14C AMS wiggle matching of raised bog deposits and models of peat accumulation

High-resolution Accelerator Mass Spectrometer (AMS) C-14 dates of selected plant macrofossils from the raised bog Engberts-dijksvenen (Eastern Netherlands) show century-scale wiggles analogous to the radiocarbon calibration curve. We used three relative time scales, viz., based on depth, mass, and pollen concentration, respectively, to match the peat AMS dates to the calibration curve. This procedure is repeated for one conventionally dated core. For each relative time scale, realistic confidence intervals are calculated. Depth appears to be the best time scale for certain stratigraphical units of a core. This justifies using depth for wiggle matching conventionally dated mire cores published by others, even when C-14 errors are larger. Our evidence shows four major sources of C-14 variation for mire deposits compared to treerings: (1) dating error, due to sample composition. This includes a reservoir effect demonstrated for many bulk peat samples; (2) hiatuses, causing a sudden 'leap' of peat C-14 age; (3) changing accumulation rates, apparent from a break in the slope of the peat C-14 ages; (4) sampling error. These results shed doubt on the assumed continuities in theoretical peat accumulation models. Both mire stratigraphy and changing accumulation rates can be explained in qualitative hydrological terms. More evidence for a previously discovered reservoir effect in bog deposits is presented, though the physical/biological mechanisms remain uncertain. (C) 2000 Elsevier Science Ltd. All rights reserved.