Drivers of the increasing Pacific inflow to the Arctic through the Bering Strait: Insights from gravity and altimetry data, and possible reasons why models fail to simulate the increasing flow
Cecilia
Peralta-Ferriz
Applied Physics Laboratory, University of Washington
Talk
The Pacific inflow to the Arctic, via the Bering Strait, has significant implications for the Arctic Ocean heat budget, including triggering the melt back of sea ice in the western Arctic. Thus, correct simulation of the Bering Strait throughflow is essential to understanding, simulating, and predicting Arctic change and polar amplification, and it is an enigma that many otherwise high-quality ocean models fail to simulate the observed increase in the Bering Strait flow.
Three decades (1991-2021) of mooring observations of the Bering Strait throughflow show significant trends of warming (0.03±0.02°C/yr), freshening (-0.010±0.007psu/yr) and northward flow increase (0.010±0.005Sv/yr, equivalent to a ~30% increase in the flow over this period). Analysis suggests the far-field, Pacific to Arctic pressure-head forcing of the flow is more important for the increasing trend in northward flow than the local atmospheric forcing. Using theoretical arguments and monthly data (2003-2014) of satellite ocean bottom pressure (OBP) from the Gravity Recovery and Climate Experiment (GRACE) and dynamic ocean topography (DOT) from satellite altimetry, we now find that decreasing OBP and DOT in the Arctic’s East Siberian Sea (ESS), forced by increasing westward winds along the Siberian shelf, drives the summer northward Bering Strait flow increase, while increasing westward winds in the northern Bering Sea drives the fall flow increase. Over the same period, the differences in DOT and OBP trends suggest a significant salinization (0.17±0.06psu/yr) of the ESS, which we attribute to a previously unrecognized increased influx of Pacific Waters into the ESS region.
Surprisingly, our results show that the OBP trends, and implied ESS salinization, are very sensitive to the GRACE OBP version used, with older versions having trends inconsistent with the observed flow increase. This suggests that models assimilating or matched to the older GRACE data may struggle to overcome this erroneous forcing. Furthermore, our results also show that ESS salinization may significantly mediate Bering Strait flow increase. Thus, a model with incorrect Pacific water salinities or pathways may also have erroneous Bering Strait forcings.
Three decades (1991-2021) of mooring observations of the Bering Strait throughflow show significant trends of warming (0.03±0.02°C/yr), freshening (-0.010±0.007psu/yr) and northward flow increase (0.010±0.005Sv/yr, equivalent to a ~30% increase in the flow over this period). Analysis suggests the far-field, Pacific to Arctic pressure-head forcing of the flow is more important for the increasing trend in northward flow than the local atmospheric forcing. Using theoretical arguments and monthly data (2003-2014) of satellite ocean bottom pressure (OBP) from the Gravity Recovery and Climate Experiment (GRACE) and dynamic ocean topography (DOT) from satellite altimetry, we now find that decreasing OBP and DOT in the Arctic’s East Siberian Sea (ESS), forced by increasing westward winds along the Siberian shelf, drives the summer northward Bering Strait flow increase, while increasing westward winds in the northern Bering Sea drives the fall flow increase. Over the same period, the differences in DOT and OBP trends suggest a significant salinization (0.17±0.06psu/yr) of the ESS, which we attribute to a previously unrecognized increased influx of Pacific Waters into the ESS region.
Surprisingly, our results show that the OBP trends, and implied ESS salinization, are very sensitive to the GRACE OBP version used, with older versions having trends inconsistent with the observed flow increase. This suggests that models assimilating or matched to the older GRACE data may struggle to overcome this erroneous forcing. Furthermore, our results also show that ESS salinization may significantly mediate Bering Strait flow increase. Thus, a model with incorrect Pacific water salinities or pathways may also have erroneous Bering Strait forcings.
Presentation file
PERALTAFERRIZ-CECILIA-POLAR-CP.pdf
(1.88 MB)