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 MBT5Me′ temperature proxy, based on bacterial
membrane lipids, detects present-day conditions (21 ± 3 ºC, 1s, n = 2)
initially, followed by warmer-than-present conditions (25 ± 3 ºC, n =
17) starting at 3.268 and ending at 2.734 Ma. This is supported by
salinity indicators from bacterial and archaeal biomarkers that reveal
lake salinity increased after 3.268 Ma. 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. dD values (-174 ± 5‰, n = 25) of plant waxes indicate
precipitation dD values (‑89 ± 5‰, n = 25) in the late Pliocene are
within the same range as the late Pleistocene precipitation dD.
Microbial biomarkers identify a deep, freshwater lake and a cooling that
corresponds to the onset of major Northern Hemisphere glaciation at
marine isotope stage MIS M2. A more saline lake persisted for
~0.6 Ma across the subsequent warmth of the late
Pliocene before the lake desiccated at the Pleistocene intensification
of Northern Hemisphere Glaciation.