More Like this

1. MIDDLE PLEISTOCENE HYDROCLIMATE CHANGES IN THE TROPICAL ANDES INFERRED FROM CARBON AND OXYGEN ISOTOPE RECORDS OF SPELEOTHEMS FROM HUAGAPO CAVE, PERU

   https://doi.org/10.1130/abs/2023AM-394169  

   Olson, Elizabeth; Parmenter, Dylan; Gillikin, David; Stoltenberg, Hailey; Clavel, Avery; Piccirillo, Laura; Verheyden, Anouk; Edwards, Lawrence; Rodbell, Donald (January 2023, Geologic Society of America)

   Glacial-interglacial transitions and abrupt millennial-scale events are the most prominent features in many paleoclimate records. Understanding these oscillations requires high-resolution time series from multiple locations to constrain the latitudinal response to forcings. Few high-resolution records exist from the Southern Hemisphere tropics that predate the last two glaciations. We present a high-resolution speleothem oxygen and carbon isotope record from Huagapo Cave in the Central Peruvian Andes covering Marine Isotope Stage (MIS) 8 glacial and MIS 9 interglacial (339 to 249 ka). Uranium-series dates on three stalagmites (n=18) with small age uncertainty ±1% allows us to resolve abrupt climate events similar in structure and duration to Dansgaard-Oescchger and Heinrich events. The South American Summer Monsoon (SASM) controls modern hydroclimate variability in the Andes, and previous records from Huagapo Cave have provided records of past SASM variability. Termination three (T-III) in our record has a steep increase in δ18O values of 5‰, punctuated by two stadial event decreases of ~3‰ (S8.1 and S8.2). This pattern is mirrored in the δ13C record, indicating that these millennial-scale events record hydroclimate and vegetation productivity changes. The same structure as our T-III record is found in other records globally, where they are noted to be Heinrich-like events. Frequency analysis indicates that the occurrence of these abrupt events changes between glacial cycles. Precession is weakly expressed in the δ18O record during MIS 8; similar to speleothem records from the region dating to the Last Glacial Maximum (LGM). Global ice cover and sea levels were similar in the LGM and MIS 8, but the Milankovitch insolation forcing differed. This change in SASM behavior is not observed in the East Asian monsoon, where the precession signal is dominant throughout. Interglacial precessional control is apparent during the latter half of MIS 9 and during Huagapo Cave intervals dating to MIS 6 and 7. These data indicate that the response to high-latitude forcing in the Southern Hemisphere tropics fluctuates through time, and potential explanations for low-latitude sensitivity to forcing factors are further explored. 

   more » « less
2. Stalagmite Records of Hydroclimate from the Peruvian Andes During the Last Deglaciation

   Olson, EL; Parmenter, D; Gillikin, D; Piccirillo, L; Forsyth, A; Litchfield, K; Verheyden, A; Edwards, L; Rodbell, D (December 2024, 2024 Fall Meeting, AGU)

   none (Ed.)

   Abstract The termination of the last glacial period is marked by the northward migration of the ITCZ and the weakening of the South American Summer Monsoon (SASM). The transition between the wetter glacial period and the more arid Holocene period across the South American continent is punctuated by several abrupt millennial-scale tropical hydroclimatic events. While the Northern Hemisphere temperature forcing of these millennial-scale events is generally accepted, recently, equatorial forcing mechanisms have been put forward. In particular, the dipole between northeastern Brazil and the western Andes of Peru is absent during Heinrich 1, with wet conditions recorded in both regions. To explain this anomalous atmospheric behavior, researchers have suggested changes in the ENSO and Walker circulation over South America and questioned whether the ‘amount effect’ relationship between δ18O and precipitation persists through time. To better resolve tropical hydroclimate changes over the last glacial termination, more robust paleoclimate proxies are needed. Here, we present a new paleo-precipitation reconstruction based on trace metal (Mg/Ca, Sr/Ca, and Ba/Ca) and isotope (δ18O and δ13C) speleothem records from Antipayarguna cave in the Peruvian Andes (3800 masl). Our records date from 2,600 to 4,700 and 7,700 to 19,000 years BP, with an average age resolution of 44 years. These records overlap the previously published speleothem records from nearby Pacupahuain and Huagapo caves. The Antipayarguna δ18O data are highly correlated with southern hemisphere summer insolation and the Huascaran ice core δ18O record. The Antipayarguna trace metal ratios and δ18O isotope values correlate well over most of the record, suggesting that the δ18O at our site reflects the amount of local precipitation. However, at the end of the Younger Dryas (11.5-10.3 ka) and Heinrich Stadial 1 (16.4-14.9 ka), there is a decoupling of these proxies. These anomalies may be due to changes in δ18O caused by shifts in moisture source region or precipitation condensation factors (e.g. convergence level or subcloud evaporation). Alternatively, this could be due to a change in trace metal sources. We explore potential causes for these brief decoupling events through comparison with other paleoclimate records. 

   more » « less
3. Antarctic temperature and CO ₂ : near-synchrony yet variable phasing during the last deglaciation

   https://doi.org/10.5194/cp-15-913-2019  

   Chowdhry Beeman, Jai; Gest, Léa; Parrenin, Frédéric; Raynaud, Dominique; Fudge, Tyler J.; Buizert, Christo; Brook, Edward J. (January 2019, Climate of the Past)

   Abstract. The last deglaciation, which occurred from 18 000 to 11 000 years ago,is the most recent large natural climatic variation of global extent. Withaccurately dated paleoclimate records, we can investigate the timings ofrelated variables in the climate system during this major transition. Here,we use an accurate relative chronology to compare temperature proxy data andglobal atmospheric CO2 as recorded in Antarctic ice cores. In addition tofive regional records, we compare a δ18O stack, representingAntarctic climate variations with the high-resolution robustly dated WAISDivide CO2 record (West Antarctic Ice Sheet). We assess the CO2 and Antarctic temperature phaserelationship using a stochastic method to accurately identify the probabletimings of changes in their trends. Four coherent changes are identified forthe two series, and synchrony between CO2 and temperature is within the95 % uncertainty range for all of the changes except the end of glacial termination 1 (T1). During the onset of the last deglaciation at 18 ka and the deglaciationend at 11.5 ka, Antarctic temperature most likely led CO2 by several centuries (by 570 years, within a range of 127 to 751 years, 68 %probability, at the T1 onset; and by 532 years, within a range of 337 to 629years, 68 % probability, at the deglaciation end). At 14.4 ka, the onsetof the Antarctic Cold Reversal (ACR) period, our results do not show a clearlead or lag (Antarctic temperature leads by 50 years, within a range of−137 to 376 years, 68 % probability). The same is true at the end of the ACR(CO2 leads by 65 years, within a range of 211 to 117 years, 68 %probability). However, the timings of changes in trends for the individualproxy records show variations from the stack, indicating regional differencesin the pattern of temperature change, particularly in the WAIS Divide recordat the onset of the deglaciation; the Dome Fuji record at the deglaciationend; and the EDML record after 16 ka (EPICA Dronning Maud Land, where EPICA is the European Project for Ice Coring in Antarctica). In addition, two changes – one at 16 ka in the CO2 record and one after the ACR onset in three of theisotopic temperature records – do not have high-probability counterparts in the other record. The likely-variable phasing we identify testify to thecomplex nature of the mechanisms driving the carbon cycle and Antarctictemperature during the deglaciation. 

   more » « less
4. Timing and structure of the Younger Dryas event and its underlying climate dynamics

   https://doi.org/10.1073/pnas.2007869117  

   Cheng, Hai; Zhang, Haiwei; Spötl, Christoph; Baker, Jonathan; Sinha, Ashish; Li, Hanying; Bartolomé, Miguel; Moreno, Ana; Kathayat, Gayatri; Zhao, Jingyao; et al (September 2020, Proceedings of the National Academy of Sciences)

   null (Ed.)

   The Younger Dryas (YD), arguably the most widely studied millennial-scale extreme climate event, was characterized by diverse hydroclimate shifts globally and severe cooling at high northern latitudes that abruptly punctuated the warming trend from the last glacial to the present interglacial. To date, a precise understanding of its trigger, propagation, and termination remains elusive. Here, we present speleothem oxygen-isotope data that, in concert with other proxy records, allow us to quantify the timing of the YD onset and termination at an unprecedented subcentennial temporal precision across the North Atlantic, Asian Monsoon-Westerlies, and South American Monsoon regions. Our analysis suggests that the onsets of YD in the North Atlantic (12,870 ± 30 B.P.) and the Asian Monsoon-Westerlies region are essentially synchronous within a few decades and lead the onset in Antarctica, implying a north-to-south climate signal propagation via both atmospheric (decadal-time scale) and oceanic (centennial-time scale) processes, similar to the Dansgaard–Oeschger events during the last glacial period. In contrast, the YD termination may have started first in Antarctica at ∼11,900 B.P., or perhaps even earlier in the western tropical Pacific, followed by the North Atlantic between ∼11,700 ± 40 and 11,610 ± 40 B.P. These observations suggest that the initial YD termination might have originated in the Southern Hemisphere and/or the tropical Pacific, indicating a Southern Hemisphere/tropics to North Atlantic–Asian Monsoon-Westerlies directionality of climatic recovery. 

   more » « less
5. LARGE SWINGS IN TROPICAL WATER BALANCE DURING A ‘WEAK’ INTERGLACIAL (MIS 15) SUGGEST A LINK TO PRECESSION-INDUCED MONSOON VARIABILITY

   https://doi.org/10.1130/abs/2023AM-392949  

   Katz, Sarah; Levin, Naomi; Abbott, Mark; Rodbell, Donald; Passey, Benjamin (January 2023, Geologic Society of America)

   Atmospheric water vapor is predominately sourced from the tropics, such that characterizing the link between the tropical water cycle and global climate is of critical importance. Studies of central Andean climate from Lake Junín (11 °S, Peru) show that tropical glacial extent tracks global ice volume at a ~100 ka periodicity for the last 6 glacial cycles, indicating a tight coupling between tropical water balance and high latitude climate. However, it can be difficult to decouple temperature, precipitation, and water balance histories from records of glacial extent, especially for older intervals. In this work, we focus on one such interval, MIS 15 (621–563 ka), when the connections between tropical Andean water balance and global climate seem different than the last glacial cycle. Globally, MIS 15 was a weak interglacial, with cool temperatures and low GHG concentrations, however, the Lake Junín glacial record suggests an amplified hydroclimate response to this interglacial, stronger than any other over the last 700 ka. Causes for this apparent tropical amplification may be due to large, precession-paced changes in meridional insolation gradients that exceed other interglacials owning to enhanced orbital eccentricity. Given that the role of precession on South American monsoon strength over the last glacial cycle is well established, we hypothesize that monsoon strength may have been highly variable during MIS 15 and forced changes in central Andean water balance and glacial extent. To test this, we reconstructed temperature and evaporation histories using carbonate clumped and triple oxygen isotopes of Lake Junín sediments. Preliminary results suggest temperatures were relatively stable, but possibly lower than both the present and Holocene, consistent with cool global climate at that time. Triple oxygen isotope values vary substantially, indicating massive swings in lake hydrology, between open and (nearly?) closed basin hydrology on a ~12 ka cycle that exactly match insolation variations. From this work, we conclude that hydrologic change in the central Andes was rapid and extreme during MIS 15, owning to profound changes in monsoon strength. Given that monsoons in other sectors are also sensitive to insolation changes, our work could suggest pervasive hydrologic variability throughout the tropics at this time. 

   more » « less