Comparison of Large and Ultra-Small Δ¹⁴C Measurements in Core Top Benthic Foraminifera from the Okhotsk Sea

Abstract

ABSTRACT. The radiocarbon activity of benthic foraminifera was investigated in surface sediments from a high deposition rate location at a depth of 1000 m in the Okhotsk Sea. Sediments were preserved and stained with Rose Bengal to identify foraminifera that contain cytoplasm. The benthic fauna at this site is dominated by large specimens of Uvigerina peregrina, and bulk samples (~150 individuals) of stained and unstained specimens were dated. The stained sample was about 240 14 C yr younger than the unstained, and the presence of bomb 14 C is inferred by comparison to water column data in the nearby open North Pacific. Using new methods, multiple measurements were also made on samples of three stained and unstained individuals (as small as 7 µg C). Results are consistent with those from the bulk samples. This suggests that similar ultra-small measurements could be made at other locations to reveal the age distribution of individuals in a sediment sample in order to assess the extent of bioturbation and the presence of bomb 14 C contamination.

Moving beyond the age–depth model paradigm in deep-sea palaeoclimate archives: dual radiocarbon and stable isotope analysis on single foraminifera

“…Many recent such studies (e.g. Barker et al, 2015;Caley et al, 2012;Simon et al, 2016) use tuning to the LR04 (Lisiecki and Raymo, 2005) benthic stack to produce an age-depth chronology. We have rerun our single-foraminifera sedimentation simulation using the average SAR of LR04 (3.9 cm ka −1 ) and found that one could expect a relative 68.2 % age range of −1330 to 2950 yr for discrete 1 cm depth intervals.…”

Ultra-Small Graphitization Reactors for Ultra-Microscale 14C Analysis at the National Ocean Sciences Accelerator Mass Spectrometry (NOSAMS) Facility

“…These authors suggest that measurements of individual foraminiferal tests would allow for the magnitude of the bioturbation effect to be investigated in different sedimentary settings. To demonstrate our ability to measure small numbers of foraminiferal tests, we analyzed live-stained and unstained benthic foraminifera (Uvigerina) from the sediment-water interface from the Sea of Okhotsk (Keigwin and Gagnon 2015) and compared the results with previously measured bulk 14 C dates ( Figure 10). The bulk 14 C ages of stained (1530 ± 25 yr BP) and unstained (1770 ± 65 yr BP) tests were measured on 2.5 mg CaCO 3 , or approximately 150 individual tests.…”

“…There is reasonable agreement between small numbers (three individuals that generated 12 µg C) of stained foraminifera and the bulk 14 C age, yet greater variability with the unstained comparison results. This variability issue, along with procedures used and other details are specifically outlined in Keigwin and Gagnon (2015). Error bars on ultra-microscale samples are inflated due to the relatively low count rates measured on the samples before the graphite in each target was completely ionized.…”

“…These authors suggest that measurements of individual foraminiferal tests would allow for the magnitude of the bioturbation effect to be investigated in different sedimentary settings. To demonstrate our ability to measure small numbers of foraminiferal tests, we analyzed live-stained and unstained benthic foraminifera (Uvigerina) from the sediment-water interface from the Sea of Okhotsk (Keigwin and Gagnon 2015) and compared the results with previously measured bulk Figure 10 were corrected for both a hydrolysis and graphite process blank, utilizing the values expressed in this manuscript. There is reasonable agreement between small numbers (three individuals that generated 12 µg C) of stained foraminifera and the bulk 14 C age, yet greater variability with the unstained comparison results.…”

Moving beyond the age-depth model paradigm in deep sea palaeoclimate archives: dual radiocarbon and stable isotope analysis on single foraminifera

“…Subsequently, high resolution sampling of core depth does not necessarily translate into high resolution sampling of time. Researchers are aware that the concealment of intra-sample age heterogeneity can pose problems for the age-depth model method (Bard, 2001;Keigwin and Gagnon, 2015;Löwemark and Grootes, 2004;Löwemark and Werner, 2001; 45 Pisias, 1983;Ruddiman and Glover, 1972), which can potentially lead to incorrect interpretation of temporal climate offsets, or apparent 14 C age offsets between different species and/or sizes of foraminifera that are, in fact, an artefact of PDSM (Löwemark et al, 2008;Löwemark and Grootes, 2004). With these problems in mind, researchers seeking to reconstruct rapid (i.e.…”