A 1500-YR RECORD OF DECADAL- TO CENTURY-SCALE CLIMATE EVENTS IN LOW ARCTIC COASTAL LAKES

Varved sediments from meromictic lakes (Ogac, Upper Soper and Winton Bay) in southern Baffin Island, Nunavut, Canada and from two laminated lakes (Vatnsdalsvatn and Thidriksvallavatn) in northwest Iceland provide high resolution records of late Holocene climatic and environmental changes. On Baffin Island, sediment and diatom analyses reveal changes associated with the beginning and end of the Medieval Warm Period (MWP), from 750-650 to 1250 BP, and the Little Ice Age (LIA), from 600-500 to 100 BP. An increase in carbon content occurs after 600 BP, along with coarser inorganic particle deposition, higher amounts of "erosion"-linked minerals such as aluminum, yttrium, and calcium, and autochthonous-like C/N ratios. After 550 BP (AD 1400), freshwater diatom concentrations increase at Ogac Lake. Higher precipitation rates and concomitant soil erosion could increase nutrient availability and productivity in the lakes, accounting for the increases in carbon and diatoms during the LIA. Changes in local (low-Arctic) and exotic (Boreal Forest) pollen assemblages are identified in the Baffin Island lakes with the aid of multivariate clustering and detrended correspondence analyses (DCA). The Ogac Lake pollen record indicates vegetation changes at 1300, 1150-650 (MWP), 500-100 BP (LIA), and in the 20th Century. There are similar trends in the Upper Soper Lake and Winton Bay Lake pollen, but their shorter records exclude events prior to 600 BP. In northwest Iceland, ICP, C/N, magnetic susceptibility and particle-size analyses were completed for each site. Carbon content, sand influx, and erosion-associated chemical species, such as calcium, potassium, magnesium, aluminum, strontium, yttrium and phosphorus, increase after 550 BP. Human settlement, in 990 BP (AD 960), immediately preceded order-of-magnitude increases in sedimentation rates. However, in northwest Iceland, vegetation and sediment characteristics changed more at the onset of the LIA than following human settlement. Repeated oscillations, of 300-400 year frequency, appear throughout both Icelandic lake records despite changes in trend due to LIA and Settlement effects. The oscillation is strongest in the erosion-related chemical species and so may be tied into long-term climate patterns, such as modes of the AO/NAO.