NOAA/WDS Paleoclimatology - Lake N3, Greenland 7,800 Year Chironomid d18O Data

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 (d18O and d2H, respectively) vary seasonally, due to seasonal changes in precipitation d18O and d2H. 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 d2H reflects winter-biased precipitation d2H at Lake N3, whereas chironomids synthesize their head capsules between late summer and winter, and their d18O reflects summer-biased precipitation d18O at Lake N3. During the middle Holocene at Lake N3, aquatic plant leaf wax was strongly 2H-depleted, while chironomid chitin was 18O-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.