Chaolu Yi

Quaternary glaciation of Muztag Ata and Kongur Shan: Evidence for glacier response to rapid climate changes throughout the Late Glacial and Holocene in westernmost Tibet

The glacial geology of two massifs, Muztag Ata and Kongur Shan, in western Tibet was examined to help define the timing and style of glaciation in the semiarid regions of western Tibet. Remote sensing, geomorphic mapping, and 10Be terrestrial cosmogenic nuclide (TCN) surface-exposure dating of boulders on the moraines and sediment in depth profiles show that glaciers advanced at least 12 times during at least the last two glacial cycles. Over this time, the style of glaciation changed progressively from one that produced ice caps to one that produced less extensive and more deeply entrenched valley glaciers. The timing of the two earliest glaciations is poorly defined, but they likely occurred prior to the penultimate glacial cycle (the Karasu glacial stage) and the early part of the last glacial cycle or during the penultimate glacial cycle (the Subaxh glacial stage). In contrast, the timing of later glacial advances (the Olimde glacial stage) is relatively well defined showing quasiperiodical oscillations on millennial time scales (17.1 ± 0.3 ka, 13.7 ± 0.5 ka, 11.2 ± 0.1 ka, 10.2 ± 0.3 ka, 8.4 ± 0.4 ka, 6.7 ± 0.2 ka, 4.2 ± 0.3 ka, 3.3 ± 0.6 ka, 1.4 ± 0.1 ka, and a few hundred years before the present). These data suggest that since the global Last Glacial Maximum (LGM), the glaciers in western Tibet likely responded to Northern Hemisphere climate oscillations (rapid climate changes), with minor influences from the south Asian monsoon. This study provides the first well-defined glacial geologic evidence to suggest that glaciers in western Tibet respond to rapid climate changes on millennial time scales throughout the Late Glacial and Holocene.

Sedimentary evidence for changes in the pollution status of Taihu in the Jiangsu region of eastern China

As part of a study using lake sediments to determine the extent and causes of human impacts to lakes along an east–west transect following the Yangtse River, sediment cores were taken from Taihu in eastern China. Previous studies have focussed on the impacts of direct inputs of pollutants from municipal and industrial wastewater but little work has been undertaken on trends in atmospheric deposition from the many industrial sources surrounding the lake. Analysis of the Taihu sediment cores for atmospheric pollutant indicators such as trace metals, magnetic parameters and spheroidal carbonaceous particles (SCPs) show the lake has become increasingly contaminated over the last 40–50 years. Sediment levels of atmospherically deposited pollutants are currently similar to some of the more contaminated lakes in Europe. Further, sediment nitrogen, phosphorus and geochemical analyses confirm the dramatic increase in eutrophication at the site and periods of recent soil erosion in the catchment.

10Be dating of boulders on moraines from the last glacial period in the Nyainqentanglha mountains, Tibet

Chronologies of glacial advances during the last glacial period in the Nyainqentanglha mountain range may provide constraints on the past climate in a transition zone of the Asian monsoon. We present 15 new 10Be exposure ages from two moraines in the Payuwang valley, on the north slope of the range. The inner moraine has exposure ages ranging from 18.0±1.7 to 30.6±2.8 ka (n=10), with a mean age of 23.8±4.0 ka, corresponding to the global Last Glacial Maximum (LGM). The outer moraine yields exposure ages ranging from 18.0±1.6 to 39.9±3.7 ka (n=5). Evidence for weathering leads us to view the oldest age as a minimum age, placing moraine formation during MIS3. Chronologies from the last glacial period from south slope of the Nyainqentanglha support this interpretation. Thus, there appears to have been a local LGM (LLGM) during MIS3 and a more limited glacial advance during the global LGM. Glacial advances during MIS3 in the Nyainqentanglha may correlate with millennial-scale climate change (Heinrich events).

Cosmogenic 10Be surface exposure dating of ‘Little Ice Age’ glacial events in the Mount Jaggang area, central Tibet:

The timing and extent of ‘Little Ice Age’ (LIA) glacial advances on the Tibetan Plateau (TP) are critical for understanding climate during the past millennium. However, the lack of LIA chronologies in central Tibet makes it difficult to fully understand the nature of LIA throughout the TP. In this study, two presumed LIA moraines in the east of Mount Jaggang, Xainza range, the central TP, were examined and dated using 10Be surface exposure dating. Eight boulders from the two moraines yielded apparent 10Be exposure-ages ranging from 41 ± 31 to 529 ± 130 years. These 10Be exposure-ages indicate that glaciers advanced at least once in the Mount Jaggang area during the LIA. A relatively extensive glacial advance occurred around 267 ± 36 years, a relatively humid period as indicated by proxy data from lake sediments in the central TP. A glacial standstill might have occurred around 151 ± 36 years. The two LIA glacial events are comparable with those across the TP. However, much more efforts should be made on dating of LIA moraines in the Mount Jaggang area to elucidate the relationships between glacial advances and climate changes during the LIA.

Two-dimensional simulation of underground seepage in a dangerous piping zone of the Jingjiang Great Levee, the middle reach of the Yangtze River

This case study simulated the seepage field at Yangjiawan using Visual Modflow software. The Yangjiawan area shows potential for dangerous piping along the Jingjiang Great Levee, on the north bank of the Yangtze River. The levee foundation sits on loam and fine sand strata and is covered with a clay layer and artificial earthfill. Ponds are present behind the levee, where piping occurs frequently. The authors analysed several models to simulate actual situations and to provide guidance for piping control. Assuming that the potential for piping increases with seepage and groundwater velocities, the models allow various engineered control measures to be assessed under different natural conditions. Parameters and features of the models included: different water heads, pressure-relief wells, seepage-proof walls, surface coverage, different hydraulic conductivities of the artificial earthfill, and pond levels during high river water levels. The results demonstrate the effectiveness of pressure-relief wells in preventing piping and also show that a decrease of the hydraulic conductivities of the artificial earthfill would reduce infiltration and seepage damage significantly, especially during high river water levels. Furthermore, pressure-relief wells and the reduction of hydraulic conductivities of artificial earthfill should prevent piping if ponds are present.

Late Glacial glacier-climate modeling in two valleys on the eastern slope of Samdainkangsang Peak, Nyaiqentanggulha Mountains

Well-preserved Late Glacial moraines in the Barenduo and Yuqiongqu valleys on the eastern slope of the Samdainkangsang Peak present an opportunity to reconstruct glacier extents and examine the character of the climate during the Late Glacial stage in the Nyaiqentanggulha Mountains. This study employs a coupled mass-balance and ice-flow model to reconstruct the glacier extents in the two valleys and assess the magnitudes of temperature and precipitation change during the Late Glacial period. Model results indicate that during the Late Glacial, the Barenduo valley contained an ice volume of 1.67×108 m3, with the equilibrium-line altitude (ELA) being ~5500 m asl; and the Yuqiongqu valley had an ice volume of 5.56×108 m3, with the ELA being ~5470 m asl. A climate scenario, temperature depression of 2.6–2.8°C and 60–70%, percent of modern (1981–2010) precipitation, can sustain both of the Late Glacial glacier extents in the two valleys. A 50% increase or decrease from modern precipitation would have been coupled with the respective Late Glacial temperature depressions of 1.6 and 3.0°C in the Barenduo valley, and 2.1 and 2.8°C in the Yuqiongqu valley.