Biomarker Evidence for an MIS M2 Glacial‐Pluvial in the Mojave Desert Before Warming and Drying in the Late Pliocene

Abstract

Ancient lake deposits in the Mojave Desert indicate that the water cycle in this currently dry place was radically different under past climates. Here we revisit a 700 m core drilled 55 years ago from Searles Valley, California, that recovered evidence for a lacustrine phase during the late Pliocene. We update the paleomagnetic age model and extract new biomarker evidence for climatic conditions from lacustrine deposits (3.373–2.706 Ma). The MBT′5Me temperature proxy detects present‐day conditions (21 ± 3°C, n = 2) initially, followed by warmer‐than‐present conditions (25 ± 3°C, n = 17) starting at 3.268 and ending at 2.734 Ma. Bacterial and archeal biomarkers reveal lake salinity increased after 3.268 Ma likely reflecting increased evaporation in response to higher temperatures. The δ13C values of plant waxes (−30.7 ± 1.4‰, n = 28) are consistent with local C3 taxa, likely expanded conifer woodlands during the pluvial with less C4 than the Pleistocene. δD values (−174 ± 5‰, n = 25) of plant waxes indicate precipitation δD values (−89 ± 5‰, n = 25) in the late Pliocene are within the same range as the late Pleistocene precipitation δD. Microbial biomarkers identify a deep, freshwater lake and a cooling that corresponds to the onset of major Northern Hemisphere glaciation at marine isotope stage marine isotope stages M2 (3.3 Ma). A more saline lake persisted for ∼0.6 Ma across the subsequent warmth of the late Pliocene (3.268–2.734 Ma) before the lake desiccated at the Pleistocene intensification of Northern Hemisphere Glaciation.

Pleistocene shifts in Great Basin hydroclimate seasonality govern the formation of lithium-rich paleolake deposits

“…Notably, all three records show a decline in δD p between 2.9 and 2.75 Ma and all three records show slightly more positive values between 2.6 and 2.2 Ma, although this change is much more muted at DSDP 475 (Figure 4). We also note that a recently-published record from Searles Lake does not cover this entire interval, but does show a shift towards more positive δD p values between 2.8 and 2.6 Ma, potentially in agreement with the pattern seen at CV (Peaple et al, 2024). Both CV and Searles Lake also show similar reconstructed late Pliocene δD p values of between -80 and−70 ‰, further increasing confidence in our approach (Peaple et al, 2024).…”

“…We also note that a recently-published record from Searles Lake does not cover this entire interval, but does show a shift towards more positive δD p values between 2.8 and 2.6 Ma, potentially in agreement with the pattern seen at CV (Peaple et al, 2024). Both CV and Searles Lake also show similar reconstructed late Pliocene δD p values of between -80 and−70 ‰, further increasing confidence in our approach (Peaple et al, 2024).…”

“…Leaf wax values are not corrected for ice volume changes (Schrag et al, 1996;Lisiecki and Raymo, 2005;Westerhold et al, 2020) to remain consistent with previous Plio-Pleistocene leaf wax studies in the region (Bhattacharya et al, 2022;Peaple et al, 2024).…”

“…This could reflect an increase in the proportion of C 4 grasses on the landscape. However, recent work combining pollen and leaf wax carbon isotopes found that in some regions of the arid southwest, a more C 4 -like signature can actually reflect a greater proportion of phreatophytic shrubs using the C 4 photosynthetic pathway, like Atriplex (Peaple et al, 2024(Peaple et al, , 2022. The increase in δ 13 C values values in the CV record may therefore reflect long-term shifts to either more C 4 grasses, or an increase in shrubs indicative of regional shifts in water tables.…”

“…However, while there is some suggestion that long-term changes in winter storms could have driven higher lake levels in the Pliocene, it remains unclear how winter storm tracks over the eastern Pacific and western North America responded to global cooling over the Plio-Pleistocene transition (Ibarra et al, 2018;Peaple et al, 2024).…”