Svetlana N. Losa

We present novel centennial-scale global climate simulations at kilometre-scale resolution utilizing the coupled IFS-FESOM model, featuring a 9 km atmosphere and a minimal 5 km ocean. Following the HighResMIP protocol, a 50-year high-resolution coupled spin-up was conducted, which was followed by a 65-year historical simulation (1950–2014) and a scenario simulation (SSP2-4.5, 2015-2050). This was accompanied by a 100-year control simulation (1950–2050) employing the 1950 radiative forcing. These simulations explicitly resolve ocean mesoscale eddies within a long-term climate context. Overall, the model demonstrates an improved mean climate state compared to CMIP6 models, with a notable reduction in persistent model biases, except for the polar regions. Performance metrics reveal reduced global errors in surface temperature, winds, and cloud formations. The very high-resolution ocean captures eddy-rich dynamics and realistic boundary current variability, contributing to an improved sea surface salinity patterns and a strengthened Atlantic Meridional Overturning Circulation (peak ~20 Sv). The simulation also reproduces internal climate variability with high fidelity, notably a realistic El Niño–Southern Oscillation with the desired quasi-periodicity (~4–5 years) and realistic winter teleconnection patterns. Sea ice and high-latitude biases have been identified as the primary remaining challenges: the model overestimates the extent of Arctic sea ice, resulting in a cold bias in the Northern high latitudes, while an initialization error in Antarctic snow cover induces a warm bias over Antarctica. Furthermore, there is a warm bias over the Weddell Sea with high ocean mix layer depth, associated with a winter devoid of sea ice. Despite persistent sea-ice and high-latitude biases, the coupled system remains stable over centennial time scales with minimal long-term drift. These results demonstrate the feasibility and scientific value of global coupled climate simulations operating in the ocean eddy-rich regime at sub-10 km resolution. The IFS–FESOM kilometre-scale configuration thus represents a significant step forward in the development of next-generation Earth system models that robustly bridge global climate dynamics and regional-scale processes over multi-decadal to centennial periods.

We present novel centennial-scale global climate simulations at kilometre-scale resolution utilizing the coupled IFS-FESOM model, featuring a 9 km atmosphere and a minimal 5 km ocean. Following the HighResMIP protocol, a 50-year high-resolution coupled spin-up was conducted, which was followed by a 65-year historical simulation (1950–2014) and a scenario simulation (SSP2-4.5, 2015-2050). This was accompanied by a 100-year control simulation (1950–2050) employing the 1950 radiative forcing. These simulations explicitly resolve ocean mesoscale eddies within a long-term climate context. Overall, the model demonstrates an improved mean climate state compared to CMIP6 models, with a notable reduction in persistent model biases, except for the polar regions. Performance metrics reveal reduced global errors in surface temperature, winds, and cloud formations. The very high-resolution ocean captures eddy-rich dynamics and realistic boundary current variability, contributing to an improved sea surface salinity patterns and a strengthened Atlantic Meridional Overturning Circulation (peak ~20 Sv). The simulation also reproduces internal climate variability with high fidelity, notably a realistic El Niño–Southern Oscillation with the desired quasi-periodicity (~4–5 years) and realistic winter teleconnection patterns. Sea ice and high-latitude biases have been identified as the primary remaining challenges: the model overestimates the extent of Arctic sea ice, resulting in a cold bias in the Northern high latitudes, while an initialization error in Antarctic snow cover induces a warm bias over Antarctica. Furthermore, there is a warm bias over the Weddell Sea with high ocean mix layer depth, associated with a winter devoid of sea ice. Despite persistent sea-ice and high-latitude biases, the coupled system remains stable over centennial time scales with minimal long-term drift. These results demonstrate the feasibility and scientific value of global coupled climate simulations operating in the ocean eddy-rich regime at sub-10 km resolution. The IFS–FESOM kilometre-scale configuration thus represents a significant step forward in the development of next-generation Earth system models that robustly bridge global climate dynamics and regional-scale processes over multi-decadal to centennial periods.

We present novel centennial-scale global climate simulations at kilometre-scale resolution utilizing the coupled IFS-FESOM model, featuring a 9 km atmosphere and a minimal 5 km ocean. Following the HighResMIP protocol, a 50-year high-resolution coupled spin-up was conducted, which was followed by a 65-year historical simulation (1950–2014) and a scenario simulation (SSP2-4.5, 2015-2050). This was accompanied by a 100-year control simulation (1950–2050) employing the 1950 radiative forcing. These simulations explicitly resolve ocean mesoscale eddies within a long-term climate context. Overall, the model demonstrates an improved mean climate state compared to CMIP6 models, with a notable reduction in persistent model biases, except for the polar regions. Performance metrics reveal reduced global errors in surface temperature, winds, and cloud formations. The very high-resolution ocean captures eddy-rich dynamics and realistic boundary current variability, contributing to an improved sea surface salinity patterns and a strengthened Atlantic Meridional Overturning Circulation (peak ~20 Sv). The simulation also reproduces internal climate variability with high fidelity, notably a realistic El Niño–Southern Oscillation with the desired quasi-periodicity (~4–5 years) and realistic winter teleconnection patterns. Sea ice and high-latitude biases have been identified as the primary remaining challenges: the model overestimates the extent of Arctic sea ice, resulting in a cold bias in the Northern high latitudes, while an initialization error in Antarctic snow cover induces a warm bias over Antarctica. Furthermore, there is a warm bias over the Weddell Sea with high ocean mix layer depth, associated with a winter devoid of sea ice. Despite persistent sea-ice and high-latitude biases, the coupled system remains stable over centennial time scales with minimal long-term drift. These results demonstrate the feasibility and scientific value of global coupled climate simulations operating in the ocean eddy-rich regime at sub-10 km resolution. The IFS–FESOM kilometre-scale configuration thus represents a significant step forward in the development of next-generation Earth system models that robustly bridge global climate dynamics and regional-scale processes over multi-decadal to centennial periods.

We present novel centennial-scale global climate simulations at kilometre-scale resolution utilizing the coupled IFS-FESOM model, featuring a 9 km atmosphere and a minimal 5 km ocean. Following the HighResMIP protocol, a 50-year high-resolution coupled spin-up was conducted, which was followed by a 65-year historical simulation (1950–2014) and a scenario simulation (SSP2-4.5, 2015-2050). This was accompanied by a 100-year control simulation (1950–2050) employing the 1950 radiative forcing. These simulations explicitly resolve ocean mesoscale eddies within a long-term climate context. Overall, the model demonstrates an improved mean climate state compared to CMIP6 models, with a notable reduction in persistent model biases, except for the polar regions. Performance metrics reveal reduced global errors in surface temperature, winds, and cloud formations. The very high-resolution ocean captures eddy-rich dynamics and realistic boundary current variability, contributing to an improved sea surface salinity patterns and a strengthened Atlantic Meridional Overturning Circulation (peak ~20 Sv). The simulation also reproduces internal climate variability with high fidelity, notably a realistic El Niño–Southern Oscillation with the desired quasi-periodicity (~4–5 years) and realistic winter teleconnection patterns. Sea ice and high-latitude biases have been identified as the primary remaining challenges: the model overestimates the extent of Arctic sea ice, resulting in a cold bias in the Northern high latitudes, while an initialization error in Antarctic snow cover induces a warm bias over Antarctica. Furthermore, there is a warm bias over the Weddell Sea with high ocean mix layer depth, associated with a winter devoid of sea ice. Despite persistent sea-ice and high-latitude biases, the coupled system remains stable over centennial time scales with minimal long-term drift. These results demonstrate the feasibility and scientific value of global coupled climate simulations operating in the ocean eddy-rich regime at sub-10 km resolution. The IFS–FESOM kilometre-scale configuration thus represents a significant step forward in the development of next-generation Earth system models that robustly bridge global climate dynamics and regional-scale processes over multi-decadal to centennial periods.

We present an assessment of the coupled ocean–sea ice–biogeochemistry model FESOM2.1–REcoM3, in which we integrated state equations for dissolved acidic polysaccharides (PCHO) and transparent exopolymer particles (TEP), as proposed by Engel et al. (2004), to explicitly describe these two organic carbon pools in the Arctic Ocean. PCHO is simulated as one fraction of the phytoplankton exudates, which can then aggregate to form larger particles, TEP. Since observational datasets on TEP are rare in time and space, we systematically assess the novel model implementation by stepwise discussing the essential components of the organic carbon cycle. Firstly, the simulated phytoplankton biomass yields good results when compared to in situ and remote-sensing products of total Chlorophyll a and particulate organic carbon. Secondly, we compare PCHO to observations in the Fram Strait, as an exemplary data-rich region, and to datasets in other regions of the Arctic Ocean. The model realistically reproduces a high phytoplankton exudation rate of PCHO under nutrient-depleted conditions. Thirdly, we assess simulated TEP concentrations by comparing them to in situ measurements from several campaigns to the Arctic Ocean. The simulation provides a first estimate of mean TEP concentrations of 200–400 µg C L⁻¹ on the continental shelves and 10–50 µg C L⁻¹ in the central basins (0–30 m depth range). Lastly, we put the model performance into a global context for TEP concentrations in the upper ocean layer. As such, the implementation of PCHO exudation, aggregation to TEP, and their remineralization processes into FESOM2.1–REcoM3 offers a reasonably good agreement with observations, on which further modeling work can build upon.

We present an assessment of the coupled ocean–sea ice–biogeochemistry model FESOM2.1–REcoM3, in which we integrated state equations for dissolved acidic polysaccharides (PCHO) and transparent exopolymer particles (TEP), as proposed by Engel et al. (2004), to explicitly describe these two organic carbon pools in the Arctic Ocean. PCHO is simulated as one fraction of the phytoplankton exudates, which can then aggregate to form larger particles, TEP. Since observational datasets on TEP are rare in time and space, we systematically assess the novel model implementation by stepwise discussing the essential components of the organic carbon cycle. Firstly, the simulated phytoplankton biomass yields good results when compared to in situ and remote-sensing products of total Chlorophyll a and particulate organic carbon. Secondly, we compare PCHO to observations in the Fram Strait, as an exemplary data-rich region, and to datasets in other regions of the Arctic Ocean. The model realistically reproduces a high phytoplankton exudation rate of PCHO under nutrient-depleted conditions. Thirdly, we assess simulated TEP concentrations by comparing them to in situ measurements from several campaigns to the Arctic Ocean. The simulation provides a first estimate of mean TEP concentrations of 200–400 μg C L⁻¹ on the continental shelves and 10–50 μg C L⁻¹ in the central basins (0–30 m depth range). Lastly, we put the model performance into a global context for TEP concentrations in the upper ocean layer. As such, the implementation of PCHO exudation, aggregation to TEP, and their remineralization processes into FESOM2.1–REcoM3 offers a reasonably good agreement with observations, on which further modeling work can build upon.

We present an assessment of the coupled ocean–sea ice–biogeochemistry model FESOM2.1–REcoM3, in which we integrated state equations for dissolved acidic polysaccharides (PCHO) and transparent exopolymer particles (TEP), as proposed by Engel et al. (2004), to explicitly describe these two organic carbon pools in the Arctic Ocean. PCHO is simulated as one fraction of the phytoplankton exudates, which can then aggregate to form larger particles, TEP. Since observational datasets on TEP are rare in time and space, we systematically assess the novel model implementation by stepwise discussing the essential components of the organic carbon cycle. Firstly, the simulated phytoplankton biomass yields good results when compared to in situ and remote-sensing products of total Chlorophyll a and particulate organic carbon. Secondly, we compare PCHO to observations in the Fram Strait, as an exemplary data-rich region, and to datasets in other regions of the Arctic Ocean. The model realistically reproduces a high phytoplankton exudation rate of PCHO under nutrient-depleted conditions. Thirdly, we assess simulated TEP concentrations by comparing them to in situ measurements from several campaigns to the Arctic Ocean. The simulation provides a first estimate of mean TEP concentrations of 200–400 μg C L⁻¹ on the continental shelves and 10–50 μg C L⁻¹ in the central basins (0–30 m depth range). Lastly, we put the model performance into a global context for TEP concentrations in the upper ocean layer. As such, the implementation of PCHO exudation, aggregation to TEP, and their remineralization processes into FESOM2.1–REcoM3 offers a reasonably good agreement with observations, on which further modeling work can build upon.

We present an assessment of the coupled ocean–sea ice–biogeochemistry model FESOM2.1–REcoM3, in which we integrated state equations for dissolved acidic polysaccharides (PCHO) and transparent exopolymer particles (TEP), as proposed by Engel et al. (2004), to explicitly describe these two organic carbon pools in the Arctic Ocean. PCHO is simulated as one fraction of the phytoplankton exudates, which can then aggregate to form larger particles, TEP. Since observational datasets on TEP are rare in time and space, we systematically assess the novel model implementation by stepwise discussing the essential components of the organic carbon cycle. Firstly, the simulated phytoplankton biomass yields good results when compared to in situ and remote-sensing products of total Chlorophyll a and particulate organic carbon. Secondly, we compare PCHO to observations in the Fram Strait, as an exemplary data-rich region, and to datasets in other regions of the Arctic Ocean. The model realistically reproduces a high phytoplankton exudation rate of PCHO under nutrient-depleted conditions. Thirdly, we assess simulated TEP concentrations by comparing them to in situ measurements from several campaigns to the Arctic Ocean. The simulation provides a first estimate of mean TEP concentrations of 200–400 μg C L⁻¹ on the continental shelves and 10–50 μg C L⁻¹ in the central basins (0–30 m depth range). Lastly, we put the model performance into a global context for TEP concentrations in the upper ocean layer. As such, the implementation of PCHO exudation, aggregation to TEP, and their remineralization processes into FESOM2.1–REcoM3 offers a reasonably good agreement with observations, on which further modeling work can build upon.

We present an assessment of the coupled ocean–sea ice–biogeochemistry model FESOM2.1–REcoM3, in which we integrated state equations for dissolved acidic polysaccharides (PCHO) and transparent exopolymer particles (TEP), as proposed by Engel et al. (2004), to explicitly describe these two organic carbon pools in the Arctic Ocean. PCHO is simulated as one fraction of the phytoplankton exudates, which can then aggregate to form larger particles, TEP. Since observational datasets on TEP are rare in time and space, we systematically assess the novel model implementation by stepwise discussing the essential components of the organic carbon cycle. Firstly, the simulated phytoplankton biomass yields good results when compared to in situ and remote-sensing products of total Chlorophyll a and particulate organic carbon. Secondly, we compare PCHO to observations in the Fram Strait, as an exemplary data-rich region, and to datasets in other regions of the Arctic Ocean. The model realistically reproduces a high phytoplankton exudation rate of PCHO under nutrient-depleted conditions. Thirdly, we assess simulated TEP concentrations by comparing them to in situ measurements from several campaigns to the Arctic Ocean. The simulation provides a first estimate of mean TEP concentrations of 200–400 μg C L⁻¹ on the continental shelves and 10–50 μg C L⁻¹ in the central basins (0–30 m depth range). Lastly, we put the model performance into a global context for TEP concentrations in the upper ocean layer. As such, the implementation of PCHO exudation, aggregation to TEP, and their remineralization processes into FESOM2.1–REcoM3 offers a reasonably good agreement with observations, on which further modeling work can build upon.