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Oceanic cooling recorded in shells spanning the Medieval Climate Anomaly in the subtropical eastern North Atlantic Ocean

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doi: 10.1016/j.quascirev.2020.106635
Authors:Parker, Wesley G.; Yanes, Yurena; Hernández, Eduardo Mesa; Surge, Donna
Author Affiliations:Primary:
University of Cincinnati, Cincinnati, OH, United States
Other:
Universidad de La Laguna, San Cristobal de La Laguna, Spain
University of North Carolina, Chapel Hill, NC, United States
Volume Title:Quaternary Science Reviews
Source:Quaternary Science Reviews, Vol.249. Publisher: Elsevier, International. ISSN: 0277-3791
Publication Date:2020
Note:In English. 130 refs.; illus., incl. 4 tables, sketch maps
Summary:The Medieval Climate Anomaly (MCA; 900-1300 AD) was the most recent period of pre-industrial climatic warming in the northern hemisphere, and thus estimations of MCA signals can illuminate possible impacts of anthropogenic climate change. Current high-resolution MCA climate signals are restricted to mid- and high-latitude regions, which confounds inferences of how the MCA impacted some global/hemispheric climate mechanisms (e.g. North Atlantic Oscillation; NAO). To address this knowledge gap, we estimate seasonally-resolved sea surface temperatures (SSTs) from the oxygen isotope composition (δ18O) of serially sampled Phorcus atratus shells from archaeological sites spanning the MCA in the Canary Islands. Twelve archaeological and six modern P. atratus shells were analyzed, and archaeological shells were dated using carbonate-target radiocarbon dating. SSTs were estimated using the published aragonite-water equilibrium fractionation equation. Modern shells showed a mean SST of 20.0 ± 1.5 °C, with a seasonal amplitude of 5.3 ± 0.9 °C. Archaeological shells exhibited a mean SST of 18.2 ± 0.7 °C, with a mean seasonal amplitude of 5.5 ± 1.0 °C. Thus, shells that span the MCA in the Canary Islands recorded SSTs that were significantly cooler than the modern (P < .05), contrasting with warming estimates and model predictions elsewhere in the Northern Hemisphere. We propose that the observed cooling resulted from increased upwelling in NW Africa due to a strengthening of the prevailing westerlies and coastal winds along the African shoreline. The intensified upwelling scenario during the MCA is partially supported by in-situ carbon isotope data (δ13C) retrieved from the archaeological shells, which was compared to the δ13C values of modern shells and dissolved inorganic carbon in the ambient seawater. These results are consistent with other low-latitude temperature/precipitation anomalies associated with a positive NAO mode, suggesting a transition to a positive NAO index during the middle and late MCA that possibly extended later into the 13th century AD.
Subjects:Archaeological sites; Cenozoic; Climate change; Cooling; Fossils; Holocene; Isotopes; Medieval Warm Period; North Atlantic Oscillation; Paleoclimatology; Quaternary; Sea-surface temperature; Shells; Stable isotopes; Subtropical environment; Atlantic Ocean; Atlantic Ocean Islands; Canary Islands; North Atlantic; Phorcus atratus
Coordinates:N274500 N293000 W0130000 W0181500
Record ID:892025-22
Copyright Information:GeoRef, Copyright 2021 American Geosciences Institute. Reference includes data from CAPCAS, Elsevier Scientific Publishers, Amsterdam, Netherlands
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