Paleoproductivity evolution off central Chile from the Last Glacial Maximum to the Early Holocene

A geochemical and paleontological reconstruction of paleoproductivity, upwelling intensity and sea surface temperature (SST) off central Chile at 35°S (GeoB3359-3) reveals marked changes from the Last Glacial Maximum (LGM) through the Early Holocene. Surface-water productivity was determined by the interaction between the atmospheric (the Southern Westerlies) and oceanographic (the Antarctic Circumpolar Current, ACC) systems from the LGM through early Termination I (TI). The northward shift of the climate zones during the LGM brought the ACC, as the main macronutrient source, closer to the GeoB3359-3, SST lowered, and surface water productivity and accumulation rates of biogenic components enhanced. With the poleward return of the Southern Westerlies and the ACC, the subtropical high-pressure system became the dominant atmospheric component southward till 35°S during the late TI and Early Holocene and caused surface water productivity to increase through enhanced upwelling.     

Last glacial megafaunal death assemblage and early human occupation at Lake Menindee, southeastern Australia

The Tedford subfossil locality at Lake Menindee preserves a diverse assemblage of marsupials, monotremes and placental rodents. Of the 38 mammal taxa recorded at the site, almost a third are of extinct megafauna. Some of the bones are articulated or semi-articulated and include almost complete skeletons, indicating that aeolian sediments rapidly buried the animals following death. New optical ages show the site dates to the early part of the last glacial (55,700 ± 1300 yr weighted mean age). This is close to the 51,200-39,800 yr Australia-wide extinction age for megafauna suggested by Roberts et al. [2001, Science 292:1888-1892], but like all previous researchers, we cannot conclusively determine whether humans were implicated in the deaths of the animals. Although an intrusive hearth at the site dating to 45,100 ± 1400 yr ago is the oldest evidence of human occupation of the Darling River, no artifacts were identified in situ within the sub-fossil-bearing unit. Non-anthropogenic causes, such as natural senescence or ecosystem stress due to climatic aridity, probably explain the mortality of the faunal assemblage at Lake Menindee.     

河西走廊末次冰期芒硝和砂楔与古气候重建

芒硝和砂楔是冷干气候环境的典型标志。河西走廊砂楔主要形成在晚更新世冲洪积砾石层中 ,楔体内充填的风成砂14 C年龄证明其是末次冰期的产物 ,古砂楔所对应的年均气温为- 5 6℃左右。芒硝主要分布在内陆河终端的盐湖中 ,花海芒硝矿粘土夹层中的陆生树枝残条普通14 C和AMS14 C年龄分别为 (116 0 0± 2 80 )aB .P .和 (11181± 54)aB .P .,证明芒硝层为末次盛冰期 (LGM )和新仙女木期 (YD)异常冷干气候的产物。计算表明 ,该区LGM年均气温较现在低 11～ 15℃ ,YD年均气温比现代低约 6～ 8℃。这一降温幅度与中国北方根据孢粉、砂楔、冰芯等所推测的气温下降值大体一致 ,亦与最近有关北半球高、中纬度冰期降温幅度的研究相符合     

New evidence on the sequence of deglacial warming in the tropical Indian Ocean

The transition from the Last Glacial Maximum to the Holocene was an internal of climate variability that was characterised by large spatial and temporal variations. Here we show that deglaciation warming in the northern Indian Ocean was initiated ca. 19 ka, which is contemporary with deglaciation warming in the Antarctica and Southern Ocean. A gradual warming occurred during the glacial/Holocene transition in the northern Indian Ocean, unlike the two‐step warming seen in Greenland and the North Atlantic. Synchronous deglacial warming ca. 19 ka in Antarctica and the northern Indian Ocean suggests a strong connection in the propagation of climate signals between Antarctica and the Indian Ocean, probably through the Indonesian Throughflow and/or Subantarctic Mode Water. Copyright © 2010 John Wiley & Sons, Ltd.     

Closely-spaced recuperated OSL dating of the last interglacial paleosol in the southeastern margin of the Chinese Loess Plateau

The objective of this study is to construct a numerically dated chronology of the last interglacial paleosol (S₁) in Chinese loess using luminescence dating. The recuperated optically stimulated luminescence (ReOSL) dating approach was applied to 18 closely-spaced (20 cm intervals) samples, with 15 of these collected from the S₁ unit at the Weinan site, which is located at the southeastern margin of the Chinese Loess Plateau (CLP). By using the multiple-aliquot regenerative-dose (MAR) approach, 18 fine-grained quartz ReOSL equivalent dose (D_E) values, spanning about 249–466 Gy, were obtained. The validity of ReOSL MAR protocol was checked by dose recovery measurements and recycling ratio tests. By comparison of the dose-response curves of all the samples, we found that it is feasible to construct a standardized growth curve (SGC) for the ReOSL signal at the Weinan site. Considering the effects of pedogenesis of the S₁ unit during formation, the dose rate during the last interglacial was corrected, which should be beneficial for constructing a more reliable chronology. Finally, a detailed chronology of the S₁ unit was established. The results show that S₁ was deposited between approximately 76–127 ka, which confirms the early suggestion that the S₁ unit in Chinese loess corresponds to the whole marine oxygen-isotope stage (MIS) 5. The detailed ReOSL chronology of S₁ indicates the consistency of the substrata of S₁ with MIS 5a-e, but cannot determine whether they are exactly coeval. According to the present ReOSL age results, it is suggested that dust deposition is continuous at timescales larger than 14.1 ± 11.8 ky during the last interglacial and there is no hiatus longer than 4.4 ± 13.0 ky at the L₂/S₁ transition. Further work, e.g. minimizing the errors on ages and reducing the luminescence sampling intervals, is needed to understand the more detailed dust deposition conditions during the last interglacial in Chinese loess.     

Deglaciation, basin formation and post-glacial climate change from a regional network of sediment core sites in Ohio and eastern Indiana

Many paleoclimate and landscape change studies in the American Midwest have focused on the Late Glacial and early Holocene time periods (~ 16–11 ka), but little work has addressed landscape change in this area between the Last Glacial Maximum and the Late Glacial (~ 22–16 ka). Sediment cores were collected from 29 new lake and bog sites in Ohio and Indiana to address this gap. The basal radiocarbon dates from these cores show that initial ice retreat from the maximal last-glacial ice extent occurred by 22 ka, and numerous sites that are ~ 100 km inside this limit were exposed by 18.9 ka. Post-glacial environmental changes were identified as stratigraphic or biologic changes in select cores. The strongest signal occurs between 18.5 and 14.6 ka. These Midwestern events correspond with evidence to the northeast, suggesting that initial deglaciation of the ice sheet, and ensuing environmental changes, were episodic and rapid. Significantly, these changes predate the onset of the Bølling postglacial warming (14.8 ka) as recorded by the Greenland ice cores. Thus, deglaciation and landscape change around the southern margins of the Laurentide Ice Sheet happened ~ 7 ka before postglacial changes were felt in central Greenland.     

Be data from meltwater channels suggest that Jameson Land, east Greenland, was ice-covered during the last glacial maximum

Along the northeast Greenland continental margin, bedrock on interfjord plateaus is highly weathered, whereas rock surfaces in fjord troughs are characterized by glacial scour. Based on the intense bedrock weathering and lack of glacial deposits from the last glaciation, interfjord plateaus have long been thought to be ice-free throughout the last glacial maximum (LGM). In recent years there is growing evidence from shelf and fjord settings that the northeast Greenland continental margin was more extensively glaciated during the LGM than previously thought. However, little is still known from interfjord settings. We present cosmogenic ¹⁰Be data from meltwater channels and weathered sandstone outcrops on Jameson Land, an interfjord highland north of Scoresby Sund. The mean exposure age of samples from channel beds (n = 3) constrains on the onset of deglaciation on interior Jameson Land to 18.5 ± 1.3–21.4 ± 1.9 ka (for erosion conditions of 0–10 mm/ka, respectively). This finding adds to growing evidence that the northeast Greenland continental margin was more heavily glaciated during the LGM than previously thought.     

Late Quaternary paleoenvironments and paleoclimatic conditions in the distal Andean piedmont, southern Mendoza, Argentina

The Andean piedmont of Mendoza is a semiarid region covered by extensive and partially vegetated dune fields consisting of mostly inactive aeolian landforms of diverse size and morphology. This paper is focused on the San Rafael plain (SRP) environment, situated in the distal Andean piedmont of Mendoza (34° 30′S), and reports the sedimentology and OSL chronology of two representative exposures of late Quaternary deposits, including their paleoenvironmental and paleoclimatic significance. Eleven facies, including channel, floodplain, fluvio–aeolian interaction, and reworked pyroclastic and aeolian deposits, were described and grouped into two facies associations (FA1 and FA2). FA1 was formed by unconfined sheet flows, minor channelized streams and fluvial–aeolian interaction processes. FA2 was interpreted as aeolian dune and sand-sheet deposits. OSL chronology from the SRP sedimentary record indicates that between ca. 58–39 ka and ca. 36–24 ka (MIS 3), aggradation was governed by ephemeral fluvial processes (FA1) under generally semiarid conditions. During MIS 2, the last glacial maximum (ca. 24–12 ka), a major climatic shift to more arid conditions is documented by significant aeolian activity (FA2) that became the dominant sedimentation process north of the Diamante–Atuel fluvial system. The inferred paleoenvironmental conditions from the SRP sections are in broad agreement with regional evidence.