ABSTRACT Annual tree‐ring oxygen‐isotope values were measured from sections of two fossil logs of Picea mariana (black spruce) recovered from last glacial maximum proglacial sediment in Illinois, USA. Collectively, the specimens date from ca. 25,130 to 24,720 cal years BP. Tree‐ring oxygen‐isotope spectral analysis series for both specimens revealed a 2–6 years periodicity. The Gulf of Mexico was the prominent moisture source during spring–summer growing seasons. Tree‐ring oxygen‐isotope based reconstruction of last glacial maximum precipitation suggests comparable values to modern El Niño Southern Oscillation‐influenced meteoric water isotopes for the Midwest. Additional factors supporting El Niño Southern Oscillation‐like late glacial maximum climate behaviour include the position of the perihelion and precession timing and a similar Earth‐Sun distance.
Labotka et al. (2026) studied this question.