Abstract. Our understanding of climate and vegetation changes throughout
the Holocene is hampered by representativeness in sedimentary
archives. Potential biases such as production and preservation of the markers
are identified by comparing these proxies with modern environments. It is
important to conduct multi-proxy studies and robust calibrations on each
terrestrial biome. These calibrations use large databases dominated by forest
samples. Therefore, including data from steppe and desert–steppe sites becomes
necessary to better calibrate arid environments. The Mongolian Plateau,
ranging from the Baikal area to the Gobi desert, is especially characterized
by low annual precipitation and continental annual air temperature. The
characterization of the climate system of this area is crucial for the
understanding of Holocene monsoon oscillations. This study focuses on the
calibration of proxy–climate relationships for pollen and glycerol dialkyl
glycerol tetraethers (GDGTs) by comparing large Eurasian calibrations with a
set of 49 new surface samples (moss polster, soil and mud from temporary dry
ponds). These calibrations are then cross-validated by an independent dataset
of top-core samples and applied to four Late Holocene paleosequences (two
brGDGT and two pollen records) surrounding the Mongolian Plateau: in the Altai
mountains, the Baikal area and the Qaidam basin, to test the accuracy of local
and global calibrations. We show that (1) preserved pollen assemblages are
clearly imprinted on the extremities of the ecosystem range but mitigated and
unclear on the ecotones; (2) for both proxies, inferred relationships depend
on the geographical range covered by the calibration database as well as on
the nature of samples; (3) even if local calibrations suffer from reduced
amplitude of climatic parameters due to local homogeneity, they better reflect
actual climate than the global ones by reducing the limits for saturation
impact; (4) a bias in climatic reconstructions is induced by the
over-parameterization of the models by the addition of artificial correlation; and
(5) paleoclimate values reconstructed here are consistent with Mongolia–China
Late Holocene climate trends and validate the application of local
calibrations for both pollen and GDGTs (closest fit to actual values and
realistic paleoclimate amplitude). We encourage the application of this
surface calibration method to reconstruct paleoclimate and especially
consolidate our understanding of the Holocene climate and environment
variations in arid central Asia.
Abstract. Our understanding of climate and vegetation changes throughout the Holocene is hampered by representativeness in sedimentary archives. Potential biases such as production and preservation of the markers are identified by comparing these proxies with modern environments. It is important to conduct multi-proxy studies and robust calibrations on each terrestrial biome. These calibrations use large data base dominated by forest samples. Therefore, including data from taiga and steppe sites becomes mandatory to better calibrate arid environments. The Mongolian plateau, ranging from the Baikal basin to the Gobi desert, is especially characterized by low annual precipitation and continental annual air temperature. The characterization of the climate system of this area is crucial for the understanding of Holocene Monsoon Oscillations. This study focuses on the calibration of proxy-climate relationships for pollen and glycerol dialkyl glycerol tetraethers (GDGTs) by comparing large published Eurasian calibrations with a set of 49 new surface samples (moss polster, soil and mud from temporary dry pond). These calibrations are then cross-validated by an independent dataset of top-core samples and applied to two Late Holocene paleosequences in the Altai mountains and the Qaidam basin. We show that: (1) preserved pollen assemblages are clearly imprinted on the extremities of the ecosystem range but mitigated and unclear on the ecotones; (2) for both proxies, inferred relationships depend on the geographical range covered by the calibration database as well as on the nature of samples; (3) even if local calibrations suffer from reduced amplitude of climatic parameter due to local homogeneity, they better reflect actual climate than the global ones by reducing the limits for saturation impact, (4) a bias in climatic reconstructions is induced by the over-parameterization of the models by addition of artificial correlation and (5) paleoclimate values reconstructed here are consistent with Mongolia-China Late Holocene climate trends, and validate the application of local calibrations for both pollen and GDGTs (closest fit to actual values and realistic paleoclimate amplitude). We encourage the application of this surface calibration method to reconstruct palaeoclimate and especially consolidate our understanding of the Holocene climate and environment variations in Arid Central Asia.
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