Material transport in a convective surface mixed layer under weak wind forcing

Abstract Four one-dimensional models which have been used to characterize surface mixed layer (ML) processes and the thermal structure are described. Although most any model can be calibrated to mimic surface water temperatures, it does not imply that the corresponding mixing processes are well described. Eddy diffusion or "K" models can exhibit this problem. If a ML model is to be useful for water quality applications, then it must be able to resolve storm events and, therefore, be able to simulate the ML depth, h, and its time rate of change, dh/dt. A general water quality model is derived from mass conservation principles to demonstrate how ML models can be used in a physically meaningful way to address water quality issues.

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Simulation of diurnal variability in vertical density structure using a coupled model

Scientific Reports ◽

10.1038/s41598-021-90426-w ◽

2021 ◽

Vol 11 (1) ◽

Author(s):

B. Yadidya ◽

A. D. Rao ◽

Sachiko Mohanty

Keyword(s):

Mixed Layer ◽

3D Model ◽

Coupled Model ◽

Wave Model ◽

Andaman Sea ◽

Surface Mixed Layer ◽

Diurnal Variability ◽

Rama Buoy ◽

Vertical Displacements ◽

Primary Advantage

AbstractThe changes in the physical properties of the ocean on a diurnal scale primarily occur in the surface mixed layer and the pycnocline. Price–Weller–Pinkel model, which modifies the surface mixed layer, and the internal wave model based on Garrett–Munk spectra that calculates the vertical displacements due to internal waves are coupled to simulate the diurnal variability in temperature and salinity, and thereby density profiles. The coupled model is used to simulate the hourly variations in density at RAMA buoy (15° N, 90° E), in the central Bay of Bengal, and at BD12 (10.5° N, 94° E), in the Andaman Sea. The simulations are validated with the in-situ observations from December 2013 to November 2014. The primary advantage of this model is that it could simulate spatial variability as well. An integrated model is also tested and validated by using the output of the 3D model to initialize the coupled model during January, April, July, and October. The 3D model can be used to initialize the coupled model at any given location within the model domain to simulate the diurnal variability of density. The simulations showed promising results which could be further used in simulating the acoustic fields and propagation losses which are crucial for Navy operations.

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Niche partitioning by photosynthetic plankton as a driver of CO2-fixation across the oligotrophic South Pacific Subtropical Ocean

The ISME Journal ◽

10.1038/s41396-021-01072-z ◽

2021 ◽

Author(s):

Julia Duerschlag ◽

Wiebke Mohr ◽

Timothy G. Ferdelman ◽

Julie LaRoche ◽

Dhwani Desai ◽

...

Keyword(s):

Mixed Layer ◽

Niche Partitioning ◽

Euphotic Zone ◽

South Pacific ◽

Niche Differentiation ◽

Surface Mixed Layer ◽

The South ◽

The Core ◽

Photosynthetic Eukaryotes ◽

Phytoplankton Communities

AbstractOligotrophic ocean gyre ecosystems may be expanding due to rising global temperatures [1–5]. Models predicting carbon flow through these changing ecosystems require accurate descriptions of phytoplankton communities and their metabolic activities [6]. We therefore measured distributions and activities of cyanobacteria and small photosynthetic eukaryotes throughout the euphotic zone on a zonal transect through the South Pacific Ocean, focusing on the ultraoligotrophic waters of the South Pacific Gyre (SPG). Bulk rates of CO2 fixation were low (0.1 µmol C l−1 d−1) but pervasive throughout both the surface mixed-layer (upper 150 m), as well as the deep chlorophyll a maximum of the core SPG. Chloroplast 16S rRNA metabarcoding, and single-cell 13CO2 uptake experiments demonstrated niche differentiation among the small eukaryotes and picocyanobacteria. Prochlorococcus abundances, activity, and growth were more closely associated with the rims of the gyre. Small, fast-growing, photosynthetic eukaryotes, likely related to the Pelagophyceae, characterized the deep chlorophyll a maximum. In contrast, a slower growing population of photosynthetic eukaryotes, likely comprised of Dictyochophyceae and Chrysophyceae, dominated the mixed layer that contributed 65–88% of the areal CO2 fixation within the core SPG. Small photosynthetic eukaryotes may thus play an underappreciated role in CO2 fixation in the surface mixed-layer waters of ultraoligotrophic ecosystems.

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Simulation and exploration of the mechanisms underlying the spatiotemporal distribution of surface mixed layer depth in a large shallow lake

Advances in Atmospheric Sciences ◽

10.1007/s00376-012-1262-1 ◽

2012 ◽

Vol 29 (6) ◽

pp. 1360-1373 ◽

Cited By ~ 10

Author(s):

Qiaohua Zhao ◽

Jihua Sun ◽

Guangwei Zhu

Keyword(s):

Mixed Layer ◽

Shallow Lake ◽

Mixed Layer Depth ◽

Spatiotemporal Distribution ◽

Surface Mixed Layer ◽

Layer Depth ◽

Large Shallow Lake

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Coherent pathways for subduction from the surface mixed layer at ocean fronts

10.1002/essoar.10504909.1 ◽

2020 ◽

Author(s):

Mara Freilich ◽

Amala Mahadevan

Keyword(s):

Mixed Layer ◽

Surface Mixed Layer ◽

Ocean Fronts

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Parameterization of Mixed Layer Eddies. Part I: Theory and Diagnosis

Journal of Physical Oceanography ◽

10.1175/2007jpo3792.1 ◽

2008 ◽

Vol 38 (6) ◽

pp. 1145-1165 ◽

Cited By ~ 353

Author(s):

Baylor Fox-Kemper ◽

Raffaele Ferrari ◽

Robert Hallberg

Keyword(s):

Mixed Layer ◽

Mixed Layer Depth ◽

Baroclinic Instability ◽

Finite Amplitude ◽

Climate Impacts ◽

Surface Mixed Layer ◽

Rotation Rates ◽

Wide Range ◽

Horizontal Density Gradient ◽

Mixed Layers

Abstract Ageostrophic baroclinic instabilities develop within the surface mixed layer of the ocean at horizontal fronts and efficiently restratify the upper ocean. In this paper a parameterization for the restratification driven by finite-amplitude baroclinic instabilities of the mixed layer is proposed in terms of an overturning streamfunction that tilts isopycnals from the vertical to the horizontal. The streamfunction is proportional to the product of the horizontal density gradient, the mixed layer depth squared, and the inertial period. Hence restratification proceeds faster at strong fronts in deep mixed layers with a weak latitude dependence. In this paper the parameterization is theoretically motivated, confirmed to perform well for a wide range of mixed layer depths, rotation rates, and vertical and horizontal stratifications. It is shown to be superior to alternative extant parameterizations of baroclinic instability for the problem of mixed layer restratification. Two companion papers discuss the numerical implementation and the climate impacts of this parameterization.

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Contrasting dynamic characteristics of shear turbulence and Langmuir circulation in the surface mixed layer

Acta Oceanologica Sinica ◽

10.1007/s13131-015-0661-4 ◽

2015 ◽

Vol 34 (5) ◽

pp. 1-11 ◽

Cited By ~ 1

Author(s):

Guojing Li ◽

Dongxiao Wang ◽

Ju Chen ◽

Jinglong Yao ◽

Lili Zeng ◽

...

Keyword(s):

Mixed Layer ◽

Dynamic Characteristics ◽

Surface Mixed Layer ◽

Langmuir Circulation ◽

Shear Turbulence

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Interannual Variability of Sea Surface Temperature off Java and Sumatra in a Global GCM*

Journal of Climate ◽

10.1175/2007jcli1753.1 ◽

2008 ◽

Vol 21 (11) ◽

pp. 2451-2465 ◽

Cited By ~ 25

Author(s):

Yan Du ◽

Tangdong Qu ◽

Gary Meyers

Keyword(s):

Indian Ocean ◽

Surface Temperature ◽

Sea Surface Temperature ◽

Mixed Layer ◽

Heat Budget ◽

Sea Surface ◽

Surface Mixed Layer ◽

Horizontal Advection ◽

Cold Anomaly ◽

Sst Anomalies

Abstract Using results from the Simple Ocean Data Assimilation (SODA), this study assesses the mixed layer heat budget to identify the mechanisms that control the interannual variation of sea surface temperature (SST) off Java and Sumatra. The analysis indicates that during the positive Indian Ocean Dipole (IOD) years, cold SST anomalies are phase locked with the season cycle. They may exceed −3°C near the coast of Sumatra and extend as far westward as 80°E along the equator. The depth of the thermocline has a prominent influence on the generation and maintenance of SST anomalies. In the normal years, cooling by upwelling–entrainment is largely counterbalanced by warming due to horizontal advection. In the cooling episode of IOD events, coastal upwelling–entrainment is enhanced, and as a result of mixed layer shoaling, the barrier layer no longer exists, so that the effect of upwelling–entrainment can easily reach the surface mixed layer. Horizontal advection spreads the cold anomaly to the interior tropical Indian Ocean. Near the coast of Java, the northern branch of an anomalous anticyclonic circulation spreads the cold anomaly to the west near the equator. Both the anomalous advection and the enhanced, wind-driven upwelling generate the cold SST anomaly of the positive IOD. At the end of the cooling episode, the enhanced surface thermal forcing overbalances the cooling effect by upwelling/entrainment, and leads to a warming in SST off Java and Sumatra.

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Challenges associated with modeling low-oxygen waters in Chesapeake Bay: a multiple model comparison

Biogeosciences ◽

10.5194/bg-13-2011-2016 ◽

2016 ◽

Vol 13 (7) ◽

pp. 2011-2028 ◽

Cited By ~ 49

Author(s):

Isaac D. Irby ◽

Marjorie A. M. Friedrichs ◽

Carl T. Friedrichs ◽

Aaron J. Bever ◽

Raleigh R. Hood ◽

...

Keyword(s):

Dissolved Oxygen ◽

Chesapeake Bay ◽

Mixed Layer ◽

Model Comparison ◽

Three Dimensional ◽

Surface Mixed Layer ◽

Multiple Model ◽

Low Oxygen ◽

Mixing Depth ◽

Biogeochemical Models

Abstract. As three-dimensional (3-D) aquatic ecosystem models are used more frequently for operational water quality forecasts and ecological management decisions, it is important to understand the relative strengths and limitations of existing 3-D models of varying spatial resolution and biogeochemical complexity. To this end, 2-year simulations of the Chesapeake Bay from eight hydrodynamic-oxygen models have been statistically compared to each other and to historical monitoring data. Results show that although models have difficulty resolving the variables typically thought to be the main drivers of dissolved oxygen variability (stratification, nutrients, and chlorophyll), all eight models have significant skill in reproducing the mean and seasonal variability of dissolved oxygen. In addition, models with constant net respiration rates independent of nutrient supply and temperature reproduced observed dissolved oxygen concentrations about as well as much more complex, nutrient-dependent biogeochemical models. This finding has significant ramifications for short-term hypoxia forecasts in the Chesapeake Bay, which may be possible with very simple oxygen parameterizations, in contrast to the more complex full biogeochemical models required for scenario-based forecasting. However, models have difficulty simulating correct density and oxygen mixed layer depths, which are important ecologically in terms of habitat compression. Observations indicate a much stronger correlation between the depths of the top of the pycnocline and oxycline than between their maximum vertical gradients, highlighting the importance of the mixing depth in defining the region of aerobic habitat in the Chesapeake Bay when low-oxygen bottom waters are present. Improvement in hypoxia simulations will thus depend more on the ability of models to reproduce the correct mean and variability of the depth of the physically driven surface mixed layer than the precise magnitude of the vertical density gradient.

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