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doi:10.2204/iodp.proc.302.202.2008

Evaluating the spliced record

Prior to ACEX, a number of expeditions to the central Arctic Ocean recovered shallow-penetrating cores from the Lomonosov Ridge. These include two cores collected near the ACEX sites: Core 96/12-1PC, a 7.22 m long piston core recovered at 87.10°N, 144.77°W in 1996 (Jakobsson et al., 2000, 2001, 2003), and Core PS-2185-6, a 7.68 m long core acquired using a square-barreled Kastenlot gravity corer from 87.53°N, 144.17°W (Fütterer, 1992) (Fig. F1). These cores have been extensively studied (Jakobsson et al., 2000, 2001, 2003) and integrated into pan-Arctic studies of paleoenvironmental change (Spielhagen et al., 2004). These cores provide an additional resource for stratigraphically aligning the near-surface material from ACEX.

Bulk density and magnetic inclination data from ACEX, Cores 96/12-1PC (courtesy of Martin Jakobsson, Stockholm University), and PS-2185-6 (available from www.pangaea.de/​PangaVista) are shown in Figure F4. Despite the difference in depth scales, bulk density and magnetic inclination records from these three “sites” are remarkably similar. The most obvious observation is that, given the ties in Figure F4, sedimentation rates at Cores 96/12-1PC and PS-2185-6 were substantially lower than at the ACEX sites. Thus, material spliced into the ACEX composite record is recovered at these other sites within a single core and can be used to assess the quality of the splicing process.

In the uppermost 10 mbsf, two regions of the published composite ACEX record appear to deviate from the piston cores. Both regions fall on tie points made in the splicing process, suggesting that the differences may be related to an error in the stratigraphic correlation procedure and the development of the mcd scale for ACEX (Fig. F4). Ideally, for the purpose of stratigraphic correlation, cores from adjacent holes are vertically offset so that the top of a core from “Hole B” falls midway between a core at an equivalent depth in “Hole A.” This maximizes the amount of material for cross-correlation and avoids reliance on tie points that fall close to the ends of cores where disturbances are generally most pronounced. During ACEX the amount of overlap between Cores 302-M0003A-1H and 2H and Cores 302-M0004C-1H and 2H was negligible in both the mbsf and mcd scales (i.e., the top and base of Core 302-M0004C-2H closely correspond to the top and base of 302-M0003A-1H). Intervals containing discrepancies between the ACEX composite and records from the other piston cores correspond to intervals in the spliced record where two or more cores overlapped, but only at the very ends.