Climate of The Past | 2021
Climate reconstructions based on GDGT and pollen surface datasets from Mongolia and Baikal area: calibrations and applicability to extremely cold–dry environments over the Late Holocene
Abstract
Abstract. Our understanding of climate and vegetation changes throughout\nthe Holocene is hampered by representativeness in sedimentary\narchives. Potential biases such as production and preservation of the markers\nare identified by comparing these proxies with modern environments. It is\nimportant to conduct multi-proxy studies and robust calibrations on each\nterrestrial biome. These calibrations use large databases dominated by forest\nsamples. Therefore, including data from steppe and desert–steppe sites becomes\nnecessary to better calibrate arid environments. The Mongolian Plateau,\nranging from the Baikal area to the Gobi desert, is especially characterized\nby low annual precipitation and continental annual air temperature. The\ncharacterization of the climate system of this area is crucial for the\nunderstanding of Holocene monsoon oscillations. This study focuses on the\ncalibration of proxy–climate relationships for pollen and glycerol dialkyl\nglycerol tetraethers (GDGTs) by comparing large Eurasian calibrations with a\nset of 49 new surface samples (moss polster, soil and mud from temporary dry\nponds). These calibrations are then cross-validated by an independent dataset\nof top-core samples and applied to four Late Holocene paleosequences (two\nbrGDGT and two pollen records) surrounding the Mongolian Plateau: in the Altai\nmountains, the Baikal area and the Qaidam basin, to test the accuracy of local\nand global calibrations. We show that (1) preserved pollen assemblages are\nclearly imprinted on the extremities of the ecosystem range but mitigated and\nunclear on the ecotones; (2) for both proxies, inferred relationships depend\non the geographical range covered by the calibration database as well as on\nthe nature of samples; (3) even if local calibrations suffer from reduced\namplitude of climatic parameters due to local homogeneity, they better reflect\nactual climate than the global ones by reducing the limits for saturation\nimpact; (4) a bias in climatic reconstructions is induced by the\nover-parameterization of the models by the addition of artificial correlation; and\n(5) paleoclimate values reconstructed here are consistent with Mongolia–China\nLate Holocene climate trends and validate the application of local\ncalibrations for both pollen and GDGTs (closest fit to actual values and\nrealistic paleoclimate amplitude). We encourage the application of this\nsurface calibration method to reconstruct paleoclimate and especially\nconsolidate our understanding of the Holocene climate and environment\nvariations in arid central Asia.