A new 1523-year-long varve sequence reveals the influence of the Atlantic Multidecal Variability on Eastern Canada hydroclimate

Grand Lake, Labrador, is a 245-m deep and 55 km long fjord lake deglaciated c.a. 8000 years ago, located at the eastern margin of North America in the high boreal forest ecozone. The lake is fed by two large rivers that transport a substantial amount of sediments, mainly during the snowmelt season. As a result, up to 13 mm thick varves are preserved in the proximal zone of the two main tributaries, while distal varves are 1.26 mm thick on average. Proximal and distal varves can be correlated thanks to cross-correlation of distinctive varves. Varve counts were made from high-resolution images of thin sections at the scanning electron microscope, and from 100 µm-resolution µXRF profiles. The age model was validated by ²¹⁰Pb, ¹³⁷Cs and ¹⁴C dating. The proximal varves are composed of 3 distinct laminae, while the distal varves contain 2 layers. This paper outlines how the proximal and distal sequences were combined to produce a 1523-year-long record allowing a very long reconstruction of past river mean discharge (Q-mean). The river discharge was higher during the Medieval Climate Anomaly (1050–1225 CE) and lower during the Little Ice Age (15th–19th centuries). The reconstructed Q-mean shows a significant co-variability with Atlantic Multidecadal Variability reconstructions and with reconstructed summer Northern Hemisphere temperature based on tree rings. This suggests that river discharge in Labrador was influenced by ocean-atmosphere interactions across the North Atlantic, and that a longer varved record from Grand Lake has the potential to reconstruct the supra-regional modes of climatic variability for most of the Holocene.