Coherent Pathways for Subduction From the Surface Mixed Layer at Ocean Fronts

Freilich, Mara; Mahadevan, Amala

doi:10.1029/2020jc017042

Cited by 25 publications

(29 citation statements)

References 85 publications

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“…It should be noted that high‐frequency entrainment events are not captured in this analysis, which uses a monthly climatology to calculate the temporal MLD variability. Resolving shorter timescales across the entire Southern Ocean, although not possible from the current Argo data coverage, would likely increase the obduction fluxes of carbon in all basins (Freilich & Mahadevan, 2021). However, high‐frequency processes, while important locally, may contribute less to the mean basin‐scale differences that we focus on here (Lévy et al., 2013; Resplandy et al., 2019).…”

Section: Resultsmentioning

confidence: 99%

“…This is why the strongest outgassing does not correspond to the highest obduction rates and deepest winter mixed layers, which occur in the Subantarctic Zone where carbon-rich isopycnals are too deep to be accessed by wintertime mixing (Figures 4d-4f). It should be noted that high-frequency entrainment events are not captured in this analysis, which uses a monthly (Freilich & Mahadevan, 2021). However, high-frequency processes, while important locally, may contribute less to the mean basin-scale differences that we focus on here (Lévy et al, 2013;Resplandy et al, 2019).…”

Section: Driving Mechanismsmentioning

confidence: 99%

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Indo‐Pacific Sector Dominates Southern Ocean Carbon Outgassing

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Gray

Talley

et al. 2022

Global Biogeochemical Cycles

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The Southern Ocean accounts for a disproportionately large percentage of the total oceanic anthropogenic carbon uptake, which results from the region's unique role in the global overturning circulation (Frölicher et al., 2015;Khatiwala et al., 2009). In the southern portion of the Antarctic Circumpolar Current (ACC), deep water returns to the upper ocean via wind-driven upwelling and is transformed into northward-flowing intermediate and bottom waters (J. Marshall & Speer, 2012). These upwelled deep waters have been isolated from the atmosphere since preindustrial times, and thus are poised both to absorb anthropogenic CO 2 and to release natural carbon that has accumulated over centuries through the remineralization of organic matter (Lovenduski et al., 2008). The net air-sea carbon exchange in the Southern Ocean is, therefore, a balance between opposing processes of carbon uptake and outgassing (DeVries et al., 2017;Gruber et al., 2019).Both uptake of anthropogenic CO 2 and outgassing of natural carbon are fundamentally tied to the physical transport of water between the surface mixed layer and ocean interior. While the circulation of the Southern Ocean has

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Section: Resultsmentioning

confidence: 99%

Section: Driving Mechanismsmentioning

confidence: 99%

Indo‐Pacific Sector Dominates Southern Ocean Carbon Outgassing

Prend

Gray

Talley

et al. 2022

Global Biogeochemical Cycles

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“…With a slow uptake rate ( λ ≪ τ −1 ), the spatial distribution of the nutrient anomaly is heavily influenced by stirring in the horizontal and the cascade to small scales driven by lateral stirring (Abraham, 1998). With a fast uptake rate ( λ ≫ τ −1 ), the nutrient anomaly is present at small spatial scales because the vertical velocity, especially the high frequency component of the vertical velocity, has relatively more small scale variability than the horizontal velocity (Freilich & Mahadevan, 2021; Mahadevan & Campbell, 2002).…”

Section: Nutrient Supply and Uptakementioning

confidence: 99%

Diversity of Growth Rates Maximizes Phytoplankton Productivity in an Eddying Ocean

Freilich

Flierl

Mahadevan

2022

Geophysical Research Letters

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The diverse community of phytoplankton and the heterotrophic ecosystem that it supplies affects the depth and efficacy of ocean primary production, as well as the cycling of carbon and other elements. Most of the world's ocean is depleted of nutrients (oligotrophic) in the sunlit (euphotic) layer where nutrients are taken up by phytoplankton, but nutrient concentration increases with depth below the euphotic layer. In such regions, the production of phytoplankton relies on the physical transport of nutrient-enriched water from depth to the euphotic zone where light enables photosynthesis (McGillicuddy et al., 1998). Over long spatial and temporal scales, the system is balanced such that the rate of export of organic matter is determined by the rate of nutrient input that contributes to photosynthetic carbon fixation (Ducklow et al., 2001;Falkowski et al., 1998).The upward transport of nutrient-rich water occurs via a range of mechanisms, including surface boundary layer turbulence, wind-driven upwelling, coastal upwelling, eddy uplift, and frontal instabilities (Denman & Gargett, 1983;Lipschultz et al., 2002). In the pelagic ocean, the physical supply of nutrients induced by vertical advection associated with fronts and eddies (Jenkins & Goldman, 1985) is thought to limit the rate of new production, which is the rate of phytoplankton production fueled by a fresh supply of macronutrients from outside the euphotic layer. Vertical velocities are typically 10 −3 -10 −4 times smaller than the horizontal velocities associated with ocean currents and eddies on scales of 1-100 km. But, submesoscale dynamics, associated with strong vertical vorticity (of the order of the planetary vorticity f) can result in vertical velocities of 𝐴𝐴  (100) m/day on spatial scales 𝐴𝐴  (1 km). These rapid vertical motions are thought to be particularly influential for phytoplankton growth (Mahadevan, 2016).Besides physical processes, the gradient in the mean nutrient distribution and the anomalies in concentration from the mean distribution also affect nutrient transport. Physical transport, as well as biological and chemical processes that create sinks (or sources) for nutrients, affect nutrient distribution. The spatial heterogeneity of

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“…To construct the second initial condition, we deepen the mixed layer by cooling the surface and recomputing the surface density profile using convective adjustment until the maximum mixed layer depth is 70 m. This process leads to a flow field characteristic of the winter season. The winter model has a more active surface-enhanced submesoscale flow field, which results in smaller scale features in the velocity gradients [50]. The model is periodic in the east-west direction (parallel to the front) and has closed walls in the north and south.…”

Section: Methodsmentioning

confidence: 99%