22-1 PLIOWEST: Drilling Pliocene and Pleistocene Lake Records in Western North America to Reconstruct Hydroclimate Dynamics

Abstract:

Perennial paleolake deposits in the Western US indicate that the Pliocene Epoch (~5.3 to 2.58 Ma) was warmer and simultaneously wetter than today, presenting a paradox as climate model projections under elevated atmospheric CO2 predict subtropical drying. The PLIOWEST International Continental Scientific Drilling Program (ICDP) project targets Pliocene to present double-cored lacustrine sequences along a 6° latitudinal transect (~1,380 km) in western North America to resolve Pacific climate dynamics. PLIOWEST cores two lacustrine basins. The northern site at Butte Valley, CA (41°N) targets ~200 m of carbonate-bearing siliciclastic lacustrine sediments extending into the early- to mid-Pliocene strata. The southern site at Searles Lake, CA (35°N) targets a ~710 m carbonate mud and evaporite sequence covering the mid-Pliocene to Holocene. Key targets include the M2 glacial (~3.3 Ma), the mid-Pliocene Warm Period (3.3–3.0 Ma), the Pliocene-Pleistocene Transition (3.0–2.5 Ma), and Pleistocene super-interglacials. Our framework tests two hypotheses for subtropical wetting. Reduced zonal sea-surface temperature gradients driven by permanent El Niño-like conditions displace the subtropical jet equatorward to increase winter precipitation in southern mediterranean regions, affecting the southern site. Alternatively, reduced meridional sea-surface temperature gradients caused by polar-amplified warmth weaken the Hadley circulation, reducing subtropical moisture divergence and boosting seasonal monsoonal rainfall at both locations. Our team will use an integrated multiproxy approach including isotope geochemical, organic, and microfossil proxies, and tephrostratigraphic and paleomagnetic dating. PLIOWEST also incorporates climate modeling and hydrogeologic modeling, as well as parallel research on the deep biosphere and critical mineral resources such as lithium brine dynamics in closed-basin evaporite systems. The ICDP project has been recently approved and the team will share the lithostratigraphy of both lake basins, outline the project objectives, solicit feedback and invite further collaboration at the meeting.

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