Mid-Wisconsin sediment record from Baldwin Lake reveals hemispheric climate dynamics (Southern CA, USA)

Abstract

Recently acquired cores from Baldwin Lake, Southern California, document the first regional, terrestrial-based evidence for glacial period millennial-to-orbital scale climate variability. Eight AMS 14C dates on a 14-m core from the lake's present day depocenter provide initial age control over the interval from 20,000 to 48,000 years before present (BP). A linear age model extends the record to a minimum age of 65,000 years BP. A combination of lithologic description and one cm contiguous sedimentological analyses indicates significant changes in the dominant type of depositional environment over the length of the record at millennial-to-orbital time scales. As a first-order interpretation, the dominant sedimentary environments alternate between permanent and ephemeral lake systems. Orbital-scale forcing includes long-term winter-summer insolation variability and its modulation of winter storm tracks and the North American monsoon, respectively. Millennial-scale variability is attributed to extra-tropical, ocean–atmosphere dynamics akin to historical interdecadal Pacific climate variability. In addition, there is notable correspondence to the independently dated Greenland Ice Core record (GISP 2) at millennial-to-orbital time scales suggesting that Baldwin Lake contains, in addition to its local/regional record, a hemispheric record of climate change — similar to Owens, Pyramid, and Summer Lake of central and northwestern North America. An initial comparison to GISP2 δ 18O (ice) indicates that North Atlantic interstadials correlate to permanent lake environments in coastal southwestern North America. These results present a notable conflict with the proposed “super-ENSO” phenomenon in the western tropical Pacific. These results also highlight the necessity for acquiring additional high-resolution glacial period records for resolving questions of spatial–temporal phasing of late-Quaternary climates.