Observations of inshore water exchange forced by a fluctuating offshore density field

Aure, Jan; Molvær, J.; Stigebrandt, Anders

doi:10.1016/s0025-326x(97)00005-2

Cited by 61 publications

(59 citation statements)

References 9 publications

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“…Generally, the fjord response increases for narrower fjords and lower forcing frequencies. This has already been contrasted with the standing wave model and the slab mode, but now we turn to the empirical relationship from Aure et al (1996), which has recently been used to estimate the shelf-driven fluxes in Greenlandic and Norwegian fjords (e.g. Sutherland et al, 2014b;Inall et al, 2015).…”

Section: Comparing Results With Previous Fjord Studiesmentioning

confidence: 99%

“…Sutherland et al, 2014b;Inall et al, 2015). For a rectangular two-layer fjord, the volume flux between fjord and shelf predicted by Aure et al (1996) in Eq. 4.1 reduces to: …”

Section: Comparing Results With Previous Fjord Studiesmentioning

confidence: 99%

“…Later studies by Aure et al (1996) and Arneborg (2004) showed that high frequency fluctuations were more efficient at driving exchange than low frequency ones. Arneborg (2004) estimated the fjord turnover time (the time for the volume in basin to be diluted by 63%) to be several weeks and found that the exchange was dominated by shelf forcing.…”

Section: Background On Shelf Forcing In Fjordsmentioning

confidence: 99%

“…First, Aure et al (1996) derived an empirical relationship for the mean exchange between fjord and shelf as a function of density variability on the shelf:…”

Section: Background On Shelf Forcing In Fjordsmentioning

confidence: 99%

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Dynamics of Greenland�s glacial fjords

Jackson¹

2016

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Glacial fjords form conduits between glaciers of the Greenland Ice Sheet and the North Atlantic. They are the gateways for importing oceanic heat to melt ice and for exporting meltwater into the ocean. Submarine melting in fjords has been implicated as a driver of recent glacier acceleration; however, there are no direct measurements of this melting, and little is known about the fjord processes that modulate melt rates. Combining observations, theory, and modeling, this thesis investigates the circulation, heat transport, and meltwater export in glacial fjords.While most recent studies focus on glacial buoyancy forcing, there are other drivers -e.g. tides, local wind, shelf variability -that can be important for fjord circulation. Using moored records from two major Greenlandic fjords, shelf forcing (from shelf density fluctuations) is found to dominate the fjord circulation, driving rapid exchange with the shelf and large heat content variability near the glacier. Contrary to the conventional paradigm, these flows mask any glacier-driven circulation in the non-summer months. During the summer, when shelf forcing is reduced and freshwater forcing peaks, a mean exchange flow transports warm Atlantic-origin water towards the glacier and exports glacial meltwater.Many recent studies have inferred submarine melt rates from oceanic heat transport, but the fjord budgets that underlie this method have been overlooked. Building on estuarine studies of salt fluxes, this thesis presents a new framework for assessing glacial fjord budgets and revised equations for inferring meltwater fluxes. Two different seasonal regimes are found in the heat/salt budgets for Sermilik Fjord, and the results provide the first time-series of submarine meltwater and subglacial discharge fluxes into a glacial fjord.Finally, building on the observations, ROMS numerical simulations and two analytical models are used to investigate the dynamics of shelf-driven flows and their importance relative to local wind forcing across the parameter space of Greenland's fjords. The fjord response is found to vary primarily with the width relative to the deformation radius and the fjord adjustment timescale relative to the forcing timescale. Understanding these modes of circulation is a step towards accurate modeling of ocean-glacier interactions.

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Section: Comparing Results With Previous Fjord Studiesmentioning

confidence: 99%

“…Sutherland et al, 2014b;Inall et al, 2015). For a rectangular two-layer fjord, the volume flux between fjord and shelf predicted by Aure et al (1996) in Eq. 4.1 reduces to: …”

Section: Comparing Results With Previous Fjord Studiesmentioning

confidence: 99%

Section: Background On Shelf Forcing In Fjordsmentioning

confidence: 99%

“…First, Aure et al (1996) derived an empirical relationship for the mean exchange between fjord and shelf as a function of density variability on the shelf:…”

Section: Background On Shelf Forcing In Fjordsmentioning

confidence: 99%

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Dynamics of Greenland�s glacial fjords

Jackson¹

2016

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“…These kind of fluctuating baroclinic currents are commonly seen in the fjords around Skagerrak (e.g., Aure et al 1996;Arneborg 2004). …”

mentioning

confidence: 94%

Observations of Turbulence Caused by a Combination of Tides and Mean Baroclinic Flow over a Fjord Sill

Staalstrøm

Arneborg

Liljebladh

et al. 2015

Journal of Physical Oceanography

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This study investigates the dissipation rates and flow conditions at the Drøbak Sill in the Oslofjord. The area was transected 13 times with a free-falling microstructure shear probe during 4 days in June 2011. At the same time, an ADCP was deployed inside the sill. During most tidal cycles, internal hydraulic jumps with high dissipation rates were found on the downstream side of the sill. However, the internal response varied strongly between different tidal cycles with similar barotropic forcing. In the beginning of the observational period, ebb tides had no hydraulic jumps, and in the end one of the flood tides did not have a hydraulic jump. During the same period, the mean baroclinic exchange flow changed from inflow to outflow in the bottom layer. The authors conclude that the conditions at the sill are on the edge of forming hydraulic jumps and that the mean baroclinic exchange may push the flow above or below the limit of a hydraulic jump depending on the situation. This conclusion is supported by two-layer hydraulic theory. The volume-integrated dissipation rates within 500 m from the sill crest compare well with estimates of energy loss in the lower layer calculated from the Bernoulli drop under the assumption of no energy loss in the upper layer. Finally, the mean dissipation rate at the sill was compared with the radiation of internal tidal energy away from the sill, and it was found that about 60%-90% of the total energy loss was dissipated locally.

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Characteristics and dynamics of two major Greenland glacial fjords

2014

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The circulation regimes of two major outlet glacial fjords in southeastern Greenland, Sermilik Fjord (SF) and Kangerdlugssuaq Fjord (KF), are investigated using data collected in summer 2009. The two fjords show similar flow patterns, with a time-dependent, vertically sheared flow structure dominating over the background estuarine flow driven by buoyancy input. We show that this time-dependent flow is consistent with circulation induced by density interface fluctuations at the fjord mouth, often referred to as intermediary circulation. One difference between the fjords is that the hydrographic and velocity structure below a surface modified layer is found to be three layer in KF in summer, compared to two layer in SF. Outside each fjord, large-scale geostrophic currents dictate the stratification at the mouth, although the way in which these large-scale flows impinge on each fjord is distinct. Combining the observations with estimates from existing theories, we find the magnitudes of the estuarine (Q e ) and intermediary (Q i ) circulation and show that Q i >> Q e , although along-fjord winds can also be significant. We expect that the critical parameter determining Q i /Q e is the sill depth compared to the fjord depth, with shallower sills corresponding to weaker intermediary circulation. Finally, we discuss the implications of strong intermediary circulation on calculating heat transport to the glacier face and its potential feedbacks on the background circulation in these highly stratified estuaries.

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Observations of inshore water exchange forced by a fluctuating offshore density field

Cited by 61 publications

References 9 publications

Dynamics of Greenland�s glacial fjords

Dynamics of Greenland�s glacial fjords

Observations of Turbulence Caused by a Combination of Tides and Mean Baroclinic Flow over a Fjord Sill

Characteristics and dynamics of two major Greenland glacial fjords

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