Seasonal Variation of Water Column
Chemical and Physical Properties across the Continental Shelf, Charleston Transect
-Caroline Dietz, Leg 02
In order to begin to understand the dynamic regime of the Charleston Transect, water column chemical and physical properties were analyzed and compared for the months of November 2003 and May 2004. Water column profiles were created for temperature, salinity, chlorophyll, and density using data gathered from CTD casts taken from nine stations along the mainline of transect. In November 2003, winter mixing was evident in the inner and mid shelf, outer margin, and surface waters of the upper slope. A thermocline, pycnocline, and halocline were all observed at approximately 80m water depth, giving evidence of the permanent thermocline that forms the base of the surface layer. Waters in May were observed to be stratified in the middle shelf, outer margin and upper slope. The inner shelf shows little variation between mixing and stratification, thought to be due to its proximity to the coast. Profiles showed temperature to be the primary factor causing stratification in the water column. Chlorophyll showed no patterns of distribution reflecting stratification, regardless of season.
School of Science and Mathematics Annual Student Research Poster Session, College of Charleston, 2005
November Water Column Phosphate
(PO4 3-) Concentrations Across the Continental Shelf off Charleston, SC
-Brett Floyd, Leg 01
Phosphate nutrient concentrations within the water column are important for biological productivity. Coastal areas often have a higher concentration of phosphate present as compared to outer continental shelf waters because of riverine and anthropogenic input. To test for this, water samples were collected aboard the research vessel Savannah during November 2003 using a CTD and Niskin rosette ranging in depths from the surface to a max of 150 meters from just off the coast of Charleston, across the continental shelf, and into the Gulf Stream. Phosphate concentrations from these water samples will be measured on a UV-VIS spectrophotometer using standard colorimeter techniques. The results from these tests will show the concentration of phosphorous present across the continental shelf off the coast of Charleston, South Carolina.
Biogenic Sulfur Production in Waters
Over the Continental Shelf Off the Coast of Charleston, SC
-Nathan Garcia, Leg 01
For years scientists have been struggling to balance the global sulfur budget. Estimates show that a sulfur compound known as dimethylsulfide (DMS) contributes approximately 50% of the biogenic sulfur input to the atmosphere. This radiatively active compound is produced largely by phytoplankton (dinoflagellates and haptophytes) and can increase the reflectance of light off the earth’s atmosphere (albedo), potentially affecting global climate. While it has been hypothesized that dimethylsulfoniopropionate (DMSP, a precursor to DMS) producing phytoplankton have the ability to regulate light levels reaching the ocean’s surface, the exact significance of its cellular production is not well understood. Recent studies support the hypothesis that these sulfur compounds may be part of an anti-oxidant system. In accordance with this hypothesis, cellular DMSP production should increase in response to oxidative stressors such as high light, low iron, and low CO2 levels. Understanding the cellular function of this compound is becoming increasingly important as global CO2 levels continue to rise. This study will examine the production of particulate DMSP (DMSPP) at the ocean surface and at depths where 50% and 1% of the surface light level occurs. Water samples were filtered on board the RV Savannah over the continental shelf off the coast of Charleston, SC. Laboratory analysis of DMSPP was performed using gas chromatography by measuring the total DMS evolved when reacted with sodium hydroxide. Concentrations of DMSPP normalized to estimates of primary production (chlorophyll a) are expected to increase with increasing light levels.
Fall Chlorophyll Maxima Depth Across
the Continental Shelf off Charleston, South Carolina
-Amanda Thomas, Leg 01
Phytoplanktonic organisms are the main primary producers in marine surface waters. In temperate climates, their vertical distribution in the water column is determined by summer stratification that occurs concomitant with a shallow thermocline. This stratification disappears during the fall as turbulence due to fall storms increases and air and surface temperatures decrease. This study measures phytoplankton accumulations at specific depths over the continental shelf off South Carolina. Phytoplankton abundance is estimated by measuring the concentration of chlorophyll-a, the principal pigment of photosynthesis. In November 2003, aboard the R/V Savannah, water samples were collected with Niskin bottles from multiple depths at 17 stations along a transect line crossing the continental shelf. Water was filtered on board onto glass fiber filters and frozen in liquid nitrogen. Following the cruise, chlorophyll-a concentrations were measured using a fluorometer. This hypothesis is also tested by analyzing vertical profiles of temperature and salinity in shelf waters.
Interannual Marine Phytoplankton Community Dynamics in Continental Shelf Waters off Charleston, South Carolina
-Morgan Cawley, Leg 05
Rarely do offshore phytoplankton surveys return to the same geographic locations at the same time of year to observe interannual changes in community structure and correlate these changes to differences in oceanographic environmental variables. This study offers an interannual comparison of continental shelf phytoplankton species composition and distribution in the fall of 2004 and 2009. Undergraduate students from the College of Charleston Transect Program collected data aboard the R/V Savannah. Oceanographic data were recorded along 2 parallel transect lines stemming from nearshore waters off Charleston, SC to the western edge of the Gulf Stream. Phytoplankton samples were collected using a 20 µm phytoplankton net towed on the surface for 3 minutes. Samples were identified using Scanning Electron Microscopy at the National Oceanic and Atmospheric Administration’s Center for Coastal Environmental Health & Biomolecular Research at Charleston (NOAA - CCEHBR). Cell counts were made using light microscopy to calculate relative abundance of different phytoplankton species and ratio of diatoms to dinoflagellates. Interannual differences in the diversity and abundance of phytoplankton communities will be described and interpreted in accordance to recorded surface water environmental parameters. The abundance and distribution of the Domoic acid producing diatom species, Pseudo-nitzschia, will be highlighted because of the potential role of this harmful algae in the mortality of marine mammals.
Spatial Distribution and Characterization
of Communities of Organisms Associated with Sargassum spp. Algae in Autumn.
-Meghan Chafee, Leg 01
Sargassum spp. is a floating brown macroalgae (Division Phaeophyta) that generally forms clumps or large mats on the ocean surface providing spawning, nursing, feeding grounds, and refuge with a high structural complexity for a variety of marine organisms. Distribution and abundance data of Sargassum spp. and neustonic organisms were collected from neuston net tows across the continental shelf off the coast of Charleston (South Carolina) in November 2003. The spatial distribution of Sargassum spp. and associated species will be analyzed along the shelf transect. Use of Sargassum spp. as a spawning substrate will be tested by correlating abundances of algal clumps with adult Halobates spp. insects, which employ floating Sargassum spp. as a substrate for egg laying. Zooplankton biomass will be used as an indicator of the amount of food available for fishes associated with Sargassum spp., in an attempt to determine if algal clumps are used by fishes for feeding or as refuge.
Autumn phytoplankton species composition
and distribution across the continental shelf from the coast of Charleston,
South Carolina, to the Gulf Stream
-Elizabeth Symon, Leg 03
In November of 2004, College of Charleston students embarked on a five day oceanographic research cruise aboard the R/V Savannah along two parallel transect lines across the continental shelf off the shore of Charleston, S.C. to the Gulf Stream. Few studies have been done on phytoplankton off the southeast coast of the U.S. Phytoplankton samples were collected using a CTD. Samples were filtered and analyzed using SEM while cell counts were done using light microscopy. A ratio of diatoms (class Bacillariophyceae) to dinoflagellates (class Dynophyceae) was determined. Diatoms and dinoflagellates were classified into genus and specie level when possible to determine percent specie composition at each site sampled. Diversity was measured using the Shannon-Weaver Diversity Index and analyzed to see if a correlation existed between diversity and distance from shore. Surface maps of chlorophyll concentration, temperature, and salinity were analyzed to hypothesize what may have affected phytoplankton species composition and distribution.
The Generic Distribution of Benthic
Foraminifera along the Charleston Transect of the Continental Shelf off Charleston
-Nicole Abdul, Leg 02
Knowledge of the distribution of benthic foraminifera can provide scientists with valuable insight into reconstructing paleo-environments, paleo-bathymetry and paleo-climates. Information dating back to the Cambrian lays hidden beneath modern day oceans, trapped in the Calcium Carbonate test of these sand-sized protists. Although in excess of 700 studies have been conducted on the distribution of benthic forams around North America (Culver 1980) very few address their distribution along the eastern continental shelf. Eight sediment grab samples, collected along the Charleston Transect of the continental shelf’s inner, middle and outer shelf, in waters 11 to 96 meters were analyzed for Benthic foraminifera distribution. Preliminary results suggests the dominance of one main genus namely Quinqueloculina; however, as one moves from the inner to outer continental shelf, a distinct shift from Milliolid- to Rotalaria-dominated facies becomes evident. Although this pattern of distribution aligns well with previously documented patterns along the Southern coast of Florida and into the Gulf of Mexico, further study is required to continue the mapping of the distribution of Benthic foraminiferal assemblages along the eastern continental shelf.
Temporal and Spatial Variability in Benthic Foraminifera Fossil Assemblages off the Continental Shelf,
-Nicole Abdul (Leg 02), Dr. Leslie Sautter, Sam Crickenberger (Leg 04), Christina Skalit (Leg 04)
Benthic foraminifera are morphologically diverse Protists found in habitats ranging from the shallow inter-tidal zones of marshes and bays to the depths of the open oceans. Although globally distributed, foraminifera genera are environmentally specific and therefore knowledge of their modern day distribution can provide valuable insight into reconstructing paleo-bathymetry, paleo-stratigraphy, and ultimately paleo-climatology. Very few studies address foram distributions along the southeastern North American continental shelf. Over a two year period, four cruises were conducted as part of the Transect Program, along the Charleston Transect of South Carolina’s continental shelf. Sediment grab sample collections were conducted on each cruise at the same eight stations, in waters with depths ranging from 11 to 96 m. Between 25 and 39 benthic foraminifera genera were identified for a single cruise, with an average of 8 “dominant” genera (> 5 % of the foram genera at any station). Dominant genera consistently included Quinqueloculina, Textularia, Hanzawaia, Cibicides, Triloculina, Bigenerina, Bolivina, Eponoides, Amphistegina and Elphidium. Additionally, genera were grouped by test texture: Miliolid (porcelain tests), Agglutinate (tests composed of cemented grains), and Hyaline (glassy tests). For each cruise collection, considerable cross-shelf assemblage variability existed. However, significant temporal variability was also observed at many of the sampling stations for the four cruise collections. Although similar foraminifera genera were identified from samples collected on each cruise, the spatial distribution of dominant genera and textural groups showed a high degree of temporal variability. To some degree the distribution of foraminifera along the Charleston Transect compliments previously established and documented patterns along the Southern coast of Florida and into the Gulf of Mexico. Further studies are required to conclusively map the distribution patterns of benthic foraminiferal assemblages along North America's southeastern continental shelf. We will report on comparisons of foram assemblage variations and distribution with respect to ongoing grain size analyses and video data collected with a remotely operated vehicle.
Benthic Foraminiferal Population Distribution off the coast of Charleston, SC, November 2003
-Daniel Boles, Leg 01
In the Fall of 2003, students from the College of Charleston sailed aboard the research vessel SAVANNAH along a southwest trending transect from south of the Charleston harbor to the continental shelf edge. Samples were collected along the transect using a Smith-MacIntyre grab apparatus, and preserved in a 4% formalin/seawater solution with rose bengal dye added to stain living organisms. Sediment collected by the grab apparatus will be analyzed and described using standard analytical techniques, and living foraminifera will be counted and classified. These data will be used to show the relationship between living populations of benthic foraminifera and the grain size distribution of their respective habitat locations. This information will serve as a reference to subsequent College of Charleston Transects cruises, and future Transects students will be able to compare data to show seasonal and inter-annual changes in foraminiferal populations.
Comparison of Benthic Foraminifera Between Two Cross-Shelf Transects off Charleston, SC
-Vikki Bernotski, Leg 05
During the Transect Program in November 2009, fourteen sediment samples were collected using a Shipek Grab Sampler along two South Carolina cross-shelf transects: the Primary Transect off Folly Beach and the Capers Transect off Capers Island. A 120 mL homogenized sub-sample was taken from each grab sample for the purpose of studying benthic foraminifera. Foraminifera specimens were picked from the > 500 mm size fraction and identified to the genus level. The most common foraminifera genera, >10% of total abundance, were compared between the two transects for the inner, middle, and outer continental shelf regions. All genera found are present in both transects, showing equal diversity. The major genera vary across the shelf and are similar between the two transects at the outer shelf, but vary greatly for the inner and mid-shelf regions.
Spatial Distribution of Benthic Foraminifera Across the Continental Shelf off the Coast of Charleston, South Carolina
-Sam Crickenberger, Leg 04
Benthic foraminifera fossil test assemblages can serve as proxies for paleoecological and paleooceanographic conditions. Sediments in the Gulf of Mexico, as well as along the Charleston Transect, are most accurately dated to the early Pleistocene, providing an environmental record during that time period. Thirteen grab samples were collected along the Charleston Transect, ranging in depth from 9.9 to 100.4 m, and were analyzed for benthic foraminifera distributions. General dominance distributions were found similar to that of Poag (1981) in the Gulf of Mexico with the exception of Textularia, Eponides, and Elphidium. Textularia was dominant at the hard grounds of the outer shelf with Eponides and Elphidium having somewhat of a role reversal in their depth related distributions.
Vertical Depth Habitats and Geographic
Distribution of Living Benthic Foraminifera within the Continental Shelf Sediments
off Charleston SC, November 2003
-C. Travis Debnam, Leg 01
Benthic foraminifera are generally known to occupy species-specific habitats within the surface and near-surface ocean bottom sediments. Few studies on living benthic foraminifera populations within the shelf sediments off Charleston SC have been conducted, as a result the geographic distribution and vertical depth habitats in this region are poorly understood. Seven push-core samples were taken across the continental shelf off Charleston SC, during November of 2003, while onboard the R/V Savannah during Leg 01 of the College of Charleston’s Transects Program. Populations of living benthic foraminifera identified were sampled and compared in 2 cm interval slices, from four of seven cores, to a depth of 10 cm. Data indicates variations in species populations vertically down-core, as well as with water depth across the continental shelf along the Transects line. This study will supplement any further research conducted through the College of Charleston’s Transects Program.
Benthic Foraminifera Distribution
across the Continental Shelf off Charleston, South Carolina
-Ross Martin, Leg 03
In November 2003 (Transect Program, Leg 01) 8 sediment stations were sampled from the inner shelf to the shelf edge, off the coast of Charleston, SC, from aboard the R/V Savannah. Benthic foraminifera were extracted from sediment to study their distribution and abundance which had only been documented by previous Transect research (Abdul, 2004). Specimens were identified to the genus level, and relative abundances (%) were calculated. Twenty-seven genera were identified, 9 of which accounted for more than five percent at one or more stations. Hanzawaia was the dominant genus at 7 of the 8 stations, whereas Textularia was dominant at the outer shelf station. Cibicidoides was the second most abundant genus at all but station #7, located on the mid-shelf. These data differ from previous unpublished studies, despite replication of methodology. Further studies are very necessary to determine the dominant genera year round.
Cross-Shelf Benthic Foraminifera Distribution off the Charleston, SC Coast
-Emily Osborne, Leg 05
Benthic foraminifera are single celled, calcium carbonate Protists found in all marine environments. These chambered organisms have proven to be invaluable proxies for reconstructing paleo-environments. The College of Charleston Transect Program has conducted five oceanographic research cruises off the Charleston coast along cross-shelf transect lines. Using a Shipek Grab Sampler, sediment samples were collected in November 2009, and foraminifera (125-500 µm) were extracted from each sample and identified to the genus level. Foraminifera were also classified by test texture, showing an overall dominance of Rotalids. Twenty genera were found across the continental shelf, seven of which were dominant. The genus Cibicidoides (a Rotalid) dominates across Charleston’s entire continental shelf. This distribution differs from Wylie Poag’s Generic Predominance Facies off the West Florida shelf, possibly the result of low bottom water temperature variance off Charleston, due to the influence of the Gulf Stream at the shelf edge.
Distribution and Variance of Modern
Benthic Foraminifera Assemblages Found off Charleston, S.C., Across the Continental
-Elizabeth Rogers, Leg 01
Participation in the College of Charleston’s Transects Program provided an opportunity to obtain seven surface sediment grab samples across the continental shelf off Charleston, S.C. in November 2003. Water depths along this main transect ranged from 10 m to 100 m. Sediments collected aboard the R/V Savannah were dried, sieved, split, and examined to identify modern benthic foraminifera to the genus level. While the predominant genera changed as the water depth increased, two genera of benthic foraminifera dominated – Quinqueloculina and Cibicides. While these genera were found in every sample, it appears that they prefer different habitats, perhaps dependent upon sediment influx into the system. Excluding these genera, the overall distribution of many other genera is widespread but only in low to medium abundances.
Benthic Foraminifera of the Continental
Shelf off Charleston, SC
-Christina Skalit, Leg 04
Benthic foraminifera were picked from surface sediments collected across the continental shelf off Charleston, SC, along the Charleston Transect. Relative abundances of genera -- defined as any genus greater than 5% in one or more sample -- were calculated, and the distributions of Generic Predominance Facies were mapped. The inner shelf (0-20m water depth) was dominated by Quinqueloculina, and the mid-shelf (20-50m), was dominated by Cibicides and Quinqueloculina. The outer shelf (50-100m), which is strongly influenced by the Gulf Stream, was dominated by Cibicides and Hanzawaia; however, one station located near a rocky outcrop (50m) was dominated by Textularia. These strong variations in predominance of foraminifera genera are due to (1) depth variations across the shelf; (2) proximity to the Gulf Stream; and (3) substrate differences. Substrates range from coarse sand mega-ripples, to hardground areas surrounded by sediment, to incised ancient river channels.
Temporal and Spatial Variability
in Benthic Foraminifera Fossil Assemblages off the Continental Shelf, Charleston,
-Skalit, Christina, Sautter, Leslie, Abdul, Nicole, Crickenberger, Sam, and White, Ransom
As part of the College of Charleston's Transect Program, four research cruises were conducted over a two-year period, sampling across the South Carolina continental shelf adjacent to Charleston. Sediment grab sample collections were conducted on each cruise at the same eight cross-shelf stations, in waters with depths ranging from 10 to 100 m. Between 25 and 39 benthic foraminifera genera (>125 micron size fraction) were identified for a single cruise, with more than 10 “dominant” genera (> 5 % of the genera at any station), including Quinqueloculina, Textularia, Hanzawaia, Cibicides, Triloculina, Bigenerina, Bolivina, Eponoides, Amphistegina, and Elphidium. The distribution of foraminifera along the Charleston Transect only partially compliments previously documented patterns along the southeast shelf and the Gulf of Mexico. For each cruise collection, considerable cross-shelf assemblage and dominant genera variability existed. Although similar foraminifera were identified from samples collected on each cruise, the spatial distribution of dominant genera showed a high degree of temporal variability for the four cruise collections. Sediments in the study region consist of a thin veneer of modern and relict sands, underlain by limestone hardground. Video of the seafloor collected with a remotely operated vehicle shows evidence of migrating sand megaripples which may be responsible for the seasonal reworking and redistribution of sediments. Sediment characteristics within the megaripples vary with respect to grain size and composition, and may be influencing the foraminiferal assemblage composition. Comparisons will be presented on foraminiferal assemblage variations and distribution with respect to grain size analyses and video data collected with a remotely operated vehicle.
GSA Abstracts with Programs, 2006, Vol. 38, No. 7.
Distribution and Diel Vertical Migration of Zooplankton in the South Atlantic Bight
-Leianna Arnold , Leg 05
The vertical and horizontal distributions of zooplankton over the South Atlantic Bight were analyzed and correlated with chlorophyll distributions. Zooplankton samples were taken with a Multiple Opening/Closing Net and Environmental Sensing System (MOCNESS) and a Neuston net in November of 2009 in continental shelf waters off Charleston, SC along two transect lines perpendicular to the coastline. The abundance and diversity of different zooplankton taxa were analyzed from preserved samples using a compound scope in order to describe distributional patterns in relationship to oceanographic variables. To characterize possible diel vertical migration (DVM) behavior patterns within the zooplankton community, MOCNESS tows were taken at discrete depths during day and night times and compared. Total zooplankton biomass was higher closer to shore, suggesting a positive correlation between zooplankton and phytoplankton densities. Also zooplankton biomass in surface waters was higher during night tows than day tows suggesting diel vertical migrations.
Zooplankton in the South Atlantic
Bight: Characterization of dispersion and
environment through biovolume correlations
-John R. Casey, Leg 04
Neuston net tows were made during both the day and night across the continental shelf off Charleston, SC during June 2004. Zooplankton biomass estimates were used to describe zooplankton distribution patterns; they were also correlated to a suite of environmental and biological factors to determine their influence in explaining these distributions. Potential biological proxies analyzed included surface chlorophyll a concentrations and the presence of floating Sargassum spp. clumps, a planktonic macroalgae which provides a unique habitat for fish, marine insects, and other natural predators of zooplankton. Sargassum is also a convenient biomarker for convergent surface currents. Our findings show that total zooplankton biomass at the surface were more than twice as high in samples containing significant (>170mL) amounts of Sargassum. Biomass was also nearly doubled during nighttime tows due to DVM. No direct correlations were observed between biomass and salinity, SST and, interestingly, chlorophyll.
Distribution of the Hyperiid
Amphipod, Lestrigonus bengalensis, across the Continental Shelf off South Carolina,
USA: Does Diel Vertical Migration Play an Important Role?
-David Couillard, Leg 01
The processes that regulate the distribution and migration of zooplankton have been studied for more than a century. The interaction of biotic (e.g., competitors, predators, and food) and abiotic (e.g., temperature, currents, and light) factors likely lead to the adoption of behaviors that attempt to optimize temporal and spatial resource use concomitant with predator avoidance. To examine diurnal and nocturnal distributions of the abundant Hyperiid amphipod, Lestrigonus bengalensis, plankton net samples were taken from the R/V Savannah between November 19-23, 2003 across the continental shelf off the coast of Charleston, South Carolina. Oblique tows of a bongo net were employed to sample the top 50 meters of the water column, while a neuston net captured only organisms in the surface layer (0.5 meters). Comparisons of diurnal and nocturnal abundances of L. bengalensis found in samples caught with bongo and neuston nets are used as a measure of the presence or absence of diel vertical migration.
Seasonal Comparison of Distribution
of the Hyperiid Amphipod, Lestrigonus bengalensis, across the Continental Shelf
off South Carolina
Wes Dukes, Leg 02
The Hyperiid amphipod, Lestrigonus bengalensis, is among the most abundant amphipod found off the coast of South Carolina. Lestrigonus bengalensis is thought to perform diel vertical migration however very few studies have been conducted to show this. Results from two cruises, fall and spring, indicate that diel vertical migration is performed by Lestrigonus bengalensis. Data from both cruises was compared in order to begin studying the seasonal distribution patterns of Lestrigonus bengalensis off the coast of Charleston, South Carolina.
Title of Paper: Compositional
Differences in Fall Zooplankton Communities across the Continental Shelf off
-Jennifer Fountain, Leg 01
Zooplankton communities were sampled across the continental shelf off Charleston, South Carolina from the oceanographic R/V Savannah in November 2003. Shallow water (0-50 m) plankton samples were taken at night using a 505 µm mesh- bongo net along a main transect that lay perpendicular to the coastline. Sample biomass was measured employing a volumetric displacement method, and organism diversity was estimated through the identification and quantification of zooplankton samples using dissecting scopes. Spatial differences in coastal phytoplankton primary productivity are hypothesized to directly affect zooplanktonic communities. Phytoplankton concentrations frequently decrease with distance from the shore, due to nutrient influx from coastal rivers. Therefore, zooplankton biomass is expected to diminish with distance from the coastline, and be positively correlated to chlorophyll-a concentrations. Zooplankton composition is predicted to vary across the continental shelf, reflecting differences in the amount of benthic organisms’ larvae (meroplankton) due to increasing depth. The ratio of pelagic zooplankton (holoplankton) to meroplankton abundance is projected to increase along the continental shelf, with maximum values achieved in the Gulf Stream sample.
Abundance of Chaetognaths (Arrow
Worms) across the Continental Shelf off Charleston, South Carolina
-Brooke Pehr, Leg 02
Abundance of chaetognaths was calculated at 7 stations in the South Atlantic Bight off Charleston, SC between May 18 and May 22, 2004. Zooplankton samples were obtained from bongo net night tows. Physical characteristics of the water, as well as zooplankton biomass estimates were considered when determining reasons for abundance or lack of abundance. Chaetognaths were present at every station, however more abundant at some stations than others. A positive correlation was found between chaetognath abundance and total zooplankton biomass estimates, which we attribute to the fact that chaetognaths prey on other zooplankton, especially copepods. We did not find a correlation between abundance and distance from shore, although a significantly lower abundance was calculated at the station closest to shore. Chaetognaths are found in a variety of temperatures and salinity. While we found the highest abundance of chaetognaths at the station with the coldest average water column temperature and one of the highest salinity averages, we did not find a correlation between temperature, salinity, and chaetognath abundance as a whole. We conclude that chaetognath abundance does vary across the shelf and is most closely related to abundance of other zooplankton.
Ichthyoplankton densities and distribution
across the continental shelf off Charleston, South Carolina.
-Michelle Bahm, Leg 03
On November 19-23, 2004, the Transects program collected larval fish from a transect line extending from the coast of Charleston, SC. Larval fish were collected with a bongo net with a mesh size of 505 µm. The fish were later quantified and identified to determine abundance and distribution of several species across the continental shelf. These data were compared to those collected in 2003 by the Transects program, and in 1973 by MARMAP. Results showed that fish are more abundant on the middle shelf, and more fish per cubic meter were obtained in 2003 than in 1973 or 2004. Pleuronectiformes and Leptocephalus larvae were the most abundant species observed per cubic meter of water, with Clupeiformes and the genus Ophidiidae being the next abundant.
Spring Distribution and Abundance of Ichthyoplankton across the Continental Shelf
-Sherena H. Coachman, Leg 02
To study the abundance and distribution across the continental shelf samples were collected during a 5-day research cruise along the Charleston Transect off the coast of Charleston, SC. The time of the cruise was from May 18th-22nd. Nine samples were collected during day and night and analysized. Larval fish were categorized into the orders of Pleuronectiforms, Clupeiforms, and Scombriforms. Those not identified were placed in the other category. Clupeiforms were one of the dominant percentages found during both the fall and spring. The distribution and abundance may have been affected by the Gulf Stream. Another factor affecting abundance is that it was not spawning season for some the larval fish used for this study.
Fall Icthyoplankton Abundance
Across the Continental Shelf Off Charleston, South Carolina
-Marilyn B. Laserna, Leg 01
The ichthyoplankton communities of the South Atlantic Bight were characterized in detail during the 1970s, as part of the Marine Resources Assessment and Prediction program (MARMAP). Ichthyoplankton communities inhabiting the shallow shelf waters were sampled in the fall of 2003 from the RV Savannah with both Bongo and Boothbay neuston net samplers. Only nocturnal tows were analyzed for this study. The nets were equipped with flow meters in order to estimate the volume of water filtered. Larval fishes were removed from the plankton samples, and the Clupeiform, Pleuronectiform and Elopomorpha (leptocephalus) larvae were identified and quantified. In order to analyze the possible historical changes in the ichthyoplankton communities of the shelf, the present overall abundance, composition and distribution of the larval fishes will be compared with the historical ichthyoplankton data collected in the fall of 1973 as part of the MARMAP program. This study attempts to describe historical changes in ichthyoplankton communities 30 years after the original study and focuses primarily on the orders Pleuronectiform (flatfishes), Clupeiform (sardines and their allies) and the super order Elopomorpha (eels and their allies). Similar abundance, relative abundance and occurrence values were found when compared to MARMAP cruise D5-73. Variations may be attributed to the fact that the MARMAP studies covered a larger sampling area and included both nocturnal and daylight samples.
Diel Differences in Ichthyoplankton
Communities Collected with a Bongo Net: Gear Avoidance or Diel Vertical Migration?
-Brad Schondelmeier, Leg 01
Differences in ichthyoplankton abundance collected with plankton nets in varying light levels have been described in a multitude of studies, including the Marine Resources Monitoring Assessment and Prediction (MARMAP) plankton surveys off the coast of South Carolina in the mid 1970’s. In November 2003, oblique shallow water tows (0-50 m) were performed with a 505 micrometer bongo net at each of 17 different stations along a main transect line perpendicular to the South Carolina coast, south of Charleston. Surface icthyplankton samples (top 50 cm) were collected at the same stations with a 1000 micrometer neuston net. All samples were preserved in 95% ethanol and later examined in order to quantify and identify planktonic fishes. It has been documented that young larval fishes tend to perform diel vertical migrations (DVM), swimming to deeper waters during daytime, primarily to avoid predators. But certain fishes with advanced swimming abilities have also been documented to avoid nets, mainly during daytime hours, due to increased visual detection of sampling gears. By comparing day and night samples, plus simultaneous bongo and neuston tows, we will attempt to determine what causes the differences in icthyoplankton composition: diel vertical migrations or visual net avoidance.
Seasonal Ichthyoplankton Distribution
Across the Continental Shelf
Off Charleston, SC
-Ryan Yaden, Leg 03
In order to compare the seasonal and spatial distribution of across the continental shelf off the coast of Charleston. The collection plankton samples took place on a 5 day cruise starting on November 19 and continuing to the 23, 2004. Seven samples were analyzed by removing the ichthyoplankton from the other zooplankton. Then those ichthyoplankton were identified into Leptocephalus, Scombridae, Ophidiidae, Pleurinectiformes, and Syngnathidae. The larval fishes that could not be classified were put into the “unknown” category. When comparing the abundance form May to November it was found that the abundance of larval fish in November is greater than the abundance in May. When comparing this to the coast of Georgia the fish abundance was greater in the spring than in the fall. The greater abundance in fall 2004 could be that the temperatures for the fall were higher then average possibility giving the fishes a longer spawning season.
Distribution of Benthic Meiofauna
across the Continental Shelf off the Coast of Charleston, SC
-Chris Giguere, Leg 02
This paper is primarily a characterization of the benthic meiofauna found across the continental shelf off the coast of Charleston, SC. Actual abundances of organisms are evaluated at 8 stations along a transect perpendicular to the coast. These abundances are compared to grain size found at each station, and a correlation is evaluated. Taxonomic richness is calculated for each station using a modified Shannon-Weaver Index. Taxonomic richness is then compared to grain size at each station, and a correlation is evaluated. Other similar studies are mentioned and compared to this study.
Seasonal Comparison of Echinodermata
across the continental shelf off Charleston, South Carolina
-Lauren Halloran, Leg 03
Echinoderm specimens were collected in November 2004 and May 2005 across the continental shelf off Charleston, SC aboard the R/V Savannah. Specimens were identified to the species level and separated into three taxonomic groups: asteroids, ophiuroids, and echinoids. Species density per 1000 m2 for all organisms collected was determined along with a seasonal comparison and overall spatial distribution of key species. Greater than 10 specimens of a species per 1000 m2, collected in November or May, defined the key species. Overall, more echinoderms were collected in May than in November. Asteroids were found in greater numbers in May compared to November and were more numerous in the mid-shelf during May and November. Similarly, more ophiuroids were collected in May, however, one key species was dominant across the shelf in both seasons. Seasonal variations and a change in dominance of echinoids were observed across the shelf.
The Effects of Depth and Primary
Sediment Composition on the Distribution of Echinoderms across the Continental
Shelf of Charleston, S.C.
-Cecilia Lewis, Leg 02
Echinoderms have been described as one of the most abundant groups of invertebrates in marine environments. The objectives of this study were to: 1) determine whether depth solely dictated the distribution of echinoderms (i.e. echinoids and asteroids) with increasing depth or 2) whether the primary sediment component occurring at each station determined echinoderm distribution across the continental shelf. Sampling for this project took place in spring 2004 from May 18 to 22nd onboard the R/V Savannah. Samples were collected along a transect line extending across the continental shelf from the southern most end of Folly Island, South Carolina. A dredge trawl was employed for benthic macrofaunal sampling and a Smith-Macintyre Grab Sampler was employed to for sediment sampling. Total counts and calculated percentages of echinoderms captured at inner shelf stations indicate that members of class echinoidea dominated the inner shelf as well as the outer shelf benthos.
Distribution of benthic meiofauna
crustaceans across the Continental shelf off Charleston, SC.
-Alison M. Cawood, Leg 03
Benthic meiofaunal communities can vary tremendously, depending on a variety of factors such as sediment type, mean grain size, water depth, and temperature. There has been little work done on the benthic meiofaunal crustaceans of the South Atlantic Bight, and no work has been done on the groups of crustaceans that inhabit the continental shelf of this area. A Smith-McIntyre grab sampler was used to collect sediments along two parallel cross-shelf transects off Charleston, SC in November 2004. Ten groups of crustaceans were found, representing fourteen families. No correlation was observed between the abundance of crustaceans and abiotic factors, such as depth, temperature, salinity, or mean grain size. Perhaps the crustacean abundance is being controlled by other factors such the type of environment (e.g., live bottom) or other environmental factors (e.g., nutrient availability and/or predator abundance).
Abundance, diversity and distribution
of micro Gastropoda across the continental shelf, off Charleston, SC.
-Thomas P. Smith, Leg 04
The depth ranges and factors affecting the micro Gastropoda off the southeast United States are poorly known. Sediment samples were collected aboard the R/V Savannah with a Smith-MacIntyre grab sampler and Gastropoda were removed and identified. The relative abundance, absolute abundance and species density were compared to depth data, sediment composition data and sediment mean grain size. The results showed that micro gastropods became more abundant and had higher species density with a decrease in mean grain size. This may be a result of mobility factors, predation effects and food source limits in small gastropods. Sediment that had a higher composition of biogenic sediment increased the species density but not the absolute abundance of micro gastropods. Higher amounts of biogenic sediment usually reflect higher diversity of organisms and higher carrying capacity of an ecosystem. Depth did not affect either absolute abundance or species density.
abundance, and diversity of micro-gastropods across the continental shelf off
Charleston, South Carolina, with consideration to sediment analyses.
-Thomas P. Smith (Leg 04), Post-Transects independent study
Surface sediments from 3 different Transect Program research cruises were collected across the continental shelf off Charleston, SC. The Charleston Transect ranged from nearshore waters to the shelf edge where water depths were 100 m. Different depth zones and cross-shelf geographic ranges were identified using these micro-gastropod assemblages. Four different micro-gastropod sediment facies can be identified by the abundance of two to three species found at each site within the inner shelf (0-20m water depth), mid-shelf (20-50m), outer shelf and shelf edge (50-100m). No seasonal variability was observed, despite the variations in sediment grain size analyses (White, 2006), indicating a well-homogenized fossil assemblage.
Relationship of Coarse-Grained Sediment Distribution and Composition
with Echinoderm Species’ Habitat Preferences
-Delynn Woodman, Leg 05
Characterizing the habitat of benthic echinoderm species requires a close examination of sediments on the ocean floor. Using sediment grab sampling devices, sediments were collected by the College of Charleston’s Transect Program from seven stations across the continental shelf off Folly Island, SC in November 2004, May 2005 and November 2009. Collection stations ranged in depth from 17 to 120 m. Grain size distributions were determined using dry sieving analysis, and the larger grain size fractions of gravel (>2.00 mm) and very coarse sand (1.00 to 2.00 mm) were examined for composition focusing on the biogenic component. Echinoderm fragments were counted and included in the percent biogenic. Using a beam trawl, echinoderm specimens were collected at the same sediment sample locations in November 2009 and compared with spatial distribution and abundance of echinoderms previously studied for the November 2004 and May 2005 cruises. Sediment characteristics showed consistent trends on the self edge for all three sampling years but the majority of the shelf showed little consistency. Echinoderm abundance was highest in May 2005 and lowest in November 2009. Based on results, the distribution and abundance of various echinoderm species have no strong, probable correlation with any sediment characteristics or depth across the continental shelf.
Abundance, Distribution and Diversity
of Benthic Fishes from the Continental Shelf off Charleston, South Carolina
-Dana B. Hughlett, Leg 03
We studied the special distribution, relative abundance and biodiversity across the Continental Shelf off Charleston, South Carolina. Using a 1 m beam trawl, we sampled eleven sites across the shelf, fixing and preserving representative samples in 10% formaldehyde and 95% Ethanol, respectively. Each segment into which the shelf was divided (Inner, Middle and Outer) was found to be dominated by a different species. The Inner Shelf had the highest relative abundance of Citharichthys sp., while the Middle shelf was dominated by Otophidium omostigmum and the Outer shelf was characterized by Otophidium dormitator and Urophycis regia. We found that biodiversity decreases with increasing distance from shore. A total of thirty-three species were identified across the entire shelf, with varying number of species at each shelf segment.
Seasonal abundance and size distribution of benthic fishes across the continental shelf off Charleston, South Carolina
-Lester Proctor, Leg 04
Seasonal changes in relative abundance and size distribution of demersal fishes were examined from samples collected across the continental shelf off Charleston, SC, in May 2005 and November 2004. Fifteen sites were sampled with a 1 meter beam trawl, catching fifty four different fish species. Each physiographic region of the continental shelf (Inner, Middle and Outer Shelf) was dominated by a different fish species. The Inner and Middle shelf had the highest relative abundance of Etropus cyclosquamus (Shelf Flounder), while the Outer shelf was dominated by Synodus foetens (Inshore Lizardfish). Demersal fish abundances variedbetween seasons however; patterns were observed suggesting possible migration and recruitment events. Size analysis of E. cyclosquamus and Prionotus carolinus showed an increased abundance but lower average size, suggesting a recruitment event occurred between seasons. The other species analyzed for seasonal size differences were Symphurus minor, Serrinaculus pumilio, and S. foetens, all observedhad increased abundance and size.
cyclosquamus and Symphurus minor: a closer look
at two South Atlantic Bight flatfishes
-Dana Hughlett and Lester Proctor, Legs 03 and 04
As part of the Transects project, in the Spring of 2005, we sampled small sized demersal fishes at seven sites across the Continental Shelf using a 1 m beam trawl. Symphurus minor (Largescale tonguefish) was found at all depths along the continental shelf, and the maximum recorded depth of 100 meters was 40 meters deeper than currently documented for this species. Both males and females were caught at the same depths, indicating a mixed sex adult habitat, although females were found to dominate the sex ratio. The only site where a juvenile was caught was located at the nearest site to shore, no mature individuals were sampled, possibly indicating its value as a recruitment site. Large captures of juvenile Etropus cyclosquamus (Shelf flounder) indicate possible recruitment events during winter months in near shore waters. We also conducted preliminary age-size analysis of juveniles E. cyclosquamus.
Habitat and spatial distribution of
benthic fishes along the Continental shelf off Charleston, South Carolina
-Benjamin Stone, Leg 04
In May of 2005, the Transects program (LEG 04) collected benthic samples along a transect line across the continental shelf off the coast of Charleston, South Carolina. Samples were collected using a beam trawl with a 1.0 meter wide opening in order to describe shelf communities of small demersal fishes. A total of 41 different species of fish were caught. Fish density and diversity were compared with depth, sediment type, and presence of live bottom. Fish distribution patterns seemed to be species specific, and were commonly correlated with depth and/or the presence of live bottom. The presence of live bottom was positively correlated with biodiversity, with the outer shelf having the highest diversity compared to the inner and mid-shelf zones.
Sediment grain size and composition
An Analysis of Microfossil Assemblages
Across the Continental Shelf off the Coast of Charleston, SC
-Adriane Cushman, Leg 03
Sediment samples were collected in November 2004 on the continental shelf off the coast of Charleston, SC aboard the R/V Savannah. Seven samples were dried and split, then grains were counted and identified as biogenic or non-biogenic sediment. The percent of biogenics present was calculated, and biogenics were divided into microfossil taxa. Results show that the inner-, middle-, and outer-shelf samples consistently contain less than 10 % biogenic sediment, most of which is fragments of bivalves and other hard part remains of organisms. In contrast, the shelf-edge station, which is influenced by the Gulf Stream and far from the source of lithogenic material, consists of nearly 70 % biogenic sediment. Planktonic and benthic foraminifera, echinoderm and coral fragments are present along with numerous bivalve shell fragments.
Sediment Analysis and Mineral Composition across the South Carolina Continental Margin
-Cody Donofrio, Leg 05
Leg 05 of College of Charleston’s Transect Program was conducted in November 2009, during which sediment samples were collected across the continental shelf off Charleston, South Carolina. Sediments were collected using a Shipek Grab Sampler at 14 locations along two transect lines, one extending from Folly Island and the other from Capers Island. Using a particle size analyzer, grain size distributions were determined along two cross-shelf transects. A Scanning Electron Microscope and binocular microscope were used to determine mineral composition contained in coarse material at the 0.5 mm size fraction. Grain size distributions and mineral composition will be related to distance from shore and proximity to the Gulf Stream. Results indicate that the sediments collected do not follow the traditional model of sediment distributions along the continental shelf.
Changes in Cross-Shelf Sand Size Distribution Off the Coast of Charleston, SC from 2003 to 2009.
-Veronica Holton, Leg 05
Temporal changes in cross-shelf sand size distribution have been studied by undergraduate students from the College of Charleston Transect Program using sediment samples collected at seven stations during three research cruises from November 2003 to November 2009. Variations in grain size demonstrate changes in wave energy, currents, and tides affecting how deposition occurs. In 2009, samples were collected along a cross-shelf transect off Folly Island, SC using a Shipek grab sampler. Ro-Tap sieve and statistical analyses were conducted, and compared to results from two previous cruises on sediment samples collected at the same stations to demonstrate temporal changes in cross-shelf grain size distribution. The mid-shelf has a higher level of variability, whereas the most of the inner and outer shelves remained constant. Variability may be due to a station’s close proximity to rocky hard ground areas.
Surface Sediment Composition and Grain Size Distribution
on the Continental Shelf off Charleston, SC.
-Glen Landon, Leg 01
Surface sediments of the continental shelf adjacent to Charleston, SC were sampled between November 19 and 23, 2003. The area sampled, referred to as the Charleston Transect, included 8 sites along one primary cross-shelf line and 8 sites sampled along four shore-parallel lines. Each shore-parallel line represents a distinct part of the continental shelf – nearshore, mid-shelf, outer shelf, and shelf edge – with water depths ranging from 10 to 100 meters. Examining the sediment composition and grain size distribution at these sites will help determine the types of current energies and characteristics of the benthic environments that occur at these locations. This sedimentological analysis will serve as a base-line study of the Charleston Transect as part of the College of Charleston Transects Program. Our results will be compared to future sampling at these locations to determine seasonal and interannual changes in sedimentology for this portion of the southeast U.S. continental shelf.
Sediment Analysis of the Continental
Shelf off Charleston, SC
-Ransom White III, Leg 03
Sediment analysis is a valuable tool for predicting water current flow patterns and energy. The ideal continental shelf model progresses from coarse grained sediments near shore to finer sediments off shore; passing over the inner-, mid-, and outer-shelf, and shelf edge. Research conducted in November 2004 on the continental shelf off Charleston, South Carolina, was designed to examine sediment grain size and composition. Fifteen sediment samples were collected along two transects, from the inner shelf to the shelf edge. The Gulf Stream appears to cause sediment size variations to deviate slightly from the model of a typical continental shelf. Grains get coarser as distance from shore increases to the outer shelf, but shelf edge sediments are finer. The Gulf Stream allows fine biogenics to settle off shore but not lithogenics. The coarse shelf sediments are relict beach deposits meaning the Gulf Stream prevents deposition at the mid-outer shelf.
analysis and grain size distribution of the continental shelf off Chalreston,
-Ranson White III
analysis of the continental shelf off Charleston, SC
-White, Ransom C., Sautter, Leslie R., and Landon, Glen
Research conducted on the continental shelf off Charleston, SC was designed to examine sediment grain size and composition. Eleven stations across the inner-, mid-, and outer-shelf regions as well as along the shelf edge were sampled at least three times during four College of Charleston Transect Program cruises. Generally, sediments in the study region are a thin veneer of modern and relict sands, underlain by limestone hardground. Grain size variations deviated from the classic fining-outward shelf model in that mean grain sizes irregularly progressed from fine sand (2.5-3.0 Phi) on the inner-shelf to medium sand (1.5-2.0 Phi) on the middle and outer shelf regions. Sediments were composed predominantly of lithogenic sands, with a higher concentration of relict lithogenics on the outer shelf, most likely remnant from shoreline migrations since the Pleistocene. Conversely, shelf-edge sediments were fine biogenic sands deposited in association with the Gulf Stream. Transitional sea level phases have sculpted the continental shelf across this area of South Atlantic Bight, leaving morphologies that skew sediment distribution across the shelf. In addition to spatial variability, temporal variations in sedimentology were observed in this study. Several samples collected on different cruises at the same location varied significantly in both grain size and composition. Videos collected of the seafloor collected by a diver and with a remotely operated vehicle show evidence of migrating sand megaripples, which may be responsible for the seasonal reworking and redistribution of sediments.
GSA Abstracts with Programs, 2006, Vol. 38, No. 7
A Geologically Based Habitat Characterization
of an Outer Continental Shelf Ledge
-Hannah Giddens, Leg 02
Habitat characterization of Lionfish Ledge was conducted with video and sediment samples collected aboard the R/V Savannah between May 17 and May 22, 2004, as part of the larger Charleston Transects program. Lionfish Ledge was located with a 100-khz sidescan sonar, video images were recorded from a ROV transect on the ledge, and sediment samples were collected with a Smith-MacIntyre grab sampler. Video image analysis quantified and described substrate and substrate morphologies. Video analysis showed the transect to consist of 84.7% sediment and 15.3% hard substrate. Grab sample analysis consisted of grain size and compositional analysis. Grain size analysis showed coarse and medium grain sizes to dominate samples. Compositional analysis determined the relative abundances of biogenic and lithogenic materials. Compositional analysis showed 3 grab samples to be composed mostly of lithogenics and 2 grab samples composed primarily of biogenics. Two lionfish were observed in the area of highest relief. Megafaunal invertebrate populations were qualitatively observed, however not quantified. Further studies of Lionfish Ledge are needed in order to characterize the fish and invertebrate community.
Habitat Characterization of Continental Shelf Seafloor off Charleston, SC
-Stephen Long, Leg 05
Habitat characterization of seafloor sites on the continental shelf off Charleston was conducted using video and sediment samples collected as part of Project Oceanica’s Transects Program. Samples were collected aboard the R/V Savannah in November 2009, using a Phantom 300 remotely operated vehicle (ROV) and a Shipek grab sampler. In addition to these samples, ROV video images from November 2003 were sub-sampled and sediment analysis data from White and Sautter (2004, unpublished) were used. Adjacent transects of the continental shelf were compared in terms of substrate and sediment. The habitats observed included soft to hard substrate with features such as mottled ripples and rock outcrops. Relief ranged from less than 0.5 m to greater than 1.5 m. Epifaunal density was found to be primarily sparse, however abundant in areas of the greatest relief. Sediment ranged from coarse silt to very coarse sand. These results can supplement additional research being conducted.
of an Inner-Shelf Hardground Area: the Harris Meander
-Philip Antman, Leg 02
An outer region of the inner continental shelf off the coast of Charleston, South Carolina was surveyed using: sidescan-sonar, ROV, and grab sample techniques. A large meandering channel was present in the image compiled from the sidescan data. 3 ROV dives were deployed transecting the study area and the meandering channel. Date from these dives were used to characterize substrate distributions in the area. Exposed hardground and soft ground areas were observed. Also quantified were varying geomorphologies of the hard and soft substrate areas. Grab samples taken at various distances from the channel help also to characterize the sediment of this area, and to prove the possible origin of this meandering channel. This study provides baseline data for comparison in future studies.
Ground-Truthing Shelf-Edge Sidescan
-Chris Stubbs, Leg 03
In May 2004, sidescan sonar data were collected along the continental shelf edge off of Charleston, SC, and compared to remotely operated vehicle (ROV) video and sediment to generate preliminary ground-truthing and habitat characterization of a 4 km2 region of the continental shelf edge (Giddens, 2005). Further comprehensive sidescan data of the same and adjacent areas were collected in November 2004, and processed into an image mosaic with associated ROV and grab sample data. Interpretations were made for the full 16 km2 sidescan region based on the features identified in the May 2004 region. Potential broken rock pavement, mega-ripple formations and homogenized sediment beds have been identified in the extended region. The November 2004 sidescan data are useful for identifying large trends on the sea floor. This research will provide background for more extensive study and sampling in May 2005.
Multibeam Mapping and Exploration of the Continental Shelf Edge
-Christopher Stubbs (Leg 03) and Ray Creede, Post-Transects Independent Study
In March 2006, the NOAA Ship Nancy Foster conducted a cruise on the continental shelf edge off South Carolina to calibrate a new Kongsberg Simrad multibeam sonar system. Students from the College of Charleston Geology Department assisted with bathymetric data collection and have begun preliminary processing and evaluation of identified seafloor features, using Caris HIPS/SIPS software. The data are being contextualized with previously quantified shelf-edge sidescan sonar data from the region collected during previous Transects Programs (Stubbs 2005, Giddens 2005) and Ocean Exploration submersible expeditions (Sedberry et al. 2002). The most prominent feature discovered is an outcropping hard-ground structure approximately 650 by 150m, with 10m vertical relief. It is oriented parallel to shore along the shelf edge in water depths of 60m. Possible geological and biological influences on the structure's origin and morphology are being explored.
Multibeam Mapping and Exploration of the Continental Shelf Edge
-Christopher Stubbs, Leslie Sautter, and Ray Creede
In March 2006, the NOAA Ship Nancy Foster conducted a cruise on the continental shelf edge off South Carolina to calibrate a new Kongsberg Simrad multibeam sonar system. Students from the College of Charleston (CofC) Geology Department assisted with bathymetric data collection and have begun preliminary processing and evaluation of identified seafloor features, using Caris HIPS/SIPS software. The data are being contextualized with previously quantified shelf-edge sidescan sonar and sub-bottom profiler data from the region collected during CofC's Transect Program cruises and NOAA Ocean Exploration submersible expeditions. The most prominent feature discovered is an outcropping hard-ground structure approximately 650 by 150 m, with 10 m vertical relief. It is oriented parallel to shore along the shelf edge in water depths of 60 m. Possible geological and biological influences on the structure's origin and morphology are being explored.
GSA Abstracts with Programs, 2006, Vol. 38, No. 7.
On the Nature of
Rocky Outcrops on the Continental Margin East of Charleston, South Carolina:
Pavements, Meander Scars, and Linear Trends as Documented through Direct Observations
and Remote Geophysical Methods
Harris, M. Scott, Sautter, Leslie, Lund, Prentiss, Stubbs, Christopher, Antman, Philip, Giddens, Hannah, and White, Ransom
The lack of sediment availability on the Continental Shelf in the South Atlantic Bight (SAB) combined with a shallow Tertiary geological framework creates a mosaic of intermittently to consistently exposed rocky features that range from very low-relief pavements to linear ridges of rocky exposures two to three meters high and several kilometers long. This paper focuses on the geophysical data results of three educational cruises conducted as part of the NSF-funded educational-focused Transects Program at the College of Charleston and highlights both geological mapping in the offshore as well as geologic mapping training and analysis of field data.
As part of the SAB and with a significant amount of unmapped critical benthic habitat, the study area along a transect extending from Charleston, South Carolina to the shelf edge contains three distinctly different bottom types ranging from 7-m to 50-m water depth. Sidescan sonar mosaics, chirp subbottom profiling, ROV-video transects, bottom grabs, and shallow sediment cores were collected to characterize and document the nature of the materials along various transect sites. The inner most, shallow site consists of primarily an extensive, intermittently exposed pavement of exposed shales and limestones. The intermediate depth site at approximately 18-m depth includes a series of entrenched tidal creek or river channel meanders that incise a rocky platform, creating areas of varied relief. The deeper offshore site at approximately 50-m depth includes a series of boulders along an extensive high-relief ridge.
Each bottom character and the potential for critical habitat in these regions is directly related to the nature of the nearsurface geological materials and stratigraphic architecture, sea level changes and fluctuations since the last glacial maximum, minimal sediment input from other than local sourcing from eroding rock, and the nature of the relief and subsequent burial and exposure due to modern shelf processes. We do not submit here a new classification for hardground and habitat types offshore, but rather provide the reader with a sense of the differences across this portion of the shelf. As these studies continue, we will further investigate the nature of the seafloor with respect to hardground distribution and type, changes in these types through time, and suitability for habitat for each type.
Published in: GSA Abstracts with Programs, 2006, Vol. 38, No. 3