Insights into the hydroclimate during the Medieval Climate Anomaly, Little Ice Age, and Industrial Era from annually resolved Southern Portuguese speleothem records

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2022-08
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Chormann, Alaina
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Wanamaker, Alan
Denniston, Rhawn
Patricola, Christina
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Geological and Atmospheric Sciences
Abstract
The Iberian Peninsula, and specifically Portugal, has been identified by climate model projections as an area where climate change will increase drought frequency and severity. Climate in Portugal is impacted by internal climate modes, most prominently the North Atlantic Oscillation (NAO) and the East Atlantic mode (EA), which are expected to shift in position and intensity due to anthropogenic climate change. Extensive research and paleoclimate reconstructions demonstrate the impacts of the NAO on Iberian climate; however, few paleo archives have investigated the behavior of the EA over the late Holocene. The development of paleoclimate records with high temporal resolution (annual to sub-decadal) from Portugal is critical for improving the predictive capability of regional climate models under future warming scenarios and for determining the extent to which different teleconnection patterns may influence regional climate. Here we present a near annually resolved stable carbon isotope (δ13C) and oxygen isotope (δ18O) time series from three stalagmites from the Algarve region of southern Portugal. U/Th dating indicates that our composite record spans the last millennium continuously through 2019 CE. Stalagmites GIA-19-1 and C-18-1 ceased growing during a dry interval around 1550 CE , while GIA-19-2 grew continuously since the 17th century. Isotope data from all three stalagmites exhibit substantial multidecadal variability indicating changes in effective precipitation. Based on our results, it is likely that both temperature and precipitation amount effects are the dominant controls on isotopic variability in these stalagmites. Hydroclimate during the Medieval Climate Anomaly (MCA), relative to modern, dry, yet variable, and conditions transitioned to an overall wetter early Little Ice Age (LIA). From ~1650 to 1700 CE, conditions in southern Portugal became increasingly dry, and hydroclimate remained fairly stable from 1700 CE to the present. Comparison of the GIA-19-2 oxygen isotope time series with two instrumental records (1900 to present) shows coherence with both index records, suggesting the EA played a prominent role in modulating southern Portugal hydroclimate over the last millennium. Hence, variability in southern Portuguese hydroclimate associated with the EA mode should also be considered by policy makers and planners as they prepare for future warming and associated water stresses.
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