Everything that happens in the Arctic Ocean, be it of physical, biological, or chemical nature, is constrained by the vertical distribution of heat and salt. In this talk, I will share recent results and on-going work aimed at examining questions directly related to vertical mixing below sea ice: (1) How accurately are the physical properties of the Canada Basin simulated in climate models? (2) How do observed changes to the size and speed of a sea ice floe and ocean stratification impact ocean mixing in 2D numerical simulations? (3) Can we, for the first time, examine seasonal ice-ocean boundary layer dynamics in a 20 m × 10 m × 3 m outdoor saltwater pool?

Our results indicate that the majority of climate models do not accurately simulate the surface freshening trend observed in the Canada Basin between 1975 and 2006-2012, nor do they simulate heat from Pacific Water in the same region. We suggest that both of these biases can be partly attributed to unrealistically deep vertical mixing in the models. We next explore one possible source of this model bias related to decadal changes to the underside of ice floes, called ice keels. Results from idealized numerical simulations highlight the importance of ice keel depth, which controls the range over which ocean mixing occurs, as well as ice keel speed and ocean stratification. Further, we estimate that observational uncertainties related to ice keel depth may translate into uncertainties in the sign of current and future changes to below-ice momentum transfer into the ocean. Lastly, we present the instrument setup for our 2022-2023 pilot experiment and on-going outreach work at the Sea-ice Environmental Research Facility (SERF) in Canada. This is a unique facility centres around an outdoor saltwater pool where sea ice evolves under natural atmospheric conditions in a semi-idealized and well-instrumented setting.

How to cite: Rosenblum, E. and the Team: Exploring ice-ocean boundary layer dynamics in climate models, idealized simulations, and outdoor lab experiments, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10302, https://doi.org/10.5194/egusphere-egu23-10302, 2023.

Arctic regions are warming at a rate faster than the global average. Superimposed on this trend, marine heatwaves and other extreme events are becoming more frequent and intense. Simultaneously the sea ice phenology with which these events interact is also changing. While sea ice can absorb atmospheric heat by melting and therefore acts as a heat buffer for the ocean, meltwater-induced stratification and albedo changes can provoke positive feedbacks on the heat content of the upper ocean. Disentangling those effects is key to better understanding and predicting the present and future state of the Arctic Ocean, including how it responds to forcing by extreme events. Using a three-dimensional regional ice-ocean coupled numerical model, we calculate a two-layer heat budget for the surface mixed layer of the Arctic Ocean, using a novel approach for the treatment of residuals. We present a statistical overview of the dominant drivers of marine heatwaves at the regional scale as well as more in-depth analyses of specific events in key regions of interest. The characteristics of marine heatwaves under different sea ice conditions is also considered, to identify anomalous ice-ocean interactions. Finally, potential feedback mechanisms are investigated to verify their existence and quantify their importance.

How to cite: Richaud, B., Oliver, E. C. J., Hu, X., Darmaraki, S., and Fennel, K.: Marine Heatwaves in the Arctic Ocean: drivers, feedback mechanisms and interactions with sea ice, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5780, https://doi.org/10.5194/egusphere-egu23-5780, 2023.

Arctic Amplification (AA) – the greater warming of the Arctic than the global average - is a prominent feature of past and projected future climate change. AA exists due to multiple positive feedbacks involving complex interactions among different components of Arctic atmosphere, ocean, and cryosphere. The loss of sea ice is a key driver of AA. Sea ice loss and resultant AA can influence the global climate system, way beyond the Arctic. The atmospheric response to sea ice loss has been studied extensively. In comparison, the oceanic response has received less attention and our understanding of it is imprecise. Here, we utilize the fully coupled model simulations from the Polar Amplification Model Comparison Project (PAMIP) to explore the oceanic response to projected Arctic sea ice loss at 2^o C global warming.

The sea surface warming signal is maximum in the Barents-Kara Sea region in all three models analysed. Results suggest that the observed northward propagation of the Arctic ‘cooling machine’ (region of intensive heat loss to the atmosphere) is largely driven by the reduced sea ice over the northern Barents Sea. Simultaneously, the atmospheric response with stronger south-westerlies over the Norwegian Seas and southern Barents Sea reduces the heat loss therein. This may partly explain the bipolar spatial structure of heat loss in the Norwegian seas and the Northern Barents-Kara Sea. This seesaw heat loss pattern can result in a warmer inflow of Atlantic Waters from the Norwegian Sea to the northern Barents Sea as projected by CMIP6 models. The mixed layer depth response in these regions is consistent with the heat loss patterns, with a deepening of the mixed layer in regions of enhanced heat loss and vice versa. The surface ocean dynamic response is most prominent in the Beaufort Sea. With reduced sea ice, the Beaufort gyre circulation is strengthened due to larger wind forcing and accumulates freshwater within. As a result, surface salinity response shows maximum freshening in this region. In summary, preliminary results from the coupled simulations under the PAMIP protocol indicate that the observed and projected changes in the Arctic Ocean during the 21st century are strongly driven by the reduction in sea ice.

How to cite: Chatterjee, S., Selivanova, J., Semmler, T., and Screen, J. A.: Ocean response to reduced Arctic sea ice in PAMIP simulations., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4822, https://doi.org/10.5194/egusphere-egu23-4822, 2023.

The Arctic sea ice cover is strongly influenced by internal variability on decadal time scales, affecting both short-term trends and the timing of the first ice-free summer. Several mechanisms of variability have been proposed, but the contributions of distinct modes of decadal variability to regional and pan-Arctic sea-ice trends has not been quantified in a consistent manner. The relative contribution of forced and unforced variability in observed Arctic sea ice changes also remains poorly quantified. Here, we identify the dominant patterns of winter and summer decadal Arctic sea-ice variability in the satellite record and their underlying mechanisms using a novel technique called low-frequency component analysis. The identified patterns account for most of the observed regional sea ice variability and trends, and thus help to disentangle the role of forced and unforced sea ice changes since 1979. In particular, we separate a mode of decadal ocean-atmosphere-sea ice variability, with an anomalous atmospheric circulation over the central Arctic, that accounts for approximately 30-50% of the accelerated decline in pan-Arctic summer sea-ice area between 2000 and 2012. For winter, we find that internal variability has so far dominated decadal trends in the Bering Sea, while it plays a smaller role in the Barents and Kara Seas. These results, which detail the first purely observation-based estimate of the contribution of internal variability to decadal trends in sea ice, suggest a lower estimate of the internal variability contribution than most model-based assessments.

How to cite: Dörr, J., Årthun, M., Bonan, D. B., and Wills, R. C. J.: Modes of decadal variability in observed Arctic sea-ice concentration, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4159, https://doi.org/10.5194/egusphere-egu23-4159, 2023.

The sea ice extent in the Arctic Ocean has reduced dramatically with the last 16 years (2007-2022) showing the 16 lowest September extents observed in the satellite era. Besides a declining sea ice cover and increase in ocean heat content in summer, the winter sea ice concentration and thickness have also become more vulnerable to changes. We present results from the Fram Strait Arctic Outflow Observatory showing that the upper ocean temperature in the East Greenland Current in the Fram Strait has increased significantly between 2003 and 2019. While the cold Polar Water now contains more heat in summer due to lower sea ice concentration and longer periods of open water upstream, the warmer returning Atlantic Water has shown a greater presence in winter the central Fram Strait, impacting the winter sea ice thickness and sea ice extent. These processes combined result in a reduced sea ice cover downstream along the whole east coast of Greenland both in summer and winter, which has consequences for winter-time ocean convection in the Greenland Sea.

How to cite: de Steur, L., Sumata, H., Divine, D., Granskog, M., and Pavlova, O.: Ocean heat increase and sea ice reduction in the Fram Strait conveys Arctic Ocean change, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3465, https://doi.org/10.5194/egusphere-egu23-3465, 2023.

Black carbon (BC) is one of the most important absorbing particles in the atmosphere. BC can reduce the albedo of snow/ice and enhance the absorption of solar radiation at ultraviolet (UV) and visible wavelengths when it deposited on snow/ice surface. The deposition of BC can lead to an acceleration of the melting of snow/ice. To quantify the changing process of BC in snow/ice and its contribution to the melting of snow/ice, a series of sensitivity numerical experiments including the impacts of BC species (hydrophobic and hydrophilic), deposition rate, and scavenging efficiency of BC was completed using the Icepack one-dimensional column model of CICE. Further, we evaluate the effects of BC deposition on Arctic albedo and ice thickness, forced by ERA5 reanalysis data and BC deposition rate from CMIP6, including two simulation results of the historical experiments with GISS-E2 model and EC-Earth3 model. The results indicate that the hydrophobic BC can cause a reduction of snow/ice albedo by 0.43% in the melting season, which is 35% larger than hydrophilic BC with the same deposition rate. When only the hydrophilic BC was considered, the impact on scavenging efficiency halved to BC content in snow/ice is similar to double the deposition rate in the melting season. Additionally, the 2D model results indicate that the existence of BC in snow could enhance the absorption of solar radiation in the snow layer and reduce the transmittance of radiation to the ice layer, leading to a thicker ice thickness before the melting season. The thermodynamic impact of BC is more significant in the marginal ice zone than that in the central Arctic, especially from Barents Sea to Laptev Sea. In this paper, we quantify the effects of BC on the melting of Arctic snow and sea ice and discuss the problems of the parameterizations of BC’s effect. This may contribute to the improvement of the sea ice model.

Key words: Black carbon; CICE model; Sensitivity experiment; Scavenging efficiency; Albedo

How to cite: Wang, Y. and Su, J.: Sensitivity study of the effects of black carbon on Arctic sea ice using CICE sea-ice model, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10572, https://doi.org/10.5194/egusphere-egu23-10572, 2023.

Historically, the Arctic Ocean has been considered an ocean of weak turbulent mixing. However, the decline in seasonal sea ice cover over the past couple of decades has led to increased coupling between the atmosphere and the ocean, with potential enhancement of turbulent mixing. Here, we review studies identifying energy sources and pathways that lead to turbulent mixing in an increasingly ice-free Arctic Ocean. We find the evolution of wind-generated, near-inertial oscillations is highly sensitive to the seasonal sea ice cycle, but that the response varies greatly between the continental shelves and the abyssal ocean. There is growing evidence of the key role of tides and continental shelf waves in driving turbulent mixing over sloping topography. Both dissipate through the development of unsteady lee waves. The importance of the dissipation of unsteady lee waves in driving mixing highlights the need for parameterization of this process in regional ocean models and climate simulations.

How to cite: Rippeth, T. P.: An increasingly turbulent Arctic Ocean?, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3547, https://doi.org/10.5194/egusphere-egu23-3547, 2023.

How to cite: Waterman, S., Dosser, H., Chanona, M., Shibley, N., and Timmermans, M.-L.: Arctic Ocean mixing maps inferred from pan-Arctic observations, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12658, https://doi.org/10.5194/egusphere-egu23-12658, 2023.

Our aim is to better understand how local winter modification and advected signals from the Siberian Shelf affect the structure of the upper Arctic Ocean along the Transpolar Drift (TPD). Hereto we use stable oxygen isotopes of the water (δ¹⁸O) in combination with salinity to quantify river water contributions (fr) and changes due to sea-ice formation or melting (fi) in the upper ~150m of the water column during the MOSAIC drift. Furthermore, ratios of fi/fr at identical salinities can be used to distinguish waters remnant from the previous summer and those modified locally.

Within the ongoing winter we observed salinification and deepening of the mixed layer (ML) due to sea-ice related brine release together with interleaving waters at the base of the ML and within the main halocline. These interleaving waters with variable sea-ice and river water signals are observed for the first time and have not been observed during summer expeditions before.

The MOSAIC floe drifted in and out of the freshwater-rich part of the TPD and into the Atlantic regime throughout the winter. Despite these strong regime changes the sea-ice related brine content accumulated during the ongoing winter remained visible within the water column. Budgets derived by integration of signals over the upper 100m result in ~1 to 5 m of pure sea-water (34.92 salinity and 0.3‰ δ¹⁸O) removed from the water column for ice formation and are much higher than ice thicknesses of ~0.5 to 2 m observed for the MOSAIC floe. For further evaluation scaling factors have to be considered accounting e.g. for the different densities of ice and water as well as for the lower salinity in the halocline relative to pure sea-water. Therefore, our analysis indicates a lower limit of the advected signal relative to local winter modification within the Arctic Ocean halocline.

How to cite: Bauch, D., Andersen, N., Damm, E., D'Angelo, A., Fang, Y., Kuznetsov, I., Laukert, G., Mellat, M., Meyer, H., Rabe, B., Schaffer, J., Schulz, K., Tippenhauer, S., and Vredenborg, M.: Stable oxygen isotopes from the MOSAIC expedition show vertical and horizontal variability of sea-ice and river water signals in the upper Arctic Ocean during winter, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3244, https://doi.org/10.5194/egusphere-egu23-3244, 2023.

Timescales of ventilation of the Arctic Ocean are still only poorly known. The commonly used tracers for ocean ventilation studies like CFCs and SF₆ are limited to young water masses that are either close to the surface or in highly ventilated deep waters. The radioisotope ³⁹Ar with its half-life of 269 years covers time scales of 50 to 1000 years, perfectly suitable to investigate ventilation timescales of deep and intermediate water masses within the Arctic Ocean. The new measurement technique called Argon Trap Trace Analysis (ArTTA) only requires samples sizes of a few liters of ocean water, instead of the previous low-level counting method, which required about 1000 liters of water. The benefit for ocean studies is evident, much more samples can be taken during one cruise if ArTTA is applied. This enables a better resolution of the water column in great depths at the desired sampling location in the Arctic Ocean. Combined with the additional data of the CFC-12 and SF₆ measurements, ventilation timescales of the complete water column from surface to bottom are obtained by constraining transit time distributions via this multi-tracer approach.

Another focus of this study is the saturation of all gaseous transient tracers. It is determined by surface conditions as well as interior mixing processes. Measurements of stable noble gas isotopes (He, Ne, Ar, Kr, Xe) are used to determine possible saturation anomalies that arise during air bubble dissolution, rapid cooling and subduction, or ice formation and subsequent interior mixing of water masses. These saturation distortions for different boundary conditions are of key importance to correct the input function for gas tracers in the Arctic Ocean and hence to constrain the ventilation timescales. The uncertainty of the age distributions will be reduced, and ocean circulation models can be improved.

This contribution presents first stable and radioactive noble gas results of the project Ventilation and Anthropogenic Carbon in the Arctic Ocean (VACAO), which is part of the Synoptic Arctic Survey carried out in summer 2021 on the Swedish icebreaker Oden.

How to cite: Arck, Y., Gerke, L., Engelhardt, E., Freundt, F., Robertz, J., Scott, S., Wachs, D., Oberthaler, M., Tanhua, T., and Aeschbach, W.: Investigating ventilation and saturation dynamics in the Arctic Ocean using noble gas tracer techniques, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6699, https://doi.org/10.5194/egusphere-egu23-6699, 2023.

At present, it is well-known that the fast increase in atmospheric carbon dioxide (CO₂) concentrations resulting from human activities (C_ant), drives the dramatic changes observed in our environment such as global warming and ocean acidification. The Arctic Ocean has been identified as one of the fastest-changing regions of the world ocean and can therefore be considered as a sentinel for future global scenarios.

Here, C_ant-rich waters coming from the Atlantic Ocean become isolated from the atmospheric input of CO₂ as they flow at an intermediate depth below the mixed layer, making the Arctic Ocean a key region for intermediate-to-long-term storage of C_ant. Despite having such an important role, the magnitude of the C_ant inventory and its change over time in the region is yet not fully understood, particularly if we are to consider future changes in ice coverage and therefore ocean circulation.

A way of estimating oceanic C_ant inventories is by applying the so-called Transit Time Distribution (TTD) method, which implies the use of transient tracers such as the anthropogenically produced CFC-12 and SF₆.

In this work we present a new estimate of C_ant inventory for the Arctic Ocean in 2015 assessed with the TTD method using both well-established tracers (CFC-12 and SF₆, both having a global source) as well as novel ones (anthropogenic radionuclides ¹²⁹I and ²³⁶U, both having primarily a point-like source represented by European nuclear reprocessing plants, as well as a global one represented by the global fallout from nuclear bomb testing).

The TTD was here applied following a relatively novel approach to infer the statistical parameters that describe the age distribution within a water sample, the mean (G) and the width (D). Unlike the “classical TTD” approach, the one used in this study allows the statistical parameters of the TTD to be constrained for each individual sample rather than finding values that are most representative of the region and time studied. We first show a comparison of the two TTD approaches by comparing mean and mode ages as well D/G ratios of this study (new TTD method) to those presented in Rajasakaren et al. 2019 (classical TTD method), using CFC-12 and SF₆ as our tracers’ pair. We then compare TTD results obtained from the two tracers’ pairs, CFC-12/SF₆ and ¹²⁹I-/²³⁶U, using the new TTD method.

Finally, we estimate and compare C_ant concentrations and inventories obtained with the two pairs of transient tracers to one-another as well as to previous estimates of C_ant in the region by Rajasakaren et al (2019) obtained with the “classical TTD”. This study demonstrates for the first time the feasibility of using anthropogenically produced radionuclides with input functions and chemical properties different than CO₂ as proxies for C_ant estimates.  

How to cite: Raimondi, L., Wefing, A.-M., and Casacuberta Arola, N.: Anthropogenic Carbon in the Arctic Ocean: Perspectives from different TTD Approaches and Tracer Pairs, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12032, https://doi.org/10.5194/egusphere-egu23-12032, 2023.

Arctic surface air temperatures are warming twice as fast as global average temperatures. This has caused ocean warming, an intensification of the hydrological cycle, snow and ice melt, and increases in river runoff. Rivers play a central role in linking the components of the water cycle and Russian rivers alone contribute ~1/4 of the total freshwater to the Arctic Ocean, maintaining the halocline that covers the Arctic and dominates circulation. Increases in river runoff could further freshen this layer and increase Arctic Ocean stratification. However, the increase in atmosphere-ocean momentum transfer with sea ice loss could counteract or alter this pattern of circulation, mixing this cold fresh water with the warm salty water that currently sits below it. Understanding the interplay between these changes is crucial for predicting the future state of the Arctic system. Historically, studies trying to understand the interplay between these changes have been challenged by the difficulty of collecting in situ data in this region.

Over most of the globe, L-band satellite acquisitions of sea surface salinity (SSS), such as from Aquarius (2011–2015), SMOS (2010- present), and SMAP (2015-present), provide an idea tool to study freshwater storage and transport. However, the low sensitivity of L-band signal in cold water and the presence of sea ice makes retrievals at high latitudes a challenge. Nevertheless, retreating Arctic sea ice cover and continuous progress in satellite product development make the satellite based SSS measurements of great value in the Arctic. This is particularly evident in the Laptev Sea, where gradients in SSS are strong and in situ measurements are sparse. Previous work has demonstrated a good consistency of satellite based SSS data against in situ measurements, enabling greater confidence in acquisitions and making satellite SSS data a truly viable potential in the Arctic. Therefore, this project aims to combine satellite data, particularly SMAP and SMOS sea surface salinity (SSS) data, with model output to improve our understanding of interactions between the components of the Arctic hydrological cycle and how this is changing with our changing climate.

The Laptev Sea was chosen as an initial region of focus for analysis as the Lena river outflows as a large, shallow plume, which is clearly observable from satellite SSS data. The spatial pattern of the Lena river plume varies considerably interannually, responding to variability in atmospheric and oceanic forcing, sea ice extent, and in the magnitude of river runoff.  Numerical model output and satellite products confirm what has previously been suggested from in-situ data: wind forcing is the main driver of river plume variability.

How to cite: Hudson, P., Martin, A., Josey, S., Marzocchi, A., and Angeloudis, A.: Drivers of Laptev Sea interannual variability in salinity and temperature from satellite data, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2446, https://doi.org/10.5194/egusphere-egu23-2446, 2023.

The Arctic Ocean has undergone a rapid decrease of sea ice extent for decades and studies have shown that the storm activity has increased in the Arctic. Regions that are seasonally ice-opened experience a greater forcing at the surface, which affects the upper-ocean through mixing, turbulence and air-sea interactions. Previous studies have shown the local and short term impacts of wind and waves on sea ice through negative or positive feedback mechanisms. For instance, increased air-sea flux during the freezing season can lead to a cooling of the upper-ocean and favor ice formation, while an increase in wind forcing can modify the vertical profile of the mixed layer, leading to melting or formation of ice. Given the potential of the mixed layer properties to be modified locally by an increased wind/wave forcing, we question whether this type of forcing could have a seasonal effect on the mixed layer and therefore on the sea ice.

We thus use a 1D coupled ocean-sea ice model (NEMO1D-SI³) to study, in the seasonal ice zone of the Beaufort Sea, the immediate change and the seasonal evolution of the mixed layer when forced by an idealized summer storm. The response of sea ice is also examined. We conduct the experiment for a range of storms varying in intensity, duration and date of forcing. Compared to a situation with no increased forcing, we first find that summer storms thicken the mixed layer through mixing which increases the upper-ocean heat content. In the fall, ice formation is consequently delayed for a maximum of 2 weeks compared to a situation with no increased forcing. Secondly, we show that storm-induced thick mixed layers isolate the sea ice from sub-surface warm waters, allowing for efficient ice growth. Ice is consequently thicker at the end of winter compared to a situation with no increased forcing (maximum difference of 10 cm). Thirdly, we find that these results are amplified for storms that happen earlier in summer and have a strong momentum input to the ocean. Our results suggest that localized storms could be a significant driver of the seasonal evolution of the mixed layer and the sea ice.

How to cite: Bent, E., Lique, C., and Sutherland, P.: Impact of an isolated summer storm on sea ice and ocean conditions in the Canadian Basin, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6564, https://doi.org/10.5194/egusphere-egu23-6564, 2023.

The NASA Salinity and Stratification at the Sea Ice Edge (SASSIE) field campaign took during place between August and October of 2022. Using three major components, the aim is to understand the relationship between both haline and thermal stratification and sea-ice advance, and to test the hypothesis that a significant fresh layer at the surface can accelerate the formation of sea ice by limiting convective processes. The three components of the field campaign include: 1) A one-month shipboard hydrographic and atmospheric survey in the Beaufort Sea, 2) A concurrent airborne campaign to observe ocean salinity, temperature, and other parameters from a low-flying aircraft, and 3) The deployment of autonomous assets, buoys, and floats that are able to observe both the melt season and the sea ice advance.

Here, we focus on the novel results from the month-long research cruise aboard the R/V Woldstad that took place during September and October of 2022, particularly measurements of salinity and temperature at radiometric depths (1-2 cm) from the salinity snake instrument. These measurements will be contextualized with all other components of the cruise, including uCTD, air-sea flux, airborne, and satellite data to examine the effects of stratification on ocean dynamics in the Beaufort Sea near at the sea ice edge.

How to cite: Schanze, J. and the Salinity and Stratification at the Sea Ice Edge (SASSIE): A First Look at Surface Ocean Measurements during the SASSIE Field Campaign in 2022, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10871, https://doi.org/10.5194/egusphere-egu23-10871, 2023.