| Summary: | Indiana University-Purdue University Indianapolis (IUPUI) === The Indian summer monsoon (ISM) is the dominant hydrometeorological
phenomenon that provides the majority of precipitation to southern Asia and southeastern
Tibet specifically. Reliable projections of ISM rainfall are critical for water management
and hinge on our understanding of the drivers of the monsoon system and how these
drivers will be impacted by climate change. Because instrumental climate records are
limited in space and time, natural climate archives are required to understand how the
ISM varied in the past in response to changes in climatic boundary climate conditions.
Lake sediments are high-resolution natural paleoclimate archive that are widely
distributed across the Tibetan Plateau, making them useful for investigating long-term
precipitation trends and their response to climatic boundary conditions. To investigate
changes in monsoon intensity during the Holocene, three lakes were sampled along an
east-west transect in southeastern Tibet: Galang Co, Nir’Pa Co, and Cuobu. Paleoclimate
records from each lake were developed using isotopic (leaf wax hydrogen isotopes; δ2H),
sedimentological, and geochemical proxies of precipitation and lake levels. Sediments
were sampled at high temporal frequencies, with most proxies resolved at decadal scales,
to capture multi-decadal to millennial-scale variability in monsoon intensity and local
hydroclimate conditions. The ISM was strongest in the early Holocene as evidenced by
leaf-wax n-alkane δ2H at both Cuobu and Galang Co corresponding with Cuobu’s higher
lake levels and effective moisture. Monsoon intensity declined at Cuobu and Galang Co
around 6 ka which corresponds to reduced riverine sediment influxes at Cuobu and
deeper lake levels at Galang Co. The antiphase relationship between lake levels and
monsoon intensity at Galang Co is attributed to air temperatures and effective moisture,
with a warmer and drier local hydroclimate driving early Holocene low lake levels. The
late Holocene ISM was more variable with wet and dry periods, as seen in the Nir’Pa Co
lake level and leaf wax n-alkane δ2H record. These records demonstrate coherent drivers
of synoptic and local hydroclimate that account for Holocene ISM expression across the
southeastern Tibetan Plateau, indicating possible drivers of future monsoon expression
under climate change.
|
|---|
