Predicting Upwelling Due to Down-Fjord Winds. Klymak, J. M., Jackson, J. M., & Hannah, C. G. J. Phys. Oceanogr., 55(9):1553–1568, 2025. doi abstract bibtex Abstract Down-fjord winds have been implicated in upwelling and exchange of water in fjords. In one temperate fjord, strong winds oxygenated and cooled water deeper than 100 m. Deep temperature minima accompanied by oxygen maxima are a common feature in fjords, yet do not have a ready prediction. Here, it is shown that the dominant process driving the upwelling is wind-driven transport divergence at the head of the fjord, as opposed to local convection due to cooling or mechanical mixing. Previous work has focused on two-layer approximations, but those fail to differentiate the depth of upwelling if the bottom layer is continuously stratified. Simulations with a constant stratification show that the depth that the densest water comes from is proportional to , where L is the length of the fjord or the horizontal scale of the wind, is the wind stress, and N 2 is the buoyancy profile. The time scale of the upwelling is similarly scaled as . These scalings apply over a wide range of forcings and geometry, so long as the depth scale does not approach the depth of the fjord. A simple procedure can be used to get a similar scaling if N ( z ) is not constant. If the wind is allowed to relax, the simulations come back to rest after a vigorous seiche, subducting the upwelled water. Despite strong turbulence, the net exchange with water outside the fjord is found to be small, and oxygen concentrations are mostly modified by air–sea gas exchange rather than diapycnal mixing. Significance Statement Upwelling in fjords due to down-fjord winds has the potential to ventilate deep water and to drive exchange with water outside the fjord. Here, we offer a simple method to predict the depth and time scale of the upwelling based on the wind strength, the initial stratification, and the length of the fjord. Vertical mixing has only a minor impact on the vertical distribution of properties in the fjord due to the wind events, and much of the transport into the fjord is reversible in the absence of other mixing sources.
@Article{ klymaketal25,
Title = {Predicting {{Upwelling}} Due to {{Down-Fjord Winds}}},
Author = {Klymak, Jody M. and Jackson, Jennifer M. and Hannah,
Charles G.},
Year = {2025},
Journal = {J. Phys. Oceanogr.},
Volume = {55},
Number = {9},
Pages = {1553--1568},
DOI = {10.1175/JPO-D-24-0176.1},
URLDate = {2025-10-10},
Abstract = {Abstract Down-fjord winds have been implicated in
upwelling and exchange of water in fjords. In one temperate
fjord, strong winds oxygenated and cooled water deeper than
100 m. Deep temperature minima accompanied by oxygen maxima
are a common feature in fjords, yet do not have a ready
prediction. Here, it is shown that the dominant process
driving the upwelling is wind-driven transport divergence
at the head of the fjord, as opposed to local convection
due to cooling or mechanical mixing. Previous work has
focused on two-layer approximations, but those fail to
differentiate the depth of upwelling if the bottom layer is
continuously stratified. Simulations with a constant
stratification show that the depth that the densest water
comes from is proportional to , where L is the length of
the fjord or the horizontal scale of the wind, is the wind
stress, and N 2 is the buoyancy profile. The time scale of
the upwelling is similarly scaled as . These scalings apply
over a wide range of forcings and geometry, so long as the
depth scale does not approach the depth of the fjord. A
simple procedure can be used to get a similar scaling if N
( z ) is not constant. If the wind is allowed to relax, the
simulations come back to rest after a vigorous seiche,
subducting the upwelled water. Despite strong turbulence,
the net exchange with water outside the fjord is found to
be small, and oxygen concentrations are mostly modified by
air--sea gas exchange rather than diapycnal mixing.
Significance Statement Upwelling in fjords due to
down-fjord winds has the potential to ventilate deep water
and to drive exchange with water outside the fjord. Here,
we offer a simple method to predict the depth and time
scale of the upwelling based on the wind strength, the
initial stratification, and the length of the fjord.
Vertical mixing has only a minor impact on the vertical
distribution of properties in the fjord due to the wind
events, and much of the transport into the fjord is
reversible in the absence of other mixing sources.},
copyright = {http://www.ametsoc.org/PUBSReuseLicenses},
Keywords = {jmkrefereed},
File = {/Users/jklymak/Zotero/storage/3UUYTMIM/Klymak et al. -
2025 - Predicting Upwelling due to Down-Fjord Winds.pdf}
}
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Deep temperature minima accompanied by oxygen maxima are a common feature in fjords, yet do not have a ready prediction. Here, it is shown that the dominant process driving the upwelling is wind-driven transport divergence at the head of the fjord, as opposed to local convection due to cooling or mechanical mixing. Previous work has focused on two-layer approximations, but those fail to differentiate the depth of upwelling if the bottom layer is continuously stratified. Simulations with a constant stratification show that the depth that the densest water comes from is proportional to , where L is the length of the fjord or the horizontal scale of the wind, is the wind stress, and N 2 is the buoyancy profile. The time scale of the upwelling is similarly scaled as . These scalings apply over a wide range of forcings and geometry, so long as the depth scale does not approach the depth of the fjord. A simple procedure can be used to get a similar scaling if N ( z ) is not constant. If the wind is allowed to relax, the simulations come back to rest after a vigorous seiche, subducting the upwelled water. Despite strong turbulence, the net exchange with water outside the fjord is found to be small, and oxygen concentrations are mostly modified by air–sea gas exchange rather than diapycnal mixing. Significance Statement Upwelling in fjords due to down-fjord winds has the potential to ventilate deep water and to drive exchange with water outside the fjord. Here, we offer a simple method to predict the depth and time scale of the upwelling based on the wind strength, the initial stratification, and the length of the fjord. Vertical mixing has only a minor impact on the vertical distribution of properties in the fjord due to the wind events, and much of the transport into the fjord is reversible in the absence of other mixing sources.","copyright":"http://www.ametsoc.org/PUBSReuseLicenses","keywords":"jmkrefereed","file":"/Users/jklymak/Zotero/storage/3UUYTMIM/Klymak et al. - 2025 - Predicting Upwelling due to Down-Fjord Winds.pdf","bibtex":"@Article{\t klymaketal25,\n Title\t\t= {Predicting {{Upwelling}} Due to {{Down-Fjord Winds}}},\n Author\t= {Klymak, Jody M. and Jackson, Jennifer M. and Hannah,\n\t\t Charles G.},\n Year\t\t= {2025},\n Journal\t= {J. Phys. Oceanogr.},\n Volume\t= {55},\n Number\t= {9},\n Pages\t\t= {1553--1568},\n DOI\t\t= {10.1175/JPO-D-24-0176.1},\n URLDate\t= {2025-10-10},\n Abstract\t= {Abstract Down-fjord winds have been implicated in\n\t\t upwelling and exchange of water in fjords. In one temperate\n\t\t fjord, strong winds oxygenated and cooled water deeper than\n\t\t 100 m. Deep temperature minima accompanied by oxygen maxima\n\t\t are a common feature in fjords, yet do not have a ready\n\t\t prediction. Here, it is shown that the dominant process\n\t\t driving the upwelling is wind-driven transport divergence\n\t\t at the head of the fjord, as opposed to local convection\n\t\t due to cooling or mechanical mixing. Previous work has\n\t\t focused on two-layer approximations, but those fail to\n\t\t differentiate the depth of upwelling if the bottom layer is\n\t\t continuously stratified. Simulations with a constant\n\t\t stratification show that the depth that the densest water\n\t\t comes from is proportional to , where L is the length of\n\t\t the fjord or the horizontal scale of the wind, is the wind\n\t\t stress, and N 2 is the buoyancy profile. The time scale of\n\t\t the upwelling is similarly scaled as . These scalings apply\n\t\t over a wide range of forcings and geometry, so long as the\n\t\t depth scale does not approach the depth of the fjord. A\n\t\t simple procedure can be used to get a similar scaling if N\n\t\t ( z ) is not constant. If the wind is allowed to relax, the\n\t\t simulations come back to rest after a vigorous seiche,\n\t\t subducting the upwelled water. Despite strong turbulence,\n\t\t the net exchange with water outside the fjord is found to\n\t\t be small, and oxygen concentrations are mostly modified by\n\t\t air--sea gas exchange rather than diapycnal mixing.\n\t\t Significance Statement Upwelling in fjords due to\n\t\t down-fjord winds has the potential to ventilate deep water\n\t\t and to drive exchange with water outside the fjord. 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