Early Paleogene precipitation patterns over East Asia: Was there a monsoon after all?

Abstract

Early Paleogene latitudinal precipitation gradients and patterns along the Pacific coast of Eurasia are studied in time and space using the Coexistence Approach, for the first time applied on an extensive regional palaeobotanical record. The palaeobotanical data used in this reconstruction are compiled from literature resources on 110 reasonably well-dated floras, including terrestrial deposits of 73 sites located in the Far East of Russia, Eastern Siberia, China, and Japan, and covering the early Palaeocene to early Eocene. Our reconstructions of precipitation for the Pacific side of Eurasia in the early Paleogene demonstrate a clear division (especially pronounced in the early Eocene) into two zones at ca. 50° N palaeolatitude on all precipitation parameters. Our results reveal very weak latitudinal precipitation gradients during the early and late Palaeocene. In the early Eocene, the gradient became more clearly pronounced, and a larger “arid” zone can be distinguished in the mid-latitudes. Our data suggest that in the early Paleogene, the global atmospheric circulation consisted of two well-defined cells, Hadley and Ferrell, while the polar cell was either absent or located over the Arctic Ocean and was very weak. Based on our reconstructions, the records could not be interpreted in terms of a monsoonal type of climate. The regional distribution of hygrophilous and xerophilous taxa in our early Eocene record largely coincides with the reconstructed precipitation pattern and generally corresponds to the distribution of coals and/or oil shales and red beds and/or evaporites, respectively.