| Summary: | We present a continuous ostracod isotope (δ 18 O and δ 13 C) record from Lake Petén Itzá, Petén, Guatemala, in the northern, lowland Neotropics that spans the last ∼43 cal ka BP. Variations in oxygen and carbon isotopes closely follow lithologic variations, which consist of alternating gypsum and clay deposits that were deposited under relatively dry and wet climate, respectively. During the last glacial period, the greatest δ 18 O and δ 13 C values coincide with gypsum deposited during lake lowstands under arid climate conditions that were correlated previously with North Atlantic Heinrich events. In contrast, interstadials and the entirety of the Last Glacial Maximum (∼24–19 cal ka BP) are marked by clay deposition and lower δ 18 O and δ 13 C values, reflecting higher lake levels and relatively moister climate. Isotope results and pollen data, along with independently inferred past water levels, show the early deglacial period (∼19–15 cal ka BP) was the time of greatest aridity and lowest lake stage of the past 43 ka. This period occurred during Heinrich Stadial 1 (HS 1), when an extensive tropical megadrought has been postulated (Stager et al., 2011). Heinrich Stadial 1 is represented by two episodes of gypsum precipitation and high δ 18 O and δ 13 C values in Petén Itzá, interrupted by an intervening period of lower δ 18 O and δ 13 C and clay deposition centered on ∼17 cal ka BP. The two periods of inferred maximum cold and/or arid conditions at ∼17.5 and 16.1 cal ka BP coincide approximately with two pulses of ice-rafted debris (IRD) recorded off southern Portugal (Bard et al., 2000). At ∼15 cal ka BP, coinciding with the start of the Bolling-Allerod period, δ 18 O and δ 13 C decrease and gypsum precipitation ceases, indicating a transition to warmer and/or wetter conditions. Gypsum precipitation resumed while δ 18 O and δ 13 C increased at the start of the Younger Dryas at 13.1 cal ka BP and continued until 10.4 cal ka BP, near the onset of the Holocene Precipitation changes during the last glacial period ...
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