Submesoscales Enhance Storm‐Driven Vertical Mixing of Nutrients: Insights From a Biogeochemical Large Eddy Simulation

Lévy, Marina; Taylor, John R.

doi:10.1029/2019jc015370

Cited by 27 publications

(19 citation statements)

References 89 publications

(200 reference statements)

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“…2 ). Although vertical diffusivities can vary significantly in space and time, the stratification strength and vertical diffusivities for our field study are consistent with independent estimates from the NEMURO-GOM biogeochemical model and with previously reported values 26 .…”

Section: Resultssupporting

confidence: 92%

Lateral advection supports nitrogen export in the oligotrophic open-ocean Gulf of Mexico

et al. 2021

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In contrast to its productive coastal margins, the open-ocean Gulf of Mexico (GoM) is notable for highly stratified surface waters with extremely low nutrient and chlorophyll concentrations. Field campaigns in 2017 and 2018 identified low rates of turbulent mixing, which combined with oligotrophic nutrient conditions, give very low estimates for diffusive flux of nitrate into the euphotic zone (< 1 µmol N m−2 d−1). Estimates of local N2-fixation are similarly low. In comparison, measured export rates of sinking particulate organic nitrogen (PON) from the euphotic zone are 2 – 3 orders of magnitude higher (i.e. 462 – 1144 µmol N m−2 d−1). We reconcile these disparate findings with regional scale dynamics inferred independently from remote-sensing products and a regional biogeochemical model and find that laterally-sourced organic matter is sufficient to support >90% of open-ocean nitrogen export in the GoM. Results show that lateral transport needs to be closely considered in studies of biogeochemical balances, particularly for basins enclosed by productive coasts.

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Section: Resultssupporting

confidence: 92%

Lateral advection supports nitrogen export in the oligotrophic open-ocean Gulf of Mexico

et al. 2021

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“…. Although vertical diffusivities can vary significantly in space and time, the stratification strength and vertical diffusivities for our field study are consistent with independent estimates from the NEMURO-GOM biogeochemical model and with previously reported values26 .As vertical mixing of nitrate and N2-fixation individually provide enough N to support<1% of sinking PON flux in our Lagrangian experiments, locally sourced new N appears insufficient to balance the measured rates of PON export. Instead, a significant role of lateral transport of organic material is suggested by the rapid horizontal displacements in our drifter experiments (up to 60 km d -1 ) and the strong coastal-offshore particulate gradients in the GoM (Supplemental Figure 3-4).…”

supporting

confidence: 90%

Lateral Advection Supports Nitrogen Export in the Oligotrophic Open-Ocean Gulf of Mexico

Kelly

Knapp

Landry

et al. 2020

Preprint

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In contrast to its productive coastal margins, the open-ocean Gulf of Mexico (GoM) is notable for highly stratified surface waters with extremely low nutrient and chlorophyll concentrations. Field campaigns in 2017 and 2018 indicate low rates of turbulent mixing, which combined with oligotrophic nutrient conditions, give very low estimates of diffusive flux of nitrate into the euphotic zone (< 1 µmol N m-2 d-1). Estimates of local N2-fixation are similarly low. In comparison, measured export rates of sinking particulate organic nitrogen (PON) from the euphotic zone are 2-3 orders of magnitude higher (i.e. 462 – 1144 µmol N m-2 d-1). We reconcile these disparate findings with regional scale dynamics inferred independently from remote-sensing products and a regional biogeochemical model and find that laterally-sourced organic matter is sufficient to support >90% of open-ocean nitrogen export in the GoM. Results show that lateral transport needs to be closely considered in studies of biogeochemical balances, particularly for basins enclosed by productive coasts.

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“…Processes that are poorly represented or excluded in these simulations may cause the sensitivity of the MLD to subseasonal winds to deviate from the results reported above in the real ocean or other simulations. For example, subseasonal winds may modify Langmuir (Fan and Griffies, ; Li et al, ; Van Roekel et al, ) and submesoscale (Fox‐Kemper et al, ; Thomas et al, , ; Whitt, Taylor, & Lévy, ; Whitt, Lévy, & Taylor, , ; Whitt and Taylor, ) turbulence, neither of which are represented in the models used in this study. In addition, subseasonal winds modify inertial oscillations and internal waves, which are only marginally represented in the global model (see sections 2.2.2 and 2.3.2).…”

Section: Discussionmentioning

confidence: 99%

Global Impacts of Subseasonal (<60 Day) Wind Variability on Ocean Surface Stress, Buoyancy Flux, and Mixed Layer Depth

Whitt

Nicholson²,

Carranza

2019

JGR Oceans

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Subseasonal surface wind variability strongly impacts the annual mean and subseasonal turbulent atmospheric surface fluxes. However, the impacts of subseasonal wind variability on the ocean are not fully understood. Here, we quantify the sensitivity of the ocean surface stress ( ), buoyancy flux (B), and mixed layer depth (MLD) to subseasonal wind variability in both a one-dimensional (1-D) vertical column model and a three-dimensional (3-D) global mesoscale-resolving ocean/sea ice model. The winds are smoothed by time filtering the pseudo-stresses, so the mean stress is approximately unchanged, and some important surface flux feedbacks are retained. The 1-D results quantify the sensitivities to wind variability at different time scales from 120 days to 1 day at a few sites. The 3-D results quantify the sensitivities to wind variability shorter than 60 days at all locations, and comparisons between 1-D and 3-D results highlight the importance of 3-D ocean dynamics. Globally, subseasonal winds explain virtually all of subseasonal variance, about half of subseasonal B variance but only a quarter of subseasonal MLD variance. Subseasonal winds also explain about a fifth of the annual mean MLD and a similar and spatially correlated fraction of the mean friction velocity, u * = √ | |∕ sw where sw is the density of seawater. Hence, the subseasonal MLD variance is relatively insensitive to subseasonal winds despite their strong impact on local B and variability, but the mean MLD is relatively sensitive to subseasonal winds to the extent that they modify the mean u * , and both of these sensitivities are modified by 3-D ocean dynamics. Key Points: • We quantify the global impact of subseasonal winds on ocean surface fluxes and mixed-layer depth (MLD) in a mesoscale-resolving model • Globally, subseasonal winds are responsible for about a fifth of the annual average MLD and about a quarter of the subseasonal MLD variance • The increase in the mean MLD with subseasonal winds is caused by a higher friction velocity, but other factors modify the sensitivity Supporting Information: • Supporting Information S1A few previous studies have looked into the sensitivity of the climatological MLD to subseasonal atmospheric variability in 3-D global ocean circulation models by explicitly modifying the wind forcing in ocean models using grids that do not fully resolve mesoscales. For example, Lee and Liu (2005) explore the impact of diurnal winds on the MLD and sea surface temperature using an eddy-parameterizing (nominal 1 • resolution) global ocean model. Their model is forced with daily averaged fluxes, except for the wind stresses, which are averaged over 12 hr or subsampled every 24 hr. The annual and zonal mean MLD increases by up to a maximum of about 10 m with 12-hr winds compared to subsampled 24-hr winds, and the response of the MLD is largely attributable to enhanced vertical mixing by high-frequency winds at middle-to-high latitudes. More recently, Condron and Renfrew (2013) parameterize the effects of unresolved mesoscale a...

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Submesoscales Enhance Storm‐Driven Vertical Mixing of Nutrients: Insights From a Biogeochemical Large Eddy Simulation

Cited by 27 publications

References 89 publications

Lateral advection supports nitrogen export in the oligotrophic open-ocean Gulf of Mexico

Lateral advection supports nitrogen export in the oligotrophic open-ocean Gulf of Mexico

Lateral Advection Supports Nitrogen Export in the Oligotrophic Open-Ocean Gulf of Mexico

Global Impacts of Subseasonal (<60 Day) Wind Variability on Ocean Surface Stress, Buoyancy Flux, and Mixed Layer Depth

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