Inner shelf intrusions of offshore water in an upwelling system affect coastal connectivity

Nidzieko, Nicholas J.; Largier, John L.

doi:10.1002/2013gl056756

Cited by 16 publications

(9 citation statements)

References 32 publications

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“…Sal within 3 hr of south of Pt. Purisima (Figure a), much too fast for a northward‐flowing current and implying onshore advection of warm water due to other processes (Nidzieko & Largier, ). Thus, the Melton et al () prior southern arrival criteria bias to inferred northward propagation and give the appearance of consistency with the Lentz and Helfrich () model.…”

Section: Discussionmentioning

confidence: 99%

Inner‐Shelf Vertical and Alongshore temperature Variability in the Subtidal, Diurnal, and Semidiurnal Bands Along the central California coastline with headlands

et al. 2020

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The temporal, vertical, and alongshore variation in inner‐shelf temperature, T, across subtidal (ST), diurnal (DU), and semidiurnal (SD) bands on coastlines with headlands is not understood. Inner‐shelf T was observed with 20 moorings in 9‐ to 16‐m depth with high vertical density during Fall 2017 along 50 km of central California coastline with headlands. The ST‐first empirical orthogonal function is largely barotropic. ST warm water events are associated with northward‐propagating buoyant plumes and onshore advection of offshore water, with headland effects, particularly for stronger events. Previous plume arrival criteria are northward propagation biased. The DU vertical structure was mixed barotropic and linear baroclinic, without surface extrema. Inner‐shelf DU‐band temperature variability was always evident, largest north of and weakest south of two headlands. The DU‐T envelope was not modulated by ST stratification and was not linked to the modeled DU‐wind envelope. North of one headland, the alongshore first complex empirical orthogonal function of DU temperature has a previously unobserved southward 2‐m/s phase propagation, even though DU frequency is subcritical, that is, not wind forced. A frictional subcritical wave mechanism is proposed for the DU propagation. The SD‐T vertical structure varies alongshore, suggesting at different locations linear internal waves and nonlinear cold bores. SD‐T variability was incoherent with barotropic tides and decorrelates alongshore in 7.5 km, contrasting with a few kilometers offshore. The SD depth‐averaged energy varied strongly alongshore particularly north and south of the headlands, and stronger and weaker SD energy was linked to nonlinear and linear baroclinic vertical structures, respectively, which are headland influenced.

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Section: Discussionmentioning

confidence: 99%

Inner‐Shelf Vertical and Alongshore temperature Variability in the Subtidal, Diurnal, and Semidiurnal Bands Along the central California coastline with headlands

et al. 2020

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“…SST images indicate that these cold and warm water masses are the result of regional water masses advected into SLO Bay from the north and south/offshore, respectively (Figure 2h). The cold water mass is likely the result of extended regional upwelling lasting several weeks prior Journal of Geophysical Research: Oceans 10.1002/2016JC012466 to the start of the observations (not shown), while the warm water mass appears to originate from the combination of a poleward warm water flow from south of Point Conception [Washburn et al, 2011] and the intrusion of offshore waters that originate from submesoscale features [Nidzieko and Largier, 2013]. The second prominent feature, and the focus of this study, is higher-frequency variability that results in large daily temperature fluctuations (up to 58C) on the same order of those driven by regional water mass advection, and the associated appearance of strong frontal features that result in the episodic stratification of the water column.…”

Section: General Observationsmentioning

confidence: 99%

Local diurnal wind‐driven variability and upwelling in a small coastal embayment

Walter

Reid

Davis

et al. 2017

J. Geophys. Res. Oceans

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The oceanic response to high‐frequency local diurnal wind forcing is examined in a small coastal embayment located along an understudied stretch of the central California coast. We show that local diurnal wind forcing is the dominant control on nearshore temperature variability and circulation patterns. A complex empirical orthogonal function (CEOF) analysis of velocities in San Luis Obispo Bay reveals that the first‐mode CEOF amplitude time series, which accounts for 47.9% of the variance, is significantly coherent with the local wind signal at the diurnal frequency and aligns with periods of weak and strong wind forcing. The diurnal evolution of the hydrographic structure and circulation in the bay is examined using both individual events and composite‐day averages. During the late afternoon, the local wind strengthens and results in a sheared flow with near‐surface warm waters directed out of the bay and a compensating flow of colder waters into the bay over the bottom portion of the water column. This cold water intrusion into the bay causes isotherms to shoal toward the surface and delivers subthermocline waters to shallow reaches of the bay, representing a mechanism for small‐scale upwelling. When the local winds relax, the warm water mass advects back into the bay in the form of a buoyant plume front. Local diurnal winds are expected to play an important role in nearshore dynamics and local upwelling in other small coastal embayments with important implications for various biological and ecological processes.

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“…Moorings have been used to characterize the three‐dimensional inner‐shelf circulation (e.g., Kirincich & Barth, ; Tilburg & Garvine, ), but the number of locations that can be observed are limited. Remote sensing using satellites and high‐frequency radar have identified patterns of inner‐shelf lateral variability associated with bathymetric features and instabilities (Kim, ; Kirincich et al, ; Nidzieko & Largier, ) but are limited to the surface. A major challenge in characterizing and assessing the importance of the three‐dimensional inner‐shelf circulation lies in observing the range of potentially important spatial and temporal scales beneath the surface.…”

Section: Introductionmentioning

confidence: 99%

High‐Resolution Observations of Subsurface Fronts and Alongshore Bottom Temperature Variability Over the Inner Shelf

Connolly

Kirincich

2019

JGR Oceans

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Circulation patterns over the inner continental shelf can be spatially complex and highly variable in time. However, few studies have examined alongshore variability over short scales of kilometers or less. To observe inner-shelf bottom temperatures with high (5-m) horizontal resolution, a fiber-optic distributed temperature sensing system was deployed along a 5-km-long portion of the 15-m isobath within a larger-scale mooring array south of Martha's Vineyard, MA. Over the span of 4 months, variability at a range of scales was observed along the cable over time periods of less than a day. Notably, rapid cooling events propagated down the cable away from a tidal mixing front, showing that propagating fronts on the inner shelf can be generated locally near shallow bathymetric features in addition to remote offshore locations. Propagation velocities of observed fronts were influenced by background tidal currents in the alongshore component and show a weak correlation with theoretical gravity current speeds in the cross-shore component. These events provide a source of cold, dense water into the inner shelf. However, differences in the magnitude and frequency of cooling events at sites separated by a few kilometers in the alongshore direction suggest that the characteristics of small-scale variability can vary dramatically and can result in differential fluxes of water, heat, and other tracers. Thus, under stratified conditions, prolonged subsurface observations with high spatial and temporal resolution are needed to characterize the implications of three-dimensional circulation patterns on exchange, especially in regions where the coastline and isobaths are not straight. Plain Language SummaryThis study examines in detail how ocean temperature varies along a 5-km stretch of coastline off of Martha's Vineyard, MA, the site of a long-term ocean observatory. In addition to the gradual changes in ocean temperature that occur over long distances of hundreds of kilometers or more along the coast, there can also be sharp fronts where temperature changes rapidly over much shorter distances. Little is known about these features because they occur below the surface, move through the ocean, and are often short lived. To learn more about small-scale fronts and how they change with time, we used traditional oceanographic sensors anchored at a few specific locations and also laid a fiber-optic cable along the ocean floor at a depth of 15 m. This fiber-optic system continuously recorded hundreds of simultaneous temperature measurements along the coastline for several months. These measurements show that small-scale fronts often occur near a shallow shoal where there are strong tidal currents. However, the fronts also travel away from the shoal, causing rapid cooling along the sea floor as they move. Because of these subsurface fronts, temperature measurements at just one location may not be representative of other nearby locations just a few kilometers away.

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Inner shelf intrusions of offshore water in an upwelling system affect coastal connectivity

Cited by 16 publications

References 32 publications

Inner‐Shelf Vertical and Alongshore temperature Variability in the Subtidal, Diurnal, and Semidiurnal Bands Along the central California coastline with headlands

Inner‐Shelf Vertical and Alongshore temperature Variability in the Subtidal, Diurnal, and Semidiurnal Bands Along the central California coastline with headlands

Local diurnal wind‐driven variability and upwelling in a small coastal embayment

High‐Resolution Observations of Subsurface Fronts and Alongshore Bottom Temperature Variability Over the Inner Shelf

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