Recent attempts to date batches of poorly preserved archaeological bone prompted a re-evaluation of existing protocols for bone sample preparation and ultrafilter cleaning methods at the Keck-Carbon Cycle Accelerator Mass Spectrometer (KCCAMS) facility. The emphasis of the study was to optimize decalcification time and ultrafiltration retention efficiency to improve overall collagen yields, especially for poorly preserved bone. Decalcification time and acid strength tests were done on four in-house bone standards of varying states of preservation. Through systematic testing, we found that 200 mg bone chip samples decalcified in 4 mL of 1.0 N HCl over 16 h showed increases of collagen yield across all samples relative to our existing protocol. Ultrafilters precleaned with weak acid (0.01 N HCl) showed greater retention efficiencies than those cleaned by sonication in ultrapure Milli-Q (MQ) water. Collagen produced from each sample were analyzed via AMS dating to check the quality of the collagen.

New radiocarbon calibration curves, IntCal04 and Marine04, have been constructed and internationally ratified to replace the terrestrial and marine components of IntCal98. The new calibration data sets extend an additional 2000 yr, from 0–26 cal kyr BP (Before Present, 0 cal BP = AD 1950), and provide much higher resolution, greater precision, and more detailed structure than IntCal98. For the Marine04 curve, dendrochronologically-dated tree-ring samples, converted with a box diffusion model to marine mixed-layer ages, cover the period from 0–10.5 cal kyr BP. Beyond 10.5 cal kyr BP, high-resolution marine data become available from foraminifera in varved sediments and U/Th-dated corals. The marine records are corrected with site-specific 14C reservoir age information to provide a single global marine mixed-layer calibration from 10.5–26.0 cal kyr BP. A substantial enhancement relative to IntCal98 is the introduction of a random walk model, which takes into account the uncertainty in both the calendar age and the 14C age to calculate the underlying calibration curve (Buck and Blackwell, this issue). The marine data sets and calibration curve for marine samples from the surface mixed layer (Marine04) are discussed here. The tree-ring data sets, sources of uncertainty, and regional offsets are presented in detail in a companion paper by Reimer et al. (this issue).

It has long been assumed that radiocarbon (Δ14C) content of dissolved inorganic carbon (DIC) is equal to that of particulate organic carbon (POC) in surface seawater; however, little research has been conducted to explicitly test this assumption. Here, we report Δ14C measurements of surface POC samples and compare them with contemporaneous DIC Δ14C measurements from the northeast Pacific Ocean (Hwang et al. 2004; Druffel et al. 2010). Samples were collected from surface waters at Station M off California between 1995 and 2004. The POC Δ14C values decreased 3.2% per year from 1995 to 2004, similar to the decline observed in the DIC Δ14C values during the same period. Overall, our results show no statistical difference between POC and DIC Δ14C—consistent with the assumption that DIC and POC Δ14C values can generally be considered equivalent. However, significant variability was observed for POC Δ14C values during several fall/summer events, where POC Δ14C signatures were lower than DIC Δ14C values. An evaluation of 2 sample pretreatments also suggests that non-homogenized POC samples deviated less from average POC Δ14C values and more closely matched the DIC Δ14C average for the time series. The presence of seasonal POC/DIC Δ14C disagreements, combined with sample processing effects, suggest that infrequent contributions of allochthonous, older carbon may have originated from deeper in the water column, especially during periods when upwelling in this area was prominent.

This paper describes the methods used to develop the Cariaco Basin PL07-58PC marine radiocarbon calibra- tion data set. Background measurements are provided for the period when Cariaco samples were run, as well as revisions lead- ing to the most recent version of the floating varve chronology. The floating Cariaco chronology has been anchored to an updated and expanded Preboreal pine tree-ring data set, with better estimates of uncertainty in the wiggle-match. Pending any further changes to the dendrochronology, these results represent the final Cariaco 58PC calibration data set.

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