Article

Persistence of full glacial conditions in the central Pacific until 15,000 years ago.

Centre Européen de Recherche et d'Enseignement des Géosciences de l'Environnement, CNRS-Aix Marseille Université, 13545 Aix en Provence, France.
Nature (Impact Factor: 38.6). 11/2007; 449(7162):591-4. DOI: 10.1038/nature06142
Source: PubMed

ABSTRACT The magnitude of atmospheric cooling during the Last Glacial Maximum and the timing of the transition into the current interglacial period remain poorly constrained in tropical regions, partly because of a lack of suitable climate records. Glacial moraines provide a method of reconstructing past temperatures, but they are relatively rare in the tropics. Here we present a reconstruction of atmospheric temperatures in the central Pacific during the last deglaciation on the basis of cosmogenic 3He ages of moraines and numerical modelling of the ice cap on Mauna Kea volcano, Hawaii--the only highland in the central Pacific on which moraines that formed during the last glacial period are preserved. Our reconstruction indicates that the Last Glacial Maximum occurred between 19,000 and 16,000 years ago in this region and that temperatures at high elevations were about 7 degrees C lower than today during this interval. Glacial retreat began about 16,000 years ago, but temperatures were still about 6.5 degrees C lower than today until 15,000 years ago. When combined with estimates of sea surface temperatures in the central Pacific Ocean, our reconstruction indicates that the lapse rate during the Last Glacial Maximum was higher than at present, which is consistent with the proposal that the atmosphere was drier at that time. Furthermore, the persistence of full glacial conditions until 15,000 years ago is consistent with the relatively late and abrupt transition to warmer temperatures in Greenland, indicating that there may have been an atmospheric teleconnection between the central Pacific and North Atlantic regions during the last deglaciation.

0 Bookmarks
 · 
89 Views
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: A positive degree-day (PDD) model was tested on Antizana Glacier 15$alpha$ (0.28 km2; 0°28' S, 78°09' W) to assess to what extent this approach is suitable for studying glacier mass balance in the inner tropics. Cumulative positive temperatures were compared with field measurements of melting amount and with surface energy balance computations. A significant link was revealed when a distinction was made between the snow and ice comprising the glacier surface. Significant correlations allowed degree-day factors to be retrieved for snow, and clean and dirty ice. The relationship between melt amount and temperature was mainly explained by the role of net shortwave radiation in both melting and in the variations in the temperature of the surface layer. However, this relationship disappeared from June to October (Period 1), because high wind speeds and low humidity cause highly negative turbulent latent heat fluxes. However, this had little impact on the computed total amount of melting at the annual time scale because temperatures are low and melting is generally limited during Period 1. At the daily time scale, melting starts when daily temperature means are still negative, because around noon incoming shortwave radiation is very high, and compensates for energy losses when the air is cold. The PDD model was applied to the 2000–2008 period using meteorological inputs measured on the glacier foreland. Results were compared to the glacier-wide mass balances measured in the field and were good, even though the melting factor should be adapted to the glacier surface state and may vary with time. Finally, the model was forced with precipitation and temperature data from the remote Izobamba station and NCEP-NCAR reanalysis data, also giving good results and showing that temperature variations are homogenous at the regional scale, meaning glacier mass balances can be modelled over large areas.
    The Cryosphere Discussions 05/2014; 8:2637-2684.
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Alluvial fans within the paraglacial Ecemiş River drainages on the Aladağlar Mountains in south central Turkey were studied using geomorphological, sedimentological, and chlorine-36 terrestrial cosmogenic nuclide (TCN) surface exposure dating methods to examine the timing of alluvial fan abandonment/incision, and to understand the role of climatic and tectonic processes in the region. These alluvial fan complexes are among the best-preserved succession of alluvial fans in Turkey and they were offset by the major strike-slip Ecemiş Fault of the Central Anatolian Fault Zone. The alluvial fans are mostly composed of well-lithified limestone cobbles (5 to 25 cm in size), and comprise crudely stratified thick beds with a total thickness reaching up to about 80 m. TCN surface exposure dating indicates that the oldest alluvial fan surface (Yalak Fan) was likely formed and subsequently abandoned latest by 136.0 ± 23.4 ka ago, largely on the transition of the Penultimate Glaciation (Marine Isotope Stage 6, MIS 6) to the Last Interglacial (MIS 5) (i.e. Termination II). The second set of alluvial fan (Emli Fan) was possibly developed during the Last Interglacial (MIS 5), and incised twice by between roughly 97.0 ± 13.8 and 81.2 ± 13.2 ka ago. A younger alluvial fan deposit placed on relatively older erosional terraces of the Emli Fan suggests that it may have been produced during the Last Glacial Cycle (MIS 2). These events are similar to findings from other fluvial and lacustrine deposits throughout central Anatolia. The incision times of the Ecemiş alluvial fan surfaces largely coincide with major climatic shifts from the cooler glacial periods to warmer interglacial/interstadial conditions. This indicates that alluvial fans were produced by outwash sedi-ments of paleoglaciers during cooler conditions, and, later, when glaciers started to retreat due to a major warming event, the excess water released from the glaciers incised the pre-existing fan surfaces. An alluvial fan in the study area was also cut by the Ecemiş Fault, highlighting the influence of tectonics on fan development. It was offset vertically 35 ± 3 m since at least 97.0 ± 13.8 ka, which suggests a 0.36 ± 0.06 mm a −1 vertical slip-rate of the fault.
    Geomorphology 01/2015; 228:512-528. · 2.58 Impact Factor
  • Source

Full-text (2 Sources)

Download
53 Downloads
Available from
May 31, 2014