Author Posting. © The Author(s), 2016. This is the author's version of the work. It is posted here under a nonexclusive, irrevocable, paid-up, worldwide license granted to WHOI. It is made available for personal use, not for redistribution. The definitive version was published in Climate Dynamics 49 (2017): 143-161, doi:10.1007/s00382-016-3332-z.
Tree rings are natural archives that annually record distinct types of past climate variability
depending on the parameters measured. Here, we use ring-width and stable isotopes in cellulose
of trees from the northwestern Iberian Peninsula (IP) to understand regional summer
hydroclimate over the last 400 years and the associated atmospheric patterns. Spatial correlations
between tree rings and gridded climate products demonstrate that isotope signatures in the
targeted Iberian pine forests are very sensitive to water availability during the summer period,
and are mainly controlled by stomatal conductance. Non-linear methods based on extreme events
analysis allow for capturing distinct seasonal climatic variability recorded by tree-ring
parameters and asymmetric signals of the associated atmospheric features. Moreover, years with
extreme high (low) values in the tree-ring records were characterised by coherent large-scale
atmospheric circulation patterns with reduced (enhanced) moisture transport onto the
northwestern IP. These analyses of extremes revealed that high/low proxy values do not
necessarily correspond to mirror images in the atmospheric anomaly patterns, suggesting
different drivers of these patterns and the corresponding signature recorded in the proxies.
Regional hydroclimate features across the broader IP and western Europe during extreme
wet/dry summers detected by the northwestern IP trees compare favourably to an independent
multicentury sea level pressure and drought reconstruction for Europe. These independent
sources of past climate validate our findings that attribute non-linear moisture signals recorded
by extreme tree-ring values to distinct large-scale atmospheric patterns and allow for 400-yr
reconstructions of the frequency of occurrence of extreme conditions in summer hydroclimate.
research was partially supported by the EU project ISONET (Contract EV K2-2001-00237)
and the EU FP6 project Millennium (GOCE 017008). L.A.H. was supported by the Marie Curie International Outgoing Fellowship PIOF-GA-2009-253277 grant within the FP7-PEOPLE-2009-IOF program. CCU was supported by the the Penzance and John P. Chase
Memorial Endowed Funds and the Investment in Science Fund at WHOI.
Sea Level Pressure (SLP)
Old World Drought Atlas (OWDA)
Woods Hole Open Access Server