Biomarker and Pollen Evidence for Late Pleistocene Pluvials in the Mojave Desert

The climate of the southwestern North America has experienced profound changes between wet and dry phases over the past 200 Kyr. To better constrain the timing, magnitude, and paleoenvironmental impacts of these changes in hydroclimate, we conducted a multiproxy biomarker study from samples collected from a new 77 m sediment core (SLAPP-SRLS17) drilled in Searles Lake, California. Here, we use biomarkers and pollen to reconstruct vegetation, lake conditions, and climate. We find that delta D values of long chain n-alkanes are dominated by glacial to interglacial changes that match nearby Devils Hole calcite delta O-18 variability, suggesting both archives predominantly reflect precipitation isotopes. However, precipitation isotopes do not simply covary with evidence for wet-dry changes in vegetation and lake conditions, indicating a partial disconnect between large scale atmospheric circulation tracked by precipitation isotopes and landscape moisture availability. Increased crenarchaeol production and decreased evidence for methane cycling reveal a 10 Kyr interval of a fresh, productive, and well-mixed lake during Termination II, corroborating evidence for a paleolake highstand from shorelines and spillover deposits in downstream Panamint Basin and Death Valley during the end of the penultimate (Tahoe) glacial (140-130 ka). At the same time brGDGTs yield the lowest temperature estimates (mean months above freezing = 9 degrees C +/- 3 degrees C) of the 200 Kyr record. These limnological conditions are not replicated elsewhere in the 200 Kyr record, suggesting that the Heinrich stadial 11 highstand was wetter than the last glacial maximum and Heinrich 1 (18-15 ka).

Automated summary

The climate of southwestern North America has undergone significant changes between wet and dry phases over the past 200,000 years. A multi-proxy biomarker study conducted on sediment cores from Searles Lake, California reveals the timing, magnitude, and paleoenvironmental impacts of these hydroclimate changes. Precipitation isotopes show a connection with glacial to interglacial changes, but do not align with evidence of wet-dry vegetation and lake conditions, suggesting a partial disconnect between atmospheric circulation and landscape moisture availability. Limnological conditions during Termination II indicate a fresh, productive, and well-mixed lake, while temperature estimates during Heinrich stadial 11 suggest wetter conditions compared to the last glacial maximum and Heinrich 1.