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  • 1
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    Impact of Cyclonic Wind Anomalies Caused by Massive Winter Sea Ice Retreat in the Barents Sea on Atlantic Water Transport Toward the Arctic: A Model Study (2023)
    Details
    Publication Date: 2023-12-05
    Description: The Arctic is warming much faster than the global average. This is known as Arctic Amplification and is caused by feedbacks in the local climate system. In this study, we explore a previously proposed hypothesis that an associated wind feedback in the Barents Sea could play an important role by increasing the warm water inflow into the Barents Sea. We find that the strong recent decrease in Barents Sea winter sea ice cover causes enhanced ocean‐atmosphere heat flux and a local air temperature increase, thus a reduction in sea level pressure and a local cyclonic wind anomaly with eastward winds in the Barents Sea Opening. By investigating various reanalysis products and performing high‐resolution perturbation experiments with the ocean and sea ice model FESOM2.1, we studied the impact of cyclonic atmospheric circulation changes on the warm Atlantic Water import into the Arctic via the Barents Sea and Fram Strait. We found that the observed wind changes do not significantly affect the warm water transport into the Barents Sea, which rejects the wind‐feedback hypothesis. At the same time, the cyclonic wind anomalies in the Barents Sea increase the amount of Atlantic Water recirculating westwards in Fram Strait by a downslope shift of the West Spitsbergen Current, and thus reduce Atlantic Water reaching the Arctic basin via Fram Strait. The resulting warm‐water anomaly in the Greenland Sea Gyre drives a local anticyclonic circulation anomaly.
    Description: Plain Language Summary: The Barents Sea has been experiencing a rapid decrease in its winter sea ice extent during the last 30 years. The loss of sea ice creates new areas where, in winter, the relatively warm ocean loses heat to the cold atmosphere. As warm air rises, the warming reduces the sea level air pressure, changing the atmospheric circulation to develop a local anticlockwise wind system centered over the northern Barents Sea. The associated eastward winds in the Barents Sea Opening and southeastward winds in Fram Strait affect how warm water from the North Atlantic moves toward the Arctic. There has been a long debate on whether this wind anomaly can increase the warm Atlantic Water transport into the Barents Sea and thus cause a positive feedback mechanism for further reducing the sea ice through melting. We find that the observed atmospheric circulation changes have no significant impact on the Barents Sea warm water inflow and thus reject the wind feedback as a strong player in contributing to Arctic Amplification. However, strong anomalous southeastward winds in Fram Strait and the northern Nordic Seas cause a southward shift of the warm Atlantic Water recirculation and reduce its flow toward the Arctic.
    Description: Key Points: A hypothesis that a wind feedback contributes to Arctic Amplification is rejected by performing dedicated wind perturbation simulations. Winter sea ice retreat in the northern Barents Sea causes anomalous cyclonic winds by locally enhancing ocean heat loss. Anomalous cyclonic winds result in less Atlantic Water transport through Fram Strait.
    Description: Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659
    Description: North‐German Supercomputing Alliance
    Description: https://github.com/FESOM/fesom2
    Description: https://doi.org/10.7265/N5K072F8
    Description: https://doi.org/10.5065/D6HH6H41
    Description: https://doi.org/10.5065/D6WH2N0S
    Description: https://github.com/FESOM/pyfesom2
    Description: https://doi.org/10.5281/zenodo.7458143
    Keywords: ddc:551 ; Barents Sea ; Arctic Amplification ; feedback ; Atlantic water ; modeling ; Fram Strait
    Language: English
    Type: doc-type:article
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  • 2
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    Sea Ice Rheology Experiment (SIREx): 2. Evaluating Linear Kinematic Features in High‐Resolution Sea Ice Simulations (2022)
    Details
    Publication Date: 2022-09-22
    Description: Simulating sea ice drift and deformation in the Arctic Ocean is still a challenge because of the multiscale interaction of sea ice floes that compose the Arctic Sea ice cover. The Sea Ice Rheology Experiment (SIREx) is a model intercomparison project of the Forum of Arctic Modeling and Observational Synthesis (FAMOS). In SIREx, skill metrics are designed to evaluate different recently suggested approaches for modeling linear kinematic features (LKFs) to provide guidance for modeling small‐scale deformation. These LKFs are narrow bands of localized deformation that can be observed in satellite images and also form in high resolution sea ice simulations. In this contribution, spatial and temporal properties of LKFs are assessed in 36 simulations of state‐of‐the‐art sea ice models and compared to deformation features derived from the RADARSAT Geophysical Processor System. All simulations produce LKFs, but only very few models realistically simulate at least some statistics of LKF properties such as densities, lengths, or growth rates. All SIREx models overestimate the angle of fracture between conjugate pairs of LKFs and LKF lifetimes pointing to inaccurate model physics. The temporal and spatial resolution of a simulation and the spatial resolution of atmospheric boundary condition affect simulated LKFs as much as the model's sea ice rheology and numerics. Only in very high resolution simulations (≤2 km) the concentration and thickness anomalies along LKFs are large enough to affect air‐ice‐ocean interaction processes.
    Description: Plain Language Summary: Winds and ocean currents continuously move and deform the sea ice cover of the Arctic Ocean. The deformation eventually breaks an initially closed ice cover into many individual floes, piles up floes, and creates open water. The distribution of ice floes and open water between them is important for climate research, because ice reflects more light and energy back to the atmosphere than open water, so that less ice and more open water leads to warmer oceans. Current climate models cannot simulate sea ice as individual floes. Instead, a variety of methods is used to represent the movement and deformation of the sea ice cover. The Sea Ice Rheology Experiment (SIREx) compares these different methods and assesses the deformation of sea ice in 36 numerical simulations. We identify and track deformation features in the ice cover, which are distinct narrow areas where the ice is breaking or piling up. Comparing specific spatial and temporal properties of these features, for example, the different amounts of fractured ice in specific regions, or the duration of individual deformation events, to satellite observations provides information about the realism of the simulations. From this comparison, we can learn how to improve sea ice models for more realistic simulations of sea ice deformation.
    Description: Key Points: All models simulate linear kinematic features (LKFs), but none accurately reproduces all LKF statistics. Resolved LKFs are affected strongest by spatial and temporal resolution of model grid and atmospheric forcing and rheology. Accurate scaling of deformation rates is a proxy only for realistic LKF numbers but not for any other LKF static.
    Description: DOE
    Description: HYCOM NOPP
    Description: Innovation Fund Denmark and the Horizon 2020 Framework Programme of the European Union
    Description: National centre for Climate Research, SALIENSEAS, ERA4CS
    Description: German Helmholtz Climate Initiative REKLIM (Regional Climate Change)
    Description: Gouvernement du Canada, Natural Sciences and Engineering Research Council of Canada (NSERC) http://dx.doi.org/10.13039/501100000038
    Description: Environment and Climate Change Canada Grants & Contributions program
    Description: Office of Naval Research Arctic and Global Prediction program
    Description: U.S. Department of Energy Regional and Global Model Analysis program
    Description: National Science Foundation Arctic System Science program
    Description: Deutsche Forschungsgemeinschaft (DFG) http://dx.doi.org/10.13039/501100001659
    Description: https://zenodo.org/communities/sirex
    Keywords: ddc:550.285
    Language: English
    Type: doc-type:article
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  • 3
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    Intensification of the Atlantic Water Supply to the Arctic Ocean Through Fram Strait Induced by Arctic Sea Ice Decline (2021)
    Details
    Publication Date: 2021-07-24
    Description: Substantial changes have occurred in the Arctic Ocean in the last decades. Not only sea ice has retreated significantly, but also the ocean at middepth showed a warming tendency. By using simulations we identified a mechanism that intensifies the upward trend in ocean heat supply to the Arctic Ocean through Fram Strait. The reduction in sea ice export through Fram Strait induced by Arctic sea ice decline increases the salinity in the Greenland Sea, which lowers the sea surface height and strengthens the cyclonic gyre circulation in the Nordic Seas. The Atlantic Water volume transport to the Nordic Seas and Arctic Ocean is consequently strengthened. This enhances the warming trend of the Arctic Atlantic Water layer, potentially contributing to the Arctic “Atlantification.” Our study suggests that the Nordic Seas can play the role of a switchyard to influence the heat budget of the Arctic Ocean.
    Keywords: 551.46 ; Arctic Ocean ; Atlantic Water ; sea ice decline ; Nordic Seas ; Greenland Sea ; Atlantification
    Language: English
    Type: article
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  • 4
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    Tropical Expansion Driven by Poleward Advancing Midlatitude Meridional Temperature Gradients (2021)
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    Publication Date: 2021-09-27
    Description: An abundance of evidence indicates that the tropics are expanding. Despite many attempts to decipher the cause, the underlying dynamical mechanism driving tropical expansion is still not entirely clear. Here, based on observations, multimodel simulations from the Coupled Model Intercomparison Project phase 5 (CMIP5) and purposefully designed numerical experiments, the variations and trends of the tropical width are explored from a regional perspective. We find that the width of the tropics closely follows the displacement of oceanic midlatitude meridional temperature gradients (MMTG). Under global warming, as a first-order response, the subtropical ocean experiences more surface warming because of the mean Ekman convergence of anomalously warm water. The enhanced subtropical warming, which is partially independent of natural climate oscillations, such as the Pacific Decadal Oscillation, leads to poleward advance of the MMTG and drives the tropical expansion. Our results, supported by both observations and model simulations, imply that global warming may have already significantly contributed to the ongoing tropical expansion, especially over the ocean-dominant Southern Hemisphere.
    Keywords: 551.6 ; Tropical Expansion ; Ocean Circulation ; Jet Stream ; Storm Track ; Mid-latitude Temperature Gradients ; Global Warming
    Language: English
    Type: map
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  • 5
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    Eddy Kinetic Energy in the Arctic Ocean From a Global Simulation With a 1-km Arctic (2021)
    Details
    Publication Date: 2021-10-12
    Description: Simulating Arctic Ocean mesoscale eddies in ocean circulation models presents a great challenge because of their small size. This study employs an unstructured-mesh ocean-sea ice model to conduct a decadal-scale global simulation with a 1-km Arctic. It provides a basinwide overview of Arctic eddy energetics. Increasing model resolution from 4 to 1 km increases Arctic eddy kinetic energy (EKE) and total kinetic energy (TKE) by about 40% and 15%, respectively. EKE is the highest along main currents over topography slopes, where strong conversion from available potential energy to EKE takes place. It is high in halocline with a maximum typically centered in the depth range of 70–110 m, and in the Atlantic Water layer of the Eurasian Basin as well. The seasonal variability of EKE along the continental slopes of southern Canada and eastern Eurasian basins is similar, stronger in fall and weaker in spring.
    Keywords: 551.46 ; Arctic Ocean ; mesoscale eddies ; eddy kinetic energy ; baroclinic instability
    Language: English
    Type: map
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  • 6
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    The Arctic Ocean in CMIP6 Models: Biases and Projected Changes in Temperature and Salinity (2022)
    Details
    Publication Date: 2022-06-17
    Description: We examine the historical evolution and projected changes in the hydrography of the deep basin of the Arctic Ocean in 23 climate models participating in the Coupled Model Intercomparison Project Phase 6 (CMIP6). The comparison between historical simulations and observational climatology shows that the simulated Atlantic Water (AW) layer is too deep and thick in the majority of models, including the multi‐model mean (MMM). Moreover, the halocline is too fresh in the MMM. Overall our findings indicate that there is no obvious improvement in the representation of the Arctic hydrography in CMIP6 compared to CMIP5. The climate change projections reveal that the sub‐Arctic seas are outstanding warming hotspots, causing a strong warming trend in the Arctic AW layer. The MMM temperature increase averaged over the upper 700 m at the end of the 21st century is about 40% and 60% higher in the Arctic Ocean than the global mean in the SSP245 and SSP585 scenarios, respectively. Salinity in the upper few hundred meters is projected to decrease in the Arctic deep basin in the MMM. However, the spread in projected salinity changes is large and the tendency toward stronger halocline in the MMM is not simulated by all the models. The identified biases and projection uncertainties call for a concerted effort for major improvements of coupled climate models.
    Description: Plain Language Summary: Coupled climate models are crucial tools for understanding and projecting climate change, especially for the Arctic where the climate is changing at unprecedented rates. A cold fresh layer of water (aka halocline) has been protecting sea‐ice at the surface from the warm layer of water (aka Atlantic Water layer) which flows underneath and could potentially accelerate sea ice melting from below. Climate change disturbs this vertical structure by changing the temperature and salinity of the Arctic Ocean (in a process known as Atlantification and Pacification) which may lead to additional sea ice basal melting and accelerate sea ice decline. We examined the simulated temperature and salinity in the Arctic Ocean deep basin in state‐of‐the‐art climate model simulations which provided the basis for the IPCC Assessment Report. We found that although there are persistent inaccuracies in the representation of Arctic temperature and salinity, the Arctic Ocean below 100 m is subject to much stronger warming than the average global ocean. On the other hand, the upper Arctic Ocean salinity is projected to decrease, which on average may strengthen the isolation of sea ice from Atlantic Water heat in the Arctic deep basin area.
    Description: Key Points: A too deep and thick Arctic Atlantic Water layer continues to be a major issue in contemporary climate models contributing to the CMIP6. The Arctic Ocean below the halocline is subject to much stronger warming than the global mean during the 21st century. The multi‐model mean upper ocean salinity is projected to decrease in the future but with high uncertainty.
    Description: European union's Horizon 2020 research and innovation programme
    Description: German Helmholtz climate initiative REKLIM
    Description: Deutsche Forschungsgemeinschaft (DFG) http://dx.doi.org/10.13039/501100001659
    Description: https://esgf-data.dkrz.de/projects/esgf-dkrz/
    Description: http://psc.apl.washington.edu/nonwp_projects/PHC/Data3.html
    Keywords: ddc:551
    Language: English
    Type: doc-type:article
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