Journal articles: 'Antarctic Cold Reversal'

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Pedro, J. B., T. D. van Ommen, S. O. Rasmussen, V. I. Morgan, J. Chappellaz, A. D. Moy, V. Masson-Delmotte, and M. Delmotte. "The last deglaciation: timing the bipolar seesaw." Climate of the Past Discussions 7, no. 1 (January 26, 2011): 397–430. http://dx.doi.org/10.5194/cpd-7-397-2011.

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Abstract. Precise information on the relative timing of north-south climate variations is a key to resolving questions concerning the mechanisms that force and couple climate changes between the hemispheres. We present a new composite record made from five well-resolved Antarctic ice core records that robustly represents the timing of regional Antarctic climate change during the last deglaciation. Using fast variations in global methane gas concentrations as time markers, the Antarctic composite is directly compared to Greenland ice core records, allowing a detailed mapping of the inter-hemispheric sequence of climate changes. Consistent with prior studies the synchronized records show that warming (and cooling) trends in Antarctica closely match cold (and warm) periods in Greenland on millennial timescales. For the first time, we also identify a sub-millennial component to the inter-hemispheric coupling: within the Antarctic Cold Reversal the strongest Antarctic cooling occurs during the pronounced northern warmth of the Bølling; warming then resumes in Antarctica during the Intra-Allerød Cold Period i.e. prior to the Younger Dryas stadial. There is little-to-no time lag between climate transitions in Greenland and opposing changes in Antarctica. Our results lend support to fast acting inter-hemispheric coupling mechanisms including recently proposed bipolar atmospheric teleconnections and/or rapid bipolar ocean teleconnections.

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Pedro, J. B., T. D. van Ommen, S. O. Rasmussen, V. I. Morgan, J. Chappellaz, A. D. Moy, V. Masson-Delmotte, and M. Delmotte. "The last deglaciation: timing the bipolar seesaw." Climate of the Past 7, no. 2 (June 24, 2011): 671–83. http://dx.doi.org/10.5194/cp-7-671-2011.

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Abstract. Precise information on the relative timing of north-south climate variations is a key to resolving questions concerning the mechanisms that force and couple climate changes between the hemispheres. We present a new composite record made from five well-resolved Antarctic ice core records that robustly represents the timing of regional Antarctic climate change during the last deglaciation. Using fast variations in global methane gas concentrations as time markers, the Antarctic composite is directly compared to Greenland ice core records, allowing a detailed mapping of the inter-hemispheric sequence of climate changes. Consistent with prior studies the synchronized records show that warming (and cooling) trends in Antarctica closely match cold (and warm) periods in Greenland on millennial timescales. For the first time, we also identify a sub-millennial component to the inter-hemispheric coupling. Within the Antarctic Cold Reversal the strongest Antarctic cooling occurs during the pronounced northern warmth of the Bølling. Warming then resumes in Antarctica, potentially as early as the Intra-Allerød Cold Period, but with dating uncertainty that could place it as late as the onset of the Younger Dryas stadial. There is little-to-no time lag between climate transitions in Greenland and opposing changes in Antarctica. Our results lend support to fast acting inter-hemispheric coupling mechanisms, including recently proposed bipolar atmospheric teleconnections and/or rapid bipolar ocean teleconnections.

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Pedro, Joel B., Helen C. Bostock, Cecilia M. Bitz, Feng He, Marcus J. Vandergoes, Eric J. Steig, Brian M. Chase, et al. "The spatial extent and dynamics of the Antarctic Cold Reversal." Nature Geoscience 9, no. 1 (November 9, 2015): 51–55. http://dx.doi.org/10.1038/ngeo2580.

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García, Juan L., Michael R. Kaplan, Brenda L. Hall, Joerg M. Schaefer, Rodrigo M. Vega, Roseanne Schwartz, and Robert Finkel. "Glacier expansion in southern Patagonia throughout the Antarctic cold reversal." Geology 40, no. 9 (September 2012): 859–62. http://dx.doi.org/10.1130/g33164.1.

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Fletcher, Michael-Shawn, Joel Pedro, Tegan Hall, Michela Mariani, Joseph A. Alexander, Kristen Beck, Maarten Blaauw, et al. "Northward shift of the southern westerlies during the Antarctic Cold Reversal." Quaternary Science Reviews 271 (November 2021): 107189. http://dx.doi.org/10.1016/j.quascirev.2021.107189.

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Jomelli, V., L. Martin, P. H. Blard, V. Favier, M. Vuillé, and J. L. Ceballos. "Revisiting the andean tropical glacier behavior during the Antarctic cold reversal." Cuadernos de Investigación Geográfica 43, no. 2 (September 15, 2017): 629. http://dx.doi.org/10.18172/cig.3201.

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The sensitivity of tropical glaciers to paleoclimatic conditions that prevailed during the Antarctic cold reversal (ACR, ca. 14.5-12.9 ka) has been the subject of a wide debate. In 2014 a paper suggested that tropical glaciers responded very sensitively to the changing climate during the ACR (Jomelli et al., 2014). In this study, we reexamine the conclusions from this study by recalculating previous chronologies based on 226 10Be and 14 3He ages respectively, and using the most up-to date production rates for these cosmogenic nuclides in the Tropical Andes. 53 moraines from 25 glaciers were selected from the previous analysis provided by Jomelli et al. (2014) located in Colombia, Peru and Bolivia. We then focused on two distinct calculations. First we considered the oldest moraine and its uncertainty for every glacier representing the preserved evidence of the maximum glacier extents during the last deglaciation period, and binned the results into 5 distinct periods encompassing the Antarctic cold reversal and Younger Dryas (YD) chronozones: pre-ACR, ACR, ACR-YD, YD and post-YD respectively. Results revealed a predominance of pre-ACR and ACR ages, accounting for 60% of the glaciers. Second we counted the number of moraines per glacier according to the different groups. 21 moraines (40%) of the selected glaciers belong to the pre-ACR-ACR chronozones while 3 moraines only (5%) were dated to the YD and YD-Holocene groups. The rest was assigned to the ACR-YD. These results suggest that moraine records are a very good proxy to document the ACR signal in the Tropical Andes.

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Putnam, Aaron E., George H. Denton, Joerg M. Schaefer, David J. A. Barrell, Bjørn G. Andersen, Robert C. Finkel, Roseanne Schwartz, Alice M. Doughty, Michael R. Kaplan, and Christian Schlüchter. "Glacier advance in southern middle-latitudes during the Antarctic Cold Reversal." Nature Geoscience 3, no. 10 (September 26, 2010): 700–704. http://dx.doi.org/10.1038/ngeo962.

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Davies, B. J., V. R. Thorndycraft, D. Fabel, and J. R. V. Martin. "Asynchronous glacier dynamics during the Antarctic Cold Reversal in central Patagonia." Quaternary Science Reviews 200 (November 2018): 287–312. http://dx.doi.org/10.1016/j.quascirev.2018.09.025.

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9

Jomelli, V., V. Favier, M. Vuille, R. Braucher, L. Martin, P. H. Blard, C. Colose, et al. "A major advance of tropical Andean glaciers during the Antarctic cold reversal." Nature 513, no. 7517 (August 24, 2014): 224–28. http://dx.doi.org/10.1038/nature13546.

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Dupont, Lydie M., Jung-Hyun Kim, Ralph R. Schneider, and Ning Shi. "Southwest African climate independent of Atlantic sea surface temperatures during the Younger Dryas." Quaternary Research 61, no. 3 (May 2004): 318–24. http://dx.doi.org/10.1016/j.yqres.2004.02.005.

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To investigate land–sea interactions during deglaciation, we compared proxies for continental (pollen percentages and accumulation rates) and marine conditions (dinoflagellate cyst percentages and alkenone-derived sea surface temperatures). The proxies were from published data from an AMS-radiocarbon-dated sedimentary record of core GeoB 1023-5 encompassing the past 21,000 years. The site is located at ca. 2000 m water depth just north of the Walvis Ridge and in the vicinity of the Cunene River mouth. We infer that the parallelism between increasing sea surface temperatures and a southward shift of the savanna occurred only during the earliest part of the deglaciation. After the Antarctic Cold Reversal, southeast Atlantic sea surface temperatures no longer influenced the vegetation development in the Kalahari. Stronger trade winds during the Antarctic Cold Reversal and the Younger Dryas period probably caused increased upwelling off the coast of Angola. A southward shift of the Atlantic anti-cyclone could have resulted in both stronger trade winds and reduced impact of the Westerlies on the climate of southwestern Africa.

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Salvi, Cristinamaria, Gianguido Salvi, Barbara Stenni, and Antonio Brambati. "Palaeoproductivity in the Ross Sea, Antarctica, during the last 15 kyr BP and its link with ice-core temperature proxies." Annals of Glaciology 39 (2004): 445–51. http://dx.doi.org/10.3189/172756404781814582.

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AbstractA detailed study of organic carbon content obtained from two sediment cores collected in the Joides basin, western Ross Sea, Antarctica, was carried out. The variations observed during the last deglaciation and the Holocene were compared to the high-resolution climatic records (EPICA DC and Taylor Dome) preserved in the ice. The importance of the carbon content as a proxy for palaeoclimatic and palaeoenvironmental changes was investigated. A dramatic decrease in the Ross Sea palaeoproductivity was observed during the Antarctic Cold Reversal (12.5–14 kyr BP). Another decrease in total organic carbon in the second half of the Holocene (after 5–6 kyr BP) confirms the climate worsening observed in previous studies.

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Sagredo, Esteban A., Michael R. Kaplan, Paola S. Araya, Thomas V. Lowell, Juan C. Aravena, Patricio I. Moreno, Meredith A. Kelly, and Joerg M. Schaefer. "Trans-pacific glacial response to the Antarctic Cold Reversal in the southern mid-latitudes." Quaternary Science Reviews 188 (May 2018): 160–66. http://dx.doi.org/10.1016/j.quascirev.2018.01.011.

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Carter, Lionel, Barbara Manighetti, Gerald Ganssen, and Lisa Northcote. "Southwest Pacific modulation of abrupt climate change during the Antarctic Cold Reversal–Younger Dryas." Palaeogeography, Palaeoclimatology, Palaeoecology 260, no. 1-2 (April 2008): 284–98. http://dx.doi.org/10.1016/j.palaeo.2007.08.013.

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14

Fogwill, C. J., C. S. M. Turney, L. Menviel, A. Baker, M. E. Weber, B. Ellis, Z. A. Thomas, et al. "Southern Ocean carbon sink enhanced by sea-ice feedbacks at the Antarctic Cold Reversal." Nature Geoscience 13, no. 7 (June 22, 2020): 489–97. http://dx.doi.org/10.1038/s41561-020-0587-0.

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15

Moreno, P. I., M. R. Kaplan, J. P. François, R. Villa-Martínez, C. M. Moy, C. R. Stern, and P. W. Kubik. "Renewed glacial activity during the Antarctic cold reversal and persistence of cold conditions until 11.5 ka in southwestern Patagonia." Geology 37, no. 4 (April 2009): 375–78. http://dx.doi.org/10.1130/g25399a.1.

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Vandergoes, Marcus J., Ann C. Dieffenbacher-Krall, Rewi M. Newnham, George H. Denton, and Maarten Blaauw. "Cooling and changing seasonality in the Southern Alps, New Zealand during the Antarctic Cold Reversal." Quaternary Science Reviews 27, no. 5-6 (March 2008): 589–601. http://dx.doi.org/10.1016/j.quascirev.2007.11.015.

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Hajdas, Irka, David J. Lowe, Rewi M. Newnham, and Georges Bonani. "Timing of the late-glacial climate reversal in the Southern Hemisphere using high-resolution radiocarbon chronology for Kaipo Bog, New Zealand." Quaternary Research 65, no. 02 (March 2006): 340–45. http://dx.doi.org/10.1016/j.yqres.2005.08.028.

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AbstractThe pattern of climate change in the Southern Hemisphere during the Younger Dryas (YD) chronozone provides essential constraint on mechanisms of abrupt climate change only if accurate, high-precision chronologies are obtained. A climate reversal reported previously at Kaipo bog, New Zealand, had been dated between 13,600 and 12,600 cal yr B.P. and appeared to asynchronously overlap the YD chron, but the chronology, based on conventionally radiocarbon-dated bulk sediment samples, left the precise timing questionable. We report a new high-resolution AMS 14C chronology for the Kaipo record that confirms the original chronology and provides further evidence for a mid-latitude Southern Ocean cooling event dated between 13,800 and 12,400 cal yr B.P. (2σ range), roughly equivalent to the Antarctic Cold Reversal.

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Chowdhry Beeman, Jai, Léa Gest, Frédéric Parrenin, Dominique Raynaud, Tyler J. Fudge, Christo Buizert, and Edward J. Brook. "Antarctic temperature and CO2: near-synchrony yet variable phasing during the last deglaciation." Climate of the Past 15, no. 3 (May 22, 2019): 913–26. http://dx.doi.org/10.5194/cp-15-913-2019.

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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. With accurately dated paleoclimate records, we can investigate the timings of related variables in the climate system during this major transition. Here, we use an accurate relative chronology to compare temperature proxy data and global atmospheric CO2 as recorded in Antarctic ice cores. In addition to five regional records, we compare a δ18O stack, representing Antarctic climate variations with the high-resolution robustly dated WAIS Divide CO2 record (West Antarctic Ice Sheet). We assess the CO2 and Antarctic temperature phase relationship using a stochastic method to accurately identify the probable timings of changes in their trends. Four coherent changes are identified for the two series, and synchrony between CO2 and temperature is within the 95 % 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 deglaciation end 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 629 years, 68 % probability, at the deglaciation end). At 14.4 ka, the onset of the Antarctic Cold Reversal (ACR) period, our results do not show a clear lead 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 individual proxy records show variations from the stack, indicating regional differences in the pattern of temperature change, particularly in the WAIS Divide record at the onset of the deglaciation; the Dome Fuji record at the deglaciation end; 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 the isotopic temperature records – do not have high-probability counterparts in the other record. The likely-variable phasing we identify testify to the complex nature of the mechanisms driving the carbon cycle and Antarctic temperature during the deglaciation.

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Mendelova, M., A. S. Hein, R. McCulloch, and B. Davies. "The Last Glacial Maximum and deglaciation in central Patagonia, 44°S–49°S." Cuadernos de Investigación Geográfica 43, no. 2 (September 15, 2017): 719. http://dx.doi.org/10.18172/cig.3263.

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This paper reviews published geochronological data on glacier fluctuations and environmental changes in central Patagonia (44° S - 49° S) from the Last Glacial Maximum (LGM) through to the Holocene. Well-dated glacial chronologies from the southern mid-latitudes can inform on the synchronicity of glacial advances worldwide and provide insight on the drivers of southern hemisphere glaciations. In central Patagonia, two large outlet lobes of the former Patagonian Ice Sheet advanced in broad synchrony with the global LGM. In contrast to other parts of Patagonia, there is no convincing evidence for a more extensive local LGM advance during Marine Isotope Stage 3. Deglaciation initiated at ca. 19 ka, earlier than in other parts of Patagonia and regionally in the Southern Hemisphere, and rapid deglaciation saw ice margins retreat in places by at least 80-120 km within a few millennia. The Lateglacial glacier margins are poorly constrained, but an ice mass substantial enough to maintain a large regional proglacial lake must have persisted at this time. The timing of lake drainage and opening of the Río Baker drainage route to the Pacific Ocean is debated; the only directly dated shoreline suggests this occurred at the end of the Antarctic Cold Reversal at 12.7 ka. Palaeoecological evidence for cooling during the Antarctic Cold Reversal or Younger Dryas remains equivocal, which may reflect both the eurythermic nature of Patagonian vegetation and shifting Southern Westerly Winds. Eastern outlet glaciers appear to have advanced or stabilised at the Lateglacial/Holocene transition when palaeoenvironmental records indicate warmer and drier conditions, but the reason for this is unclear. Our review reveals both spatial and temporal gaps in available data that provide avenues for future research.

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Blunier, T., J. Schwander, B. Stauffer, T. Stocker, A. Dällenbach, A. Indermühle, J. Tschumi, J. Chappellaz, D. Raynaud, and J. M. Barnola. "Timing of the Antarctic cold reversal and the atmospheric CO2increase with respect to the Younger Dryas Event." Geophysical Research Letters 24, no. 21 (November 1, 1997): 2683–86. http://dx.doi.org/10.1029/97gl02658.

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Montade, Vincent. "Magellanic Moorland Expansion during the Antarctic Cold Reversal from Coastal Vegetation Changes in the Taitao Peninsula, Chile." Quaternary International 279-280 (November 2012): 333. http://dx.doi.org/10.1016/j.quaint.2012.08.966.

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Mendelová, Monika, Andrew S. Hein, Ángel Rodés, Rachel K. Smedley, and Sheng Xu. "Glacier expansion in central Patagonia during the Antarctic Cold Reversal followed by retreat and stabilisation during the Younger Dryas." Quaternary Science Reviews 227 (January 2020): 106047. http://dx.doi.org/10.1016/j.quascirev.2019.106047.

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23

Haas, Christian, David N. Thomas, and Jörg Bareiss. "Surface properties and processes of perennial Antarctic sea ice in summer." Journal of Glaciology 47, no. 159 (2001): 613–25. http://dx.doi.org/10.3189/172756501781831864.

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AbstractIce-core and snow data from the Amundsen, Bellingshausen and Weddell Seas, Antarctica, show that the formation of superimposed ice and the development of seawater-filled gap layers with high algal standing stocks is typical of the perennial sea ice in summer. The coarse-grained and dense snow had salinities mostly below 0.1‰. A layer of fresh superimposed ice had a mean thickness of 0.04–0.12 m. Gap layers 0.04–0.08 m thick extended downwards from 0.02 to 0.14 m below the water level. These gaps were populated by diatom standing stocks up to 439 μg L−1 chlorophyll a. We propose a comprehensive heuristic model of summer processes, where warming and the reversal of temperature gradients cause major transformations in snow and ice properties. The warming also causes the reopening of incompletely frozen slush layers caused by flood-freeze cycles during winter. Alternatively, superimposed ice forms at the cold interface between snow and slush in the case of flooding with negative freeboard. Combined, these explain the initial formation of gap layers by abiotic means alone. The upward growth of superimposed ice above the water level competes with a steady submergence of floes due to bottom and internal melting and accumulation of snow.

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Udisti, Roberto, Silvia Becagli, Silvia Benassai, Martine De Angelis, Margareta E. Hansson, Jean Jouzel, Jacob Schwander, Jørgen P. Steffensen, Rita Traversi, and Eric Wolff. "Sensitivity of chemical species to climatic changes in the last 45 kyr as revealed by high-resolution Dome C (East Antarctica) ice-core analysis." Annals of Glaciology 39 (2004): 457–66. http://dx.doi.org/10.3189/172756404781814096.

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AbstractTo assess the cause/effect relationship between climatic and environmental changes, we report high-resolution chemical profiles of the Dome C ice core (788m, 45 kyr), drilled in the framework of the European Project for Ice Coring in Antarctica (EPICA). Snow-concentration and depositional-flux changes during the last deglaciation were compared with climatic changes, derived by δD profile. Concentration and temperature profiles showed an anticorrelation, driven by changes in source intensity and transport efficiency of the atmospheric aerosol and by snow accumulation-rate variations. The flux calculation allowed correction for accumulation rate. While sulphate and ammonium fluxes are quite constant, Na+, Mg2+ and Ca2+ underwent the greatest changes, showing fluxes respectively about two, three and six times lower in the Holocene than in the Last Glacial Maximum. Chloride, nitrate and methanesulphonic acid (MSA) also exhibited large changes, but their persistence depends on depositional and post-depositional effects. The comparison between concentrations and δD profiles revealed leads and lags between chemical and temperature trends: Ca2+ and nitrate preceded by about 300 years the δD increase at the deglaciation onset, while MSA showed a 400 year delay. Generally, all components reached low Holocene values in the first deglaciation step (18.0–14.0 kyr BP), but Na+, Mg2+ and nitrate show changes during the Antarctic Cold Reversal (14.0– 12.5 kyr BP).

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Fogwill, C. J., and P. W. Kubik. "A glacial stage spanning the antarctic cold reversal in torres del paine (51°s), chile, based on preliminary cosmogenic exposure ages." Geografiska Annaler: Series A, Physical Geography 87, no. 2 (June 2005): 403–8. http://dx.doi.org/10.1111/j.0435-3676.2005.00266.x.

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McGlone, Matt S., Chris S. M. Turney, and Janet M. Wilmshurst. "Late-glacial and Holocene vegetation and climatic history of the Cass Basin, central South Island, New Zealand." Quaternary Research 62, no. 3 (November 2004): 267–79. http://dx.doi.org/10.1016/j.yqres.2004.09.003.

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Lithology, pollen, macrofossils, and stable carbon isotopes from an intermontane basin bog site in southern New Zealand provide a detailed late-glacial and early Holocene vegetation and climate record. Glacial retreat occurred before 17,000 cal yr B.P., and tundra-like grassland"shrubland occupied the basin shortly after. Between 16,500 and 14,600 cal yr B.P., a minor regional expansion of forest patches occurred in response to warming, but the basin remained in shrubland. Forest retreated between 14,600 and 13,600 cal yr B.P., at about the time of the Antarctic Cold Reversal. At 13,600 cal yr B.P., a steady progression from shrubland to tall podocarp forest began as the climate ameliorated. Tall, temperate podocarp trees replaced stress-tolerant shrubs and trees between 12,800 and 11,300 cal yr B.P., indicating sustained warming during the Younger Dryas Chronozone (YDC). Stable isotopes suggest increasing atmospheric humidity from 11,800 to 9300 cal yr B.P. Mild (annual temperatures at least 1°C higher than present), and moist conditions prevailed from 11,000 to 10,350 cal yr B.P. Cooler, more variable conditions followed, and podocarp forest was completely replaced by montane Nothofagus forest at around 7500 cal yr B.P. with the onset of the modern climate regime. The Cass Basin late-glacial climate record closely matches the Antarctic ice core records and is in approximate antiphase with the North Atlantic.

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Henríquez, William I., Rodrigo Villa-Martínez, Isabel Vilanova, Ricardo De Pol-Holz, and Patricio I. Moreno. "The last glacial termination on the eastern flank of the central Patagonian Andes (47 ° S)." Climate of the Past 13, no. 7 (July 14, 2017): 879–95. http://dx.doi.org/10.5194/cp-13-879-2017.

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Abstract. Few studies have examined in detail the sequence of events during the last glacial termination (T1) in the core sector of the Patagonian Ice Sheet (PIS), the largest ice mass in the Southern Hemisphere outside of Antarctica. Here we report results from Lago Edita (47°8′ S, 72°25′ W, 570 m a.s.l.), a small closed-basin lake located in a valley overridden by eastward-flowing Andean glaciers during the Last Glacial Maximum (LGM). The Lago Edita record shows glaciolacustrine sedimentation until 19 400 yr BP, followed by organic sedimentation in a closed-basin lake and a mosaic of cold-resistant hygrophilous conifers and rainforest trees, along with alpine herbs between 19 400 and 11 000 yr BP. Our data suggest that the PIS retreated at least ∼ 90 km from its LGM limit between ∼ 21 000 and 19 400 yr BP and that scattered, low-density populations of cold-resistant hygrophilous conifers, rainforest trees, high-Andean and steppe herbs thrived east of the Andes during the LGM and T1, implying high precipitation levels and southern westerly wind (SWW) influence at 47° S. The conifer Podocarpus nubigena increased between 14 500 and 13 000 yr BP, suggesting even stronger SWW influence during the Antarctic Cold Reversal, after which it declined and persisted until 11 000 yr BP. Large increases in arboreal pollen at ∼ 13 000 and ∼ 11 000 yr BP led to the establishment of forests near Lago Edita between 10 000 and 9000 yr BP, suggesting a rise in the regional tree line along the eastern Andean slopes driven by warming pulses at ∼ 13 000 and ∼ 11 000 yr BP and a subsequent decline in SWW influence at ∼ 11 000 yr BP. We propose that the PIS imposed a regional cooling signal along its eastern, downwind margin through T1 that lasted until the separation of the northern and southern Patagonian ice fields along the Andes during the Younger Dryas period. We posit that the withdrawal of glacial and associated glaciolacustrine environments through T1 provided a route for the dispersal of hygrophilous trees and herbs from the eastern flank of the central Patagonian Andes, contributing to the afforestation of the western Andean slopes and pacific coasts of central Patagonia during T1.

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Vogel, H., C. Meyer-Jacob, M. Melles, J. Brigham-Grette, A. A. Andreev, V. Wennrich, P. E. Tarasov, and P. Rosén. "Detailed insight into Arctic climatic variability during MIS 11c at Lake El'gygytgyn, NE Russia." Climate of the Past 9, no. 4 (July 15, 2013): 1467–79. http://dx.doi.org/10.5194/cp-9-1467-2013.

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Abstract. Here we present a detailed multi-proxy record of the climate and environmental evolution at Lake El'gygytgyn, Far East Russian Arctic during the period 430–395 ka covering the marine isotope stage (MIS) 12/11 transition and the thermal maximum of super interglacial MIS 11c. The MIS 12/11 transition at Lake El'gygytgyn is characterized by initial warming followed by a cold reversal implying similarities to the last deglaciation. The thermal maximum of MIS 11c is characterized by full and remarkably stable interglacial conditions with mean temperatures of the warmest month (MTWM) ranging between ca. 10–15 °C; annual precipitation (PANN) ranging between ca. 300–600 mm; strong in-lake productivity coinciding with dark coniferous forests in the catchment; annual disintegration of the lake ice cover; and full mixis of the water column. Such conditions persisted, according to our age model, for ca. 27 ± 8 kyr between ca. 425–398 ka. The Lake El'gygytgyn record closely resembles the climate pattern recorded in Lake Baikal (SE Siberia) sediments and Antarctic ice cores, implying interhemispheric climate connectivity during MIS 11c.

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Traversi, Rita, Carlo Barbante, Vania Gaspari, Ilaria Fattori, Ombretta Largiuni, Lorenzo Magaldi, and Roberto Udisti. "Aluminium and iron record for the last 28 kyr derived from the Antarctic EDC96 ice core using new CFA methods." Annals of Glaciology 39 (2004): 300–306. http://dx.doi.org/10.3189/172756404781814438.

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AbstractSpectrofluorimetric and spectrophotometric continuous flow analysis (CFA) methods were developed and applied to the determination of aluminium and iron in EPICA Dome C (East Antarctica) ice-core samples (6–585m depth). The methods are able to measure the fraction of Al and Fe which can be detected once the sample is filtered on a 5.0 μm membrane and acidified to pH 2. Both the methods present high sensitivity (detection limit of 10 ng L–1 for Al and 50 ng L–1 for Fe) and reproducibility (5% at sub-ppb level). The Fe and Al profiles show sharp decreases in concentrations in the last glacial/interglacial transition, reflecting the decreasing dust aerosol load. The two elements show a different pattern during the Antarctic Cold Reversal (ACR) climatic change, with high iron concentrations (similar to the glacial period) and low but increasing Al content during the ACR minimum. In order to interpret the Al and Fe data obtained by CFA, a comparison with Al and Fe composition, as measured by inductively coupled plasma sector field mass spectrometry (ICP-SFMS), was performed for Holocene, ACR and glacial periods. The percentage of CFA-Al with respect to ICP-SFMS-Al in the three periods shows a lower variability than CFA-Fe (3% in the glacial period and 64% in the ACR). This pattern may be explained by the different dominant iron sources in the different climatic periods. During the Last Glacial Maximum, Fe is proposed to arise mainly from insoluble continental dust, while a variety of ocean-recycled Fe, mainly distributed in fine particles and as more soluble species, shows a higher contribution in the ACR and, to a lesser extent, in the Holocene.

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Metcalf, Jessica L., Chris Turney, Ross Barnett, Fabiana Martin, Sarah C. Bray, Julia T. Vilstrup, Ludovic Orlando, et al. "Synergistic roles of climate warming and human occupation in Patagonian megafaunal extinctions during the Last Deglaciation." Science Advances 2, no. 6 (June 2016): e1501682. http://dx.doi.org/10.1126/sciadv.1501682.

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The causes of Late Pleistocene megafaunal extinctions (60,000 to 11,650 years ago, hereafter 60 to 11.65 ka) remain contentious, with major phases coinciding with both human arrival and climate change around the world. The Americas provide a unique opportunity to disentangle these factors as human colonization took place over a narrow time frame (~15 to 14.6 ka) but during contrasting temperature trends across each continent. Unfortunately, limited data sets in South America have so far precluded detailed comparison. We analyze genetic and radiocarbon data from 89 and 71 Patagonian megafaunal bones, respectively, more than doubling the high-quality Pleistocene megafaunal radiocarbon data sets from the region. We identify a narrow megafaunal extinction phase 12,280 ± 110 years ago, some 1 to 3 thousand years after initial human presence in the area. Although humans arrived immediately prior to a cold phase, the Antarctic Cold Reversal stadial, megafaunal extinctions did not occur until the stadial finished and the subsequent warming phase commenced some 1 to 3 thousand years later. The increased resolution provided by the Patagonian material reveals that the sequence of climate and extinction events in North and South America were temporally inverted, but in both cases, megafaunal extinctions did not occur until human presence and climate warming coincided. Overall, metapopulation processes involving subpopulation connectivity on a continental scale appear to have been critical for megafaunal species survival of both climate change and human impacts.

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Lowry, Daniel P., Nicholas R. Golledge, Laurie Menviel, and Nancy A. N. Bertler. "Deglacial evolution of regional Antarctic climate and Southern Ocean conditions in transient climate simulations." Climate of the Past 15, no. 1 (January 30, 2019): 189–215. http://dx.doi.org/10.5194/cp-15-189-2019.

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Abstract. Constraining Antarctica's climate evolution since the end of the Last Glacial Maximum (∼18 ka) remains a key challenge, but is important for accurately projecting future changes in Antarctic ice sheet mass balance. Here we perform a spatial and temporal analysis of two transient deglacial climate simulations, one using a fully coupled GCM (TraCE-21ka) and one using an intermediate complexity model (LOVECLIM DGns), to determine regional differences in deglacial climate evolution and identify the main strengths and limitations of the models in terms of climate variables that impact ice sheet mass balance. The greatest continental surface warming is observed over the continental margins in both models, with strong correlations between surface albedo, sea ice coverage, and surface air temperature along the coasts, as well as regions with the greatest decrease in ice surface elevation in TraCE-21ka. Accumulation–temperature scaling relationships are fairly linear and constant in the continental interior, but exhibit higher variability in the early to mid-Holocene over coastal regions. Circum-Antarctic coastal ocean temperatures at grounding line depths are highly sensitive to the meltwater forcings prescribed in each simulation, which are applied in different ways due to limited paleo-constraints. Meltwater forcing associated with the Meltwater Pulse 1A (MWP1A) event results in subsurface warming that is most pronounced in the Amundsen and Bellingshausen Sea sector in both models. Although modelled centennial-scale rates of temperature and accumulation change are reasonable, clear model–proxy mismatches are observed with regard to the timing and duration of the Antarctic Cold Reversal (ACR) and Younger Dryas–early Holocene warming, which may suggest model bias in large-scale ocean circulation, biases in temperature reconstructions from proxy records, or that the MWP1A and 1B events are inadequately represented in these simulations. The incorporation of dynamic ice sheet models in future transient climate simulations could aid in improving meltwater forcing representation, and thus model–proxy agreement, through this time interval.

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Kylander, Malin E., Mikaela Holm, Jennifer Fitchett, Stefan Grab, Antonio Martinez Cortizas, Elin Norström, and Richard Bindler. "Late glacial (17,060–13,400 cal yr BP) sedimentary and paleoenvironmental evolution of the Sekhokong Range (Drakensberg), southern Africa." PLOS ONE 16, no. 3 (March 17, 2021): e0246821. http://dx.doi.org/10.1371/journal.pone.0246821.

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Southern Africa sits at the junction of tropical and temperate systems, leading to the formation of seasonal precipitation zones. Understanding late Quaternary paleoclimatic change in this vulnerable region is hampered by a lack of available, reliably-dated records. Here we present a sequence from a well-stratified sedimentary infill occupying a lower slope basin which covers 17,060 to 13,400 cal yr BP with the aim to reconstruct paleoclimatic variability in the high Drakensberg during the Late Glacial. We use a combination of pollen, total organic carbon and nitrogen, δ13C, Fourier transform infrared spectroscopy attenuated total reflectance (FTIR-ATR) spectral and elemental data on contiguous samples with high temporal resolution (10 to 80 years per sample). Our data support a relatively humid environment with considerable cold season precipitation during what might have been the final stage of niche-glaciation on the adjoining southern aspects around 17,000 cal yr BP. Then, after an initial warmer and drier period starting ~15,600 cal yr BP, we identify a return to colder and drier conditions with more winter precipitation starting ~14,380 cal yr BP, which represents the first local evidence for the Antarctic Cold Reversal (ACR) in this region. On decadal to centennial timescales, the Late Glacial period was one marked by considerable climatic fluctuation and bi-directional environmental change, which has not been identified in previous studies for this region. Our study shows complex changes in both moisture and thermal conditions providing a more nuanced picture of the Late Glacial for the high Drakensburg.

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Traversi, Rita, Silvia Becagli, Emiliano Castellano, Alessio Migliori, Mirko Severi, and Roberto Udisti. "High-resolution fast ion chromatography (FIC) measurements of chloride, nitrate and sulphate along the EPICA Dome C ice core." Annals of Glaciology 35 (2002): 291–98. http://dx.doi.org/10.3189/172756402781816564.

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AbstractFast ion chromatographic (FIC) analysis of the first European Project for Ice Coring in Antarctica (EPICA) Dome C ice core (788m deep) was used to obtain high-resolution profiles for Cl–, NO3– and SO42–, spanning the last 45000 years. About 19 000 determinations for each component, with an average resolution of 4.0 cm, were performed in the field on continuously melted firn- and ice-core sections. the measured core covers the Holocene, the glacial/interglacial transition and about one-third of the last ice age. In the glacial period, mean concentrations of 93.8, 24.4 and 178.4 mg L–1 were calculated for Cl–, NO3– and SO42–, respectively. the mean levels significantly increase in the Last Glacial Maximum (LGM), when these compounds reach values of 149.6, 53.9 and 219.3 mg L–1. During the glacial/interglacial transition, the mean concentrations quickly decrease reaching the typical Holocene values of 19.1, 12.9 and 93.3 mg L–1, for Cl–, NO3– and SO42–, respectively. All species settle on Holocene-like values about 4000 years before the beginning of the warm period (from the isotopic curve) showing a low (chloride) and no (nitrate and sulphate) sensitivity to Antarctic Cold Reversal climatic change. the sulphate decrease is consistent with the dilution factor due to the higher accumulation rate in the interglacial conditions (about 2.5), suggesting no significant change in source intensity or transport efficiency occurred for this component. on the contrary, the Holocene values for chloride and nitrate, being much lower than those measured in the LGM, suggest a source-intensity and transport-efficiency enhancement during the LGM and/or a more effective fixing of HCl and HNO3 in the snow layers through the neutralizing effect of the higher atmospheric dust load.

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Rainsley, Eleanor, Chris S. M. Turney, Nicholas R. Golledge, Janet M. Wilmshurst, Matt S. McGlone, Alan G. Hogg, Bo Li, et al. "Pleistocene glacial history of the New Zealand subantarctic islands." Climate of the Past 15, no. 2 (March 14, 2019): 423–48. http://dx.doi.org/10.5194/cp-15-423-2019.

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Abstract. The New Zealand subantarctic islands of Auckland and Campbell, situated between the subtropical front and the Antarctic Convergence in the Pacific sector of the Southern Ocean, provide valuable terrestrial records from a globally important climatic region. Whilst the islands show clear evidence of past glaciation, the timing and mechanisms behind Pleistocene environmental and climate changes remain uncertain. Here we present a multidisciplinary study of the islands – including marine and terrestrial geomorphological surveys, extensive analyses of sedimentary sequences, a comprehensive dating programme, and glacier flow line modelling – to investigate multiple phases of glaciation across the islands. We find evidence that the Auckland Islands hosted a small ice cap 384 000 ± 26 000 years ago (384±26 ka), most likely during Marine Isotope Stage 10, a period when the subtropical front was reportedly north of its present-day latitude by several degrees, and consistent with hemispheric-wide glacial expansion. Flow line modelling constrained by field evidence suggests a more restricted glacial period prior to the LGM that formed substantial valley glaciers on the Campbell and Auckland Islands around 72–62 ka. Despite previous interpretations that suggest the maximum glacial extent occurred in the form of valley glaciation at the Last Glacial Maximum (LGM; ∼21 ka), our combined approach suggests minimal LGM glaciation across the New Zealand subantarctic islands and that no glaciers were present during the Antarctic Cold Reversal (ACR; ∼15–13 ka). Instead, modelling implies that despite a regional mean annual air temperature depression of ∼5 ∘C during the LGM, a combination of high seasonality and low precipitation left the islands incapable of sustaining significant glaciation. We suggest that northwards expansion of winter sea ice during the LGM and subsequent ACR led to precipitation starvation across the middle to high latitudes of the Southern Ocean, resulting in restricted glaciation of the subantarctic islands.

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Vogel, H., C. Meyer-Jacob, M. Melles, J. Brigham-Grette, A. A. Andreev, V. Wennrich, and P. Rosén. "Detailed insight into Arctic climatic variability during MIS 11 at Lake El'gygytgyn, NE Russia." Climate of the Past Discussions 8, no. 6 (December 19, 2012): 6309–39. http://dx.doi.org/10.5194/cpd-8-6309-2012.

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Abstract. Here we present a detailed multiproxy record of the climate and environmental evolution at Lake El'gygytgyn/Far East Russian Arctic during the period 430–395 ka covering the Marine Isotope Stage (MIS) 12/11 transition and the thermal maximum of super interglacial MIS 11. The MIS 12/11 transition at Lake El'gygytgyn is characterized by initial warming followed by a cold reversal implying similarities to the Bølling/Allerød (B/A) to Younger Dryas (YD) pattern of the last deglaciation. Full and remarkably stable interglacial conditions with mean temperatures of warmest month (MTWM) ranging between ca. 10–15 °C, annual precipitation (PANN) ranging between ca. 300–600 mm, strong in-lake productivity, coincide with dark coniferous forests in the catchment, annual disintegration of the lake ice cover and full mixis of the water column. Such conditions persisted for ca. 27 kyrs between ca. 425–398 ka. The Lake El'gygytgyn record closely resembles the climate pattern recorded in Lake Baikal (SE Siberia) sediments and Antarctic ice cores implying strong teleconnections between Northern and Southern Hemispheres during MIS 11. A peak warm period between ca. 418–415.5 ka and a precipitation anomaly at ca. 401 ka at Lake El'gygytgyn, in contrast, appear to be an expression of more regionally confined climate variations.

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Palacios, D. "The state of knowledge on the deglaciation of America in 2017." Cuadernos de Investigación Geográfica 43, no. 2 (September 15, 2017): 361. http://dx.doi.org/10.18172/cig.3318.

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This work presents a summary of all contributions included in this Special Issue on the deglaciation of America. It analyses the differences and coincidences between the phases of glacial evolution and their chronology in each of the regions studied, and seeks a possible explanation for asynchronies, according to the opinions of the authors of the contributions. Most of the papers show significant diversity within each region due to local factors and different approaches to their study. Often, local differences are even more important than differences with other regions. In North and Central America glacial evolution appears quite uniform, in line with the evolution of the temperature in the North Atlantic. The differences found between some regions may be due to slight variations in the impact of the temperature of the Atlantic in each region, and to differences in approaching their study. The glacial evolution of the Andes presents a greater diversity, probably due to the existence of arid areas along most of the mountain range, which show a greater sensitivity to the reception of humidity than to temperature in their glacial balance. In general, researchers have detected an attenuation of the influence of the temperature of the North Atlantic towards the south, and of the Antarctic Cold Reversal towards the north.

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Berg, Sonja, Duanne A. White, Sandra Jivcov, Martin Melles, Melanie J. Leng, Janet Rethemeyer, Claire Allen, Bianca Perren, Ole Bennike, and Finn Viehberg. "Holocene glacier fluctuations and environmental changes in subantarctic South Georgia inferred from a sediment record from a coastal inlet." Quaternary Research 91, no. 1 (October 30, 2018): 132–48. http://dx.doi.org/10.1017/qua.2018.85.

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AbstractThe subantarctic island of South Georgia provides terrestrial and coastal marine records of climate variability, which are crucial for the understanding of the drivers of Holocene climate changes in the subantarctic region. Here we investigate a sediment core (Co1305) from a coastal inlet on South Georgia using elemental, lipid biomarker, diatom, and stable isotope data to infer changes in environmental conditions and to constrain the timing of late-glacial and Holocene glacier fluctuations. Because of the scarcity of terrestrial macrofossils and the presence of redeposited and relict organic matter in the sediments, age control for the record was obtained by compound-specific radiocarbon dating of mostly marine-derived n-C16 fatty acids. A basal till layer recovered in Little Jason Lagoon was likely deposited during an advance of local glaciers during the Antarctic cold reversal. After glacier retreat, an oligotrophic lake occupied the site, which transitioned to a marine inlet around 8.0±0.9 ka because of relative sea-level rise. From 7.0±0.6 to 4.0±0.4 ka, reduced vegetation coverage in the catchment, as well as high siliciclastic input and deposition of ice-rafted debris, indicates glacier advances in the terrestrial catchment and likely in the adjacent fjord. A second, less extensive period of glacier advances occurred in the late Holocene, after 1.8±0.3 ka.

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Köhler, P., G. Knorr, D. Buiron, A. Lourantou, and J. Chappellaz. "Rapid changes in ice core gas records – Part 2: Understanding the rapid rise in atmospheric CO2 at the onset of the Bølling/Allerød." Climate of the Past Discussions 6, no. 4 (August 11, 2010): 1473–501. http://dx.doi.org/10.5194/cpd-6-1473-2010.

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Abstract. During the last glacial/interglacial transition the Earth's climate underwent rapid changes around 14.6 kyr ago. Temperature proxies from ice cores revealed the onset of the Bølling/Allerød (B/A) warm period in the north and the start of the Antarctic Cold Reversal in the south. Furthermore, the B/A is accompanied by a rapid sea level rise of about 20 m during meltwater pulse (MWP) 1A, whose exact timing is matter of current debate. In situ measured CO2 in the EPICA Dome C (EDC) ice core also revealed a remarkable jump of 10±1 ppmv in 230 yr at the same time. Allowing for the age distribution of CO2 in firn we here show, that atmospheric CO2 rose by 20–35 ppmv in less than 200 yr, which is a factor of 2–3.5 larger than the CO2 signal recorded in situ in EDC. Based on the estimated airborne fraction of 0.17 of CO2 we infer that 125 Pg of carbon need to be released to the atmosphere to produce such a peak. Most of the carbon might have been activated as consequence of continental shelf flooding during MWP-1A. This impact of rapid sea level rise on atmospheric CO2 distinguishes the B/A from other Dansgaard/Oeschger events of the last 60 kyr, potentially defining the point of no return during the last deglaciation.

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Rother, H., and J. Shulmeister. "Synoptic climate change as a driver of late Quaternary glaciations in the mid-latitudes of the Southern Hemisphere." Climate of the Past Discussions 1, no. 3 (December 1, 2005): 231–53. http://dx.doi.org/10.5194/cpd-1-231-2005.

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Abstract. The relative timing of late Quaternary glacial advances in mid-latitude (40–55° S) mountain belts of the Southern Hemisphere (SH) has become a critical focus in the debate on global climate teleconnections. On the basis of glacial data from New Zealand and southern South America it has been argued that interhemispheric synchrony or asynchrony of Quaternary glacial events is due to Northern Hemisphere (NH) forcing of SH climate through either the ocean or atmosphere systems. Here we present a glacial snow-mass balance model that demonstrates that large scale glacial advances in the temperate and hyperhumid Southern Alps of New Zealand can be generated with very little thermal forcing. This is because the rapid conversion of precipitation from rainfall to snowfall drives massive ice accumulation at small thermal changes (1–4°C). Our model is consistent with recent paleo-environmental reconstructions showing that glacial advances in New Zealand during the Last Glacial Maximum (LGM) and the Last Glacial Interglacial Transition (LGIT) occurred under very moderate cooling. We suggest that such moderate cooling could be generated by changes in synoptic climatology, specifically through enhanced regional flow of moist westerly air masses. Our results imply that NH climate forcing may not have been the exclusive driver of Quaternary glaciations in New Zealand and that synoptic style climate variations are a better explanation for at least some Late Quaternary glacial events, in particular during the LGIT (e.g. Younger Dryas and/or Antarctic Cold Reversal).

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Cosentino, Nicolás J., Diego M. Gaiero, Gabriela Torre, Andrea I. Pasquini, Renata Coppo, Juan M. Arce, and Georgina Vélez. "Atmospheric dust dynamics in southern South America: A 14-year modern dust record in the loessic Pampean region." Holocene 30, no. 4 (September 18, 2019): 575–88. http://dx.doi.org/10.1177/0959683619875198.

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Mineral aerosols profoundly impact global climate. Modeling of the dust cycle is the main tool used to gauge this effect. However, the scarcity of in situ modern dust flux measurements is the main reason why validation of existing models is hampered. We present the first long-term (14-year) record of dust flux in the Pampas, southern South America, home to the largest loess deposit in the Southern Hemisphere. Measured 14-year mean deposition (40 g m−2 year−1) and horizontal (362 g m−2 year−1) fluxes imply that current models underestimate the power of the central Pampas as a dust sink. Based on cross-spectral analysis, both wet and, to a lesser extent, dry deposition are found to play significant roles in atmospheric dust extraction. Dust is sourced regionally from the South American Arid Diagonal and from the shores of Mar Chiquita lake (~260 km), which we find to be the main contributor of dust particles >30 µm. Cross-spectral and satellite image analyses show that surface wind speed and precipitation at the Puna-Altiplano Plateau are controlling factors for horizontal dust flux in the Pampas. El Niño Southern Oscillation probably plays a role in controlling interannual horizontal dust flux periodicities. Finally, preliminary comparisons between modern vertical dust fluxes and loess accumulation rates point to the Pampas as a more powerful dust sink during the last deglaciation and Antarctic Cold Reversal (18–12.5 ka).

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Rother, H., and J. Shulmeister. "Synoptic climate change as a driver of late Quaternary glaciations in the mid-latitudes of the Southern Hemisphere." Climate of the Past 2, no. 1 (May 12, 2006): 11–19. http://dx.doi.org/10.5194/cp-2-11-2006.

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Abstract. The relative timing of late Quaternary glacial advances in mid-latitude (40-55° S) mountain belts of the Southern Hemisphere (SH) has become a critical focus in the debate on global climate teleconnections. On the basis of glacial data from New Zealand (NZ) and southern South America it has been argued that interhemispheric synchrony or asynchrony of Quaternary glacial events is due to Northern Hemisphere (NH) forcing of SH climate through either the ocean or atmosphere systems. Here we present a glacial snow-mass balance model that demonstrates that large scale glaciation in the temperate and hyperhumid Southern Alps of New Zealand can be generated with moderate cooling. This is because the rapid conversion of precipitation from rainfall to snowfall drives massive ice accumulation at small thermal changes (1-4°C). Our model is consistent with recent paleo-environmental reconstructions showing that glacial advances in New Zealand during the Last Glacial Maximum (LGM) and the Last Glacial Interglacial Transition (LGIT) occurred under very moderate cooling. We suggest that such moderate cooling could be generated by changes in synoptic climatology, specifically through enhanced regional flow of moist westerly air masses. Our results imply that NH climate forcing may not have been the exclusive driver of Quaternary glaciations in New Zealand and that synoptic style climate variations are a better explanation for at least some late Quaternary glacial events, in particular during the LGIT (e.g. Younger Dryas and/or Antarctic Cold Reversal).

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Zheng, Yixi, David P. Stevens, Karen J. Heywood, Benjamin G. M. Webber, and Bastien Y. Queste. "Reversal of ocean gyres near ice shelves in the Amundsen Sea caused by the interaction of sea ice and wind." Cryosphere 16, no. 7 (July 28, 2022): 3005–19. http://dx.doi.org/10.5194/tc-16-3005-2022.

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Abstract. Floating ice shelves buttress the Antarctic Ice Sheet, which is losing mass rapidly mainly due to ocean-driven melting and the associated disruption to glacial dynamics. The local ocean circulation near ice shelves is therefore important for the prediction of future ice mass loss and related sea-level rise as it determines the water mass exchange, heat transport under the ice shelf and resultant melting. However, the dynamics controlling the near-coastal circulation are not fully understood. A cyclonic (i.e. clockwise) gyre circulation (27 km radius) in front of the Pine Island Ice Shelf has previously been identified in both numerical models and velocity observations. Mooring data further revealed a potential reversal of this gyre during an abnormally cold period. Here we present ship-based observations from 2019 to the west of Thwaites Ice Shelf, revealing another gyre (13 km radius) for the first time in this habitually ice-covered region, rotating in the opposite (anticyclonic, anticlockwise) direction to the gyre near Pine Island Ice Shelf, despite similar wind forcing. We use an idealised configuration of MITgcm, with idealised forcing based on ERA5 climatological wind fields and a range of idealised sea ice conditions typical for the region, to reproduce key features of the observed gyres near Pine Island Ice Shelf and Thwaites Ice Shelf. The model driven solely by wind forcing in the presence of ice can reproduce the horizontal structure and direction of both gyres. We show that the modelled gyre direction depends upon the spatial difference in the ocean surface stress, which can be affected by the applied wind stress curl filed, the percentage of wind stress transferred through the ice, and the angle between the wind direction and the sea ice edge. The presence of ice, either it is fast ice/ice shelves blocking the effect of wind or mobile sea ice enhancing the effect of wind, has the potential to reverse the gyre direction relative to ice-free conditions.

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Alcalá-Reygosa, J. "El Último Máximo Glaciar local y la deglaciación de la Zona Volcánica Central Andina: El caso del volcán HualcaHualca y del altiplano de Patapampa (Sur de Perú)." Cuadernos de Investigación Geográfica 43, no. 2 (September 15, 2017): 649. http://dx.doi.org/10.18172/cig.3231.

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The aim of this study is to constrain the timing of the deglaciation process since the Last Local Glacial Maximum in HualcaHualca volcano and Patapampa Altiplano, located in the Andean Central Volcanic Zone. Nine 36Cl cosmogenic surface exposure dating of moraine boulders as well as polished and striated bedrock surfaces are presented. The 36Cl cosmogenic exposure ages indicate that the glaciers reached their maximum extent at ~ 17 - 16 ka on the HualcaHualca volcano during the Heinrich 1 event and the Tauca paleolake cycle. Since then glaciers began to retreat until ~ 12 ka, when they went through a phase of readvance or stillstand. The deglaciation of HualcaHualca was constant since ~ 11.5 ka, coinciding with the disappearance of the ice cap from the Patapampa Altiplano. These glacial ages do not corroborate a Last Local Glacial Maximum prior to the global Last Glacial Maximum but they indicate a sensitive reaction of the glacier system to precipitation fluctuations. According to the analysis of cosmogenic exposure ages reported from HualcaHualca, Sajama and Tunupa volcanoes, the onset of deglaciation since Last Local Glacial Maximum occurred at the end of the Heinrich 1 event and the Tauca paleolake cycle in the Andean Central Volcanic Zone. However, the glacier retreat was not continuous because at least one significant readvance or stillstand phase has been reported in most of the volcanoes studied in this region although the ages cannot be clearly related to the Younger Dryas and/or the Antarctic Cold Reversal cold events. After this readvance or stillstand, the glaciers of the Central Volcanic Zone retreated, but at least three clear minor readvances evidence a not homogeneous warm and/or dry climate during the Holocene. Even though in situ cosmogenic exposure provides important glacial chronological data, it is difficult to establish a consistent regional glacial reconstruction and clear connections with the main Late Pleistocene cold episodes due to limitations associated with in situ cosmogenic production rates and the use of different scaling schemes. To reduce the uncertainty and compare the available cosmogenic ages, it would be necessary to determine a precise in situ cosmogenic production rate for each isotope in the Central Andes, a standard scaling scheme and recalculate the published chronological data.

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Shulmeister, J., D. T. Rodbell, M. K. Gagan, and G. O. Seltzer. "Inter-hemispheric linkages in climate change: paleo-perspectives for future climate change." Climate of the Past Discussions 2, no. 1 (February 22, 2006): 79–122. http://dx.doi.org/10.5194/cpd-2-79-2006.

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Abstract. The Pole-Equator-Pole (PEP) projects of the PANASH (Paleoclimates of the Northern and Southern Hemisphere) programme have significantly advanced our understanding of past climate change on a global basis and helped to integrate paleo-science across regions and research disciplines. PANASH science allows us to constrain predictions for future climate change and to contribute to the management and mitigation of such changes. We identify three broad areas where PEP science makes key contributions. 1. The patterns of global changes: Knowing the exact timing of glacial advances (synchronous or otherwise) during the last glaciation is critical to understanding inter-hemispheric links in climate. Work in PEPI demonstrated that the tropical Andes in South America was deglaciated earlier than the Northern Hemisphere (NH) and that an extended warming began there ca. 21 000 cal years BP. The general pattern is consistent with Antarctica and has now been replicated from studies in Southern Hemisphere (SH) regions of the PEPII transect. That significant deglaciation of SH alpine systems and Antarctica led deglaciation of NH ice sheets may reflect either i) faster response times in alpine systems and Antarctica, ii) regional moisture patterns that influenced glacier mass balance, or iii) a SH temperature forcing that led changes in the NH. This highlights the limitations of current understanding and the need for further fundamental paleoclimate research. 2. Changes in modes of operation of oscillatory climate systems: Work across all the PEP transects has led to the recognition that the El Niño Southern Oscillation (ENSO) phenomenon has changed markedly through time. It now appears that ENSO operated during the last glacial termination and during the early Holocene, but that precipitation teleconnections even within the Pacific Basin were turned down, or off. In the modern ENSO phenomenon both inter-annual and seven year periodicities are present, with the inter-annual signal dominant. Paleo-data demonstrate that the relative importance of the two periodicities changes through time, with longer periodicities dominant in the early Holocene. 3. The recognition of climate modulation of oscillatory systems by abrupt climate events: We examine the relationship of ENSO to an abrupt SH climate event, the Antarctic cold reversal (ACR), in the New Zealand region. We demonstrate that the onset of the ACR was associated with the apparent switching on of an ENSO signal in New Zealand. We infer that this related to enhanced zonal SW winds with the amplification of the pressure fields allowing an existing but weak ENSO signal to manifest itself. Teleconnections of this nature would be difficult to predict for future abrupt change as boundary conditions cannot readily be specified. Paleo-data are critical to predicting the teleconnections of future abrupt changes.

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Shulmeister, J., D. T. Rodbell, M. K. Gagan, and G. O. Seltzer. "Inter-hemispheric linkages in climate change: paleo-perspectives for future climate change." Climate of the Past 2, no. 2 (October 26, 2006): 167–85. http://dx.doi.org/10.5194/cp-2-167-2006.

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Abstract. The Pole-Equator-Pole (PEP) projects of the PANASH (Paleoclimates of the Northern and Southern Hemisphere) programme have significantly advanced our understanding of past climate change on a global basis and helped to integrate paleo-science across regions and research disciplines. PANASH science allows us to constrain predictions for future climate change and to contribute to the management of consequent environmental changes. We identify three broad areas where PEP science makes key contributions. 1. The pattern of global changes. Knowing the exact timing of glacial advances (synchronous or otherwise) during the last glaciation is critical to understanding inter-hemispheric links in climate. Work in PEPI demonstrated that the tropical Andes in South America were deglaciated earlier than the Northern Hemisphere (NH) and that an extended warming began there ca. 21 000 cal years BP. The general pattern is consistent with Antarctica and has now been replicated from studies in Southern Hemisphere (SH) regions of the PEPII transect. That significant deglaciation of SH alpine systems and Antarctica led deglaciation of NH ice sheets may reflect either i) faster response times in alpine systems and Antarctica, ii) regional moisture patterns that influenced glacier mass balance, or iii) a SH temperature forcing that led changes in the NH. This highlights the limitations of current understanding and the need for further fundamental paleoclimate research. 2. Changes in modes of operation of oscillatory climate systems. Work across all the PEP transects has led to the recognition that the El Niño Southern Oscillation (ENSO) phenomenon has changed markedly through time. It now appears that ENSO operated during the last glacial termination and during the early Holocene, but that precipitation teleconnections even within the Pacific Basin were turned down, or off. In the modern ENSO phenomenon both inter-annual and seven year periodicities are present, with the inter-annual signal dominant. Paleo-data demonstrate that the relative importance of the two periodicities changes through time, with longer periodicities dominant in the early Holocene. 3. The recognition of climate modulation of oscillatory systems by climate events. We examine the relationship of ENSO to a SH climate event, the Antarctic cold reversal (ACR), in the New Zealand region. We demonstrate that the onset of the ACR was associated with the apparent switching on of an ENSO signal in New Zealand. We infer that this related to enhanced zonal SW winds with the amplification of the pressure fields allowing an existing but weak ENSO signal to manifest itself. Teleconnections of this nature would be difficult to predict for future abrupt change as boundary conditions cannot readily be specified. Paleo-data are critical to predicting the teleconnections of future changes.

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Zech, R., Ch Kull, P. W. Kubik, and H. Veit. "Exposure dating of Late Glacial and pre-LGM moraines in the Cordon de Doña Rosa, Northern/Central Chile (~31° S)." Climate of the Past 3, no. 1 (January 15, 2007): 1–14. http://dx.doi.org/10.5194/cp-3-1-2007.

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Abstract. Despite the important role of the Central Andes (15–30° S) for climate reconstruction, knowledge about the Quaternary glaciation is very limited due to the scarcity of organic material for radiocarbon dating. We applied 10Be surface exposure dating (SED) on 22 boulders from moraines in the Cordon de Doña Rosa, Northern/Central Chile (~31° S). The results show that several glacial advances in the southern Central Andes occurred during the Late Glacial between ~14.7±1.5 and 11.6±1.2 ka. A much more extensive glaciation is dated to ~32±3 ka, predating the temperature minimum of the global LGM (Last Glacial Maximum: ~20 ka). Reviewing these results in the paleoclimatic context, we conclude that the Late Glacial advances were most likely caused by an intensification of the tropical circulation and a corresponding increase in summer precipitation. High-latitude temperatures minima, e.g. the Younger Dryas (YD) and the Antarctic Cold Reversal (ACR) may have triggered individual advances, but current systematic exposure age uncertainties limit precise correlations. The absence of LGM moraines indicates that moisture advection was too limited to allow significant glacial advances at ~20 ka. The tropical circulation was less intensive despite the maximum in austral summer insolation. Winter precipitation was apparently also insufficient, although pollen and marine studies indicate a northward shift of the westerlies at that time. The dominant pre-LGM glacial advances in Northern/Central Chile at ~32 ka required lower temperatures and increased precipitation than today. We conclude that the westerlies were more intense and/or shifted equatorward, possibly due to increased snow and ice cover at higher southern latitudes coinciding with a minimum of insolation.

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47

Köhler, P., G. Knorr, D. Buiron, A. Lourantou, and J. Chappellaz. "Abrupt rise in atmospheric CO2 at the onset of the Bølling/Allerød: in-situ ice core data versus true atmospheric signals." Climate of the Past 7, no. 2 (May 4, 2011): 473–86. http://dx.doi.org/10.5194/cp-7-473-2011.

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Abstract. During the last glacial/interglacial transition the Earth's climate underwent abrupt changes around 14.6 kyr ago. Temperature proxies from ice cores revealed the onset of the Bølling/Allerød (B/A) warm period in the north and the start of the Antarctic Cold Reversal in the south. Furthermore, the B/A was accompanied by a rapid sea level rise of about 20 m during meltwater pulse (MWP) 1A, whose exact timing is a matter of current debate. In-situ measured CO2 in the EPICA Dome C (EDC) ice core also revealed a remarkable jump of 10 ± 1 ppmv in 230 yr at the same time. Allowing for the modelled age distribution of CO2 in firn, we show that atmospheric CO2 could have jumped by 20–35 ppmv in less than 200 yr, which is a factor of 2–3.5 greater than the CO2 signal recorded in-situ in EDC. This rate of change in atmospheric CO2 corresponds to 29–50% of the anthropogenic signal during the last 50 yr and is connected with a radiative forcing of 0.59–0.75 W m−2. Using a model-based airborne fraction of 0.17 of atmospheric CO2, we infer that 125 Pg of carbon need to be released into the atmosphere to produce such a peak. If the abrupt rise in CO2 at the onset of the B/A is unique with respect to other Dansgaard/Oeschger (D/O) events of the last 60 kyr (which seems plausible if not unequivocal based on current observations), then the mechanism responsible for it may also have been unique. Available δ13CO2 data are neutral, whether the source of the carbon is of marine or terrestrial origin. We therefore hypothesise that most of the carbon might have been activated as a consequence of continental shelf flooding during MWP-1A. This potential impact of rapid sea level rise on atmospheric CO2 might define the point of no return during the last deglaciation.

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Zech, R., C. Kull, P. W. Kubik, and H. Veit. "Exposure dating of Late Glacial and pre-LGM moraines in the Cordon de Doña Rosa, Northern/Central Chile (∼31° S)." Climate of the Past Discussions 2, no. 5 (September 25, 2006): 847–78. http://dx.doi.org/10.5194/cpd-2-847-2006.

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Abstract. Despite the important role of the Central Andes (15–30° S) for climate reconstruction, knowledge about the Quaternary glaciation is very limited due to the scarcity of organic material for radiocarbon dating. We applied 10Be surface exposure dating (SED) on 22 boulders from moraines in the Cordon de Doña Rosa, Northern/Central Chile (~31° S). The results show that several glacial advances in the southern Central Andes occurred during the Late Glacial between ~14.7±1.5 and 11.6±1.2 ka BP. A much more extensive glaciation is dated to ~32±3 ka BP, predating the temperature minimum of the global LGM (Last Glacial Maximum: ~20 ka BP). Reviewing these results in the paleoclimatic context, we note that the Late Glacial advances coincide with (i) lower temperatures during the Younger Dryas (YD) and the Antarctic Cold Reversal (ACR), (ii) the intensification of the tropical circulation and a corresponding increase in summer precipitation and (iii) a minimum in austral summer insolation favouring reduced ablation. The absence of LGM moraines indicates that moisture advection was too limited to allow significant glacial advances at ~20 ka BP. The tropical circulation was much less intensive despite the maximum in austral summer insolation. Winter precipitation was apparently also insufficient, although pollen and marine studies indicate a northward shift of the westerlies at that time. The dominant pre-LGM glacial advances in Northern/Central Chile at ~32 ka BP required lower temperatures and increased precipitation than today. They coincide with (i) a minimum of southern high-latitude insolation suggesting an equatorward shift of the westerlies due to increased snow and ice cover, (ii) a maximum winter insolation resulting in ocean-continental temperature and pressure gradients favouring moisture advection, (iii) minimum summer insolation suggesting lower temperatures and reduced ablation and (iv) low high-latitude temperatures corroborating that they affect subtropical and tropical temperatures. More glacier-climate modelling is necessary to quantify the influence of the various forcings on the dated glacial advances.

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Suwa, Makoto. "Termination V in the Vostok (Antarctica) ice core." Journal of Glaciology 54, no. 185 (2008): 229–32. http://dx.doi.org/10.3189/002214308784886153.

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AbstractThe age–depth relationship of the Vostok (Antarctica) ice core has been reconstructed in the depth interval 3300–3347 m, by comparing three gas properties in ice (CO2, CH4 and δ18Oatm) with those in the EPICA Dome C (Antarctica) core. Fourteen Vostok depths were examined in this interval, and it was found that nine samples are uniquely dated if candidate ages are restricted to the interval between 400 and 650 kyr. One of these samples is uniquely dated without restriction. The analysis supports previous reports that this section contains ice from Termination V, but that the stratigraphic order of ice is reversed. The top of the overturned layer lies between 3316 and 3319 m. At least one other stratigraphic disturbance was found between 3340 and 3343 m, as indicated by another reversal of the age–depth relationship. Finally, the oldest ice in this section is dated at ≥440 kyr, confirming the existence of ice from the cold marine isotope stage (MIS) 12 interval.

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Mark, B., N. Stansell, and G. Zeballos. "The last deglaciation of Peru and Bolivia." Cuadernos de Investigación Geográfica 43, no. 2 (September 15, 2017): 591. http://dx.doi.org/10.18172/cig.3265.

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The tropical Andes of Peru and Bolivia are important for preserving geomorphic evidence of multiple glaciations, allowing for refinements of chronology to aid in understanding climate dynamics at a key location between hemispheres. This review focuses on the deglaciation from Late-Pleistocene maximum positions near the global Last Glacial Maximum (LGM). We synthesize the results of the most recent published glacial geologic studies from 12 mountain ranges or regions within Peru and Bolivia where glacial moraines and drift are dated with terrestrial cosmogenic nuclides (TCN), as well as maximum and minimum limiting ages based on radiocarbon in proximal sediments. Special consideration is given to document paleoglacier valley localities with topographic information given the strong vertical mass balance sensitivity of tropical glaciers. Specific valley localities show variable and heterogeneous sequences ages and extensions of paleoglaciers, but conform to a generally cogent regional sequence revealed by more continuous lake sedimentary records. There are clear distributions of stratigraphically older and younger moraine ages that we group and discuss chronologically. The timing of the local LGM based on average TCN ages of moraine groups is 25.1 ka, but there are large uncertainties (up to 7 ka) making the relative timing with the global LGM elusive. There are a significant number of post-LGM moraines that date to 18.9 (± 0.5) ka. During the Oldest Dryas (18.0 to 14.6 ka), moraine boulders date to 16.1 (± 1.1) ka, suggesting that glaciers either experienced stillstands or readvances during this interval. The Antarctic Cold Reversal (ACR; 14.6 to 12.6 ka) is another phase of stillstanding or readvancing glaciers with moraine groups dating to 13.7 (± 0.8) ka, followed by retreating ice margins through most of the Younger Dryas (YD; 12.9 to 11.8 ka). During the early Holocene, groups of moraines in multiple valleys date to 11.0 (± 0.4) ka, marking a period when glaciers either readvanced or paused from the overall trend of deglaciation. The pattern of glacial variability during the Late Glacial after ~14.6 ka appears to be more synchronous with periods of cooling in the southern high latitudes, and out-of-phase with the overall deglacial trend in the Northern Hemisphere. While insolation and CO2 forcing likely drove the general pattern of deglaciation in the southern tropical Andes, regional ocean-atmospheric and hypsometric controls must have contributed to the full pattern of glacial variability.

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Journal articles on the topic 'Antarctic Cold Reversal'

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