Vertical eddy iron fluxes support primary production in the open Southern Ocean

Uchida, Takaya; Balwada, Dhruv; Abernathey, Ryan; McKinley, Galen A.; Smith, Shafer; Lévy, Marina

doi:10.1038/s41467-020-14955-0

Cited by 68 publications

(52 citation statements)

References 50 publications

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“…If nutrients are transported upward primarily by ocean plumes, we would expect detrainment to release these nutrients in the ocean interior. In Earth's ocean, it has been shown that adiabatic mixing, or stirring along isopycnals, can be an important pathway for nutrient delivery to the surface and modulate productivity there [26].…”

Section: Discussionmentioning

confidence: 99%

A pole-to-equator ocean overturning circulation on Enceladus

et al. 2021

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Under ReviewEnceladus is believed to have a saltwater global ocean with a mean depth of at least 30 km [1,2], heated from below at the ocean-core interface and cooled at the top [3], where the ocean loses heat to the icy lithosphere above. This scenario suggests an important role for vertical convection to influence the interior properties and circulation of Enceladus' ocean. Additionally, the ice shell that encompasses the ocean has dramatic meridional thickness variations that, in steady state, must be sustained against processes acting to remove these ice thickness anomalies. One mechanism that would maintain variations in the ice shell thickness involves spatially-separated regions of freezing and melting at the ocean-ice interface. Here, we use an idealized, dynamical ocean model forced by an observationally-guided density forcing at the ocean-ice interface to argue that Enceladus' interior ocean should support a meridional overturning circulation. This circulation establishes an interior density structure that is more complex than in studies that have focused only on convection, including a shallow freshwater lens in the polar regions. Spatially-separated sites of ice formation and melt enable Enceladus to sustain a significant vertical and horizontal stratification, which impacts interior heat transport, and is critical for understanding the relationship between a global ocean and the planetary energy budget. The presence of low salinity layers near the polar ocean-ice interface also influences whether samples measured from the plumes [4] are representative of the global ocean.

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Section: Discussionmentioning

confidence: 99%

A pole-to-equator ocean overturning circulation on Enceladus

et al. 2021

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“…They form preferentially in the upper and bottom turbulent boundary layers (Lévy et al, 2012) and are characterized by O(1) Richardson and Rossby numbers, with horizontal scales between 100 m and a few kilometers, and characteristic time scales from hours to days . The vertical velocity field induced by submesoscale circulations is ephemeral but can exceed 10 −3 m s −1 and may extend to several hundred meters of depth, bringing nutrient-rich waters into or out of the euphotic layer, and exporting organic carbon out of the surface layer (e.g., Omand et al, 2015;Uchida et al, 2020). The rapid physical exchange between surface and deep waters may affect the structure and functions of the local marine ecosystem by stimulating near-surface or sub-surface phytoplankton blooms or by changing the properties of water masses (Mahadevan and Archer, 2000;Lévy et al, 2001;Pidcock et al, 2010;Clayton et al, 2014;Lévy et al, 2018).…”

Section: Introductionmentioning

confidence: 99%

Submesoscale Mixing Across the Mixed Layer in the Gulf of Mexico

2021

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Submesoscale circulations influence momentum, buoyancy and transport of biological tracers and pollutants within the upper turbulent layer. How much and how far into the water column this influence extends remain open questions in most of the global ocean. This work evaluates the behavior of neutrally buoyant particles advected in simulations of the northern Gulf of Mexico by analyzing the trajectories of Lagrangian particles released multiple times at the ocean surface and below the mixed layer. The relative role of meso- and submesoscale dynamics is quantified by comparing results in submesoscale permitting and mesoscale resolving simulations. Submesoscale circulations are responsible for greater vertical transport across fixed depth ranges and also across the mixed layer, both into it and away from it, in all seasons. The significance of the submesoscale-induced transport, however, is far greater in winter. In this season, a kernel density estimation and a detailed vertical mixing analysis are performed. It is found that in the large mesoscale Loop Current eddy, upwelling into the mixed layer is the major contributor to the vertical fluxes, despite its clockwise circulation. This is opposite to the behavior simulated in the mesoscale resolving case. In the “submesoscale soup,” away from the large mesoscale structures such as the Loop Current and its detached eddies, upwelling into the mixed layer is distributed more uniformly than downwelling motions from the surface across the base of the mixed layer. Maps of vertical diffusivity indicate that there is an order of magnitude difference among simulations. In the submesoscale permitting case values are distributed around 10–3 m2 s–1 in the upper water column in winter, in agreement with recent indirect estimates off the Chilean coast. Diffusivities are greater in the eastern portion of the Gulf, where the submesoscale circulations are more intense due to sustained density gradients supplied by the warmer and saltier Loop Current.

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“…Winds and waves strongly modulate ocean mixing (Thorpe, 2007;Toffoli et al, 2012), biological production (Nicholson et al, 2016;Uchida et al, 2020), air-sea gas exchange (Wanninkhof et al, 2009;Gruber et al, 2019), sea ice dynamics Vichi et al, 2019) and sea spray emission (Figure 1f), relevant for cloud formation (Schmale et al, 2019;Quinn et al, 2017;Bigg, 1973). This storm track region is characterised by the frequent passage of extratropical cyclones leading to the formation of a quasi-persistent low-level cloud deck and regular precipitation (Figure 1g) (Catto et al, 2012).…”

Section: Introductionmentioning

confidence: 99%

Biogeochemistry and Physics of the Southern Ocean-Atmosphere System Explored With Data Science

Landwehr¹,

Volpi²,

Haumann³

et al. 2021

Preprint

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Abstract. The Southern Ocean is a critical component of Earth’s climate system, but its remoteness makes it challenging to develop a holistic understanding of its processes from the small to the large scale. As a result, our knowledge of this vast region remains largely incomplete. The Antarctic Circumnavigation Expedition (ACE, austral summer 2016/2017) surveyed a large number of variables describing the dynamic state of the ocean and the atmosphere, the freshwater cycle, atmospheric chemistry, ocean biogeochemistry and microbiology. This circumpolar cruise included visits to twelve remote islands, the marginal ice zone, and the Antarctic coast. Here, we use 111 of the observed variables to study the latitudinal gradients, seasonality, shorter term variations, the geographic setting of environmental processes, and interactions between them over the duration of 90 days. To reduce the dimensionality and complexity of the dataset and make the relations between variables interpretable, we applied a sparse Principal Component Analysis (sPCA), which describes environmental processes through 14 latent variables. To derive a robust statistical perspective on these processes and to estimate the uncertainty in the sPCA decomposition, we have developed a bootstrap approach. We identified temporal patterns from diurnal to seasonal cycles, as well as geographical gradients and “hotspots” of interaction. Our results establish connections of oceanic, atmospheric, biological and terrestrial processes in an innovative way, while confirming many well known relations of the Southern Ocean system. More specifically, we identify: the important role of the oceanic circulations, frontal zones, and islands in shaping the nutrient availability that controls biological community composition and productivity; that sea ice predominantly controls sea water salinity, dampens the wave field, and is associated with increased phytoplankton growth and net community productivity possibly due to iron fertilization and reduced light limitation; and clear regional patterns of aerosol characteristics emerged, stressing the role of the sea state, atmospheric chemical processing, as well as source processes near “hotspots” for the availability of cloud condensation nuclei and hence cloud formation. A set of key variables and their combinations, such as the difference between the air and sea surface temperature, atmospheric pressure, sea surface height, geostrophic currents, upper ocean layer light intensity, surface wind speed and relative humidity, played an important role in the majority of latent variables, highlighting their importance for a large variety of processes and the necessity for Earth System Models to represent them adequately. In conclusion, our study highlights the use of sPCA to identify key ocean-atmosphere interactions across physical, chemical, and biological processes and their associated spatio-temporal scales. The sPCA processing code is available as open-access and we believe that our approach is widely applicable to other environmental field studies.

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Vertical eddy iron fluxes support primary production in the open Southern Ocean

Cited by 68 publications

References 50 publications

A pole-to-equator ocean overturning circulation on Enceladus

A pole-to-equator ocean overturning circulation on Enceladus

Submesoscale Mixing Across the Mixed Layer in the Gulf of Mexico

Biogeochemistry and Physics of the Southern Ocean-Atmosphere System Explored With Data Science

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