Seasonal precipitation variability on Svalbard inferred from Holocene sedimentary leaf wax δ2H

Abstract

Svalbard spans large climate gradients, associated with atmospheric circulation patterns and variations in ocean heat content and sea ice cover. Future precipitation increases are projected to peak in the northeast and to mainly occur in winter, but uncertainties underscore the need for reconstructions of long-term spatial and temporal variations in precipitation amounts and seasonality. We use lipid biomarkers from four sedimentary lake records along a climatic gradient from western to northeastern Svalbard to reconstruct Holocene water cycle changes. We measured the leaf wax hydrogen isotopic composition of long-chain (terrestrial) and mid-chain (aquatic) n-alkanoic acids, reflecting δ²H of precipitation (δ²H_precip) and lake water (δ²H_lake), respectively. δ²H_precip values mainly reflect summer precipitation δ²H and evapotranspiration, whereas δ²H_lake values can reflect various precipitation seasonality due to varying lake hydrology. For one lake, we used the difference between δ²H_precip and δ²H_lake (ε_precip-lake) to infer summer evapotranspiration changes. Relatively ²H-enriched δ²H_precip values and higher ε_precip-lake in the Early and Middle Holocene suggest warm summers with higher evapotranspiration, and/or more proximal summer moisture. After c. 6 cal. ka BP, ²H-depleted δ²H_precip values and lower ε_precip-lake indicate summer cooling, less evapotranspiration, or more distally derived moisture. Early to Middle Holocene decrease in δ²H_lake values in two northern Spitsbergen lakes reflects an increase in the proportion of winter relative to summer precipitation, associated with regional warming and increased moisture supply, which may be due to increased distal moisture supply and/or reduced sea ice cover. Our northern Svalbard δ²H_lake records suggest great Late Holocene climate variability with periodic winter precipitation increases or decreases in summer precipitation inflow to the lakes. We find that Holocene summer precipitation δ²H values mainly follow changes in summer insolation and temperature, whereas the seasonal distribution of precipitation is sensitive to catchment hydrology, regional ocean surface conditions, and moisture source changes.