An Assessment of the Southern Ocean Mixed Layer Heat Budget

2007 ◽  
Vol 20 (17) ◽  
pp. 4425-4442 ◽  
Author(s):  
Shenfu Dong ◽  
Sarah T. Gille ◽  
Janet Sprintall
Keyword(s):  
Southern Ocean ◽  
Mixed Layer ◽  
Seasonal Cycle ◽  
Heat Budget ◽  
Mixed Layer Depth ◽  
Heat Fluxes ◽  
Layer Depth ◽  
Mixed Layer Temperature ◽  
Advection Term

Abstract The mixed layer heat balance in the Southern Ocean is examined by combining remotely sensed measurements and in situ observations from 1 June 2002 to 31 May 2006, coinciding with the period during which Advanced Microwave Scanning Radiometer-Earth Observing System (EOS) (AMSR-E) sea surface temperature measurements are available. Temperature/salinity profiles from Argo floats are used to derive the mixed layer depth. All terms in the heat budget are estimated directly from available data. The domain-averaged terms of oceanic heat advection, entrainment, diffusion, and air–sea flux are largely consistent with the evolution of the mixed layer temperature. The mixed layer temperature undergoes a strong seasonal cycle, which is largely attributed to the air–sea heat fluxes. Entrainment plays a secondary role. Oceanic advection also experiences a seasonal cycle, although it is relatively weak. Most of the seasonal variations in the advection term come from the Ekman advection, in contrast with western boundary current regions where geostrophic advection controls the total advection. Substantial imbalances exist in the regional heat budgets, especially near the northern boundary of the Antarctic Circumpolar Current. The biggest contributor to the surface heat budget error is thought to be the air–sea heat fluxes, because only limited Southern Hemisphere data are available for the reanalysis products, and hence these fluxes have large uncertainties. In particular, the lack of in situ measurements during winter is of fundamental concern. Sensitivity tests suggest that a proper representation of the mixed layer depth is important to close the budget. Salinity influences the stratification in the Southern Ocean; temperature alone provides an imperfect estimate of mixed layer depth and, because of this, also an imperfect estimate of the temperature of water entrained into the mixed layer from below.

In Situ Observations of Madden–Julian Oscillation Mixed Layer Dynamics in the Indian and Western Pacific Oceans

2012 ◽  
Vol 25 (7) ◽  
pp. 2306-2328 ◽  
Author(s):  
Kyla Drushka ◽  
Janet Sprintall ◽  
Sarah T. Gille ◽  
Susan Wijffels
Keyword(s):  
Heat Flux ◽  
Indian Ocean ◽  
Mixed Layer ◽  
Heat Budget ◽  
Mixed Layer Depth ◽  
Layer Depth ◽  
Temperature Variations ◽  
Central Indian Ocean ◽  
Mixed Layer Temperature

Abstract The boreal winter response of the ocean mixed layer to the Madden–Julian oscillation (MJO) in the Indo-Pacific region is determined using in situ observations from the Argo profiling float dataset. Composite averages over numerous events reveal that the MJO forces systematic variations in mixed layer depth and temperature throughout the domain. Strong MJO mixed layer depth anomalies (>15 m peak to peak) are observed in the central Indian Ocean and in the far western Pacific Ocean. The strongest mixed layer temperature variations (>0.6°C peak to peak) are found in the central Indian Ocean and in the region between northwest Australia and Java. A heat budget analysis is used to evaluate which processes are responsible for mixed layer temperature variations at MJO time scales. Though uncertainties in the heat budget are on the same order as the temperature trend, the analysis nonetheless demonstrates that mixed layer temperature variations associated with the canonical MJO are driven largely by anomalous net surface heat flux. Net heat flux is dominated by anomalies in shortwave and latent heat fluxes, the relative importance of which varies between active and suppressed MJO conditions. Additionally, rapid deepening of the mixed layer in the central Indian Ocean during the onset of active MJO conditions induces significant basin-wide entrainment cooling. In the central equatorial Indian Ocean, MJO-induced variations in mixed layer depth can modulate net surface heat flux, and therefore mixed layer temperature variations, by up to ~40%. This highlights the importance of correctly representing intraseasonal mixed layer depth variations in climate models in order to accurately simulate mixed layer temperature, and thus air–sea interaction, associated with the MJO.

scholarly journals Decadal to Multidecadal Variability of the Mixed Layer to the South of the Kuroshio Extension Region

2020 ◽  
Vol 33 (17) ◽  
pp. 7697-7714
Author(s):  
Baolan Wu ◽  
Xiaopei Lin ◽  
Lisan Yu
Keyword(s):  
Heat Flux ◽  
Pacific Ocean ◽  
Mixed Layer ◽  
Kuroshio Extension ◽  
Mixed Layer Depth ◽  
Layer Depth ◽  
Multidecadal Variability ◽  
Mixed Layer Temperature ◽  
The Kuroshio ◽  
The Western Pacific

AbstractThe decadal to multidecadal mixed layer variability is investigated in a region south of the Kuroshio Extension (130°E–180°, 25°–35°N), an area where the North Pacific subtropical mode water forms, during 1948–2012. By analyzing the mixed layer heat budget with different observational and reanalysis data, here we show that the decadal to multidecadal variability of the mixed layer temperature and mixed layer depth is covaried with the Atlantic multidecadal oscillation (AMO), instead of the Pacific decadal oscillation (PDO). The mixed layer temperature has strong decadal to multidecadal variability, being warm before 1970 and after 1990 (AMO positive phase) and cold during 1970–90 (AMO negative phase), and so does the mixed layer depth. The dominant process for the mixed layer temperature decadal to multidecadal variability is the Ekman advection, which is controlled by the zonal wind changes related to the AMO. The net heat flux into the ocean surface Qnet acts as a damping term and it is mainly from the effect of latent heat flux and partially from sensible heat flux. While the wind as well as mixed layer temperature decadal changes related to the PDO are weak in the western Pacific Ocean. Our finding proposes the possible influence of the AMO on the northwestern Pacific Ocean mixed layer variability, and could be a potential predictor for the decadal to multidecadal climate variability in the western Pacific Ocean.

scholarly journals Eastern Tropical Atlantic Mixed Layer Depth: Assessment of Methods from In Situ Profiles in the Gulf of Guinea from Coastal to High Sea

2019 ◽  
Vol 36 (1) ◽  
pp. 201-212
Author(s):  
Benjamin Kouadio N’Guessan ◽  
Aka Marcel Kouassi ◽  
Albert Trokourey ◽  
Elisée Toualy ◽  
Desiré Kouamé Kanga ◽  
...  
Keyword(s):  
Mixed Layer ◽  
Mixed Layer Depth ◽  
Tropical Atlantic ◽  
Gulf Of Guinea ◽  
Layer Depth

scholarly journals Modeling submerged biofouled microplastics and their vertical trajectories

2021 ◽  
Author(s):  
Reint Fischer ◽  
Delphine Lobelle ◽  
Merel Kooi ◽  
Albert Koelmans ◽  
Victor Onink ◽  
...  
Keyword(s):  
Southern Ocean ◽  
Mixed Layer ◽  
Mixed Layer Depth ◽  
Euphotic Zone ◽  
Equatorial Pacific ◽  
Open Ocean ◽  
Subtropical Gyre ◽  
Layer Depth ◽  
High Biological Activity ◽  
Near Surface

Abstract. The fate of (micro)plastic particles in the open ocean is controlled by physical and biological processes. Here, we model the effects of biofouling on the subsurface vertical distribution of spherical, virtual plastic particles with radii of 0.01–1 mm. For the physics, four vertical velocity terms are included: advection, wind-driven mixing, tidally induced mixing, and the sinking velocity of the biofouled particle. For the biology, we simulate the attachment, growth and loss of algae on particles. We track 10,000 particles for one year in three different regions with distinct biological and physical properties: the low productivity region of the North Pacific Subtropical Gyre, the high productivity region of the Equatorial Pacific and the high mixing region of the Southern Ocean. The growth of biofilm mass in the euphotic zone and loss of mass below the euphotic zone result in the oscillatory behaviour of particles, where the larger (0.1–1.0 mm) particles have much shorter average oscillation lengths (< 10 days; 90th percentile) than the smaller (0.01–0.1 mm) particles (up to 130 days; 90th percentile). A subsurface maximum concentration occurs just below the mixed layer depth (around 30 m) in the Equatorial Pacific, which is most pronounced for larger particles (0.1–1.0 mm). This occurs since particles become neutrally buoyant when the processes affecting the settling velocity of the particle and the motion of the ocean are in equilibrium. Seasonal effects in the subtropical gyre result in particles sinking below the mixed layer depth only during spring blooms, but otherwise remaining within the mixed layer. The strong winds and deepest average mixed layer depth in the Southern Ocean (400 m) result in the deepest redistribution of particles (> 5000 m). Our results show that the vertical movement of particles is mainly affected by physical (wind-induced mixing) processes within the mixed layer and biological (biofilm) dynamics below the mixed layer. Furthermore, positively buoyant particles with radii of 0.01–1.0 mm can sink far below the euphotic zone and mixed layer in regions with high near-surface mixing or high biological activity. This work can easily be coupled to other models to simulate open-ocean biofouling dynamics, in order to reach a better understanding of where ocean (micro)plastic ends up.

Climatology of mixed layer depth in the Gulf of Aden derived from in situ temperature profiles

2019 ◽  
Vol 75 (4) ◽  
pp. 335-347 ◽  
Author(s):  
Cheriyeri P. Abdulla ◽  
Mohammed A. Alsaafani ◽  
Turki M. Alraddadi ◽  
Alaa M. Albarakati
Keyword(s):  
Mixed Layer ◽  
Mixed Layer Depth ◽  
Temperature Profiles ◽  
Gulf Of Aden ◽  
Layer Depth

Decadal Variation in Winter Mixed Layer Depth South of the Kuroshio Extension and Its Influence on Winter Mixed Layer Temperature

2016 ◽  
Vol 29 (3) ◽  
pp. 1237-1252 ◽  
Author(s):  
Shusaku Sugimoto ◽  
Shin’ichiro Kako
Keyword(s):  
Mixed Layer ◽  
North Pacific ◽  
Kuroshio Extension ◽  
Mixed Layer Depth ◽  
Positive Anomaly ◽  
Surface Cooling ◽  
Layer Depth ◽  
Mixed Layer Temperature ◽  
Winter Mixed Layer ◽  
The Kuroshio

Abstract The long-term behavior of the wintertime mixed layer depth (MLD) and mixed layer temperature (MLT) are investigated in a region south of the Kuroshio Extension (KE) (30°–37°N, 141°–155°E), an area of the North Pacific subtropical gyre where the deepest MLD occurs, using historical temperature profiles of 1968–2014. Both the MLD and MLT in March have low-frequency variations, which show significant decadal (~10 yr) variations after the late 1980s. Observational data and simulation outputs from a one-dimensional turbulent closure model reveal that surface cooling is the main control on winter MLD in the late 1970s and 1980s, whereas there is a change in the strength of subsurface stratification is the main control after ~1990. In the latter period, a weak (strong) subsurface stratification is caused by a straight path (convoluted path) of the KE and by a deepening (shallowing) of the main thermocline depth due to oceanic Rossby waves formed as a result of positive (negative) anomalies of wind stress curl associated with a southward (northward) movement of the Aleutian low in the central North Pacific. During deeper (shallower) periods of winter MLD, the strong (weak) vertical entrainment process, resulting from a rapid (slow) deepening of the mixed layer (ML) in January and February, forms a negative (positive) anomaly of temperature tendency. Consequently, the decadal variations in wintertime MLT are formed.

Genesis of Indian Ocean Mixed Layer Temperature Anomalies: A Heat Budget Analysis

2010 ◽  
Vol 23 (20) ◽  
pp. 5375-5403 ◽  
Author(s):  
Agus Santoso ◽  
Alexander Sen Gupta ◽  
Matthew H. England
Keyword(s):  
Indian Ocean ◽  
Time Scales ◽  
Mixed Layer ◽  
Heat Budget ◽  
Heat Fluxes ◽  
Temperature Anomalies ◽  
Mixed Layer Temperature ◽  
The Indian Ocean ◽  
The Tropics

Abstract The genesis of mixed layer temperature anomalies across the Indian Ocean are analyzed in terms of the underlying heat budget components. Observational data, for which a seasonal budget can be computed, and a climate model output, which provides improved spatial and temporal coverage for longer time scales, are examined. The seasonal climatology of the model heat budget is broadly consistent with the observational reconstruction, thus providing certain confidence in extending the model analysis to interannual time scales. To identify the dominant heat budget components, covariance analysis is applied based on the heat budget equation. In addition, the role of the heat budget terms on the generation and decay of temperature anomalies is revealed via a novel temperature variance budget approach. The seasonal evolution of the mixed layer temperature is found to be largely controlled by air–sea heat fluxes, except in the tropics where advection and entrainment are important. A distinct shift in the importance and role of certain heat budget components is shown to be apparent in moving from seasonal to interannual time scales. On these longer time scales, advection gains importance in generating and sustaining anomalies over extensive regions, including the trade wind and midlatitude wind regimes. On the other hand, air–sea heat fluxes tend to drive the evolution of thermal anomalies over subtropical regions including off northwestern Australia. In the tropics, however, they limit the growth of anomalies. Entrainment plays a role in the generation and maintenance of interannual anomalies over localized regions, particularly off Sumatra and over the Seychelles–Chagos Thermocline Ridge. It is further shown that the spatial distribution of the role and importance of these terms is related to oceanographic features of the Indian Ocean. Mixed layer depth effects and the influence of model biases are discussed.

Towards a revised climatology of summertime dimethylsulfide concentrations and sea–air fluxes in the Southern Ocean

2016 ◽  
Vol 13 (2) ◽  
pp. 364 ◽  
Author(s):  
Tereza Jarníková ◽  
Philippe D. Tortell
Keyword(s):  
High Resolution ◽  
Southern Ocean ◽  
Chlorophyll A ◽  
Mixed Layer ◽  
Mixed Layer Depth ◽  
Cloud Formation ◽  
Layer Depth ◽  
High Resolution Data ◽  
Mean Values ◽  
Data Coverage

Environmental context The trace gas dimethylsulfide (DMS) is emitted from surface ocean waters to the overlying atmosphere, where it forms aerosols that promote cloud formation and influence Earth’s climate. We present an updated climatology of DMS emissions from the vast Southern Ocean, demonstrating how the inclusion of new data yields higher regional sources compared with previously derived values. Our work provides an important step towards better quantifying the oceanic emissions of an important climate-active gas. Abstract The Southern Ocean is a dominant source of the climate-active gas dimethylsulfide (DMS) to the atmosphere. Despite significant improvements in data coverage over the past decade, the most recent global DMS climatology does not include a growing number of high-resolution surface measurements in Southern Ocean waters. Here, we incorporate these high resolution data (~700000 measurements) into an updated Southern Ocean climatology of summertime DMS concentrations and sea–air fluxes. Owing to sparse monthly data coverage, we derive a single summertime climatology based on December through February means. DMS frequency distributions and oceanographic properties (mixed-layer depth and chlorophyll-a) show good general coherence across these months, providing justification for the use of summertime mean values. The revised climatology shows notable differences with the existing global climatology. In particular, we find increased DMS concentrations and sea–air fluxes south of the Polar Frontal zone (between ~60 and 70°S), and increased sea–air fluxes in mid-latitude waters (40–50°S). These changes are attributable to both the inclusion of new data and the use of region-specific parameters (e.g. data cut-off thresholds and interpolation radius) in our objective analysis. DMS concentrations in the Southern Ocean exhibit weak though statistically significant correlations with several oceanographic variables, including ice cover, mixed-layer depth and chlorophyll-a, but no apparent relationship with satellite-derived measures of phytoplankton photophysiology or taxonomic group abundance. Our analysis highlights the importance of using regional parameters in constructing climatological DMS fields, and identifies regions where additional observations are most needed.

scholarly journals Drivers of Interannual Variability of Summer Mixed Layer Depth in the Southern Ocean Between 2002 and 2011

2018 ◽  
Vol 123 (8) ◽  
pp. 5077-5090 ◽  
Author(s):  
E. Panassa ◽  
C. Völker ◽  
D. Wolf‐Gladrow ◽  
J. Hauck
Keyword(s):  
Southern Ocean ◽  
Interannual Variability ◽  
Mixed Layer ◽  
Mixed Layer Depth ◽  
Layer Depth
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