The new Arctic in the global context - Modelling
- 15:00 FEATURED TALK: Evaluating impacts of the Arctic sea ice loss and variation on the northern hemisphere climate
Authors: Torben Koenigk ( Swedish Meteorological and Hydrological Institute ); Yongqi Gao ( Nansen Environmental and Remote Sensing Center ); Guillaume Gastineau ( Sorbonne Universites ); Noel Keenlyside ( Geophysical Institute, University of Bergen ); Tetsu Nakamura ( Hokkaido University ); Fumiaki Ogawa ( Geophysical Institute, University of Bergen ); Yvan Orsolini ( NILU - Norwegian Institute for Air Research ); Vladimir Semenov ( A. M. Obukhov Institute of Atmospheric Physics RAS ); Lingling Suo ( Nansen Environmental and Remote Sensing Center ); Tian Tian ( Danish Meteorological Institute ); Tao Wang ( Nansen-Zhu International Research Center ); Jonathan J. Wettstein ( Oregon State University ); Shuting Yang ( Danish Meteorological Institute )
Arctic sea ice loss during the recent decades of global warming could have contributed to Arctic amplification and colder winters over Eurasia. However, recent reviews suggest that the impact of sea ice changes in the Arctic vary regionally and seasonally, and the results from individual modelling studies differ widely, which led to a debate on the role of sea ice in the polar amplification and Eurasian cooling trend. Here we show that the impact of the recent sea ice decline is rather limited to the high-latitude lower troposphere, through coordinated experiments with six atmospheric general circulation models (AGCMs) forced by observed and climatological daily sea ice concentration and sea surface temperature (SST). The Arctic amplification is strongly coupled with sea ice loss over the Arctic lower troposphere throughout winter, while the warming aloft is mostly associated with remote SST changes. Sea ice changes do not significantly lead to colder winters over Eurasia. The observed temperature trends and corresponding circulation trends are reproduced in a small number of ensemble members but not by the multi-model ensemble mean, suggesting that atmospheric internal dynamics could have played a major role in the observed trends.
Further, we show that Arctic sea ice variations are important for the interannual two meter air temperature (T2m) variations in northern Europe but have limited impact on all other mid and high latitude land regions. In particular, sea ice variations do not contribute to the observed opposite variations in the Arctic and mid-latitudes. The spread across ensemble members is large and many ensemble members are required to reproduce the observed T2m variations over northern Europe in our models.
The amplitude of T2m anomalies in the coldest observed winters over northern Europe is not reproduced by our multi-model ensemble means, but the sea ice conditions in these respective winters lead to an enhanced likelihood for occurrence of colder than normal winters and extremely cold winters. However, the main reason for the observed extreme cold winters seems to be related to internal atmospheric dynamics.
The coldest simulated northern European winters between 1982 and 2014 reproduce the large scale T2m and atmospheric circulation anomaly patterns in the observed coldest winters, indicating that the models are well able to reproduce the processes, which cause these cold anomalies.
The results are robust across all six models used in this study.
- 15:30 Modeling Arctic sea-ice algae: Physical drivers of spatial distribution and algae phenology
Authors: Giulia Castellani ( Alfred Wegener Institut (AWI) ); Martin Losch ( Alfred Wegener Institut (AWI) ); Benjamin A. Lange ( Fisheries and Oceans Canada ); Hauke Flores ( Alfred Wegener Institut (AWI) )
Algae growing in sea ice represent a source of carbon for sympagic and pelagic ecosystems, and contribute to the biological carbon pump. The biophysical habitat of sea ice on large scales and the physical drivers of algae phenology are key to understanding Arctic ecosystem dynamics and for predicting its response to ongoing Arctic climate change. In addition, quantifying potential feedback mechanisms between algae and physical processes is particularly important during a time of great change. These mechanisms include a shading effect due to the presence of algae, and increased basal ice melt. The present study shows pan-Arctic results obtained from a new Sea Ice Model for Bottom Algae (SIMBA) coupled with a 3D sea-ice–ocean model. The model is evaluated with data collected during a ship-based campaign to the Eastern Central Arctic in summer 2012. The algal bloom is triggered by light, and shows a latitudinal dependency. Snow and ice also play a key role in ice algal growth. Simulations show that after the spring bloom, algae are nutrient-limited before the end of summer and finally they leave the ice habitat during ice melt. The spatial distribution of ice algae at the end of summer agrees with available observations, and it emphasizes the importance of thicker sea-ice regions for hosting biomass. Particular attention is given to the distinction between level ice and ridged ice. Ridge-associated algae are strongly light-limited, but they can thrive towards the end of summer, and represent an additional carbon source during the transition into polar night.
- 15:45 Atlantic Water and sea ice variability in the 20th century Arctic Ocean from a global ocean model and observations.
Authors: Morven Muilwijk ( University of Bergen & Bjerknes Centre for Climate Research ); Lars Henrik Smedsrud ( University of Bergen & Bjerknes Centre for Climate Research ); Mehmet Ilicak ( Uni Research & Bjerknes Centre for Climate Research ); Helge Drange ( University of Bergen & Bjerknes Centre for Climate Research )
Both historical observations and outcome from a fully coupled earth system model show a warming trend in core temperature of Atlantic Water entering the Arctic Ocean over the last few decades (1977-2015). The Atlantic Water is also observed to rise systematically in the water column since the 1990’s. This suggests an “Atlantification” of the Arctic Ocean, i.e. an ongoing expansion of the Atlantic domain. A portion of this “Atlantification” and recent warming has been attributed to the current global warming and possibly anthropogenic activity. However, past periods of warm Atlantic Water (1930-1940) have been documented, a period often termed “Early Warming”. We believe that the Atlantic Water warming trend in the Arctic Ocean may be part of long-term
multidecadalvariability, which is influenced and reinforced by strong anthropogenic forcing.
We have therefore investigated the interannual, decadal and multidecadal variability of Atlantic Water and sea ice in the Arctic Ocean using a global ocean model. Here we present simulations for the period 1871-2009 with the ocean-sea ice component of the Norwegian Earth System Model (NorESM-O) forced by a Twentieth Century Reanalysis data set. These are compared with available Atlantic
Water andsea ice observations inthe Fram Strait and north of Svalbard.
The simulation and observations show several periods of relatively warm Atlantic Water and “Atlantification” to a certain degree, also before the 1970s. In the Eurasian Basin, north of
Svalbardthere appears to be a direct correlation between Atlantic Water heat and Arctic sea ice volume. We find, for example, that the 1930s warm period was followed by a loss of Arctic sea ice volume.
In addition, passive tracers were released in the model simulation to explore the circulation pattern of Atlantic Water, the variability of recirculation of Atlantic Water in the Fram Strait and distribution of freshwater from different river sources. These tracers show that most Atlantic Water either circulates in the Nansen Basin or recirculates back to the Fram Strait relatively quickly, and that only a very small portion crosses over to the Canadian side of the Lomonosov Ridge.
- 16:00 Observation and model synthesis: Combining observations and radiative transfer modeling to analyze penetrating shortwave radiation through sea ice within the Community Earth System Model
Authors: Alexandra Arntsen ( Dartmouth College ); Donald Perovich ( Dartmouth College )
An important goal of large scale global climate models is to incorporate observational data from multiple platforms into a comprehensive and rigorous description of interacting processes that can be used as a powerful predictive tool. To improve the functionality and precision of these models, parameterization and configuration considerations for a changing Arctic should be prioritized in the analytical framework of observational experiments in this region. In this study, we examine the partitioning of penetrating shortwave radiation within Arctic sea ice and observe how seasonal and spatial variability of the in-ice and under-ice light fields can have an impact on total surface energy budget, ice algae bloom dynamics, and overall primary production. Our analysis is guided by output from the Community Earth System Model (CESM) and utilizes a multiplatform observation suite as well as independent radiative transfer modeling to assess and scale optical properties of sea ice in the Beaufort and Chukchi Sea regions. We characterize light available to springtime algal blooms and bio-optical feedbacks related to a younger ice cover. Incorporated into CESM, our results demonstrate how pronounced physical changes associated with a warming Arctic can have an effect on both regional ecology and the greater Arctic energy budget.
- 16:15 On the statistical properties of sea ice lead fraction and heat fluxes in Arctic
Authors: Einar Olason ( Nansen Environmental Remote Sensing Center ); Pierre Rampal ( Nansen Environmental Remote Sensing Center ); Sylvain Bouillon ( Nansen Environmental Remote Sensing Center )
Heat flux through leads and polynyas is an order of magnitude larger than that through unbroken ice. In this presentation we explore some statistical properties observed in Arctic sea ice lead fraction, showing that our model (neXtSIM) does a good job at reproducing the observed statistics. Given the importance of heat flux through leads we then use the model to explore the statistical properties of the modelled heat fluxes. We show that the model reproduces well the probability density function (PDF) and the mono-fractal spatial scaling of observed lead fluxes in the Central Arctic. We then explore the PDF and spatial scaling of simulated heat fluxes, showing that the heat fluxes have a multi-fractal scaling in the Central Arctic which we attribute to lead formation, while coastal polynyas destroy the scaling in the wider Arctic. Finally we show that the scaling of simulated lead fraction is preserved for different model resolutions, while further work on a sub-grid scale parametrisation of surface heterogeneity is required to preserve the scaling of heat fluxes for different model resolutions.
- 16:30 Using the Lagrangian Ice Tracking System (LITS) to respond to risks in a warming world
Authors: Robert Newton ( Columbia University ); Stephanie Pfirman ( Barnard College ); Bruno Tremblay ( McGill University ); Patricia DeRepentigny ( University of Colorado )
Starting from satellite-based estimates of sea ice drift vectors we have developed a user-friendly system for tracking sea ice forward and backward in time from an arbitrary set of locations and start times between 1979 and 2015. We have used the system to analyze changes in sea ice exchanges between the exclusive economic zones of the Arctic nations, as well as changes in ice formation and melt rates; formation and melt locations; and the timing of open water in the Arctic peripheral seas. We are extending LITS by integrating climate model outputs so that users can track ice formation, transport and melt as projected through the twenty-first century.
In this contribution we will summarize previous results on inter-EEZ transport and present initial results on shifting transport projections over the next 100 years. We apply LITS to several critical societal issues, including: transports forward in time from the locations of oil leases on the Siberian shelves, which localize, and highlight, risks due to oil exploration, recovery and transport; backward tracking of ice from a proposed marine protected area (the Last Ice Area), which demonstrate the need for Arctic-wide policy processes to protect local resources; and ways that hemispheric-scale atmospheric changes impact Arctic regional and local sea-ice conditions in the Arctic.
Global climate change is making dramatic changes in the distribution of thick, multi-year, vs thin, first-year, ice--a critical environmental basis for current Arctic eco-zones. Not only are the overall size and thickness distribution of ice cover important; so too are the timing and location of formation and melt, along with transport patterns. Sea ice transport moves freshwater, sediments and living organisms, which are critical to ice-obligate species from diatoms to polar bears. In addition, ice formation and melt patterns impact the distribution of buoyancy and dense waters, which modulate deep water formation and affects global climate. Visualizing current trends and likely future shifts in sea ice dynamics is fundamental to policy formulation and implementation. The results from LITS, both retrospective and projections, will be placed in the context of our earlier work on diverging stakeholder interests in the Arctic (White Arctic vs Blue Arctic; Newton et al. (2016). Earth’s Future, ). That is: we provide input for analysts to think concretely about how stakeholders are likely to align and where openings may occur for consensus building and policy development as the global climate, including the Arctic, warms.
- 16:45 Simulating variability in the Fram Strait sea ice export and related Arctic sea ice response
Authors: Lars H. Smedsrud ( University of Bergen & Bjerknes Centre ); Morven Muilwijk ( University of Bergen ); Mehmet Ilicak ( Uni Research )
The long-term annual Fram Strait sea ice area export is about 880 000 km², representing about 10% of the sea-ice-covered area inside the Arctic basin. This export has large inter-annual and multi-decadal variability, but apparently no long-term trend. However, during the last decades, the amount of ice exported has increased, with several years having annual ice exports that exceeded 1 million km². This large recent export has likely played an important role in the recent Arctic sea ice loss, explaining some of the observed summer ice loss and some of the general thinning (ice volume loss) occurring throughout the year.
Generally simulations only capture parts of the recent sea ice loss, and the role of natural variability in the ice loss remains a somewhat controversial issue. Because changes in the larger scale wind forcing is the primary cause of the ice export variability one would expect that regional and global ice-ocean models forced by observed (re-analysis) winds should re-produce the variability quite well. The global coupled air-ice-ocean models (CMIP5 type) have well documented correlations between large export anomalies and thinning, but generally export too much sea ice area.
This work evaluates simulated Fram Strait sea ice area export in a range of models used for the coordinated FAMOS (Forum for Arctic Modeling and Observational Synthesis) Climate Response Functions (CRF) set-up. Our initial focus is on the Greenland Sea wind forcing perturbations. Initial evaluation of the Norwegian Earth System Model (NorESM) shows that there is a large simulated variability correlating well with observations for 1935 - 2015. However, the mean export is about 10% larger than observations, which may explain a low bias in sea ice area. We anticipate that an increased ice export during winter results in new ice growth and contribute to thinning inside the Arctic Basin, while increased summer or spring export will contribute directly the following September minima. Preliminary analysis suggest that the wind perturbation indeed decreases sea ice export, with the main response being a larger Arctic sea ice volume and ice covered area, with largest response in the Atlantic sector during winter. Creating a response with increase in export appears more challenging, and the wind patterns driving this response will be discussed.
Tuesday 23rd January 2018
15:00 - 16:45