automated carbonate preparation device (KIEL-III) coupled to a gas-ratio mass spectrometer (Finnigan MAT 252).

Sediment characterization by X-ray diffractometry was completed at the University of Pittsburgh?s Materials Micro-Characterization Laboratory using a Phillips X?Pert Powder Diffractometer over a 2? range of 10?80�. X-ray diffraction results indicate that calcite is the only detectable mineral in the fine-grained, carbonate sediment at Lime Lake.

Sediment sampleswere disaggregated for approximately 24 h in 7% H2O2 solution and sieved
at 63 μm to isolate authigenic (i.e., precipitated in-lake) carbonate material
and to limit contamination by biogenic carbonate shell material. The captured
<63 μm fraction of the sediment was settled from rinse water and then
centrifuged, and the remaining liquid was decanted. The resulting fine grained
 carbonate sediment was bleached (using a 50% bleach, 50% water
 solution), rinsed three times using deionized water, freeze-dried, and homogenized
using an agate mortar and pestle.

Our results indicate that during the Medieval Climate Anomaly (MCA) (900-1300 AD) the Pacific Northwest experienced exceptional wetness in winter and that during the Little Ice Age (LIA) (1450-1850 AD) conditions were drier, contrasting with hydroclimatic anomalies in the desert Southwest and consistent with climate dynamics related to the El Nii¿½o Southern Oscillation (ENSO) and the Pacific Decadal Oscillation (PDO).

Castor Lake water and sediment oxygen isotope values are primarily influenced by catchment water balance variations resulting from precipitation-evaporation forcing; To establish a meteoric water baseline for the Castor Lake record, we mean centered the independently dated (SI Appendix, Table S1) Lime Lake ?18O data and subtracted these variations from the mean centered Castor Lake ?18O values (Figs. 2 and 3) thereby isolating the isotopic influence of hydrologic forcing on the Castor lake-catchment system (8). The resulting ??18O record represents the cumulative isotopic effects of evaporation