Seasonal Variability of the Cold Pool Over the Mid‐Atlantic Bight Continental Shelf

Curchitser, Enrique N.; Chant, Robert J.; Kang, Dujuan

doi:10.1029/2018jc014148

Cited by 46 publications

(58 citation statements)

References 41 publications

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“…Coldest subsurface waters observed around year day 206 at the shelf transect (Figure b) are consistent with temperature being set in late March or early April over the northern MAB shelf (e.g., Lentz, ). Warmest near‐bottom waters over the shelf occur in fall, presumably as warmer surface waters are mixed downward by storms (e.g., Chen et al, ; Fleming, ).…”

Section: Resultsmentioning

confidence: 99%

Export of Middle Atlantic Bight Shelf Waters Near Cape Hatteras From Two Years of Underwater Glider Observations

Todd

2020

JGR Oceans

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Equatorward flow of Middle Atlantic Bight (MAB) shelf waters meets poleward flowingSouth Atlantic Bight shelf waters over the continental shelf near Cape Hatteras, NC, leading to net export of shelf waters into the deep ocean. This export occurs in close proximity to the Gulf Stream, which separates from the continental margin near Cape Hatteras. Observations from sustained underwater glider surveys of the outer continental shelf and slope north of Cape Hatteras from spring 2017 to spring 2019 are used to examine the mean and variability of MAB shelf water export in the region. The 0.3 Sv (1 Sv = 10 6 m 3 s −1 ) time-mean export of MAB shelf water south of 37 • N was dominated by discrete export events; 50% of export occurred during the 17% of the time during which transport was more than 1 standard deviation above the mean. These events typically occurred in late spring and summer of both years when equatorward flow into the region peaked. Export of MAB shelf water was correlated with equatorward flow into the region, which was itself correlated with the density gradient across the continental shelf break. Observations during specific time periods that capture extrema in MAB shelf water export are examined to highlight the variability in shelf-deep ocean exchange scenarios in the Hatteras region. These include near-surface export driven by hurricanes, subsurface export below the northern edge of the Gulf Stream, and a multi-month near-cessation of export. Plain Language SummaryThe coastal ocean circulation near Cape Hatteras, NC, is characterized by convergence of waters from the Middle Atlantic Bight (MAB) and South Atlantic Bight. The resulting shelf water export takes place under the influence of forcing by variable winds (including passing tropical cyclones) and variable Gulf Stream strength and position just seaward of the continental shelf. As part of a program to understand the physical processes controlling exchange between the continental shelf and deep ocean at Cape Hatteras, autonomous underwater gliders surveyed the outer continental shelf and upper continental slope north of Cape Hatteras from spring 2017 through spring 2019. These observations are used to characterize the mean and annual cycle of the hydrography and circulation in the region and to examine temporal variability in the export of MAB shelf waters from the shelf. Time-mean MAB shelf water export of 0.3 Sv (1 Sv = 10 6 m 3 s −1 ) was dominated by export events in late spring and summer of both years. Variability in shelf water export was associated with variability in equatorward flow into the region and density gradients across the continental shelf break. To demonstrate the variety of export-related events in the region, several specific time periods are examined. Figure 1. (a) Map of the U.S. mid-Atlantic coast with the Cape Hatteras region outlined in black and shown in detail in (b); the gray 200-m isobath marks the shelf break. Schematic surface currents shown entering the region are the Gulf Stream (GS, dark red), the shelfbreak ...

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Section: Resultsmentioning

confidence: 99%

Export of Middle Atlantic Bight Shelf Waters Near Cape Hatteras From Two Years of Underwater Glider Observations

Todd

2020

JGR Oceans

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“…As Cold Pool presence in the SMAB can be broadly represented by large differences between surface and bottom water temperatures [17,18], we utilized the difference between satellite-derived sea surface temperature and in-situ receiver-recorded bottom water temperature as an index of temperature strati cation associated with the Cold Pool. In addition to the SMAB, this metric, ΔT, has previously been used as an index of thermal strati cation in other systems [2,48].…”

Section: Methodsmentioning

confidence: 99%

“…A seasonal thermocline, fueled by a combination of advection of bottom water from higher latitudes and surface heating [17], overwhelms salinity-driven mixing and forms in mid-to late-April, strengthening through the summer months. This cold bottom water, known as the Mid-Atlantic Cold Pool, persists in the shelf waters of the SMAB into late-summer when it is rapidly destroyed through surface mixing via tropical storms, offshore advection, and reduced thermal input [18][19][20]. After destruction of the Cold Pool, buoyancy-driven mixing once again becomes the dominant thermohaline process and lasts through the winter.…”

Section: Introductionmentioning

confidence: 99%

Influence of thermal stratification and storms on acoustic telemetry detection efficiency: a year-long test in the US Southern Mid-Atlantic Bight

O’Brien

Secor

2020

Preprint

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Background: The detection efficiency of ultrasonic transmitters is seasonally variable, requiring long-term studies to evaluate key environmental features that mask, alter speed, bend, or reflect transmissions. The US Southern Mid-Atlantic Bight shelf is characterized by a strong summer thermocline capping remnant winter water, known as the Cold Pool, and a well-mixed water column in other seasons. To investigate the effects of interactions between temperature stratification and storm-induced noise on transmission detectability, we conducted a year-long range test in the bottom waters of the US Southern Mid-Atlantic Bight. We used generalized additive models and cross-validation to develop and evaluate a predictive model of detection efficiency and visualize variability in detection distance throughout the year of deployment.Results: The most-predictive model utilized the interaction between temperature stratification and ambient noise, predicting that stratification results in a 54% increase in detectability and 56% increase in detection distance. The model had an overall error rate of 16.3% and an 18.7% error at a distance of 800 m, predicting 9% detectability when the water column was not stratified and 63% when the difference between surface and bottom temperatures was greater than 4.6 °C. The distance at 50% detectability increased with the formation of the Cold Pool during spring, shifting from 559 ± 149 m to 872 ± 81 m over 3 days. All seasons were associated with storm-induced reductions in overall detectability and distance at 50% detectability.Conclusion: Thermal stratification within the Southern Mid-Atlantic Bight increases bottom water ultrasonic transmitter detection distance and reduces the impact of surface noise associated with large storms. This effect leads to a seasonal increase in detection distance from the late-spring through the summer. To our knowledge, this study is the first to report and quantify an increase in detection range as a result of temperature stratification, likely due to placing transmitters and receivers on the same side of a strong thermocline.

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“…The long‐term (1958–2007) high‐resolution (~7 km in the horizontal; 40 vertical terrain‐following levels) numerical simulation of the NWA Ocean was performed with the Regional Ocean Modeling System (ROMS), a split‐explicit, free‐surface, terrain‐following, hydrostatic, primitive equation (Shchepetkin & McWilliams, 2005). The model grid and the model settings that include vertical mixing scheme, initial and oceanic boundary conditions, atmospheric forcing, river discharges runoff, and tides have been described in detail in previous studies (e.g., Chen et al, 2018; Kang & Curchitser, 2013, 2015). Model standard circulation state variables are archived at a daily interval.…”

Section: Methodsmentioning

confidence: 99%

Interannual Variability of the Mid‐Atlantic Bight Cold Pool

Curchitser

2020

JGR Oceans

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The Mid‐Atlantic Bight (MAB) Cold Pool is a bottom‐trapped, cold (temperature below 10°C) and fresh (practical salinity below 34) water mass that is isolated from the surface by the seasonal thermocline and is located over the midshelf and outer shelf of the MAB. The interannual variability of the Cold Pool with regard to its persistence time, volume, temperature, and seasonal along‐shelf propagation is investigated based on a long‐term (1958–2007) high‐resolution regional model of the northwest Atlantic Ocean. A Cold Pool Index is defined and computed in order to quantify the strength of the Cold Pool on the interannual timescale. Anomalous strong, weak, and normal years are categorized and compared based on the Cold Pool Index. A detailed quantitative study of the volume‐averaged heat budget of the Cold Pool region (CPR) has been examined on the interannual timescale. Results suggest that the initial temperature and abnormal warming/cooling due to advection are the primary drivers in the interannual variability of the near‐bottom CPR temperature anomaly during stratified seasons. The long persistence of temperature anomalies from winter to summer in the CPR also suggests a potential for seasonal predictability.

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Seasonal Variability of the Cold Pool Over the Mid‐Atlantic Bight Continental Shelf

Cited by 46 publications

References 41 publications

Export of Middle Atlantic Bight Shelf Waters Near Cape Hatteras From Two Years of Underwater Glider Observations

Export of Middle Atlantic Bight Shelf Waters Near Cape Hatteras From Two Years of Underwater Glider Observations

Influence of thermal stratification and storms on acoustic telemetry detection efficiency: a year-long test in the US Southern Mid-Atlantic Bight

Interannual Variability of the Mid‐Atlantic Bight Cold Pool

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