Solar forcing for nutricline depth variability inferred by coccoliths in the pre-industrial northwestern Mediterranean

Alessandro Incarbona*, Sergio Bonomo, Isabel Cacho, Fabrizio Lirer, Giulia Margaritelli, Delia Pecoraro, Patrizia Ziveri

*Autor corresponent d’aquest treball

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Resum

The oceanic system has been rapidly changing under human-induced climate change that is taking place at unprecedented rates. The paleoclimate archive of the last two millennia is often adopted to discern the ongoing anthropogenic global warming from the pre-industrial natural climate variability. The Mediterranean Sea is an especially critical system, being particularly affected by climate change. A common group of marine unicellular planktonic calcifiers, coccolithophores, are forming calcite plates, coccoliths. When reaching the sediments, they have been employed as a proxy in many paleoenvironmental reconstructions and are increasingly used in the last centuries. Recent studies indicate a subtle response to historical climate changes, except for primary productivity switches during the Little Ice Age and, most importantly, across the Industrial age. In this work, we use coccolith decadal-scale resolution data from core HER-MC-MR3.3, recovered in the Balearic Sea, exploring their variability over the pre-industrial age, from 700 BCE to 1740 CE. Results are compared to planktonic foraminifera stable isotopes, planktonic foraminiferal assemblages, alkenone-derived SSTs and foraminiferal Mg/Ca-derived SSTs, previously acquired in the same sediment core. Abundance variations in coccolith assemblages, expressed as Shannon-Wiener diversity H-index changes or as trends and fluctuations in ecological groups are associated with historical climate changes, among others the Medieval Climatic Anomaly and the Little Ice Age, indicating repeated modifications in surface water conditions, in response to hydrological and atmospheric changing patterns. A tight relationship between deep nutricline and upper water column stratified conditions, derived from high abundance of Florisphaera profunda, and high solar irradiation levels is established. The solar activity fingerprint in the F. profunda distribution pattern is further assessed by spectral analysis, with the emergence of significant periodicities observed in solar activity proxies, among others the well-known de Vries-Suess cycle. Finally, we notice small but statistically significant abundance fluctuations in holococcoliths (solution susceptible coccolith forms) that may be tied to their enhanced preservation during increased rainfall in western Europe. This implies the advection of westerlies and long-lasting blocking events that may have promoted deep-water formation and seafloor ventilation during this time. The comparison with sedimentological proxies of bottom current strength shows some inconsistencies but still defines variable and intermittent deep-water formation rates in the Gulf of Lions over the pre-industrial period.

Idioma originalEnglish
Número d’article104102
Nombre de pàgines15
RevistaGlobal and Planetary Change
Volum224
Data online anticipada29 de març 2023
DOIs
Estat de la publicacióPublicada - de maig 2023

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