DOI: 10.1594/pangaea.773254
title: AMS C-14 ages of coretops collected on RRS Charles Darwin cruise CD159, July 2004, N. Atlantic, for the NERC RAPID programme

description: Material and data were collected at 41 sites in the subpolar North Atlantic Ocean between Scotland and Newfoundland, during the RRS CharlesDarwin CD159 cruise in July 2004 (McCave, 2005). Sites were selected to reflect the major inputs of water that becomes the North Atlantic Deep Water (NADW); the Iceland-Scotland Overflow Water (ISOW), the Denmark Strait Overflow Water (DSOW) and the Labrador Sea Water (LSW). Areas cored were the south Iceland Rise, SE Greenland slope/rise and Eirik Drift, and the Labrador margin. A total of 29 box cores, 19 piston cores, 6 kasten cores, 9 short gravity cores and 20 CTD casts as well as 28 surface water samples were collected during the cruise. Here we present sediment core-top sample ages. The cores were sampled at 1 or 0.5 cm intervals and we used the top 1 or 2 cm, depending on availability of foraminifera in the samples. Sediment samples were disaggregated on an end-over-end wheel, wet sieved at &gt;63 um, and dry sieved to 63-150 and &gt;150 um. Accelerator Mass Spectrometer (AMS) radiocarbon dating was done for each core top based on between 900-1600 monospecific planktonic foraminifera (Globigerina bulloides or Neogloboquadrina pachyderma (sinistral)). All dates were of modern or late Holocene age except site RAPID-08-5B (9806 ± 38 uncorrected 14C years BP) and site RAPID-14-10B (11543 ± 40 uncorrected 14C years BP). The &gt;150 um fraction was split until approximately 300 foraminifera remained and counted for number of lithic grains, benthic foraminifera, planktonic foraminifera and foraminifera fragments. In all but the shallowest sample (Greenland rise, 761m water depth) benthic foraminifera constituted less than 2% of the total &gt;150 um fraction of the sample.
description: 1. 14C results have been normalised to d13C [per mil PDB] -25 using the d13C values2. Estimated d13C value - insufficient sample material for an independent d13C measurement3. Absolute % Modern involves a mathematical adjustment to account for ongoing radioactive decay of the international reference standard (oxalic acid) since AD 1950. (Stuiver and Polach, Radiocarbon vol.19 No.3, pp.355-363). This method of reporting may be used for modelling 14C and/or for 14C results which are greater than 100% modern 14C.4. Sample RAPiD-27-15B, SUERC-16529, 0-1cm contained 300 µg C and was too small for routine analysis. The sample was prepared to graphite using a dedicated vacuum line" for small samples and analysed on the 5MVAMS at low current. The 13C/12C ratio for this sample was measured on the SUERC AMS during 14C determination and used to model the d13C value by comparison to the Craig (1957) 13C/12C value for PDB. This value is shown in brackets and was considered the most appropriate to normalise 14C data to d13C [per mil VPDB] = -25, but is not necessarily representative of the d13C in the original sample material. The sample was too small for acid etching (usually carried out for shells to remove the outer shell surface) prior to hydrolysis to CO2.5. Samples RAPiD-08-5B and RAPiD-14-10B: These two old ages come from sites under the core of the deep western Boundary current south of Iceland and have a winnowed surface: 5B was only a surface scrape from a hard bottom, and 10B was 'gravelly' in part.