2026-03-27 スタンフォード大学
＜関連情報＞
- https://news.stanford.edu/stories/2026/03/antarctic-sea-ice-growth-decline-study-research
- https://www.pnas.org/doi/10.1073/pnas.2530832123
- https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2024GL112639
南極海の海氷域の近年の極端な変動は、海洋の熱換気によって調節されている Recent extremes in Antarctic sea ice extent modulated by ocean heat ventilation
Earle A. Wilson, Lexi Arlen, and Ethan C. Campbell
Proceedings of the National Academy of Sciences Published:March 23, 2026
DOI:https://doi.org/10.1073/pnas.2530832123
Significance
Antarctic sea ice is an integral component of the climate system, regulating heat and CO2 exchange between the surface and deep ocean. Contrary to the gradual ice loss predicted by climate models, we have observed ice expansion until 2015, followed by an abrupt and sustained decline in subsequent years. Using nearly two decades of under-ice Argo float data, we find that the ice expansion was partly due to surface freshening from enhanced precipitation that trapped subsurface ocean heat. After 2015, intensified wind-driven upwelling reversed freshening trends, releasing years of accumulated ocean heat that contributed to unprecedented sea ice loss. These results demonstrate the potential for wind-driven upwelling and freshwater fluxes to drive multiyear Antarctic sea ice trends.
Abstract
Antarctic sea ice extent (SIE) has experienced unprecedented variability in recent decades, with record expansion through 2015, followed by an abrupt transition to sustained decline. Using over two decades of under-ice Argo float observations, we show that changes in ocean heat ventilation have modulated these extreme sea ice variations on interannual timescales. Between 2007 and 2015, the ocean thermocline warmed and shoaled within the Weddell Sea and off East Antarctica, with the former accounting for most of the interannual variability in Antarctic SIE. After 2016, as Antarctic SIE declined, surface salinity increased, enhancing exchange between the sharpened thermocline and surface waters. Idealized modeling of the Weddell Sea indicates that these upper ocean trends were due to concurrent variations in wind-driven Ekman upwelling and precipitation. During the sea ice expansion phase, increased precipitation enhanced ocean stratification, suppressing the upward flux of subsurface heat while promoting sea ice growth. However, between 2014 and 2016, a nearly three-fold increase in upwelling rates weakened the upper ocean stratification, releasing the accumulated subsurface heat. Though a similar sequence of events occurred along the East Antarctic margin, distinct upper-ocean trends and surface forcing in the Pacific sector of the Southern Ocean imply alternative drivers of recent sea ice loss in that region. Nevertheless, these results suggest that future multiyear Antarctic SIE variability will depend on the competing influences of wind-driven upwelling and surface freshwater fluxes.
過小評価された南極海の塩分低下が、シミュレーションされた過去の海面水温傾向に与える影響 The Impact of Underestimated Southern Ocean Freshening on Simulated Historical Sea Surface Temperature Trends
Zachary Kaufman, Earle Wilson, Ariaan Purich, Rebecca Beadling, Yuchen Li
Geophysical Research Letters Published: 27 March 2025
DOI:https://doi.org/10.1029/2024GL112639
Abstract
Climate models generally overestimate observed Southern Ocean surface warming trends over the past three decades. This discrepancy could be due to biased surface freshwater fluxes in climate models, which underestimate observed precipitation increases and do not account for Antarctic Ice Sheet and shelf mass loss. Though past modeling experiments show surface cooling in response to freshwater perturbations, sea surface temperature (SST) responses vary widely across models. To address these ambiguities, we compute linear SST response functions for standardized freshwater flux increases across a subset of CMIP6 models. For 1990–2021, underestimated freshwater fluxes can explain up to 60% of the model-observation SST trend difference. The response functions reveal that Southern Ocean SST trends are more sensitive to freshwater fluxes concentrated along the Antarctic margin versus more spatially distributed fluxes. Our results quantify, for the first time, the impact of missing freshwater forcing on Southern Ocean SST trends across a multi-model ensemble.
Plain Language Summary
While most of Earth’s surface has warmed over the satellite era, the Southern Ocean sea surface experienced a prolonged cooling trend. One proposed driver of this anomalous cooling is the increasing flux of freshwater into the Southern Ocean, which restricts the exchange of surface waters with warmer waters at depth. Climate model simulations underestimate the Southern Ocean freshening trend and fail to simulate the observed surface cooling. Here, we quantify the impact of missing freshwater fluxes on sea surface temperatures across a range of climate models and assess their importance for historical climate trends. We focus on freshwater contributions from the melting Antarctic Ice Sheet and changes in precipitation, which play an important role in the Southern Ocean. A key conclusion is that underestimated freshwater fluxes into the Southern Ocean help explain climate models’ inability to reproduce observed sea surface temperature trends.
