Seasonal Characteristics of Bottom Boundary Layer Detachment at the Shelfbreak Front in the Middle Atlantic Bight PDF Download
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Languages : en
Pages : 0
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The seasonality of various characteristics of the detached bottom boundary layer of the Middle Atlantic Bight shelfbreak front is examined using a collection of high resolution transects across the front. The analysis follows previous methodology in which accumulated temperature change along isopycnals within the front is used to infer the location of the detached layer. The seasonal mean isopycnal at which detachment occurs (approximately 26.0 kg cu.m) is fairly constant throughout the year. However, the vertical scale of the detached layer varies significantly with season, extending 60-80 m above the bottom in winter and spring, but only 20-40 m above the bottom in summer. The vertical scale is controlled by the strength and depth of the seasonal pycnocline. The observations suggest that the detached layer is capable of extending into the euphotic zone during winter and spring. INDEX TERMS: 4528 Oceanography: Physical: Fronts and jets; 4211 Oceanography: General: Benthic boundary layers; 4219 Oceanography: General: Continental shelf processes; 4279 Oceanography: General: Upwelling and convergences.
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Languages : en
Pages : 0
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Book Description
The seasonality of various characteristics of the detached bottom boundary layer of the Middle Atlantic Bight shelfbreak front is examined using a collection of high resolution transects across the front. The analysis follows previous methodology in which accumulated temperature change along isopycnals within the front is used to infer the location of the detached layer. The seasonal mean isopycnal at which detachment occurs (approximately 26.0 kg cu.m) is fairly constant throughout the year. However, the vertical scale of the detached layer varies significantly with season, extending 60-80 m above the bottom in winter and spring, but only 20-40 m above the bottom in summer. The vertical scale is controlled by the strength and depth of the seasonal pycnocline. The observations suggest that the detached layer is capable of extending into the euphotic zone during winter and spring. INDEX TERMS: 4528 Oceanography: Physical: Fronts and jets; 4211 Oceanography: General: Benthic boundary layers; 4219 Oceanography: General: Continental shelf processes; 4279 Oceanography: General: Upwelling and convergences.
Author: Kuoping Chiang
Publisher: Frontiers Media SA
ISBN: 2832515401
Category : Science
Languages : en
Pages : 534
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Author: Christopher Anthony Linder
Publisher:
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Category : Climatology
Languages : en
Pages : 96
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Description of the shelfbreak front in the Middle Atlantic Bight is hampered by the extreme variability of the front. In order to gain more insight into the mean frontal structure and associated baroclinic jet, historical data is used to produce two dimensional climatological fields of temperature and salinity for the region south of Nantucket shoals. Associated cross-shelf fields of density, geostrophic velocity, relative vorticity, and shallow water potential vorticity have also been computed. Historical data from a quality-controlled database (HydroBase) in the region 69-72°W, 39.5-41°N is included. Cross-shelf sections are obtained by averaging the data in nine depth bins with an average cross-shelf spacing of 10 km but an increased resolution of 4 km near the shelfbreak. The vertical averaging interval was 10 m over the shelf and upper slope waters, increasing to 50 m in the deep slope waters. The data were averaged in bimonthly periods to study seasonal trends. For inter-regional comparison, similar analyses were performed for the south flank of Georges Bank and the shelf off New Jersey. The climatological temperature and salinity are consistent with previous descriptions of the frontal hydrography (e.g. Wright [1976], Beardsley and Flagg [1976], and Flagg [1987]). Most importantly, features such as the "cold pool", the upper slope pycnostad, and the frontal boundary are well resolved when compared with synoptic sections. The temperature contrast across the front varies seasonally between 2-6°C near the surface and at depths of 45-65 m. The salinity contrast is 1.5-2 PSS, with little seasonal variation. The resulting cross-frontal near surface density gradients are strongest during the winter and weakest during the summer, when the seasonal thermocline is established. The crossfrontal density gradients are stronger near the bottom outcrop of the front, consistent with previous modeling studies [Gawarkiewicz and Chapman, 1992]. Despite the inherent smearing of frontal gradients incurred by averaging over large temporal and spatial scales, the geostrophic velocity field shows a strong (20-30 cm s-1) baroclinic jet associated with the cross-frontal density gradients. The core of the jet, having a width of 15-20 km, is located between the 100-120 m isobaths. The core of the jet is well shoreward of the surface expression of the front, resulting from strong density gradients at the foot of the front. The horizontal velocity shear on the cyclonic, offshore edge of the front is roughly 0.2-0.4 * 10-4 s-1, with shears on the anticyclonic, offshore edge of the jet being half as large. The potential vorticity structure is drastically affected by the seasonal pycnocline during the summer but remains relatively uniform during the winter months. Comparisons of the mean fields from Georges Bank, Nantucket Shoals, and New Jersey show that the foot of the front shoals as the flow progresses to the southwest. The seasonal migration of the frontal boundary experiences a phase shift consistent with an alongshelf propagation of minimum salinities to the southwest. Finally, transport calculations for the flow over the outer shelf and slope give values in the range of 0.1-0.6 Sv to the west. This is comparable to the estimated transport shoreward of the 100 m isobath of 0.38 Sv [Beardsley et al., 1985], which suggests that the shelfbreak frontal jet may be an extremely important element in the alongshelf transport of fresh water in this region.
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Category : Marine meteorology
Languages : en
Pages : 824
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Category : Astrophysics
Languages : en
Pages : 534
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Author: Andrew Joseph Hirzel
Publisher:
ISBN:
Category : Chlorophyll
Languages : en
Pages : 0
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The Middle Atlantic Bight (MAB) is a highly productive ecosystem, supporting several economically important commercial fisheries. Chlorophyll enhancement at the MAB shelf-break front has been observed only intermittently, despite numerous studies that suggest persistent upwelling at the front. High resolution cross-frontal transect crossings were collected from three two-week cruises in April 2018, May 2019, and July 2019. Chapter 2 focused on applying a novel method of classifying planktonic images taken by a Video Plankton Recorder to enable processing of the large volumes of data collected with the instrument. Chapter 3 investigated cross-frontal trends by temporally averaging in both Eulerian and frontally-aligned coordinates. For April 2018, transient chlorophyll enhancement was seen at the front in individual transects and within the frontally-aligned mean transect, but not within the Eulerian mean transect. The Eulerian mean for May 2019 showed chlorophyll enhancement as a result of frontal eddies, which were further explored in chapter 4. No frontal enhancement was observed in July 2019. The frontal eddies observed in May 2019 were simulated using an idealized model, which showed that upwelling occurred within both of the frontal eddies, despite having opposite rotational directions. This result was consistent with nutrient enhancement observed within the centers of both eddies. Biological enhancement within each eddy was observed, which may have been a result of advection from source waters and/or a local response to upwelled nutrients. The influence of frontal variability and frontal eddies on nutrients and plankton at the front argues for the necessity for 3-D models to fully explain frontal behavior and its effects on biological responses.
Author: Derek Maxwell Burrage
Publisher:
ISBN:
Category : Continental shelf
Languages : en
Pages : 770
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Author: Roland L. Wigley
Publisher:
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Category : Continental shelf
Languages : en
Pages : 214
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Category :
Languages : en
Pages : 0
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Analysis of the Shelfbreak PRIMER data sets are described. These data sets, consisting of primarily high-resolution hydrographic surveys, show important shelfbreak processes including interaction of a slope eddy with the front, large-amplitude frontal meandering, and frontal response to wind forcing. In addition, collaborative work with acousticians on acoustic propagation across the front is also described. In general, the front is shown to contain large horizontal and vertical velocity shears, leading to large day-to-day variability. In addition to analysis of these data sets, analysis of drifter tracks near the front have also shown new perspectives on exchange across the front, and a stability analysis of the front was also performed.
Author: Derek Maxwell Burrage
Publisher:
ISBN:
Category :
Languages : en
Pages : 385
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