The iBox-FC: A new containment vessel for Itrax X-ray fluorescence core-scanning of freeze cores

A combination of Itrax micro-X-ray fluorescence core scanning (μXRF-CS) and freeze coring can facilitate the development of high-resolution (e.g. sub-decadal) paleoclimate records in lacustrine systems where low sedimentation rates and poorly consolidated “colloidal soup” at the sediment/water interface prevents retrieval and Itrax-μXRF-CS analysis of undisturbed cores using conventional gravity corers. The iBox-FC containment vessel described and tested here delays thawing of highly perishable freeze cores for up to two hours, providing adequate time to carry out high-resolution Itrax-μXRF-CS analysis. The iBox-FC is comprised of an open-topped Styrofoam box divided into chambers using high-density polyethylene (HDPE) that are filled with freeze pack gel. When the vessel is frozen, core slabs up to 13 cm long may be positioned into a central chamber and then scanned following normal Itrax-μXRF-CS methodology. To test the reliability of μXRF-CS analysis obtained from frozen sediments, a freeze core recovered from Control Lake, Northwest Territories, Canada, was sub-sectioned and analyzed using μXRF-CS and then subsampled for ICP-MS following near-total acid digestion. Comparison of μXRF-CS and ICP-MS results showed strong correlations (R2 > 0.8) for six of nine elements calibrated, and moderate correlations (R2 > 0.3) for the remaining three. Additive log-ratio transformation of data minimized specimen, matrix and edge effects associated with the high porewater contents of the freeze cores and slight melting of the sediment during analysis. These analytical effects had more impact on the lower concentration elements (As, Zn, Ni, Cu) than the higher concentration elements (Ti, K, Mn, Fe, Ca).