A New Analytical Approach to Detect Cryptotephras in Arctic Lake Sediment Cores

Volcanic eruptions produce the most abrupt climate perturbations to the Arctic climate system by altering the Earth's radiative balance. Widespread tephras from explosive eruptions are key marker beds that allow for near-instantaneous chronostratigraphic constraints in terrestrial, marine, and ice archives. In the North Atlantic, Iceland is the foremost source for wide-spread Quaternary tephras. Tephras from select eruptions in Iceland have been detected in marine and terrestrial sediment archives throughout the northern North Atlantic, however their progressively finer dispersal leaves many tephras concealed in distal archives due to their low abundances and fine grain sizes.

New sub-millimeter resolution data acquired by the ITRAX X-ray fluorescence (XRF) core scanner now allows for the detection of cryptotephra – tephra not visible to the naked eye (<80 µm). This study uses the ITRAX mico-XRF scanner to develop a new analytical approach to easily discern cryptotephras in distal lacustrine archives. In order to target cryptotephras in actual sediment cores, “synthetic lake cores” are created to replicate cryptotephra deposition in lacustrine material. These cores use known quantities of archetypal lacustrine sediments, as well as known quantities of cryptotephras from explosive Icelandic eruptions over a range of chemical compositions. The synthetic cores are spiked with cryptotephras at known intervals, and then analyzed with the ITRAX micro-XRF scanner.

ITRAX results indicate the successful detection of cryptotephras within gyttja (organic-rich) laminae in the synthetic cores. Statistical analyses calculate the optimum ratio of diagnostic chemical elements (Ca, K, Ti, Sr, Mn) to constrain and distinguish cryptotephras of varying compositions from its surrounding background materials. This analytical approach is currently being applied to actual lake cores from the Canadian Arctic and other sites distal to Icelandic eruptive centers. Cryptotephras may provide absolute age dating and correlation among sediment records in the Arctic.