Stratification and mixing regimes in biological thin layers over the Mid‐Atlantic Bight

Benoit‐Bird, Kelly J.; Nash, Jonathan D.; Moum, James N.

doi:10.4319/lo.2014.59.4.1349

Cited by 11 publications

(4 citation statements)

References 47 publications

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“…This layer differs from other deep chlorophyll maxima in lakes due to the former's reduced thickness ( < 2 m, Leach et al 2018) and from similar structures in the ocean due to its temporal persistence (~6 months). Marine thin layers typically last for a few hours to a few days (Dekshenieks et al 2001;Durham and Stocker 2012), by which time advection or turbulent mixing typically disrupt the layers (Steinbuck et al 2009;Shroyer et al 2014).…”

Section: Introductionmentioning

confidence: 99%

Inhibited vertical mixing and seasonal persistence of a thin cyanobacterial layer in a stratified lake

et al. 2021

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Harmful blooms of the filamentous cyanobacteria Planktothrix rubescens have become common in many lakes as they have recovered from eutrophication over the last decades. These cyanobacteria, capable of regulating their vertical position, often flourish at the thermocline to form a deep chlorophyll maximum. In Lake Zurich (Switzerland), they accumulate during stratified season (May–October) as a persistent metalimnetic thin layer (~2 m wide). This study investigated the role of turbulent mixing in springtime layer formation, its persistence over the summer, and its breakdown in autumn. We characterised seasonal variation of turbulence in Lake Zurich with four surveys conducted in April, July and October of 2018 and September of 2019. Surveys included microstructure profiles and high-resolution mooring measurements. In July and October, the thin layer occurred within a strong thermocline ($$N \gtrsim 0.05$$ N ≳ 0.05 s$$^{-1}$$ - 1 ) and withstood significant turbulence, observed as turbulent kinetic energy dissipation rates ($$\varepsilon \approx 10^{-8}$$ ε ≈ 10 - 8 W kg$$^{-1}$$ - 1 ). Vertical turbulent overturns –monitored by the Thorpe scale– went mostly undetected and on average fell below those estimated by the Ozmidov scale ($$L_O \approx 1$$ L O ≈ 1 cm). Consistently, vertical diffusivity was close to molecular values, indicating negligible turbulent fluxes. This reduced metalimnetic mixing explains the persistence of the thin layer, which disappears with the deepening of the surface mixed layer in autumn. Bi-weekly temperature profiles in 2018 and a nighttime microstructure sampling in September 2019 showed that nighttime convection serves as the main mechanism driving the breakdown of the cyanobacterial layer in autumn. These results highlight the importance of light winds and convective mixing in the seasonal cycling of P. rubescens communities within a strongly stratified medium-sized lake.

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Section: Introductionmentioning

confidence: 99%

Inhibited vertical mixing and seasonal persistence of a thin cyanobacterial layer in a stratified lake

et al. 2021

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“…Thin layers are often related to the pycnocline, thermocline or halocline (Dekshenieks et al 2001; Steinbuck et al 2009; Breckenridge and Bollens 2010) and have been reported in environments with both low shear and turbulent mixing. Shroyer et al (2014) identified thin biological layers in regions where intense mixing events were rare, within the pycnocline (close to maximum stratification) and at the base of the pycnocline. Talapatra et al (2013) found several peaks of Chaetoceros socialis colonies, nonmotile diatoms, near the pycnocline, in a region of almost zero shear, low rates of dissipation and high stratification.…”

Section: Study Sitementioning

confidence: 99%

Thin layers in the coastal zone of Ubatuba, Brazil: Mechanisms of formation and dissipation

Penninck

Lopes²,

Lima³

et al. 2020

Limnology & Oceanography

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Thin layers are vertically compressed, horizontally extensive, highly concentrated features comprised of plankton and/or particles. They are critical components of the marine ecosystem, likely playing a key role in the life histories and evolutionary trajectories of species found in, or, interacting with them. These structures have been reported in diverse marine environments around the globe. However, the mechanisms of thin layer formation/dissipation in the southwestern Atlantic Ocean were unknown until this contribution. To assess the temporal evolution of thin phytoplankton layers on the inner shelf off Ubatuba, Brazil, we conducted two oceanographic fixed station cruises, including optics, acoustics, and imaging techniques. Over a period of 2 days, three thin layers were observed: within the pycnocline close to the maximum stratification, and below the pycnocline where phytoplankton were affected by enhanced nutrient supply provided by the South Atlantic Central Water (SACW). Changes in regional wind patterns influenced the presence of SACW, which directly affected shear and stratification: the primary physical mechanisms we attribute to thin layer formation in this region. The associated biological mechanisms contributing to thin layer formation were biomass accumulation (in situ growth) and likely the mobility of dinoflagellates. The dominant organisms in the thin layer depths and surroundings, by our in situ imaging system, were cyanobacteria, diatoms, dinoflagellates, and crustaceans. Thin Layers likely have crucial importance for meso‐oligotrophic environments, representing important feeding resources for higher trophic levels.

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“…Both diffuse and intense layers were characterized at 38 kHz because the intense layers were clearly observed at 38 kHz while the diffuse layers appeared at both 38 and 70 kHz. We used a series of criteria to identify 2 layer structures following Shroyer et al (2014). (1 , excluding the noise from analysis.…”

Section: Acoustic Datamentioning

confidence: 99%

Spatial variability of deep scattering layers shapes the Bahamian mesopelagic ecosystem

Sato¹,

Benoit‐Bird²

2017

Mar. Ecol. Prog. Ser.

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Deep scattering layers (DSLs) play an important role in pelagic food webs, serving as a vehicle for transferring energy between productive surface waters and the deep sea. We explored the spatial dynamics of DSLs off the Bahamas in shaping oligotrophic ecosystems. We compared 2 areas known to be important foraging habitats for a deep-diving predator, Blainville's beaked whales: the Tongue of the Ocean (TOTO), an oceanographically isolated habitat, and the waters off Abaco Island, an oceanographically connected habitat. Using ship-based multifrequency echosounders and direct net sampling, we identified common layer structures characterized by diffuse, broad layers (>100 m in thickness) observed across the study areas. Within those diffuse layers, we occasionally observed distinctively bounded intense layers (~20 m in thickness) located at the upper edges of the DSLs. We found that spatial variability of layer structures shaped the Bahamian ecosystem. By comparing common layer types across the sampling locations, 2 potential mechanisms were identified. The area off Abaco Island was characterized by diffuse layers comprised of larger animals with greater migration distance and biomass than the habitat in TOTO, suggesting that Abaco may transfer more energy between energy-rich surface waters and the deep sea. Within TOTO, habitat most frequently used by beaked whales was characterized by the highest occurrence of intense layers dominated by thinner layers, suggesting such fine-scale structures may increase foraging efficiency by layer predators. Spatial variability of the DSL structures reveals the dynamics of the Bahamian mesopelagic ecosystem, potentially driving the beaked whales through bottom-up control of their prey.

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Stratification and mixing regimes in biological thin layers over the Mid‐Atlantic Bight

Cited by 11 publications

References 47 publications

Inhibited vertical mixing and seasonal persistence of a thin cyanobacterial layer in a stratified lake

Inhibited vertical mixing and seasonal persistence of a thin cyanobacterial layer in a stratified lake

Thin layers in the coastal zone of Ubatuba, Brazil: Mechanisms of formation and dissipation

Spatial variability of deep scattering layers shapes the Bahamian mesopelagic ecosystem

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