Paul T. Gayes

Records of prehistoric hurricanes on the South Carolina coast based on micropaleontological and sedimentological evidence, with comparison to other Atlantic Coast records

Singleton Swash on the South Carolina coast provides an extended record of storm events for this coast. We used experience gained by looking at storm traces detected as layers of offshore foraminifera intercalated with marsh sediments from a known storm in the area ( Hugo, which occurred in 1989) to detect storm horizons from the sediments that have been accumulating in Singleton Swash since 5700 yr B.P. We suggest here that the most intense storm activity occurred in the 0–1000 yr B.P. interval (six storms); only three occurred in the 1000–2000 yr B.P. interval and two in the 2000–3000 yr B.P. time interval (calibrated radiocarbon years). There was one giant storm in the pre–5000 yr B.P. interval; a sea-level oscillation in the 3500–5000 yr B.P. interval appears to have destroyed most records during that period. Previous work suggests that the position of the Bermuda (or Azores) High influences the direction of general storm paths for major North Atlantic hurricanes: a position of the Bermuda High farther to the south tends to force storms into the Gulf of Mexico, whereas a northern position allows them to track up the Atlantic Coast. Results here combined with results of other workers on the Gulf Coast suggest a more southern position for the Bermuda High, causing more storms on the Gulf Coast in the interval of 1000–3400 yr B.P. Conversely, a more northern position during the past 1000 yr is suggested to have contributed to higher frequencies of storms on the Atlantic Coast in that period. To test this hypothesis, modern records of the movement of the North Atlantic Oscillation (NAO, which controls the position of the Bermuda High) have been compared with historical records of hurricane tracks over the twentieth century. There does appear to be a strong correlation between the position of the NAO and the track the storms have pursued in modern times.

Geologic Evidence for Onshore Sediment Transport from the Inner Continental Shelf: Fire Island, New York

ABSTRACT Schwab, W.C.; Baldwin, W.E.; Hapke, C.J.; Lentz, E.E.; Gayes, P.T.; Denny, J.F.; List, J.H., and Warner, J.C., 2013. Geologic evidence for onshore sediment transport from the inner continental shelf: Fire Island, New York. Sediment budget analyses along the south shore of Fire Island, New York, have been conducted and debated in the scientific and coastal engineering literature for decades. It is well documented that a primary component of sediment transport in this system is directed alongshore from E to W, but discrepancies in volumetric sediment budget calculations remain. An additional quantity of sand, averaging about 200,000 m3/y is required to explain the growth of the western segment of the barrier island, a prograding spit. Littoral sediment derived from updrift erosion of the coast, addition of beach nourishment fill, and onshore transport of inner continental shelf, shoreface sediments, or both have all been proposed as potential sources of the additional sediment needed to balance the sediment budget deficit. Analysis of high-resolution seafloor mapping data collected in 2011, including seismic reflection profiles and inteferometric sonar acoustic backscatter and swath bathymetry; comparison with seafloor mapping data collected in 1996–1997; and shoreline change analysis from 1933 to 2011 support previous suggestions that the inner-shelf Holocene sedimentary deposit is a likely source to resolve this sediment budget discrepancy.

A Review of Sediment Budget Imbalances along Fire Island, New York: Can Nearshore Geologic Framework and Patterns of Shoreline Change Explain the Deficit?

Abstract Sediment budget analyses conducted for annual to decadal timescales report variable magnitudes of littoral transport along the south shore of Long Island, New York. It is well documented that the primary transport component is directed alongshore from east to west, but relatively little information has been reported concerning the directions or magnitudes of cross-shore components. Our review of budget calculations for the Fire Island coastal compartment (between Moriches and Fire Island Inlets) indicates an average deficit of 217,700 m3/y. Updrift shoreline erosion, redistribution of nourishment fills, and reworking of inner-shelf deposits have been proposed as the potential sources of additional sediment needed to rectify budget residuals. Each of these sources is probably relevant over various spatial and temporal scales, but previous studies of sediment texture and provenance, inner-shelf geologic mapping, and beach profile comparison indicate that reworking of inner-shelf deposits is the source most likely to resolve budget discrepancies over the broadest scales. This suggests that an onshore component of sediment transport is likely more important along Fire Island than previously thought. Our discussion focuses on relations between geomorphology, inner-shelf geologic framework, and historic shoreline change along Fire Island and the potential pathways by which reworked, inner-shelf sediments are likely transported toward the shoreline.

Quaternary Geomorphology and Modern Coastal Development in Response to an Inherent Geologic Framework: An Example from Charleston, South Carolina

Abstract Coastal landscapes evolve over wide-ranging spatial and temporal scales in response to physical and biological processes that interact with a wide range of variables. To develop better predictive models for these dynamic areas, we must understand the influence of these variables on coastal morphologies and ultimately how they influence coastal processes. This study defines the influence of geologic framework variability on a classic mixed-energy coastline, and establishes four categorical scales of spatial and temporal influence on the coastal system. The near-surface, geologic framework was delineated using high-resolution seismic profiles, shallow vibracores, detailed geomorphic maps, historical shorelines, aerial photographs, and existing studies, and compared to the long- and short-term development of two coastal compartments near Charleston, South Carolina. Although it is clear that the imprint of a mixed-energy tidal and wave signal (basin-scale) dictates formation of drumstick barriers and that immediate responses to wave climate are dramatic, island size, position, and longer-term dynamics are influenced by a series of inherent, complex near-surface stratigraphic geometries. Major near-surface Tertiary geometries influence inlet placement and drainage development (island-scale) through multiple interglacial cycles and overall channel morphology (local-scale). During the modern marine transgression, the halo of ebb-tidal deltas greatly influence inlet region dynamics, while truncated beach ridges and exposed, differentially erodable Cenozoic deposits in the active system influence historical shoreline dynamics and active shoreface morphologies (block-scale). This study concludes that the mixed-energy imprint of wave and tide theories dominates general coastal morphology, but that underlying stratigraphic influences on the coast provide site-specific, long-standing imprints on coastal evolution.

Iceberg scours along the southern U.S. Atlantic margin

Rapid climate fluctuations associated with ice-sheet oscillations have resulted in pulses of iceberg discharge that are recorded by iceberg scour marks along continental shelves and ice-rafted debris deposits across the North Atlantic. Iceberg transport is largely controlled by ocean surface currents; therefore, iceberg trajectories can serve as a proxy for paleo-circulation studies. Records of iceberg transport from ice-rafted debris (i.e., Heinrich layers) in the North Atlantic suggest that most icebergs released during Quaternary glaciations were entrained in a cyclonic subpolar gyre restricted to polar and mid-latitudes; however, new data suggest that there may have been an additional southerly component of transport along the western Atlantic margin. Here, we present evidence of extensive iceberg scouring across the upper slope offshore of South Carolina, ~1000 km south of the proximal ice margin during Quaternary glacial maximums. The location and orientation of the keel marks suggest that icebergs were entrained in a southwestward-flowing coastal current. At present, warm waters of the rapid, northeastward-flowing Gulf Stream bathe the upper slope off the southeastern United States. An offshore shift in the Gulf Stream axis during sea-level lowstand may have allowed glacially fed coastal currents to penetrate farther south. This may be the first evidence of iceberg rafting to subtropical latitudes in the North Atlantic.

Migration of the Pee Dee River system inferred from ancestral paleochannels underlying the South Carolina Grand Strand and Long Bay inner shelf

Several generations of the ancestral Pee Dee River system have been mapped beneath the South Carolina Grand Strand coastline and adjacent Long Bay inner shelf. Deep boreholes onshore and high-resolution seismic-reflection data offshore allow for reconstruction of these paleochannels, which formed during glacial lowstands, when the Pee Dee River system incised subaerially exposed coastal-plain and continental-shelf strata. Paleochannel groups, representing different generations of the system, decrease in age to the southwest, where the modern Pee Dee River merges with several coastal-plain tributaries at Winyah Bay, the southern terminus of Long Bay. Positions of the successive generational groups record a regional, southwestward migration of the river system that may have initiated during the late Pliocene. The migration was primarily driven by barrier-island deposition, resulting from the interaction of fluvial and shoreline processes during eustatic highstands. Structurally driven, subsurface paleotopography associated with the Mid-Carolina Platform High has also indirectly assisted in forcing this migration. These results provide a better understanding of the evolution of the region and help explain the lack of mobile sediment on the Long Bay inner shelf. Migration of the river system caused a profound change in sediment supply during the late Pleistocene. The abundant fluvial source that once fed sand-rich barrier islands was cut off and replaced with a limited source, supplied by erosion and reworking of former coastal deposits exposed at the shore and on the inner shelf.

Monitoring Beach Renourishment along the Sediment-Starved Shoreline of Grand Strand, South Carolina

Abstract In this paper, we examine temporal and spatial beach profile volume changes, sediment budget changes, and side-scan sonar images at nourished beaches of northeastern South Carolina. Results of bulk volume change indicate that most sands eroded from the subaerial beach section remain and circulate within the coastal system. The results also indicate more active sediment exchange between the nearshore and offshore zones than expected, indicating that the offshore can be both a sink and a source for the nearshore morphologic change. Our profile volume change results do not show a unidirectional net southerly transport pattern in the study area during the initial postnourishment period. Instead, results show that the net downdrift direction alternates along the shore and that longshore volume drift patterns are often disrupted by the seaward cross-shore transport events that occur at erosional hotspots. Prenourishment erosional patterns, particularly local areas of elevated erosion rates, were re-established after nourishment. Furthermore, those erosional locations often correspond to the offshore locations of paleoriver channel fill sands with low relief, indicating existence of the specific seaward transport pathways along the shore in the study area.

Impact of the Charleston Ocean Dredged Material Disposal Site on nearby hard bottom reef habitats

The deepening of shipping and entrance channels in Charleston Harbor (South Carolina, USA) was completed in April 2002 and placed an estimated 22 million cubic yards (mcy) of material in the offshore Charleston Ocean Dredged Material Disposal Site (ODMDS). To determine if sediments dispersed from the ODMDS were negatively affecting invertebrate and/or finfish communities at hard bottom reef areas around the disposal area, six study sites were established: three close to and downdrift of the ODMDS and three upcurrent and farther from the ODMDS. These sites were monitored biannually from 2000 to 2005 using diver surveys and annually using simultaneous underwater video tows and detailed sidescan-sonar. In general, the sediment characteristics of downdrift sites and reference sites changed similarly over time. Overall, the hard bottom reef areas and their associated communities showed little evidence of degradation resulting from the movement of sediments from the Charleston ODMDS during the study period.

Systematic Coastal Monitoring: The S. Carolina Coast (USA)

A statewide monitoring program has been documenting changes within the beach and nearshore system along the South Carolina coast since 1993. Additional beach and geophysical surveys completed at recent beach nourishment projects have provided a consistent means to assess project behavior over long periods. Response of three recently nourished beaches has generally, followed the pre-nourishment patterns of erosion. Historical hotspots and highly vulnerable areas rapidly lost the constructed subaerial beach sand while adjacent areas maintained volume near or in some cases above expected levels. Localized exchange of sediment across the shoreface, observed in profiles and time series of side scan sonar mosaics, may explain some of the deviation between theoretical and observed fill behavior.

Great Lakes Water Levels: Decomposing Time Series for Attribution

Great Lakes water levels have been trending downwards throughout the 20th and into the 21st Centuries. Potential causes are numerous. There have been dredging and water diversion projects over the last 110 years, increasing demand for fresh water consumption from a rising population, and considerable variations in environmental factors (rainfall, snowfall, air temperature and wind), all causal in nature. A thorough assessment of United States federal agency and laboratory data archives of time series of winds, air temperatures, rainfall and snowfall, and water level data, reveals that falling lake levels can be linked to rising air temperatures. Non-uniform, post-glacial, isostatic adjustments of the entire Great Lakes region has further complicated the system as land mass tilting causes localized uplift or subsidence that has also altered relative water levels. A mathematical decomposition of the various data sets and accessory calculations strongly indicate regional atmospheric temperature increases over the entire 20th century and the early 21st century resulting in increased evaporation, is the dominant driving factor in the continued downward trend of water levels in the Great Lakes. Moreover, a high degree of correlation was discovered in comparing water level in the Great Lakes with the comparable temporal variability and record length trends evident both the Global (Land and Ocean) Surface Temperature Anomaly time series and the Atlantic Multi-Decadal Oscillation. It is of note that there have been several water level events since 2013 from which the long term losses of fresh water have undergone a change and the lakes have gained fresh water. This received a great deal of attention in both the public press and a scientific newsletter and shows that there is a danger in only dealing with a small portion, 2 years, of a 120 year climate record.