Displays

North of Svalbard is a key region for the Arctic Ocean heat and salt budget as it is the gateway for one of the main branches of Atlantic Water in the Arctic. As the Atlantic Water layer advances into the Arctic Ocean, its core deepens from about 250 m depth around the Yermak Plateau to 350 m in the Laptev Sea, and gets colder and less saline due to mixing with surrounding waters. The complex topography in the region facilitates vertical and horizontal exchanges between the water masses and, together with strong shear and tidal forcing driving increased mixing rates, impacts the heat and salt content of the Atlantic Water layer that will circulate the Arctic Ocean.

In summer 2018, 6 moorings organized in 2 arrays were deployed across the Atlantic Water Boundary current for a year, within the framework of the Nansen Legacy project. In parallel, turbulence structure in the Atlantic Water boundary current was measured north of Svalbard in two different periods (July and September), using a Vertical Microstructure Profiler (Rockland Scientific) in both cruises and a Microrider (Rockland Scientific) mounted on a Slocum glider in September.

Using mooring observations, we investigated the background properties of the Atlantic Water boundary current (transport, vertical structure, seasonal variations) and the possible sources of the low-frequency variations (period of more than 2 weeks).

Using observations during the cruise periods, we investigated changes in the mixed layer through the summer and the sources of vertical mixing in the water column. In the mixed layer, depth-integrated turbulent dissipation rate is about 10^-4 W m^-2. Variations in the turbulent heat, salinity and buoyancy fluxes are strong, and hypothesized to be affected by the evolution of the surface meltwater layer through summer. When integrated over the Atlantic Water layer, the turbulent dissipation rate is about 3.10^-3 W m^-2. Whilst the wind work exerted in the mixed layer accounts for most of the variability in the mixed layer, tidal forcing plays an important role in setting the dissipation rates deeper in the water column.

How to cite: Koenig, Z., Kolås, E., Kalhagen, K., and Fer, I.: The Atlantic Water boundary current North of Svalbard in 2018-2019: background properties, dynamics and turbulence. , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6981, https://doi.org/10.5194/egusphere-egu2020-6981, 2020.

The winter trend in the sea ice coverage in the Atlantic sector of the Arctic Ocean has been linked to the Atlantic Water heat transport, providing significant skill to decadal prediction (Yeager et al, 2015, Årthun et al., 2019). The Atlantic Water meets the sea ice north of Svalbard where it has the potential to melt significant amounts of ice and contribute to the formation of a cool, fresh surface layer (Rudels et al., 2004). In this study we investigate the origin of the intra-seasonal variability of winter sea ice melt north of Svalbard and evaluate its contribution to recurrent sea ice openings in this region. 

Based on outputs of a simulation with a high resolution regional ice-ocean model over the period 1995-2017, a number of large, short-term ice melt events could be identified in winter which can contribute up to 40% of the total winter ice melt. Most of these events show enhanced signature along the Atlantic Water path. However different types of events have been established depending on the scenario responsible for enhanced sea ice melt. Enhanced melt can happen concomitantly to large ice edge convergence over preexisting warm surface waters, a scenario which predominates during close-up of large ice openings. Large melt rates can also be driven by entrainment of warm water into the mixed layer in response to strong winds or to enhanced advection of warm water during episodes of increased transport in the boundary current. The latter process is however less efficient than entrainment. We conclude that increased southerly winds, which can sustain altogether ice edge retreat and efficient ice melt through entrainment and advection of heat into the region, create optimal conditions for major ice openings such as those observed north of Svalbard.

How to cite: Herbaut, C., Houssais, M.-N., and Blaizot, A.-C.: Ocean role in the winter sea ice openings north of Svalbard, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20578, https://doi.org/10.5194/egusphere-egu2020-20578, 2020.

The summer polynya along the northern coast of Greenland has been observed only six months later after the winter polynya in 2018, which has prompted concerns about the stability of some of the thickest sea-ice in the Arctic region. This study combines retrospective remotely sensed sea-ice measurements with results from the Regional Arctic System Model (RASM) to examine the causes, effect, and evolution of open-water areas/polynyas in the region.

RASM is a limited-domain, fully-coupled climate model, consisting of the atmosphere (Weather Research and Forecasting, WRF3.7), ocean (Los Alamos National Laboratory Parallel Ocean Program, POP2), sea-ice (Community Sea Ice Model, CICE5), land hydrology (Variable Infiltration Capacity, VIC4) and streamflow routing (RVIC) components. The ocean and sea-ice models are configured with the horizontal resolution of 1/12-degree with 45 vertical levels and 5 sea-ice thickness categories, respectively. The atmosphere and land hydrology components are set up on a 50-km grid with 40-vertical levels and 3-soil layers, respectively. The Climate Forecast System Reanalysis (CFSR) and version 2 (CFSv2) output are used as boundary conditions for dynamic downscaling.

Analysis of the sea-ice conditions off the coast of northern Greenland revealed that RASM, in agreement with satellite measurements, has simulated five summer polynya events, i.e. in August of 1984, 1985, 2002, 2004 and 2018, over the 39-year period (1980-2018). All these events were primarily dynamically forced, with the thermodynamic forcing playing the secondary, yet still important role. While the thermodynamically driven sea-ice melting exhibited a relatively little year-to-year variability, between 87 km³ and 115 km³, its relative contribution to the total sea-ice loss increased by 2.5 times, from 16% in 1984 to 40% in 2018. This implies that with continuing thinning of sea-ice, increasingly less mechanical forcing may be required to generate and maintain a polynya or open water north of Greenland in summers to come.  

How to cite: Lee, Y., Maslowski, W., Osinski, R., Clement Kinney, J., Craig, A., Cassano, J., Nijssen, B., and Seefeldt, M.: Causality and Evolution of Summer Polynyas off the Coast of Northern Greenland, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6076, https://doi.org/10.5194/egusphere-egu2020-6076, 2020.

The Nordic Seas have a significant impact on global climate due to their role in providing dense overflows to the North Atlantic Ocean. However, the dramatic loss of sea ice in recent decades is creating a new atmosphere-ice-ocean environment where large swathes of the ocean that were previously ice-covered are now exposed to the atmosphere. Despite the largest sea-ice loss occurring in summer and autumn, the sea-ice loss in winter and spring is arguably more important for the climate system. Atmosphere-ocean coupling is the most intense in the extended winter, when convective mixing leads to water-mass modification processes, impacting the densest waters of the Atlantic Meridional Overturning Circulation. Here we focus on the marginal-ice-zone of the Nordic Seas where the air-sea temperature difference is large, promoting high heat flux events during periods of off-ice winds. We use both transient and control simulations of the coupled climate model HiGEM, which allows us to isolate the climate change response from the sea-ice retreat response. We find that wintertime sea-ice retreat leads to remarkable changes in ocean surface heat exchanges and wind energy input. As the sea ice edge retreats towards the Greenland coastline, there is a band of exposed ocean which was previously covered by ice. This exposure allows enhanced mechanical mixing by the wind and a greater loss of buoyancy from the ocean leading to deeper vertical mixing in the upper ocean. Sensible and latent heat fluxes from the ocean to the atmosphere provide the greatest loss of buoyancy. However, climate warming inhibits this process as the atmosphere warms more rapidly than the ocean which reduces the sea-air temperature difference. Further away from the retreating ice edge, toward the centre of the Greenland Sea, the upper ocean warms, resulting in a more stratified water column. As a consequence, the depth of convective mixing reduces over the deep ocean and increases over shallower regions close to the coast. This leads to changes in the formation and properties of some of the water masses that enter the North Atlantic and thus may modify the ocean circulation in the subpolar seas in response to sea-ice decline. 

How to cite: Wu, Y., Stevens, D., Renfrew, I., and Zhai, X.: The impact of wintertime sea-ice retreat on convection in the Nordic Seas, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-462, https://doi.org/10.5194/egusphere-egu2020-462, 2020.

In the recent few years the topic of accelerated sea ice loss, and related changes in the vertical structure of water masses in the East-Atlantic sector of the Arctic Ocean, including the Barents Sea and the western part of the Nansen Basin, has been in the foci of multiple studies. This region even earned the name the “Arctic warming hotspot”, due to the extreme retreat of sea ice and clear signs of change in the vertical hydrographic structure from the Arctic type to the sub-Arctic one. A gradual increase in temperature and salinity in this area has been observed since the mid-2000s. This trend is hypothetically associated with a general decrease in the volume of sea ice in the Arctic Ocean, which leads to a decrease of ice import in the Barents Sea, salinization, weakening of density stratification, intensification of vertical mixing and an increase of heat and salt fluxes from the deep to the upper mixed layer. The result of such changes is a further reduction of sea ice, i.e. implementation of positive feedback, which is conventionally refereed as the “atlantification. Due to the fact that the Barents Sea is a relatively shallow basin, the process of atlantification might develop here much faster than in the deep Nansen Basin. Thus, theoretically, the hydrographic regime in the northern part of the Barents Sea may rapidly transform to a “Nordic Seas – wise”, a characteristic feature of which is the year-round absence of the ice cover with debatable consequences for the climate and ecosystem of the region and adjacent land areas. Due to the obvious reasons, historical observations in the Barents Sea mostly cover the summer season. Here we present a rare oceanographic data, collected during the late winter - early spring in 2019. Measurements were occupied at four sequential oceanographic surveys from the boundary between the Norwegian Sea and the Barents Sea – the so called Barents Sea opening to the boundary between the Barents Sea and the Kara Sea. Completed hydrological sections allowed us to estimate the contribution of the winter processes in the Atlantic Water transformation at the end of the winter season. Characteristic feature of the observed transformation is the homogenization of the near-to-bottom part of the water column with remaining stratification in the upper part. A probable explanation of such changes is the dominance of shelf convection and cascading of dense water over the open sea convection. In this case, complete homogenization of the water column does not occur, since convection in the open sea is impeded by salinity and density stratification, which is maintained by melting of the imported sea ice in the relatively warm water. The study was supported by RFBR grant # 18-05-60083.

How to cite: Ivanov, V., Frolov, I., and Filchuk, K.: Transformation of Atlantic Water in the Barents Sea in winter: overview of “Transarctika-2019” cruise results, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11531, https://doi.org/10.5194/egusphere-egu2020-11531, 2020.

In an experiment to validate an ice forecast and route optimization system, an array of 15 ice drift beacons/buoys were deployed between Edgeøya and Kong Karls Land in the east of Svalbard to measure the sea ice movement. These beacons recorded data at a sampling frequency of 15 minutes in the duration from March 2014 to May 2014 with different start and end dates based on their life. The particularly short time step captures the small scale effect of tides on the drifting ice. In this region of the Barents Sea, the frequency of the inertial motion is very close to the M2 tidal frequency. Hence, it is not possible to extract the tidal motion from the time series data of the buoys by using a Fourier analysis. It is also likely that these effects will interact. Instead, we develop a physics-based free drift ice model that can simulate the drift at all tidal and other frequencies.

The model is forced by winds obtained from the ERA5 Reanalysis dataset of ECMWF and ocean currents obtained from the Global Ocean Analysis product of CMEMS. Due to the effect of tides, the model is also forced by the tides obtained from the Global Tide and Surge Model (GTSM v3.0) which is built upon Delft3D-FM unstructured mesh code. This free drift model is validated against 8 of the 15 beacon trajectories. The model along with the observed data can be then be used to obtain insights on the relationship between the sea ice velocities and the tides. This will be particularly useful to obtain the effect of ice drift on tides in tidal models.

The model uncertainty is mainly due to oceanic and atmospheric drag coefficients, C_dw and C_da, respectively, and the sea ice thickness, h_i. This study also focuses on optimizing the ratio of drag coefficients (C_dw/C_da) for the different beacon trajectories while varying the ice thickness between 0.1 m - 1.5 m and the ice-air drag coefficient between (0.5-2.5)x10^-3. This ratio facilitates the evaluation of the frictional drag between the ice-water interface and thus, helps in determining the effect of ice on tides in tidal models.

How to cite: Vasulkar, A., Kaleschke, L., Verlaan, M., and Slobbe, C.: Analysis of tidal sea-ice movement using a drifting ice beacon array in the Barents Sea, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7544, https://doi.org/10.5194/egusphere-egu2020-7544, 2020.

Anthropogenic chemical tracers are powerful tools to study ocean circulation timescales, water mass provenance and mixing regimes. In the Arctic Ocean, the releases of artificial radionuclides from European nuclear reprocessing plants (RPs) act as valuable transient tracers as they label the inflowing Atlantic Waters with a distinct anthropogenic signal. In recent years, the combination of the two long-lived radionuclides ¹²⁹I and ²³⁶U has emerged as a new tracer pair and several studies have shown their potential to track pathways and timescales of Atlantic Water circulation in the Arctic Ocean and Fram Strait.

The circulation times of Atlantic-origin waters in the Arctic Ocean that were inferred using this tracer pair (in combination with the naturally occurring ²³⁸U) agree to those obtained by means of other transient tracers. Moreover, the combination of ¹²⁹I and ²³⁶U promises to be a useful marker of water mass mixing regimes both in the surface waters and the subsurface Atlantic layer. In particular, the interface between Atlantic and Pacific Waters in the polar surface layer of the Arctic Ocean can be easily identified as these two water masses are labelled by very different ¹²⁹I/²³⁶U and ²³⁶U/²³⁸U atom ratios.

Here we present a compilation of ¹²⁹I and ²³⁶U in a quasi-synoptic pan-arctic section including the Fram Strait and we show how this data can be used to gain information about circulation patterns. We discuss timescales and transport characteristics of Atlantic Water flow, the position and variability of the front between Atlantic and Pacific Waters and the temporal variability of Pacific Waters in the Fram Strait.

How to cite: Wefing, A.-M., Casacuberta, N., Christl, M., Smith, J. N., Dodd, P. A., Chamizo, E., López-Lora, M., and Synal, H.-A.: The long-lived anthropogenic radionuclides I-129 and U-236 as tracers of water mass provenance, circulation timescales and mixing in the Arctic Ocean and Fram Strait, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8697, https://doi.org/10.5194/egusphere-egu2020-8697, 2020.

Arctic heat and freshwater budgets are highly sensitive to volume transports through Arctic-Subarctic straits. Here we investigate how the volume transports through these straits adjust to each other to maintain a mass balance in the Arctic on annual timescales. To this end, we use three models; two coupled global climate models, one with a third-degree horizontal ocean resolution (HiGEM1.1) and one with a twelfth-degree horizontal ocean resolution (HadGEM3), and one ocean-only model with an idealized polar basin (tenth-degree horizontal resolution). The two global climate models indicate that there is a strong anti-correlation between the Bering Strait throughflow and the transport through the Nordic Seas, a second strong anti-correlation between the transport through the Canadian Artic Archipelago (CAA) and the Nordic Seas transport, and a third strong anti-correlation between the Fram Strait and the Barents Sea throughflows. We find that part of the strait correlations is due to the strait transports being coincidentally driven by large-scale atmospheric forcing patterns such as the Arctic Oscillation. However, there is also a role for fast wave adjustments of some straits flows to perturbations in other straits since atmospheric forcing of individual strait flows alone cannot lead to near mass balance fortuitously every year. Idealized experiments with an ocean model (NEMO3.6) that investigate such causal strait relations suggest that perturbations in the Bering Strait are compensated preferentially in the Fram Strait due to the narrowness of the western Arctic shelf and the deeper depth of the Fram Strait.

How to cite: De Boer, A., Gavilan Pascual-Ahuir, E., Stevens, D., Chafik, L., Hutchinson, D., Zhang, Q., Sime, L., and Willmott, A.: On the inter-connectivity of volume transports through Arctic Straits, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8569, https://doi.org/10.5194/egusphere-egu2020-8569, 2020.

Lagrangian particle tracking and associated diagnostics may be used to examine advective pathways of material and to identify coherent structures in the flow.  Lagrangian coherent structures are material transport barriers and act to separate different flow regimes.

The drift of the International Multidisciplinary Observatory for the Study of Arctic Climate (MOSAiC) expedition onboard R/V Polarstern began in October 2019 and will continue for the full year.   Our study has the goals to (i) characterise advective pathways and (ii) examine potential predictability of the MOSAiC drift.  Eddies, jets and boundary currents feature large spatiotemporally varying velocity gradients.  Since operational ocean forecasts have a limited time horizon (~weeks), we focused on hindcast to examine typical sea ice/ocean circulation scenarios for 2005-15.  We applied off-line ARIANE particle tracking in an eddying 1/12 deg. global NEMO sea ice-ocean model to estimate the most likely drift pathways. 

Over 10,000 trajectories were initialised in October each year, started at the best estimated MOSAiC location, advected for one year and analysed for key coherent drift structures.  The advection and deformation of the initial particle cluster provided information about MOSAiC drift predictability, but also elucidated transport processes of the biogeochemical tracers, such as nutrients and carbon, and spread of pollution and microplastics. We analysed observations from a newly curated dataset of the Arctic to examine various watermass properties, their origin, fate and connectivity.

The MOSAiC surface drift trajectories depend on release time and location, but to leading-order, they are governed by the interannual variability of the wind and of the underlying ocean circulation.  Mesoscale flow deformation is linked to a spreading of the cluster of particles and is associated with reduced potential predictability of separation of particles within the cluster (~ 450 km after 12 months).  Gyre-scale flow affects the ensemble drift path over long times and influences whether particular coherent structures are encountered by the particles, their location and strength (in terms of velocity magnitude and gradient).  Saddle-type structures play a major role in bifurcation of particle trajectories.  In the examples studied, saddles north of Nares Strait, near Northern Greenland and Northern Iceland, topologically associated with streamline connectivity between gyres, coastal boundary currents and inflow/outflow at the Arctic gateways, were significant.  On seasonal-interannual scales, the position and strength of the Beaufort Gyre, as well as an anomalous cyclonic gyre in the eastern basin, affected both the ensemble drift path and the coherent flow structures.

The variability of ensemble drift path, cluster deformation and coherent flow structures across the full Arctic basin were often very different from the climatological advective behaviour of Trans-Polar Drift.  For estimation of advective pathways and sea ice drift it is important to consider the varying flow from gyre-scale to mesoscale, where velocity gradients are large, and to identify robust Lagrangian measures for steady features.

The study is supported from NE/R012865/1 (APEAR), part of the Changing Arctic Ocean programme, jointly funded by the UKRI Natural Environment Research Council (NERC) and the German Federal Ministry of Education and Research (BMBF).

How to cite: Wilson, C., Rynders, S., Vredenborg, M., Kelly, S., and Aksenov, Y.: Variability of Lagrangian pathways and coherent structures in the Arctic and its effect on the predictability of MOSAiC drift and material transport, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6748, https://doi.org/10.5194/egusphere-egu2020-6748, 2020.

The Arctic Ocean is a host to major ocean circulation systems, many of which generate eddies that can transport water masses and corresponding tracers over long distances from their formation sites. However, comprehensive observations of critical eddy characteristics are currently not available and are limited to spatially and temporally sparse in situ observations.

Here we use multi-mission high‐resolution spaceborne synthetic aperture radar (SAR) measurements to detect eddies over open ocean and marginal ice zones (MIZ) of Fram Strait and Beaufort Gyre regions. We provide the first estimate of eddy properties, including their locations, size, vorticity sign and monthly distribution during summer period (from June to October). The results of historical Envisat ASAR observations for 2007 and 2011 are then compared to Sentinel-1 and ALOS-2 PALSAR-2 measurements acquired in 2016 and 2018, to infer the possible changes in the intensity and locations of eddy generation over the last decade.

The most prominent feature of the obtained results is that cyclonic eddies strongly dominate over anticyclones. Eddies range in size between 0.5 and 100 km and are frequently found over the shelf and near continental slopes but also present in the deep basin. For MIZ eddies, the number of eddies clearly depends on sea ice concentration with more eddies detected at the ice edge and over low ice concentration regions. The obtained results clearly show that eddies are ubiquitous in the Arctic Ocean even in the presence of sea ice and emphasize the need for improved ocean observations and modeling at eddy scales.

A special focus is also given to infer eddy dynamics over the Arctic marginal ice zones. The use of sequential Sentinel-1 SAR images enables to retrieve high-resolution velocity field over MIZ on a daily basis and observe eddy-driven MIZ dynamics down to submesoscales. The obtained eddy orbital velocities are in agreement with historical observations and may reach up to 0.5-0.7 m/s. We believe that this information is critical for better understanding of the key dynamical processes governing the MIZ state, as well as for improving and validation of sea ice and coupled ice-ocean models.

The analysis of eddies in this work was supported by RFBR grant 18‐35‐20078. Processing and analysis of Sentinel‐1 and ALOS‐2 Palsar‐2 data were done within RSF grant 18‐77‐00082. Software development for data analysis in this work was made under the Ministry of Science and Higher Education of the Russian Federation contract 0555‐2019‐0001.

How to cite: Kozlov, I., Artamonova, A., Petrenko, L., Plotnikov, E., Manucharyan, G., and Kubryakov, A.: Understanding eddy field in the Arctic Ocean from high-resolution satellite observations, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21849, https://doi.org/10.5194/egusphere-egu2020-21849, 2020.

We explore dense water cascading (DWC; a type of bottom-trapped gravity current) on multi-decadal time scales using a pan-Arctic regional ocean-ice model. DWC is particularly important in the Arctic Ocean as the main mechanism of ventilation of interior waters when open ocean convection is blocked by strong density stratification. We identify the locations where the most intense DWC events occur and evaluate the associated cross-shelf mass, heat and salt fluxes. 

A detailed analysis of specific cascading sites around the Beaufort Gyre and adjacent regions is performed. We find that autumn upwelling of warm and saltier Atlantic waters on the shelf and subsequent cooling and mixing of uplifted waters trigger the cascading on the West Chukchi Sea shelf break. We also perform Lagragian particle tacking of low salinity Pacific waters originating at the surface in the Bering Strait; these waters are shown to be modified by brine rejection and cooling, and through subsequent mixing become dense enough to reach depths of 160-200m and below. We examine the role of cascading and shelf upwelling on the shelf waters transformation, pathways and spread of the biological important tracers (O18, Si., DIC snd DIN).

How to cite: Luneva, M., Aksenov, Y., Ivanov, V., Kelly, S., and Tuzov, F.: Cascading and the pathways of the key biogeochemical tracers in the Canadian Basin: from models and observations., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13159, https://doi.org/10.5194/egusphere-egu2020-13159, 2020.

We collect seawater samples from 32 stations for N₂O analysis between August 6 and August 25, during 2017 ARA08B cruise in western Arctic Ocean (WAO), covering from Southern Chukchi Sea (SC) to Northern Chukchi Sea (NC). At surface depth (~50 m), N₂O concentrations were 10.9‒19.4 nmol L^-1, and distinct pattern was observed between SC and NC. N₂O concentrations were increased from surface to bottom (~50 m) at SC, corresponding to positive relationship of ∆N₂O (N₂O_measured - N₂O_equilibrium) with DIN (NO_3­^- + NO₂^-) and negative relationship between ∆N₂O and N^*. It suggests that nitrification and denitrification are the main processes to produce N₂O at SC. On the other hand, N₂O concentration at NC increased from the south to north, and remained vertically constant. It may be the result of physical processes such as dilution by sea ice melting water, and high solubility that affected by low temperature and low salinity. The highest N₂O concentrations were observed at intermediate depth (50‒200 m), ranging 13.4‒21.9 nmol L^-1. It would be determined by high solubility and active biogeochemical processes synthetically. Concentrations of N₂O were rapidly diminished to 400 m, ranging 10.2‒14.1 nmol L^-1, and did not be remarkably altered under 400 m, ranging 11.3‒13.7 nmol L^-1. It might be affected by advection of Atlantic Water (AW) and existence of Arctic Bottom Water (ABW), and influence of biogeochemical processes was negligible at deep and bottom depth (below 200 m). N₂O flux was calculated to determine that the WAO is sources or sinks region for atmospheric N₂O. Positive N₂O flux was observed at SC, and it indicate that N₂O gas is released to atmosphere at SC. Negative value of N₂O flux at NC suggest that atmospheric N₂O is absorbed into NC. Furthermore, positive relationship of N₂O flux with environmental parameters (temperature, salinity, and ∆N₂O) also observed in WAO. These results provide comprehensive information of the spatial N₂O distribution and main processes which decide N₂O distribution in WAO, and also suggest that air-sea N₂O flux could be affected by changing environments of the Arctic Ocean.

How to cite: Kim, S.-S., Kang, S.-H., Yang, E. J., and Kim, I.-N.: Summer N₂O dynamics in the western Arctic Ocean : Distributions, Processes, and Fluxes, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11874, https://doi.org/10.5194/egusphere-egu2020-11874, 2020.

In Arctic, because of the ongoing diminution of the sea ice coverage, it is speculated that anthropogenic activities such as cargo transportation and oil explorations/exploitations could increase in the Canadian Arctic Archipelago (CAA). However, the vast majority of the channels within the CAA, as well as the adjoining continental shelf and slopes, are characterized by a substantial knowledge gap regarding the regional-scale sediment composition and associated contaminants. Overall, knowing that sediments are a sink for pollutants, a wider spatial coverage of sedimentary records across the marine CAA is essential to provide fundamental baseline information on the physical and geochemical sediment properties in this Arctic region. In this context, a total of 118 surface sediment samples were collected over a large area covering the Canadian Beaufort Sea to the Baffin Bay in order to characterize the modern spatial distribution patterns and the temporal trends of polycyclic aromatic hydrocarbons (PAHs) within the CAA. Sampling was performed in 2016, 2017, 2018 and 2019 aboard the CCGS Amundsen as part of the ArticNet program. Extractions were performed using one-step accelerated solvent extraction and clean-up, followed by gas chromatography coupled to a mass spectrometer analysis. To characterize the temporal concentrations of PAHs, the top 10 cm of 8 push-cores distributed across the archipelago were sub-sampled and analyzed just as the surface samples. Sedimentation rates for each core were obtained by ²¹⁰Pb dating and allow to reconstruct the PAHs inputs from the last century. Results of the surface sediment samples indicate that the sum concentrations of 23 PAHs ranged from 6 ng/g (dry weight basis) in the North Baffin Bay to 437 ng/g in the Canadian Beaufort Shelf, with a mean value of 67 ng/g. PAHs source characterization was investigated through diagnostic ratio: fluoranthene over the sum of fluoranthene and pyrene. This ratio tends to point a profile with mainly petrogenic sources (i.e., igneous rock-derived, petroleum or crude oil spill) for the majority of the CAA. Some samples in the Beaufort Sea have a mixed profile with petrogenic sources and pyrogenic sources from incomplete combustion of fossil fuel that could indicate an anthropogenic input. Along Ellesmere Island, ratios are mainly pyrogenic from biomass combustion. Results of the push-cores suggest that the inputs of PAHs to the sediment in CAA were relatively stable during the last years. Taken as a whole, our study will provide a baseline of PAHs levels in surface sediment within the CAA before an increase in maritime transport in this area and a comparison of the modern concentrations versus the last century tendencies.

How to cite: Corminboeuf, A., Montero-Serrano, J.-C., and St-Louis, R.: Spatial and temporal distribution of polycyclic aromatic hydrocarbons in sediments from the Canadian Arctic Archipelago, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2418, https://doi.org/10.5194/egusphere-egu2020-2418, 2020.

The Sea of Okhotsk is a marginal sea of the western Pacific Ocean. It is one of the world's richest in biological resources and famous for the fishing industry. In winter, navigation on the Sea is difficult, if not impossible, due to the harsh conditions of the North and the presence of sea ice. On average, the ice-free period lasts from June to November. However, the start and end dates of the ice season vary from year to year within a month. Such variability is impossible to capture by meteorological methods, which have a limit of predictability for 10 days. The absence of a long-term forecast of the navigational period in the Sea of Okhotsk affects the safety of navigation and the reliability of transit transport.

Most of the studies of the distribution of ice floes focus on such factors as the location, time of year, water currents, and sea temperatures. In our study, we use the distribution of temperature in the atmosphere and wind direction (NCEP/NCAR re-analyses data set) because most of the area of the Sea of Okhotsk is located in monsoon climate zone. We propose a new approach to forecast predicting the upcoming ice advance/ retreat date by developing our Tipping element approach [1] elaborated for prediction of the Indian Summer Monsoon, which proved to be successful for prediction upcoming monsoon four years in a row (2016-2019).

The physical mechanism underlying forecast is the following. There is an atmospheric feature that appears at the beginning of the transition to the ice season. We show, for the first time, the evidence in observational data that a transition from open water season to ice season begins when the near-surface air temperature crosses a critical threshold. It appears in the form of spatially organized critical transitions in the atmosphere over the see. This event happening 2-3 months before the ice season is a starting point forecasting date of ice advance. We perform forecast in critical areas - tipping elements of the spatial structure of ice formation, which we identified via data analysis.

The retrospective test (over the period 2001-2017) confirms that the methodology allows forecasting the ice advance/retreat date more than one month in advance, with a success rate in 88% of the years within the error of +/- 4 days. Forecasts of the upcoming season 2018-2019 show successful results as well.

Climate change affects the ice season in the Sea of Okhotsk in the following aspects: there has been a declining trend in sea ice cover in recent years due to delays in the ice advance date. Season shift because it takes for the atmosphere longer time cooling down in autumn. The novel approach allows for accounting climate change effects.

ES acknowledges financial support of the EPICC project (18_II_149_Global_A_Risikovorhersage) funded by BMU, RM acknowledges the Russian Foundation for Basic Research (RFBR) (No. 20-07-01071)

[1] Stolbova, V., E. Surovyatkina, B. Bookhagen, and J. Kurths (2016): Tipping elements of the Indian monsoon: Prediction of onset and withdrawal. GRL 43, 1–9 [doi:10.1002/2016GL068392]

How to cite: Surovyatkina, E. and Medvedev, R.: Ice Season forecast under ClimateChange: Tipping element approach, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20073, https://doi.org/10.5194/egusphere-egu2020-20073, 2020.

The interdecadal changes in layer of the Atlantic water (AW) and the fresh water content (FWC)  in the  Arctic Basin  (AB) are traced for the 1960s - 2010s  in order to assess the influence of the influx from the Atlantic on the FWC changes. The results showed that the upper boundary of the AB layer, identified on zero isotherm, everywhere rose in the 1990s - 2010s by several tens of meters relative to its position before the start of the warming in the 1970s. The lower boundary of the layer, also determined by the depth of the zero isotherm, fell. Such displacements of the layer boundaries indicate an increase in the volume of the AW in the AB. A reduction in the volume of the upper freshened layer it is necessary to maintain balance. Our calculations confirmed that in the 1990s, the FWC in the layer 0–100 m decreased to 2 m or more in the Eurasian part of the Arctic Basin west of 180 °E and increased to east of 180 °E closer to the shores of Alaska and the Canadian archipelago,. This trend intensified in the 2000s and in the 2010s. A comparison of the distributions of the FWC and the position of the upper boundary of the AB layer over different decades by the method of spatial correlation confirmed a close relationship between both distributions. The response on changes of water temperature in the tropical region of the Atlantic is traced in the Barents Sea and in the Arctic basin.  That indicates the influence of low latitude SST on changes in AW layer and serves as an indicator of tropical effect on the Arctic processes. The study is supported by the RFBR grant 18-05-60107.

How to cite: Alekseev, G., Pnyushkov, A., Smirnov, A., Vyazilova, A., and Glok, N.: Atlantic influence on content of freshwater in upper layer of the Arctic Ocean, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4076, https://doi.org/10.5194/egusphere-egu2020-4076, 2020.

Most Atlantic Water (AW) enters the Arctic Ocean through the West Spitzbergen Current, passing north of Svalbard, either moving along the upper slope or passing over and around the Yermak Plateau. Recent model studies (Koenig et al. 2017 and Crews et al. 2019) have improved our understanding of these pathways but were limited to periods of 1-5 years. This is insufficient for examining the contributions of AW inflow to climate-scale problems such as the ‘Atlantification’ of the Arctic.

In this study we use 23 years (1995-2018) of high resolution (~1/24°) velocity fields from a NEMO 3.6 model (DOI: 10.5281/zenodo.2682406) allowing us to examine the geographic distributions and strengths of AW inflow pathways using a Lagrangian particle tracking approach. Virtual particles were released on a section at 30° E and tracked backwards in time using the PARCELS 2.0 particle tracking system (Delandmeter and van Sebille 2019).

For the present analysis, we focus on trajectories of particles which are contained in AW layer at the release line (SA>34.9 and CT>2°C) and could be tracked backwards to the Nowegian Sea (here taken as south of 75° N). A control line was selected across the Yermak Plateau to allow us to separate particles passing through the Svalbard and Yermak branches. Using these particle trajectories, we created a time-series of transport of AW reaching the southern rim of the western Nansen Basin. The transport was found to vary between 0.5 Sv and 3.75 Sv, comparable to previous studies (e.g. Beszczynska-Möller et al. 2012), and to be dominated, on average, by the Yermak Branch.

How to cite: Roach, C., Herbaut, C., and Houssais, M.-N.: Assessing the Atlantic Water Pathways To The Arctic In a High-Resolution NEMO Model, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-15246, https://doi.org/10.5194/egusphere-egu2020-15246, 2020.

As part of the Nansen Legacy project, waters north of Svalbard are studied. The warm and saline Atlantic water, brought northward by the West Spitsbergen Current cools and freshens as it flows eastward along the slope north of Svalbard, bringing heat and salt into the Arctic Ocean. Hydrographic CTD data are available from various cruises and databases, the main source here being the UNIS Hydrographic Database. Changes in the Atlantic water properties and its horizontal and vertical location on the slope and shelf are mapped from decadal averages of historical data from 1899 to 2018. The mean width of the boundary current following the slope eastward is estimated for five cross-shelf/slope sections from the decadal averages. An Atlantification is present from 1996-2005 to 2006-2018 with warmer and more saline water covering a larger area across the slope and reaching further east.

How to cite: Marnela, M., Nilsen, F., Skogseth, R., and Kalhagen, K.: Atlantic water north of Svalbard 1899-2018, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22642, https://doi.org/10.5194/egusphere-egu2020-22642, 2020.

The high-frequency dynamics (including tidal and inertial currents, internal and coastal-trapped waves) on the shelf break/slope southwest of Svalbard were explored in September-October 2019 using a variety of mobile and fixed sensors operated as part of the NARVAL19 Sea Trial. Ocean currents, temperature and salinity were measured in the water column with 6 moorings, 3 gliders and a wirewalker profiler. In addition near-surface (15 m) currents were measured with 24 satellite-tracked drifters.

The collected data show some variability, mostly near the surface, associated with the lateral displacements or meandering of the Polar Front separating cool and low salinity waters on the shelf and warmer/saltier waters of Atlantic origin. The most striking signal, however, is at depth (in and below the thermocline) in the form of internal waves at semidiurnal tidal frequency.

Preliminary results of spectral and harmonic analyses of the data collected by all the platforms are presented and discussed.

How to cite: Poulain, P.-M., Cozzani, E., Pennucci, G., Lewis, C., Lathuiliere, C., Bordoix, L., and Centurioni, L.: High-frequency dynamics near the shelf break southwest of Svalbard, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-15215, https://doi.org/10.5194/egusphere-egu2020-15215, 2020.

The Nordic Seas play an important role in global climate change. Compared with other areas, this region has the largest ocean surface and air positive temperature anomalies in the world. It is particularly important for the water masses formation and modification and for interactions between the ocean and atmosphere. This region is also the main route for freshwater and heat exchange between the North Atlantic and the Arctic Ocean.

Because the ship-borne measurements are performed usually during the spring to the autumn season, there is no data to analyze seasonal changes in the intermediate and deep water. The Argo floats, operating throughout the whole year, allow observation of seasonal changes that occur in particular regions. This is especially important in the Nordic Seas, where conditions of the oceanographic observations are very difficult even during the summer.

In this study we analyze hydrographic data collected by the Argo floats in the eastern part of the Nordic Seas region in 2008-2017. Based on the data, both the temporal and spatial variability of the basic physical parameters of the intermediate and deep water were analyzed. It allowed determining how the properties of these waters changed both seasonally and spatially.

The study was funded by the Ministry of Science and Higher Education, Poland under grant agreement No. DIR/WK/2016/12 for the research infrastructure EURO-ARGO ERIC and the National Science Centre, Poland within the DWINS Project (2016/21/N/ST10/02920).

How to cite: Merchel, M. and Walczowski, W.: Deep and intermediate water properties based on Argo floats data in the eastern Nordic Seas, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8815, https://doi.org/10.5194/egusphere-egu2020-8815, 2020.

Isfjorden, a broad Arctic fjord in western Spitsbergen, has shown significant changes in hydrography and inflow of Atlantic Water (AW) the last decades that only recently have been observed in the Arctic Ocean north of Svalbard. Variability and trends in this fjord’s climate and circulation are therefore analysed from observational and reanalysis data during 1987 to 2017. Isfjorden experienced a shift in summer ocean structure in 2006, from AW generally in the bottom layer to AW (with increasing thickness) higher up in the water column. This shift, and a concomitant shift to less fast ice in Isfjorden are linked to positive trends in the mean sea surface temperature (SST) and volume weighted mean temperature (VT) in winter (SST_w/VT_w: 0.7 ± 0.1/0.9 ± 0.3 °C 10yr^-1) and summer (SST_S/VT_S: 0.7 ± 0.1/0.6 ± 0.1 °C 10yr^-1). The local mean air temperature shows similar trends in winter (1.9 ± 0.4 °C 10yr^-1) and summer (0.7 ± 0.1 °C 10yr^-1). Positive trends in volume weighted mean salinity in winter (0.21 ± 0.06 10yr^-1) and summer (0.07 ± 0.05 10yr^-1) suggest increased AW advection as a main reason for Isfjorden’s climate change. Local mean air temperature correlates significantly with sea ice cover, SST, and VT, revealing the fjord’s impact on the local terrestrial climate. In line with the shift in summer ocean structure, Isfjorden has changed from an Arctic type fjord dominated by Winter Deep and Winter Intermediate thermal and haline convection, to a fjord dominated by deep thermal convection of Atlantic type water (Winter Open). AW indexes for the mouth and Isfjorden proper show that AW influence has been common in winter over the last decade. Alternating occurrence of Arctic and Atlantic type water at the mouth mirrors the geostrophic control imposed by the Spitsbergen Polar Current (carrying Arctic Water) relative to the strength of the Spitsbergen Trough Current (carrying AW). During high AW impact events, Atlantic type water propagates into the fjord according to the cyclonic circulation along isobaths determined by the winter convection. This study demonstrates that Isfjorden and its ocean climate can be used as an indicator for climate change in the Arctic Ocean. The used methods may constitute a set of helpful tools for future studies also outside the Svalbard Archipelago.

How to cite: Skogseth, R., Olivier, L. L. A., Nilsen, F., Jonassen, M. O., and Falck, E.: Variability and decadal trends in the Isfjorden (Svalbard) ocean climate and circulation - an indicator for climate change in the European Arctic, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11821, https://doi.org/10.5194/egusphere-egu2020-11821, 2020.

Recent satellite passive microwave observations indicate significant negative Arctic sea ice extent trends in all months and substantial reduction of winter sea ice in the Atlantic sector. Warm and salty oceanic water masses from the North Atlantic flow towards the Arctic Ocean along the eastern Fram Strait, carried by the West Spitsbergen Current (WSC). Fram Strait, as well as the region north of Svalbard, play a key role in controlling the amount of oceanic heat supplied to the Arctic Ocean and are the place of dynamic interaction between the ocean and sea ice. The north of Svalbard area is one of the regions where the substantial changes in sea ice concentrations are observed both in summer and in winter. One of the possible reasons can be sought in the observed warming of Atlantic water, carried through Fram Strait into the Arctic Ocean. The main goal of this work is to analyse and explain the sea ice variability along main pathways of the Atlantic origin water (AW) in the context of observed warming of Atlantic water layer. Shrinking sea ice cover in the southern part of Nansen Basin (north of Svalbard) and shifting the ice edge in Fram Strait are driven by the interplay between increased advection of oceanic heat in the Atlantic origin water and changes in the local atmospheric conditions that result in the increased ocean-air-sea ice exchange in winter seasons. The basis for this hypothesis is warming of winter mean surface air temperature observed north of Svalbard and withdrawal of the sea ice cover towards the northeast, along with the pathways of water inflow in the Atlantic sector of the Arctic Ocean. Hydrographic data from vertical CTD profiles were collected during annual summer expeditions of the research vessel "Oceania", conducted in Fram Strait and the southern part of the Nansen Basin over the past two decades. The measurement strategy of the original research program AREX, which consists of the performance of cross-sections perpendicular to the presumed direction of the West Spitsbergen Current, allowed to observe changes in the properties and transport of the Atlantic Water carried to the Arctic Ocean. The analysis of past and present changes in the sea ice cover in relation to Atlantic water variability and atmospheric forcing employs hydrographic data from the repeated CTD sections, systematically collected since 1996 during annual summer Arctic long-term monitoring program AREX, satellite products of sea ice concentration and drift, and selected reanalysis data sets.

How to cite: Grynczel, A., Beszczynska-Moeller, A., and Walczowski, W.: Impact of Atlantic water variability on sea ice changes in the Fram Strait and north of Svalbard, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8142, https://doi.org/10.5194/egusphere-egu2020-8142, 2020.

The transport of warm Atlantic waters north of Svalbard is one of the major heat and salt sources to the Arctic Ocean. The circulation pathway and the associated heat transport influence the variability in the Arctic sea ice extent and the onset of freezing. We present observations obtained from research cruises and autonomous underwater glider missions in summer and fall 2018 to describe the hydrographic structure, volume transport rates and circulation patterns of the warm boundary current between 12E and 24E north of Svalbard.

A composite section is constructed along a representative, average bathymetry across the shelf break, using all available observations in order to obtain the hydrographic structure and the absolute geostrophic transport of the boundary current. The Atlantic water volume transport reaches a maximum of 3.0 ± 0.2 Sv in October, with an intraseasonal variability of 1 Sv. During summer and late fall, we observed Atlantic water flowing eastward (a counter current), in the outer part of the section away from the shelf break, in the Sofia Deep. The intensity of the Atlantic water counter current and the Atlantic water boundary current are very sensitive to the wind stress curl: we observed a near doubling of the volume transport in less than a week.

The composite section also reveals a bottom-intensified current flowing parallel to the boundary current, between the 1500 m and 2000 m isobaths. A composite of all historical data collected in the region, constructed identical to our observations, support the presence of the bottom intensified current.

How to cite: Hugaas Kolås, E., Koenig, Z., Fer, I., Nilsen, F., and Marnela, M.: Structure and transport of Atlantic water north of Svalbard from observations in summer and fall 2018, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18793, https://doi.org/10.5194/egusphere-egu2020-18793, 2020.

Sea ice concentration along the Arctic continental margin north of Svalbard is in decline, but superimposed on this trend is considerable interannual variability. Many factors impact sea ice in this region, including atmospheric cooling and heating, winds, sea ice advection, and oceanic heat transport associated with the inflow of Atlantic Water, and regional sea ice cover remains difficult to predict. We present observations of upper ocean temperature between 2012 and 2017 from an ocean mooring located on the continental shelf break north of the Barents Sea, together with concurrent time series of atmospheric variables and sea ice concentration, drift, and thickness, derived from satellite and reanalysis data. While the inflow of Atlantic Water undoubtedly plays a key role in maintaining the area north of Svalbard ice-free through much of the year, variations in upper ocean temperature do not explain major interannual sea ice anomalies during the study period. Instead, we find that the magnitude of sea ice advection from the north and east was a major driver of interannual sea ice variability during our study.

How to cite: Lundesgaard, Ø., Sundfjord, A., and Renner, A. H. H.: Drivers of interannual sea ice variability on the Arctic continental margin north of Svalbard, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19977, https://doi.org/10.5194/egusphere-egu2020-19977, 2020.

In this study we develop a novel sea ice classification scheme based on remote sensing Synthetic-aperture Radar (SAR) data, and use it to classify sea ice types over the spatial and temporal range of the Norwegian Young sea ICE cruise (N-ICE2015). Ice type classification will be conducted on wide-swath SAR datasets including RADARSAT-2 and Sentinel-1 data. We use a classification scheme that takes into account different rates of decrease in backscatter intensity with incidence angle variation for different classes. In addition, it examines texture features of different sea ice types, and also variations of surface texture with changing incidence angles, and incorporates this relationship into the classification process. Sea ice classifications using high-resolution SAR images collected over the same period and also field data retrieved from the N-ICE2015 expedition will be used for ground truthing. Earlier N-ICE2015 studies with high resolution SAR and deformation suggest high lead and pressure ridge formation. We will use our lower-resolution results to explore potential increase in the fraction of deformed and lead ice from January to June 2015 in the region north of Svalbard.

How to cite: Guo, W., Itkin, P., and Philipp Lohse, J.: Sea ice classification using wide-swath SAR data considering incidence angle depenency of backscatter intensity and surface texture, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11045, https://doi.org/10.5194/egusphere-egu2020-11045, 2020.

In the Arctic Ocean, semidiurnal-band processes including tides and wind-forced inertial oscillations are significant drivers of ice motion, ocean currents and shear contributing to mixing. Two years (2013-2015) of current measurements from seven moorings deployed along 125°E from the Laptev Sea shelf (~50 m) down the continental slope into the deep Eurasian Basin (~3900 m) are analyzed and compared with models of baroclinic tides and inertial motion to identify the primary components of semidiurnal-band current (SBC) energy in this region. The strongest SBCs, exceeding 30 cm/s, are observed during summer in the upper ~30 m throughout the mooring array. The largest upper-ocean SBC signal consists of wind-forced oscillations during the ice-free summer. Strong barotropic tidal currents are only observed on the shallow shelf.  Baroclinic tidal currents, generated along the upper continental slope, can be significant. Their radiation away from source regions is governed by critical latitude effects: the S₂ baroclinic tide (period = 12.000 h) can radiate northwards into deep water but the M₂ (~12.421 h) baroclinic tide is trapped to the continental slope. Baroclinic upper-ocean tidal currents are sensitive to varying stratification, mean flows and sea ice cover.  This time-dependence of baroclinic tides complicates our ability to separate wind-forced inertial oscillations from tidal currents. Since the shear from both sources contributes to upper-ocean mixing that affects the seasonal cycle of the surface mixed layer properties, a better understanding of both, inertial motion and baroclinic tides is needed for projections of mixing and ice-ocean interactions in future Arctic climate states.

How to cite: Baumann, T., Polyakov, I., Padman, L., Danielson, S., Fer, I., Howard, S., Hutchings, J., Janout, M., Nguyen, A., and Pnyushkov, A.: Semidiurnal current dynamics in the Arctic Ocean's eastern Eurasian Basin, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5592, https://doi.org/10.5194/egusphere-egu2020-5592, 2020.

As sea ice and ocean models are moving to higher resolution it becomes possible to permit eddy formation even in the Arctic Ocean. Eddies can affect the three dimensional ocean state through causing mixing and even ventilation of subsurface ocean layers if they are deep enough. To ensure models have the potential to simulate the density structure correctly it is therefore necessary to start doing model validation of not only the large scale ocean state, but also of the eddy field. Eddy statistics for the Arctic are available from satellite for the Western Arctic Ocean and the Fram Strait, in particular on number, size and cyclonicity of eddies for open ocean versus ice covered sites. These are compared to a NEMO-LIM 1/12 degree sea ice and ocean simulation (resolution 2-5km), upon which the model based statistics are expanded to the whole Arctic. In the model it is also possible to examine the depth structure of eddies, allowing to generate size vs. depth statistics. This, together with climatological mixed layer depth, provides a first estimate to get satellite-based information on mixing from eddies in the Arctic. We also map the maximum depth of eddies, to examine ventilation and identify sites with especially deep eddies, for instance at the boundary current. Acknowledgements: Grant NE/R000654/1 “Towards a Marginal Sea Ice Cover” funded by the UK Natural Research Council (NERC) and the UK-Russia Arctic bursaries program funded by the United Kingdom’s Department for Business, Energy and Industrial Strategy. The study is also supported from the project “The Advective Pathways of nutrients and key Ecological substances in the Arctic (APEAR)” (grant NE/R012865/1) funded by the Joint UK NERC/German Federal Ministry of Education and Research Changing Arctic Ocean Programme. This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 821926 (IMMERSE). IK acknowledges the support from RFBR grant No 18-35-20078.

How to cite: Rynders, S., Akesenov, Y., and Kozlov, I.: Eddy statistics validation of an ORCA12 ocean and sea ice model for the Arctic with satellite data, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8445, https://doi.org/10.5194/egusphere-egu2020-8445, 2020.

Recent decades have seen a strong intensification of major circulation systems in the Arctic Ocean, namely the Beaufort Gyre and Transpolar Drift. Observing and studying seasonal, interannual and decadal variability of large-scale Arctic Ocean surface circulation is a key element to understand changes in climate-relevant export of both sea ice and fresh surface water from the Arctic. However, lack of in-situ ocean surface velocity observations have prevented further investigation until recently.

In the past decade, charts of the Arctic geostrophic surface flow field have been derived from new satellite altimetry missions over the ice-covered oceans, such as CryoSat-2, which was launched in 2010. The altimetric measurements allow the detection of leads and therefore to retrieve sea surface height (SSH) across the ice-covered Arctic Ocean. Aiming to characterize the seasonal to interannual variability of geostrophic surface currents in the Transpolar Drift, we use SSH observations from the Cryosat-2 mission between 2011 and 2018.

Here we present an evaluation of optimally interpolated altimetric SSH anomalies against in situ ocean observations of both bottom pressure and dynamic Height in Fram Strait and north of Arctic Cape, in the years between 2016 and 2018. Following the assessment of the quality of altimetry-based SSH, we discuss the timescales of SSH variability in seasonally ice-covered regions. Moreover, from the comparison with ocean bottom pressure and dynamic height we will attribute the relative importance of mass and steric contributions to the variability of SSH along the two transects. From first preliminary results in a test year (2011), SSH at a meridional transect in central Fram Strait between 78°N and 80°N shows a seasonal cycle with minimum in the months of March and April, enhanced at the most southern mooring. 

How to cite: Doglioni, F., Ricker, R., Rabe, B., and Kanzow, T.: Arctic Ocean near-surface circulation: altimetry and in situ observations along the Transpolar Drift., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1013, https://doi.org/10.5194/egusphere-egu2020-1013, 2020.

The last 10 years of Arctic Ocean observations showed the dramatic changes and new records of the sea ice minimum. The largest variations were observed in the Eastern Arctic: the Kara, the Laptev, the East-Siberian seas. This region is a key area of the important freshwater input from the great Siberian rivers (Ob’, Yenisei, Lena). This remote area remains one of the less studied in the Arctic Ocean, although several regular expeditions (such as NABOS or Transdrift) together with special expeditions following the Northern Route, such as Tara-2013 expedition, or recent Transarktika-2019 expedition help to monitor the changes of surface waters in recent years.

The use of new satellite-derived datasets, (e.g., SST blended product from Danish Meteorological Institute or REMSS, SSS SMOS from LOCEAN University of Sorbonne) fill the gaps and help to better understand the complex dynamics of surface waters in the Eastern Arctic ocean.

In this work, we discuss the surface waters variations using in situ and satellite data at different scales.  Synoptic scales are studied with continuous and point in situ measurements (thermosalinographs and CTD data). The recent scientific results of Transarktika-2019 expedition are presented. In the summer season of 2019 (July-October) Transarktika expedition did oceanographic measurements following the Northern Route twice, from Vladivistok to Murmansk and back to Vladivostok. The seasonal variations are analyzed over the period of 10 years, comparing with climatological data. The difference between the climatological values of SST or SSS can reach 5 or more units in some areas of the Eastern Arctic. The results of interannual variations analysis using satellite data, suggest the salinification (“Atlantification”) of the southern areas and freshening of the northern parts of the Eastern Arctic.

The development of SSS SMOS Arctic product was supported by the French CNES-TOSCA SMOS-OCEAN project. Anastasiia Tarasenko, Nikita Kusse-Tiuz, Mikhail Makhotin and Vladimir Ivanov acknowledge financial support from the Ministry of Science and Higher Education of the Russian Federation, project RFMEFI61619X0108

How to cite: Tarasenko, A., Supply, A., Boutin, J., Kusse-Tiuz, N., Makhotin, M., Ivanov, V., and Reverdin, G.: Variations of surface waters characteristics in the Eastern Arctic Ocean in 2010-2019 at different scales: in situ and satellite study, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21510, https://doi.org/10.5194/egusphere-egu2020-21510, 2020.

The volume, characteristics and sources of freshwater circulating in the Arctic Ocean vary in time and are expected to change under a declining sea ice cover, influencing the physical environment and Arctic ecosystem. Relatively fresh (S = 32) Pacific Water, which enters the Arctic Ocean via the Bering Strait makes up a significant part of the liquid freshwater exiting the Arctic Ocean through Fram Strait. If transported to the Nordic Seas and North Atlantic via the East- and West Greenland Currents freshwater from the Pacific could have an effect on convection and dense water formation in those regions.

More than 30 repeated sections of nutrient measurements have been collected across Fram Strait between 1980 and 2019. The fraction of Pacific Water along these repeated sections can be estimated from the ratio of nitrate to phosphate. The time-series of repeated Fram Strait sections indicates that the fraction of Pacific Water passing out of the Arctic Ocean has changed significantly over the last 30 years. Pacific water fractions remained high from 1980 to 1998, but in 1999 Pacific water almost disappeared from Fram Strait, reappearing from 2011 to 2012, when there was a peak in freshwater export though Fram Strait.

Several hypotheses suggest how variations in the large-scale atmospheric circulation over the Arctic Ocean may influence the transport and pathways of Pacific Water. We show how anomalies in reanalysis wind fields are associated with the reappearance of Pacific Water in Fram Strait in recent years. Repeated sections across Fram Strait are compared with sea ice back-trajectories in the Polar Pathfinder 4 product and a simulated Pacific Water tracer in the NAOSIM numerical model to investigate likely Pacific water pathways through the Arctic Ocean and upstream drivers of changes observed in Fram Strait.

How to cite: Dodd, P. A., Hattermann, T., Karcher, M., Kauker, F., and Stedmon, C.: Pacific Water Pathways through the Arctic Ocean, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-15898, https://doi.org/10.5194/egusphere-egu2020-15898, 2020.

During the last few decades we observe fast climatic changes. These changes are well expressed in the Polar Region that is more sensitive to all environmental shifts. The temperature and salinity anomalies were observed not only on the surface but also in the Pacific origin halocline layer. Due to hydrostatic imbalance and atmospheric circulation, water from the North Pacific flows through the Bering Strait, transits the upper levels of the Arctic Ocean, and penetrates to the North Atlantic. Pacific Summer Water (PSW) (flows through the Bering Strait in summer) is a main freshwater source in the Canadian Basin and influences thermohaline structure of the whole Arctic Ocean. Based on the field oceanographic data obtained during 1991-2014 we found the high interannual variability of PSW extent and maximum temperatures of PSW core. Since 1991 the area of PSW distribution decreased and the boundary of PSW extension shifted from the Makarov Basin towards the Canada Basin. At the end of the 2000s the PSW boundary extension returned to approximately early 1990s conditions. Rapid changes in the Arctic wind forcing regime occurred in 2007 led to anomaly extension of the PSW boundary towards the Lomonosov Ridge in 2008. For study the distribution of PSW under the conditions of a lack of field data, we used the modeling data of the GLORYS12V1 product of Copernicus Marine Environment Monitoring Service (http://marine.copernicus.eu/). The model component is the NEMO platform driven at the surface by ECMWF ERA-Interim reanalysis. Based on the calculated data we revealed the maximum temperatures and extension of PSW core in the Arctic Ocean from 1993 to 2018. As a result of comparing of field and calculated data, we found a good correspondence the values of maximum temperatures and the position of the PSW core in the centre of the Canada Basin. For example, in 2011 observed (1.0 °С) and calculated (0.9 °С) maximum temperature of PSW were very close. Based on model data we calculated the heat content of PSW which reached maximum values in recent years. The research was supported by the Ministry of Science and Higher Education of the Russian Federation (project RFMEFI61619X0108).

How to cite: Makhotin, M. and Timokhov, L. A.: Extension of Pacific summer waters in the Arctic Ocean based on field and model data, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10530, https://doi.org/10.5194/egusphere-egu2020-10530, 2020.

In the summer Arctic, bump-like vertical temperature profiles of the upper layer in the Canada Basin suggest a near-surface temperature maximum (NSTM) beneath the mixed layer. This paper concentrates on describing the decadal variance of these NSTMs. Essentially, the temporal evolution of the summer NSTM revealed three decadal phases. The first period is before 2003, when the summer NSTM could rarely be observed except around the marginal of the Canada Basin. The second period is between 2003 and 2015, when the summer NSTM nearly occurred over the whole basin as accelerated decline of summer sea ice. The third period is from 2016 to 2017, when the summer NSTM almost disappeared due to prevailing warm surface water. Furthermore, for the background behind the decadal variance of summer NSTM, linear trends of the September minimum sea ice extent and surface water heat content in the Canada Basin from 2003 to 2017 were –2.75±1.08×10⁴km²yr^–1 and 2.29±1.36MJ m^–2yr^–1, respectively. According to a previous theory, if we assume that the trend of the summer surface water heat content was only contributed by NSTM, it would cause a decrease in sea ice thickness of approximately 13 cm. The analysis partially explains the reason for sea ice decline in recent years.

How to cite: Lin, L. and He, H.: Decadal variance of summer near-surface temperature maximum in Canada Basin of Arctic Ocean, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6853, https://doi.org/10.5194/egusphere-egu2020-6853, 2020.

Knowledge of sea ice state (distribution, characteristics and movement) is interesting both from a practical point of view and for fundamental science. The western part of the Barents Sea is a region of increasing activity – oil and gas exploration may growth in addition to traditional fishing and transport. So theinformation is requested by industry and safety authorities.

Three last years (2017-19) the Arctic Technology Department of the University Centre in Svalbard (UNIS) performed expeditions on MS Polarsyssel in April in the sea ice-marginal zone of the Western Barents Sea, as a part of teaching and research program. In (Marchenko 2018), sea ice maps were compared with observed conditions. The distinguishing feature of ice in this region is the existence of relatively small ice floes (15-30 m wide) up to 5 m in thickness, containing consolidated ice ridges. In (Marchenko 2019) we described several such floes investigated by drilling, laser scanning and ice mechanical tests, on a testing station in the place with very shallow water (20 m) where ice concentrated. In this article, we summarise three years results with more attention for level ice floes and ice floe composition, continuing to feature ice condition in comparison with sea ice maps and satellite images.

These investigations provided a realistic characterization of sea ice in the region and are a valuable addition to the long-term studies of sea ice in the region performed by various institutions.

How to cite: Marchenko, N.: Three years (2017-19) of field observation of the marginal ice the Western Barents Sea, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4043, https://doi.org/10.5194/egusphere-egu2020-4043, 2020.

Rapid decline in seasonal sea ice has been linked to increased surface wave activity and shoreline erosion in the coastal Arctic. This trend poses a risk to communities vulnerable to flooding and storm surges. Here we focus on quantifying the relationship between coastal erosion, increasing wave activity and the role of sea ice in protecting the coast. 

In November 2019, we observed a three day wave event in the Chukchi Sea along the coastal barrier system near Icy Cape, Alaska. The wave event was sampled using multiple drifting SWIFT (Surface Wave Instrument Float with Tracking) buoys, a cross-shore mooring array, and ship-based CTD casts.  This provided datasets for different ice types in both Eulerian and Lagrangian reference frames. Pancake and frazil sea ice near the coast attenuated the incident wave field, such that the significant wave height reduced from 3 to 1.5 m over less than 5 kilometers. The wave data combined with in-situ ice observations and satellite imagery are used to calculate spectral attenuation of wave energy segregated by ice type. Furthermore, observed temperature, mean circulation and surface heat fluxes are used to address the evolution of sea ice throughout the event. 

Supported by the National Science Foundation and the Office of Naval Research. 

How to cite: Hosekova, L., Malila, M., Thomson, J., Kumar, N., Rogers, E. W., Roach, L., and Eidam, E.: Wave and coastal sea ice interaction along the Arctic coast, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6089, https://doi.org/10.5194/egusphere-egu2020-6089, 2020.

How to cite: Chen, M., Xiao, K., Wang, Q., Wang, X., and Zhang, W.: Low-frequency Sea Level Variability and Impact of Recent Sea Ice Decline on the Sea Level Trend in the Arctic Ocean from a High-Resolution Simulation, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8580, https://doi.org/10.5194/egusphere-egu2020-8580, 2020.

During the last 3 decades, the Arctic rivers have increased their discharge around 10%, mainly due to the increase of the global atmospheric temperature. The increase of the river discharge carries higher loads of dissolved organic matter (DOM) and suspended matter (SM) entering to the Arctic Ocean. This results in increased absorption of solar energy in the mixed layer, which can potentially contribute to the general sea ice retreat. Observation based studies (e.g. Bauch et al., 2013) showed correlation between river water discharge and local sea ice melting on the Laptev sea shelf due to the change on the ocean heat. Previous studies are based with a limited number of observations, both in space and in time.

Thanks to the ESA SMOS (Soil Moisture and Ocean Salinity) and NASA SMAP (Soil Moisture Active Passive) missions we have daily the sea surface salinity (SSS) maps from the Arctic, which permit to observe the salinity variations due to the river discharges. The Arctic sea surface salinity products obtained from SMOS measurements have been improved considerable by the Barcelona Expert Center (BEC) team thanks to the project Arctic+Salinity, funded by ESA. The new version of the product (v3) covers the years from 2011 up to 2018, have a spatial resolution of 25km and are daily maps with 9 day averages. The Arctic+ SSS maps provide a better description of the salinity gradients and a better effective spatial resolution than the previous versions of the Arctic product, so the salinity fronts are better resolved. The quality assessment of the Arctic+SSS product is challenging because, in this region, there are scarce number of in-situ measurements.

The high effective spatial resolution of the Arctic+ SSS maps will permit to study for the first time scientific physical processes that occurs in the Arctic. We will explore if a correlation between the Lena and Ob rivers discharge with the sea ice melting and freeze up is observed with satellite data, as already stated with in-situ measurements by Bauch et al. 2013. Salinity and sea ice thickness maps from SMOS and sea ice concentration from OSISAF will be used in this study.

Bauch, D.,Hölemann, J. , Nikulina, A. , Wegner, C., Janout, M., Timokhov, L. and Kassens, H. (2013): Correlation of river water and local sea-ice melting on the Laptev Sea shelf (Siberian Arctic) , Journal of Geophysical Research C: Oceans, 118 (1), pp. 550-561 . doi: 10.1002/jgrc.20076

How to cite: Gabarro, C., Martinez, J., Gonzalez-Gambau, V., González-Haro, C., Olmedo, E., Turiel, A., Bertino, L., Xie, J., Raj, R., Catany, R., Arias, M., Sabia, R., and Fernandez, D.: Correlation between Arctic river discharge and sea ice formation in Laptev Sea using sea surface salinity from SMOS satellite, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10052, https://doi.org/10.5194/egusphere-egu2020-10052, 2020.

The Laptev Sea is influenced by synoptic regions of the Atlantic-Eurasian sector of the Northern Hemisphere. Types of large-scale processes are consider according to the G. J. Vangengeim typization: West (W) circulation form, with dominating zonal transport of air masses, East (E) and meridional (C) circulation forms with opposite phases of geographic orientation in the troposphere of the anticyclones ridges axes, blocking the Western transfer of air masses and developing the meridional circulation at high and middle latitudes. The Laptev Sea ice extent at the end of the melting season has a strong interannual variability, the oscillations amplitude reaches 86%.

The paper considers analysis of long-term trends of the large-scale atmosphere processes realignment and multiyear variability of the air temperature and ice cover anomalies in the Laptev Sea. According to multiyear course of integral anomalies values four steady periods of homogeneous  tendency of climatic processes revealed and described for data series from 1942 to 2019 (air reconnaissance and satellite data).

The types of ice conditions development (severe, medium, mild) at the end of the melting season were determined for the entire series of observations. More than half of cases during 78 years are distinguished as medium type of ice conditions. The repeatability of severe and mild types is almost the same numerically but varies in time according to revealed periods.

During 1942-1947 years in the Laptev Sea the “warming” period occurred (same for the whole polar region), known as the warming of the Arctic of 30th. At this period positive temperature anomalies and negative anomalies of sea ice extent (mean -2%) were dominated. During subsequent period 1948-1989 years the positive temperature trend has changed to the steady negative. The most dramatic temperature drops were observed in the 60-70^th. Positive ice anomalies increased (mean 9%), in August Laptev Sea remained mostly covered by ice. Of the 42 years 28 refer to the medium type of ice conditions, 11 to the severe. During the period 1990-2004 years frequent interannual rearrangements of the atmosphere circulation and multidirectional fluctuations of temperature and ice cover anomalies were observed. On average, the temperature and ice cover during the period are close to the long-term norm. After 2005 temperature regime in the polar climate system has changed. This period is the warmest for the whole observations series in the Laptev Sea. Ice extent at the end of the melting season steady decreases and shows dramatic growth of negative anomalies values and occur of extremely low anomaly for the entire observation period (up to -54-55%). The average negative ice anomaly for the period is -26.4 %. Of the 15 years 9 refer to the mild type of ice conditions.

How to cite: Timofeeva, A., Ivanov, V., Yulin, A., and Khotchenkov, S.: Multiyear variability of atmospheric processes and ice cover in the Laptev Sea since 1942 to 2019, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12269, https://doi.org/10.5194/egusphere-egu2020-12269, 2020.

The Arctic has been rapidly changing over the last decade, with more frequent unusually early ice retreats in late spring and summer. Vast Arctic areas that were usually covered by sea ice are now exposed to the atmosphere because of earlier ice retreat and later arrival. Assessment of consequential changes in the energy cycle of the Arctic and their potential feedback to the variability of Arctic sea ice and marine ecosystems critically depends on the accuracy of surface flux estimates. In the Pacific sector of the Arctic, earlier ice retreat generally follows the warm Pacific water inflow into the Arctic through the Bering and Chukchi Seas. Due to ice coverage and irregularity of seasonal ice retreats, air-sea flux measurements following the ice retreats has been difficult to plan and execute. A recent technology development is the Unmanned Surface Vehicles (USVs): The long-range USV saildrones are powered by green energy with wind for propulsion and solar energy for instrumentation and vehicle control. NOAA/PMEL and University of Washington scientists have made surface measurements of the ocean and atmosphere in the Pacific Arctic using saildrones for the past several years. In 2019, for the 1^st time a fleet of six saildrones capable of measuring both turbulent and radiative heat fluxes, wind stress, air-sea CO₂ flux and upper ocean currents was deployed to follow the ice retreat from May to October, with five of the USVs into the Chukchi and Beaufort Seas while one staying in the Bering Sea. These in situ measurements provide rare opportunities of estimating air-sea energy fluxes during a period of rapid reduction in Arctic sea ice in different scenarios: open water after ice melt, free-floating ice bands, and marginal ice zones. In this study, Arctic air-sea heat and momentum fluxes measured by the saildrones are compared to gridded flux products based on satellite data and numerical models to investigate the circumstances under which they agree and differ, and the main sources of their discrepancies. The results will quantify the uncertainty margins in the gridded flux products and provide insights needed to improve their accuracy. We will also discuss the feasibility of using USVs in sustained Arctic observing system to collect benchmark datasets of the changing surface energy fluxes due to rapid sea ice reduction and provide real time data for improved weather and ocean forecasts.  

How to cite: Zhang, D., Zhang, C., Cross, J., Mordy, C., Cokelet, E., Gentemann, C., Chiodi, A., Stabeno, P., Jenkins, R., Meinig, C., Lawrence-Slava, N., Tabisola, H., and Wang, M.: Air-Sea Fluxes following the Unusually Early Ice Retreats in the Arctic, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20077, https://doi.org/10.5194/egusphere-egu2020-20077, 2020.

We present analysis of Arctic sea ice and ocean dynamics in the ensemble of the UK Earth System Model (UK ESM1) simulations completed under the Coupled Model Intercomparison Project Phase 6 (CMIP6) protocol. The focus of the investigation is on the future changes in the Arctic sea ice and oceanic connections and on the impact of the nutrient advection on the Arctic marine biogeochemistry and ecosystems. Changes in the balance of the oceanic inflows from the North Atlantic and North Pacific Oceans are found to have a first order effect on the watermasses and nutrients balances in the central Arctic Ocean. The simulations show that the total primary production in the Arctic Ocean is increased by 100% in the 2090s as compared to the present climate. This is caused by higher nutrients availability in the Atlantic inflowing waters and prolonged ice- free season. The faster connections through the Arctic and milder oceanic environment allows species to survive through the winter and from the second half of the century the Arctic Ocean could become a key oceanic gateway connecting the global oceans. The study is supported from the project APEAR (NE/R012865/1) NERC-BMBF and from the NERC ACSIS Programme (NE/N018044/1).

How to cite: Aksenov, Y., Yool, A., Palmieri, J., Popova, K., Kelly, S., Rynders, S., Schroeder, D., and Sinha, B.: Arctic connections between sea ice, ocean dynamics and biogeochemistry in the UK Earth System Model (UK ESM1): present climate and future scenarios, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8178, https://doi.org/10.5194/egusphere-egu2020-8178, 2020.

Sea ice is a crucial component of the Earth’s climate system, which helps regulate global ocean and atmosphere’s temperature. The alarming decline in sea-ice extent and thickness under modern climate conditions has created the urgency to understand the long-term sea-ice variability and mechanisms of change. In recent years, the highly branched isoprenoid (HBI) lipid biomarker IP₂₅ has emerged as a powerful proxy measure of past sea ice in the Arctic, and its analysis in a variety of marine sediments has provided the foundation for a large number of palaeo sea ice reconstructions spanning thousands to millions of years before present. To date, IP₂₅ and related HBI-based studies have focussed largely on reconstructions of sea-ice extent and seasonal dynamics. Here we aim to further develop such sea ice proxies by measuring the changes in distribution and isotopic composition of HBIs in HBI-producing diatoms grown under different controlled laboratory conditions. We present preliminary results from the diatom Haslea ostrearia and outline the next steps of our research in the coming year.

How to cite: Sánchez-Montes, M. L., Pedentchouk, N., Mock, T., Belt, S., and Smik, L.: Further development on sea-ice HBI biomarker proxies., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17906, https://doi.org/10.5194/egusphere-egu2020-17906, 2020.