17:15 〜 18:30
[MIS16-P11] Mid- to late Holocene variability of the Aleutian Low Atmospheric Pressure Cell: Forcing by the Western Jet
キーワード：アリューシャン低気圧、完新世、酸素同位体比、偏西風
The North Pacific Ocean is the largest geographic feature in the Northern Hemisphere and its interactions with the overlying atmosphere drives critical components of the global climate system. The Aleutian Low (AL) is one of the major atmospheric systems that determines environmental conditions during winter in the North Pacific Ocean, with impacts that affect the climates of both Asia and North America. However, the multi-centennial and longer scale dynamics of the AL during the Holocene is not fully understood.
The climate mechanism(s) that are responsible for generating AL intensity and position changes over recent instrumental timescales are also poorly understood. One important component is the Westerly Jet (WJ), which is closely associated with the AL through its alternations on cyclogenesis, monsoon development, and storm tracks (e.g., White and Barnett, 1972; Lau, 1988; Dole and Black, 1990; Nakamura et al., 2002; Yang et al., 2002; Athanasiadis et al., 2010; Park and An, 2014). However, at timescales that exceed the recent instrumental record, the interactions between the AL and the WJ are virtually unknown. Therefore, it is critical to reconstruct paleoclimatic history of the AL and examine its interactions with other components of the climate system.
Here we conducted principal component analysis (PCA) using published δ18O records from Alaska, northwestern Canada, and the western United States, thus eliminating local environmental effects on each record. The analysis was used to 1) identify common pattern(s) of δ18O anomalies across the study area since 7.5 ka in order to trace multi-centennial and longer AL variations; 2) compare the reconstructed AL variations with proxy reconstructions of the WJ in East Asia and the western North Pacific Ocean to determine linkages; and 3) use these combined AL and WJ datasets to better clarify dynamic changes in North Pacific atmospheric circulation and elucidate the potential triggers of Holocene climate variability (after Nagashima et al., 2021).
The extracted Principal Component 1 (PC1) represents a dramatic change from the mid- to late Holocene, and appears to reflect long-term intensified AL related to interactions between orbitally-driven southward shift of the Westerly Jet (WJ) over East Asia and the northwestern Pacific, and intensification of the El Niño–Southern Oscillation. In contrast, PC2 is characterized by multi-centennial to millennial-scale oscillations, with a spatial loading pattern that suggests PC2 reflects AL intensity and position shifts; AL intensification with a westward shift during 7.5–5.1, 2.4–1.2 and 0.7–0.4 ka. These oscillations are contemporaneous with both WJ latitude and/or the meandering path shifts over East Asia and solar activity change, suggesting that a decrease/increase in solar irradiance is related to AL variability via interactions with the WJ (Nagashima et al., 2021).
The climate mechanism(s) that are responsible for generating AL intensity and position changes over recent instrumental timescales are also poorly understood. One important component is the Westerly Jet (WJ), which is closely associated with the AL through its alternations on cyclogenesis, monsoon development, and storm tracks (e.g., White and Barnett, 1972; Lau, 1988; Dole and Black, 1990; Nakamura et al., 2002; Yang et al., 2002; Athanasiadis et al., 2010; Park and An, 2014). However, at timescales that exceed the recent instrumental record, the interactions between the AL and the WJ are virtually unknown. Therefore, it is critical to reconstruct paleoclimatic history of the AL and examine its interactions with other components of the climate system.
Here we conducted principal component analysis (PCA) using published δ18O records from Alaska, northwestern Canada, and the western United States, thus eliminating local environmental effects on each record. The analysis was used to 1) identify common pattern(s) of δ18O anomalies across the study area since 7.5 ka in order to trace multi-centennial and longer AL variations; 2) compare the reconstructed AL variations with proxy reconstructions of the WJ in East Asia and the western North Pacific Ocean to determine linkages; and 3) use these combined AL and WJ datasets to better clarify dynamic changes in North Pacific atmospheric circulation and elucidate the potential triggers of Holocene climate variability (after Nagashima et al., 2021).
The extracted Principal Component 1 (PC1) represents a dramatic change from the mid- to late Holocene, and appears to reflect long-term intensified AL related to interactions between orbitally-driven southward shift of the Westerly Jet (WJ) over East Asia and the northwestern Pacific, and intensification of the El Niño–Southern Oscillation. In contrast, PC2 is characterized by multi-centennial to millennial-scale oscillations, with a spatial loading pattern that suggests PC2 reflects AL intensity and position shifts; AL intensification with a westward shift during 7.5–5.1, 2.4–1.2 and 0.7–0.4 ka. These oscillations are contemporaneous with both WJ latitude and/or the meandering path shifts over East Asia and solar activity change, suggesting that a decrease/increase in solar irradiance is related to AL variability via interactions with the WJ (Nagashima et al., 2021).