Structure and dynamics of mesoscale eddies over the Laptev Sea continental slope in the Arctic Ocean

Heat fluxes steered by mesoscale eddies may be a significant, but still not quantified, source of heat to the surface mixed layer and sea ice cover in the Arctic Ocean, as well as a source of nutrients for enhancing seasonal productivity in the near-surface layers. Here we use 4 years (2007–2011) of velocity and hydrography records from a moored profiler over the Laptev Sea slope and 15 months (2008–2009) of acoustic Doppler current profiler data from a nearby mooring to investigate the structure and dynamics of eddies at the continental margin of the eastern Eurasian Basin. Typical eddy scales are radii of the order of 10&thinsp;km, heights of 600&thinsp;m, and maximum velocities of  ∼ 0.1&thinsp;m&thinsp;s−1. Eddies are approximately equally divided between cyclonic and anticyclonic polarizations, contrary to prior observations from the deep basins and along the Lomonosov Ridge. Eddies are present in the mooring records about 20&thinsp;%–25&thinsp;% of the time, taking about 1 week to pass through the mooring at an average frequency of about one eddy per month.We found that the eddies observed are formed in two distinct regions – near Fram Strait, where the western branch of Atlantic Water (AW) enters the Arctic Ocean, and near Severnaya Zemlya, where the Fram Strait and Barents Sea branches of the AW inflow merge. These eddies, embedded in the Arctic Circumpolar Boundary Current, carry anomalous water properties along the eastern Arctic continental slope. The enhanced diapycnal mixing that we found within EB eddies suggests a potentially important role for eddies in the vertical redistribution of heat in the Arctic Ocean interior.</p

Fluctuating Atlantic inflows modulate Arctic atlantification

Enhanced warm, salty subarctic inflows drive high-latitude atlantification, which weakens oceanic stratification, amplifies heat fluxes, and reduces sea ice. In this work, we show that the atmospheric Arctic Dipole (AD) associated with anticyclonic winds over North America and cyclonic winds over Eurasia modulates inflows from the North Atlantic across the Nordic Seas. The alternating AD phases create a “switchgear mechanism.” From 2007 to 2021, this switchgear mechanism weakened northward inflows and enhanced sea-ice export across Fram Strait and increased inflows throughout the Barents Sea. By favoring stronger Arctic Ocean circulation, transferring freshwater into the Amerasian Basin, boosting stratification, and lowering oceanic heat fluxes there after 2007, AD+ contributed to slowing sea-ice loss. A transition to an AD− phase may accelerate the Arctic sea-ice decline, which would further change the Arctic climate system.acceptedVersio

A Steady Regime of Volume and Heat Transports in the Eastern Arctic Ocean in the Early 21st Century

Mooring observations in the eastern Eurasian Basin of the Arctic Ocean showed that mean 2013–2018 along-slope volume and heat (calculated relative to the freezing temperature) transports in the upper 800 m were 4.8 ± 0.1 Sv (1 Sv = 106 m3/s) and 34.8 ± 0.6 TW, respectively. Volume and heat transports within the Atlantic Water (AW) layer (∼150–800 m) in 2013–2018 lacked significant temporal shifts at annual and longer time scales: averaged over the two periods of mooring deployment in 2013–2015 and 2015–2018, volume transports were 3.1 ± 0.1 Sv, while AW heat transports were 31.3 ± 1.0 TW and 34.8 ± 0.8 TW. Moreover, the reconstructed AW volume transports over longer, 2003–2018, period of time showed strong interannual variations but lacked a statistically significant trend. However, we found a weak positive trend of 0.08 ± 0.07 Sv/year in the barotropic AW volume transport estimated using dynamic ocean topography (DOT) measurements in 2003–2014 – the longest period spanned by the DOT dataset. Vertical coherence of 2013–2018 transports in the halocline (70–140 m) and AW (∼150–800 m) layers was high, suggesting the essential role of the barotropic forcing in constraining along-slope transports. Quantitative estimates of transports and their variability discussed in this study help identify the role of atlantification in critical changes of the eastern Arctic Ocean.publishedVersio

Heat, salt, and volume transports in the eastern Eurasian Basin of the Arctic Ocean from 2 years of mooring observations

This study discusses along-slope volume, heat, and salt transports derived from observations collected in 2013–2015 using a cross-slope array of six moorings ranging from 250 to 3900&thinsp;m in the eastern Eurasian Basin (EB) of the Arctic Ocean. These observations demonstrate that in the upper 780&thinsp;m layer, the along-slope boundary current advected, on average, 5.1±0.1&thinsp;Sv of water, predominantly in the eastward (shallow-to-right) direction. Monthly net volume transports across the Laptev Sea slope vary widely, from  ∼ 0.3±0.8 in April 2014 to  ∼ 9.9±0.8&thinsp;Sv in June 2014; 3.1±0.1&thinsp;Sv (or 60&thinsp;%) of the net transport was associated with warm and salty intermediate-depth Atlantic Water (AW). Calculated heat transport for 2013–2015 (relative to −1.8&thinsp;°C) was 46.0±1.7&thinsp;TW, and net salt transport (relative to zero salinity) was 172±6&thinsp;Mkg&thinsp;s−1. Estimates for AW heat and salt transports were 32.7±1.3&thinsp;TW (71&thinsp;% of net heat transport) and 112±4&thinsp;Mkg&thinsp;s−1 (65&thinsp;% of net salt transport). The variability of currents explains  ∼ 90&thinsp;% of the variability in the heat and salt transports. The remaining  ∼ 10&thinsp;% is controlled by temperature and salinity anomalies together with the temporal variability of the AW layer thickness. The annual mean volume transports decreased by 25&thinsp;% from 5.8±0.2&thinsp;Sv in 2013–2014 to 4.4±0.2&thinsp;Sv in 2014–2015, suggesting that changes in the transports at interannual and longer timescales in the eastern EB may be significant.</p

Влияние притока из Атлантики на содержание пресной воды в верхнем слое Арктического бассейна

Inter-decadal changes in the water layer of Atlantic origin and freshwater content (FWC) in the upper 100 m layer were traced jointly to assess the influence of inflows from the Atlantic on FWC changes based on oceanographic observations in the Arctic Basin for the 1960s – 2010s. For this assessment, we used oceanographic data collected at the Arctic and Antarctic Research Institute (AARI) and the International Arctic Research Center (IARC). The AARI data for the decades of 1960s – 1990s were obtained mainly at the North Pole drifting ice camps, in high-latitude aerial surveys in the 1970s, as well as in ship-based expeditions in the 1990s. The IARC database contains oceanographic measurements acquired using modern CTD (Conductivity – Temperature – Depth) systems starting from the 2000s. For the reconstruction of decadal fields of the depths of the upper and lower 0 °С isotherms and FWC in the 0–100 m layer in the periods with a relatively small number of observations (1970s – 1990s), we used a climatic regression method based on the conservativeness of the large-scale structure of water masses in the Arctic Basin. Decadal fields with higher data coverage were built using the DIVAnd algorithm. Both methods showed almost identical results when compared.  The results demonstrated that the upper boundary of the Atlantic water (AW) layer, identified with the depth of zero isotherm, raised everywhere by several tens of meters in 1990s – 2010s, when compared to its position before the start of warming in the 1970s. The lower boundary of the AW layer, also determined by the depth of zero isotherm, became deeper. Such displacements of the layer boundaries indicate an increase in the volume of water in the Arctic Basin coming not only through the Fram Strait, but also through the Barents Sea. As a result, the balance of water masses was disturbed and its restoration had to occur due to the reduction of the volume of the upper most dynamic freshened layer. Accordingly, the content of fresh water in this layer should decrease. Our results confirmed that FWC in the 0–100 m layer has decreased to 2 m in the Eurasian part of the Arctic Basin to the west of 180° E in the 1990s. In contrast, the FWC to the east of 180° E and closer to the shores of Alaska and the Canadian archipelago has increased. These opposite tendencies have been intensified in the 2000s and the 2010s. A spatial correlation between distributions of the FWC and the positions of the upper AW boundary over different decades confirms a close relationship between both distributions. The influence of fresh water inflow is manifested as an increase in water storage in the Canadian Basin and the Beaufort Gyre in the 1990s – 2010s. The response of water temperature changes from the tropical Atlantic to the Arctic Basin was traced, suggesting not only the influence of SST at low latitudes on changes in FWC, but indicating the distant tropical impact on Arctic processes. На основе данных океанографических наблюдений в Арктическом бассейне за 1960– 2010-е гг. прослежены междесятилетние совместные изменения в слое воды атлантического происхождения и содержания пресной воды (СПВ) в верхнем слое для того, чтобы оценить влияние притока из Атлантики на изменения СПВ. Полученные результаты показали, что верхняя граница слоя АВ, отождествляемая с глубиной нулевой изотермы, повсеместно под­нялась в 1990–2010-е гг. на несколько десятков метров относительно ее положения до начала потепления в 1970-е гг. Нижняя граница слоя, также определяемая по глубине нулевой изо­термы, опустилась. Такие смещения границ слоя свидетельствуют об увеличении объема воды в Арктическом бассейне, поступившей не только через пролив Фрама, но и через Баренцево море. Для сохранения баланса должно было произойти сокращение объема верхнего наиболее динамичного опресненного слоя и, соответственно, уменьшиться содержание пресной воды в этом слое. Наши расчеты подтвердили, что в 1990-е гг. СПВ в слое 0–100 м уменьшилось до 2 м и более в евразийской части Арктического бассейна к западу от 180° в.д., а к востоку от 180° в.д. ближе к берегам Аляски и Канадского архипелага, возросло. Эта тенденция усилилась в 2000-е и в 2010-е гг. Сравнение распределений СПВ и положения верхней границы слоя АВ в разные десятилетия методом пространственной корреляции полей подтвердило тесную связь между обоими распределениями. Прослежен отклик температуры АВ в проливе Фрама, Барен­цевом море и в Арктическом бассейне на аномалии температуры воды в тропической области Атлантики, который свидетельствует о тропическом воздействии на арктические процессы. 

Combining physical and geochemical methods to investigate lower halocline water formation and modification along the Siberian continental slope

A series of cross-slope transects were occupied in 2013 and 2015 that extended eastward from St. Anna Trough to the Lomonosov Ridge. High-resolution physical and chemical observations collected along these transects revealed fronts in the potential temperature and the stable oxygen isotopic ratio (δ18O) that were observed north of Severnaya Zemlya (SZ). Using linear regressions, we describe mixing regimes on either side of the front that characterize a transition from a seasonal halocline to a permanent halocline. This transition describes the formation of lower halocline water (LHW) and the cold halocline layer via a mechanism that has been previously postulated by Rudels et al. (1996). Initial freshening of Atlantic Water (AW) by sea-ice meltwater occurs west of SZ, whereas higher influences of meteoric water and brine result in a transition to a separate mixing regime that alters LHW through mixing with overlying waters and shifts the characteristic temperature–salinity bend from higher (34.4  ≤  S  ≤  34.5) toward lower (34.2  ≤  S  ≤  34.3) salinities. These mixing regimes appear to have been robust since at least 2000

Growth of landfast ice and its thermal interaction with bottom sediments in the Braganzav{\r a}gen Gulf (West Spitsbergen)

The results of ice and hydrological studies of the shallow Bay of Braganzavågen (Van Mayen Fjord Bay, West Spitsbergen Island) in March 2016 and 2018, supplemented with model calculations using a thermodynamic model, are presented. The model uses both known methods of localizing the phase transition region-the classical (frontal) for fast ice and in an extended area (two-phase zone) for bottom sediments. For real atmospheric conditions of winter 2015-2016, the new qualitative features of the process of ice formation in the adjacent layers of sea water and bottom soil are revealed. However, due to insufficient knowledge of the heat and mass transfer properties of bottom sediments, the question of quantitative estimates of the process remains open and can be clarified in special field experiments