Hydrology and Ecological Evolution in a Permafrost Region in Northeast China Since the Late Pleistocene.

Northeast China is the southern margin of the Eurasian permafrost region, which is very sensitive to global change. However, the historical hydrology and ecological evolution in a concentrated distribution of permafrost in this region remain unclear, hindering our understanding of past and future changes in this region in the context of global warming. Here, we obtained a complete permafrost core from the Mohe Basin in the Greater Khingan Mountains in Northeast China. We reconstructed the hydrology and ecological evolution of the permafrost region since the Late Pleistocene (30 cal. ka BP) using organic geochemical evidence (including TOC, TN, C/N ratio, stable isotopes δC and δN) from a permafrost core, as well as AMSC dating. The results indicate that the environment in the permafrost region in the Mohe Basin closely aligned with the glacial, deglaciation, and interglacial. Between the Last Mega-Interstadial and the Last Glacial Maximum (30-19 cal. ka BP), the surface runoff gradually decreased, primary productivity was low, the wetlands shrank until they disappeared, and a grassland ecosystem formed. During the Last Deglaciation (19-11.5 cal. ka BP), although the organic matter content fluctuated, the surface runoff and primary productivity increased, and the catchment area of the watershed expanded, leading to redevelopment of the wetlands, and a coniferous-dominated mixed forest wetland ecosystem formed. In the Early to Middle Holocene (11.5-5.8 cal. ka BP), primary productivity and surface runoff increased further, gradual wetland expansion reached the maximum extent, and a mixed coniferous-broadleaved forest wetland ecosystem formed. During the Middle to Late Holocene (since 5.8 cal. ka BP), primary productivity and surface runoff decreased, and the wetland water level declined, initiating peatland development and ultimately a coniferous forest swamp ecosystem formed. We believe that the ice volume in the Northern Hemisphere and the East Asian summer monsoon alternately controlled the regional hydrology and ecological evolution during different periods.