SEDIMENTOLOGICAL APPROACH TO STORM SURGE AND FLOOD IDENTIFICATION IN A CLIMATE SENSITIVE ICELAND LAKE

Compiled historical records of storm surge and flooding events in Iceland have revealed major impacts to coastal communities all over the country. These events are preserved in the sediment record of a back-barrier lake, Rekavíkurvatn (Rekavík: 66°24'50.40"N, 23° 1'47.06"W, 1m), in northwest Iceland. Because of its proximity to the North Atlantic Ocean and near sea level elevation, Rekavík is extremely sensitive to storm surge inflows. Normally a freshwater lake, Rekavík is likely to experience large magnitude hydrodynamic changes from barrier over-wash events. Evidence of periodic marine incursion is supported by the alternating presence/absence of marine bivalve shells in the sediment core REK96-6. Here we distinguish probable storm surge and flood events and compare them with historic flood records (provided by Björn Erlingsson, Icelandic Meteorology Office). To identify these changes, we investigate sediment cores from field seasons in 1996, 2012 and 2013, using particle-size distribution, frequency dependent magnetic susceptibility (FDMS), loss-on-ignition (LOI), ICP-OES geochemistry, and ²¹⁰Pb and AMS ¹⁴C dating. Preliminary interpretations of ICP geochemistry suggest two events affecting the sediment characteristics in cores REK13-PSU1 (at 18 cm and 35 cm) and REK13-PSU2 (at 13 cm and 27 cm). The more recent event, at 18 cm and 13 cm, respectively, is concurrent with a time period of frequent storm surge and flooding in northwest Iceland (1895-1925 A.D.), documented in historical records. This interval in the cores is marked by increased sediment accumulation, according to ²¹⁰Pb results, median particle-sizes of 11.5 µm, increases in Mn and Fe concentrations, Al/Ti values, and FDMS, and decreases in LOI. The earlier event is marked by increases in K, Mn, Na, and Sr concentrations and increased FDMS, decreases in Fe/Mn and Ca/Sr ratios and slightly coarser median particle-sizes (13.5 µm). Additional statistical analysis on specific parameters in the sediment record might serve to distinguish storm surge from terrestrial flooding.