A ∼43-ka record of paleoenvironmental change in the Central American lowlands inferred from stable isotopes of lacustrine ostracods

Abstract

We present a continuous ostracod isotope (δ18O and δ13C) 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 δ18O and δ13C 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 δ18O and δ13C 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 δ18O and δ13C values in Petén Itzá, interrupted by an intervening period of lower δ18O and δ13C 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, δ18O and δ13C decrease and gypsum precipitation ceases, indicating a transition to warmer and/or wetter conditions. Gypsum precipitation resumed while δ18O and δ13C 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 in the northern hemisphere Neotropics were closely linked with freshwater forcing to the high-latitude North Atlantic, and sensitive to changes in the location of meltwater input. Climate was coldest/driest when meltwater directly entered the high-latitude North Atlantic, permitting sea ice expansion and weakening of Atlantic Meridional Overturning Circulation (AMOC), which resulted in a more southerly position of the Intertropical Convergence Zone (ITCZ). Upon deglaciation, when meltwater was directed to the Gulf of Mexico, at ∼17 ka and during the Bolling-Allerod period (15–13 ka), precipitation increased in the northern hemisphere Neotropics as North Atlantic sea ice retreated and the ITCZ shifted northward. Results from Lake Petén Itzá offer some support for the meltwater routing hypothesis of Clark et al. (2001).