Mesoscale Eddies Modulate Mixed Layer Depth Globally

Gaube, Peter; McGillicuddy, Dennis J.; Moulin, Aurélie J.

doi:10.1029/2018gl080006

Cited by 105 publications

(115 citation statements)

References 31 publications

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“…The mixed layer is characterized by nearly uniform properties such as temperature and salinity throughout the layer. Mesoscale eddies can significantly modulate spatial and temporal evolution of the mixed layer [36,37]. The mixed layer depth (MLD) is a layer in which active turbulence is assumed to be mixed and homogeneous to a certain level.…”

Section: Mixed Layermentioning

confidence: 99%

Anatomy of a Cyclonic Eddy in the Kuroshio Extension Based on High-Resolution Observations

Zhang

Chen

2019

Atmosphere

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Mesoscale eddies are common in the ocean and their surface characteristics have been well revealed based on altimetric observations. Comparatively, the knowledge of the three-dimensional (3D) structure of mesoscale eddies is scarce, especially in the open ocean. In the present study, high-resolution field observations of a cyclonic eddy in the Kuroshio Extension have been carried out and the anatomy of the observed eddy is conducted. The temperature anomaly exhibits a vertical monopole cone structure with a maximum of −7.3 • C located in the main thermocline. The salinity anomaly shows a vertical dipole structure with a fresh anomaly in the main thermocline and a saline anomaly in the North Pacific Intermediate Water (NPIW). The cyclonic flow displays an equivalent barotropic structure. The mixed layer is deep in the center of the eddy and thin in the periphery. The seasonal thermocline is intensified and the permanent thermocline is upward domed by 350 m. The subtropical mode water (STMW) straddled between the seasonal and permanent thermoclines weakens and dissipates in the eddy center. The salinity of NPIW distributed along the isopycnals shows no significant difference inside and outside the eddy. The geostrophic relation is approximately set up in the eddy. The nonlinearity-defined as the ratio between the rotational speed to the translational speed-is 12.5 and decreases with depth. The eddy-wind interaction is examined by high resolution satellite observations. The results show that the cold eddy induces wind stress aloft with positive divergence and negative curl. The wind induced upwelling process is responsible for the formation of the horizontal monopole pattern of salinity, while the horizontal transport results in the horizontal dipole structure of temperature in the mixed layer. species composition (EDDIES) in the Sargasso Sea off Bermuda [5], meso-and submesoscale processes in an intense front (AlborEx) [6] and the northwestern Pacific eddies, internal waves and mixing Experiment (NPEIM) [7], and so forth. Nowadays, main observation methods for field experiment include Argo floats, moored instrumentation, underwater gliders and shipboard survey.Argo profiling floats, which are designed to measure underwater ocean temperature and salinity (T/S) [8], are one of the effective methods to obtain 3D mesoscale eddy structures [9][10][11][12][13]. However, due to the drift features, the detailed structure of a specific eddy is difficult to acquire unless a large number of Argo floats are deployed inside the targeted mesoscale eddy. Reference [14] deployed 17 rapid-sampling Argo floats to study the anticyclonic eddies effects on mode water subduction in the south of the Kuroshio Extension to the east of Japan. In situ mooring observations can usually collect temperature, salinity and current data from the bottom to the surface at a fixed-point where the eddy moves through. Reference [15] designed and conducted a multi-month field campaign to capture the full-depth 3D structure of a pair of anticyclonic and c...

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Section: Mixed Layermentioning

confidence: 99%

Anatomy of a Cyclonic Eddy in the Kuroshio Extension Based on High-Resolution Observations

Zhang

Chen

2019

Atmosphere

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“…In addition, it is well known that subseasonal variability in the atmosphere substantially impacts the surface exchange of mass, momentum, and energy (Foltz and McPhaden, 2004;Foltz and McPhaden, 2005;Goubanova et al, 2013;Gulev, 1994;Hughes et al, 2012;Illig et al, 2014;Lin et al, 2018;Munday and Zhai, 2017;Ponte and Rosen, 2004;Wanninkhof, 1992;Wu et al, 2016;Zhang, 2005;Zhai et al, 2012;Zhai, 2013;Zolina and Gulev, 2003). It is also well known that strong atmospheric synoptic variability (e.g., tropical; (Price et al, 1978;Sanford et al, 2011) and extratropical; (Carranza and Gille, 2015;Dohan and Davis, 2011;Pollard et al, 1972;Swart et al, 2015) cyclones) and intraseasonal 30-90 day variability (e.g., the Madden-Julian Oscillations; (Keerthi et al, 2016;Zhang, 2005)) as well as oceanic variability (e.g., mesoscale; (Gaube et al, 2018;Hausmann et al, 2017); and submesoscale (Buckingham et al, 2017;Thompson et al, 2016) eddies) all modulate the MLD on subseasonal time scales. Further, high-frequency mooring and vertical profiler observations reveal substantial subseasonal variability in the MLD across essentially all subseasonal frequencies and in a range of oceanic regimes from the tropics to the poles (e.g., Buckingham et al, 2016;Damerell et al, 2016;Dickey et al, 2001;Moum et al, 2009;Swart et al, 2015;Toole et al, 2010;Thompson et al, 2016).…”

Section: Introductionmentioning

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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“…Additionally, trophic web dynamics 6 contribute to the removal of CO2 from the atmosphere, through sedimentation of 7 inorganic and organic carbon compounds included in fecal pellets, and to the 8 appropriate functioning of the biological or carbon pump [3]. 9 Typically, zooplankton biomass is indicative of secondary production and estimation 10 of this parameter is essential to evaluate trophic structure and function in any aquatic 11 ecosystem [5]. Changes in zooplankton biomass are closely related to several factors, 12 including variations in the salinity field [6], the temperature regime [7], and the 13 availability of food [8].…”

Section: Introductionmentioning

confidence: 99%

“…These hydrodynamic processes 19 are present throughout the water column at different scales, including internal waves, 20 fronts, and eddies [10]. 21 Mesoscale eddies (radii 10-100 km) are high energy hydrological structures of prime 22 importance in any marine ecosystem [11]. These structures, are recognized as cyclonic, 23 anticyclonic, and mode-water with a noticeable impact on the planktonic ecosystem [12].…”

Section: Introductionmentioning

confidence: 99%

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Seasonal variability in copepod biomass in a cyclonic eddy in the Bay of La Paz, southern Gulf of California, Mexico

Diaz

Monreal‐Gómez

Coria-Monter

et al. 2020

Preprint

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As one of the main groups composing marine zooplankton, copepods play an important role due to the position they occupy in the trophic web. Study of their biomass and relationship with the physical conditions of the water column are essential in order to evaluate the trophic structure and functions of any aquatic ecosystem. As a contribution to this topic, we assessed the copepod biomass inside a cyclonic eddy system during two different seasons in the Bay of La Paz in the southern Gulf of California, a region characterized by high biological productivity. Two oceanographic expeditions took place in the winter of 2006 and summer of 2009 on which a conductivity-temperature-depth (CTD) probe was used to determine the physical structure of the water column and oblique zooplankton hauls collected zooplankton samples. Satellite data were used to visualize chlorophyll-a distribution patterns. The results showed the presence of a well-defined mesoscale cyclonic eddy in both seasons, with high chlorophyll-a (CHLA) values at the edges of the eddy. Maximum values for copepod biomass were observed in winter and their distribution corresponded well with the circulation pattern and the CHLA values, forming a belt shape following the periphery of the eddy. The results presented herein highlight the impact of the mesoscale eddy on the planktonic ecosystem through its influence on hydrographic conditions in the water column. Other factors, such as ecological interactions, population dynamics, and feeding habits may play a role as well. Feeding behavior in particular is affected by high CHLA concentrations observed around the eddy which represent a source of food for these organisms.

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Mesoscale Eddies Modulate Mixed Layer Depth Globally

Cited by 105 publications

References 31 publications

Anatomy of a Cyclonic Eddy in the Kuroshio Extension Based on High-Resolution Observations

Anatomy of a Cyclonic Eddy in the Kuroshio Extension Based on High-Resolution Observations

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

Seasonal variability in copepod biomass in a cyclonic eddy in the Bay of La Paz, southern Gulf of California, Mexico

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