Environmental and climate evolution in the Southwest USA since the last interglacial deduced from the pollen record from Stoneman lake, Arizona

Abstract

Long and continuous lake sedimentary records offer enormous potential for interpreting the paleoenvironmental histories of the past and for understanding how terrestrial environments might adapt in the context of current global warming. However, sedimentary records that contain multiple glacial-interglacial cycles are scarce in continental basins. An ∼80 m sediment core was recently obtained from Stoneman Lake (STL), Arizona, containing a unique record of the last ∼1.3 Ma. Here we show a detailed pollen study of the topmost ∼10 m of the record, covering the last climatic cycle since the Last Interglacial period (MIS5-MIS1; last ∼130,000 years = 130 kyr), with the goal of broadening our knowledge of the paleoenvironmental history of the arid North American Southwest in the past. The STL pollen record shows that the MIS5e interglacial was the warmest period of the last 130 kyr. This is deduced by the abundance of pollen types from plants that today exist at lower elevations that occurred around the STL at that time. These include Pinus edulis and other associated low elevation thermophilous plants such as Juniperus, Ambrosia, Amaranthaceae, Asteraceae and Artemisia. Climate cooled rapidly and dramatically at the MIS5-4 boundary, which triggered a displacement of forest species towards lower elevation, causing P. ponderosa to occupy the study area. MIS3 was characterized by relatively warmer climate conditions with 3 prominent climatic oscillations (MIS3a, b and c). The coldest conditions were reached during MIS2 (LGM), when a ∼1000 m displacement towards lower elevations of the subalpine forest species relative to present is observed. This is deduced by the highest abundance of Picea (∼20–25%) and Abies in the STL record, indicating their occurrence in the study area. Warming during the last deglaciation is evidenced by a shift of vegetation towards higher altitudes and the development of a montane forest composed mainly of Pinus ponderosa and Quercus replacing the LGM subalpine species. This montane forest remained abundant throughout the Holocene. This study shows that orbital-scale climate changes (mainly precession and eccentricity changes) forced vegetation and lake-level oscillations, documenting that insolation had a main role in controlling environmental change in this area. Climate projections of enhanced warming predict that P. edulis and Juniperus forest species will occupy the study area in the near future.