Seasonality in submesoscale turbulence

Callies, Jörn; Ferrari, Raffaele; Klymak, Jody M.; Gula, Jonathan

doi:10.1038/ncomms7862

Cited by 304 publications

(346 citation statements)

References 43 publications

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“…Another interesting feature of these spectra at these larger scales (λ > 1000 m) is the apparent change of slope to λ 3 , perhaps indicating the start of the quasi-geostrophic turbulent cascade, known to follow that slope well into the mesoscales. For example, similar spectral slope and its flattening on smaller scales was suggested by [43].…”

Section: Discussionsupporting

confidence: 71%

Airborne Remote Sensing of the Upper Ocean Turbulence during CASPER-East

et al. 2018

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This study takes on the challenge of resolving upper ocean surface currents with a suite of airborne remote sensing methodologies, simultaneously imaging the ocean surface in visible, infrared, and microwave bands. A series of flights were conducted over an air-sea interaction supersite established 63 km offshore by a large multi-platform CASPER-East experiment. The supersite was equipped with a range of in situ instruments resolving air-sea interface and underwater properties, of which a bottom-mounted acoustic Doppler current profiler was used extensively in this paper for the purposes of airborne current retrieval validation and interpretation. A series of water-tracing dye releases took place in coordination with aircraft overpasses, enabling dye plume velocimetry over 100 m to 10 km spatial scales. Similar scales were resolved by a Multichannel Synthetic Aperture Radar, which resolved a swath of instantaneous surface velocities (wave and current) with 10 m resolution and 5 cm/s accuracy. Details of the skin temperature variability imprinted by the upper ocean turbulence were revealed in 1-14,000 m range of spatial scales by a mid-wave infrared camera. Combined, these methodologies provide a unique insight into the complex spatial structure of the upper ocean turbulence on a previously under-resolved range of spatial scales from meters to kilometers. However, much attention in this paper is dedicated to quantifying and understanding uncertainties and ambiguities associated with these remote sensing methodologies, especially regarding the smallest resolvable turbulent scales and reference depths of retrieved currents.Keywords: airborne remote sensing; ocean surface currents; upper ocean turbulence BackgroundCapabilities for spatial measurements of ocean surface turbulence are highly desirable for a wide variety of needs ranging from basic studies of upper ocean mixing processes to data assimilation into high-resolution coastal and ocean circulation models. On the global scale, presently available observations of the ocean currents are provided by satellite altimeters, which are limited to mesoscales and resolve only the geostrophic component of the surface current. Much anticipated launches of the

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Section: Discussionsupporting

confidence: 71%

Airborne Remote Sensing of the Upper Ocean Turbulence during CASPER-East

et al. 2018

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“…, and a shoaling of the spectra during winter to values close to k 22 (Callies et al 2015). This wintertime shoaling is an indication that a larger fraction of the total kinetic energy resides at smaller scales.…”

mentioning

confidence: 94%

“…This offers a higher degree of granularity than recent studies that have analyzed bulk seasonal differences in flow characteristics, which are then used to infer submesoscale activity. Both numerical models (Mensa et al 2013;Sasaki et al 2014) and observations (Callies et al 2015;Swart et al 2015;Buckingham et al 2016) provide strong evidence that there are seasonal modulations in submesoscale activity. In general, these reflect a steepening of the kinetic energy spectra during summer, typically with slopes around k…”

Section: Introductionmentioning

confidence: 99%

Open-Ocean Submesoscale Motions: A Full Seasonal Cycle of Mixed Layer Instabilities from Gliders

Thompson

Lazar

Buckingham

et al. 2016

Journal of Physical Oceanography

174

227

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The importance of submesoscale instabilities, particularly mixed layer baroclinic instability and symmetric instability, on upper-ocean mixing and energetics is well documented in regions of strong, persistent fronts such as the Kuroshio and the Gulf Stream. Less attention has been devoted to studying submesoscale flows in the open ocean, far from long-term, mean geostrophic fronts, characteristic of a large proportion of the global ocean. This study presents a year-long, submesoscale-resolving time series of near-surface buoyancy gradients, potential vorticity, and instability characteristics, collected by ocean gliders, that provides insight into open-ocean submesoscale dynamics over a full annual cycle. The gliders continuously sampled a 225 km 2 region in the subtropical northeast Atlantic, measuring temperature, salinity, and pressure along 292 short (;20 km) hydrographic sections. Glider observations show a seasonal cycle in near-surface stratification. Throughout the fall (September-November), the mixed layer deepens, predominantly through gravitational instability, indicating that surface cooling dominates submesoscale restratification processes. During winter (December-March), mixed layer depths are more variable, and estimates of the balanced Richardson number, which measures the relative importance of lateral and vertical buoyancy gradients, depict conditions favorable to symmetric instability. The importance of mixed layer instabilities on the restratification of the mixed layer, as compared with surface heating and cooling, shows that submesoscale processes can reverse the sign of an equivalent heat flux up to 25% of the time during winter. These results demonstrate that the openocean mixed layer hosts various forced and unforced instabilities, which become more prevalent during winter, and emphasize that accurate parameterizations of submesoscale processes are needed throughout the ocean.

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“…Some methods of estimating the physicallydriven fluxes such as eddy correlation measurements and turbulent energy dissipation measurements provide a snapshot of conditions over very small spatiotemporal scales (Gregg, 1987;Wüest et al, 1996;Fairall et al, 2000;Kunze et al, 2006). Gas tracers, in contrast, integrate over timescales of days to weeks in the surface ocean or years in the deep ocean and are a valuable tool for determining the average rates of these physical processes (Hamme and Emerson, 2002;Ito and Deutsch, 2006;Hamme and Severinghaus, 2007;Stanley and Jenkins, 2013), which are inherently patchy in space and time (Callies et al, 2015;Thompson et al, 2016).…”

Section: Inert Gas Tracersmentioning

confidence: 99%

Insight into chemical, biological, and physical processes in coastal waters from dissolved oxygen and inert gas tracers

Manning¹

2017

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In this thesis, I use coastal measurements of dissolved O 2 and inert gases to provide insight into the chemical, biological, and physical processes that impact the oceanic cycles of carbon and dissolved gases. Dissolved O 2 concentration and triple isotopic composition trace net and gross biological productivity. The saturation states of inert gases trace physical processes, such as air-water gas exchange, temperature change, and mixing, that affect all gases.First, I developed a field-deployable system that measures Ne, Ar, Kr, and Xe gas ratios in water. It has precision and accuracy of 1 % or better, enables near-continuous measurements, and has much lower cost compared to existing laboratory-based methods. The system will increase the scientific community's access to use dissolved noble gases as environmental tracers.Second, I measured O 2 and five noble gases during a cruise in Monterey Bay, California. I developed a vertical model and found that accurately parameterizing bubble-mediated gas exchange was necessary to accurately simulate the He and Ne measurements. I present the first comparison of multiple gas tracer, incubation, and sediment trap-based productivity estimates in the coastal ocean. Net community production estimated from 15 NO -3 uptake and O 2 /Ar gave equivalent results at steady state. Underway O 2 /Ar measurements revealed submesoscale variability that was not apparent from daily incubations.Third, I quantified productivity by O 2 mass balance and air-water gas exchange by dual tracer ( 3 He/SF 6 ) release during ice melt in the Bras d'Or Lakes, a Canadian estuary. The gas transfer velocity at >90 % ice cover was 6 % of the rate for nearly ice-free conditions. Rates of volumetric gross primary production were similar when the estuary was completely ice-covered and ice-free, and the ecosystem was on average net autotrophic during ice melt and net heterotrophic following ice melt. I present a method for incorporating the isotopic composition of H 2 O into the O 2 isotope-based productivity calculations, which increases the estimated gross primary production in this study by 46-97 %.In summary, I describe a new noble gas analysis system and apply O 2 and inert gas observations in new ways to study chemical, biological, and physical processes in coastal waters.

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Seasonality in submesoscale turbulence

Cited by 304 publications

References 43 publications

Airborne Remote Sensing of the Upper Ocean Turbulence during CASPER-East

Airborne Remote Sensing of the Upper Ocean Turbulence during CASPER-East

Open-Ocean Submesoscale Motions: A Full Seasonal Cycle of Mixed Layer Instabilities from Gliders

Insight into chemical, biological, and physical processes in coastal waters from dissolved oxygen and inert gas tracers

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