Winter Depth Research Articles

Suppression of Cold Air Outbreaks over the Interior of North America in a Warmer Climate

Abstract In spite of the mean warming trend over the last few decades and its amplification in the Arctic, some studies have found no robust decline or even a slight increase in wintertime cold air outbreaks over North America. But fossil evidence from warmer paleoclimate periods indicates that the interior of North America never dropped below freezing even in the depths of winter, which implies that the maintenance of cold air outbreaks is unlikely to continue indefinitely with future warming. To identify key mechanisms affecting cold air outbreaks and understand how and why they will change in a warmer climate, we examine the development of North American cold air outbreaks in both a preindustrial and a roughly 8×CO2 scenario using the Community Earth System Model, version 2 (CESM2). We observe a sharp drop-off in the wintertime temperature distribution at the freezing temperature, suppressing below-freezing conditions in the warmer climate and above-freezing conditions in the preindustrial case. The disappearance of Arctic sea ice and loss of the near-surface temperature inversion dramatically decrease the availability of below-freezing air in source regions. Using an air parcel trajectory analysis, we demonstrate a remarkable similarity in both the dynamics and diabatic effects acting on cold air masses in the two climate scenarios. Diabatic temperature evolution along cold air outbreak trajectories is a competition between cooling from longwave radiation and warming from boundary layer mixing. Surprisingly, while both diabatic effects strengthen in the warmer climate, the balance remains the same, with a net cooling of about −6 K over 10 days. Significance Statement We compare a preindustrial climate scenario to a much warmer climate circa the year 2300 under high emissions to understand the physical processes that influence the coldest wintertime temperatures and how they will change with warming. We find that enhanced warming in the Arctic, and particularly over the Arctic Ocean due to the loss of wintertime sea ice, dramatically reduces the availability of cold air to be swept into North America. By tracing these cold air masses as they travel, we also find that they experience the same total amount of cooling in the much warmer climate as they did in the preindustrial climate even though many of the individual heating and cooling processes have gotten stronger.

Spatio-temporal Distribution and Population Dynamics of the Red Mullet Mullus barbatus Linnaeus, 1758 from the South-east Black Sea

A total of 2930 Mullus barbatus individuals collected from the Southeastern Black Sea coast between March 2017 and April 2018 were investigated regarding growth, mortality rates and the distribution determined by depth and season. M. barbatus is abundant along of 30-45 m depth in winter. Total length-weight relationship was determined as W=0.005L3.2344. Von Bertalanffy growth parameters for all individuals were calculated as L∞=28.19 cm, K=0.16 years-1, t0=-0.144 years. The maximum age was 5 years. The total length at 50% maturity was estimated as 11.63 cm in males and 11.68 cm in females. Exponential coefficients of natural mortality, total mortality, and fishing mortality rate of red mullet are estimated as 0.33 year-1, 1.001 year-1 and 0.67 year-1, respectively. The exploitation rate of population was calculated as 0.66 year-1. The fact that exploitation rate is above 0.5 may reflect a high fishing pressure on stock.

Modeling Spatio-Temporal Variations in the Habitat Utilization of Swordtip Squid (Uroteuthis edulis) in the East China Sea and Southern Yellow Sea.

Accurately modeling the distribution of keystone species is of utmost importance to gain a comprehensive understanding of their complex ecological dynamics and to develop effective strategies for sustainable scientific management. In the coastal China ecosystem, the swordtip squid (Uroteuthis edulis) stands out as a keystone species with significant commercial and ecological value. Despite its importance, research on the ecological dynamics of this species remains limited and requires further investigation. To investigate the spatial and temporal variability in the distribution of U. edulis and identify the key environmental drivers in the East China Sea (ECS) and southern Yellow Sea across different seasons, we generated ensemble models using oceanographic variables and fishery-independent scientific survey data collected from 2016 to 2018. Our results revealed that U. edulis predominantly inhabited the central and southern regions of the ECS throughout the year. The primary environmental variables driving its distribution varied by season, with the sea surface temperature being the most important in spring, sea surface height in summer and autumn, and depth in winter. During summer and autumn, the suitable habitats of U. edulis were found to be largest and extended northwards towards the coastline. However, they migrated southwards to the waters near the edge of the ECS continental shelf with smaller suitable areas in the spring and winter. These results suggested that U. edulis exhibited season-specific habitat preferences and responded to changing environmental conditions throughout the year. The observed seasonal distribution patterns were likely influenced by the fluctuating mixture of waters (ocean currents) from different sources, with varying physical and chemical characteristics throughout the year. Our study provides baseline data for comprehending the population dynamics of U. edulis and highlights the significance of considering species' habitat preferences in a dynamic environment.

Temporal Variations in Temperature and Moisture Soil Profiles in a Mediterranean Maquis Forest in Greece

Soil moisture (SM) and temperature (ST) are critical factors in forest eco-hydrological research. In this study, we investigated the inter- and intra-annual changes in SM and ST profiles in a mixed Mediterranean maquis forest stand together with soil and meteorological parameters. Hourly data from three field measurements points at four depths (−5, −20, −40 and −70 cm) for 6 years were interpolated using the kriging method to produce annual SM and ST profiles. The results indicate that air temperature highly affects the upper 5 cm of the mineral soil. In general, it increases with depth in winter at an average rate of 0.036 °C/cm and decreases in summer (0.035 °C/cm), presenting higher values compared to air temperature from April to August and lower ones during the rest of the period. Precipitation is the main factor driving SM variations up to a superficial soil depth of 40 cm. The upper soil layer (0–40 cm) infiltrates water faster and presents high SM variability, especially in monthly and seasonal (year to year) time steps. The maquis forest stands are likely to be strongly affected by climate change, therefore the results of this study could be useful in hydrological and climate change studies focused on maquis vegetation water management.

Culture depth effect on Scenedesmus sp. growth, photo-physiology and nutrient removal rate in anaerobically digested abattoir effluent

Here, we evaluated the effect of culture depth on the growth and nutrient removal rate of Scenedesmus sp. grown in anaerobically digested abattoir effluent (ADAE) and cultivated semi-continuously in raceway ponds at depths of 14 cm, 17 cm, 20 cm, and 23 cm during Austral winter and summer. Culture medium pH was kept constant at pH 6.5 for all treatments throughout the experimental period using a pH–stat system. Algal cultures grown in summer had 2.3- 2.7 times higher biomass productivity than the same grown in winter. In both seasons, maximum volumetric productivity of this alga was achieved at 14 cm depth (14 cm depth⩾ 17 cm depth⩾ 20 cm depth⩾ 23 cm depth). However, areal biomass productivity of culture grown at 23 cm depth was 12% and 29% higher than that of culture grown at 14 cm depth in winter and summer, respectively. In addition, nitrogen, phosphorus and COD areal removal rates were significantly higher in cultures operated at 23 cm among all treatments in both seasons. The effective quantum yield (Fq'/Fm') in summer was 23 cm depth = 20 cm depth > 17 cm depth = 14 cm depth while it followed 14 cm depth⩾ 17 cm depth⩾ 20 cm depth⩾ 23 cm depth in winter, indicating significance of operational conditions on algal photosynthesis. The outcome of this study shows that, irrespective of the season, operating the culture in higher depths significantly increased areal biomass productivity as well as areal nutrient removal rates when treating ADAE.

Sonotoki

This film takes inspiration from the work of Kon Wajiro,- an architect, ethnologist and sociologist who created detailed sketches of everyday life on the streets of Tokyo in the 1920s. Shot in Aomori City, Japan in the depths of winter, Sonotoki captures fleeting movements through the snowy streets as they play out before a static camera. Humans are made of generations of cycles; each leaving subtle indications that are part of an inexpressible whole.

Measuring and Predicting the In-Ground Temperature Profile for Geothermal Energy Systems in the Desert of Arid Regions

Instead of fossil fuels, clean renewable energy resources are being used to meet space heating and cooling needs, to reduce global warming and air pollution worldwide. In the desert of the Arabian Peninsula, extensive solar irradiance and drastic variations in air temperatures (daily and/or seasonally) are common; thus, geothermal energy resources are a promising solution that is nearly independent of weather fluctuations. Due to a lack of information about in-ground temperature profiles in these regions, the use of geothermal energy resources for domestic applications is very limited. Therefore, this study aimed to measure the in-ground temperature (Tg) up to 3.5 m in depth for one year. Due to the difficulty of digging in the ground (i.e., gravelly sand; rocky, dry soil), numerical equations were adopted and used to simulate the in-ground temperature (Tg) for a depth > 3 m. These equations were validated by comparing the measured and simulated values of Tg for depths ≤ 3 m under extreme weather conditions. The validation yielded a mean absolute error (EMA) of ≤ 1.2 °C and a root mean square error (ERMS) of ≤ 1.42 °C. The measurements showed that at 3 m depth, the in-ground temperature was 32 °C in summer and 29 °C in winter. The simulation showed that values of Tg increased with depth in winter and decreased in summer and became constant as 30 °C at 13 m depth throughout the year (i.e., the undisturbed ground temperature (UGT)). This temperature would provide considerable heating and cooling capacity if an earth-to-air heat exchanger were implemented in arid regions where ambient temperatures exceed 47 °C on summer days and drop below 10 °C on winter nights. The theoretical prediction of Tg using the proposed equations is a useful tool for designers who use geothermal effects for indoor space cooling and heating in the desert of arid regions.

Parameterization of ocean surface wave-induced mixing using Large Eddy Simulations (LES) II

The ocean surface boundary layer links the atmosphere to the ocean. At the air-sea interface, ocean surface waves play an important role in momentum, energy and gas exchange. A new parameterization with wave-induced mixing is developed based on a set of Large Eddy Simulation experiments under different wind speeds and mixed layer depths. The new parameterization scheme is then incorporated into a one-dimensional turbulence model for verification. The inclusion of wave-induced mixing reduces the excessively high surface temperature simulated in summer and reduces the underestimation of the mixed layer depth in winter. Compared to the observation at Ocean Station Papa, the parameterization scheme with wave effects produces statistically more accurate results than the parameterization scheme without wave effects.

The role of winter net heat fluxes on the modulation of the upper mixed layer temperature and depth in the North Atlantic by the reanalysis data

The role of winter net heat fluxes (NHF) on the upper mixed layer (UML) temperature and depth variability over the North Atlantic is studied using ocean reanalysis data products. The monthly data from the ORA-S3 (1959–2011), GODAS (1980–2020), GECCO3 (1948–2018) datasets were used. The correlation coefficients were calculated between the anomalies of the NHF on the ocean surface and the UML temperature and depth with a shift of 1 month when the former were leading. In most of the North Atlantic, negative correlations between the UML temperature and the NHF preceding 1 month were found. Here, the UML temperature anomalies are probably caused by changes in heat exchange with the atmosphere. Areas of significant positive correlations across all data sets are concentrated in the area of the transition of the Gulf Stream to the North Atlantic Current. Almost the entire water area of the North Atlantic is occupied by positive correlations between the mixed layer depth in winter and the NHF on the ocean surface, with the latter leading for 1 month.

Nourishing the soul with food and keeping well in the depths of winter

Deborah Duval describes her experience of building a positive relationship with food

Seasonal variation of <em>Microcystis aeruginosa</em> and factors related to blooms in a deep warm monomictic lake in Mexico

The occurrence of cyanobacterial blooms has increased globally over the last decades, with the combined effect of climate change and eutrophication as its main drivers. The seasonal dynamic of cyanobacterial blooms is a well-known phenomenon in lakes and reservoirs in temperate zones. Nevertheless, in the tropics, most studies have been performed in shallow and artificial lakes; therefore, the seasonal dynamic of cyanobacterial blooms in deep and eutrophic tropical lakes is still under research. We studied the seasonal variation of the phytoplankton community and the factors associated with Microcystis aeruginosa blooms along the water column of Lake Alberca de Tacámbaro, a warm monomictic crater lake located in Mexico, during 2018 and 2019. According to previous studies performed in 2006 and 2010, this lake was mesotrophic-eutrophic, with Chlorophyta and Bacillariophyta as the dominant groups of the phytoplankton community. During 2018 and 2019, the lake was eutrophic and occasionally, hypertrophic, a phenomenon likely associated with the increase of farmland area around the lake. The dominant species was M. aeruginosa, forming blooms from the surface to 10 m depth in winter, in the hypolimnion in spring and summer, and along the full water column in autumn. These findings suggest that M. aeruginosa in Lake Alberca de Tacámbaro displays seasonal and spatial population dynamics. Total phosphorus, dissolved inorganic nitrogen, water temperature and photosynthetically active radiation were the environmental factors related to M. aeruginosa blooms. Our results suggest that the changes in the structure of the phytoplankton community through time, and M. aeruginosa blooms in Lake Alberca de Tacámbaro, are mainly related to changes in land use from forest to farmland in areas adjacent to the lake, which promoted its eutrophication in the last years through runoffs. Comparative studies with other deep and eutrophic lakes will allow us to gain a deeper understanding of the dynamic of cyanobacterial blooms in natural and artificial water reservoirs strongly stressed by human activities.

Phylogenetic origin of two Japanese Torreya taxa found in two regions with strongly contrasting snow depth.

The Japanese archipelago exhibits a notable difference in snow depth in winter, deep snow on the Sea of Japan side and low snow cover on the Pacific Ocean side. This contrasting pattern has shaped the distribution of infraspecific taxon pairs in a range of woody plants, with taxa found on the Sea of Japan side typically exhibiting a stunted shrub form with multiple decumbent stems. The phylogenetic origin of these taxon pairs is unknown, i.e., whether the two taxa diverged from the same species or if they have different origins. This study aimed to reveal the phylogenetic origin of two varieties of Torreya nucifera (Taxaceae); var. nucifera is a tree found on the Pacific Ocean side, whereas var. radicans is a shrub found on the Sea of Japan side. We examined the phylogenetic relationships of the two varieties and worldwide Torreya taxa using whole chloroplast genomes, chloroplast DNA fragments, and the nuclear ribosomal internal transcribed spacer (ITS). The whole chloroplast genome phylogeny indicated that T. nucifera var. radicans was a sister taxon to Chinese T. grandis, rather than to var. nucifera. In contrast, the nuclear ITS phylogeny indicated that while several haplotypes of T. nucifera var. radicans were closely related to T. grandis, most haplotypes of T. nucifera var. radicans formed a single clade with those of var. nucifera. This implies that the homogenization of the ITS has occurred between the two taxa, while taxon-specific chloroplast DNA haplotypes were retained. These discordant phylogenies suggested that the two taxa have different phylogenetic origins, but have an intricate evolutionary history, involving inter-taxa hybridization and gene flow, possibly when their distributions were confined to sympatric refugia. Given the genetic evidence and distinct difference in growth form, we propose that T. nucifera var. radicans should be taxonomically treated as a distinct species, T. fruticosa.

Daily and annual shell growth in a long-lived freshwater bivalve as a proxy for winter snowpack

To assess the potential of long-lived freshwater bivalve shells as a proxy for river environments, we examined daily and annual growth increments and analysed trace elements in the shells of Margaritifera laevis collected alive from the Shiribetsu River, located in the central western region of Hokkaido, Japan. The sum of the daily growth lines within a single annual increment corresponded to the days when the average daily water temperature was greater than 9 °C, suggesting that shell deposition occurred from spring to autumn. The growing degree days (GDD) are correlated with the maximum snow depth in winter and the average river discharge in spring. We conducted trace element microanalysis across daily and annual growth increments by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) and compared the results with in situ environmental data. Sharp peaks in the barium/calcium ratio (Ba/Ca) observed during spring river discharge also suggest that the growth of Margaritifera shells is influenced by winter snow volume and meltwater. A 67-year profile of the standard growth index (SGI) estimated from twelve individual annual growth histories correlates to the annual snowfall accumulation. Distinct decadal variability is observed in the SGI and synchronized with the North Pacific Index and Pacific Decadal Oscillation. Sclerochronological approaches using Margaritifera shells could be valuable for reconstructing river and atmospheric conditions during the winter season, which is influenced by the Asian winter monsoon in the central Hokkaido region.

Seasonal and Spatial Variability of Primary Production in the Mozambique Channel

The surface circulation in the Mozambique Channel changes from the northern part, where the system is under dominance of the monsoons, to the central and southern parts, where mesoscale eddies are more frequent. Despite these differences in the physics between the three regions, satellite-based primary production shows that the whole region is characterized by similar seasonal variability of primary production, in which winter is the most productive season. A coupled physical-biogeochemical model configuration applied for the Mozambique Channel is used to investigate how wind stress and heat fluxes modulate seasonally and spatially the distribution of new and primary production in the region. Higher new production integrated over the euphotic layer depth in winter accounts for about 50% of the total primary production in the Mozambique Channel, indicating the seasonality of primary production is driven by new nutrients upwelled from bellow the euphotic zone. During the other seasons of the year the depth-integrated primary production is low, which is the period when the system depends on remineralization of the organic matter to sustain phytoplankton growth at the subsurface. Stronger wind stress is the dominant surface forcing in the northern part of the Mozambique Channel, which is responsible for vertical advection and entrainment of nitrate from below the euphotic zone that sustain the primary production during winter, while intense negative net heat flux is the dominant forcing in the central/southern parts. However, it is important to note that mesoscale eddies also enhance primary productivity in the region with a focus on the winter period.

Stochastic Resonance Observed in Aerosol Optical Depth Time Series

We analyzed the aerosol optical depth time series retrieved from daily satellite Moderate-Resolution Imaging Spectroradiometer measurements. The investigated geographic area includes Italy and the Mediterranean Sea. By performing second- and fourth-order statistics analyses, the dynamics can be decomposed into two sources, the main of which is the annual cycle. The residence time distribution is made of local maxima over an exponential behavior. The two successive peaks are located at about 200 and 600 days. This allows us to hypothesize a stochastic resonance phenomenon in the dynamics of aerosol optical depth. The characteristic periodicity of the resonance is on the annual timescale, and the asymmetric double-well potential is provided by two different regimes for the values of the aerosol optical depth in winter and summer time. This means that a simple, although stochastic, differential equation can represent the time evolution of the optical depth, at least concerning its component related to the annual cycle.

Carbon and phosphorus transformation during the deposition of particulate matter in the large deep reservoir

As the running time of reservoirs is increasing, a large number of reservoirs are becoming eutrophicated. Organic phosphorus (OP) is a key factor in eutrophication. However, the mechanism and extent to which organic matter degradation affects P recycling in water column of large deep reservoirs are unclear, especially for the newly-built ones. In this study, different forms of carbon (C) and P in the water column of Hongjiadu Reservoir were investigated. The contents of particulate organic carbon (POC) and particulate organic phosphorus (POP) both decreased with depth in summer, indicating that organic matter was degraded during the deposition of particulates. In contrast, the contents of POC and POP varied slightly with depth in winter. This difference may result from the double thermal stratification and the corresponding double oxygen stratification in summer. The POC/POP ratios were lower in the epilimnion and increased with depth, suggesting that P was preferentially regenerated relative to C during organic matter degradation. The contents of particulate inorganic phosphorus (PIP) and POP were significantly negatively correlated, indicating that POP transformed into PIP in deeper water. The double thermoclines and oxyclines in Hongjiadu Reservoir lead to very low dissolved oxygen (DO) concentrations in the hypolimnion, which should receive sufficient attention. If water becomes hypoxic, enhanced P release during organic matter degradation will promote phytoplankton growth, leading to higher phytoplankton biomass and more severe DO depletion. Thus, a positive feedback loop may form among hypoxia, enhanced P release, higher primary productivity, and more severe hypoxia, accelerating P recycling in large deep reservoirs. Once if eutrophication occurs in these reservoirs, it will be very difficult to restore the water ecosystem. Thus, it is particularly important to prevent the occurrence of eutrophication and the formation of positive feedback loop as early as possible. This highlights the importance of both reducing external loading and improving DO level in large deep reservoirs.

Body length-dependent diel vertical migration of Antarctic krill in relation to food availability and predator avoidance in winter at South Georgia

We analyzed diel vertical migration (DVM) of overwintering Antarctic krill at South Georgia, a region that remains ice-free during the austral winter. We considered DVM in relation to krill body length, based on Japanese krill fishery data (1990-2012), and examined DVM in relation to food availability and predator (Antarctic fur seal) avoidance. We report that diel changes in median trawling depth (a proxy for krill vertical distribution) showed significant interannual variation; the overall trend was such that during both daytime and nighttime, the larger the average size of krill, the deeper their median depth. Consistent with the literature, this size-dependent DVM relates to food availability and size-dependent diet; that is, with increasing body length, krill tend to rely less on phytoplankton (which are available in surface layers) as a winter food source. Concerning predator avoidance, and based on analyses using an optimal foraging dive model for fur seals, DVM showed close agreement with size-dependent predation risk; that is, larger krill remained deeper, thereby reducing mortality from fur seals. Therefore, DVM of overwintering krill appears to reflect a compromise between adequate feeding conditions and minimizing predation risk. There was, however, an exception that krill occurred at a shallow depth in winter 2006 when phytoplankton abundance was particularly low and krill density was very high. This supports the hypothesis that physiological demands (i.e. hunger) may become a more important factor affecting DVM than predator avoidance under conditions of insufficient food availability.

Simulated sheep urine causes the formation of acidic subsurface layers in soil under field conditions

This study aimed to ascertain whether application of sheep urine led to the development of acidic subsurface layers of a pasture soil. Deionised water or simulated urine solution delivering urea-nitrogen (N) at 44.8 g m–2 and potassium at 25 g m–2 was applied to soil in either winter or spring. Treatments were applied to the soil surface within 10.3 cm internal diameter PVC tubes inserted 20 cm into the soil either under ryegrass or kept bare. Main sampling times corresponded to the completion of various soil N transformations as determined by periodic sampling. Main samplings involved the collection of above ground plant material and soil sampling in 2 cm depth increments in 0–10 cm and 5 cm intervals in 10–20 cm depths. Following treatment application, urea and ammonium-N moved to a depth no greater than 20 cm but the extent of movement was greater in winter than spring due to the influence of initial soil moisture. Following urea hydrolysis, soil pH increased in the 0–15 cm depth. Subsequent nitrification significantly acidified soil under pasture by 0.8–1.0 pH units in the 2–8 and 2–6 cm depths in winter and spring respectively. This created a net acidic subsurface layer of 0.2–0.4 pH units compared with soil at the beginning of the experiment. Subsurface acidification was 0.5–0.7 pH units greater in bare soil compared with the presence of pasture. Transformations of N resulting from application of simulated urine solution formed acidic subsurface layers in the field regardless of the season of application.

WEATHER FORECASTING IN THE PRACTICE OF REINDEER HERDERS FROM THE SUBPOLAR URALS

The present article considers a complex of various signs used for predicting significant weather phenomena in the practice of reindeer herders from the Subpolar Urals. The authors obtained empirical data in the course of ethnographic expeditions (2007, 2012 and 2018) by conducting semi-structured interviews with hereditary reindeer herders, managers and specialists from the reindeer herding company of Saranpaul village (Beryozovsky District, Khanty-Mansi Autonomous Area — Yugra). Systematisation along with the thematic classification of the field data revealed that the practical knowledge and skills of reindeer herders include prompt and long-term weather observation, experience in predicting and evaluating changes in hydrometeorological conditions, the ability to determine their impact on the food supply, as well as on the behaviour and health of deer. A complex of various signs helps to predict short-term weather changes or seasonal prospects: incoming of spring / summer / winter, rainy weather and summer temperature, snow depth in winter, bad weather, rain, snow, snowstorm, wind, cold, frost, heat and other meteorological changes. For making a short-term forecast, the following points are taken into account: wind direction in the mountains; presence and location of fog in the mountains; colour of sunset; twinkling of stars; halo around the moon; beauty of Northern Lights; quality of carried sounds (voiced and voiceless); fire draught and smoke movement; cloud form; bird cries; and animal behaviour (deer, dogs, insects). For the most part, these signs are rationally explained by changes in atmospheric pressure and humidity. As a result of long-term weather observations, reindeer herders have noted certain climate mitigation, as well as an increase in the number of anomalous weather phenomena, which are uncharacteristic of their seasons.

Izmenchivost' tolshchiny peremeshannogo sloya v Chernom more i ee svyaz' s dinamikoy vod i atmosfernym vozdeystviem

Purpose . Spatio-temporal variability of the mixed layer depth (MLD) in different regions of the Black Sea in 1985–2017, its relationship with large- and meso-scale dynamics and wind velocity are investigated. Metods and Results . The study is based on the hydrological data archive for 1985–2017 including the measurements of the ship expeditions, the Argo buoys and the moored buoy “Aqalog”. Seasonal and interannual variability of the mixed layer depth was determined using the density criterion ( dr = = 0,07kg/m 3 ) between the surface layers and the base of the upper mixed layer. Conclusions . In January – March, the large-scale and mesoscale dynamics significantly affects the mixed layer depth variability. Minimum monthly average values of the mixed layer depth in winter are observed in the mesoscale cyclonic eddies and in the center of the sea (20–30 m), the moderate values – on the periphery of the basin (40–45 m) and the maximum ones – in the mesoscale anticyclones (60–70 m). Several times the mixed layer depth values exceeding 150 m were detected in the downwelling areas of the basin. Analysis of the whole period (1985–2017) shows that the mixed layer density was never more than 1015 kg/m 3 . This isopycnal limits the maximum possible depth of the upper mixed layer. The impact of wind velocity on the spatial and temporal variability of the mixed layer thickness is the largest in spring and autumn when the seasonal thermocline is weak. It is less important in summer when solar heating stabilizes the upper layer, and in winter when the mixed layer depth is large. Rise of the mixed layer depth in summer is observed in recent years that is associated with rise of the wind speed in a warm period of a year.