Climate driven changes in river channel morphology and base level during the holocene and late pleistocene of southeastern west Virginia

Rivers commonly respond to climate change by aggrading or incising. This is well documented for North American rivers in arid and proglacial regions, but is also true of rivers in unglaciated, humid-temperate regions. Here, we present a record of Holocene hydroclimatology for a humid, temperate watershed in the Appalachian Mountains of eastern North America. We use stable isotope geochemistries of a stalagmite and clastic cave sediments to reconstruct Holocene climate and ecology in the Greenbrier River catchment (3,600 km²) of southeastern West Virginia. Independently, we use river-deposited cave sediments to construct a history of incision, aggradation, and morphological change in the surface channel. The clastic cave deposits display enriched (less negative) values of sedimentary d¹³C_org during the Holocene Climatic Optimum (HCO), which regional pollen records indicate was warm compared to later climes. The river channel had aggraded by.4 m during or prior to the HCO and adopted an alluvial morphology, probably due to the mobilization of hillslope sediments accumulated during the colder, drier full-glacial conditions of the Late Pleistocene. As climate moistened during the Holocene, the Greenbrier River incised through channel-filling sediments and back onto bedrock, but not until,3,500 cal. years B.P. Therefore, the bedrock morphology of many streams in the Appalachian Mountains may not have existed for much of the Holocene, which highlights the effect of climate variability on channel processes. The base-level rise is more evidence that bedrock incision by rivers is often episodic and that slow, long-term incision rates reported for Appalachian Rivers are probably not representative of short-term incision rates.