Small‐Scale Topographic Form Stress and Local Dynamics of the Southern Ocean

Zhang, Xihan; Nikurashin, Maxim

doi:10.1029/2019jc015420

Cited by 5 publications

(5 citation statements)

References 41 publications

(83 reference statements)

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“…The EKE over the shelf is generally suppressed in the SRTM15 simulation. The response of the ocean circulation to seafloor roughness over the continental shelf is consistent with the results and mechanisms described in previous studies of the Southern Ocean 50,71 , showing that seafloor roughness applies a drag to the deepreaching currents and eddies leading to a decrease in their kinetic energy. In the SRTM15 simulation, the AACC experiences a stronger drag from seafloor roughness over the shelf, and becomes weaker and less efficient at transporting water westward across the region.…”

Section: Regional Circulationsupporting

confidence: 90%

“…As a result, the presence of CDW over the shelf is reduced. Previous studies for the Southern Ocean show that it is the topographic form stress arising from seafloor roughness that impacts the large-scale motions such as currents and eddies 50,71 . Some of the topographic form stress is associated with the lee wave generation 75 , while some can be associated with Rossby waves and other non-radiating motions generated by topographic features 76 .…”

Section: Discussionmentioning

confidence: 99%

“…Seafloor roughness in ocean basins, referred to as abyssal hills 49 , has been found to play an important role for the circulation and properties in the ocean in two ways. First, it applies a drag in the form of topographic form stress 50 to the deep-reaching currents and eddies in the Southern Ocean, having an impact on their magnitude [51][52][53] and sensitivity to wind 54,55 . Second, the interaction between abyssal hills and deep currents, eddies, and tides generates small-scale internal waves that radiate away, break, and drive mixing, transforming water masses in the ocean interior [56][57][58] .…”

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confidence: 99%

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Seafloor roughness reduces melting of East Antarctic ice shelves

Liu,

Nikurashin,

Peña-Molino

2024

Commun Earth Environ

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Heat delivered by the ocean circulation is melting the Antarctic ice sheet from below. This melt is largest where warm Circumpolar Deep Water accesses the continental shelf and reaches the ice shelf cavities. Future melt rate projections are based on ocean thermal forcing derived from climate models, which tend to be biased warm around Antarctica. The bias has been attributed to unresolved ocean processes that occur at scales poorly represented in models. Using a high-resolution model of the Denman Glacier region we show that seafloor roughness unresolved in climate models suppresses the impact of warm water on ice sheet melting. Seafloor roughness slows down the shelf circulation, reducing the presence of warm water over the shelf and the heat transport towards the ice cavities. As a result, the total meltwater discharge drops by 4 Gt year−1. Our results suggest a mechanism missing in global ocean and climate models that could reduce the spread in climate projections.

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Section: Regional Circulationsupporting

confidence: 90%

Section: Discussionmentioning

confidence: 99%

mentioning

confidence: 99%

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Seafloor roughness reduces melting of East Antarctic ice shelves

Liu,

Nikurashin,

Peña-Molino

2024

Commun Earth Environ

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“…Previous studies also found the inclusion of rough topography can modify the mean flow path (e.g., de Marez et al, 2020;Zhang & Nikurashin, 2020). This influence of the rough topography on mean flow may further affect the eddy energy, since the eddies are mainly generated through instabilities of the mean flow.…”

Section: Reduced Eddy Scales In the Ocean Interiormentioning

confidence: 96%

The Role of Small‐Scale Topography in Modulating Eddy Scale in the Northern South China Sea

2023

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The ocean is intrinsically turbulent in nature and as a result of non-linear interactions energy in the ocean can transfer across spatial scales. Geostrophic turbulence theory predicts an inverse energy cascade (from small scales to large scales) of ocean eddy kinetic energy where the eddy length scale increases until it is halted at the Rhines scale by planetary wave propagation (Rhines, 1975;Salmon, 1998). However, satellite observations reveal that the dominate eddy scales in many regions of the oceans are only slightly larger than the local Rossby deformation radius (Stammer, 1997). This indicates that the inverse cascade is often arrested by other physical processes before it reaches the Rhines scale.For example, Arbic and Flierl (2004) found that the bottom friction, or bottom drag, can arrest the inverse cascade and thereby modulate the eddy length scale. Eddies in their model simulations tend to have larger horizontal scales than observations under weak bottom drag. Another possible candidate process that can affect eddy scale is the generation of lee waves over small-scale topography (wave drag), which is believed to be an efficient way to cascade the mesoscale energy to small-scales that are more readily to be dissipated (Nikurashin et al., 2013). The downscale or forward eddy energy cascade (from large scales to small scales) above the small-scale rough topography may contribute to the arrest of inverse cascade and thereby reduce the eddy scales. However, the manner in which wave drag affects the eddy scales may be quite different from that of bottom drag. For example, different from the bottom drag which only occurs in the bottom boundary layer, lee waves can radiate away from the ocean bottom into ocean interior and interact with the mean flows (

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“…It has been shown that the eddy saturation regime is approached when the horizontal resolution of ocean models is high enough to resolve the eddy energy generation processes (i.e., the Rossby radius of deformation; Farneti et al., 2010; Hallberg & Gnanadesikan, 2001, 2006; Morrison & Hogg, 2013; Munday et al., 2013; Tansley & Marshall, 2001). However, the eddy energy dissipation processes have also been shown to impact the eddy characteristics in the Southern Ocean (e.g., Trossman et al., 2013, 2016; Zhang & Nikurashin, 2020) and thus can potentially contribute to the ACC transport sensitivity to winds. The eddy dissipation processes occur at spatial scales that are much smaller than the horizontal resolution of eddy‐resolving ocean models (Fox‐Kemper et al., 2019) and are currently not accurately represented in models.…”

Section: Introductionmentioning

confidence: 99%

Lee Waves Break Eddy Saturation of the Antarctic Circumpolar Current

Yang

Nikurashin

Hogg

et al. 2023

Geophysical Research Letters

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Eddy‐resolving ocean models suggest that the transport of the Antarctic Circumpolar Current (ACC) may be insensitive to increasing wind. This insensitivity is due to eddies that flatten the isopycnals and compensate for their wind‐driven steepening. However, the eddy‐resolving models do not accurately represent the eddy dissipation processes that occur at scales smaller than the model resolution, including lee wave generation at rough topography. Using a lee wave parameterization in an idealized model of the Southern Ocean, we show that the ACC transport becomes more sensitive to wind when the lee wave drag is included. The sensitivity arises from the dependence of the lee wave drag on the bottom stratification. When the bottom stratification increases in response to wind, it increases the lee wave generation, and hence the eddy dissipation, at rough topography. As a result, the ACC shear (baroclinic transport) increases to drive stronger eddy generation to compensate.

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Small‐Scale Topographic Form Stress and Local Dynamics of the Southern Ocean

Cited by 5 publications

References 41 publications

Seafloor roughness reduces melting of East Antarctic ice shelves

Seafloor roughness reduces melting of East Antarctic ice shelves

The Role of Small‐Scale Topography in Modulating Eddy Scale in the Northern South China Sea

Lee Waves Break Eddy Saturation of the Antarctic Circumpolar Current

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