Mixing in the Southern Ocean

Gille, Sarah T.; Sheen, Katy; Swart, Sebastiaan; Thompson, Andrew F.

doi:10.1016/b978-0-12-821512-8.00019-0

Cited by 9 publications

(9 citation statements)

References 236 publications

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“…The particles were tracked for 1 year and the time‐integration was completed with a fourth order Runge‐Kutta scheme in 1‐day time‐steps. Unresolved eddy diffusion was accounted for by introducing a random‐walk term (e.g., Ross & Sharples, 2004) with a horizontal diffusivity of 1,000 m 2 s −1 , a representative value for the Southern Ocean (Gille et al., 2022), but this choice had little impact on the results. Salinity at the particles' positions was obtained through linear interpolation of the annual‐mean fields from Roemmich and Gilson (2009).…”

Section: Methodsmentioning

confidence: 99%

Subtropical Contribution to Sub‐Antarctic Mode Waters

Fernández-Castro

Mazloff

Williams

et al. 2022

Geophysical Research Letters

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Sub‐Antarctic Mode Waters (SAMW) form to the north of the Antarctic Circumpolar Current (ACC) through deep winter mixing. SAMW connect the atmosphere with the oceanic pycnocline, transferring heat and carbon into the ocean interior and supplying nutrients to the northern ocean basins. The processes controlling SAMW ventilation and properties remain poorly understood. Here, we investigate the significance and origin of a ubiquitous feature of SAMW formation regions: The seasonal build‐up of a subsurface salinity maximum. With biogeochemical Argo floats, we show that this feature influences SAMW mixed‐layer dynamics, and that its formation is associated with a decline in preformed nutrients comparable to biological drawdown in surface waters (∼0.15 mol m−2 y−1). Our analysis reveals that these features are driven by advection of warm, salty, nutrient‐poor waters of subtropical origin along the ACC. This influx represents a leading‐order term in the SAMW physical and biogeochemical budgets, and can impact large‐scale nutrient distributions.

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Section: Methodsmentioning

confidence: 99%

Subtropical Contribution to Sub‐Antarctic Mode Waters

Fernández-Castro

Mazloff

Williams

et al. 2022

Geophysical Research Letters

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“…The Southern Ocean has traditionally been identified as a region preconditioned for strong submesoscale activity due to strong surface wind and buoyancy forcing and a weak vertical stratification (Gille et al., 2022; Su et al., 2018). Yet, despite strong wind stress and surface cooling (Figure S3 in Supporting Information ), the glider sections presented here show limited signatures of submesoscale variability and ventilation throughout the southern Drake Passage.…”

Section: Discussionmentioning

confidence: 99%

Controls on Wintertime Ventilation in Southern Drake Passage

Dove

Viglione

Thompson

et al. 2023

Geophysical Research Letters

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Drake Passage is a key region for transport between the surface and interior ocean, but a mechanistic understanding of this exchange remains immature. Here, we present wintertime, submesoscale‐resolving hydrographic transects spanning the southern boundary of the Antarctic Circumpolar Current and the Polar Front (PF). Despite the strong surface wind and buoyancy forcing, a freshwater lens suppresses surface‐interior exchange south of the PF; ventilation is instead localized to the PF. Multiple lines of the analysis suggest submesoscale processes contribute to ventilation at the PF, including small‐scale, O(10 km), frontal structure in water mass properties below the mixed layer and modulation of a surface eddy diffusivity at sub‐50 km scales. These results show that ventilation is sensitive to both submesoscale properties near fronts and non‐local processes, for example, sea‐ice melt, that set stratification and mixed layer properties. This highlights the need for adaptive observing strategies to constrain Southern Ocean heat and carbon budgets.

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“…The Southern Ocean's characteristically weak stratification, deep mixed layers [ 73 ] and steeply tilted isopycnals mean that relatively small energy inputs can mix the ocean vertically, thereby increasing the potential to transport properties between the deeper ocean interior, surface ocean and to the lower atmosphere via air-sea exchange. The air-sea exchanges can feedback to the surface ocean by altering buoyancy and stratification to enhance or arrest mixing processes and are thus essential to thermocline ventilation [ 74 ].…”

Section: Coupling Between the Fine-scale Ocean And Air-ocean-ice Flux...mentioning

confidence: 99%

The Southern Ocean mixed layer and its boundary fluxes: fine-scale observational progress and future research priorities

Swart

Plessis

Nicholson³

et al. 2023

Phil. Trans. R. Soc. A.

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Interactions between the upper ocean and air-ice-ocean fluxes in the Southern Ocean play a critical role in global climate by impacting the overturning circulation and oceanic heat and carbon uptake. Remote and challenging conditions have led to sparse observational coverage, while ongoing field programmes often fail to collect sufficient information in the right place or at the time-space scales required to constrain the variability occurring in the coupled ocean-atmosphere system. Only within the last 10 years have we been able to directly observe and assess the role of the fine-scale ocean and rapidly evolving atmospheric marine boundary layer on the upper limb of the Southern Ocean's overturning circulation. This review summarizes advances in mechanistic understanding, arising in part from observational programmes using autonomous platforms, of the fine-scale processes (1–100 km, hours-seasons) influencing the Southern Ocean mixed layer and its variability. We also review progress in observing the ocean interior connections and the coupled interactions between the ocean, atmosphere and cryosphere that moderate air-sea fluxes of heat and carbon. Most examples provided are for the ice-free Southern Ocean, while major challenges remain for observing the ice-covered ocean. We attempt to elucidate contemporary research gaps and ongoing/future efforts needed to address them. This article is part of a discussion meeting issue 'Heat and carbon uptake in the Southern Ocean: the state of the art and future priorities'.

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Mixing in the Southern Ocean

Cited by 9 publications

References 236 publications

Subtropical Contribution to Sub‐Antarctic Mode Waters

Subtropical Contribution to Sub‐Antarctic Mode Waters

Controls on Wintertime Ventilation in Southern Drake Passage

The Southern Ocean mixed layer and its boundary fluxes: fine-scale observational progress and future research priorities

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