Kazuki Nakata

The Arctic is the fastest changing region in the world. Its atmosphere is warming 3–4 times the global average; the ocean is warming through increased advection of heat from the Atlantic and Pacific; the sea ice cover is disappearing, thinning, and becoming more mobile. The interactions between ocean, ice and atmosphere are also evolving. These changes are manifest in polynyas, openings in the sea ice that are crucial for exchanges of heat, moisture, momentum and gases between ocean and atmosphere, but also for ecosystems, Indigenous communities, and navigation. We here review how polynyas and their impact on the climate system have changed throughout the satellite record, focussing on the last twenty years. The trend is of fewer but larger polynyas that open for longer, unless they depend on ice arches (in which case they are shorter-lived). Many regions have switched from ''latent heat'' polynyas, only driven by dynamics, to ''hybrid'', where the heat from ocean or atmosphere matters. Consistent with that switch and with an overall warming and wetting of the atmosphere, moisture fluxes from polynyas in winter seem to be decreasing despite an increase in polynya area. How this will impact the low altitude clouds, generated by polynyas and that help maintain polynyas, has not been studied. Similarly, sea ice production in polynyas is decreasing at the pan-Arctic scale. In the ocean's Eurasian basin, process studies suggest a conflict between this switch to hybrid polynyas (suppressing dense water formation) and Atlantification (favouring it). In the Amerasian basin, where upwelling of warm water is necessary for dense water formation, this should be enhanced, but it also facilitates the inflow of warm water into the Greenland glacial fjords. In all components of the climate system, large uncertainties remain because of the lack of direct observations and the lack of continuous time series in the atmosphere, ice, and ocean.

The primary production and zooplankton life cycles in the Southern Ocean synchronize with seasonal sea ice melting, during which particulate organic carbon (POC) and nitrogen (PN), including ice algae, are supplied from sea ice into the water column. To understand carbon flow through food webs in productive marginal ice zones, it is necessary to determine the quantity and quality of organic carbon and nitrogen in sea ice. However, knowledge regarding brash sea ice is scarce, even though it is the predominant form at the Antarctic ice edge. In this study, 102 sea-ice samples were collected from the Indian sector (20–160° E) during summer to clarify variations in isotopic baselines and the potential contribution of sea ice-derived carbon and nitrogen to the water column. The δ ¹³ C and δ ¹⁵ N values of all sea-ice particulate matter samples were -24.6±3.2 ‰ and +1.5±2.2 ‰ (mean ± standard deviation), respectively, showing greater variability compared to those in seawater (-28.8±1.0 ‰ for δ ¹³ C and -0.5±1.4 ‰ for δ ¹⁵ N). We identified correlations of δ ¹³ C and δ ¹⁵ N with organic matter and nutrient concentrations and their ratios (e.g., silicate : nitrate), suggesting that nutrient consumption and organic matter decomposition influenced those isotopic characteristics in sea ice. Using freshwater flux from sea ice melt and the measured sea-ice POC concentrations, the POC supply was estimated to be 4.1±0.3 Tg C yr ⁻¹ , equivalent to 14.7±2.8 % of primary production in the marginal ice zone of the studied region. This result suggests that sea ice melt provides significant portion of organic matters potentially supporting Antarctic ecosystems in the seasonal sea ice zone, which could be traced by difference of sea-ice and seawater stable isotope compositions.

The Arctic is the fastest changing region in the world. Its atmosphere is warming 3–4 times the global average; the ocean is warming through increased advection of heat from the Atlantic and Pacific; the sea ice cover is disappearing, thinning, and becoming more mobile. The interactions between ocean, ice and atmosphere are also evolving. These changes are manifest in polynyas, openings in the sea ice that are crucial for exchanges of heat, moisture, momentum and gases between ocean and atmosphere, but also for ecosystems, Indigenous communities, and navigation. We here review how polynyas and their impact on the climate system have changed throughout the satellite record, focussing on the last twenty years. The trend is of fewer but larger polynyas that open for longer, unless they depend on ice arches (in which case they are shorter-lived). Many regions have switched from ''latent heat'' polynyas, only driven by dynamics, to ''hybrid'', where the heat from ocean or atmosphere matters. Consistent with that switch and with an overall warming and wetting of the atmosphere, moisture fluxes from polynyas in winter seem to be decreasing despite an increase in polynya area. How this will impact the low altitude clouds, generated by polynyas and that help maintain polynyas, has not been studied. Similarly, sea ice production in polynyas is decreasing at the pan-Arctic scale. In the ocean's Eurasian basin, process studies suggest a conflict between this switch to hybrid polynyas (suppressing dense water formation) and Atlantification (favouring it). In the Amerasian basin, where upwelling of warm water is necessary for dense water formation, this should be enhanced, but it also facilitates the inflow of warm water into the Greenland glacial fjords. In all components of the climate system, large uncertainties remain because of the lack of direct observations and the lack of continuous time series in the atmosphere, ice, and ocean.

The primary production and zooplankton life cycles in the Southern Ocean synchronize with seasonal sea ice melting, during which particulate organic carbon (POC) and nitrogen (PN), including ice algae, are supplied from sea ice into the water column. To understand carbon flow through food webs in this productive marginal ice zones, it is necessary to determine the quantity and quality of organic carbon and nitrogen in sea ice. However, knowledge regarding brash sea ice is scarce, even though it is the predominant form at the Antarctic ice edge. In this study, 102 sea-ice samples were collected from the Indian sector (20–160°E) during summer to clarify variations in isotopic baselines and the potential contribution of sea ice-derived carbon and nitrogen to the water column. The δ¹³C and δ¹⁵N values of sea-ice particulate matter were −24.5±3.2‰ and +1.6±2.2‰ (mean±standard deviation), respectively, showing greater variability compared to those in seawater (−28.8±1.0‰ for δ¹³C and −0.5±1.4‰ for δ¹⁵N). We identified correlations of δ¹³C and δ¹⁵N with organic matter and nutrient concentrations and their ratios (e.g., silicate:nitrate), indicating that nutrient consumption and organic matter decomposition influenced those isotopic characteristics in sea ice. Using freshwater flux from sea ice melt and the measured sea-ice POC concentrations, this supply was estimated to be 4.6±0.3 Tg C year⁻¹, equivalent to >14% of primary production in the marginal ice zone of the studied region. These results suggest that the carbon supply from sea ice is a crucial factor supporting ecosystems in the seasonal sea ice zone.

The primary production and zooplankton life cycles in the Southern Ocean synchronize with seasonal sea ice melting, during which particulate organic carbon (POC) and nitrogen (PN), including ice algae, are supplied from sea ice into the water column. To understand carbon flow through food webs in this productive marginal ice zones, it is necessary to determine the quantity and quality of organic carbon and nitrogen in sea ice. However, knowledge regarding brash sea ice is scarce, even though it is the predominant form at the Antarctic ice edge. In this study, 102 sea-ice samples were collected from the Indian sector (20–160°E) during summer to clarify variations in isotopic baselines and the potential contribution of sea ice-derived carbon and nitrogen to the water column. The δ¹³C and δ¹⁵N values of sea-ice particulate matter were −24.5±3.2‰ and +1.6±2.2‰ (mean±standard deviation), respectively, showing greater variability compared to those in seawater (−28.8±1.0‰ for δ¹³C and −0.5±1.4‰ for δ¹⁵N). We identified correlations of δ¹³C and δ¹⁵N with organic matter and nutrient concentrations and their ratios (e.g., silicate:nitrate), indicating that nutrient consumption and organic matter decomposition influenced those isotopic characteristics in sea ice. Using freshwater flux from sea ice melt and the measured sea-ice POC concentrations, this supply was estimated to be 4.6±0.3 Tg C year⁻¹, equivalent to >14% of primary production in the marginal ice zone of the studied region. These results suggest that the carbon supply from sea ice is a crucial factor supporting ecosystems in the seasonal sea ice zone.

The Arctic is the fastest changing region in the world. Its atmosphere is warming 3–4 times the global average; the ocean is warming through increased advection of heat from the Atlantic and Pacific; the sea ice cover is disappearing, thinning, and becoming more mobile. The interactions between ocean, ice and atmosphere are also evolving. These changes are manifest in polynyas, openings in the sea ice that are crucial for exchanges of heat, moisture, momentum and gases between ocean and atmosphere, but also for ecosystems, Indigenous communities, and navigation. We here review how polynyas and their impact on the climate system have changed throughout the satellite record, focussing on the last twenty years. The trend is of fewer but larger polynyas that open for longer, unless they depend on ice arches (in which case they are shorter-lived). Many regions have switched from ''latent heat'' polynyas, only driven by dynamics, to ''hybrid'', where the heat from ocean or atmosphere matters. Consistent with that switch and with an overall warming and wetting of the atmosphere, moisture fluxes from polynyas in winter seem to be decreasing despite an increase in polynya area. How this will impact the low altitude clouds, generated by polynyas and that help maintain polynyas, has not been studied. Similarly, sea ice production in polynyas is decreasing at the pan-Arctic scale. In the ocean's Eurasian basin, process studies suggest a conflict between this switch to hybrid polynyas (suppressing dense water formation) and Atlantification (favouring it). In the Amerasian basin, where upwelling of warm water is necessary for dense water formation, this should be enhanced, but it also facilitates the inflow of warm water into the Greenland glacial fjords. In all components of the climate system, large uncertainties remain because of the lack of direct observations and the lack of continuous time series in the atmosphere, ice, and ocean.

The primary production and zooplankton life cycles in the Southern Ocean synchronize with seasonal sea ice melting, during which particulate organic carbon (POC) and nitrogen (PN), including ice algae, are supplied from sea ice into the water column. To understand carbon flow through food webs in this productive marginal ice zones, it is necessary to determine the quantity and quality of organic carbon and nitrogen in sea ice. However, knowledge regarding brash sea ice is scarce, even though it is the predominant form at the Antarctic ice edge. In this study, 102 sea-ice samples were collected from the Indian sector (20–160°E) during summer to clarify variations in isotopic baselines and the potential contribution of sea ice-derived carbon and nitrogen to the water column. The δ¹³C and δ¹⁵N values of sea-ice particulate matter were −24.5±3.2‰ and +1.6±2.2‰ (mean±standard deviation), respectively, showing greater variability compared to those in seawater (−28.8±1.0‰ for δ¹³C and −0.5±1.4‰ for δ¹⁵N). We identified correlations of δ¹³C and δ¹⁵N with organic matter and nutrient concentrations and their ratios (e.g., silicate:nitrate), indicating that nutrient consumption and organic matter decomposition influenced those isotopic characteristics in sea ice. Using freshwater flux from sea ice melt and the measured sea-ice POC concentrations, this supply was estimated to be 4.6±0.3 Tg C year⁻¹, equivalent to >14% of primary production in the marginal ice zone of the studied region. These results suggest that the carbon supply from sea ice is a crucial factor supporting ecosystems in the seasonal sea ice zone.

The primary production and zooplankton life cycles in the Southern Ocean synchronize with seasonal sea ice melting, during which particulate organic carbon (POC) and nitrogen (PN), including ice algae, are supplied from sea ice into the water column. To understand carbon flow through food webs in this productive marginal ice zones, it is necessary to determine the quantity and quality of organic carbon and nitrogen in sea ice. However, knowledge regarding brash sea ice is scarce, even though it is the predominant form at the Antarctic ice edge. In this study, 102 sea-ice samples were collected from the Indian sector (20–160°E) during summer to clarify variations in isotopic baselines and the potential contribution of sea ice-derived carbon and nitrogen to the water column. The δ13C and δ15N values of sea-ice particulate matter were −24.5±3.2‰ and +1.6±2.2‰ (mean±standard deviation), respectively, showing greater variability compared to those in seawater (−28.8±1.0‰ for δ13C and −0.5±1.4‰ for δ15N). We identified correlations of δ13C and δ15N with organic matter and nutrient concentrations and their ratios (e.g., silicate:nitrate), indicating that nutrient consumption and organic matter decomposition influenced those isotopic characteristics in sea ice. Using freshwater flux from sea ice melt and the measured sea-ice POC concentrations, this supply was estimated to be 4.6±0.3 Tg C year−1, equivalent to >14% of primary production in the marginal ice zone of the studied region. These results suggest that the carbon supply from sea ice is a crucial factor supporting ecosystems in the seasonal sea ice zone.

The Amundsen and Bellingshausen Seas are among the most rapidly changing regions of the Southern Ocean, playing a pivotal role in Antarctic ice‐shelf mass loss and global sea‐level rise. Several ocean models have been developed to investigate these changes, revealing complex interactions among the atmosphere, ocean, sea ice, and ice shelves. However, the diversity of model configurations, parameter choices, and model versions often hampers user-friendliness, limits meaningful intercomparison, and constrains broader multidisciplinary use. Here, we present a regional ocean model configuration of the Amundsen and Bellingshausen Seas with a horizontal resolution of 2.2–3.9 km based on MITgcm, downscaled from the global ECCO-LLC270 ocean state estimate, and further optimized using regional observations. We conduct extensive model evaluation and demonstrate its applications through multiple examples and previously published analyses, with the goal of providing model configuration and their outputs – achieving good model-data agreement – to the broad scientific community. The model reproduces key hydrographic features of the region, including realistic temperature and salinity profiles and water mass distributions that closely align with local CTD and mooring observations. Simulated sea-ice concentration and extent are consistent with satellite observations, capturing the observed seasonal cycle and spatial variability. Ice-shelf basal melt rates fall within the range of available satellite and in situ estimates. The configuration also includes passive tracers for surface water, ice-shelf meltwater, and Circumpolar Deep Water, as well as Lagrangian particle-tracking capabilities that facilitate studies of water-mass transformation and tracer pathways. By providing open access to the model code, configuration, diagnostics, tracer outputs, and sensitivity experiments, we aim to support data interpretation, hypothesis testing, and observational planning across the broad scientific community.