Deeper Water Layers Research Articles

Реакция планктонных копепод Белого моря на изменения солености воды в острых и хронических экспериментах

In the White Sea, planktonic copepods Calanus glacialis, Pseudocalanus spp., Triconia borealis, and Metridia longa are usually not considered as tolerant to the water salinity decrease, and Oithona similis is generally attributed to the euryhaline species. However, the life cycle of the first two genera includes active feeding during the spring ice melting, when a large part of their food sources are concentrated in the upper water layer characterized by salinity less than 18‰. M. longa and T. borealis are considered to be deep-dwelling species. The first one reproduces in autumn and thus relies on the spring phytoplankton bloom the least, the second spawns in spring in deep water layers; however, they are both found in the productive (photic) layer during this season. In order to study if these copepods can use food-rich freshened water layers to get enough energy for growth and reproduction, a series of experiments were performed in July 2019 and March 2020, including chronic and acute ones. The copepod mortality was analyzed at 25‰ or 26‰ (control), 18‰ and 15‰ (experiment). Surprisingly, C. glacialis and Pseudocalanus spp. stood the salinity decrease with minor mortality rates ranging from 0 up to 1.1 ± 0.2% in short-term 24-h experiments. The mortality rate in these species was the highest after five days of gradual water freshening down to 15‰ (12.1 ± 1.8%), while the mortality rate was half as much in control vials at 25/26‰ and at 18‰ (6.4 ± 0.5% and 6.9 ± 0.6%, respectively). T. borealis was the most stenohaline species, exhibiting the 100% mortality rate already at 18‰ after 2 hours of exposure. M. longa did not tolerate the salinity stress at 15‰, reaching 100% mortality in 24 h. O. similis tolerated the salinity decrease well and thus exhibited euryhaline features as reported for this species in different areas of its range.

Рекультивація озера методом пульверизаційної аерації води в умовах розташування метеорологічної станції Рава-Руська

Розглянуто технологію рекультивації озера технічним методом в умовах розташування метеорологічної станції Рава-Руська. Проаналізовано досвід і результати роботи польських науковців. Відзначено позитивні результати внаслідок застосування у рекультивації природних і штучних водойм пульверизаційних аераторів, які розпилюють воду в повітрі. Представлено розподіл пульверизаційних аераторів води, що використовуються під час рекультивації озер. Охарактеризовано пульверизаційний аератор із вітровим приводом концепції Подсядловського. Ця технологія передбачає використання енергії вітру для насичення киснем нижньої зони озера. Робота аератора забезпечує утворення на кумулятивній глибині життєвого простору, в якому інтенсивно розвиваються фіто- і зоопланктон, а також риби, які ним харчуються. Регулярне виловлювання швидко зростаючої риби дає змогу знизити трофність озера та систематично покращити якість води. Пульверизаційний аератор води із вітровим приводом в умовах розташування метеостанції Рава-Руська може забезпечити розчинення кисню в донних водах в межах від 4,86 до 5,53 г·м-3. Найнижчі концентрації розчиненого кисню у воді зафіксовано в липні та серпні (4,86 г·м-3), а найвищі (>5,24 г·м-3) – із жовтня по травень. Опрацьовано і описано номограму для визначення вмісту кисню, розчиненого у воді впродовж певного місяця, внаслідок функціонування пульверизаційний аератор із вітровим приводом в умовах розташування метеостанції Рава-Руська. Рекомендовано застосування пульверизаційного аератора із вітровим приводом для рекультивації озер України.

Waste water discharge from a large Ni-Zn open cast mine degrades benthic integrity of Lake Nuasjärvi (Finland)

The Talvivaara/Terrafame multi-metal mining company is Europe’s largest nickel open cast mine, it is also known for the largest wastewater leakage in the Finnish mining history and a series of other accidents. In this paleolimnological study, influences of a recently constructed treated waste water discharge pipeline into Lake Nuasjärvi were investigated by analyzing past (pre-disturbance) and present community compositions of key aquatic organism groups, including diatoms, Cladocera and Chironomidae, along spatial (distance, water depth) gradients. In addition to defining ecological changes and impacts of saline mine waters in the lake, chironomids were used to quantitatively reconstruct bottom water oxygen conditions before and after the pipe installation (in 2015). The diatom and cladoceran communities, which reflect more the open-water habitat, showed only relatively minor changes throughout the lake, but a general decrease in diversity was observed within both groups. Chironomids, which live on substrates, showed more significant changes, including complete faunal turnovers and deteriorated benthic quality, especially at the sites close to the pipe outlet, where also chironomid diversity was almost completely lost. Furthermore, the reconstructed hypolimnetic oxygen values indicated a major oxygen decline and even anoxia at the sites near the pipe outlet. The limnoecological influence of the pipe decreased at sites located counter-flow or behind underwater barriers suggesting that the waste waters currently have location-specific impacts. Our study clearly demonstrates that whereas the upper water layers appear to have generally maintained their previous state, the deep-water layers close to the pipe outlet have lost their ecological integrity. Furthermore, the current hypolimnetic anoxia close to the pipe indicates enhanced lake stratification caused by the salinated mine waters. This study clearly exhibits the need to investigate different water bodies at several trophic levels in a spatiotemporal context to be able to reliably assess limnoecological impacts of mining.

Studies of Spatiotemporal Structure of the Acoustic Field Formed in Deep Water by a Broadband Pulsed Signal Source on the Shelf of the Sea of Japan

The article discusses the results of experiments conducted in September 2017 to prove the applicability of positioning underwater objects during their operation at depths substantially exceeding the depth of the underwater sound channel axis. The authors present results of experimental studies and numerical analysis of the effect of focusing of the acoustic energy in the near-bottom layer on the shelf and its transition into deep-water (up to 500 m) layers of the Sea of Japan for summer–autumn hydrological conditions. Experiments on reception of broadband pulsed signals with a center frequency of 400 Hz were carried out at various distances (20, 68, 86, 90, and 198 km) from a source of navigation signals moored at a depth of 35 m at the shoreline near Cape Schulz. The receiving of acoustic signals was performed by a system of distributed over depth up to 500 meters hydrophones, with the possibility of long-term signal recording at fixed depths and during submergence. The experimental results allowed to study the impulse responses of acoustic waveguides, and estimate the effective propagation velocities of navigation signals received at different depths, and to draw conclusions about the possibility of solving positioning problems for autonomous underwater vehicles at depths up to 500 m and distances up to 200 km from the source of navigation signals. Mathematical modeling of acoustic wave propagation in a waveguide reproducing the experimental conditions by the normal mode technique was also carried out.

Effect of Culture Depth and Season on the Condition and Reproductive Indices of Blue Mussels (Mytilus edulis L.) Cultured in a Cold-Water Coastal Environment

Condition, growth, and reproductive indices of blue mussels (Mytilus edulis) grown in deep and shallow sites were studied from May to December 2016 in the South Arm region of Notre Dame Bay, Newfoundland. The region was shown to be characterized by a seasonal thermocline that formed in April and lasted to October annually, resulting in a cold-water deep layer (mean annual temperature: 4.36 ± 5.1°C) and a comparatively warmer surface layer (mean annual temperature: 5.81 ± 6.3°C). The deepwater culture sites extended into the cold-water layer and the shallow sites were typically in the warmer layer above. Mussels grown in shallow sites had longer and heavier shells than those from deepwater sites, likely linked to warmer surface waters. Both reproductive and physiological condition indices were high for mussels from both culture depths in May. Physiological condition declined for both deep and shallow cultured mussels from May through to August. Mussels from deep sites, however, had a higher overall mean dry tissue weight: wet tissue weight ratio for the study period. Reproductive indices, including measurements of reproductive output, declined for shallow mussels from May through to August, but remained high for deep mussels until August when a significant spawn occurred for mussels from both depths. In addition, mussels from deep sites were observed to maintain themselves in a prespawning ripe stage for a longer period than those from shallow sites. Variations in physiological and reproductive indices for mussels from each respective culture depth were thought to be linked to differences in the environmental characteristics of the deep and shallow water layers, including rate of temperature change and potential differences in phytoplankton quality and energetics. The additional data provided in the present study add to the current understanding of the effects of the deepwater environment on mussel reproduction patterns and its relationship to production meat yield. The data will help in highlighting the benefits of using deepwater sites leading to increased environmental sustainability for mussel culture in subarctic coastal environments such as those on the north coast of Newfoundland.

On deep-water reception of pseudorandom acoustical signals propagating from the shelf zone to the deep ocean

The results of an experiment conducted in September 2017 to substantiate the applicability of the “acoustic mudslide” effect when solving the positioning problems of autonomous underwater vehicles in cases of their operation at depths substantially exceeding the depth of the axis of the underwater sound channel are discussed. The results of the experimental studies and numerical analysis of the effect of an acoustic energy focusing in the near-bottom layer of the shelf and its transition into deep-water (up to 500 m) layers of the Sea of Japan for summer-autumn hydrological conditions are presented. Mathematical modelling of the propagation of acoustic waves in a model waveguide reproducing the experimental conditions using the parabolic equation method has been performed. The observed effective signal propagation speeds are explained using the normal wave method.

Epifaunal communities across marine landscapes of the deep Chukchi Borderland (Pacific Arctic)

Epifaunal communities from the poorly studied Arctic deep sea of the Chukchi Borderland region were investigated to: (1) determine differences in community structure among ridges, plateau with pockmarks, and much deeper basins as three main habitat types, (2) analyse the environmental factors that might shape these communities, and (3) investigate biogeographic affinities dominating the epifaunal communities. Epifaunal samples were collected in summer 2016 with a beam trawl (6 stations) and ROV (10 stations) from 486 to 2610 m depth. Seventy-eight and eighty-six taxa were registered from ROV images and trawl samples, respectively, with Echinodermata and Arthropoda dominating overall taxon richness. Epifaunal densities were estimated at 2273 to 14,346 ind/1000 m2 based on ROV images but only 342 to 2029 ind/1000 m2 based on trawl samples. Epifaunal biomass based on trawl catches ranged from 173 to 906 g wet weight/1000 m2. There was no significant difference in density, biomass and community composition between plateau and ridge communities, though the western and eastern parts of the study area differed in plateau/ridge community properties. Abundance in the eastern part of the study area was dominated by annelids (Ampharetidae and Sabellidae), and the western part by an unknown cnidarian (likely polyps of Atolla). Trawl samples from both western and eastern regions were dominated by the echinoderms Ophiopleura borealis and Pontaster tenuispinus. Deep basin communities differed from shallower plateau/ridge stations by significantly lower number of taxa and densities based on the images, and by lower biomass based on trawl catches. Polynoid annelids and sponges were characteristic taxa of the basin stations. Water depth and number of stones providing hard substrate significantly influenced epifaunal community structure, with sediment pigments and grain size also being influential. Arcto-boreal-Atlantic species dominated communities in the Chukchi Borderland, presumably mediated by Atlantic water dominance in the deep water layers of the Pacific Arctic. This study adds to the limited knowledge of ecology of the Arctic deep sea and improves existing baseline data that can be used to assess future effects of climate change on the system.

Seasonal changes in particulate organic matter (POM) concentrations and properties measured from deep areas of the Baltic Sea

Summary In seawater particulate organic matter (POM) serves as a food source for heterotrophic bacteria and zooplankton and is a source of dissolved organic compounds and nutrients. POM plays a critical role in transporting carbon to marine sediments where a fraction of it is buried in subsurface sediments and thus avoids conversion to carbon dioxide on shorter time scales. Distribution and properties of POM were investigated in the Baltic Proper from 2013 to 2015. Particulate organic carbon (POC) was used to investigate POM sources and dynamics. Stable carbon isotopes (δ13C), elemental composition (C, N), chlorophyll a and POM contribution to suspended particulate matter (SPM) were also measured and interpreted. The water column exhibited concentrations ranging from 0.2 mg POC/l (deep water layer – DWL, cold season – CS) to 1.7 mg POC/l (surface water layer – SWL, warm season – WS). POM represented 0.15 to 0.45 of SPM during respective cold and warm seasons. Stable carbon isotopes (δ13CPOC) ranged from −22.5‰ (WS) to −28.0‰ (CS), while the POC/Chl a ratio ranged from 180 g/g (SWL-WS) to 300 g/g (DWL-CS). Seasonal changes were attributed to high primary production in the SWL during the WS, which represented a major POM source. Continuous mineralization/sedimentation throughout the water column constituted a major POM sink.

Vosproizvedenie glubokovodnoy tsirkulyatsii Chernogo morya s pomoshch'yu modeli INMOM i sopostavlenie rezul'tatov s dannymi buev ARGO

Purpose. The present paper is focused on theoretical analysis of hydrophysical characteristics of the Black Sea in 2011. Methods and Results. The Black Sea hydrophysical characteristics are calculated using a version of the marine circulation σ -model (Institute of Numerical Mathematics Ocean Model – INMOM) for the Black, Azov and Marmara seas (BAMS) with high spatial 1 km resolution and 20 σ -levels distributed non-uniformly over the depth. Quality of the simulated salinity and temperature fields is assessed by their comparison with the data of the ARGO deep-profiling floats available for the period under consideration. Degree of correspondence of the modeled current fields to the observed ones is estimated based on the average deep-sea current velocities calculated from the data on the Argo profiling floats’ movements. Conclusion. The comparative analysis results show that the INMOM adequately reproduced vertical distribution of the Black Sea hydrophysical characteristics. Comparison of the simulated temperature and salinity fields with those derived from the ARGO buoys data demonstrates the fact that the strong-est deviations of the characteristics under study are observed in the sea upper layers (0–100 m); whereas in the deep-water layers (300–1500 m), the degree of consistency between the simulated results and the field data is much more higher. On the depths below 800 meters, the deep-sea anticyclonic flows with the velocities attaining 1.5 cm/s are present. The revealed feature is not typical of the generally accepted scheme of the Black Sea cyclonic circulation.

Distribution of Suspended Sediment in the Gulf of Gdansk off the Vistula River mouth (Baltic Sea, Poland)

The Vistula River mouth is situated on the southern coast of the Gulf of Gdańsk (Poland). Considering the average flow and draining area of the Vistula River, it is one of the largest rivers in the Baltic Sea catchment area. It is also one of the largest sources of terrigenous material supplied to the Baltic Sea. The particle size analysis of the material transported in suspension shows that it consists of fractions ranging in size between 1 and 600 μm. The silt fraction constitutes the biggest share (55%), while the medium and fine sands amount to 30%. Close to 15% of the material transported in suspension belongs to the clay fraction. During field research in April 2014, many parameters were measured at the stations in the Gulf of Gdansk. The variation in suspension characteristics and water parameters was determined with the LISST-25X sensor and CTD probe, respectively. The flow and current directions were assessed by means of ADCP. In the Vistula River mouth, the mean concentration of suspended matter in the surface layer (0–3 m) varied from 30 to 1 099 μL/L. The Sauter mean diameter of suspended sediment ranged from 44 to 172 μm, wherein the smallest and the biggest particle sizes were 22 μm and 360 μm, respectively. At a depth of 10 m, differences in mean diameter (36–54 μm) and concentration (16–47 μL/L) were much lower. The changes observed in these waters occurred over time, reflecting changes in the intensity of the Vistula River discharge. As distance from the river mouth increases, at the surface and at depth of 10 m, the average particle concentration and the mean particle diameter were lower. In deeper water layers (below the developing thermocline), the mean concentration of suspended sediment was clearly lower (2.5 μL/L), while the mean particle diameter was higher (32 μm). Different characteristics of water masses containing suspension were recorded in the marine waters, which are not directly influenced by the Vistula River freshwater inflow. In marine waters, the mean values of suspension concentration ranged from 1 to 2 μL/L, with relatively large particle sizes between 50 and 60 μm. As the distance from the Vistula River mouth increased, the influence of riverine waters on the particle size distribution and suspension concentration became increasingly less visible. The observed distributions of salinity, temperature and suspension concentration indicate that freshwater is spreading in the surface layer in a fan-shaped form. The spreading of suspension occurs along the dominant directions of the river water movement. Changes in the suspension concentration and particle size in the water column are caused by flocculation.

Long-Term Variability of the Dissolved Oxygen Content and Water Temperatures in the Upper Layer of the Black Sea

Based on the archival oceanographic databank of the Institute of Natural and Technical Systems, the annual and interannual variability was analyzed for the dissolved oxygen content and temperatures in the upper deep-water layer and northwestern parts of the Black Sea from 1923 to 2013. The seasonal variations in the dissolved oxygen content and temperatures are in antiphase. On average, over the considered time frame, the dissolved oxygen content was maximum in winter in the northwestern area of the sea and minimum in the open parts in summer. The amplitude of seasonal variations was over 50 µM/L. In general, this is in agreement with earlier publications. However, the seasonal trend changes considerably within certain 20- to 30-year time intervals, which is related to quasiperiodic variability of the oxygen content on a typical time scale of several decades, exhibited differently in different seasons and sea areas.

ГЕТЕРОТРОФНЫЙ МИКРОПЛАНКТОН ЮЖНОЙ ОКОНЕЧНОСТИ ЖЕЛОБА СВЯТОЙ АННЫ В ОСЕННИЙ ПЕРИОД (КАРСКОЕ МОРЕ)

The paper concerns the pelagic microbial community of the southern part of the St.Anna trough in the late vegetation period. in 2007 and 2011. The abundance, biomass and production of bacterioplankton, as well as the abundance and species composition of heterotrophic flagellates and ciliates were analyzed. The abundance and bacterial production values observed in the trough were significantly lower than the values typical of the surface brackish water layer above the Kara Sea shelf. The bacterioplankton abundance values of the upper warm layer in 2007 were several times lower than in 2011 (10-60*103 cells/ml and 24-147*103 cells/ml, respectively). In the deeper water layers, this difference diminished. The interannual differences in the values of bacterioplankton production were also most pronounced in the upper 60-meter layer: 0-0.17 and 0.05-0.87 mgC/m3 per day in 2007 and 2011, respectively. The distribution of the abundance of heterotrophic flagellates and ciliates is significantly influenced by the contour current along the slope of the trench. In the area of its influence in 2007, high values of the number of flagellates (154 ± 29 cells/ml) were observed throughout the water column, whereas in 2011 maximal values were confined to the upper 50-meter layer, exceeding almost twice the abundance at neighboring stations (810 ± 102 and 481 ± 61 cells/ml, respectively).The results of multifactor analysis showed that the number of heterotrophic flagellates, as well as the number of protozoan species decreased with depth. However in the euphotic layer there was a difference between two years of observations: in 2007, the abundance of consumers depended on the state of primary producers, whereas in 2011 the main factor affecting their abundance was the number of bacteria. Analysis of the species composition of heterotrophic flagellates suggests that the complex vertical hydrophysical structure of the water column does not affect substantially the microbial community of the region. However the influence of main currents of the area under consideration may be traced regarding the distribution of the abundance and species composition of heterotrophic microorganisms.

Preconditioning and Formation of Maud Rise Polynyas in a High-Resolution Earth System Model

AbstractOpen-ocean polynyas (OOPs) in the Southern Ocean are ice-free areas within the winter ice pack that are associated with deep convection, potentially contributing to the formation of Antarctic Bottom Water. To enhance the credibility of Earth system models (ESMs), their ability to simulate OOPs realistically is thus crucial. Here we investigate OOPs that emerge intermittently in a high-resolution (HR) preindustrial simulation with the Energy Exascale Earth System Model, version 0.1 (E3SMv0), an offspring of the Community Earth System Model (CESM). While low-resolution (LR) simulations with E3SMv0 show no signs of OOP formation, the preindustrial E3SMv0-HR simulation produces both large Weddell Sea polynyas (WSPs) as well as small Maud Rise polynyas (MRPs). The latter are associated with a prominent seamount in the eastern Weddell Sea, and their preconditioning and formation is the focus of this study. The steep flanks of the rugged topography in this region are in E3SMv0-HR sufficiently well resolved for the impinging flow to produce pronounced Taylor caps that precondition the region for convection. Aided by an accumulation of heat in the Weddell Deep Water layer, the ultimate trigger of convection that leads to MRPs is the advection of anomalously high upper-ocean-layer salinity. The crucial difference to WSP-producing LR ESM simulations is that in E3SMv0-HR, WSPs are realistically preceded by MRPs, which in turn are a result of the flow around bathymetry being represented with unprecedented detail.

Climate warming increases vertical and seasonal water temperature differences and inter-annual variability in a mountain lake

Lakes around the world are warming, but not all water layers are warming at the same rate, and some are even cooling. Most studies have focused on summer lake water surface temperatures or analyzed short-time series. Here, we analyze a 44-year time series of water temperature from nine depths in a small mountain lake using dynamic linear models and temporal trend decomposition. We observe a significant long-term warming trend, but this occurred only from August to December in all water layers. The lake warmed ca. twice as fast (0.23 °C decade−1) as the air, but warming of the epilimnion slowed down remarkably (from 0.65 to 0.10 °C per decade) after 1993, a consequence of changing stratification timing. Deeper water layers even cooled thereafter, pointing to a stronger isolation from surface layers, which were still warming over the whole study period. This differential warming of the lake was accompanied by significant shifts of lake freezing and thawing dates leading to shorter ice-cover periods (~ 5 days decade−1). As a result, the thermal Schmidt stability of the water column strengthened, but also temperature variance in the epilimnion increased significantly, together with increasing variance and extremes of local air temperature. Our results show a significant autumn/winter warming effect of lake water together with an increasing intensity of temperature fluctuations in this seasonally ice-covered mountain lake, suggesting that current broad scale estimates of climate change impacts on lakes, based on summer temperature measurements and surface layers, do not fully reflect the effect of climate change.

Positive cerium anomaly in the Doushantuo cap carbonates from the Yangtze platform, South China: Implications for intermediate water column manganous conditions in the aftermath of the Marinoan glaciation

Oxygenation exerted an important control on the emergence and diversification of metazoans in the aftermath of the Marinoan glaciation. However, the relationship between the oceanic dissolved O2 (DO) levels and early metazoan evolution remains equivocal. To provide a temporal and spatial reconstruction of the redox conditions for this critical interval, this study investigates the early Ediacaran cap carbonate deposits within intra shelf facies at three localities in the Three Gorges area, the Yangtze platform, South China. Trace and rare earth elements are sequentially extracted from the carbonate fraction for pristine temporal seawater signals. The Member II dolostones of the Duoshantuo Formation, which overlies the cap carbonates, show a negative Ce anomaly. No Ce anomaly is observed in the lower units of the cap carbonates. In contrast, positive Ce anomalies (Ce/Ce* > 1.3) in the uppermost part of the cap carbonates are observed in all studied sections. These positive Ce anomalies are accompanied by high Mn/Fe ratios (ranging from 5.04 to 14.96) and slightly positive MREE anomalies, suggesting that a Fe-Mn-(oxyhydro) oxide coparticipation occurred during the cap carbonate deposition. The positive Ce anomalies may result from the reductive dissolution of the Ce-enriched Mn-(oxyhydro) oxides across a Mn(IV)/Mn(II) redoxcline, in a distinct manganous water wedge that was sandwiched between well-oxygenated and anoxic ferruginous deep water layers. This wedge may have exhibited low oxygen conditions, with approximately 10 µM DO (dissolved oxygen), in comparison to the >90 µM DO expected in an oxic setting and 0 µM DO in an anoxic setting. Therefore, the presence of a positive Ce anomaly in the uppermost part of the cap carbonates indicates a new intermediate manganous condition and further elucidates the water column redox structure that existed following the end of the Marinoan glaciation. Early Ediacaran metazoans were possibly restricted to fully oxygenated conditions and were absent in the manganous or ferruginous-rich environments.

Oceanic Heat Delivery to the Antarctic Continental Shelf: Large‐Scale, Low‐Frequency Variability

AbstractOnshore penetration of oceanic water across the Antarctic continental slope (ACS) plays a major role in global sea level rise by delivering heat to the Antarctic marginal seas, thus contributing to the basal melting of ice shelves. Here the time‐mean (Φmean) and eddy (Φeddy) components of the heat transport (Φ) across the 1,000‐m isobath along the entire ACS are investigated using a 0.1∘ global coupled ocean/sea ice simulation based on the Los Alamos Parallel Ocean Program (POP) and sea ice (Community Ice CodE) models. Comparison with in situ hydrography shows that the model successfully represents the basic water mass structure, with a warm bias in the Circumpolar Deep Water layer. Segments of on‐shelf Φ, with lengths of O(100–1,000 km), are found along the ACS. The circumpolar integral of the annually averaged Φ is O(20 TW), with Φeddy always on‐shelf, while Φmean fluctuates between on‐shelf and off‐shelf. Stirring along isoneutral surfaces is often the dominant process by which eddies transport heat across the ACS, but advection of heat by both mean flow‐topography interactions and eddies can also be significant depending on the along‐ and across‐slope location. The seasonal and interannual variability of the circumpolarly integrated Φmean is controlled by convergence of Ekman transport within the ACS. Prominent warming features at the bottom of the continental shelf (consistent with observed temperature trends) are found both during high‐Southern Annular Mode and high‐Niño 3.4 periods, suggesting that climate modes can modulate the heat transfer from the Southern Ocean to the ACS across the entire Antarctic margin.

Occurrence of microplastics in the water column and sediment in an inland sea affected by intensive anthropogenic activities

Microplastics may lose buoyancy and occur in deeper waters and ultimately sink to the sediment and this may threaten plankton inhabiting in various water layers and benthic organisms. Here, we conduct the first survey on microplastics in the water column and corresponding sediment in addition to the surface water in the Bohai Sea. A total of 20 stations covering whole Bohai Sea were selected, which included 6 stations specified for water column studying. Seawater was sampled every 5 m, with maximal depth of 30 m in the water column using Niskin bottles coupled with a ship-based conductivity, temperature and depth sensor (CTD) system and surface sediment samples were collected using box corer. The results indicated that higher microplastic levels accumulated at a depth range of 5–15 m in the water column in some stations, suggesting the surface water survey was not sufficient to reflect microplastics loading in a water body. Fibers predominated microplastic types in both seawater and sediment of the Bohai Sea, which accounted for 75%–96.4% of the total microplastics. However the relatively proportion of the fibers in the deeper water layers and sediment was lower than that in the surface water. Microplastic shapes are more diverse in the sediment than in the seawater in general. The microplastic sizes changed with depth in the water column and the proportion of the size-fraction < 300 μm increased with depth, probably as a result of rapid biofouling on the small microplastics due to their higher specific surface area. Such depth distribution also implied that sampling with manta net (>330 μm) that commonly used in the oceanographic survey might underestimate microplastics abundance in the water column. Further studies are recommended to focus on the sinking behavior of microplastics and their effects on marine organisms.

Propagation of Impact of the Recent Major Baltic Inflows From the Eastern Gotland Basin to the Gulf of Finland

Major Baltic Inflows (MBI) have a significant impact on physics, biogeochemistry and marine life in the Baltic Sea. Spreading of the North Sea water from the Danish Straits to the Eastern Gotland Basin has been rigorously studied in recent decades. Investigations of lateral signal propagation using in-situ measurements, which cover the area from the Eastern Gotland Basin to the Gulf of Finland, are missing. Estonian-Swedish-German-Finnish oceanographic data from January 2014 to March 2017 were merged and analyzed to fill the gap. Recent MBIs caused considerable changes in water column properties, and salinity reached the highest values of the last 40–60 years. The arrivals of MBI waters were detected as peaks in the salinity and temperature time-series in the near-bottom layer of the Gotland Deep 4–5 months after the MBI events. Similar peaks were also identified in the Faro Deep, Northern Deep and Kopu West (Northern Baltic Proper) with a further delay of 2–3 months, 3–5 months and 4–6 months, respectively. The first impact of the 2014 December MBI occurred in the Gulf of Finland in nine months as the arrival of the former Northern Baltic Proper deep layer water. Water renewal in the Faro Deep occurred as a gravity current over the sill between Faro and Gotland Deep. Deep layer water in the Northern Baltic Proper and the Gulf of Finland originated from the sub-halocline layer (110–120 m) of the Eastern Gotland Basin. The pre-condition for such mid-layer advection was a denser deep layer in the Gotland and Faro Deep. Fresh oxygen, which arrived in the Gotland Deep in April 2015 and February 2016, was consumed in the near-bottom layer within 3–6 months. Since summer 2016, oxygenated waters occurred in the Gotland Deep in the layer from the halocline to 160 m depth. This oxygen did not reach the area further in the north, except a slight sign of ventilation of the Faro Deep in February 2017. Thus, MBIs did not improve the oxygen conditions in the area north of the Gotland Deep and oxygen conditions rather worsened in the Northern Baltic Proper and the Gulf of Finland.

100 years of atmospheric and marine observations at the Finnish Utö Island in the Baltic Sea

Abstract. The Utö Atmospheric and Marine Research Station introduced in this paper is located on Utö Island (59∘46.84′ N, 21∘22.13′ E) at the outer edge of the Archipelago Sea, by the Baltic Sea towards the Baltic Proper. Meteorological observations at the island started in 1881 and vertical profiling of seawater temperature and salinity in 1900. Since 1980, the number of observations at Utö has rapidly increased, with a large number of new meteorological, air quality, aerosol, optical and greenhouse gas parameters, and recently, a variety of marine observations. In this study, we analyze long-term changes of atmospheric temperature, cloudiness, sea salinity, temperature and ice cover. Our main dataset consists of 248 367 atmospheric temperature observations, 1632 quality-assured vertical seawater temperature and salinity profiles and 8565 ice maps, partly digitized for this project. We also use North Atlantic Oscillation (NAO), major Baltic inflow (MBI) and Baltic Sea river runoff data from the literature as reference variables to our data. Our analysis is based on a statistical method utilizing a dynamic linear model. The results show an increase in the atmospheric temperature at Utö, but the increase is significantly smaller than on land areas and has taken place only since the early 1980s, with a rate of 0.4 ∘C decade−1 during the last 35 years. We also see an increase in seawater temperatures, especially on the surface, with an increase of 0.3 ∘C decade−1 for the last 100 years. In deeper water layers, the increase is smaller and influenced by vertical mixing, which is modulated by inflow of saline water from the North Sea and freshwater inflow from rivers and by wind-driven processes influenced by the local bathymetry. The date when air temperature in the spring exceeds +5 ∘C became 5 days earlier from the period 1951–1980 to the period 1981–2010 and the date when sea surface water temperature exceeds +4 ∘C changed to 9 days earlier. Sea ice cover duration at Utö shows a decrease of approximately 50 % during the last 35 years. Based on the combined results, it is possible that the climate at Utö has changed into a new phase, in which the sea ice no longer reduces the local temperature increase caused by the global warming.

Modeling Multiple Interacting Nutrient Stocks:Application to the Baltic Sea

Eutrophication of water bodies is a worldwide ecological problem caused by excessive amounts of nutrients. This paper develops an accounting method for modeling multiple interacting stocks of nutrients, which applies the dynamic nutrient balance approach to calculate empirical nutrient budgets. The proposed model of multiple interacting stocks draws an explicit connection between nutrient stocks on land and nutrient stocks in the sea, which in turn links estimated marine nutrient stocks with the empirical data of nutrient concentrations. The model is applied to the Baltic Sea, where stocks of nitrogen and phosphorus are calculated for six basins, drawing distinction between surface, middle and deep water layers of the basins, and taking into account spatial interactions of nutrients within the water layers and between the basins. The model is calibrated using empirical data on nutrient loads and concentrations. Finally, we apply the model to forecast future development of nitrogen and phosphorus concentrations under different abatement scenarios. Keywords: Dynamic Nutrient Model; Multiple Interacting Stocks; Nitrogen; Phosphorus; Eutrophication; Baltic Sea