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

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)

An 85-ka record of climate change in lowland Central America

Drill cores obtained from Lake Petén Itzá, Petén, Guatemala, contain a ∼85-kyr record of terrestrial climate from lowland Central America that was used to reconstruct hydrologic changes in the northern Neotropics during the last glaciation. Sediments are composed of alternating clay and gypsum reflecting relatively wet and dry climate conditions, respectively. From ∼85 to 48 ka, sediments were dominated by carbonate clay indicating moist conditions during Marine Isotope Stages (MIS) 5a, 4, and early 3. The first gypsum layer was deposited at ∼48 ka, signifying a shift toward drier hydrologic conditions and the onset of wet–dry oscillations. During the latter part of MIS 3, Petén climate varied between wetter conditions during interstadials and drier states during stadials. The pattern of clay–gypsum (wet–dry) oscillations during the latter part of MIS 3 (∼48–23 ka) closely resembles the temperature records from Greenland ice cores and North Atlantic marine sediment cores and precipitation proxies from the Cariaco Basin. The most arid periods coincided with Heinrich Events when cold sea surface temperatures prevailed in the North Atlantic, meridional overturning circulation was reduced, and the Intertropical Convergence Zone (ITCZ) was displaced southward. A thick clay unit was deposited from 23 to 18 ka suggesting deposition in a deep lake, and pollen accumulated during the same period indicates vegetation consisted of a temperate pine-oak forest. This finding contradicts previous inferences that climate was arid during the Last Glacial Maximum (LGM) chronozone (21±2 ka). At ∼18 ka, Petén climate switched from moist to arid conditions and remained dry from 18 to 14.7 ka during the early deglaciation. Moister conditions prevailed during the warmer Bolling–Allerod (14.7–12.8 ka) with the exception of a brief return to dry conditions at ∼13.8 ka that coincides with the Older Dryas and meltwater pulse 1A. The onset of the Younger Dryas at 12.8 ka marked the return of gypsum and hence dry conditions. The lake continued to precipitate gypsum until ∼10.3 ka when rainfall increased markedly in the early Holocene

Re-evaluation of Climate Change in Lowland Central America During the Last Glacial Maximum Using New Sediment Cores from Lake Petén Itzá, Guatemala

Glaciological data derived from moraines, and multiproxy data from lake sediment cores (e.g. fossil pollen, diatoms, and isotope data) indicate cooling in the Central American tropics during the last ice age. Contrary to prior inferences, however, new lake core data from Lake Petén Itzá, lowland Guatemala, indicate that climate was not particularly dry on the Yucatan Peninsula during the last glacial maximum (LGM) chronozone, around 23,000–19,000 cal. yr BP. We present pollen and lithologic data from Lake Petén Itzá and an improved chronology for climate changes in lowland Central America over the last 25,000 years. The driest period of the last glaciation was not the LGM, but rather the deglacial period (∼18,000–11,000 cal. yr BP). Causes of climate shifts during the last glaciation are ascribed to precessional changes in insolation, the position of the Inter-Tropical Convergence Zone, and southward penetration of polar air masses