UTILIZING ORGANIC MATTER TO INTERPRET CLIMATE VARIABILITY IN LAKE VATNSDALSVATN, ICELAND

The stratigraphy of dated sediment cores from Vatnsdalsvatn, a lake in the Westfjörðs region of Iceland, was studied to understand the organic productivity and environmental conditions of the past millennium. Additionally, organic samples from the watershed were analyzed to constrain sediment core proxy data. Vatnsdalsvatn is a north-south trending lake, 3.5 km long and 0.9 km wide with an area of 200 ha and maximum depth of 41 m. The main water supply is from Vatnsdalsá, the major river flowing in and out of the lake. Sediment core analysis was conducted on an archived 70.5 cm freeze core obtained in 1996 (VATN 96-3) and a 34.5 cm gravity core collected in 2011 (VATN11 GC2). Age constraints were acquired from a previously published radiometric age model (VATN 96-4), that was stratigraphically correlated to the cores reported here. Core sediment was analyzed at 5mm resolution, representative of an approximate 7 year temporal resolution. Elemental concentrations of organic carbon, nitrogen, and sulfur as well as the respective isotopic ratios (δ¹³C, δ¹⁵N, and δ³⁴S) were quantified by an EA/IRMS. Volume magnetic susceptibility (MS) was quantified with a Bartington point sensor. Watershed samples analyzed to constrain the elemental/isotopic variability in the sediment cores include particulate matter filtered from the inflows and outflows during select days during the 2012 field season, representative vegetation samples, and soil probe samples. Results reveal two significant conclusions. First, spectral analysis of productivity proxies in the sediment cores indicates significant multi-decadal periodicities. These cycles are likely associated with North Atlantic region teleconnection patterns through a climatic forcing of productivity in the lake combined with variability in the efficiency of terrigenous fluxes to the lake. Second, the upper sediment of the 2011 core contains anomalously high values of MS, %OC, δ¹⁵N, OC/N and OC/S, likely deposited during an episodic flood event known to have occurred in 2008. This observation provides a signature for such events, allowing for the identification of similar events during the past millennium.