Late Holocene multi-decadal to centennial scale oceanic variability on the eastern Canadian shelf linked to North Atlantic climatic changes
Final Report Abstract
Within the frame of the ‘CanClim’ project foraminiferal studies from cores collected during the MSM46 cruise in 2015 provide unique insight into the composition of bottom water condition in the Gulf of St. Lawrence (GSL) and the Lower St. Lawrence Estuary (LSLE) since the last Glacial period. Analysis of the foraminiferal assemblage from recent (2015) surface sediments, benthic and planktonic, along a transect in the GSL/LSLE including the Esquiman Channel, reveal a clear trend from a well oxygenized (Cabot Strait) to a hypoxic benthic habitat (LSLE). The marked differences in the distribution of an-/suboxic and hypoxic benthic foraminiferal species along this transect demonstrates the prominent influence of warm Atlantic Water inflow into the Gulf of St. Lawrence area on bottom water conditions. Expanding these analyses on sediment cores that cover the time since the Little Ice Age, reveals a time transgressive distribution of hypoxia in the Gulf of St. Lawrence area controlled by the interplay of sea ice formation in surface waters and the inflow of warm Atlantic waters. The results show that during the cold period of the Little Ice Age no hypoxia occurs, due to the absence of warm Atlantic waters. A possible local mechanism, that blocks the inflow of warm Atlantic waters into the Gulf of St. Lawrence area, is the formation of deep (brine) waters via enhanced vertical mixing during the Little Ice Age. High resolution studies on a core from the Laurentian Channel in the centre of the Gulf of St. Lawrence, reveals that with fading Little Ice Age conditions and hence surface water warming, i.e. reduced sea ice formation, warm Atlantic waters and hypoxic conditions dominate the bottom water conditions since the late 1920s. The longer-term Glacial to Holocene studies from the Gulf of St. Lawrence /Lower St. Lawrence Estuary demonstrate that such a mechanism might have played an important role during late Holocene cold phases, i.e. Dark Ages and the 2.8 ka BP cold event. The spread of hypoxia seems to be restricted during warm phases to the outer parts of the Gulf of St. Lawrence/Lower St. Lawrence Estuary area, while during phases of pronounced sea ice formation hypoxia did not reach the inner parts of the Lower St. Lawrence Estuary. Results achieved during ‘CanClim’ demonstrated once more the importance of high resolution foraminiferal studies in reconstructing palaeoceanographic condition and set a sound baseline for further investigations.
Publications
- (2018) Exploring the recent temperate to sub-arctic benthic foraminiferal assemblages on the eastern Canadian shelf the size fraction issue. FORAMS, June 2018
Perner, K.
- (2018). Paleoenvironmental change on the eastern Canadian continental margin during the last 100 years: implications from Lake Melville and the Gulf of St. Lawrence. European Geoscience Union, April 2018
Perner, K., Moros, M., de Vernal, A., Lajeunesse, P.
- (2021). The signal of climate changes over the last two millennia in the Gulf of St. Lawrence, eastern Canada. Quaternary Research 1–16
Wu, X., de Vernal, A., Fréchette, B., Moros, M., Perner, K.
(See online at https://doi.org/10.1017/qua.2021.56)
