Control of Mode and Intermediate Water Mass Properties in Drake Passage by the Amundsen Sea Low

Close, Sally; Garabato, Alberto C. Naveira; McDonagh, Elaine L.; King, Brian; Biuw, Martin; Boehme, Lars

doi:10.1175/jcli-d-12-00346.1

Cited by 23 publications

(20 citation statements)

References 70 publications

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“…Indeed, seasonal patterns reasonably reflect the different physics that are expected to modulate the MLD anomalies during summer (dominated by wind‐driven mechanical forcing variations) and winter (when heat fluxes may play the most important role). Given the patterns identified, a distinct impact of SAM variations on winter AAIW and SAMW formation can be expected (see also Close et al, ; Naveira Garabato et al, ), as well as on the summer phytoplankton blooms (e.g., Ardyna et al, ; Rohr et al, ).…”

Section: Mld Variabilitymentioning

confidence: 93%

“…As MLD during summer is expected to be dominated by the wind‐driven mechanical forcings, the strong (positive) anomaly observed in Figure f could be related to the local increase in wind intensities associated with positive SAM. The different wind‐driven export of freshwater from the southernmost regions is then presumed also to impact the AAIW formation in winter (Close et al, ; Naveira Garabato et al, ). On the other hand, the strong anticorrelation in the Atlantic sector and eastern Indian sector, where most of the primary production is observed, Ardyna et al () suggest that in fact SAM can strongly modulate the biological component of the carbon export in the SO.…”

Section: Mld Variabilitymentioning

confidence: 99%

See 1 more Smart Citation

Southern Ocean Mixed‐Layer Seasonal and Interannual Variations From Combined Satellite and In Situ Data

et al. 2017

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The depth of the upper ocean mixed layer provides fundamental information on the amount of seawater that directly interacts with the atmosphere. Its space‐time variability modulates water mass formation and carbon sequestration processes related to both the physical and biological pumps. These processes are particularly relevant in the Southern Ocean, where surface mixed‐layer depth estimates are generally obtained either as climatological fields derived from in situ observations or through numerical simulations. Here we demonstrate that weekly observation‐based reconstructions can be used to describe the variations of the mixed‐layer depth in the upper ocean over a range of space and time scales. We compare and validate four different products obtained by combining satellite measurements of the sea surface temperature, salinity, and dynamic topography and in situ Argo profiles. We also compute an ensemble mean and use the corresponding spread to estimate mixed‐layer depth uncertainties and to identify the more reliable products. The analysis points out the advantage of synergistic approaches that include in input the sea surface salinity observations obtained through a multivariate optimal interpolation. Corresponding data allow to assess mixed‐layer depth seasonal and interannual variability. Specifically, the maximum correlations between mixed‐layer anomalies and the Southern Annular Mode are found at different time lags, related to distinct summer/winter responses in the Antarctic Intermediate Water and Sub‐Antarctic Mode Waters main formation areas.

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Section: Mld Variabilitymentioning

confidence: 93%

Section: Mld Variabilitymentioning

confidence: 99%

Southern Ocean Mixed‐Layer Seasonal and Interannual Variations From Combined Satellite and In Situ Data

et al. 2017

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“…The negative sensitivity of the Pacific MWFR to zonal wind stress on 1-3 year lags in the region of 120W to 90W and South of 60S (the Amundsen Sea, see figure 4) is consistent with the results of Close et al 2013, who find a link between an increased Amundsen Sea Low (ASL, resulting in weaker zonal wind stress) and warmer SAMW. However, this sensitivity is relatively weak compared with zonal and meridional (see figure S6 in the supplementary information) wind stress sensitivities over, to the north of, and upstream of the MWFR, whilst Close et al (2013) believe the ASL is significant in determining SAMW properties. This may be because although the region shows low sensitivity relative to other regions, the actual wind-stress changes in the region are significantly larger than those in other regions, although this does not appear to be the case for climatological anomalies, see figure S7.…”

Section: Experiments Designmentioning

confidence: 94%

Local and remote influences on the heat content of Southern Ocean mode water formation regions.

Boland¹,

Harle²,

Meijers³

et al. 2019

Preprint

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The Southern Ocean (SO) is a crucial region for the global ocean uptake of heat and carbon. There are large uncertainties in the observations of fluxes of heat and carbon between the atmosphere and the ocean mixed layer, which leads to large uncertainties in the amount entering into the global overturning circulation. In order to better understand where and when fluxes of heat and momentum have the largest impact on near-surface heat content, we use an adjoint model to calculate the linear sensitivities of heat content in SO mode water formation regions to surface fluxes. We find that the heat content of these regions is most sensitive to recent, local heat fluxes, and to non-local wind stress fluxes on the order of one to eight years previously. This is supported by the calculation of sensitivities to kinematic potential temperature changes, which reveal the sources of the mode water formation regions, and by sensitivities to dynamic potential temperature changes, which reveal dynamic links with boundary currents, the ACC, Kelvin and Rossby waves. A series of forward perturbation experiments in the fully non-linear model confirm that the adjoint model can accurately predict linear changes in heat content of fixed volume mode water formation regions. These experiments also highlight that nonlinear effects can also be of importance, depending on the time and region investigated, and that the contribution of volume changes to heat content changes can be as large or larger than temperature changes.

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“…As a result of this overturning circulation, the properties of SAMW and AAIW are potentially sensitive to anomalies in near-Antarctic waters. For example, the variability of the Amundsen Sea low (ASL) can affect the interannual and interdecadal variability of SAMW in the Southeast Pacific via cross-frontal Ekman transport of Antarctic surface waters (Garabato et al 2009;Close et al 2013). In 2008-2010, a deep ASL enhanced the meridional wind-driven sea ice export from the eastern Ross Sea; the sea ice melt introduced a cold surface freshwater anomaly that was advected across the PF and SAF by Ekman transport and then transported into the SAMW formation region by the ACC (Cerovecki et al 2019).…”

Section: Discussionmentioning

confidence: 99%

The Sensitivity of Southeast Pacific Heat Distribution to Local and Remote Changes in Ocean Properties

Jones

Boland

Meijers

et al. 2020

Journal of Physical Oceanography

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The Southern Ocean features ventilation pathways that transport surface waters into the subsurface thermocline on time scales from decades to centuries, sequestering anomalies of heat and carbon away from the atmosphere and thereby regulating the rate of surface warming. Despite its importance for climate sensitivity, the factors that control the distribution of heat along these pathways are not well understood. In this study, we use an observationally constrained, physically consistent global ocean model to examine the sensitivity of heat distribution in the recently ventilated subsurface Pacific (RVP) sector of the Southern Ocean to changes in ocean temperature and salinity. First, we define the RVP using numerical passive tracer release experiments that highlight the ventilation pathways. Next, we use an ensemble of adjoint sensitivity experiments to quantify the sensitivity of the RVP heat content to changes in ocean temperature and salinity. In terms of sensitivities to surface ocean properties, we find that RVP heat content is most sensitive to anomalies along the Antarctic Circumpolar Current (ACC), upstream of the subduction hotspots. In terms of sensitivities to subsurface ocean properties, we find that RVP heat content is most sensitive to basin-scale changes in the subtropical Pacific Ocean, around the same latitudes as the RVP. Despite the localized nature of mode water subduction hotspots, changes in basin-scale density gradients are an important controlling factor on heat distribution in the southeast Pacific.

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Control of Mode and Intermediate Water Mass Properties in Drake Passage by the Amundsen Sea Low

Cited by 23 publications

References 70 publications

Southern Ocean Mixed‐Layer Seasonal and Interannual Variations From Combined Satellite and In Situ Data

Southern Ocean Mixed‐Layer Seasonal and Interannual Variations From Combined Satellite and In Situ Data

Local and remote influences on the heat content of Southern Ocean mode water formation regions.

The Sensitivity of Southeast Pacific Heat Distribution to Local and Remote Changes in Ocean Properties

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