Late Pleistocene–Holocene environmental and climatic history of a freshwater paramo ecosystem in the northern Andes
Luisa Fernanda PatiñoMaría I. VélezMarion WeberCésar A. Velásquez-R.Santiago DavidM. RuedaIvonne CastañedaDiana Arboleda
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ABSTRACT This study presents the first multi‐proxy palaeoenvironmental and palaeoclimatic history for northern South America based on the palaeolimnological reconstruction of a pond located in a dry paramo at 3570 masl. During the Last Glacial Maximum (LGM), the study area was under glacial conditions, then during global events Heinrich Stadial 1 (HS1), Bølling–Allerød (BA), and the Younger Dryas (YD), the pond expanded, accumulation rates and proxies for erosion reached the highest values, indicative of humid conditions, with maxima in humidity during the BA and YD. Dry conditions and pond desiccation occurred in the Greenlandian–Northgrippian and by 6010 cal a bp the area was transformed into the mire of today. Comparisons with records from other sites in South America indicate that changes in humidity are most likely controlled by the Intertropical Convergence Zone, mainly during the glacial and postglacial, and by changes in the Pacific Ocean, more pronounced after the YD.Keywords:
Stadial
Intertropical Convergence Zone
Last Glacial Maximum
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Stadial
Allerød oscillation
Abrupt climate change
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Stadial
Deglaciation
Meltwater
Abrupt climate change
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Mangerud, J., Gulliksen, S. & Larsen, E. 2009: 14 C‐dated fluctuations of the western flank of the Scandinavian Ice Sheet 45–25 kyr BP compared with Bølling–Younger Dryas fluctuations and Dansgaard–Oeschger events in Greenland. Boreas , 10.1111/j.1502‐3885.2009.00127.x. ISSN 0300‐9483. We present 32 accelerator mass spectrometry (AMS) 14 C dates obtained on well‐preserved bones from caves in western Norway. The resulting ages of 34–28 14 C kyr BP demonstrate that the coast was ice‐free during the so‐called Ålesund Interstadial. New AMS 14 C dates on shells aged 41–38 14 C kyr BP are evidence of an earlier (Austnes) ice‐free period. The Ålesund Interstadial correlates with Greenland interstadials 8–7 and the Austnes Interstadial with Greenland interstadials 12–11. Between and after the two interstadials, the ice margin reached onto the continental shelf west of Norway. These events can be closely correlated with the Greenland ice core stratigraphy, partly based on identification of the Laschamp and Mono Lake palaeomagnetic excursions. We found that the pattern of the NGRIP δ 18 O curves for the two periods Greenland Interstadial (GI) 8 to Greenland Stadial (GS) 8 and GI 1–GS 1 (Bølling–Younger Dryas) were strikingly similar, which leads us to suggest that the underlying causes of these climate shifts could have been the same. We therefore discuss some aspects of glacial fluctuations during the Bølling–Younger Dryas in order to elucidate processes during Dansgaard–Oeschger events.
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Abstract Establishing the atmospheric expression of abrupt climate change during the last glacial termination is key to understanding driving mechanisms. In this paper, we present a new 14 C chronology of glacier behavior during late‐glacial time from the Scottish Highlands, located close to the overturning region of the North Atlantic Ocean. Our results indicate that the last pulse of glaciation culminated between ~12.8 and ~12.6 ka, during the earliest part of the Younger Dryas stadial and as much as a millennium earlier than several recent estimates. Comparison of our results with existing minimum‐limiting 14 C data also suggests that the subsequent deglaciation of Scotland was rapid and occurred during full stadial conditions in the North Atlantic. We attribute this pattern of ice recession to enhanced summertime melting, despite severely cool winters, and propose that relatively warm summers are a fundamental characteristic of North Atlantic stadials.
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Abstract A paradigm in paleoclimatology holds that shifts in the mean position of the Intertropical Convergence Zone were the dominant climatic mechanism controlling rainfall in the tropics during the last glacial period. We present a new paleo-rainfall reconstruction based on speleothem stable oxygen isotopes record from Colombia, which spans most of the last glacial cycle. The strength and positioning of the Intertropical Convergence Zone over northern South America were more strongly affected by summer insolation at high northern latitudes than by local insolation during the last glacial cycle, resulting in an antiphased relationship with climate in the Cariaco Basin. Our data also provide new insight into how orbital forcing amplified/dampened Intertropical Convergence Zone precipitation during millennial-scale events. During Greenland Stadial events, the Intertropical Convergence Zone was positioned close to the latitude of El Peñon, as expressed by more negative δ 18 O values. Greenland Interstadial events are marked by relatively high stable oxygen isotope values and reduced rainfall in the El Peñon record, suggesting a northward withdrawal of the Intertropical Convergence Zone. During some Heinrich Stadial events, and especially Heinrich Stadial 1, the Intertropical Convergence Zone must have been displaced away from its modern location near El Peñon, as conditions were very dry at both El Peñon and Cariaco.
Intertropical Convergence Zone
Stadial
Speleothem
Paleoclimatology
Convergence zone
Last Glacial Maximum
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Abstract The present author thinks that the Younger Dryas Stadial include three colder phases separated by two warmer intervals. In Sweden and Finland there are three terminal moraine zones which should be correlated mutually. However, different opinions about this question have been expressed. The Baltic Ice Lake is believed to have been drained just at the end of the Younger Dryas Stadial and to show no other drastic changes in level (i.e. neither sudden damming nor drainage).
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Allerød oscillation
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Deglaciation
Allerød oscillation
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Stadial
Deglaciation
Allerød oscillation
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Summary Aim The paper addresses the classical question of possible plant survival in Iceland during the last glacial period in the light of a palaeobotanical record from northern Iceland, spanning the period 11,300–9000 BP , including the Younger Dryas stadial. We review the Late Cenozoic fossil plant record, the past debate on glacial plant refugia in Iceland, and the evidence for ice‐free areas during the Weichselian. Location The investigated lake sediment record comes from Lake Torfadalsvatn, which is situated in the northwestern part of the Skagi peninsula in northern Iceland. Methods The sediment chronology was constructed from the cccurrence of the Vedde Ash and the Saksunarvatn ash, two well‐dated Icelandic tephras, together with the results from five AMS and conventional radiocarbon dates performed on bulk sediment samples. The vegetational reconstruction was based on detailed pollen analysis of the sediment sequence. Results The pollen analysis revealed that many of the taxa present in the area prior to the Younger Dryas stadial continued to produce pollen during that cold event. The more or less immediate reappearance of a few other pollen taxa at the Younger Dryas‐Preboreal boundary suggests that these plants also survived, even if they did not produce sufficient pollen to be recorded during the Younger Dryas stadial. Main conclusions We conclude that the relatively high plant diversity found in high Arctic areas and present‐day nunataks in Iceland and Greenland, together with the fact that many plant species were able to survive the Younger Dryas stadial on the Skagi peninsula, suggest that species with high tolerance for climate fluctuations also survived the whole Weichselian in Iceland. This conclusion is supported by recent palaeoclimatic data from ice‐cores and deep‐sea sediments, indicating that Icelandic climate during the last glacial was only occasionally slightly colder than during the Younger Dryas stadial.
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