Interpreting inter- and intra-annual environmental signals in tree-ring δ18O using isotope-enabled modeling

Area of Science:

• Dendrochronology
• Isotope Geochemistry
• Paleoclimatology

Background:

• Interpreting tree-ring oxygen isotopes (δ18Oring) is complex due to combined influences from source water (δ18Osw) and relative humidity (RH).
• Accurate climate reconstruction from tree rings requires disentangling these environmental signals.

Purpose of the Study:

• To investigate intra- and inter-annual δ18Oring signals in Scots pine stands in Finland.
• To disentangle the influences of RH and δ18Osw on δ18Oring using correlation analysis and process-based modeling.
• To evaluate the role of oxygen exchange and xylogenesis in δ18Oring interpretation.

Main Methods:

• Correlation analysis of δ18Oring, δ18Osw, and RH data from Scots pine (2010-2019).
• Process-based modeling of intra-annual δ18O and δ13C incorporating xylogenesis and oxygen exchange.
• Dual isotope modeling to assess uncertainties related to xylogenesis.

Main Results:

• δ18Oring signals were primarily dominated by RH due to its higher variability compared to δ18Osw.
• Inter-annual correlations were generally stronger than intra-annual correlations.
• Seasonal variations in oxygen exchange influence intra-annual δ18Oring signals, complicating direct RH interpretation.

Conclusions:

• Relative humidity is the dominant driver of δ18Oring signals at inter-annual scales.
• Incorporating variable oxygen exchange improves mechanistic model performance for δ18Oring.
• Accurate dating of tree-ring subsections and understanding oxygen exchange are crucial for robust intra-annual isotope-based climate reconstructions.