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Results for “Estuarine and Continental Shelf Science”

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USGS2012

Over 100 years of environmental change recorded by foraminifers and sediments in a large Gulf of Mexico estuary, Mobile Bay, AL, USA

The marine microfauna of Mobile Bay has been profoundly influenced by the development and expansion of the primary shipping channel over the last ∼100 years. Foraminifers and sediments from seven box cores with excess lead-210 chronology document that channel dredging and spoil disposal have altered circulation, reduced estuarine mixing, changed sedimentation patterns, and caused a faunal turnover within the bay. Beginning in the late 1800s, changes in estuarine mixing allowed for greater low-pH freshwater influence in the bay, and ultimately began environmental changes that resulted in the loss of calcareous foraminifers. By the early 1900s, box cores throughout Mobile Bay record a ∼100-year trend of increasing calcareous test dissolution that continues to the present. Since the completion of the current shipping channel in the 1950s, restricted tidal flushing and increased terrestrial organic matter, documented by carbon-to-nitrogen ratios, stimulated an increase in agglutinated foraminiferal densities. However, in deeper areas of the bay, hypoxic water has negatively impacted the marine microfauna. Comparisons of the present-day foraminiferal assemblage with foraminifers collected in the early 1970s indicate that the continued biologic loss of calcareous foraminifers in the bay has allowed the introduction of a new agglutinated foraminiferal species into the bay.

Alabama↗

USGS2017

Distribution of foraminifera in Chincoteague Bay and the marshes of Assateague Island and the adjacent vicinity, Maryland and Virginia

Scientists from the U.S. Geological Survey (USGS), St. Petersburg Coastal and Marine Science Center conducted a seasonal collection of estuarine, marsh, and sandy washover surface sediments from Chincoteague Bay, Tom’s Cove, and the surrounding Assateague Island and Delmarva Peninsula in March–April and October 2014, after Hurricane Sandy. Micropaleontology samples were collected as part of a complementary USGS Coastal and Marine Geology Program Sea-level and Storm Impacts on Estuarine Environments and Shorelines project study. For comparison with estuarine and overwash deposited foraminifera, a group of scientists from the USGS Woods Hole Coastal and Marine Science Center in Massachusetts collected samples offshore of Assateague Island on the inner continental shelf during a seafloor mapping study in the summer of 2014 and shipped select samples to the St. Petersburg Coastal and Marine Science Center. The micropaleontological subsamples analyzed for foraminifera at each site can be used to establish a foraminiferal baseline assemblage that takes into consideration the seasonal variability of the various species, regarding density and geographic extent, which are influenced by transient and stable environmental parameters. By understanding what parameters affect the various foraminiferal assemblages, researchers can delineate how alterations in salinity, temperature, or marsh-to-bay interactions, such as marsh erosion, might affect that assemblage.

Maryland, Virginia↗

USGS2023

Metabarcoding analysis of meiobenthic biodiversity along the Gulf of Mexico continental shelf

This study explores how diverse the meiobenthic (meiofauna and other benthic micro-eukaryotes) community is throughout the United States Gulf of Mexico (GOM) continental shelf. In late 2010 and 2011, 51 sediment samples were collected along GOM from Texas through Florida at a range of depths (40m–496m). An additional six deep-sea slope sediment cores were collected in December 2010 near the Deepwater Horizon platform (1370–1385m and 1865m). Metabarcoding of the 18S hypervariable V9 region was conducted to assess biodiversity. Within continental shelf samples, there was greater meiobenthic diversity off the Eastern GOM coast in comparison to both Central and Western GOM coast locations. The Eastern GOM coast has known sediment differences from Western GOM sites. These sediment differences along with influences from the Gulf of Mexico Loop Current may account for observed variations in GOM meiobenthic diversity.

Gulf of Mexico↗

USGS2002

Influence of fluvial processes on the quaternary geologic framework of the continental shelf, North Carolina, USA

Digital, single-channel, high-resolution seismic reflection profiles were acquired from the insular continental shelf of North Carolina, USA along a data grid extending from Oregon Inlet northward 48 km to Duck, North Carolina and from the nearshore zone seaward approximately 28 km (total surveyed area= 1334 km2). These data were processed and interpreted to delineate principal reflecting horizons and develop a three-dimensional seismic stratigraphic framework for the continental shelf that was compared to stratigraphic data from the shoreward back-barrier (estuarine) and barrier island system. Six principal reflecting horizons (designated R0 through R5) were present within the upper 60 m of the shelf stratigraphic succession. Three-dimensional mapping of reflector R1 demonstrated its origin from fluvial incision of the continental shelf during an episode (or episodes) of lowered sea-level. Fluvial processes during development of reflector R1 were responsible for extensive reworking and re-deposition of sediment throughout most of the northern half of the study area. Five seismic stratigraphic units (designated S1 through S5) were tentatively correlated with depositional sequences previously identified from the North Carolina back-barrier (estuarine) and barrier island system. These five stratigraphic units span the Quaternary Period (S1 = early Holocene; S2 = 51-78 ka; S3 = 330-530 ka; S4 = 1.1-1.8 Ma; S5 = earliest Pleistocene). Unit S1 is composed of fine-grained fluvial/estuarine sediment that back-filled incised streams during early Holocene sea-level rise. The four other stratigraphic units (S2-S5) display tabular depositional geometries, low total relief, and thicken toward the east-southeast as their basal reflectors dip gently between 0.41 m km-1 (0.02??) and 0.54 m km-1 (0.03??). Knowledge of the three-dimensional subsurface stratigraphic architecture of the continental shelf enhances understanding of the development of shelf depositional successions and provides a framework for development of better Quaternary sea-level data, especially offshore North Carolina where such data are sparse. ?? 2002 Elsevier Science B.V. All rights reserved.

Marine Geology↗

USGS2020

Nitrogen budgets of the Long Island Sound estuary

Nitrogen (N) inputs to coastal ecosystems have significant impacts on coastal community structure. In N limited systems, increases in N inputs may lead to excess productivity and hypoxia. Like many temperate estuaries, Long Island Sound (LIS), a major eastern U.S. estuary, is a N limited system which has experienced seasonal hypoxia since the 1800s. This study is the first effort to constrain the total N cycle in this estuary. The approach utilizes data collected over the last two decades in the LIS time series with hydrodynamic model results to generate both monthly and annual N budgets between 1995 and 2016. Of the total N that is delivered to LIS through rivers and atmospheric inputs, 40% is exported to the adjacent continental shelf on the order of 10.8 ± 8.9 × 10 6 kg N/year. Of this export, 41% is dissolved organic N, 29% is particulate organic N, 32% is nitrate + nitrite, and −3% is ammonium. The remaining 60% of the N delivered to LIS is either buried in sediments or lost through denitrification. This inferred internal loss rate is equivalent to 5.4 g N/(m 2 year). This study serves as an example of the significant inter-annual variations that estuarine budgets undergo as efforts to understand coastal biogeochemical cycles move forward.

Connecticut, New York↗

USGS2021

Amazon sediment transport and accumulation along the continuum of mixed fluvial and marine processes

Sediment transfer from land to ocean begins in coastal settings and, for large rivers such as the Amazon, has dramatic impacts over thousands of kilometers covering diverse environmental conditions. In the relatively natural Amazon tidal river, combinations of fluvial and marine processes transition toward the ocean, affecting the transport and accumulation of sediment in floodplains and tributary mouths. The enormous discharge of Amazon fresh water causes estuarine processes to occur on the continental shelf, where much sediment accumulation creates a large clinoform structure and where additional sediment accumulates along its shoreward boundary in tidal flats and mangrove forests. Some remaining Amazon sediment is transported beyond the region near the river mouth, and fluvial forces on it diminish. Numerous perturbations to Amazon sediment transport and accumulation occur naturally, but human actions will likely dominate future change and now is the time to document, understand, and mitigate their impacts.

Amazon↗

USGS2023

Dissolved organic carbon dynamics and fluxes in Mississippi-Atchafalaya deltaic system impacted by an extreme flood event and hurricanes: A multi-satellite approach using Sentinel-2/3 and Landsat-8/9 data

Transport of riverine and wetland-derived dissolved organic carbon (DOC) spanning tidal wetlands, estuaries, and continental shelf waters functionally connects terrestrial and aquatic carbon reservoirs, yet the magnitude and ecological significance of this variable and its spatiotemporal linkage remains uncertain for coastal deltaic regions, such as Mississippi River Delta Plain, which includes Mississippi (MR) and Atchafalaya (AR) rivers and estuaries with vast expanses of wetlands and coastal forests. We examined DOC dynamics and fluxes in this large river-dominated wetland-estuarine system for the period between 2019 and 2021 that included an extreme river flood event in 2019, two major hurricanes (Barry in 2019 and Ida in 2021), and cold front passage using an improved adaptive quasi-analytical algorithm (QAA-AD) applied to multi-satellite sensors (Sentinel 3A/B OLCI, Landsat-8/OLI and Sentinel-2A/B MSI) with varying spectral and spatial (10/30/300 m) resolutions. The DOC estimates from multi-satellite sensors in combination with water fluxes were used to assess DOC fluxes from two large rivers (MR and AR) and small channels across the delta plain. Overall, this system delivered a total of 6.7 Tg C yr -1 (1 Tg = 10 12 g) into the estuarine zone and the northern Gulf of Mexico (nGoM) during 2019. High DOC fluxes from the AR (1.3 Tg C yr -1 ) and MR (4.5 Tg C yr -1 ) were associated with the extreme flood event in 2019. Hurricanes that occurred in the study period also contributed to the wetland and estuarine DOC fluxes into continental shelf waters; for example, the passage of Hurricane Barry in July 2019, delivered over a 3-day period ~1.33 ×10 9 g DOC from Barataria Basin into the nGoM. Sentinel 2-MSI land and water classification revealed that Hurricane Ida eroded a total of 1.34×10 8 m 2 of marshes in middle Barataria Basin, converting those habitats into open water with 3.0 m inundation depth and high DOC concentrations (16.4 mg L -1 ), a potentially large DOC source to the coastal waters. Overall, storms and flood events are major sources of DOC flux that facilitate transport of upstream carbon as well as transformation of carbon in the wetlands, through the conversion of vegetated wetland to open water.

Louisiana↗

USGS2003

Benthic foraminifers from the continental shelf and slope of the Gulf of Mexico: An indicator of shelf hypoxia

Benthic foraminifers from 74 core-top sediment samples collected primarily from the continental shelf of the Gulf of Mexico were analyzed to determine a microfaunal indicator for shelf hypoxia to be used in future paleoenvironmental studies. Principal component analysis (PCA) and cluster analysis (CA) of 93 species recognized factors/clusters that were similar to previous investigations of the benthic foraminifers, except that both analyses also identified PCA6/CA6 in the area where hypoxic conditions have been observed. Three low-oxygen-tolerant species, Pseudononion atlanticum, Epistominella vitrea, and Buliminella morgani have high factor loadings in PCA6. The cumulative percentage of three species is defined as the PEB (PEB, Pseudononion, Epistominella, Buliminella) index. The highest PEB values observed in the 74 surface sediment samples occur in the zone of recognized hypoxia on the Louisiana shelf. Values of the PEB index are also elevated along the southern Texas coastline, suggesting that this area may experience periodic hypoxia as well. ?? 2003 Elsevier Ltd. All rights reserved.

Estuarine, Coastal and Shelf Science↗

USGS1981

Temporal and spatial variations in suspended matter in continental shelf and slope waters off the north-eastern United States

Seston in waters of Georges Bank originates primarily from biological production and from resuspension of bottom sediments. The concentrations of suspended matter observed on the central shoals are more influenced by storms than by seasonal changes. Winter storms produce highest concentrations of non-combustible material throughout the water column, and summer storms appear to increase biological production by mixing additional nutrients into the photic zone. On the south-east flank of the bank, in water depths between 80 and 200 in, the concentrations of total suspended matter and non-combustible material show little variation compared with the central shoals, and storm effects are far less noticeable. Highest concentrations (>15 mg 1 −1 ) of suspended matter occur in bottom waters south of Nantucket Island after winter storms and appear to be primarily resuspended bottom sediment. Resuspended sediment is also common in near-bottom waters of the south-western Gulf of Maine, and occasionally near the intersection of the shelf/slope water mass front and the bottom. Seasonal variations were observed in the distribution and species composition of phytoplankton. Coccoliths are predominant on the central bank during the winter, but during the spring and summer they are concentrated on the eastern flank at deeper depths.

Georges Bank↗