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Hydrological changes in Asian inland since late pleistocene and
climatic implications of interactions between westerlies and East
Asian summer monsoon
Song, Mu; 宋木
Song, M. [宋木]. (2016). Hydrological changes in Asian inland
since late pleistocene and climatic implications of interactions
between westerlies and East Asian summer monsoon. (Thesis).
University of Hong Kong, Pokfulam, Hong Kong SAR. Retrieved
from http://dx.doi.org/10.5353/th_b5719460.
2016
http://hdl.handle.net/10722/223610
The author retains all proprietary rights, (such as patent rights)
and the right to use in future works.
Abstract of thesis entitled
HYDROLOGICAL CHANGES IN ASIAN INLAND SINCE
LATE PLEISTOCENE AND CLIMATIC IMPLICATIONS
OF INTERACTIONS BETWEEN WESTERLIES AND
EAST ASIAN SUMMER MONSOON
Submitted by
Mu Song
for the Degree of Doctor of Philosophy
at The University of Hong Kong
in January 2016
The vast region of arid Asian inland, where evaporation strongly affects the
fragile ecosystem and hydrological balance, serves as an ideal place to study the
“natural background information” of climate changes since the late Pleistocene. This
thesis presents the multi-proxy-based hydrological records from lakes across the
forest-steppe ecotone in south Western Siberia and steppe-desert ecotone in
northwestern (NW) China since the late Pleistocene, emphasizing the hydrological
evolution of Westerly-dominated regions, potential forcing factors, and interactions
between Westerlies and East Asian Summer Monsoon (EASM).
Firstly, substantial environmental controls, especially salinity, on the occurrence
and compositional patterns of long-chain alkenone (LCA) in lacustrine sediments,
NW China, were found, validating the use of LCA proxies as terrestrial
paleoenvironmental indicators. Predominance of C37:4 LCA and the occurrence of
∗
C38ME and C37:3 isomeric LCA (C37:3
) were suggested as responses to low salinity. An
arched content-salinity relationship was apparent, with no or very low LCA contents
in freshwater and hypersaline environments. The %C37:4 showed a negative
K′
relationship with salinity and the U37
index was suggested to be a better terrestrial
K
temperature proxy than U37
who showed a weakly positive relationship with salinity.
Solar imprints on Asian inland moisture fluctuations over the last millennium
were found from a high-resolution shoreline-core record in Lake Manas, Westerlydominated NW China. It consistently showed frequent and substantial lake level
fluctuations, resembling solar activity changes, especially during the Little Ice Age
(LIA). Wavelet spectral analyses of the X-ray fluorescence data indicated strong
cycles coinciding with the~11-year Schwabe cycle, ~70-100-year Gleissberg cycle,
and the ~200-year Suess-de Vries cycle. Significant lake-level influence on the
accumulation and variation of elements was also identified based on the PCA results.
Desert sands prevailed dry intervals, especially Current Warm Period (CWP) and
Medieval Warm Period (MWP). Salt marsh prevailed MWP and occurred shortly in
LIA. LIA was indicated the wettest over the last millennium.
Further, LCA and n-alkane records of Lake Chany depicted climate changes
since the middle Holocene in south Western Siberia and extended the northern limit
∗
of Westerly-dominated climate to 54°N. C37:3
was present and thus included in the
K′
conventional U37
and %C37:4. The lake didn’t occur until ~ 5ka and achieved its
highest level during the LIA. Both decreased temperature and increased precipitation
during prevalent negative North Atlantic Oscillation/Arctic Oscillation phase might
have contributed to the cold-wet climate during the LIA, but low temperature during
the solar minima was suggested to be more crucial.
Lastly, biomarker-based record at Lake Yanhaizi indicated broadly synchronous
effective moisture evolution of the EASM marginal region since the late Pleistocene
and followed the pattern of EASM precipitation. The Holocene Climate Optimal, thus
the strongest EASM occurred during the middle Holocene, and showed out-of-phase
relationship with Westerlies. The 8.2 ka event changed from a short-lived shift in the
central monsoonal region to a prolonged dry anomaly in Westerly-dominant region,
suggesting increased influence of evaporation and the Westerlies. Tripartite
subdivisions of Holocene were suggested with 8.2 ka and 4.0 ka dry events as the
boundaries of early-middle and middle-late Holocene.
(An abstract of exactly 498 words)