Reconstructing Arctic Precipitation Seasonality Using Aquatic Leaf Wax δ2H in Lakes With Contrasting Residence Times

Arctic precipitation is predicted to increase this century. Records of past precipitation seasonality provide baselines for a mechanistic understanding of the dynamics controlling Arctic precipitation. We present an approach to reconstruct Arctic precipitation seasonality using stable hydrogen isotopes (delta H-2) of aquatic plant waxes in neighboring lakes with contrasting water residence times and present a case study of this approach in two lakes on western Greenland. Residence time calculations suggest that growing season lake water delta H-2 in one lake reflects summer precipitation delta H-2, while the other reflects amount-weighted annual precipitation delta H-2 and evaporative enrichment. Aquatic plant wax delta H-2 in the summer lake is relatively constant throughout the Holocene, perhaps reflecting competing effects of local summer warmth and increased distal moisture transport due to a strengthened latitudinal temperature gradient. In contrast, aquatic plant wax delta H-2 in the mean annual lake is 100 parts per thousand H-2 depleted from 6 to 4 ka relative to the beginning and end of the record. Because there are relatively minor changes in summer precipitation delta H-2, we interpret the 100 parts per thousand H-2 depletion in mean annual precipitation to reflect an increase in winter precipitation amount, likely accompanied by changes in winter precipitation delta H-2 and decreased evaporative enrichment. Thus, unlike the summer lake, the mean annual lake records changes in winter precipitation. This dual-lake approach may be applied to reconstruct past changes in precipitation seasonality at sites with strong precipitation isotope seasonality and minimal lake water evaporative enrichment.