculty Publications

[1] An apparent link between upwelling‐related physical signatures, macronutrients, and toxic diatom blooms in the various “hotspots” throughout California has motivated attempts to forecast harmful algal blooms (HABs) as a function of select environmental variables. Empirical models for predicting toxic Pseudo‐nitzschia blooms in one such region, the Santa Barbara Channel (SBC), are tested in a nowcast mode using predictions based on merging data from MODIS ocean color geophysical products and the Regional Ocean Modeling System (ROMS) applied to the Southern California Bight. Thresholds for each model generate event forecasts. Spatially‐explicit, monthly HAB maps are compared to shipboard observations and California …

A Comparative Integrated Geophysical Study Of Horseshoe Chimney Cave, Colorado Bend State Park, Texas, Wesley A. Brown, Kevin W. Stafford, Melinda G. Shaw-Faulkner, Andy Grubbs

Faculty Publications

An integrated geophysical study was performed over a known cave in Colorado Bend State Park (CBSP), Texas, where shallow karst features are common within the Ellenberger Limestone. Geophysical survey such as microgravity, ground penetrating radar (GPR), direct current (DC) resistivity, capacitively coupled (CC) resistivity, induced polarization (IP) and ground conductivity (GC) measurements were performed in an effort to distinguish which geophysical method worked most effectively and efficiently in detecting the presence of subsurface voids, caves and collapsed features. Horseshoe Chimney Cave (HCC), which is part of a larger network of cave systems, provides a good control environment for this research. …

Shelf Edge Tide Correlated Eddies Along The Southeastern United States, Dana K. Savidge, Jonathan Norman, Colton Smith, Julie A. Amft, Trent Moore, Catherine Edwards, George Voulgaris

Faculty Publications

High frequency radar observations in the Southeastern United States have revealed sequences of small short‐lived cyclonic eddies along the shoreward edge of the Gulf Stream, that spin up as the local tide turns alongshelf antiparallel to the Stream. Eddies propagate equatorward along the shelf edge, sometimes progressing shoreward before dissipating one to three hours later. They are distinctly different from Gulf Stream meander eddies, which propagate poleward. In this article, radar and mooring data are used to establish three important aspects of these neweddies: they represent an instability process operating at a previously unidentified frequency, scale, and cross‐Stream position; they …

Bedrock Erosion By Root Fracture And Tree Throw: A Coupled Biogeomorphic Model To Explore The Humped Soil Production Function And The Persistence Of Hillslope Soils, Emmanuel Gabet, Simon Mudd

Faculty Publications

In 1877, G. K. Gilbert reasoned that bedrock erosion is maximized under an intermediate soil thickness and declines as soils become thinner or thicker. Subsequent analyses of this “humped” functional relationship proposed that thin soils are unstable and that perturbations in soil thickness would lead to runaway thinning or thickening of the soil. To explore this issue, we developed a numerical model that simulates the physical weathering of bedrock by root fracture and tree throw. The coupled biogeomorphic model combines data on conifer population dynamics, rootwad volumes, tree throw frequency, and soil creep from the Pacific Northwest (USA). Although not …

Insights Into Particle Formation And Remineralization Using The Short-Lived Radionuclide, Thorium-234, Kanchan Maiti, Claudia R. Benitez-Nelson, Ken O. Buesseler

Faculty Publications

[1] Simple mass balance models are applied to a high resolution 234Th profile from the northwest Pacific to examine the magnitude, rate, and depth distribution of particle remineralization processes below the euphotic zone (Ez). Here, excess 234Th (234Th > 238U) below the Ez is attributed to fragmentation processes that result in the conversion of sinking to non‐sinking particles. By considering particulate organic carbon (POC) to 234Th ratios on particles, we show that POC flux attenuation is larger than for 234Th, which we attribute to bacterial and zooplankton consumption of sinking POC. Three case studies are used to demonstrate how different combinations …

Wind Speed Dependence Of Single-Site Wave-Height Retrievals From High-Frequency Radars, Brian K. Haus, Lynn K. Shay, Paul A. Work, George Voulgaris, Rafael J. Ramos, Jorge Martinez-Pedraja

Faculty Publications

Wave-height observations derived from single-site high-frequency (HF) radar backscattered Doppler spectra are generally recognized to be less accurate than overlapping radar techniques but can provide significantly larger sampling regions. The larger available wave-sampling region may have important implications for observing system design. Comparison of HF radar–derived wave heights with acoustic Doppler profiler and buoy data revealed that the scale separation between the Bragg scattering waves and the peak energy-containing waves may contribute to errors in the single-site estimates in light-to-moderate winds. A wave-height correction factor was developed that explicitly considers this scale separation and eliminates the trend of increasing errors …