Coupled atmosphere-ice-ocean dynamics during Heinrich Stadial 2

Abstract

Our understanding of climate dynamics during millennial-scale events is incomplete, partially due to the lack of their precise phase analyses under various boundary conditions. Here we present nine speleothem oxygen-isotope records from mid-to-low-latitude monsoon regimes with sub-centennial age precision and multi-annual resolution, spanning the Heinrich Stadial 2 (HS2) — a millennial-scale event that occurred at the Last Glacial Maximum. Our data suggests that the Greenland and Antarctic ice-core chronologies require +320- and +400-year adjustments, respectively, supported by extant volcanic evidence and radiocarbon ages. Our chronological framework shows a synchronous HS2 onset globally. Our records precisely characterize a centennial-scale abrupt “tropical atmospheric seesaw” superimposed on the conventional “bipolar seesaw” at the beginning of HS2, implying a unique response/feedback from low-latitude hydroclimate. Together with our observation of an early South American monsoon shift at the HS2 termination, we suggest a more active role of low-latitude hydroclimate dynamics underlying millennial events than previously thought.

Interdecadal to Centennial Climate Variability Surrounding the 8.2 ka Event in North China Revealed Through an Annually Resolved Speleothem Record From Beijing

“…In theory, current dating uncertainties of the Greenland ice cores (∼45 years), the HS‐4 (>100 years) and BH‐2 (∼30 years) still leave room for allowing different correlations within decadal to multi‐decadal uncertainties. However, from climate dynamic point of view, we prefer the new correlation framework mentioned above (Figure 4), because this is consistent with the dynamics that the abrupt climatic signals from the North Atlantic can rapidly propagate through atmospheric processes globally, including the ASM domain (X. Dong et al., 2022; Duan, Cheng, et al., 2016; Y. Liu et al., 2013; Ruth et al., 2007) as well as Antarctica (Markle et al., 2017).…”

Milankovitch theory and monsoon

“…Recent studies show that, during the termination processes of millennial-scale events such as HSs, a multi-centennial drying trend occurred as a precursor event in the vast SAM domain, which would have caused a decrease in Amazon River discharge into the tropical Atlantic Ocean ( Figures 8 and 9 ). 150 , 161 Reduced freshwater input may have induced a positive sea-surface salinity anomaly in the huge Amazon plume region, 166 , 167 ultimately advected to the deep-water formation areas in the North Atlantic via the great ocean conveyor 162 and contributing to the strengthening of the AMOC 164 , 165 and vice versa. A strengthened AMOC would induce positive feedback by transporting more saline water to the north, facilitating northward heat transport and a shift in the tropic rain belts, intensification of the AM, 62 , 149 , 150 , 161 and Greenland warming.…”

“… 150 , 161 Reduced freshwater input may have induced a positive sea-surface salinity anomaly in the huge Amazon plume region, 166 , 167 ultimately advected to the deep-water formation areas in the North Atlantic via the great ocean conveyor 162 and contributing to the strengthening of the AMOC 164 , 165 and vice versa. A strengthened AMOC would induce positive feedback by transporting more saline water to the north, facilitating northward heat transport and a shift in the tropic rain belts, intensification of the AM, 62 , 149 , 150 , 161 and Greenland warming. 168 This dynamic process provides another example showing that low-latitude monsoon rainfall may affect high-latitude climate.…”

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Figure 9 Conceptual diagram depicting the climatic dynamics during termination of the millennial-scale climate events. Based on cave records, 150 , 161 the weakened SAM resulted in reduced Amazon River runoff into the tropical Atlantic Ocean and, thus, a small Amazon plume region (APR; depicted by the red dashed line) about multi-centuries prior to the millennial event termination at Greenland. The long-term drying trend in the SAM domain may have induced a relatively positive SSS anomaly in the APR, which was subsequently advected to the North Atlantic, 162 , 163 ultimately contributing to AMOC strengthening.

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“… 150 and Dong et al. 161 The map shows surface salinity in 2011 as measured by the National Aeronautics and Space Administration (NASA) Aquarius satellite. Orange colors indicate higher salinity and blue colors lower salinity ( https://news.uga.edu/wp-content/uploads/2017/12/Amazon-River-Plume.jpg ).…”