Leaf Wax Hydrogen Isotopes Provide Insight into Hydrologic Changes During the Little Ice Age on Svalbard

Abstract:

Hydroclimate changes are an important aspect of arctic climate variability and are coupled to other components of the Arctic system, such as sea ice extent and modes of atmospheric circulation. Here we examine past hydroclimate change on Svalbard, where regional climate is associated with northern North Atlantic oceanic and atmospheric circulation dynamics. We measured the hydrogen isotopic composition of leaf waxes from a lake sediment core collected from NW Svalbard (Amsterdamøya; 79.77°N, 10.76°E). δD values were measured at sub-centennial scale resolution spanning the last 2,000 years on long-chain n-alkanes (n-C₂₉, n-C₃₁). δD of n-C₂₉ and n-C₃₁ range from -180 to -194‰ and -173 to -195‰, respectively, and are strongly correlated. There is little variability in the δD from AD 100-1250. However starting at c. AD 1250, there is a gradual increasing trend that continues until c. AD 1800. After c. AD 1800 values increase sharply and are more variable up to the present. In many Arctic regions, temperature appears to be the primary control on precipitation isotopes. On Svalbard, previous studies have shown that regional precipitation isotopes can also be influenced by the delivery of moisture from the south. If the trends in our data were interpreted as a response to temperature, the records would suggest increasing temperatures starting at AD 1250, which is at odds with regional air and sea-surface temperature reconstructions that generally show cooling associated with the Little Ice Age. Therefore, the increase in δD at these sites more likely reflects changes in either the seasonality of precipitation, or a change in the trajectory of air masses delivering precipitation to the region. We examine the possibility for these changes by assessing trends in local water isotopes from modern observations and from isotope-enabled GCM output for the region.