Covariation of Precipitation δ18O and Relative Humidity and the Implication for Changing the Atmospheric Circulation Pattern between Glacial and Interglacial Periods
Abstract
It has been demonstrated that the oxygen and hydrogen isotopic compositions of tree rings contain information about the isotopic composition of the source water and the relative air humidity during photosynthesis. More recently, Shu et al. showed that the slope of the δD vs. δ18O plot contains information about covariation between isotopic composition of the source water (or approximately precipitation) and the relative humidity of the atmosphere. If the variation of the precipitation δ18O or δD is independent of the variation in the prevailing relative humidity, the δD vs. δ18O plot of tree rings should have the same slope as that of the meteoric water line. If, on the other hand, the precipitation δ18O is positively (or negatively) correlated with the relative humidity, the δD vs. δ18O plot of tree rings would have a greater (or smaller) slope than that of the meteoric water line. Shu et al. demonstrated a positive precipitation δ18O - relative humidity covariation using cellulose analyses from trees across a precipitation gradient in the Olympic Mountains, Washington, USA. Here we use this concept to compare the δD vs. δ18O relationship in Holocene samples with those from the last glaciation in the mid-latitude continental United States. The data are separated into three groups, Holocene (age < 10 kyr), Glacial (age > 14 kyr) and Transition (10 kyr < age < 14 kyr). We found that during the Holocene the δD vs. δ18O relationship has a slope of 13.7±2.3, significantly greater than the slope of the global meteoric water line of 8. For the last glaciation, the slope is 5.3±0.9, and the slope for the transition period is 4±1.2, both significantly smaller than 8. One possible explanation is a northward extension of the north boundary of the Hadley cell in the northern hemisphere, which would have caused mid-latitude precipitation to be deep convective in nature, producing the amount effect similar to that of low-latitude precipitation today. These results may imply a general circulation pattern in glacial times different from that of interglacial times.
- Publication:
-
AGU Spring Meeting Abstracts
- Pub Date:
- May 2005
- Bibcode:
- 2005AGUSMPP21A..01F
- Keywords:
-
- 1040 Isotopic composition/chemistry;
- 1610 Atmosphere (0315;
- 0325);
- 3309 Climatology (1620);
- 3319 General circulation;
- 3344 Paleoclimatology