CR7.4 | Atmosphere-ocean-sea ice interactions in the polar climate system
Atmosphere-ocean-sea ice interactions in the polar climate system
Co-organized by CL2
Convener: Priscilla Mooney | Co-conveners: Jennie L. Thomas, Risto Makkonen
Orals
| Wed, 26 Apr, 10:45–12:30 (CEST)
 
Room 1.14
Posters on site
| Attendance Tue, 25 Apr, 14:00–15:45 (CEST)
 
Hall X5
Posters virtual
| Attendance Tue, 25 Apr, 14:00–15:45 (CEST)
 
vHall CR/OS
Orals |
Wed, 10:45
Tue, 14:00
Tue, 14:00
The interactions between the atmosphere, ocean and sea ice play an important role in shaping the polar climates. However, existing knowledge of the physical, chemical, and biogeochemical processes that underly the exchanges of mass, energy and momentum between these components remain poorly understood.

Closing knowledge gaps on the interactions between the atmosphere, ocean and sea-ice can considerably advance our ability to understand recent changes, and anticipate future changes in the Arctic and Antarctic climate systems. In particular, closing these knowledge gaps will improve our ability to represent them in our modelling systems and increase confidence in projections of future climate change in the polar regions.

This session will highlight 1) recent advances in our knowledge of atmosphere-ocean-sea ice interactions and 2) new and emerging tools and datasets that can close these knowledge gaps.

We welcome observational and numerical modelling studies of physical and chemical atmospheric and ocean processes that underly interactions in the coupled climate system in both the Arctic and Antarctic. This includes but is not limited to:

Cloud microphysics and aerosol-cloud interactions, and their role in the coupled system;
Atmospheric Boundary Layer (ABL) dynamics and its interactions with the sea-ice surface;
Sea ice dynamics and thermodynamics, e.g. wind driven sea-ice drift, snow on ice;
Upper ocean mixing processes;
Sea ice biogeochemistry and interactions at interfaces with sea ice;
Snow on sea ice and it’s role in the coupled ocean-ice-atmosphere system;
Surface energy budget of the coupled system, including contributions of ABL-dependent turbulent fluxes, clouds and radiative fluxes, precipitation and factors controlling snow/sea ice albedo.
Presentations showcasing recent or emerging tools, observational campaigns, or remote sensing datasets are encouraged.

Orals: Wed, 26 Apr | Room 1.14

Chairpersons: Priscilla Mooney, Jennie L. Thomas
10:45–10:50
10:50–11:00
|
EGU23-6309
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Virtual presentation
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Hiroshi Sumata, Laura de Steur, Dmitry Divine, Mats Granskog, and Sebastian Gerland

Fram Strait is an ideal location to monitor long-term changes of sea ice properties in the central Arctic since the major fraction of ice export from the Arctic occurs here. The Fram Strait Arctic Outflow observatory has been monitoring sea ice and ocean outflows at ~79°N for the last three decades. We examined changes of monthly mean sea ice thickness distributions obtained from upward looking sonars deployed in the observatory. We found that the thickness distributions can be reasonably approximated by lognormal functions except for fractions of very thin ice classes. We fitted the observed distributions with lognormal functions and used three parameters of the functions (modal thickness, modal peak height and variance) to describe the long-term changes of the thickness distribution. We found that these parameters exhibit a concurrent change and indicate a shift of the Arctic sea ice regime. The first regime is represented by a thick and deformed ice pack, described by thicker modal thickness with a smaller and more broad modal peak with larger variance of the distribution. The second regime has a thinner and more uniform ice cover, represented by thinner modal thickness with more compact distribution around the mode and smaller fraction of deformed ice. We examine factors causing this shift and introduce a stochastic sea ice thickening model which can explain the change of the ice thickness distribution.

How to cite: Sumata, H., de Steur, L., Divine, D., Granskog, M., and Gerland, S.: Changes in Arctic sea ice thickness distribution in Fram Strait over the last three decades, 1990 – 2019, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6309, https://doi.org/10.5194/egusphere-egu23-6309, 2023.

11:00–11:10
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EGU23-2377
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ECS
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On-site presentation
Assia Arouf, Hélène Chepfer, Jennifer E. Kay, Tristan S. L’Ecuyer, and Jean Lac

During the Arctic night, clouds regulate surface energy budgets through longwave warming alone. During fall, any increase in low-level opaque clouds will increase surface cloud warming and could potentially delay sea ice formation. While more clouds due to fall sea ice loss have been observed, quantifying the surface warming caused by these cloud increases is observationally challenging. Here, we quantify surface cloud warming using spaceborne lidar observations. By instantaneously co-locating surface cloud warming and sea ice observations in regions where sea ice varies, we find October large surface cloud warming values (> 80 W m −2) are much more frequent (~+50%) over open water than over sea ice. Notably, in November large surface cloud warming values (> 80 W m −2) occur more frequently (∼+200%) over open water than over sea ice. These results suggest more surface warming caused by low-level opaque clouds in the future as open water persists later into the fall.

How to cite: Arouf, A., Chepfer, H., Kay, J. E., L’Ecuyer, T. S., and Lac, J.: Quantifying surface cloud warming increase as Fall Arctic sea ice cover decreases, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2377, https://doi.org/10.5194/egusphere-egu23-2377, 2023.

11:10–11:20
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EGU23-13126
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Virtual presentation
|
Emily Down and Thomas Lavergne

Sea-ice drift is a key variable for understanding sea ice in a changing climate, and an Essential Climate Variable (ECV) product for the Global Climate Observing System (GCOS). In the Arctic, sea ice has been reported to drift faster in recent years (e.g. Rampal et al., 2009), associated with its reduction in area, thinning, and loss of multiyear ice. In the Antarctic, trends in sea-ice drift have been linked to trends in wind patterns (e.g. Hollands and Kwok, 2012). 

In this contribution, we present a new 30-year Climate Data Record (CDR) of global, year-round sea-ice drift vectors covering 1991 to 2020. This uses the continuous maximum cross-correlation technique (CMCC) for measuring sea-ice drift from pairs of brightness temperature images of passive microwave satellite missions (Lavergne et al., 2010). During summer, this technique becomes less accurate due to surface melting and higher atmospheric humidity. We therefore employ a parametric free-drift model to fill the data gaps in the summer. This model calculates the ice drift based on wind vectors from the ERA5 wind reanalysis, under the assumption that the internal stresses of the ice can be neglected. We describe the algorithm baseline for the new CDR as well as results of validation against the sparse network of on-ice buoy trajectories. We finally describe the merits and known limitations of the new data record. This CDR was created in the context of the EUMETSAT Ocean and Sea Ice Satellite Application Facility (OSI SAF) and is readily available at https://doi.org/10.15770/EUM_SAF_OSI_0012.

References:

Holland, P., Kwok, R. Wind-driven trends in Antarctic sea-ice drift. Nature Geosci 5, 872–875 (2012). https://doi.org/10.1038/ngeo1627

Lavergne, T., Eastwood, S., Teffah, Z., Schyberg, H., and Breivik, L.-A. (2010), Sea ice motion from low-resolution satellite sensors: An alternative method and its validation in the Arctic, J. Geophys. Res., 115, C10032, doi:10.1029/2009JC005958.

Rampal, P., Weiss, J., and Marsan, D. (2009), Positive trend in the mean speed and deformation rate of Arctic sea ice, 1979–2007, J. Geophys. Res., 114, C05013, doi:10.1029/2008JC005066.

 

How to cite: Down, E. and Lavergne, T.: A Climate Data Record of Global Sea-Ice Drift from the EUMETSAT OSI SAF, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13126, https://doi.org/10.5194/egusphere-egu23-13126, 2023.

11:20–11:30
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EGU23-14048
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ECS
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On-site presentation
|
Nils Slättberg, Marion Maturilli, and Sandro Dahlke

The rapidly transforming Svalbard and Fram Strait region is characterised by strong air-sea exchanges and represents a major gateway of oceanic and atmospheric transport between the Arctic and lower latitudes. In winter, Marine Cold Air Outbreaks (MCAOs) extract large amounts of energy from the ocean in the form of surface sensible and latent heat fluxes. We investigate how the spatiotemporal variability in Fram Strait MCAOs affects the heat fluxes in ERA5 and the novel Arctic reanalysis CARRA over ocean, sea-ice and land during November-March 1991-2020.

We find that the daily mean heat fluxes are strongly correlated with the MCAO index and that wind speed only plays a large role for the heat fluxes when the MCAO index is positive. The sensible heat flux from the surface to the atmosphere reaches greater values in CARRA than in ERA5 while the opposite is true for the latent heat flux. The difference between the reanalyses scale with the magnitude of the heat fluxes, leading to large disagreement over ice-free ocean, where the fluxes have their highest values. When accounting for the differences in magnitude, we find the largest disagreement between the reanalyses over sea ice. 

In addition, we find that although sea ice loss drives positive ocean-to-atmosphere heat flux trends around much of Svalbard, negative trends in the monthly mean heat fluxes are seen in Fram Strait during the winter, especially in January. These negative trends reflect the decline in the surface-atmosphere potential temperature difference which forms the basis for the MCAO index. 

Finally, we examine the vertical structure of the atmosphere during MCAOs and find anomalously northerly winds, low temperature and low specific humidity throughout the troposphere. The specific humidity anomalies are strongest at low altitudes over the ice-free ocean in southern Fram Strait, while the temperature anomalies reach their maximum in the vicinity of the ice edge. Over the ice-free ocean, where the heat fluxes warm the air from below, the strongest temperature anomalies are found around the altitude of the 800 hPa level.

How to cite: Slättberg, N., Maturilli, M., and Dahlke, S.: Fram Strait Marine Cold Air Outbreaks and associated surface heat fluxes in the ERA5 & CARRA reanalyses, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14048, https://doi.org/10.5194/egusphere-egu23-14048, 2023.

11:30–11:40
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EGU23-3956
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Virtual presentation
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Oliver Gutjahr and Carolin Mehlmann

Polar lows are intense subsynoptic cyclones on the meso-α to meso-β scale that develop over polar maritime environments. So far, only regional atmospheric models have been able to resolve polar lows due to their small spatiotemporal scales. Investigations with coupled regional atmosphere-ocean models are limited to a single study. We demonstrate the simulation of polar lows and their effects on the ocean and sea ice with the recently developed storm- and eddy-resolving configuration of the ICOsahedral Nonhydrostatic (ICON) model, called ICON-Sapphire. ICON-Sapphire globally couples the atmosphere, land, sea ice and ocean with a horizontal resolution of 2.5 km.
Although we focus on the Nordic Seas, ICON-Sapphire simulates polar lows in the northern and southern hemispheres covering the entire mesoscale. They form in different environments, for instance during marine cold air outbreaks or in low-level baroclinic areas at the marginal sea ice zone. Albeit short-lived phenomena, polar lows considerably affect the underlying ocean in ICON-Sapphire, leading to large heat losses, in particular close to the marginal sea ice zone, where they themselves induce cold air outbreaks. This ICON-Sapphire simulation is the first to show how polar lows interact with sea ice to create leads and polynyas due to strong wind stress. Leads and polynyas induce additional heat loss from the ocean that initiates the formation of new ice. Representing polar lows in global climate models increases the heat loss and ice formation from polar oceans, which are otherwise underestimated.

How to cite: Gutjahr, O. and Mehlmann, C.: Polar lows in a globally coupled storm- and eddy-resolving (2.5 km) climate model (ICON-Sapphire), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3956, https://doi.org/10.5194/egusphere-egu23-3956, 2023.

11:40–11:50
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EGU23-14090
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ECS
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On-site presentation
Abraham Torres-Alavez, Oskar Landgren, Fredrik Boberg, Ole Bøssing Christensen, Ruth Mottram, Martin Olesen, Bert Van Ulft, Kristiina Verro, and Yurii Batrak

We present results from a new high resolution regional climate model, configured for both the Arctic and the Antarctic, assessed with a range of in-situ and remote sensing datasets. Under the Horizon 2020 PolarRES project, a set of simulations are performed at a spatial resolution of ~12 km over the Arctic and Antarctic regions using the latest version (cy43) of the HCLIM-ALADIN regional climate model. The model includes a thermodynamic sea ice scheme and has been updated with the latest ice sheet masks and improved topography and other physiographic fields. 

The model will be used to provide climate projections over the 100-year period 2001-2100 for two emission scenarios, and driven on the boundaries by General Circulation Models (GCMs) from the Coupled Model Inter-comparison Project (CMIP6). We also present and evaluate hindcast simulations for the period of 2001 to 2020 over both domains, forced by ERA5 on the boundaries. Model precipitation, temperature, sea ice, and other variables are evaluated with observations from automatic weather stations and satellite data in the polar regions, and additionally compared against the new high resolution (2.5km) Copernicus Arctic Regional ReAnalysis (CARRA) dataset. We also examine the effect of spectral nudging on simulation output. Preliminary results show that HCLIM improves on ERA5, capturing the precipitation, temperature, sea ice cover and ice sheet surface mass balance in both polar regions.

In addition, we show that the wealth of earth observation data now available via the ESA climate change initiative and the EUMETSAT climate data programmes are extremely useful tools to the regional climate modelling community. We use example scripts for model evaluation using EO data via an open repository and present user cases that can be replicated by other modelling groups. 

How to cite: Torres-Alavez, A., Landgren, O., Boberg, F., Christensen, O. B., Mottram, R., Olesen, M., Van Ulft, B., Verro, K., and Batrak, Y.: Assessing Performance of a new High Resolution polar regional climate model with remote sensing and in-situ observations: HCLIM in the Arctic and Antarctica, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14090, https://doi.org/10.5194/egusphere-egu23-14090, 2023.

11:50–12:00
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EGU23-9205
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On-site presentation
Joy Romanski, James Williams, Anastasia Romanou, Bruno Tremblay, and Sandrine Trotechaud

We study the temporal variability of the wintertime Labrador Sea ice area.  The driving factors of these intraseasonal and interannual variations are related to large scale atmospheric variability and cyclone variability both of which can be characterized by the Arctic Oscillation (AO) index.  We observe negative trends in the maximum sea-ice area over the past 40 years, and a positive correlation between the AO index and Labrador Sea ice area.  Using satellite-derived daily ice area along with reanalysis-derived cyclones, turbulent flux, wind, humidity, air and sea temperature fields, we delve into the physical coupling mechanisms by which cyclones influence the position of the ice edge in the Labrador Sea throughout the winter.

How to cite: Romanski, J., Williams, J., Romanou, A., Tremblay, B., and Trotechaud, S.: The impact of large scale atmospheric and cyclone variability on the sea-ice edge in the Labrador Sea, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9205, https://doi.org/10.5194/egusphere-egu23-9205, 2023.

12:00–12:10
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EGU23-12728
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ECS
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Virtual presentation
Rémy Lapere, Jennie L. Thomas, Louis Marelle, Annica M. L. Ekman, Markus M. Frey, Marianne T. Lund, Risto Makkonen, Ananth Ranjithkumar, Matthew E. Salter, Bjørn H. Samset, Michael Schulz, Larisa Sogacheva, Xin Yang, and Paul Zieger

We present an inter-comparison of simulated sea-salt aerosols (SSA) in CMIP6 models, including an evaluation against station observations in the Artic and Antarctic regions and satellite data. Drivers of model diversity are investigated. Historical and future trends are also explored and connected to their driving mechanisms. Additionally, the sensitivity of the polar radiative budget to SSA in CMIP6 models is quantified and put in relation to present-day uncertainties and future trends. 

Comparisons suggest (i) a large inter-model spread in SSA surface concentrations mostly driven by the diversity in source functions, (ii) an important overestimation of SSA surface concentrations compared to measurement stations but reasonable agreement with optical depth from satellite data, (iii) difficulties in properly capturing the annual cycle of SSA at both poles, particularly at higher latitude. A generally increasing trend in SSA concentrations is found in CMIP6 over the last decades and in future scenarios. CMIP6 models show that SSA contribute to cooling the poles significantly, implying possible uncertainties of several W/m2 in the present-day polar radiative budget.

How to cite: Lapere, R., Thomas, J. L., Marelle, L., Ekman, A. M. L., Frey, M. M., Lund, M. T., Makkonen, R., Ranjithkumar, A., Salter, M. E., Samset, B. H., Schulz, M., Sogacheva, L., Yang, X., and Zieger, P.: Polar sea-salt aerosols in CMIP6 models, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12728, https://doi.org/10.5194/egusphere-egu23-12728, 2023.

12:10–12:20
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EGU23-6392
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ECS
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On-site presentation
Anderson Da Silva, Louis Marelle, and Jean-Christophe Raut

The Arctic region is subject to polar amplification, causing it to warm approximately four times faster than the global average. The predominance of ice and mixed-phase clouds in high latitude regions causes strong uncertainties in the determination of the cloud radiative effect and the cloud feedback. The representation of these clouds in models is therefore a crucial point for climate prediction. Solid and liquid water phases partitioning in mixed-phase clouds is mostly driven by their formation and growth processes, in which aerosol particles play a major role, especially in the Arctic where those particles are scarce. Although ice nucleating particles (INPs) may have relevant impact on weather and climate, their physical and chemical properties stay poorly understood. One of the main reasons is the lack of knowledge about their nature; the latter being mainly determined by their sources and thereby their geographical origins.

In this study, in situ measurements from several recent data-sets are used to determine the likely origins of warm Arctic INPs (activated between -10°C and -20°C). A statistical method is applied on the backtrajectories derived from the lagrangian dispersion model FLEXPART-WRF, allows to characterize the seasonal variability of the identified INPs’ sources encountered over the arctic basin.

The seasonal analysis shows that contributions of continental and marine sources to INPs concentrations are highly time- and space-dependent. Arctic INPs do not come exclusively from local sources and can originate from long-range transport. However, the general strong contribution of sea ice and open ocean regions to high concentrations of INPs, and its seasonal variability, is a clue about the importance of local sources. It emphasizes the hypothesis that marine biologic sources are among the main contributors to INPs emissions in the Arctic, when air masses coming from continental regions are often weak contributors. Also, the discrete strong contribution of sea ice regions, particularly in Autumn, suggests that mechanisms like blowing snow or emission of sea sprays from leads and marginal sea ice could have a relevant impact on Arctic INPs production.

These results show the potential of this approach to characterize the origins of in situ measured species, and call for the method to be used in future studies on aerosols emissions.

How to cite: Da Silva, A., Marelle, L., and Raut, J.-C.: Seeking the origins of Arctic ice nucleating particles with FLEXPART-WRF, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6392, https://doi.org/10.5194/egusphere-egu23-6392, 2023.

12:20–12:30
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EGU23-14769
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On-site presentation
Jacqueline Stefels, Maria van Leeuwe, Deborah Bozzato, Alison Webb, and Ellen Damm

This presentation is a contribution to the Multidisciplinary drifting Observatory for the Study of Arctic Climate(MOSAiC) expedition. The MOSAiC field campaign took place on board of RV Polarstern, drifting with the Arctic sea ice, from October 2019 to October 2020. As partner of the MOSAiC team, our project contributed to the production of a time series of sulphur compounds in Arctic sea ice and underlying seawater. The aim of our project was to address how seasonality, sea ice dynamics and water characteristics in the Arctic Ocean affect the cycling of organic sulfur compounds. The sampling of sea ice and surface water was part of the concerted actions of the BGC, ICE and ECO teams during MOSAiC.

A crucial compound for organisms to survive the cold and saline environment of sea ice is the organic sulfur compound dimethylsulfoniopropionate (DMSP) that is mainly synthesized by algae. Between 1 and 10% of total primary production is invested in DMSP, thereby making it a key compound in the lower - and potentially also higher - trophic levels. DMSP is also the precursor of the climate active semi-volatile compound dimethylsulfide (DMS).

Our work combines measurements of concentrations of DMSP, DMS and the (photo-)oxidation product of DMS, dimethyl sulfoxide (DMSO), transformation rates of these compounds using stable isotope additions and identification of the microorganisms driving these processes.

In this presentation, we will show persistent features of DMS(P) distribution in vertical profiles of the MOSAiC floe; link these profiles to algal community structure and discuss the connection between ice and surface water DMS(P) concentrations. We will present a conceptual model of how the growth of sea ice in the Central Arctic Ocean results in specific DMS(P) distribution patterns.

How to cite: Stefels, J., van Leeuwe, M., Bozzato, D., Webb, A., and Damm, E.: DMS(P) distribution in Arctic sea ice related to algal community structure and ice dynamics – results from the MOSAiC expedition, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14769, https://doi.org/10.5194/egusphere-egu23-14769, 2023.

Posters on site: Tue, 25 Apr, 14:00–15:45 | Hall X5

Chairperson: Jennie L. Thomas
X5.302
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EGU23-2674
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ECS
Holly Ayres and David Ferreira

The Weddell Sea Polynya is a seasonal opening within the sea ice cover of the Weddell Sea sector, typically found over the Maud Rise and inside the Weddell Gyre. It has been a rare occurrence in the satellite period, appearing in austral spring between 1973 and 1976 and again in 2016/17. The polynya formation has been shown to be complex, requiring a combination of ocean and atmospheric mechanisms to develop. The region is often poorly resolved in global climate models, with little agreement in ocean or sea ice dynamics. When Weddell Sea polynyas have occurred in models without forcing, it is not understood how they occur within the model, or why some models produce frequent polynyas and others produce none. Some studies have shown that increasing horizontal resolution improves the dynamics of the Southern Ocean, allowing for better parameterisation of small-scale features. Here, we use multi-model data of different resolutions, from the PRIMAVERA HighResMIP experiments, to determine how models of different atmospheric and ocean resolution resolve Weddell Sea polynyas. We assess the frequency, size, and location of polynyas in different resolutions, in addition to studying the ocean and atmospheric processes associated with the polynya in these models. Initial results of models that resolve frequent polynya show preconditioning in both the ocean and atmosphere, in addition to a small response to the polynya in the months following.

How to cite: Ayres, H. and Ferreira, D.: Atmosphere and ocean climate model resolution in resolving Weddell Sea polynyas and their ocean-atmosphere interactions., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2674, https://doi.org/10.5194/egusphere-egu23-2674, 2023.

X5.303
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EGU23-3640
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Vladimir Maderich, Roman Bezhenar, Igor Brovchenko, Antonina Bezhenar, Fabio Boeira Dias, and Petteri Uotila

The objective of the study is to construct Lagrangian pathways under the Filchner-Ronne ice shelf (FRIS) and in the Weddell Sea using the data of numerical simulation of currents and Lagrangian numerical methods. The yearly cycled results of modeling for the circulation, temperature, and salinity in the Weddell Sea and the FRIS cavity from the Whole Antarctica Ocean Model (WAOM) were used to run the particle-tracking model (Parcels) for computing Lagrangian particle trajectories. The original version of the Parcels model does not have an option for particle reflection from the solid boundaries including the ice shelf. Therefore, the corresponding kernel was developed in the current study. The Parcels model gives an error in interpolation when it cannot find enough grid nodes around the particle. To avoid these errors, the function of particle recovery was developed. To analyze the variations of movement of the water masses under the FRIS, a set of particles was released in the Ronne Depression near the ice shelf front. Particles were released at two depths: 350 m and 500 m under the sea surface. Particles were released each 4 hr within 365 days. Simulation continued for 20 years of particle movement. The results of Lagrangian analysis generally agreed with schemes based on water mass analysis. The released particles first move southward along the Ronne Trough. The flow then turns to the east reaching the passage between Berkner Island and Henry Rise after 3 years. After 10 years, the flow of transformed water reaches the Filchner Trough through which water flows out to the shelf of the southern part of the Weddell Sea. Over time, the particles penetrate into all parts of the cavity. Some of the particles cross the Ronne Shelf front, and then they are carried away by currents on the Weddell Sea shelf. In 20 years, almost the same number of particles left the cavity through the Ronne ice front (43%) and the Filchner ice front (37%) whereas the rest of the particles (20%) remained under FRIS.

How to cite: Maderich, V., Bezhenar, R., Brovchenko, I., Bezhenar, A., Dias, F. B., and Uotila, P.: Lagrangian pathways under the Filchner-Ronne ice shelf and in the Weddell Sea, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3640, https://doi.org/10.5194/egusphere-egu23-3640, 2023.

X5.304
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EGU23-9684
Tomas Torsvik

Global Earth System Models (ESMs) seek to simulate physical, chemical and biological processes that are relevant for the evolution of global climate. One key feature of an ESM is the ability to simulate fluxes of greenhouse gases and aerosols between the atmosphere and ocean, keep track of the inventories in the respective model components and allow for feedback on the climate system. These fluxes are usually calculated based on bulk formulations derived from open water measurements, and are restricted by the sea ice fraction in regions covered by sea ice.

The air-sea gas exchange is determined by the difference in concentration across the air-sea interface, and a gas transfer velocity that is specific for the gas in question. Using CO2 as example, the air-sea gas exchange is
          FCO2 = (1 - βCsea-ice ) ⋅ kw(CO2) ⋅ ( [CO2]sea - α[CO2]air)   (1)
where Csea-ice is the sea ice concentration, kw(CO2) is the gas transfer velocity, and α is the Ostwald solubility coefficient. Traditional formulas use β = 1 (complete barrier), but in order to account for cracks and leads in the sea ice, Steiner et al. (2013) proposed a modified formula with β ∈ [0, 1], allowing the sea ice to act as a partial barrier (0 < β < 1) or allowing free exchange in sea ice covered regions (β = 0).

We implement the modified gas exchange formula (eq. 1) in the Norwegian Earth System Model NorESM2, for all model tracers exchanged over the air-sea interface (CO2, O2, N2, N2O, DMS). Experimenting with different β values, we find that small increases (β ∈ [0.01, 0.02]) may result in either increased or decreased gas fluxes in high latitude regions. This can be attributed to the internal variability of the sea ice area, in particular for the summer minimum, which responds to changes in greenhouse gases and aerosols in the atmosphere. For β ∈ [0.1, 0.2] we find an increase in CO2 flux of 16% — 22% north of 68°N, and 5% — 8% south of 60°S. Observational datasets based on eddy covariance data for CO2 in the atmospheric boundary layer will be used in
future work in order to determine a realistic range for β.

REFERENCES:

N. S. Steiner, W. G. Lee, and J. R. Christian. Enhanced gas fluxes in small sea ice leads and cracks: Effects on CO2 exchange and ocean acidification. Journal of Geophysical Research: Oceans, 118(3):1195–1205, 2013. doi: 10.1002/jgrc.20100.

How to cite: Torsvik, T.: Modeling influence of sea ice on gas exchanges between atmosphere and  ocean in a global Earth System Model, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9684, https://doi.org/10.5194/egusphere-egu23-9684, 2023.

X5.305
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EGU23-13035
Maria van Leeuwe, Jacqueline Stefels, Michael Meredith, and Alison Webb

The Southern Ocean is a hotspot of the climate-relevant organic sulphur compound dimethyl sulphide (DMS). Spatial and temporal variability in DMS concentration is higher than in any other oceanic region, especially in the marginal ice zone (MIZ). The MIZ is also an area of rich microalgal communities, including algal species that are renown for the production of dimethyl sulphoniopropionate (DMSP), the precursor of DMS. The link between DMS and microalgae has been studied closely over a five-year period (2012 to 2017) near Rothera Station in Ryder Bay (Western Antarctic Peninsula). Algal community structure and spatial heterogeneity of DMS and DMSP was studied and linked with environmental conditions, including sea ice melt. Concentrations of sulphur compounds, particulate organic carbon (POC) and chlorophyll a in the surface waters varied by orders of magnitude in time and space. Highest concentrations of DMS(P) were recorded in spring, associated with the dominance of autotrophic flagellates, including haptophytes and chlorophytes. These microalgae most likely originated from sea-ice communities, stressing the role of sea ice as a seeding vector for the spring bloom and as a potential source of DMS. The strong sea-ice signal in the distribution of haptophyte algal species and DMS(P) implies that DMS(P) production is likely to decrease with ongoing reductions in sea ice cover along the Western Antarctic Peninsula. This has implications for feedback processes on the region’s climate system.

How to cite: van Leeuwe, M., Stefels, J., Meredith, M., and Webb, A.: Impact of sea-ice melt on DMS(P) inventories associated with algal community dynamics in Antarctic surface waters., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13035, https://doi.org/10.5194/egusphere-egu23-13035, 2023.

X5.306
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EGU23-15723
Clara Lambin, Christoph Kittel, and Xavier Fettweis

Arctic changes are at the centre of climate concerns. Notably, recent Arctic warming drives rapid sea ice decline making the Arctic increasingly vulnerable. To better anticipate the consequences of this strong Arctic warming, it is crucial to better understand the driving processes responsible for large uncertainties in future climate projections. Interactions at the atmosphere-ocean-sea ice interface require particular attention. In this context, the PolarRES project aims at developing the coupled system MAR (atmosphere) - NEMO (ocean-sea ice) over the Arctic region at high spatial resolution (25 km). Such coupling will enable the climate community to access precise data at large scale. Since this coupling has never been applied to the Arctic, a proper model evaluation is required. Here standalone model simulations are compared against a newly compiled dataset including land station and buoys data. We find high correlations between the modelled and observed data. Our evaluation marks an important step in in the ongoing development of coupled models.

How to cite: Lambin, C., Kittel, C., and Fettweis, X.: Towards a high-resolution MAR-NEMO coupling to explore atmosphere-ocean-ice interactions in the Arctic, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15723, https://doi.org/10.5194/egusphere-egu23-15723, 2023.

X5.307
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EGU23-7086
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Agnieszka Herman and Katarzyna Bradtke

Coastal (latent heat) polynyas are regions of extremely strong ocean–atmosphere heat, moisture and momentum exchange, often with wind speed and surface turbulent heat flux exceeding 30 m·s1 and 1000 W·m2, respectively, and air temperature below –20°C. Consequently, polynyas play a very important role in shaping the local and regional weather, are crucial for sea ice production and the associated formation of dense water masses. The ocean mixed layer (OML) during polynya events is highly turbulent, with turbulent dissipation due to wind shear, waves and convective mixing. Crystals of frazil ice forming in those very dynamic conditions are transported throughout the OML along irregular, three-dimensional trajectories. The manifestation of those processes at the surface are characteristic elongated strips with high frazil concentration – so called frazil streaks – forming in convergence zones of the Langmuir circulation (https://egusphere.copernicus.org/preprints/2022/egusphere-2022-1435/). The presence of frazil streaks and open water areas between them leads to high spatial variability of OML and, crucially, sea surface properties. In particular, the bulk water viscosity within streaks is much higher and the sea surface roughness much lower than in open water. This in turn affects the momentum flux from the atmosphere and the evolution of wind waves. Wave breaking is suppressed, and short waves are dissipated by frazil/grease ice. Therefore, the whole spectral energy balance is modified. In this paper, satellite data and spectral wave modelling are used to analyse fetch-limited, deep-water wave growth during selected polynya events in the Terra Nova Bay, Antarctica. It is shown that wave growth in the presence of frazil streaks is slower than in analogous ice-free situations, and that wave–ice interactions are the only plausible explanation for observations. Simulations with a spectral wave model SWAN (Simulating Waves Nearshore) are used to examine different scenarios of how the source terms related to wind input, quadruplet wave–wave interactions, whitecapping, and dissipation in grease ice contribute to the net wave energy growth with distance from shore. Additionally, the role of across-wind variations of wind speed and wave properties is examined in detail, illustrating the inherently two-dimensional character of the polynyas’ wave field. Overall, the study shows that polynya events provide a unique, very valuable setting for studying wave–ice interactions, in many respects fundamentally different from the ‘standard’ case of swell entering the marginal ice zone from the open ocean.

How to cite: Herman, A. and Bradtke, K.: Interactions between wind waves and frazil ice in the turbulent surface boundary layer of an Antarctic coastal polynya, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7086, https://doi.org/10.5194/egusphere-egu23-7086, 2023.

X5.308
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EGU23-16224
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ECS
Alistair Duffey, Robbie Mallet, Julia Steckling, Antoine Hermant, Victoria Dutch, Jonathan Day, and Felix Pithan

The atmospheric boundary layer in the Arctic winter is characterised by strong and long-lived low level stability which arises from long-wave radiative cooling of the surface during the polar night. This atmospheric temperature inversion is a necessary condition for the positive lapse rate feedback, which is a major contributor to Arctic Amplification. In this study, we assess the low-level stability of the winter-time Arctic boundary layer using ground-based and radiosonde observations collected during the MOSAiC (2019-2020) and SHEBA (1997-1998) expeditions, and from Soviet drifting stations (1955-1991). We compare these observations with the representation of Arctic boundary layer stability in models participating in the latest phase of the Coupled Model Intercomparison Project (CMIP6). The observations show a bimodal distribution of clear and cloudy states which has been reported previously. In the clear state, longwave radiative cooling from the surface leads to strong inversions and a stably stratified boundary layer. Whereas, in the cloudy state, inversions are weaker and not confined to the surface. Previous work has shown that many CMIP5-era climate models fail to realistically represent the cloudy state and often overestimate low-level stability. Here, we assess the extent to which the CMIP6 models also show such biases and examine the representation of surface net longwave radiation and turbulent heat fluxes as potential sources of the biases. Finally, we show that across CMIP6 models, low level stability over sea-ice is correlated with inter-model variation in Arctic amplification.

How to cite: Duffey, A., Mallet, R., Steckling, J., Hermant, A., Dutch, V., Day, J., and Pithan, F.: Stability of the winter-time Arctic Ocean boundary layer in CMIP6 climate models evaluated against Soviet drifting stations, SHEBA and MOSAiC observations, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16224, https://doi.org/10.5194/egusphere-egu23-16224, 2023.

X5.309
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EGU23-16638
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ECS
Damien Maure, Christoph Kittel, Clara Lambin, and Xavier Fettweis

Understanding the future evolution of the climate over Antarctica is crucial, as the continent holds the potential for a 3-meter rise in sea levels by 2300. However, the Antarctic climate is impacted by various processes and interactions, particularly at the ocean-atmosphere-sea ice interface, which are not fully implemented in Global Climate Models (GCMs). We are developing a high-resolution two-way coupling between the reginal climate model MARv3.13 and ocean/sea-ice model NEMO4.2/SI3 to study these processes, such as blowing snow over sea-ice, and their potential impact on future polar climate scenarios selected by the PolarRES consortium. We evaluated the standalone models' performance in simulating current climate conditions using various meteorological observations, satellite data, and ship observations. The results of this study are a first step to check the setup before moving to a fully coupled interface, and already show the importance of regional modelling to better resolve specific processes. 

How to cite: Maure, D., Kittel, C., Lambin, C., and Fettweis, X.: High resolution atmospheric and oceanic modelling over Antarctica: a coupling interface to study sea-ice processes, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16638, https://doi.org/10.5194/egusphere-egu23-16638, 2023.

X5.310
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EGU23-17080
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ECS
Felix Pithan, Marylou Athanase, Sandro Dahlke, Antonio Sánchez-Benítez, Matthew Shupe, Anne Sledd, Jan Streffing, Gunilla Svensson, and Thomas Jung

Comparing the output of general circulation models to observations is essential for assessing and improving the quality of models. While numerical weather prediction models are routinely assessed against a large array of observations, comparing climate models and observations usually requires long time series to build robust statistics.

Here, we show that by nudging the large-scale atmospheric circulation in coupled climate models, model output can be compared to local observations for individual days. We illustrate this for three climate models during a period in April 2020 when a warm air intrusion reached the MOSAiC expedition in the central Arctic. Radiosondes, cloud remote sensing and surface flux observations from the MOSAiC expedition serve as reference observations. The climate models AWI-CM1/ECHAM and AWI-CM3/IFS miss the diurnal cycle of surface temperature in spring, likely because both models assume the snow pack on ice to have a uniform temperature. CAM6, a model that uses three layers to represent snow temperature, represents the diurnal cycle more realistically. During a cold and dry period with pervasive thin mixed-phase clouds, AWI-CM1/ECHAM only produces partial cloud cover and overestimates downwelling shortwave radiation at the surface. AWI-CM3/IFS produces a closed cloud cover but misses cloud liquid water. All models overestimate downward turbulent heat fluxes under stable stratification, a long-standing issue in weather and climate models.

Our results show that nudging the large-scale circulation to the observed state allows a meaningful comparison of climate model output even to short-term observational campaigns. We suggest that nudging can simplify and accelerate the pathway from observations to climate model improvements and substantially extends the range of observations suitable for model evaluation.

How to cite: Pithan, F., Athanase, M., Dahlke, S., Sánchez-Benítez, A., Shupe, M., Sledd, A., Streffing, J., Svensson, G., and Jung, T.: Evaluating nudged coupled climate models against MOSAiC observations reveals weaknesses in the representation of clouds, boundary-layer turbulence and snow pack, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17080, https://doi.org/10.5194/egusphere-egu23-17080, 2023.

X5.311
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EGU23-12357
Ioanna Merkouriadi, Glen Liston, and Heidi Salilla

Snow is a crucial component of the Arctic sea ice system. It dominates the exchanges of heat and light between the atmosphere and the ocean, with important physical and biological implications. To address the imperative need for more realistic representation of snow on sea ice, recent efforts have focused on reanalysis-based snow depth and density reconstructions. However, none of the recent snow products account for snow losses due to snow and sea ice interactions.

This study quantifies the snow loss in snow-ice formation, and its effect in SnowModel-LG snow depth and density product. We coupled SnowModel-LG, a snow modeling system adapted for snow depth and density reconstruction over sea ice, with HIGHTSI, a 1-D sea ice thermodynamic model, to simulate snow-ice and thermal ice growth: SnowModel-LG_HS. We assumed that all negative freeboard would result in snow-ice formation. Pan-Arctic model simulations were performed over the period 1 August 1980 through 31 July 2021, and they were guided by observations where available. In SnowModel-LG_HS, snow depth was lower (domain average: 18%), and snow density was higher (2.3%) compared to SnowModel-LG. The differences were much larger in the Atlantic sector. Our simulations suggest that when snow models do not account for snow and ice interactions, snow depth can be significantly overestimated. In this talk we will discuss the magnitude of this overestimation in relation to the sub-grid parameterization of sea ice dynamics and their effect in snow redistribution over the ice floes. Sea ice dynamics (e.g. deformed ice formation), are likely an additional important snow sink that is not yet accounted for in snow models.

Finally, we use our snow depth and density results from SnowModel-LG_HS to obtain sea ice thickness retrievals from CryoSat-2. A validation of these retrievals against Airborne Electromagnetic Measurements shows that SnowModel-LG_HS performed better when compared to SnowModel-LG and snow climatologies.

 

 

How to cite: Merkouriadi, I., Liston, G., and Salilla, H.: Quantifying the effect of snow and sea ice interactions on SnowModel-LG snow depth and density product, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12357, https://doi.org/10.5194/egusphere-egu23-12357, 2023.

Posters virtual: Tue, 25 Apr, 14:00–15:45 | vHall CR/OS

Chairperson: Priscilla Mooney
vCO.4
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EGU23-13518
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ECS
Ehlke Hepworth, Marcello Vichi, and Gabriele Messori

This study analyses the association of Southern Ocean extratropical cyclones and atmospheric rivers (ARs) with extreme temperature and/or moisture atmospheric anomalies over Antarctic sea ice. The hypothesis we test is whether the circulations associated with cyclones and ARs may routinely lead to the presence of unusually warm, moist airmasses over ice-covered regions. The analysis is conducted over the extended Austral winter seasons (May – September) between May 1979 and September 2012, based on the European Centre for Medium-Range Weather Forecasts Interim reanalysis data. Approximately 27% of intense Southern Ocean cyclones and 20% of ARs occur in the vicinity of extreme temperature anomalies, while 12% of intense cyclones and 46% of ARs occur in the vicinity of extreme moisture anomalies. We summarize our results as follows: (1) extreme atmospheric anomalies over sea ice often occur in the absence of cyclones or ARs; (2) intense cyclones have a stronger association with extreme temperature  anomalies than ARs; (3) approximately half of the ARs are in the vicinity of extreme moisture anomalies, while the latter’s link with cyclones is weak; (4) if an AR is in the vicinity of an extreme temperature anomaly, there will likely be a concurrent extreme moisture anomaly. This points to a strong association between ARs and moisture extremes, and a nuanced link between Southern Ocean polar cyclones and atmospheric anomalies over Antarctic sea ice.

How to cite: Hepworth, E., Vichi, M., and Messori, G.: Association between extreme atmospheric anomalies over Antarctic sea ice, Southern Ocean polar cyclones and atmospheric rivers, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13518, https://doi.org/10.5194/egusphere-egu23-13518, 2023.

vCO.5
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EGU23-4860
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ECS
Wayne de Jager and Marcello Vichi

Satellite-derived sea-ice concentration measurements have traditionally been used to evaluate the impact of climate change on polar regions. However, concentration-based measurements of sea-ice variability do not allow the discrimination of the relative contributions made by thermodynamic and dynamic processes. This prompts the need to use sea-ice drift and type products and develop new methods to quantify changes in sea-ice properties that would indicate trends in the ice characteristics. A component of the sea-ice variability is driven by local weather events, and in some cases is the dominant driver of variability over larger-scale atmospheric features. Previous work by de Jager & Vichi (2022) has suggested that sea-ice vorticity (derived from low resolution sea-ice displacement vectors) may be a useful metric for quantifying dynamical features in Antarctic sea ice; specifically shorter term changes in the ice-interior driven by atmospheric storms. However, this study hypothesised that much of the rotational drift in the underlying sea-ice field was blurred as a result of the relatively large 48-hr temporal resolution of the drift product, therefore highlighting the necessity of measuring sea-ice properties at higher temporal frequencies. This study will therefore assess the usefulness of an overlapping swath-based method of sea-ice displacement retrieval recently made available by the EUMETSAT OSI-SAF. This swath-based method of retrieval allows for analysis of sea-ice variability at sub-daily timescales, which may be more suitable for measuring the effect of weather events on the sea-ice landscape than using daily averages of merged swaths. In situ data of sea-ice conditions were collected on board the SA Agulhas II research vessel in the Atlantic Sector in July, 2022, which will be compared to swath-based satellite estimates. Furthermore, the newly released 24-hr OSI-SAF drift product will also be compared. To complement these drift estimates, a modified swath-based ice-type retrieval method will be presented to add further context to any potential thermodynamic changes affecting the optical properties of the sea-ice surface.

How to cite: de Jager, W. and Vichi, M.: Sub-daily Antarctic sea-ice variability estimates using swath-based retrieval methods, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4860, https://doi.org/10.5194/egusphere-egu23-4860, 2023.

vCO.6
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EGU23-5458
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ECS
Riesna R. Audh, Sarah E. Fawcett, Siobhan Johnson, Tokoloho Rampai, and Marcello Vichi

The study of Antarctic first-year ice as a biogeochemical habitat has been limited by samples mostly collected in pack ice during summer. Fewer winter data are available, and due to the harsh conditions, data from the marginal ice zone (MIZ) are even more difficult to obtain. The MIZ is broad and circumpolar in the Southern Ocean; it is found at different latitudes during the year with sufficient light and nutrients to sustain primary production and affect ecosystem functioning. We present the first dataset of biogeochemical properties of first-year ice collected in the Atlantic sector of the Southern Ocean during winter 2019, obtained from young pancake ice and consolidated first-year ice. Temperature, salinity, crystal structure, δ18O, chl-a and bulk macronutrient data were used to investigate the winter habitat and explain the transition from young ice to first year ice through exchanges with the ocean biogeochemistry. Data suggests that the sea ice sampled at the consolidated station was a result of thermodynamic processes combined with possibly multiple cycles of breaking and rafting induced by waves and dynamics, which ultimately enhanced the biogeochemical activity beyond what expected for first-year ice. A numerical model was used to support the hypothesis that winter first-year ice buffers biogeochemical components differently from the upper ocean winter concentrations, and this may determine the conditions for the biogeochemical development later in spring.

How to cite: Audh, R. R., Fawcett, S. E., Johnson, S., Rampai, T., and Vichi, M.: Enhanced winter biogeochemical activity in Antarctic first-year sea ice, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5458, https://doi.org/10.5194/egusphere-egu23-5458, 2023.