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Foraminiferal evidence of major environmental changes driven by the sun-climate coupling in the western Portuguese coast (14th century to present)

Moreno J., Fatela F., Leorri E., Gonšalves M.A, Gˇmez-Navarro, J.J., Ara˙jo M.F., Freitas M.C., Trigo R.M., Blake W.H., Moreno F.
Estuarine, Coastal and Shelf Science, 218, pp. 106-118, DOI: http://doi.org/10.1016/j.ecss.2018.11.030

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Abstract

New paleoclimatic data from the Casa Branca salt marsh, in the southwest coast of Portugal, are compared with records previously published on the northwest coast (Caminha salt marsh) to offer a more comprehensive overview of the environmental evolution of the west Iberian margin over the last six centuries. These reconstructions are based on the foraminiferal records of two dated sediment cores retrieved from the high marsh settings and supported by geochemical-sedimentological data. Both marshes were originally formed in the AD 1300s, between the Medieval Climatic Anomaly (MCA) and the Little Ice Age (LIA), highlighting a major episode of increased sediment supply in lower estuaries linked to climate-driven changes in continental runoff. Afterwards, the two marshes evolved under different climatic regimes as reflected by their foraminiferal assemblages. The environmental conditions are characterized by higher salinity in Casa Branca (southwest), with Jadammina macrescens and Trochammina inflata as dominant species, than in Caminha (northwest), where Haplophragmoides spp. dominates. We suggest that a long-term trend of a net gain in evapotranspiration at Casa Branca inducing a higher marsh salinity baseline may explain this microfaunal contrast. Trochammina inflata seems to be a good indicator of drier periods in the studied area, connected to key events of aeolian large-dust input to the southwest coast of Portugal. The influence of the most important climate drivers was assessed, namely external (solar) and internal (North Atlantic Oscillation ľ NAO) forcings. Spectral and wavelet transform coherence analyses were used to detect solar footprints on foraminiferal and climate-related time series. A main significant quasi-periodicity was identified within the range of the secular Gleissberg cycle of solar activity modulating the annual NAO and regional spring-summer (simulated) temperatures after AD 1700. This stronger solar-climate coupling may be related to the known upward secular trend in the total solar irradiance after the Maunder Minimum.