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Reconstructing 800 Years of Carbonate Ion Concentration in the Cariaco Basin Using the Area Density of Planktonic Foraminifera Shells
Author(s) -
Davis A. N.,
Davis C. V.,
Thunell R. C.,
Osborne E. B.,
Black D. E.,
BenitezNelson C. R.
Publication year - 2019
Publication title -
paleoceanography and paleoclimatology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.927
H-Index - 127
eISSN - 2572-4525
pISSN - 2572-4517
DOI - 10.1029/2019pa003698
Subject(s) - upwelling , foraminifera , globigerinoides , plankton , oceanography , structural basin , sea surface temperature , geology , carbon dioxide in earth's atmosphere , climate change , carbonate , environmental science , period (music) , climatology , paleontology , chemistry , physics , organic chemistry , acoustics , benthic zone
Anthropogenically mediated ocean acidification (OA) has negative impacts on many marine organisms, especially calcifiers. However, systematic measurements of OA have only been made over the past four decades. In order to improve future predictions and understand how ongoing OA compares to natural variability on longer timescales, it is critical to extend records beyond observational time series. In the Cariaco Basin, located in the tropical Atlantic, near‐surface dissolved inorganic carbon reflects atmospheric carbon dioxide concentrations (CO 2 ) since the Industrial Revolution, making it an ideal site for examining longer‐term variability. We extend the record of Cariaco Basin near‐surface [CO 3 2− ] back to 1240 CE, using the area density (shell weight (μg)/shell area (μm 2 )) of the planktonic foraminifer Globigerinoides ruber (pink). Multidecadal variability is observed throughout the record. Since the Industrial Revolution (1760–2007 CE), [CO 3 2− ] has declined by 0.22 μmol kg −1 year −1 , in agreement with the magnitude and direction of change captured in the shorter instrumental time series. During the Little Ice Age (1500–1760 CE), a period marked by regional drought, substantial variability but no long‐term trend is observed, while a decrease in [CO 3 2− ] of 0.11 μmol kg −1 y −1 occurs at the end of the Medieval Climate Anomaly (MCA) (1240 – 1500 CE). Both the MCA and Little Ice Age contain substantial natural variability in near surface [CO 3 2− ] that we attribute to changes in regional upwelling and atmospheric CO 2 . However, the decline in [CO 3 2− ] occurring in the Post‐Industrial Period is anomalous against a backdrop of 800 years of natural variability, reflecting OA associated with anthropogenic increases in atmospheric CO 2 .