Using A Paired Chironomid Delta O-18 And Aquatic Leaf Wax Delta H-2 Approach To Reconstruct Seasonality On Western Greenland During The Holocene

The Arctic hydrological cycle is predicted to intensify as the Arctic warms, due to increased poleward moisture transport during summer and increased evaporation from seas once ice-covered during winter. Records of past Arctic precipitation seasonality are important because they provide a context for these ongoing changes. In some Arctic lakes, stable isotopes of oxygen and hydrogen (delta O-18 and delta H-2, respectively) vary seasonally, due to seasonal changes in precipitation delta O-18 and delta H-2. We reconstruct precipitation seasonality from Lake N3, a well-dated lake sediment archive in Disko Bugt, western Greenland, by generating Holocene records of two proxies that are produced at different times of the year, and therefore record different lake water seasonal isotopic compositions. Aquatic plants synthesize waxes throughout the summer, and their delta H-2 reflects winter-biased precipitation delta H-2 at Lake N3, whereas chironomids synthesize their head capsules between late summer and winter, and their delta O-18 reflects summer-biased precipitation delta O-18 at Lake N3. During the middle Holocene at Lake N3, aquatic plant leaf wax was strongly H-2-depleted, while chironomid chitin was O-18-enriched. We guide interpretations of these records using sensitivity tests of a lake water and energy balance model, where we change precipitation amount and isotope seasonality inputs. The sensitivity tests suggest that the contrasting trends between proxies were likely caused by an increase in precipitation amount during all seasons and an increase in precipitation isotope seasonality, in addition to proxy-specific mechanisms, highlighting the importance of understanding lake- and proxy-specific systematics when interpreting records from sediment archives.