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 (δ 18 O prcp ) variability for much of the eastern and central United States, but the nature of this δ 18 O 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 δ 18 O 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 δ 18 O 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 δ 18 O 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 δ 18 O prcp variability increases to the north and west, the fraction of δ 18 O prcp variability explained by temperature increases due to wider annual temperature ranges, producing stronger relationships in these regions. When our δ 18 O 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 δ 18 O prcp values that simply covaries seasonally with temperature.