SEASONAL TEMPERATURE AND PRECIPITATION AMOUNT RECORDED IN MONTHLY OXYGEN ISOTOPE MEASUREMENTS OF METEORIC WATER

The oxygen isotope composition of meteoric water (δ¹⁸O_MW) is commonly reconstructed from a wide variety of substrates in order to reconstruct mean annual climate at a given site. These reconstructions are based on robust relationships showing that temperature, latitude, altitude, and precipitation all affect δ¹⁸O_MW values. However, a quantitative relationship to assess how seasonal climate affects seasonal changes in δ¹⁸O_MW (Δδ¹⁸O_MW) has not been determined. Here we use the International Atomic Energy Agency’s Global Network of Isotopes in Precipitation database to produce a global relationship relating seasonal climate (i.e., temperature and precipitation) to Δδ¹⁸O_MW. We include in our analysis 365 stations that reported a complete suite of monthly temperature, precipitation, and δ¹⁸O_MW data. From these data, we produced a global relationship between average monthly temperature (T) and average monthly δ¹⁸O_MW value (R = 0.80, n = 4312) and identified a non-linear δ¹⁸O_MW/T gradient that decreases with increasing temperature. This relationship was able to explain most of the variability in Δδ¹⁸O_MW for the sites located >37^o from the equator (R = 0.88, n = 219), but was a poor-predictor of Δδ¹⁸O_MW at all other sites (R = 0.30, n = 146). By incorporating the effect of changes in seasonal precipitation amount (which is greatest in the tropics) to our relationship, we hoped to reconcile the poor fit observed within our low latitude sites. Towards this, we calculated a δ¹⁸O_MW depletion rate = 0.0082 ‰/mm, that when applied to all 365 sites, allowed us to predict the Δδ¹⁸O_MW value for all sites through knowledge of seasonal changes in temperature and precipitation amount (R = 0.83, n = 365). The wide applicability of this relationship to diverse climates and geographic locations makes it particularly relevant towards reconstructing seasonal climate from geologic substrates containing seasonal δ¹⁸O_MW information (e.g., tree-rings, teeth, speleothems).