Last Century Warming Over the Canadian Atlantic Shelves Linked to Weak Atlantic Meridional Overturning Circulation

Abstract

The Atlantic meridional overturning circulation (AMOC) is a key component of the global climate system. Recent studies suggested a twentieth‐century weakening of the AMOC of unprecedented amplitude (~15%) over the last millennium. Here we present a record of δ18O in benthic foraminifera from sediment cores retrieved from the Laurentian Channel and demonstrate that the δ18O trend is linked to the strength of the AMOC. In this 100‐year record, the AMOC signal decreased steadily to reach its minimum value in the late 1970s, where the weakest AMOC signal then remains constant until 2000. We also present a longer δ18O record of 1,500 years and highlight the uniqueness of the last century δ18O trend. Moreover, the Little Ice Age period is characterized by statistically heavier δ18O, suggesting a relatively weak AMOC. Implications for understanding the mechanisms driving the intensity of AMOC under global warming and high‐latitude freshwater input are discussed.

Variability in the Northern North Atlantic and Arctic Oceans Across the Last Two Millennia: A Review

“…A combination of Labrador and Baffin Island algal time series indicates increased sea ice throughout the LIA and a steep long-term ice decline in the industrial period ; Figure 6k). A recent benthic δ 18 O record from the Laurentian Channel within the Gulf of St Lawrence reveals a recent (~1900 years CE) step shift to lighter δ 18 O interpreted as an increase in subsurface temperatures in the NW Atlantic (Thibodeau et al, 2018) similar to the patterns found in the coralline algae records (Figures 6i, 6j, and 6k). This shift is interpreted as a fingerprint for a recent AMOC weakening, and it is argued that albeit less abruptly, the AMOC weakening started at around the onset of the LIA (~1600 years CE; Thibodeau et al, 2018).…”

“…(a) Sea ice concentration from central west Greenland shelf (GA306‐BC/GC4 spliced with lower res GA306‐GC3; Sha et al, ; Sha et al, ), (b) benthic foraminifera assemblages at 855 m on the West Greenland Shelf bathed by WGC (343310‐MC/GC; Perner et al, ), Disco Bugt surface ocean reconstructions; (c) biomarker sea ice reconstructions (343310GC; Kolling et al, ); (d) sea ice cover reconstructed from dinocysts (343310‐MC/GC; Allan et al, ); (e) organic biomarkers as indicators of melting (343310; Moros et al, ), (f) diatom assemblages July sea surface temperature reconstructions (black) and April sea ice cover (343310; (Krawczyk et al, ); (g) alkenone‐based sea surface temperatures from NE Newfounland (AI07‐04BC/3G) and (h) (AI07‐11BC/12G; Sicre et al, ). (i) Benthic δ 18 O foram record at 300 m within the Laurentian Channel GR02‐23 and MD99‐2220 (Thibodeau et al, ). (j) Multispecimen record of coralline algae from Labrador and Baffin Island generated by averaging the normalized and annually averaged Mg/Ca (Moore et al, ) and (k) annual growth rates (Halfar et al, ) giving equal weight to each of the time series.…”

“…Unfortunately, no records with suitable resolutions were identified from the Canadian Arctic north of Baffin Bay. High-resolution records derived from sediment cores in the subarctic and Arctic northwest Atlantic are largely concentrated on bays and fjord systems off eastern and southern Newfoundland, which are perhaps not representative of open ocean conditions (Sheldon et al, 2015;Sicre et al, 2014;Thibodeau et al, 2018). In addition, a single record is available off northern Labrador within a midshelf trough in a small basin protected in the north from iceberg scouring (Rashid et al, 2017).…”

DeepMIP: Model intercomparison of early Eocene climatic optimum (EECO) large-scale climate features and comparison with proxy data

“…These new parameterizations in CAM5 produce a cloud simulation that agrees much better with satellite observations (Kay (Feng et al, 2019), the last glacial maximum (Zhu et al, 2017a), Heinrich events (Zhu et al, 2017b), and the last millennium (Otto-Bliesner et al, 2015;Thibodeau et al, 2018). To make the model suitable for a paleoclimate simulation with a high CO 2 level, the model code has been slightly modified to incorporate an upgrade to the radiation code that corrects the missing diffusivity angle specifications for certain longwave bands.…”

Growth Response of Arctica Islandica to North Atlantic Oceanographic Conditions Since 1850

“…In the oceanic realm, analysis of the carbonate hard structures of marine species could potentially extend instrument-derived observations by several decades or centuries. For example, a recent study (Thibodeau et al, 2018) carried out on benthic foraminifera from sediment cores retrieved from the Laurentian Channel demonstrates the link existing between paleo environmental information and processes ruling the North Atlantic oceanic circulation. As shown by several studies (e.g., Witbaard et al, 1997;Schöne et al, 2005b;Wanamaker et al, 2012;Butler et al, 2013;Bonitz et al, 2018) the shells of the bivalve mollusc A. islandica (Linnaeus, 1767) can also be used as a high-resolution archive of paleoclimate dynamics.…”