Reassessing the role of temperature in precipitation oxygen isotopes across the eastern and central United States through weekly precipitation-day data

Air temperature is correlated with precipitation oxygen isotope (delta O-18(prcp)) variability for much of the eastern and central United States, but the nature of this delta O-18(prcp)-temperature relationship is largely based on data coarsely aggregated at a monthly resolution. We constructed a database of 6177 weeks of isotope and precipitation-day air temperature data from 25 sites to determine how more precise data change our understanding of this classic relationship. Because the delta O-18(prcp)-temperature relationship is not perfectly linear, trends in the regression residuals suggest the influence of additional environmental factors such as moisture recycling and extratropical cyclone interactions. Additionally, the temporal relationships between delta O-18(prcp) and temperature observed in the weekly data at individual sites can explain broader spatial patterns observed across the study region. For 20 of 25 sites, the delta O-18(prcp)-temperature relationship slope is higher for colder precipitation than for warmer precipitation. Accordingly, northern and western sites with relatively more cold precipitation events have steeper overall relationships with higher slope values than southeastern sites that have more warm precipitation events. Although the magnitude of delta O-18(prcp) variability increases to the north and west, the fraction of delta O-18(prcp) variability explained by temperature increases due to wider annual temperature ranges, producing stronger relationships in these regions. When our delta O-18(prcp)-temperature data are grouped by month, we observe significant variations in the relationship from month to month. This argues against a principal causative role for temperature and suggests the existence of an alternative environmental control on delta O-18(prcp) values that simply covaries seasonally with temperature. Plain Language Summary In the eastern and central United States, the oxygen isotope ratio of rain or snow is linked to the air temperature while it rains or snows: warmer temperatures have higher isotope ratios and colder temperatures have lower isotope ratios. If we have a record of these isotope ratios dating back into the past, we can estimate how the weather has changed for a given location over time. However, we need a solid understanding of how isotope ratios are controlled in the present day in order to make any estimations about the past. Previous research studying the present day effect of air temperature on isotope ratios have used databases that average an entire month of weather and isotope ratios. This blurs out any possible effects from short-term weather changes. Our study uses a newly-created database with nearly 6200 weekly precipitation samples that better capture rapid weather changes and any resulting effects on isotope ratios. The high number of samples in this database also lets us learn why different sites have different relationships between temperature and isotope ratios depending on their geography and season. Our improved understanding of these relationships can now help produce better estimates of past weather changes.