10-5 Ecosystem-Specific Fire Responses to Abrupt Hydroclimate Change During Heinrich Stadial 1

Session: Geochemistry and Mineralogy (Posters)

Poster Booth No.: 42

Presenting Author:

Zhao Wang

Authors:

Wang, Zhao¹, Hren, Michael T², Tabor, Clay³, Montañez, Isabel P⁴, Oster, Jessica L⁵, Burstyn, Yuval⁶, de Wet , Cameron⁷, Atekwana, Eliot A⁸, Zyba, Aida ⁹, Bowen, Gabriel J¹⁰, Griffith, Elizabeth M¹¹, Smolen, Jonathan D¹², Pederzani, Sarah¹³

(1) Earth Sciences, University of Connecticut, Storrs, , (2) Earth Sciences, University of Connecticut, Storrs, , (3) Earth Sciences, University of Connecticut, Storrs, , (4) Earth and Planetary Sciences, University of California, Davis, Davis, , (5) Earth and Environmental Sciences, Vanderbilt University, Nashville, , (6) Earth and Planetary Sciences, University of California, Davis, Davis, , (7) Earth and Climate Sciences, Middlebury College, Middlebury, , (8) Earth and Planetary Sciences, University of California, Davis, Davis, , (9) Earth and Environmental Sciences, Vanderbilt University, Nashville, , (10) Geology & Geophysics, University of Utah, Salt Lake City, , (11) Earth Sciences, Ohio State University, Columbus, , (12) Human Evolutionary Biology, Harvard University, Cambridge, , (13) Geology & Geophysics, University of Utah, Salt Lake City, ,

Abstract:

Understanding how fire regimes respond to abrupt hydroclimate change is essential for predicting ecosystem resilience under future climate instability. During Heinrich Stadial 1 (HS1; ~18.0–14.7 kyr BP), glacial meltwater discharge into the North Atlantic weakened the Atlantic Meridional Overturning Circulation (AMOC), driving pronounced shifts in moisture availability, seasonality, and fire activity across western North America. Here, we reconstruct fire–hydroclimate–vegetation interactions in California during HS1 using terrestrial ecosystem–derived molecular compounds preserved in speleothem carbonates from Lake Shasta Cavern (LSC; 40.804°N) and McLean’s Cave (ML1; 38.067°N). We quantify high–molecular–weight polycyclic aromatic hydrocarbons (HMW PAHs; 5- and 6-ring) as indicators of high-temperature biomass burning, alongside phytosterols and conifer-derived diterpenoids to trace vegetation productivity and fuel composition. At LSC, persistently elevated HMW PAH concentrations during early HS1 (~18.0–16.0 kyr BP) indicate frequent, high-intensity fires coincident with sustained terrestrial inputs from flowering plant–dominated ecosystems, suggesting that enhanced fuel production under wetter conditions promoted fire without long-term ecosystem collapse. In contrast, ML1 records show pronounced declines in diterpenoids (“resin oils”) during intervals of elevated PAHs toward the end of HS1 (~15.0 kyr BP), reflecting conifer forest loss under intensified fire stress linked to hydroclimate deterioration. These records demonstrate that HS1 fire regimes were governed by hydroclimate-driven fuel accumulation and vegetation-specific recovery capacity, rather than temperature or aridity alone. Our findings imply that future AMOC weakening could amplify fire risk in western North America by altering moisture seasonality and fuel dynamics, potentially pushing ecosystems toward critical fire-hydroclimate tipping points.

Geological Society of America Abstracts with Programs. Vol. 58, No. 2, 2026

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