Late Holocene paleolimnology and paleoclimatology from sub-arctic lakes in Nunavut, Canada and Iceland

Sediment cores from five lakes in the western North Atlantic region were studied to establish a detailed record of regional climate change during the past two millennia, against a backdrop of more localized limnological changes. To accomplish this, proxy-climate records from three varved-sediment lakes on Baffin Island, Ogac Lake, Upper Soper Lake and Winton Bay Lake, were compared to similar records from two lakes in northwest Iceland, Vatnsdalsvatn and Thiðriksvallavatn. These records include results from environmental magnetism, ICP-OES geochemistry, carbon content, C/N, and pollen analyses. AMS 14C and 210Pb analyses provide chronologies for each site. The longest records, from Baffin Island, cover the interval from the mid-20th Century to 1900 BP. The records from Iceland extend from the mid-20th Century to 950 BP, at Vatnsdalsvatn, and to about 500 BP, at Thiðriksvallavatn. On Baffin Island, sediment, diatom and pollen analyses reveal gradual changes associated with lake uplift and marine isolation, and relatively rapid changes associated with climate changes at the beginning and end of the Medieval Warm Period (MWP), from about 1250–650 BP, and the Little Ice Age (LIA), from about 550–100 BP. High resolution (20–40 year/sample) pollen records from each of the Baffin Island sites reveal these climate changes in both local (low-Arctic) and exotic (Boreal Forest) pollen assemblages, aided by multivariate clustering and detrended correspondence analyses (DCA). Enhanced algal productivity and higher levels of sedimentary carbon occur during the LIA at Ogac and Upper Soper lakes on Baffin Island, and at Vatnsdalsvatn, on Iceland. Human disturbance is not a distinguishable factor in the Iceland records, except for abrupt changes in lake chemistry and sediment influx after a dam was constructed at Thiðriksvallavatn. Geochemistry changes in the Iceland lake, associated with erosion, show a 100–130 yr. periodicity, lasting over nine centuries at Vatnsdalsvatn and over four centuries at Thiðriksvallavatn. These erosion cycles may be associated with long-term stability in the positive mode of the North Atlantic Oscillation.