Deglacial reconstruction of the spatial extent and intensity of the North Atlantic Subtropical High

David Fastovich, Tripti Bhattacharya , Stephen T. Jackson, Teresa R. Krause, James M. Russell, Timothy M. Shanahan, Chijun Sun, John Warren Williams 

Rainfall-related hazards are growing in southeastern North America (SENA) but well-documented climate-model biases cast doubt on projected rainfall changes. Using leaf-wax biomarkers (δDwax) at White Pond, SC and Hall’s Cave, TX, we reconstruct North Atlantic Subtropical High (NASH) variability across the last deglaciation (21 to 10 ka) to assess model fidelity. During the Younger Dryas, when Atlantic Ocean heat transport weakened, the NASH expanded westward, increasing rainfall in SENA. In contrast, the NASH gradually contracted eastward and weakened as deglacial greenhouse-gas concentrations increased, likely decreasing rainfall in SENA. An isotope-enabled simulation captures the first NASH response but severely underestimates the second. Because the NASH delivers moisture that drives extreme rainfall in SENA, this underestimation suggests that models cannot yet produce confident projections of regional rainfall extremes, or that those extremes will exceed current projections. Rainfall hazards facing SENA may be larger or less certain than current models suggest.