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This work was supported by the projects IlModelS, project no. CGL2014-726 59644-R and GReatModelS, project no. RTI2018-102305-B-C21. The work used resources of the Deutsches Klimarechenzentrum (DKRZ) granted by its Scientific Steering Committee (WLA) under project ID bm1026. Vladimir Alexeev was supported by the Interdisciplinary Research for Arctic Coastal Environments (InteRFACE) project through the Department of Energy, Office of Science, Biological and Environmental Research Program's Regional and Global Model Analysis program, and by NOAA project NA18OAR4590417. We also wish to thank Veronika Gayler for technical support on JSBACH and Christian Reick for helpful comments and discussion., Previous analytical and simulation-based analyses suggest that deeper land surface models are needed to realistically simulate the terrestrial thermal state in climate models, with implications for land-atmosphere interactions. Analytical approaches mainly focused on the subsurface propagation of harmonics such as the annual temperature signal, and a direct comparison with climate-change model output has been elusive. This study addresses the propagation of a harmonic pulse fitted to represent the timescale and amplitude of anthropogenic warming. Its comparison to land model simulations with stepwise increased bottom boundary depth leads to an agreement between the simulation-based and analytical frameworks for long-term climate trends. Any depth increase gradually decreases the relative error in the subsurface thermodynamics, and a minimum depth of 170 m is recommended to simulate the ground climate adequately. The approach provides an accurate estimate of the required land-model depth for climate-change simulations and assesses the relative bias in insufficiently deep land models. Plain Language Summary Many current-generation climate models have land components that are too shallow. Under climate change conditions, the long-term warming trend at the surface propagates deeper into the ground than the commonly used 3-10 m. Shallow models alter the terrestrial heat storage and distribution of temperatures in the subsurface, influencing the simulated land-atmosphere interactions. Previous studies focusing on annual timescales suggest that deeper models are required to match subsurface-temperature observations and the classic analytical heat conduction solution. However, for a systematic investigation of land-model deepening in the frame of anthropogenic climate change, the classic analytical solution is inaccurate because it does not mimic the timescale and amplitude of the simulated warming trend. This study intends to bridge the gap between analytical and simulatio, Ministerio de Economía y Competitividad (MINECO), Scientific Steering Committee (WLA), Interdisciplinary Research for Arctic Coastal Environments (InteRFACE) project through the Department of Energy, Office of Science, Biological and Environmental Research Program's Regional and Global Model Analysis program, NOAA project, Depto. de Física de la Tierra y Astrofísica, Fac. de Ciencias Físicas, TRUE, pub

Copyright 2008 by the American Geophysical Union. This research was funded by grants from NSERC Discovery, AIF (ACOA), CFCAS, and ACEnet (HB); Ramón y Cajal (JFGR); NSERC PGS-D (MBS); and NSERC USRA (AHM)., Shallow bottom boundary conditions (BBCs) in the soil components of general circulation models (GCMs) impose artificial limits on subsurface heat storage. To assess this problem we estimate the subsurface heat content from two future climate simulations and compare to that obtained from an offline soil model (FDLSM) driven by GCM skin temperatures. FDLSM is then used as an offline substitute for the subsurface of the GCM ECHO-G. With a 600-m BBC and driven by ECHO-G future temperatures, the FDLSM subsurface absorbs 6.2 (7.5) times more heat than the ECHO-G soil model (10 m deep) under the Intergovernmental Panel on Climate Change (IPCC) A2 (B2) emission scenario. This suggests that shallow BBCs in GCM simulations may underestimate the heat stored in the subsurface, particularly for northern high latitudes. This effect could be relevant in assessing the energy balance and climate change in the next century., Natural Sciences and Engineering Research Council of Canada (NSERC), Atlantic Innovation Fund (AIF), Canadá, Canadian Foundation for Climate and Atmospheric Sciences (CFCAS), Atlantic Computational Excellence Network (ACEnet), Canadá, Programa Ramón y Cajal (MEC), NSERC PGS-D, Undergraduate Student Research Awards (USRA), NSERC, Atlantic Canada Opportunities Agency (ACOA), Depto. de Física de la Tierra y Astrofísica, Fac. de Ciencias Físicas, TRUE, pub

Copyright 2010 by the American Geophysical Union. This research was supported by grants from the Canadian Foundation for Climate and Atmospheric Sciences (CFCAS), the Natural Sciences and Engineering Research Council of Canada (NSERC), and the Atlantic Innovation Fund (ACOA-AIF). A. H. M. D. and M. B. S. are grateful for their support received from NSERC as a PGS-M and a PGS-D respectively. JFGR acknowledges support from projects CGL2008-06558-C02-01, MMARM-200800050084028 and MMARM-20080005008354., Heat fluxes in the continental subsurface were estimated from general circulation model (GCM) simulations of the climate of the last millennium and compared to those obtained from subsurface geothermal data. Since GCMs have bottom boundary conditions (BBCs) that are less than 10 m deep and thus may be thermodynamically restricted in the continental subsurface, we used an idealized land surface model (LSM) with a very deep BBC to estimate the potential for realistic subsurface heat storage in the absence of bottom boundary constraints. Results indicate that there is good agreement between observed fluxes and GCM simulated fluxes for the 1780-1980 period when the GCM simulated temperatures are coupled to the LSM with deep BBC. These results emphasize the importance of placing a deep BBC in GCM soil components for the proper simulation of the overall continental heat budget. In addition, the agreement between the LSM surface fluxes and the borehole temperature reconstructed fluxes lends additional support to the overall quality of the GCM (ECHO-G) paleoclimatic simulations., Canadian Foundation for Climate and Atmospheric Sciences (CFCAS), Natural Sciences and Engineering Research Council of Canada (NSERC), Atlantic Innovation Fund (ACOA - AIF), Ministerio de Medio Ambiente, Medio Rural y Marino de España (Ministerio de Medio Ambiente, Medio Rural y Marino de España (MARM), España, Depto. de Física de la Tierra y Astrofísica, Fac. de Ciencias Físicas, TRUE, pub

Gradually decaying Arctic sea ice changes the boundary conditions at the surface, separating ocean and atmosphere. In recent years, substantial reductions in sea ice during winter have been observed in the Atlantic sector of the Arctic Ocean, which forms the gateway for warm water inflow from the midlatitudes. In this study, we used routine output from the Mercator Ocean global operational system (MOGOS) to assess the efficiency of winter thermohaline convection transporting heat from deep layers to the ocean surface along the Atlantic origin water (AW) pathway, between Svalbard and Franz Joseph Land in the Nansen Basin. Positive temperature extremes in the AW layer in midwinter promote favorable prerequisite conditions for deep‐reaching thermohaline convection, with explicit signs captured by the MOGOS. Balance equations with several assumptions for the compact region around the position (81.30°N, 31°E) of the long‐term (2004–2010) mooring demonstrated that winter heat loss at the ocean surface is mainly compensated by convective heat flux from the AW layer. Heat and salt fluxes, associated with horizontal advection, are compatible with convective fluxes, while contribution of ice formation/melt is substantially smaller. Conclusion about the dominant role of vertical convection in shaping thermohaline structure and reducing sea ice in winter is supported by correlation analysis of the MOGOS output and mooring‐based measurements. Unfavorable background conditions (thick and consolidated sea ice in combination with specific directions of ice drift) may significantly alter convection development, as demonstrated for two sequential years with substantially different external forcing.

Gradually decaying Arctic sea ice changes the boundary conditions at the surface, separating ocean and atmosphere. In recent years, substantial reductions in sea ice during winter have been observed in the Atlantic sector of the Arctic Ocean, which forms the gateway for warm water inflow from the midlatitudes. In this study, we used routine output from the Mercator Ocean global operational system (MOGOS) to assess the efficiency of winter thermohaline convection transporting heat from deep layers to the ocean surface along the Atlantic origin water (AW) pathway, between Svalbard and Franz Joseph Land in the Nansen Basin. Positive temperature extremes in the AW layer in midwinter promote favorable prerequisite conditions for deep‐reaching thermohaline convection, with explicit signs captured by the MOGOS. Balance equations with several assumptions for the compact region around the position (81.30°N, 31°E) of the long‐term (2004–2010) mooring demonstrated that winter heat loss at the ocean surface is mainly compensated by convective heat flux from the AW layer. Heat and salt fluxes, associated with horizontal advection, are compatible with convective fluxes, while contribution of ice formation/melt is substantially smaller. Conclusion about the dominant role of vertical convection in shaping thermohaline structure and reducing sea ice in winter is supported by correlation analysis of the MOGOS output and mooring‐based measurements. Unfavorable background conditions (thick and consolidated sea ice in combination with specific directions of ice drift) may significantly alter convection development, as demonstrated for two sequential years with substantially different external forcing.