末次冰期东亚冰川规模与冰川进退异时性问题

1 IntroductionIthas been accepted thatthe glacialextentin the early stage w as largerthan thatin the late stagein Eastern A sia during the Last G laciation and w as different from Europe and N orth A m erica(Li, 1992; Cui et al., 2000). M any scholars hav…     

The glacial extent and glacial advance/retreat asynchroncity in East Asia during Last Glaciation

New dates for last glacial cycle in Tibetan bordering mountains and in East Asia show the glacial extent during the early/middle (MIS3-4) stage is larger than that of the late stage (MIS2) in last glacial cycle. It is asynchronous with the Northern Hemisphere ice sheets maximum and changes in oceanic circulation that predominately control global climate. In research areas, three seasonal precipitation patterns control the accumulation and ablation of glaciers. The modes of the westerlies and the East Asian mountains/islands in and along the Pacific Ocean are favorable to glacier advance with mainly winter precipitation accumulation. There was a global temperature-decreasing phase in the middle stage (MIS3b, 54-44 ka BP), when the glacier extent was larger than that in Last Glaciation Maximum due to the low temperature combined with high moisture. It is revealed that the Quaternary glaciers not only evolved with localization, but also maybe with globalization. The latest studies show a fact that the developmental characteristics of glaciers in high mountains or islands along the western Pacific Ocean are not in accord with those inland areas. Therefore, it can be concluded that glacier development exhibits regional differences. The study validates the reasonableness of the asynchronous advance theory, and ascertains that both the synchronous and asynchronous advance/retreat of glaciers existed from 30 ka BP to 10 ka BP. It is not suitable to emphasize the synchronicity between global ice-volume and glacier change.     

OSL dating of glacier extent during the Last Glacial and the Kanas Lake basin formation in Kanas River valley, Altai Mountains, China

The Kanas River originates on the southern slope of Youyi Peak, the largest center of modern glaciers in Altai Mountains, China. Three sets of moraines and associated glacial sediments are well preserved near the Kanas Lake outlet, recording a complex history and landscape evolution during the Last Glacial. Dating the moraines allows the temporal and spatial glacier shift and climate during the Last Glacial to be determined, and then constrains when and how the Kanas Lake basin was formed. Dating of the glacial tills was undertaken by utilizing the optically stimulated luminescence (OSL) method. Results date four samples from the three sets of moraines to 28.0, 34.4, 38.1, and 49.9 ka and one sample from outwash sediment to 6.8 ka. The Kanas Lake basin is a downfaulted basin and was eroded by glacier before 28.0 ka, and the glacial moraines blocked the glacier-melt water after the glacier retreat, which made the present-day Kanas Lake eventually form at least before 6.8 ka BP. In Altai Mountains, the glacier advance was more extensive in Marine Isotope Stage (MIS) 3 than MIS 2, probably because the mid-latitude westerlies shifted northward and/or intensified during the MIS 3, resulting in a more positive glacier mass balance. Nevertheless, the Siberian High dominated the Altai Mountains in MIS 2, resulting in a relative decrease in precipitation.     

Till fabric and grain-size analysis of glacial sequences in the Upper Sil River Basin,Cantabrian Mountains,NW Spain

Fabric and grain-size analysis of eight deposits present in the Upper Sil River Basin palaeoglacial system of northwest Spain were used to interpret till types and to reconstruct the glacial paleoprocess history of this region. They are represented by lodgement, deformation, and melt-out tills. The first, representative of glacial advance stages, present cluster fabrics and are generally composed of poorly sorted and finer sediments. Melt-out and deformation tills, representative of stages of glacial stability followed by fast recession, present transitional to girdle fabrics and are composed of poorly sorted coarser sediments. In any case, multiple criteria, including lithological, clast-shape, or structural data, support these directional and grain-size observations. These sequences, most of them located in the snout area of the Sil palaeoglacier, are important in the reconstruction of glacial dynamics due to poor preservation of landforms related to the maximum glacial advance. This palaeoglacial system was formed by multiple tributaries and had an extension of over 450 km², with the Sil paleoglacier being 51 km long during its maximum glacial advance.     

Global climatic changes since the last glacial maximum: evidence from paleolimnology and paleoclimate modeling

Recognition that Earth/Sun orbital changes are the basic cause for Quaternary climatic variations provides a context for explaining global environmental changes, many of which are preserved in the stratigraphic and geomorphic record of lakes. Paleoclimatic numerical models suggest the mechanisms. In subtropical latitudes such as North Africa the enhanced summer insolation culminating about 10 000 years ago resulted in the increased monsoonal rains that explain the widespread expansion of lakes in now-desert basins. But in the American Southwest lake expansion dates to 18 000–15 000 years ago, when storm tracks were displaced to the south by the ice sheets—themselves a product of earlier orbital changes. The dynamics in the resopnse of different components of the natural system to climatic change are recorded in the stratigraphy of lake sediments, not only by their pollen content as a manifestation of the regional vegetation but also by their microfossils and chemical composition as reflections of lake development.This is the 10th in a series of papers published in this special AMQUA issue. These papers were presented at the 1994 meeting of the American Quaternary Association held 19–22 June, 1994, at the University of Minnesota, Minneapolis, Minnesota, USA. Dr Linda C. K. Shane served as guest for these papers.     

Summer temperatures during the Medieval Warm Period and Little Ice Age inferred from varved proglacial lake sediments in southern Alaska

For the heavily glaciated mountains of southern Alaska, few high-resolution, millennial-scale proxy temperature reconstructions are available for comparison with modern temperatures or with the history of glacier fluctuations. Recent catastrophic drainage of glacier-dammed Iceberg Lake, on the northern margin of the Bagley Icefield, exposed subaerial outcrops of varved lacustrine sediments that span the period 442–1998 AD. Here, an updated chronology of varve thickness measurements is used to quantitatively reconstruct melt-season temperature anomalies. From 1958 to 1998, varve thickness has a positive and marginally significant correlation with May–June temperatures at the nearest coastal measurement stations. Varve sensitivity to temperature has changed over time, however, in response to lake level changes in 1957 and earlier. I compensate for this by log-transforming the varve thickness chronology, and also by using a 400-year-long tree-ring-based temperature proxy to reconstruct melt-season temperatures at Iceberg Lake. Regression against this longer proxy record is statistically weak, but spans the full range of occupied lake levels and varve sensitivities. Reconstructed temperature anomalies have broad confidence intervals, but nominally span 1.1°C over the last 1500+ years. Maximum temperatures occurred in the late twentieth century, with a minimum in the late sixth century. The Little Ice Age is present as three cool periods between 1350 and 1850 AD with maximum cooling around 1650 AD. A Medieval Warm Period is evident from 1000 to 1100 AD, but the temperature reconstruction suggests it was less warm than recent decades—an observation supported by independent geological evidence of recent glacier retreat that is unprecedented over the period of record. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.

Ice-rafted detritus events in the Arctic during the last glacial interval, and the timing of the Innuitian and Laurentide ice sheet calving events

Ice-rafted detritus (IRD) layers in the Arctic Ocean not only indicate the source of this detrital sediment, but give insights into the ice drift and ice sheet history. Detrital sand-sized Fe oxide mineral grains that are matched to precise sources using the microprobe chemical fingerprint of each grain, along with elevated coarse IRD abundance and radiocarbon ages, are used to define IRD peaks from the Innuitian and Arctic portions of the Laurentide ice sheets. Because grains from these two areas can be entrained by sea ice from the shelves just offshore of the calving areas, peaks in these grains must be correlated to coarse IRD to identify iceberg calving events, and to distinguish them from sea-ice rafting. The sequence of IRD peaks deposited by icebergs from these two ice sheets indicate that both ice sheets calved bergs at accelerated numbers, six or seven times, from 11 to 36 Kya. The relatively short times between most of these IRD events suggest that the ice sheets did not completely collapse with each IRD event, except the last event. Although there is some indication that one ice sheet may have begun calving bergs before the other, the resolution of the Arctic cores does not allow definitive determination of this. This emphasizes the need for higher resolution cores from the central Arctic, as well as from near the terminus of large Pleistocene ice sheets. Sea-ice rafting occurs throughout the last glacial stage, even during some glacial IRD events, as indicated by Fe grains from non-glacial sources.     

Simulation and construction of the glacier mass balance in the Manas River Basin,Tianshan, China from 2000 to 2016

The glacier mass balance(GMB) is an important link between climate and water resources and has remarkable regulatory functions in river runoff. To simulate changes of the GMB and to analyze the recharge rates of glacier meltwater to runoff in the Manas River Basin(MRB) during 2000–2016, MOD11 C3, TRMM 3 B43 and other multi-source remote sensing data were used to drive the degree-day model. The results showed that:(1) the accuracy of the remote sensing meteorological data can be corrected effectively by constructing the temperature and precipitation inversion models, and the characteristics of glacial climate can be finely described through downscaling. The average annual temperature was –7.57 °C and the annual precipitation was 410.71 mm in the glacier area of the MRB. The zone at an altitude of about 4200 m was a severe climate change zone, and above and below that zone, the temperature drop rates were –0.03°C/100 m and –0.57°C/100 m, respectively, while precipitation gradients were –2.66 mm/100 m and 4.89 mm/100 m, respectively.(2) The overall GMB was negative with a cumulative GMB of up to –9811.19 mm w.e. and the average annual GMB fluctuated between –464.85 and –632.19 mm w.e. Besides, the glacier melted slowly during 2000–2002 and 2008–2010, but rapidly for 2002–2008 and 2010–2016, while the most serious loss of the glacier occurred in 2005–2009. Moreover, the vertical changes of the GMB increased at 244.83 mm w.e./100 m in the ablation zone but only at 18.77 mm w.e./100 m in the accumulation zone.(3) The intraannual runoff strongly responded to the change of the GMB especially in July and August when the loss of the GMB accounted for 75.4% of the annual loss, and when runoff accounted for 55.1% of the annual total. Due to differences in the annual precipitation and snow meltwater outside the glacier, the interannual glacier meltwater recharge rates fluctuated between 19% and 31%. The recharge rate of glacier meltwater to runoff in the MRB was close to that for other basins in the Tianshan Mountains, which may be used as a basis to confirm the reliability of the estimated GMB results. Furthermore, based on the present findings, it is recommended that the research community pursue studies on the GMB in other alpine river basins.