TY  - JOUR
A1  - Purinton, Benjamin
A1  - Bookhagen, Bodo
T1  - Tracking downstream variability in large grain-size distributions in the South-Central Andes
JF  - Journal of geophysical research : F, Earth surface
N2  - Mixed sand- and gravel-bed rivers record erosion, transport, and fining signals in their bedload size distributions. Thus, grain-size data are imperative for studying these processes. However, collecting hundreds to thousands of pebble measurements in steep and dynamic high-mountain river settings remains challenging. Using the recently published digital grain-sizing algorithm PebbleCounts, we were able to survey seven large (>= 1,000 m2) channel cross-sections and measure thousands to tens-of-thousands of grains per survey along a 100-km stretch of the trunk stream of the Toro Basin in Northwest Argentina. The study region traverses a steep topographic and environmental gradient on the eastern margin of the Central Andean Plateau. Careful counting and validation allows us to identify measurement errors and constrain percentile uncertainties using large sample sizes. In the coarse >= 2.5 cm fraction of bedload, only the uppermost size percentiles (>= 95th) vary significantly downstream, whereas the 50th and 84th percentiles show less variability. We note a relation between increases in these upper percentiles and along-channel junctions with large, steep tributaries. This signal is strongly influenced by lithology and geologic structures, and mixed with local hillslope input. In steep catchments like the Toro Basin, we suggest nonlinear relationships between geomorphic metrics and grain size, whereby the steepest parts of the landscape exert primary control on the upper grain-size percentiles. Thus, average or median metrics that do not apply weights or thresholds to steeper topography may be less predictive of grain-size distributions in such settings.
KW  - digital grain sizing
KW  - downstream fining
KW  - fluvial geomorphology
KW  - grain-size distribution
KW  - pebblecounts
Y1  - 2021
U6  - https://doi.org/10.1029/2021JF006260
SN  - 2169-9003
SN  - 2169-9011
VL  - 126
IS  - 8
SP  - 1
EP  - 29
PB  - American Geophysical Union
CY  - Washington
ER  - 
TY  - JOUR
A1  - Lu, Yin
A1  - Dewald, Nico
A1  - Koutsodendris, Andreas
A1  - Kaboth-Bahr, Stefanie
A1  - Rösler, Wolfgang
A1  - Fang, Xiaomin
A1  - Pross, Jörg
A1  - Appel, Erwin
A1  - Friedrich, Oliver
T1  - Sedimentological evidence for pronounced glacial-interglacial climate fluctuations in NE Tibet in the latest Pliocene to early Pleistocene
JF  - Paleoceanography and Paleoclimatology
N2  - The intensification of Northern Hemisphere glaciation (iNHG) and uplift of the Tibetan Plateau have been argued to be among the main drivers of climate change in midlatitude Central Asia during the Pliocene/Pleistocene. While most proxy records that support this hypothesis are from regions outside the Tibetan Plateau (such as from the Chinese Loess Plateau), detailed paleoclimatic information for the plateau itself during that time has yet remained elusive. Here we present a temporally highly resolved (similar to 500 years) sedimentological record from the Qaidam Basin situated on the northeastern Tibetan Plateau that shows pronounced glacial-interglacial climate variability during the interval from 2.7 to 2.1 Ma. Glacial (interglacial) intervals are generally characterized by coarser (finer) grain size, minima (maxima) in organic matter content, and maxima (minima) in carbonate content. Comparison of our results with Earth's orbital parameters and proxy records from the Chinese Loess Plateau suggests that the observed climate fluctuations were mainly driven by changes in the Siberian High/East Asian winter monsoon system as a response to the iNHG. They are further proposed to be enhanced by the topography of the Tibetan Plateau and its impact on the position and intensity of the westerlies.
KW  - Western Qaidam Basin
KW  - grain-size distribution
KW  - lake Donggi Cona
KW  - Chinese loess
KW  - Central-Asia
KW  - transport processes
KW  - Qilian mountains
KW  - dust sources
KW  - plateau
KW  - record
Y1  - 2020
VL  - 35
IS  - 5
PB  - John Wiley & Sons, Inc.
CY  - New Jersey
ER  -