RECORD OF THE 1918/1919 EL NINO AND A LONG-DURATION POSITIVE PHASE OF THE NORTH ATLANTIC OSCILLATION WITHIN AN ADIRONDACK LAKE

Kanfoush (2005) reported strong correlations in characteristics of Adirondack lake sediments with long-term (centennial) changes in climate, including northern hemisphere temperature, CO₂, and solar irradiance. She also saw tentative evidence that sediment characteristics were changing in response to shorter term (decadal) climate variations, including the Atlantic Multidecadal Oscillation (AMO) and North Atlantic Oscillation (NAO). Although results suggested existence of such a linkage, the sampling interval of the core (1cm) was deemed insufficient for this interpretation to be conclusive. Thus further research was needed to support or negate preliminary findings.

Another core was collected in 2008 from the same lake, ~500 meters southwest of the first and sectioned at 0.5cm intervals. Magnetic susceptibility, loss-on-ignition, and grain size were examined. An age model was constructed using ²¹⁰Pb and checked with ¹³⁷Cs, yielding a basal age of ~1835. Sediment characteristics were each compared with the AMO, NAO, and El Niño Southern Oscillation (ENSO). These climate cycles showed no consistent relationship with the sediment characteristics throughout the length of the core. However, grain size data showed a spike in sand percentage deposited in the lake around 1920, coupled with a decrease in silt and clay. Accumulation rate and mean grain diameter also saw a spike around 1920. A broader decrease in carbonates corresponds with this time period as well. We propose the ~1920 anomaly in these parameters was caused by a particularly extreme El Niño event at this time accompanied by an unusually long-duration positive phase of the NAO (Giese et al., 2010). Sedimentation rate variations due to natural and anthropogenic disturbances may have masked the lake sediment response to El Niño and other climatic events of smaller magnitude.