Puruogangri Ice Field Research Articles

Characterizing the behavior of surge-type glaciers in the Puruogangri Ice Field, Tibetan Plateau

Characterizing the behavior of surge-type glaciers in the Puruogangri Ice Field, Tibetan Plateau

Multitemporal Glacier Mass Balance and Area Changes in the Puruogangri Ice Field during 1975–2021 Based on Multisource Satellite Observations

Due to climate warming, the glaciers of the Tibetan Plateau have experienced rapid mass loss and the patterns of glacier changes have exhibited high spatiotemporal heterogeneity, especially in interior areas. As the largest ice field within the Tibetan Plateau, the Puruogangri Ice Field has attracted a lot of attention from the scientific community. However, relevant studies that are based on satellite data have mainly focused on a few periods from 2000–2016. Long-term and multiperiod observations remain to be conducted. To this end, we estimated the changes in the glacier area and mass balance of the Puruogangri Ice Field over five subperiods between 1975 and 2021, based on multisource remote sensing data. Specifically, we employed KH-9 and Landsat images to estimate the area change from 1975 to 2021 using the band ratio method. Subsequently, based on KH-9 DEM, SRTM DEM, Copernicus DEM and ZY-3 DEM data, we evaluated the glacier elevation changes and mass balance over five subperiods during 1975–2021. The results showed that the total glacier area decreased from 427.44 ± 12.43 km2 to 387.87 ± 11.02 km2 from 1975 to 2021, with a decrease rate of 0.86 km2 a−1. The rate of area change at a decade timescale was −0.74 km2 a−1 (2000–2012) and −1.00 km2 a−1 (2012–2021). Furthermore, the rates at a multiyear timescale were −1.23 km2 a−1, −1.83 km2 a−1 and −0.42 km2 a−1 for 2012–2015, 2015–2017 and 2017–2021, respectively. In terms of the glacier mass balance, the region-wide results at a two-decade timescale were −0.23 ± 0.02 m w.e. a−1 for 1975–2000 and −0.29 ± 0.02 m w.e. a−1 for 2000–2021, indicating a sustained and relatively stable mass loss over the past nearly five decades. After 2000, the loss rate at a decade timescale was −0.04 ± 0.01 m w.e. a−1 for 2000–2012 and −0.17 ± 0.01 m w.e. a−1 for 2012–2021, indicating an increasing loss rate over recent decades. It was further found that the mass loss rate was −0.12 ± 0.02 m w.e. a−1 for 2012–2015, −0.03 ± 0.01 m w.e. a−1 for 2015–2017 and −0.40 ± 0.03 m w.e. a−1 for 2017–2021. These results indicated that a significant portion of the glacier mass loss mainly occurred after 2017. According to our analysis of the meteorological measurements in nearby regions, the trends of precipitation and the average annual air temperature both increased. Combining these findings with the results of the glacier changes implied that the glacier changes seemed to be more sensitive to temperature increase in this region. Overall, our results improved our understanding of the status of glacier changes and their reaction to climate change in the central Tibetan Plateau.

Accelerated glacier mass loss (2011–2016) over the Puruogangri ice field in the inner Tibetan Plateau revealed by bistatic InSAR measurements

The temporal variation of glacier mass balance during recent years remains poorly known for the mountain glaciers in the inner Tibetan Plateau (ITP), due to the lack of field measurements. In this study, we retrieved the annual glacier mass balance of the Puruogangri ice field, which is the largest modern ice mass in the ITP, by differencing multi-temporal digital elevation models (DEMs) generated with five pairs of TanDEM-X bistatic interferometric synthetic aperture radar (InSAR) images acquired between April 2011 and January 2016. We compared the TanDEM-X DEMs in January and April 2012 to estimate the X-band radar penetration depth difference (0.61 ± 0.06 m), which enabled systematic bias correction in the estimation of annual glacier mass balance. The observed mass balance reveals a glacier mass gain of 0.44 ± 0.10 m w.e. yr−1 in 2011–12, which was followed by accelerated glacier mass loss in 2012–16. Glacier mass balances of −0.13 ± 0.03, −0.34 ± 0.06, and − 0.52 ± 0.10 m w.e. yr−1 were estimated for the periods of 2012–13, 2013–14, and 2014–16, respectively. This accelerating trend of glacier mass loss is likely caused by the continuous decrease in annual precipitation, according to the climate data recorded by adjacent meteorological stations. This study demonstrates that repeated bistatic InSAR measurement is a promising method for monitoring glacier elevation change and mass balance at regular intervals.

Morphometric Controls on Glacier Mass Balance of the Puruogangri Ice Field, Central Tibetan Plateau

Evaluating the impacts of climatic changes and morphometric features on glacier mass balance is crucial to providing insight into glacier changes and their effects on regional water resources and ecosystems. Here, we presented an evaluation of morphometric effects on the glacier mass balances of the Puruogangri ice field (PIF) on the Tibetan Plateau. A clear spatial variability of glacier mass balances, ranging from −0.035 to +0.019 m·w.e.·year−1, was estimated by comparing the TanDEM-X DEM (2012) with the SRTM-X DEM (2000). In general, the observed glacier mass changes were consistent with our fieldwork investigations. Furthermore, by applying the method of linear regression analysis, we found that the mass changes of individual glaciers on the PIF were mainly dominated by the mean altitude (R = 0.84, p < 0.001), however, they were statistically independent of glacier size, aspect, and surface velocity. At a local scale (grid size of 10 × 10 pixels), apart from the factor of altitude, surface velocity was correlated with glacier mass change.

Glacier elevation changes (2012–2016) of the Puruogangri Ice Field on the Tibetan Plateau derived from bi-temporal TanDEM-X InSAR data

ABSTRACTThis study aims to evaluate the potential of TerraSAR-X (TSX) add-on for Digital Elevation Measurement (TanDEM-X) bi-static synthetic aperture radar (SAR) data sets for the retrieval of glacier digital elevation models (DEMs) and elevation changes over mountain regions. We exploited two pairs of TanDEM-X SAR data sets acquired in 2012 and 2016 over the Puruogangri Ice Field (PIF), which is the largest modern glacier on the Tibetan Plateau (TP). Two fine-detail and high-precision DEMs for 2012 and 2016 over the PIF were generated by differential interferometric processing, and were validated against height measurements from global positioning system (GPS) and Ice, Cloud, and land Elevation Satellite (ICESat) altimetry, yielding a vertical accuracy of 1.91 ± 0.76 m and 1.69 ± 0.83 m, respectively. The elevation changes were derived by differencing the bi-temporal TanDEM-X DEMs and revealed predominant glacier surface thinning on the PIF. An annual surface thinning rate of −0.317 ± 0.027 m year−1 was estimated in the period 2012–2016, which is much larger than the estimate of −0.049 ± 0.200 m year−1 for the period 2000–2012 reported in previous studies. This accelerating trend of glacier surface thinning might be attributable to the continued increase in summer temperature since the 1980s and decrease in annual precipitation between two periods of investigation. This study demonstrates that comparison of the bi-temporal TanDEM-X DEMs is an efficient method for accurate and detailed retrieval of the latest surface elevation changes of mountain glaciers.

An ice-core record of vegetation and climate changes in the central Tibetan Plateau during the last 550 years

We present a 550-year ice-core pollen record with a 5-year resolution from the Puruogangri ice field in the central Tibetan Plateau. Analysis of the relationship between pollen record and instrumental observations suggests that the sum of the steppe and meadow pollen taxa is a good indicator of summer (June-August) temperature, whereas the ratios of Cyperaceae/(Gramineae+Artemisia) [Cy/(G+A)] as well as M/S (meadow to steppe percentages) are indicative of humidity changes in this region. Together with delta (18)O and glacial accumulation records, the response of vegetation to climate change over the past 500 years was revealed. Desert vegetation dominated during 1450-1640 AD, a time period characterized by cold-wet climate, while steppe vegetation expanded during 1640-1915 when warm-dry climate prevailed. Afterwards, during a cold and humid period, desert vegetation expanded again. Since 1980-2002, due to the increase of summer temperatures, steppe and meadow vegetation predominates, while areas with desert vegetation are reduced. This proxy series is the first high-resolution ice-core pollen record spanning the last 550 years for the central Tibetan Plateau.

Temperature changes on the Tibetan Plateau during the past 600 years inferred from ice cores and tree rings

The climatological signal of δ 18O variations preserved in ice cores recovered from Puruogangri ice field in the central Tibetan Plateau (TP) was calibrated with regional meteorological data for the past 50 years. For the period AD 1860–2000, 5-yearly averaged ice core δ 18O and a summer temperature reconstruction derived from pollen data from the same ice core were compared. The statistical results provide compelling evidence that Puruogangri ice core δ 18O variations represent summer temperature changes for the central TP, and hence regional temperature history during the past 600 years was revealed. A comparison of Puruogangri ice core δ 18О with several other temperature reconstructions shows that broad-scale climate anomalies since the Little Ice Age occurred synchronously across the eastern and southern TP, and the Himalayas. Common cold periods were identified in the 15th century, 1625–1645 AD, 1660–1700 AD, 1725–1775 AD, 1795–1830 AD, 1850–1870 AD, 1890–1920 AD, 1940–1950 AD, and 1975–1985 AD. The period 1725–1775 AD was one of the most prolonged cool periods during the past 400 years and corresponded to maximum Little Ice Age glacier advance of monsoonal temperate glaciers of the TP.

Summer temperature reconstruction on the central Tibetan Plateau during 1860–2002 derived from annually resolved ice core pollen

We present a 140‐year ice core pollen record with annual time resolution from the Puruogangri ice field in the central Tibetan Plateau. A linear regression model between the sum of the steppe and meadow pollen taxa and summer temperature at Naqu accounts for 66% of the summer temperature variance for the period 1955–2002. On the basis of this model, we reconstructed summer temperature history for the central Tibetan Plateau from 1860 to 2002. Three marked warm periods during the 1870s, 1890s, and 1990s and five cold periods during the 1860s, 1880s, 1900s, 1950s, and 1960–1970s were identified. Within the last 100 years, late 20th century warming is distinctive and may have had a major role in the present retreat of most glaciers on the Tibetan Plateau. The pollen record is also significantly correlated with average annual temperatures over the whole Tibetan Plateau, suggesting that these proxy data have the potential for reflecting large‐scale regional temperature change. The statistically significant similarity between the Puruogangri ice core pollen record and the δ18O time series indicates that both are reliable indicators of temperature change at annual to multiyear timescales in this region.

Precipitation record since AD 1600 from ice cores on the central Tibetan Plateau

Abstract. Lack of reliable long-term precipitation record from the northern Tibetan Plateau has constrained our understanding of precipitation variations in this region. We drilled an ice core on the Puruogangri Ice Field in the central Tibetan Plateau in 2000 to reveal the precipitation variations. The well dated part of the core extends back to AD 1600, allowing us to construct a 400-year annual accumulation record. This record shows that the central Tibetan plateau experienced a drier period with an average annual precipitation of ~300 mm in the 19th century, compared to ~450 mm in the wetter periods during 1700–1780 and the 20th century. This pattern agrees with precipitation reconstructions from the Dunde and Guliya ice cores on the northern Plateau but differs from that found in the Dasuopu ice cores from the southern Plateau The north-south contrasts in precipitation reconstruction reveals difference in moisture origin between the south Tibetan Plateau dominated by the Asian monsoon and the north Tibetan Plateau dominated by the continental recycling and the westerlies.

Temperature variations over the past millennium on the Tibetan Plateau revealed by four ice cores

AbstractTemperature variation on the Tibetan Plateau over the last 1000 years has been inferred using a composite δ18O record from four ice cores. Data from a new ice core recovered from the Puruogangri ice field in the central Tibetan Plateau are combined with those from three other cores (Dunde, Guliya and Dasuopu) recovered previously. The ice-core δ18O composite record indicates that the temperature change on the whole Tibetan Plateau is similar to that in the Northern Hemisphere on multi-decadal timescales except that there is no decreasing trend from AD 1000 to the late 19th century. The δ18O composite record from the northern Tibetan Plateau, however, indicates a cooling trend from AD 1000 to the late 19th century, which is more consistent with the Northern Hemisphere temperature reconstruction. The δ18O composite record reveals the existence of the Medieval Warm Period and the Little Ice Age (LIA) on the Tibetan Plateau. However, on the Tibetan Plateau the LIA is not the coldest period during the last millennium as in other regions in the Northern Hemisphere. The present study indicates that the 20th-century warming on the Tibetan Plateau is abrupt, and is warmer than at any time during the past 1000 years.

Formation of proglacial dunes in front of the Puruogangri Icefield in the central Qinghai–Tibet Plateau: Implications for reconstructing paleoenvironmental changes since the Lateglacial

There are sand dunes and stony desert surfaces (gobi) on the piedmont along the western side of the Puruogangri Icefield in central Qinghai–Tibet Plateau. The dunes formed on the gobi, probably after 16 ka. Their sediment derived from the underling till deflated by mid-latitude westerly winds and the Qiangtang high-pressure system. The gobi contains granitic moraine boulders, ventifacts of limestone and secondary CaCO 3 precipitates at subsurface. Occasional humus layers are present within the sand dunes. A total of 13 humus layers were collected for radiocarbon dating and 20 samples for particle size analysis. The dune particle size distribution is generally negatively skewed. The radiocarbon ages range from 12,709 to 922 calendar years BP. It is likely that the humus layers correspond to warm times and can be correlated to the results from oxygen isotopic data in the ice cores from Guliya in the western Kunlun Mountains and Dunde in the Qilian Mountains. These results initially provide an outline of Lateglacial climate history for the ice field area.

δ 18O record and temperature change over the past 100 years in ice cores on the Tibetan Plateau

The 213 m ice core from the Puruogangri Ice Field on the Tibetan Plateau facilitates the study of the regional temperature changes with its δ 18O record of the past 100 years. Here we combine information from this core with that from the Dasuopu ice core (from the southern Tibetan Plateau), the Guliya ice core (from the northwestern Plateau) and the Dunde ice core (from the north-eastern Plateau) to learn about the regional differences in temperature change across the Tibetan Plateau. The δ 18O changes vary with region on the Plateau, the variations being especially large between South and North and between East and West. Moreover, these four ice cores present increasing δ 18O trends, indicating warming on the Tibetan Plateau over the past 100 years. A comparative study of Northern Hemisphere (NH) temperature changes, the δ 18O-reflected temperature changes on the Plateau, and available meteorological records show consistent trends in overall warming during the past 100 years.