UNC Coastal Studies Institute

Nags Head, United States

UNC Coastal Studies Institute

Nags Head, United States
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Walsh J.P.,East Carolina University | Walsh J.P.,UNC Coastal Studies Institute | Corbett D.R.,East Carolina University | Corbett D.R.,UNC Coastal Studies Institute | And 4 more authors.
Continental Shelf Research | Year: 2014

The stratigraphic record is the manifestation of a wide range of processes, interactions and responses to environmental drivers. Understanding the functioning of river sediment dispersal systems is necessary to determine the fate of sediment and associated material in the marine environment and differentiate key influences in the development of the stratigraphic record. To that end, this study uses sediment cores collected on four successive cruises (January, May and September 2010 and February 2011) on the Waipaoa River margin, New Zealand, to provide insight into spatial and temporal variability in sediment deposition and seabed character.The Waipaoa River discharges a large sediment load into an energetic coast that has a complex margin morphology. Several flood and wave events occurred during the study, and sedimentation varied spatially and temporally. X-radiographs and short-lived radioisotopes indicate emplacement of new event layers prior to all cruises. Notable variation in surficial seabed character (grain-size composition, loss-on-ignition percentage) was apparent on the inner shelf (water depths <40m), but mid-shelf areas and seaward had more homogeneous sediment properties. 7Be inventories indicate variable patterns of deposition related to fluvial and oceanographic conditions prior to cruises. Ephemeral sediment storage occurs on the inner-shelf of Poverty Bay, into which the Waipaoa River discharges directly, and subsequent export and dispersal patterns are linked to the relative timing and size of flood and wave events. Surficial deposits with characteristics of fluid muds and wave-enhanced sediment gravity flows were noted at some (<25 sites total) mid-shelf and shallower sites from all cruises. During the last cruise considerable inter- and intra-site seabed variability occurred in the interbedded river-proximal inner-shelf deposits over spatial scales of less than a few kilometers. Evidence from earlier sidescan data infer that this could be related to variation in bedform development or influence. Contrasts in the observed event layering recorded over the experiment with the longer pattern of accumulation suggests stochastic dispersal behavior and reworking over time must shape the seabed to produce the time-averaged pattern of shelf sediment accumulation. This research highlights our improved ability to comprehend strata development and sheds light on the challenge of interpreting historical and ancient strata across spatial and temporal scales. © 2014 Elsevier Ltd.


Kniskern T.A.,Virginia Institute of Marine Science | Mitra S.,East Carolina University | Orpin A.R.,NIWA - National Institute of Water and Atmospheric Research | Harris C.K.,Virginia Institute of Marine Science | And 4 more authors.
Continental Shelf Research | Year: 2014

An ephemeral oceanic-flood deposit adjacent to a well-studied small mountainous river (SMR), the Waipaoa River in northeastern New Zealand, was characterized using multiple proxies, including radioisotopes (234Th, 7Be, and 210Pb), bulk organic carbon abundance and isotopic signature (%OC, δ13C), as well as a biomarker of terrigenous organic matter (lignin). Field sampling was conducted within two weeks after a 1-in-8 year flood that occurred between January 30 and February 6, 2010. Geochemical analyses indicated that initial deposition of fresh riverine material extended alongshore to the north and south from the river mouth. A comparison of prior- and post-flood 7Be inventories revealed that flood sediments were widely dispersed between 20 and 70m water depth, accounting for 50-80% of the estimated flood load. Surface (0-2cm) isotopic carbon values increased with distance from Poverty Bay, positively correlating with total 210Pb activities, potentially reflecting increasing marine influence with water depth. Abundances of sedimentary organic carbon (OC) were 0.18-0.76% dry weight, and the total nitrogen varied from 0.02 to 0.13%. Stable isotope signatures of carbon (δ13COC), nitrogen (δ15N), and lignin abundances (λ6) throughout the study area ranged from -23.6 to -27.7‰, 1.9 to 5.3‰, and 0.93 to 9.0mg 100mg OC-1, respectively. The spatial distribution pattern of terrigenous organic matter (OM) abundance and interclass ratios (indicative of freshness of organic matter) varied along and across-shelf. Lignin abundances were high and interclass ratios were low in the southern depocenter and inner shelf areas, suggesting that this zone had recently received vascular-plant enriched OM, minimally altered by shelf-bed mixing processes. In contrast, sediments in the northern depocenter and outer shelf also contained elevated amounts of terrigenous sedimentary OM, but this material was generally lower in lignin abundance and had higher interclass ratios (greater degradation). Collectively, these results suggest that the flood-derived sediment and fresh terrigenous OM were mostly constrained between 20 and 70m water depth, with enhanced deposition overlapping the tectonic-controlled depocenters located to the northeast and southeast of Poverty Bay. © 2014 Elsevier Ltd.


Romans B.W.,Virginia Polytechnic Institute and State University | Castelltort S.,University of Geneva | Covault J.A.,University of Texas at Austin | Fildani A.,Statoil | And 2 more authors.
Earth-Science Reviews | Year: 2015

Earth-surface processes operate across erosionally dominated landscapes and deliver sediment to depositional systems that can be preserved over a range of timescales. The geomorphic and stratigraphic products of this source-to-sink sediment transfer record signals of external environmental forcings, as well as internal, or autogenic, dynamics of the sedimentary system. Here, we evaluate environmental signal propagation across sediment-routing systems with emphasis on sediment supply, Qs, as the carrier of up-system forcings. We review experimental, numerical, and natural examples of source-to-sink sediment routing and signal propagation during three timescales: (1) historic, which includes measurement and monitoring of events and processes of landscape change and deposition during decades to centuries; (2) centuries to several millions of years, referred to as intermediate timescale; and (3) deep time. We discuss issues related to autogenic dynamics of sediment transport, transient storage, and release that can introduce noise, lags, and/or completely mask signals of external environmental forcings. We provide a set of conceptual and practical tools for evaluating sediment supply within a source-to-sink context, which can inform interpretations of signals from the sedimentary record. These tools include stratigraphic and sediment-routing system characterization, sediment budgets, geochronology, detrital mineral analysis (e.g., thermochronology), comparative analog approaches, and modeling techniques to measure, calculate, or estimate the magnitude and frequency of external forcings compared to the characteristic response time of the sediment-routing systems. © 2015 Elsevier B.V.


Muglia M.,UNC Coastal Studies Institute | Seim H.,University of North Carolina at Chapel Hill | Haines S.,University of North Carolina at Chapel Hill
OCEANS 2012 MTS/IEEE: Harnessing the Power of the Ocean | Year: 2012

Surface currents off of Cape Hatteras North Carolina observed with a 5 MHz coastal ocean radar were analyzed to determine the location and variability of the shoreward edge of the Gulf Stream based on the region of maximum horizontal shear. The method for identifying the front is described in detail. A Coastal Ocean Radar (Codar) from Codar Ocean Sensors installed on the beach in Buxton, North Carolina has been operating from the fall of 2003 until the present. The Codar measures the radial component of the surface current and has a range from 100 to 200 km with spatial resolution decreasing as a function of range in 5.85 km range cell increments. Each radial vector produced is an average in an annulus bounded by a 5.85 km range difference and a five-degree bearing difference. The most probable location for the shoreward location of the Gulf Stream front is identified by the maximum horizontal shear in the radial velocities. Frontal locations are estimated by the maximum derivative of the radial speed with respect to bearing at a given range, and by the maximum derivative with respect to range at a given bearing. A third order piecewise spline curve was then fit to the combined set of gradient components. The locations where the Gulf Stream first enters and exits the radar coverage area are apparent in the large radial speeds measured by the radar, however in a region between these two zones the Gulf Stream is perpendicular to the radar, and the radar can not provide a good approximation for stream location based on this method. © 2012 IEEE.


Muglia M.,UNC Coastal Studies Institute | Seim H.,University of North Carolina at Chapel Hill | Haines S.,University of North Carolina at Chapel Hill
2015 IEEE/OES 11th Current, Waves and Turbulence Measurement, CWTM 2015 | Year: 2015

A decade of coastal ocean radar surface current observations of the Gulf Stream off Cape Hatteras, NC have been collected that offer to provide key new insights into the temporal and spatial variability of the Gulf Stream in this region. The Gulf Stream is believed to have a profound influence on the complex current dynamics off of Cape Hatteras, NC that result from the convergence of many different water masses in the region. Although essential to understanding oceanography off the NC coast, and to linkages beyond the region, Gulf Stream variability in this area has been difficult to quantify because of the challenge involved in obtaining observations of consistent spatial and temporal resolution over long time periods. Analysis of Long Range Seasonde Coastal Ocean Radar (Codar) ocean surface current measurements from two sites in NC may provide estimates of the landward Gulf Stream edge over a nearly continuous ten-year period. Radar surface current measurements are made hourly, more frequently than satellite measurements, and provide more consistent coverage of the Gulf Stream than many historical measurement techniques. The 5MHz radars typically make surface current measurements across the entire cyclonic shear zone on the landward side of the Gulf Stream. These measurements may provide methods to define Gulf Stream location, width, transport and variability of these properties over time and alongshore, providing insights into the current dynamics off Cape Hatteras, NC. We here present a method to identify the landward Gulf Stream position and width of the cyclonic shear zone from radar surface currents. The method of front detection developed associates the landward Gulf Stream front with maxima in the radial current shears. Maxima are chosen within regions of consistent coverage over the time period sampled. The locations where the Gulf Stream first enters and exits the radar coverage area are apparent as large radial speeds measured by the radar, and one bearing is chosen from each region for analysis. However in a region between these two zones the Gulf Stream is perpendicular to the radials and the method can not be used. This method can be applied to each of three radars located in the vicinity of Cape Hatteras. © 2015 IEEE.


Eulie D.O.,East Carolina University | Walsh J.P.,East Carolina University | Walsh J.P.,UNC Coastal Studies Institute | Corbett D.R.,East Carolina University | Corbett D.R.,UNC Coastal Studies Institute
Limnology and Oceanography: Methods | Year: 2013

Previous studies of shorelines have relied on satellite imagery or airplane-based aerial photography, which can be costly, of limited availability, and of restricted resolution. These factors limit the usefulness of such imagery for detailed shoreline-change measurements that require frequent observations with high spatial accuracy. Easily deployed balloon-based photography systems can provide high spatial and temporal resolution images at relatively low cost. This study used an Aerostat balloon photography system along with real-time kinematic (RTK) GPS to observe subannual changes in the shoreline position of the Albemarle-Pamlico Estuarine System (APES), North Carolina, USA. The fine (0.03 m-pixel) resolution of Aerostat images is ideal for mapping shoreline areas although limited in spatial extent. Features digitized from these images compare well in position (0.5 ± 0.5 m) and accuracy (± 0.4 m) to in situ RTK-GPS surveys. The balloon system is best used concurrently with RTK-GPS surveys to obtain the highest possible georectification accuracy. Results demonstrate that this method is well suited to high-accuracy analysis of shoreline positions over short timescales (annual to subannual), and that the balloon images provide a valuable spatial context for any measured changes. Preliminary analysis of shoreline change across the APES highlights great spatial and temporal complexity. Annualized rates of change reached > 30 m/y, but average net changes were modest for survey periods (-0.5 m to 0.04 m). Tropical systems (e.g., Hurricane Earl) can be key drivers of the observed shoreline response, and the associated sediment dynamics likely have important ecological (e.g., submerged-aquatic-vegetation and water quality) ramifications. © 2013, by the American Society of Limnology and Oceanography, Inc.


Muglia M.,UNC Coastal Studies Institute | Lowcher C.,University of North Carolina at Chapel Hill | Taylor P.,UNC Coastal Studies Institute | He R.,North Carolina State University | And 3 more authors.
OCEANS 2015 - MTS/IEEE Washington | Year: 2015

North Carolina and Florida are likely the only two states on the US east coast that have practical access to energy extraction from the Gulf Stream. After leaving the Florida Straits, the Gulf Stream in the region offshore of Cape Hatteras, NC exhibits the least variability in position of any location on the east coast, while simultaneously being closest to land. Gulf Stream current speeds exceed 2 m/s. These important characteristics have made this area the focus of observations and regional model estimates to quantify the hydrokinetic energy that may be available from the Gulf Stream for the state of North Carolina. © 2015 MTS.


Muglia M.,UNC Coastal Studies Institute | He R.,North Carolina State University | Lowcher C.,University of North Carolina at Chapel Hill | Bane J.,University of North Carolina at Chapel Hill | And 2 more authors.
MTS/IEEE OCEANS 2015 - Genova: Discovering Sustainable Ocean Energy for a New World | Year: 2015

North Carolina and Florida are likely the only two states on the US east coast that have practical access to energy extraction from the Gulf Stream. After leaving the Florida Straits, the Gulf Stream in the region offshore of Cape Hatteras, NC exhibits the least variability in position of any location on the east coast, while simultaneously being closest to land. Gulf Stream current speeds exceed 2 m/s. These important characteristics have made this area the focus of observations and regional model estimates to quantify the hydrokinetic energy that may be available from the Gulf Stream for the state of North Carolina. Three types of observations to quantify the energy resource off NC began in 2013. A 150 kHz Acoustic Doppler Current Profiler (ADCP) was moored on the 225-m isobath at the location estimated to be best for energy extraction, and recovered after two consecutive nine- and ten-month deployments, respectively. Another ADCP was moored in nearly the same location to continue observations, and will be retrieved in August 2015. Currents from the first deployment averaged 1.15 m/s, and the power density was 779 W/m2 at a depth of 30m over the 9-month duration. Significant variability in current speed, and thus power, occurred over the deployment period. Additionally, current measurements from a vessel mounted 300 kHz ADCP were made from water depths of 100m to 1000 m on a cross-isobath transect that passed over the location of the ADCP mooring. Currents measured from the vessel compare favorably with those from the moored 150 kHz ADCP in both magnitude and direction, and provide valuable information about the spatial variability of the current and its dependence on depth. In 2013, a coastal ocean radar (Codar) was added to an existing radar network that had been measuring ocean surface currents for more than a decade in the region to expand coverage over the entire study area. The radar current measurements provide consistent spatial and temporal coverage throughout the Gulf Stream cyclonic shear zone, and are being used to measure the variability in Gulf Stream position off of Cape Hatteras, NC. One method being developed using measurements from individual radars assumes the landward Gulf Stream front lies along selected maxima in the radial current shears chosen for consistency over the time period sampled, and magnitude. The locations where the Gulf Stream first enters and exits the radar coverage area are apparent in the large radial speeds measured by the radar, and the width and variability of the Gulf Stream cyclonic shear zone is estimated using maxima in velocity and velocity shears. Favorable comparisons between the three current observations will provide confidence that power estimates can be extrapolated from the radar surface currents alone over long time periods when ADCP information may not be available. Finally, observations are being compared with a regional specific Mid-Atlantic Bight and South Atlantic Bight (MABSAB) Model. Moored ADCP current measurements compared favorably with the model, demonstrating the skill of the model for power estimates in this area. Averaged current measurements 30 m below the surface from the ADCP mooring made between August 2013-April 2014 and model estimates at the same location were nearly identical, both having average current speeds of 1.15 m/s. The model is more conservative than the observations with respect to higher frequency fluctuations in speed and direction. © 2015 IEEE.

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