An official website of the United States government
The Common Era history of effective moisture in the Central Andes is poorly understood, as most Andean proxy records reflect large-scale atmospheric circulation over the South American lowlands rather than localized precipitation vs. evaporation. Here we present 1800-year leaf wax hydrogen and carbon isotope sedimentary records from Lake Chacacocha (13.96°S, 71.08°W, 4,860 m asl.) in the Central Andes. Leaf wax δ2H from different chain lengths offers information about large-scale atmospheric conditions and local-scale effective moisture. Our leaf wax δ2H data record a gradual intensification of the South American summer monsoon (SASM) beginning around ~1250 CE, prior to the external forcings of the Little Ice Age (LIA). Despite peak SASM intensification, our leaf wax δ13C data reveal a locally arid interval between ca. 1600 and 1800 CE. The arid interval was most likely driven by enhanced evaporation and reduced local precipitation, as indicated by the hydrogen isotope fractionation between mid- and long-chain n-alkanes as well as by climate model simulations. Our results help to reconcile conflicting interpretations of the SASM, glacial, and lake-level histories in the Central Andes during the Common Era.
more »
« less
This content will become publicly available on December 10, 2025
Local to Regional Hydroclimate Changes in the Tropical Andes Since the Mid-Holocene
Climate changes during the mid- to late-Holocene, after the last vestiges of glacial ice sheets dwindled, provide important context for climate change today. In the tropical Andes, most of the continuous paleoclimate records covering the late Holocene are derived from the oxygen isotope composition of ice cores, speleothems, and lake carbonates. These archives are powerful recorders of large-scale changes in circulation and monsoon intensity, but they do not necessarily capture local moisture balance, and so reconstructions of local precipitation and aridity remain scarce. Here we present contrasting histories of local effective moisture vs. regional circulation from several new biomarker records preserved in lakes and peat in the Colombian and Peruvian Andes. We focus on the hydrogen isotope composition of long-chain plant waxes, which reflects precipitation δ2H similarly to δ18O from ice cores and speleothems; and the δ13C of waxes and the δ2H of mid-chain waxes, which reflect local water stress and effective moisture. In both the Northern and Southern Hemisphere tropical Andes, fairly gradual δ2H shifts during the late Holocene indicate a progressive intensification of circulation in the South American lowlands. On the other hand, plant wax δ13C and mid-chain δ2H records indicate abrupt transitions into and out of intervals of water stress and aridity – similar to findings from pollen and sediment lithology from elsewhere in the tropical Andes. We draw on climate models and proxy data syntheses to help reconcile these curiously different accounts of effective moisture in the tropical Andes since the mid-Holocene and discuss implications for modern climate research.
more »
« less
- Award ID(s):
- 2103062
- PAR ID:
- 10566684
- Publisher / Repository:
- American Geophysical Union
- Date Published:
- Subject(s) / Keyword(s):
- Holocene tropics Andes deuterium plant wax hydrogen isotope hydroclimate
- Format(s):
- Medium: X
- Location:
- Washington DC
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Paleo water isotope records can elucidate how the Arctic water cycle responded to past climate changes. We analyze the hydrogen isotope composition (δ2H) of plant‐derived n‐alkanoic acids (waxes) from Lake Qaupat, Baffin Island, Nunavut, Canada, to assess moisture sources and seasonality during the past 5.8 ka. We compare this record to a sedimentary ancient DNA (sedaDNA)‐inferred vascular plant record from the same lake, aiming to overcome the uncertainty of plant community impacts on leaf waxes. As the sedaDNA record reveals a stable plant community after the colonization of Betula sp. at 6.1 ka, we interpret plant wax δ2H values to reflect climate, specifically mean annual precipitation δ2H. However, the distributions of n‐alkanoic acid homologs suggest that aquatic mosses, which are not represented in the sedaDNA record, may become more abundant towards the present. Therefore, we cannot exclude the possibility that changes in the plant community cause changes in the plant wax δ2H record, particularly long‐chain waxes, which become less abundant through this record. We find that Lake Qaupat mid‐chain plant wax δ2H is enriched coincident with high Labrador Sea summer surface temperature, which suggests that local moisture sources in summer and early autumn have the greatest impact on precipitation isotopes in this region.more » « less
-
Paleo water isotope records can elucidate how the Arctic water cycle responded to past climate changes. We analyze the hydrogen isotope composition (δ2H) of plant‐derived n‐alkanoic acids (waxes) from Lake Qaupat, Baffin Island, Nunavut, Canada, to assess moisture sources and seasonality during the past 5.8 kiloannum (ka). We compare this record to a sedimentary ancient DNA (sedaDNA)‐inferred vascular plant record from the same lake, aiming to overcome the uncertainty of plant community impacts on leaf waxes. As the sedaDNA record reveals a stable plant community after the colonization of Betula sp. at 6.1 ka, we interpret plant wax δ2H values to reflect climate, specifically mean annual precipitation δ2H. However, the distributions of n‐alkanoic acid homologs suggest that aquatic mosses, which are not represented in the sedaDNA record, may become more abundant towards the present. Therefore, we cannot exclude the possibility that changes in the plant community cause changes in the plant wax δ2H record, particularly long‐chain waxes, which become less abundant through this record. We find that Lake Qaupat mid‐chain plant wax δ2H is enriched coincident with high Labrador Sea summer surface temperature, which suggests that local moisture sources in summer and early autumn have the greatest impact on precipitation isotopes in this region.more » « less
-
Abstract Climate variability over glacial-interglacial timescales is not well characterized in the tropical Andes, and paleoclimate records are lacking in this region. To offset this gap in knowledge, we analyzed organic compounds from sediment cores from Lake Junin (the Peruvian Andes) to better understand climate variability in the region since the LGM. We measured the δD of long and mid-chain n-alkanes (nC29 – terrestrial vegetation and nC23 – aquatic vegetation) to characterize changes in the intensity of the South American Summer Monsoon (SASM) and evaporative enrichment of lake water. We also measured the δ13C of these compounds to better understand the hydrology of the region and constrain the sources of organic matter through time. Additionally, we used the fractional abundances of brGDGTs to estimate changes in temperature over the same time period. Our results suggest that SASM intensity is controlled by insolation in the southern hemisphere. During the late Pleistocene, the δD of both nC29 and nC23 are relatively D-depleted indicating a wetter time period. This is followed by progressive D-enrichment of both nC29 and nC23 which suggests increasing aridity until the Holocene. The early Holocene is characterized by a decoupling between the δD of nC23 and nC29.The δD of nC23 becomes relatively more D-enriched, matching trends in a carbonate oxygen isotope record from Lake Junin, indicating increased lake-water evaporation during this time. Finally, the late Holocene is characterized by a return to wetter conditions. The δ13C of both nC29 and nC23 further confirms the hydrologic history of this region, while shedding light on vegetation dynamics. During the Pleistocene, the δ13C of both n-alkanes suggests DIC uptake, but at the start of the Holocene they diverge, showing two distinct plant communities, one entirely aquatic and one entirely terrestrial. Our brGDGT-based temperature reconstruction shares similar trends with alkenone-based SST reconstructions off the coast of Peru, indicating a consistent regional climate signal.more » « less
-
Changes in ice-sheet size impact atmospheric circulation, a phenomenon documented by models but constrained by few paleoclimate records. We present sub-centennial-scale records of summer temperature and summer precipitation hydrogen isotope ratios (δ2H) spanning 12–7 kiloannum (ka) from a lake on Baffin Island. In a transient model simulation, winds in this region were controlled by the relative strength of the high-pressure systems and associated anticyclonic circulation over the retreating Greenland and Laurentide ice sheets. The correlation between summer temperature and precipitation δ2H proxy records changed from negative to positive at 9.8 ka. This correlation structure indicates a shift from alternating local and remote moisture, governed by the two ice-sheet high-pressure systems, to only remote moisture after 9.8 ka, governed by the strong Greenland high-pressure system after the Laurentide Ice Sheet retreated. Such rapid atmospheric circulation changes may also occur in response to future, gradual ice-sheet retreat.more » « less
