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  • 11
    Online Resource
    Online Resource
    Subduction over the Southern Indian Ocean in a High-Resolution Atmosphere–Ocean Coupled Model
    American Meteorological Society ; 2011
    In:  Journal of Climate Vol. 24, No. 15 ( 2011-08-01), p. 3830-3849
    Details
    In: Journal of Climate, American Meteorological Society, Vol. 24, No. 15 ( 2011-08-01), p. 3830-3849
    Abstract: This study examines the subduction of the Subantarctic Mode Water in the Indian Ocean in an ocean–atmosphere coupled model in which the ocean component is eddy permitting. The purpose is to assess how sensitive the simulated mode water is to the horizontal resolution in the ocean by comparing with a coarse-resolution ocean coupled model. Subduction of water mass is principally set by the depth of the winter mixed layer. It is found that the path of the Agulhas Current system in the model with an eddy-permitting ocean is different from that with a coarse-resolution ocean. This results in a greater surface heat loss over the Agulhas Return Current and a deeper winter mixed layer downstream in the eddy-permitting ocean coupled model. The winter mixed layer depth in the eddy-permitting ocean compares well to the observations, whereas the winter mixed layer depth in the coarse-resolution ocean coupled model is too shallow and has the wrong spatial structure. To quantify the impacts of different winter mixed depths on the subduction, a way to diagnose local subduction is proposed that includes eddy subduction. It shows that the subduction in the eddy-permitting model is closer to the observations in terms of the magnitudes and the locations. Eddies in the eddy-permitting ocean are found to 1) increase stratification and thus oppose the densification by northward Ekman flow and 2) increase subduction locally. These effects of eddies are not well reproduced by the eddy parameterization in the coarse-resolution ocean coupled model.
    Type of Medium: Online Resource
    ISSN: 0894-8755 , 1520-0442
    URL: Article
    DOI: 10.1175/2011JCLI3888.1
    RVK:
    UA 4548
    Language: English
    Publisher: American Meteorological Society
    Publication Date: 2011
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    detail.hit.zdb_id: 2021723-7
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  • 12
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    Southern Ocean Thermocline Ventilation
    American Meteorological Society ; 2010
    In:  Journal of Physical Oceanography Vol. 40, No. 3 ( 2010-03-01), p. 509-529
    Details
    In: Journal of Physical Oceanography, American Meteorological Society, Vol. 40, No. 3 ( 2010-03-01), p. 509-529
    Abstract: An approximate mass (volume) budget in the surface layer of the Southern Ocean is used to investigate the intensity and regional variability of the ventilation process, discussed here in terms of subduction and upwelling. Ventilation resulting from Ekman pumping is estimated from satellite winds, the geostrophic mean component is assessed from a climatology strengthened with Argo data, and the eddy-induced advection is included via the parameterization of Gent and McWilliams, together with eddy mixing estimates. All three components contribute significantly to ventilation. Finally, the seasonal cycle of the upper ocean is resolved using Argo data. The circumpolar-averaged circulation shows an upwelling in the Antarctic Intermediate Water (AAIW) density classes, which is carried north into a zone of dense Subantarctic Mode Water (SAMW) subduction. Although no consistent net production is found in the light SAMW density classes, a large subduction of Subtropical Mode Water (STMW) is observed. The STMW area is fed by convergence of a southward and a northward residual meridional circulation. The eddy-induced contribution is important for the water mass transport in the vicinity of the Antartic Circumpolar Current. It balances the horizontal northward Ekman transport as well as the vertical Ekman pumping. While the circumpolar-averaged upper cell structure is consistent with the average surface fluxes, it hides strong longitudinal regional variations and does not represent any local regime. Subduction shows strong regional variability with bathymetrically constrained hotspots of large subduction. These hotspots are consistent with the interior potential vorticity structure and circulation in the thermocline. Pools of SAMW and AAIW of different densities are found along the circumpolar belt in association with the regional pattern of subduction and interior circulation.
    Type of Medium: Online Resource
    ISSN: 1520-0485 , 0022-3670
    URL: Article
    DOI: 10.1175/2009JPO4291.1
    Language: English
    Publisher: American Meteorological Society
    Publication Date: 2010
    detail.hit.zdb_id: 2042184-9
    detail.hit.zdb_id: 184162-2
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  • 13
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    Isopycnal Mixing Suppression by the Antarctic Circumpolar Current and the Southern Ocean Meridional Overturning Circulation
    American Meteorological Society ; 2017
    In:  Journal of Physical Oceanography Vol. 47, No. 8 ( 2017-08), p. 2023-2045
    Details
    In: Journal of Physical Oceanography, American Meteorological Society, Vol. 47, No. 8 ( 2017-08), p. 2023-2045
    Abstract: The meridional overturning circulation (MOC) in the Southern Ocean is investigated using hydrographic observations combined with satellite measurements of sea surface height. A three-dimensional (spatial and vertical) estimate of the isopycnal eddy diffusivity in the Southern Ocean is obtained using the theory of Ferrari and Nikurashin that includes the influence of suppression of the diffusivity by the strong, time-mean flows. It is found that the eddy diffusivity is enhanced at depth, reaching a maximum at the critical layer near 1000 m. The estimate of diffusivity is used with a simple diffusive parameterization to estimate the meridional eddy volume flux. This estimate of eddy volume flux is combined with an estimate of the Ekman transport to reconstruct the time-mean overturning circulation. By comparing the reconstruction with, and without, suppression of the eddy diffusivity by the mean flow, the influence of the suppression on the overturning is illuminated. It is shown that the suppression of the eddy diffusivity results in a large reduction of interior eddy transports and a more realistic eddy-induced overturning circulation. Finally, a simple conceptual model is used to show that the MOC is influenced not only by the existence of enhanced diffusivity at depth but also by the details of the vertical structure of the eddy diffusivity, such as the depth of the critical layer.
    Type of Medium: Online Resource
    ISSN: 0022-3670 , 1520-0485
    URL: Article
    DOI: 10.1175/JPO-D-16-0263.1
    Language: Unknown
    Publisher: American Meteorological Society
    Publication Date: 2017
    detail.hit.zdb_id: 2042184-9
    detail.hit.zdb_id: 184162-2
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  • 14
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    The Thermohaline Modes of the Global Ocean
    American Meteorological Society ; 2019
    In:  Journal of Physical Oceanography Vol. 49, No. 10 ( 2019-10), p. 2535-2552
    Details
    In: Journal of Physical Oceanography, American Meteorological Society, Vol. 49, No. 10 ( 2019-10), p. 2535-2552
    Abstract: The first 2000 m of the global thermohaline structure of the ocean are statistically decomposed into vertical thermohaline modes, using a multivariate functional principal component analysis (FPCA). This method is applied on the Monthly Isopycnal and Mixed-Layer Ocean Climatology (MIMOC). The first three modes account for 92% of the joint temperature and salinity ( T – S ) variance, which yields a surprisingly good reduction of dimensionality. The first mode (69% of the variance) is related to the thermocline depth and delineates the subtropical gyres. The second mode (18%) is mostly driven by salinity and mainly displays the asymmetry between the North Pacific and Atlantic basins and the salty circumpolar deep waters in the Southern Ocean. The third mode (5%) identifies the low- and high-salinity intermediate waters, covarying with the freshwater inputs of the upper ocean. The representation of the ocean in the space defined by the first three modes offers a simple visualization of the global thermohaline structure that strikingly emphasizes the role of the Southern Ocean in linking and distributing water masses to the other basins. The vertical thermohaline modes offer a convenient framework for model and observation data comparison. This is illustrated by projecting the repeated Pacific section P16 together with profiles from the Array for Real-Time Geostrophic Oceanography (ARGO) global array of profiling floats on the modes defined with the climatology MIMOC. These thermohaline modes have a potential for water mass identification and robust analysis of heat and salt content.
    Type of Medium: Online Resource
    ISSN: 0022-3670 , 1520-0485
    URL: Article
    URL: Article
    DOI: 10.1175/JPO-D-19-0120.1
    DOI: 10.1175/jpo-d-19-0120.s1
    Language: Unknown
    Publisher: American Meteorological Society
    Publication Date: 2019
    detail.hit.zdb_id: 2042184-9
    detail.hit.zdb_id: 184162-2
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  • 15
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    Frontal Circulation and Submesoscale Variability during the Formation of a Southern Ocean Mesoscale Eddy
    American Meteorological Society ; 2017
    In:  Journal of Physical Oceanography Vol. 47, No. 7 ( 2017-07), p. 1737-1753
    Details
    In: Journal of Physical Oceanography, American Meteorological Society, Vol. 47, No. 7 ( 2017-07), p. 1737-1753
    Abstract: Observations made in the Scotia Sea during the May 2015 Surface Mixed Layer Evolution at Submesoscales (SMILES) research cruise captured submesoscale, O (1–10) km, variability along the periphery of a mesoscale O (10–100) km meander precisely as it separated from the Antarctic Circumpolar Current (ACC) and formed a cyclonic eddy ~120 km in diameter. The meander developed in the Scotia Sea, an eddy-rich region east of the Drake Passage where the Subantarctic and Polar Fronts converge and modifications of Subantarctic Mode Water (SAMW) occur. In situ measurements reveal a rich submesoscale structure of temperature and salinity and a loss of frontal integrity along the newly formed southern sector of the eddy. A mathematical framework is developed to estimate vertical velocity from collocated drifter and horizontal water velocity time series, under certain simplifying assumptions appropriate for the current dataset. Upwelling (downwelling) rates of O (100) m day −1 are found in the northern (southern) eddy sector. Favorable conditions for submesoscale instabilities are found in the mixed layer, particularly at the beginning of the survey in the vicinity of density fronts. Shallower mixed layer depths and increased stratification are observed later in the survey on the inner edge of the front. Evolution in temperature–salinity ( T – S ) space indicates modification of water mass properties in the upper 200 m over 2 days. Modifications along σ θ = 27–27.2 kg m −3 have climate-related implications for mode and intermediate water transformation in the Scotia Sea on finer spatiotemporal scales than observed previously.
    Type of Medium: Online Resource
    ISSN: 0022-3670 , 1520-0485
    URL: Article
    DOI: 10.1175/JPO-D-16-0266.1
    Language: Unknown
    Publisher: American Meteorological Society
    Publication Date: 2017
    detail.hit.zdb_id: 2042184-9
    detail.hit.zdb_id: 184162-2
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  • 16
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    Jets and Topography: Jet Transitions and the Impact on Transport in the Antarctic Circumpolar Current
    American Meteorological Society ; 2012
    In:  Journal of Physical Oceanography Vol. 42, No. 6 ( 2012-06-01), p. 956-972
    Details
    In: Journal of Physical Oceanography, American Meteorological Society, Vol. 42, No. 6 ( 2012-06-01), p. 956-972
    Abstract: The Southern Ocean’s Antarctic Circumpolar Current (ACC) naturally lends itself to interpretations using a zonally averaged framework. Yet, navigation around steep and complicated bathymetric obstacles suggests that local dynamics may be far removed from those described by zonally symmetric models. In this study, both observational and numerical results indicate that zonal asymmetries, in the form of topography, impact global flow structure and transport properties. The conclusions are based on a suite of more than 1.5 million virtual drifter trajectories advected using a satellite altimetry–derived surface velocity field spanning 17 years. The focus is on sites of “cross front” transport as defined by movement across selected sea surface height contours that correspond to jets along most of the ACC. Cross-front exchange is localized in the lee of bathymetric features with more than 75% of crossing events occurring in regions corresponding to only 20% of the ACC’s zonal extent. These observations motivate a series of numerical experiments using a two-layer quasigeostrophic model with simple, zonally asymmetric topography, which often produces transitions in the front structure along the channel. Significantly, regimes occur where the equilibrated number of coherent jets is a function of longitude and transport barriers are not periodic. Jet reorganization is carried out by eddy flux divergences acting to both accelerate and decelerate the mean flow of the jets. Eddy kinetic energy is amplified downstream of topography due to increased baroclinicity related to topographic steering. The combination of high eddy kinetic energy and recirculation features enhances particle exchange. These results stress the complications in developing consistent circumpolar definitions of the ACC fronts.
    Type of Medium: Online Resource
    ISSN: 0022-3670 , 1520-0485
    URL: Article
    DOI: 10.1175/JPO-D-11-0135.1
    Language: English
    Publisher: American Meteorological Society
    Publication Date: 2012
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  • 17
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    SUSTAINED MONITORING OF THE SOUTHERN OCEAN AT DRAKE PASSAGE: PAST ACHIEVEMENTS AND FUTURE PRIORITIES
    American Geophysical Union (AGU) ; 2011
    In:  Reviews of Geophysics Vol. 49, No. 4 ( 2011-12-02)
    Details
    In: Reviews of Geophysics, American Geophysical Union (AGU), Vol. 49, No. 4 ( 2011-12-02)
    Type of Medium: Online Resource
    ISSN: 8755-1209
    URL: Article
    DOI: 10.1029/2010RG000348
    Language: English
    Publisher: American Geophysical Union (AGU)
    Publication Date: 2011
    detail.hit.zdb_id: 2035391-1
    detail.hit.zdb_id: 209852-0
    detail.hit.zdb_id: 209853-2
    SSG: 16,13
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  • 18
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    Observational evidence for on-shelf heat transport driven by dense water export in the Weddell Sea
    Springer Science and Business Media LLC ; 2023
    In:  Nature Communications Vol. 14, No. 1 ( 2023-03-07)
    Details
    In: Nature Communications, Springer Science and Business Media LLC, Vol. 14, No. 1 ( 2023-03-07)
    Abstract: The transport of oceanic heat towards the Antarctic continental margin is central to the mass balance of the Antarctic Ice Sheet. Recent modeling efforts challenge our view on where and how the on-shelf heat flux occurs, suggesting that it is largest where dense shelf waters cascade down the continental slope. Here we provide observational evidence supporting this claim. Using records from moored instruments, we link the downslope flow of dense water from the Filchner overflow to upslope and on-shelf flow of warm water.
    Type of Medium: Online Resource
    ISSN: 2041-1723
    URL: Article
    DOI: 10.1038/s41467-023-36580-3
    Language: English
    Publisher: Springer Science and Business Media LLC
    Publication Date: 2023
    detail.hit.zdb_id: 2553671-0
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  • 19
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    Subpolar Southern Ocean Seasonal Variability of the Geostrophic Circulation From Multi‐Mission Satellite Altimetry
    American Geophysical Union (AGU) ; 2022
    In:  Journal of Geophysical Research: Oceans Vol. 127, No. 6 ( 2022-06)
    Details
    In: Journal of Geophysical Research: Oceans, American Geophysical Union (AGU), Vol. 127, No. 6 ( 2022-06)
    Abstract: A novel satellite altimetry data set is used to describe the subpolar Southern Ocean circulation seasonal cycle Large scale variations of surface winds are the main drivers of the Southern Ocean circulation seasonal variability Sea ice modulates locally the surface stress and induces an unphased seasonal mode of variability
    Type of Medium: Online Resource
    ISSN: 2169-9275 , 2169-9291
    URL: Article
    DOI: 10.1029/2021JC018096
    Language: English
    Publisher: American Geophysical Union (AGU)
    Publication Date: 2022
    detail.hit.zdb_id: 2016804-4
    detail.hit.zdb_id: 161667-5
    detail.hit.zdb_id: 3094219-6
    SSG: 16,13
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  • 20
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    Ventilation of the abyss in the Atlantic sector of the Southern Ocean
    Springer Science and Business Media LLC ; 2021
    In:  Scientific Reports Vol. 11, No. 1 ( 2021-03-24)
    Details
    In: Scientific Reports, Springer Science and Business Media LLC, Vol. 11, No. 1 ( 2021-03-24)
    Abstract: The Atlantic sector of the Southern Ocean is the world’s main production site of Antarctic Bottom Water, a water-mass that is ventilated at the ocean surface before sinking and entraining older water-masses—ultimately replenishing the abyssal global ocean. In recent decades, numerous attempts at estimating the rates of ventilation and overturning of Antarctic Bottom Water in this region have led to a strikingly broad range of results, with water transport-based calculations (8.4–9.7 Sv) yielding larger rates than tracer-based estimates (3.7–4.9 Sv). Here, we reconcile these conflicting views by integrating transport- and tracer-based estimates within a common analytical framework, in which bottom water formation processes are explicitly quantified. We show that the layer of Antarctic Bottom Water denser than 28.36 kg m $$^{-3}$$ - 3 $$\gamma _{n}$$ γ n is exported northward at a rate of 8.4 ± 0.7 Sv, composed of 4.5 ± 0.3 Sv of well-ventilated Dense Shelf Water, and 3.9 ± 0.5 Sv of old Circumpolar Deep Water entrained into cascading plumes. The majority, but not all, of the Dense Shelf Water (3.4 ± 0.6 Sv) is generated on the continental shelves of the Weddell Sea. Only 55% of AABW exported from the region is well ventilated and thus draws down heat and carbon into the deep ocean. Our findings unify traditionally contrasting views of Antarctic Bottom Water production in the Atlantic sector, and define a baseline, process-discerning target for its realistic representation in climate models.
    Type of Medium: Online Resource
    ISSN: 2045-2322
    URL: Article
    DOI: 10.1038/s41598-021-86043-2
    Language: English
    Publisher: Springer Science and Business Media LLC
    Publication Date: 2021
    detail.hit.zdb_id: 2615211-3
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