Multi-proxy approaches to isolating low-frequency climate signals from tree-ring δ13C, δ18O and ring-widths
Abstract
Tree-ring stable isotope records have been increasingly used as climate proxies and have often improved the coherence of climate signals compared to ring-width variability. Here we explore the potential for combining tree ring 13C, 18O and ring-width data to isolate low-frequency climate variation from 1) bur oak trees from mid-continental USA and 2) coastal California redwood trees. For modern mid-continental oaks, Δ13C [carbon isotope discrimination] and Δ18O [isotopic enrichment above source water] are negatively correlated across space and time, conditions representative of the bioclimatic envelope for this species. Correlations with the vapor pressure deficit at the growing season maximum temperature (VPDmax) were greatest for the dual isotopic signal as compared to Δ13C or Δ18O alone (r = 0.79, 0.69 and 0.75, respectively). As applied to 59 sub-fossil oak logs [14C-dated to 9.97-13.64k Cal yrs BP] from Missouri, USA, this dual isotope signal indicates that the Pleistocene-Holocene transition was characterized by an abrupt transition near the end of the Younger-Dryas period from a cold, wet and relatively stable growing season climate to a more variable early Holocene climate characterized by periods of greater growing season VPD and maximum temperatures. Our data further suggest that correlations between Δ13C or Δ18O and ring-width chronologies may provide a record of decadal to multi-decadal variability in VPDmax. For coastal California redwoods, from 1951-2003, we demonstrate drastic differences in both sign and magnitude of 11-year running correlations between northern California regional Δ13C or δ18O chronologies for 'middlewood' or 'latewood' (MW or LW) and a regional ring-width chronology. Comparisons of trends in these correlations to 11-year means of Pacific Decadal Oscillation index (PDO, May-September) show similarities with MW or LW Δ13C (r = 0.70 and 0.53, respectively) and stronger correspondence with inverted MW and LW δ18O (r = 0.74 and 0.94, respectively). However, correlations between the ring-width chronology and a dual isotope chronology, or a composite of the inverted δ18O chronologies more accurately identified the timing of the 1976/77 phase shift in the PDO (r = 0.96 and 0.97, respectively). Hence, our current endeavor of establishing redwood Δ13C, δ18O and ring-width chronologies with annual to sub-annual resolution over the past 1000+ years shows substantial promise for reconstructing low-frequency variation in the PDO across the late Holocene. Taken together, these results paint an exciting picture of the potential for multiple tree-ring proxies to provide novel insights on past climates and climatic drivers.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2013
- Bibcode:
- 2013AGUFMPP23D..05V
- Keywords:
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- 0454 BIOGEOSCIENCES Isotopic composition and chemistry;
- 0473 BIOGEOSCIENCES Paleoclimatology and paleoceanography;
- 1605 GLOBAL CHANGE Abrupt/rapid climate change;
- 1813 HYDROLOGY Eco-hydrology