The abrupt weakening of the East Asian summer monsoon (EASM) during Younger Dryas (YD) has been attributed to freshwater discharge into the North Atlantic ocean and resultant Northern Hemisphere cooling. Recent studies have found that sea ice variability in the Nordic Sea during the YD exerted a great influence upon the northern high-latitude climate. However, the influence of sea ice upon EASM evolution during YD event remains unclear. In this paper, we report two precisely-dated speleothem oxygen isotope records from the EASM-dominated region of central China. Our records archive abrupt changes in EASM variability during the YD event. Initially, there was a significant strengthening of the EASM during the mid-YD following the gradually increased Atlantic meridional overturning circulation (AMOC). Later this trend reversed at ∼12.15 ka due to northern high-latitude sea ice fluctuations and a consequent reduction of AMOC. At the YD termination, abrupt intensification of the EASM was synchronous with the rapid decline of sea-ice and recovery of the AMOC indicating that sea ice variability was a significant influence on high latitude climate and EASM variation during the YD.
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Latest Pleistocene to Holocene hydroclimates from Lake Elsinore, California
The hydroclimate of the southwestern United States (US) region changed abruptly during the latest
Pleistocene as the continental ice sheets over North America retreated from their most southerly extent.
To investigate the nature of this change, we present a new record from Lake Elsinore, located 36 km
inland from the Pacific Ocean in Southern California and evaluate it in the context of records across the
coastal and interior southwest United States, including northwest Mexico. The sediment core recovered
from Lake Elsinore provides a continuous sequence with multi-decadal resolution spanning 19e9 ka BP.
Sedimentological and geochemical analyses reveal hydrologic variability. In particular, sand and carbonate
components indicate abrupt changes at the Oldest Dryas (OD), BøllingeAllerød (BA), and Younger
Dryas (YD) transitions, consistent with the timing in Greenland. Hydrogen isotope analyses of the C28 nalkanoic
acids from plant leaf waxes (dDwax) reveal a long term trend toward less negative values across
19 9 ka BP. dDwax values during the OD suggest a North Pacific moisture source for precipitation,
consistent with the dipping westerlies hypothesis. We find no isotopic evidence for the North American
Monsoon reaching as far west as Lake Elsinore; therefore, we infer that wet/dry changes in the coastal
southwest were expressed through winter-season precipitation, consistent with modern climatology.
Comparing Lake Elsinore to other southwest records (notably Cave of Bells and Fort Stanton) we find
coincident timing of the major transitions (OD to BA, BA to YD) and hydrologic responses during the OD
and BA. The hydrologic response, however, varied during the YD consistent with a dipole between the
coastal and interior southwest. The coherent pattern of hydrologic responses across the interior
southwest US and northwest Mexico during the OD (wet), the BA (drier), and YD (wet) follows changes in
the Atlantic Meridional Overturning Circulation, presumably via its combined influence on North Pacific
winter storm tracks and the extent/magnitude of the North American Monsoon. In contrast, Lake Elsinore
and the coastal southwest experiences a deglacial drying trend punctuated by abrupt change at the
OD to BA and BA to YD transitions. This trend tracks rising greenhouse gases through the deglacial, with
an apparent southward shift in westerly moisture sources adjusting to the retreating ice sheet.
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- Award ID(s):
- 1203549
- PAR ID:
- 10469673
- Publisher / Repository:
- Elsevier
- Date Published:
- Journal Name:
- Quaternary Science Reviews
- Volume:
- 76
- Issue:
- C
- ISSN:
- 0277-3791
- Page Range / eLocation ID:
- 1 to 15
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract The Younger Dryas (YD, 12.9–11.7 ka) is the most recent, near‐global interval of abrupt climate change with rates similar to modern global warming. Understanding the causes and biodiversity effects of YD climate changes requires determining the spatial fingerprints of past temperature changes. Here we build pollen‐based and branched glycerol dialkyl glycerol tetraether‐based temperature reconstructions in eastern North America (ENA) to better understand deglacial temperature evolution. YD cooling was pronounced in the northeastern United States and muted in the north central United States. Florida sites warmed during the YD, while other southeastern sites maintained a relatively stable climate. This fingerprint is consistent with an intensified subtropical high during the YD and demonstrates that interhemispheric responses were more complex spatially in ENA than predicted by the bipolar seesaw model. Reduced‐amplitude or antiphased millennial‐scale temperature variability in the southeastern United States may support regional hotspots of biodiversity and endemism.
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High resolution pollen analyses of sediment core LEDC10-1 from Lake Elsinore yield the first well-dated, terrestrial record of sub-centennial-scale ecologic change in coastal southern California between ~32 and 9 ka. In the Lake Elsinore watershed, the initial, mesic montane conifer forests dominated by Pinus, and Cupressaceae with trace amounts of Abies and Picea were replaced by a sequence of multiple, extended severe mega-droughts between ~27.5 and ~25.5 ka, in which halophytic and xerophytic herbs and shrubs occupied an ephemeral lake. This prolonged and extended dry interval, which corresponds with warm waters offshore, imply strengthening of the North Pacific High and persistent below-average winter precipitation. The subsequent, contrasting monotonic occurrence of montane conifers reflects little variation in cold, mesic climate until ~15 ka. Postglacial development of Quercus woodland and chaparral mark the return to more xeric, warmer conditions at this time. A brief reversal at ~13.1e~12.1 ka, as reflected by an expansion of Pinus, is correlative with the Younger Dryas and interrupts development of warm, postglacial climate. Subsequent gradual expansion of xeric vegetation post e Younger Dryas denotes the establishment of a winter hydroclimate regime in coastal southern California that is more similar to modern conditions. Pollen-based reconstructions of temperature and precipitation at Lake Elsinore are generally correlative with pollen-based paleoclimatic reconstructions and foraminifera based sea surface temperatures from Santa Barbara Basin in marine core ODP 893. The conspicuous absence of the ~27.5e~25.5 ka glacial “mega-drought” in the Santa Barbara Basin pollen record highlights the sensitivity of Lake Elsinore to hydroclimate change, and thus, the importance of this new record that indicates that mega-drought can occur during the full glacial when climatic boundary conditions and forcings differed substantially from the present.more » « less
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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
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Abstract Climate is currently warming due to anthropogenic impact on the Earth’s atmosphere. To better understand the processes and feedbacks within the climate system that underlie this accelerating warming trend, it is useful to examine past periods of abrupt climate change that were driven by natural forcings. Glaciers provide an excellent natural laboratory for reconstructing the climate of the past as they respond sensitively to climate oscillations. Therefore, we study glacier systems and their behavior during the transition from colder to warmer climate phases, focusing on the period between 15 and 10 ka. Using a combination of geomorphological mapping and beryllium-10 surface exposure dating, we reconstruct ice extents in two glaciated valleys of the Silvretta Massif in the Austrian Alps. The mountain glacier record shows that general deglaciation after the Last Glacial Maximum (LGM) was repeatedly interrupted by glacier stabilization or readvance, perhaps during the Oldest Dryas to Bølling transition (landform age: 14.4 ± 1.0 ka) and certainly during the Younger Dryas (YD; 12.9–11.7 ka) and the Early Holocene (EH; 12–10 ka). The oldest landform age indicates a lateral ice margin that postdates the ‘Gschnitz’ stadial (ca. 17–16 ka) and predates the YD. It shows that local inner-alpine glaciers were more extensive until the onset of the Bølling warm phase (ca. 14.6 ka), or possibly even into the Bølling than during the subsequent YD. The second age group, ca. 80 m below the (pre-)Bølling ice margin, indicates glacier extents during the YD cold phase and captures the spatial and temporal fine structure of glacier retreat during this period. The ice surface lowered approximately 50–60 m through the YD, which is indicative of milder climate conditions at the end of the YD compared to its beginning. Finally, the third age group falls into a period of more substantial warming, the YD–EH transition, and shows discontinuous glacier retreat during the glacial to interglacial transition. The new geochronologies synthesized with pre-existing moraine records from the Silvretta Massif evidence multiple cold phases that punctuated the general post-LGM warming trend and illustrate the sensitive response of Silvretta glaciers to abrupt climate oscillations in the past.
- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1016/j.quascirev.2013.05.023
