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Abstract. The last glacial period is characterized by a number of millennial climateevents that have been identified in both Greenland and Antarctic ice coresand that are abrupt in Greenland climate records. The mechanisms governingthis climate variability remain a puzzle that requires a precisesynchronization of ice cores from the two hemispheres to be resolved.Previously, Greenland and Antarctic ice cores have been synchronizedprimarily via their common records of gas concentrations or isotopes fromthe trapped air and via cosmogenic isotopes measured on the ice. In thiswork, we apply ice core volcanic proxies and annual layer counting toidentify large volcanic eruptions that have left a signature in bothGreenland and Antarctica. Generally, no tephra is associated with thoseeruptions in the ice cores, so the source of the eruptions cannot beidentified. Instead, we identify and match sequences of volcanic eruptionswith bipolar distribution of sulfate, i.e. unique patterns of volcanicevents separated by the same number of years at the two poles. Using thisapproach, we pinpoint 82 large bipolar volcanic eruptions throughout thesecond half of the last glacial period (12–60 ka). Thisimproved ice core synchronization is applied to determine the bipolarphasing of abrupt climate change events at decadal-scale precision. Inresponse to Greenland abrupt climatic transitions, we find a response in theAntarctic water isotope signals (δ18O and deuterium excess)that is both more immediate and more abrupt than that found with previousgas-based interpolar synchronizations, providing additional support for ourvolcanic framework. On average, the Antarctic bipolar seesaw climateresponse lags the midpoint of Greenland abrupt δ18O transitionsby 122±24 years. The time difference between Antarctic signals indeuterium excess and δ18O, which likewise informs the timeneeded to propagate the signal as described by the theory of the bipolarseesaw but is less sensitive to synchronization errors, suggests anAntarctic δ18O lag behind Greenland of 152±37 years.These estimates are shorter than the 200 years suggested by earliergas-based synchronizations. As before, we find variations in the timing andduration between the response at different sites and for different eventssuggesting an interaction of oceanic and atmospheric teleconnection patternsas well as internal climate variability. 

Abstract. During the last glacial period Northern Hemisphere climate was characterizedby extreme and abrupt climate changes, so-called Dansgaard–Oeschger (DO)events. Most clearly observed as temperature changes in Greenland ice-corerecords, their climatic imprint was geographically widespread. However, thetemporal relation between DO events in Greenland and other regions isuncertain due to the chronological uncertainties of each archive, limitingour ability to test hypotheses of synchronous change. In contrast, theassumption of direct synchrony of climate changes forms the basis of manytimescales. Here, we use cosmogenic radionuclides (¹⁰Be,³⁶Cl, ¹⁴C) to link Greenland ice-core records toU∕Th-dated speleothems, quantify offsets between the two timescales, andimprove their absolute dating back to 45000 years ago. This approach allowsus to test the assumption that DO events occurred synchronously betweenGreenland ice-core and tropical speleothem records with unprecedentedprecision. We find that the onset of DO events occurs within synchronizationuncertainties in all investigated records. Importantly, we demonstrate thatlocal discrepancies remain in the temporal development of rapid climatechange for specific events and speleothems. These may either be related tothe location of proxy records relative to the shifting atmospheric fronts orto underestimated U∕Th dating uncertainties. Our study thus highlightsthe potential for misleading interpretations of the Earth system whenapplying the common practice of climate wiggle matching.

 

Abstract. We present a 2700-year annually resolved chronology and snow accumulationhistory for the Roosevelt Island Climate Evolution (RICE) ice core, Ross IceShelf, West Antarctica. The core adds information on past accumulationchanges in an otherwise poorly constrained sector of Antarctica. The timescale was constructed by identifying annual cycles inhigh-resolution impurity records, and it constitutes the top part of theRoosevelt Island Ice Core Chronology 2017 (RICE17). Validation by volcanicand methane matching to the WD2014 chronology from the WAIS Divide ice coreshows that the two timescales are in excellent agreement. In a companionpaper, gas matching to WAIS Divide is used to extend the timescale for thedeeper part of the core in which annual layers cannot be identified. Based on the annually resolved timescale, we produced a record of past snowaccumulation at Roosevelt Island. The accumulation history shows thatRoosevelt Island experienced slightly increasing accumulation rates between700 BCE and 1300 CE, with an average accumulation of 0.25±0.02 mwater equivalent (w.e.) per year. Since 1300 CE, trends in the accumulationrate have been consistently negative, with an acceleration in the rate ofdecline after the mid-17th century. The current accumulation rate atRoosevelt Island is 0.210±0.002 m w.e. yr−1 (average since 1965 CE, ±2σ), and it is rapidly declining with a trend corresponding to0.8 mm yr−2. The decline observed since the mid-1960s is 8 times fasterthan the long-term decreasing trend taking place over the previouscenturies, with decadal mean accumulation rates consistently being belowaverage. Previous research has shown a strong link between Roosevelt Islandaccumulation rates and the location and intensity of the Amundsen Sea Low,which has a significant impact on regional sea-ice extent. The decrease inaccumulation rates at Roosevelt Island may therefore be explained in termsof a recent strengthening of the ASL and the expansion of sea ice in the easternRoss Sea. The start of the rapid decrease in RICE accumulation ratesobserved in 1965 CE may thus mark the onset of significant increases inregional sea-ice extent. 

Water-stable isotopes in polar ice cores are a widely used temperature proxy in paleoclimate reconstruction, yet calibration remains challenging in East Antarctica. Here, we reconstruct the magnitude and spatial pattern of Last Glacial Maximum surface cooling in Antarctica using borehole thermometry and firn properties in seven ice cores. West Antarctic sites cooled ~10°C relative to the preindustrial period. East Antarctic sites show a range from ~4° to ~7°C cooling, which is consistent with the results of global climate models when the effects of topographic changes indicated with ice core air-content data are included, but less than those indicated with the use of water-stable isotopes calibrated against modern spatial gradients. An altered Antarctic temperature inversion during the glacial reconciles our estimates with water-isotope observations.

 

Strategies for 21st-century environmental management and conservation under global change require a strong understanding of the biological mechanisms that mediate responses to climate- and human-driven change to successfully mitigate range contractions, extinctions, and the degradation of ecosystem services. Biodiversity responses to past rapid warming events can be followed in situ and over extended periods, using cross-disciplinary approaches that provide cost-effective and scalable information for species’ conservation and the maintenance of resilient ecosystems in many bioregions. Beyond the intrinsic knowledge gain such integrative research will increasingly provide the context, tools, and relevant case studies to assist in mitigating climate-driven biodiversity losses in the 21st century and beyond.