HIGH-RESOLUTION RECORD OF PALEOPRECIPITATION PATTERNS OVER THE PAST 8,000 YEARS FROM CENTRAL NORTH AMERICA: IMPLICATIONS FOR THE PACIFIC NORTH AMERICAN PATTERN

In central North America climatic oscillations such as the Pacific North America (PNA) pattern, Pacific Decadal Oscillation, and even the El Niño Southern Oscillation have been correlated with varying continental precipitation patterns. For example, modern δ¹⁸O values of precipitation from the central North American region have been significantly correlated with the PNA pattern via the PNA index (Birks and Edwards, 2009). This suggests that high-resolution records of paleoprecipitation can be used as a proxy for the PNA index through time. However, these climate patterns typically vary on the order of years in contrast to the majority of paleoclimate records that are only at decadal resolution at best, limiting their use for studying these processes. Therefore higher resolution records are needed in order to more accurately quantify past variability. Stable isotope analysis of authigenic lake carbonate can provide a unique archive of paleoprecipitation through time. Oxygen isotope composition of lake carbonate preserves the climatological history recorded in lakewater helping to elucidate moisture source information and changes in atmospheric circulation patterns through time.

We present a high-resolution (millimetre scale, 1–3 years) record of climate from the southern boundary of the boreal forest in central Saskatchewan, Canada detailing climate change over the past 8,000 years. The Mid Holocene (8,000 to 4,200 years BP) is characterized by a large variability in both δ¹³C and δ¹⁸O values implying variable moisture sources suggesting a more prevalent PNA pattern. This stronger PNA pattern induces increased meridional flow resulting in a greater variety of moisture sources to the study region. The 4,200-year event is characterized by the lowest δ¹⁸O values throughout the entire record, indicating increased effective moisture at this time. The beginning of the Late Holocene (4,200 to 1,750 years BP) displays a more muted PNA pattern with a reduction in the variety of moisture sources due to more zonal flow evident from a reduced variance in δ¹⁸O values. After 1,750 years BP increased δ¹⁸O variance indicates that the PNA pattern is re-established coincident with the onset of ENSO conditions in the Pacific.