The influence of geostrophic strain on oceanic ageostrophic motion and surface chlorophyll

Zhang, Zhengguang; Qiu, Bo; Klein, Patrice; Travis, Seth

doi:10.1038/s41467-019-10883-w

Cited by 75 publications

(77 citation statements)

References 56 publications

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“…Similar ambiguities regarding the role of the submesoscale in ocean ecosystems exist in the biogeochemical literature. Submesoscale features are apparent in surface chlorophyll observations from high‐resolution remote sensing data (Mahadevan, ; Lee & Kim, ; Choi et al, ), and recent studies have argued submesoscale vertical transport to be an important pathway in supplying nutrients to the euphotic layer (e.g., Lévy, Ferrari, et al, ; Levy & Martin, ; Mahadevan, ; Lévy et al, ; Zhang et al, ). Precisely isolating the relative contribution of this mechanism, however, has remained challenging since, as noted earlier, submesoscale physics can feed back onto the large‐scale state.…”

Section: Introductionmentioning

confidence: 99%

The Contribution of Submesoscale over Mesoscale Eddy Iron Transport in the Open Southern Ocean

Uchida

Balwada

Abernathey

et al. 2019

J Adv Model Earth Syst

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Biological productivity in the Southern Ocean is limited by iron availability. Previous studies of iron supply have focused on mixed-layer entrainment and diapycnal fluxes. However, the Southern Ocean is a region highly energetic mesoscale and submesoscale turbulence. Here we investigate the role of eddies in supplying iron to the euphotic zone, using a flat-bottom zonally re-entrant model, configured to represent the Antarctic Circumpolar Current region, that is coupled to a biogeochemical model with a realistic seasonal cycle. Eddies are admitted or suppressed by changing the model's horizontal resolution. We utilize cross spectral analysis and the generalized Omega equation to temporally and spatially decompose the vertical transport attributable to mesoscale and submesoscale motions. Our results suggest that the mesoscale vertical fluxes provide a first-order pathway for transporting iron across the mixing-layer base, where diapycnal mixing is weak, and must be included in modeling the open-Southern Ocean iron budget. Plain Language SummaryOcean currents at the surface on the spatial scales of 1-200 km are energetic due to heating by the sun and stirring by the winds. These currents contribute to the climate system by transporting heat and carbon horizontally towards the poles and vertically into the deep ocean. By running a numerical simulation at very high spatial resolution that resolve these currents, we show that these currents are also responsible for transporting iron from the ocean interior to the surface in the Southern Ocean, where phytoplankton growth is limited by the lack of iron-a key nutrient for most living organisms on Earth. Our results highlight the importance of accurately representing these ocean currents and associated iron transport, in order to understand the Southern Ocean ecosystem and its impact on the climate via photosynthesis, the process in which carbon dioxide is converted to organic carbon and oxygen is produced as a bi-product.

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Section: Introductionmentioning

confidence: 99%

The Contribution of Submesoscale over Mesoscale Eddy Iron Transport in the Open Southern Ocean

Uchida

Balwada

Abernathey

et al. 2019

J Adv Model Earth Syst

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“…A second approach is to avoid switching between prediction submodels (9) and (10). A fixed prediction model could be based on the submodel with smaller gain, i.e.…”

Section: A Conventional Mpcmentioning

confidence: 99%

“…Therefore, it can be used for a fine-scale observation of the ocean to make up for the shortcomings of other observation methods [9] (e.g., fixed-point Euler observation using ADCP, self-propelled observation using AUV, glider and vessel, etc.). For example, [10] reveal the influence of geostrophic strain on oceanic ageostrophic motion and surface chlorophyll using the surface drifter; [11] use the drifter to observe submesoscale flow kinematics in the coastal ocean, etc. However, the existing drifters only can follow the two-dimensional flow at the ocean surface or near surface because of their positive buoyancy.…”

Section: Introductionmentioning

confidence: 99%

Complementary Constrained Model Predictive Depth Control of a Hybridly-Actuated Submarine Drifter

Song

Hou

et al. 2020

IEEE Access

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The submarine drifter is a novel Lagrangian-based observation platform to explore the ocean, but its precise and rapid depth control system design is still an open issue. The major challenge would be the complex hybrid actuation system, which contains anisotropic characteristics and switching issues. In this paper, we proposed an modified complementary constrained model predictive control (MCC-MPC) scheme to meet the metrics. The scheme reformulates complex drifter and hybrid actuation system dynamics into a solvable system with complementary constraints. The nonlinear component inside the system is approximated by applying a sgn-sigmoid approximation function for the sake of linearization and computation. Then the customized online optimizer predicts the system dynamics with complementary constraints and computes the optimal control outputs in the finite horizon in an iterative loop. The validation results prove that the proposed controller can effectively control the submarine drifter to achieve the desired depth and the key metrics are 10x, 4x, and 2x better than conventional PID control, disturbance observerbased control, and conventional MPC methods, respectively.

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“…Recent studies have argued submesoscale vertical transport to be an important pathway in supplying nutrients to the euphotic layer (e.g. Lévy, Ferrari, et al, 2012;Levy & Martin, 2013;Mahadevan, 2016;Lévy et al, 2018;Zhang et al, 2019). Precisely isolating the relative contribution of this mechanism, however, has remained challenging since as was noted earlier, submesoscale physics can feed back onto the large-scale state.…”

Section: Introductionmentioning

confidence: 99%

The contribution of submesoscale over mesoscale eddy iron transport in the open Southern Ocean

Uchida¹,

Balwada²,

Abernathey³

et al. 2019

Preprint

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In order to examine the roles of ocean dynamics in supplying iron, the limiting nutrient in the open Southern Ocean, to the surface where it can be effectively utilized for photosynthesis, we run a flat-bottom zonally re-entrant channel model configured to represent the Antarctic Circumpolar Current region and couple it to a full biogeochemical model. The model was forced with monthly varying physical and biogeochemical boundary conditions to incorporate seasonality. Much focus on previous studies on iron pathways in the open ocean region has been on mixed-layer entrainment and diapycnal fluxes of iron. The Southern Ocean, however, is a region with strong meso- and submeso-scale turbulence and we would expect eddy fluxes to transport tracers including iron. Spatial resolution is, therefore, chosen as the parameter to control the effect of eddy transport. We utilize cross spectral analysis and the generalized Omega equation to temporally and spatially decompose the vertical transport attributable to meso- and submeso-scale motions. Our results suggest that the mesoscale vertical fluxes provide a first-order pathway for transporting iron across the mixing-layer base where diapycnal mixing is weak and must be included in modelling the open-Southern-Ocean iron budget.

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The influence of geostrophic strain on oceanic ageostrophic motion and surface chlorophyll

Cited by 75 publications

References 56 publications

The Contribution of Submesoscale over Mesoscale Eddy Iron Transport in the Open Southern Ocean

The Contribution of Submesoscale over Mesoscale Eddy Iron Transport in the Open Southern Ocean

Complementary Constrained Model Predictive Depth Control of a Hybridly-Actuated Submarine Drifter

The contribution of submesoscale over mesoscale eddy iron transport in the open Southern Ocean

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