A new ~ 900-year varved record in Lake Walker, Québec North Shore, eastern Canada: insight on late Holocene climate mode of variability

This paper presents a new annually laminated record (varves) from Lake Walker, Québec North Shore (eastern Canada) spanning the period from ~ 3230 to 2320 ± 20 cal BP. A ~ 3.5-m-long composite sequence was established with the best regular and continuous laminated intervals using computed tomography and high-resolution photographs. The varve chronology was built based on two methods: manual multi-parameter counting using the PeakCounter software, and manual counting on thin-section images obtained by scanning electron microscopy (SEM). The latter correlates more closely with the ages derived from AMS radiocarbon dating, suggesting that thin-section analysis is here a more reliable counting technique. Varves are clastic, composed of a silt layer deposited in spring and summer, and a clay layer deposited in winter. Annually resolved grain size obtained using image analysis technique on SEM images of thin sections and elemental composition from X-ray microfluorescence analyses performed on the floating varve chronology suggests that the record is sensitive to the North Atlantic Oscillation (NAO), as revealed by the strong co-variability with another lower resolution record from Greenland. This suggests that periods of negative winter NAO promoted a thicker snow cover that resulted in higher river discharges and stronger clastic component in the varves. In modern times, cooling of the North Atlantic in the mid 1970s to the late 1980s was also characterized by concurrent negative phase of NAO, which condition translated into increase snow precipitation over the region. Overall, these results highlight that the new Lake Walker varve record presents remarkable prospects of developing a longer and high-resolution paleoclimatological reconstruction of the NAO in a region where similar records are scarce.