09:00 〜 09:15
[ACG52-01] Decadal Variability in Sea Ice Meltwater Amount in the Beaufort Gyre and Its Association with Multi-Year Ice Loss
キーワード：西部北極海、海氷融解水、ボーフォート循環、多年氷
The Beaufort Gyre (BG) is the largest freshwater reservoir in the Arctic Ocean, intermittently releasing freshwater into the Atlantic through the Nares Strait and Fram Strait. When released, this freshwater influences the Labrador Sea salinity, affecting the formation of North Atlantic Deep Water (NADW) and the Atlantic Meridional Overturning Circulation (AMOC). As Arctic warming intensifies and sea ice continues to decline, understanding the contribution of meltwater to the BG's freshwater budget is crucial. However, the role of the multi-year ice (MYI) melting in the freshwater accumulation remains unclear, particularly following the substantial loss of MYI associated with an Arctic Sea Ice regime shift in 2007.
In this study, we quantify the meltwater amount in the Pacific Arctic as meltwater thickness (MWT) and investigates its decadal variability. We updated the water mass analysis methodology of Mensah et al. (2025), utilizing historical T-S-δ18O data from ~1950 to the present to separate meltwater into "new meltwater", representing annual sea ice melt, and "total meltwater", which includes MYI-derived meltwater accumulated over time.
Results indicate a mean value of 2.25 m for the new MWT in the BG vs. 8.20 m for the total MWT, i.e., approximately 27% of the total MWT originates from annual sea ice melt. A strong regional contrast in meltwater multidecadal trends is observed: in the Chukchi Sea, the new MWT has declined by -20.2 cm per decade since 1990 due to reduced seasonal ice, whereas in the BG, the new MWT has increased by 13.2 cm per decade from 1990 to 2020.
Following the 2007 Arctic sea ice regime shift, the total meltwater volume in the BG increased by ~1600 km3 between 2005 and 2008, and the mean total MWT increased by 1.54 m between 1990-2007 and 2008-2020, consistent with the loss of MYI. This highlights the key role played by the MYI decline in the long-term freshwater accumulation in the BG. Lastly, we examined the influence of the Beaufort Sea High (BSH) atmospheric pressure system on the spatial distribution of meltwater. Strong BSH years correspond to positive meltwater anomalies in the northwestern BG, whereas weak BSH years shift these anomalies southeast, a pattern confirmed by Sea Surface Height Anomalies (SSHA).
The findings of our study highlight the interplay between MYI melting, atmospheric forcing, and freshwater storage, providing a better understanding of freshwater variability in the Pacific Arctic under a changing climate.
In this study, we quantify the meltwater amount in the Pacific Arctic as meltwater thickness (MWT) and investigates its decadal variability. We updated the water mass analysis methodology of Mensah et al. (2025), utilizing historical T-S-δ18O data from ~1950 to the present to separate meltwater into "new meltwater", representing annual sea ice melt, and "total meltwater", which includes MYI-derived meltwater accumulated over time.
Results indicate a mean value of 2.25 m for the new MWT in the BG vs. 8.20 m for the total MWT, i.e., approximately 27% of the total MWT originates from annual sea ice melt. A strong regional contrast in meltwater multidecadal trends is observed: in the Chukchi Sea, the new MWT has declined by -20.2 cm per decade since 1990 due to reduced seasonal ice, whereas in the BG, the new MWT has increased by 13.2 cm per decade from 1990 to 2020.
Following the 2007 Arctic sea ice regime shift, the total meltwater volume in the BG increased by ~1600 km3 between 2005 and 2008, and the mean total MWT increased by 1.54 m between 1990-2007 and 2008-2020, consistent with the loss of MYI. This highlights the key role played by the MYI decline in the long-term freshwater accumulation in the BG. Lastly, we examined the influence of the Beaufort Sea High (BSH) atmospheric pressure system on the spatial distribution of meltwater. Strong BSH years correspond to positive meltwater anomalies in the northwestern BG, whereas weak BSH years shift these anomalies southeast, a pattern confirmed by Sea Surface Height Anomalies (SSHA).
The findings of our study highlight the interplay between MYI melting, atmospheric forcing, and freshwater storage, providing a better understanding of freshwater variability in the Pacific Arctic under a changing climate.