Speleothem annual layers revealed by seasonal SIMS δ 18O measurements

Abstract

In-situ seasonal δ 18 O measurements of section 236.3-235.6 cm of speleothem HS4, from Qingjiang Valley of the Middle reaches of Yangtze River, China, were performed by an Secondary Ionization Mass Spectrometry (SIMS) with Oka (Chinese primary calcite standard GBW04481) and UWC-3 (international calcite standard from University of Wisconsin). The potential of using SIMS δ 18 O measurements to establish speleothem time series has been explored and the differences between conventional and SIMS δ 18 O values have been discussed. During a 3-day period, UWC-3 δ 18 O has been measured on Cameca IMS 1280 Ion Microprobe Mass Spectrometer against "Oka" external standard. The measured mean value of UWC-3 (δ 18 O VPDB = 17.85‰±0.22‰, 1SD) matches well with its recommended value (δ 18 O VPDB =17.83‰0.08‰), suggesting that the instrument was stable. The same method applied on HS4 produced δ 18 O measurements at seasonal resolution with distinct annual cycles and the total cycle number in agreement with that from Mg/Ca cycles and lamination layer counting of the same section, so it offers an alternative for accessing speleothem time series. However, compared with conventional δ 18 O values of HS4, SIMS δ 18 O values are more negative by 0.90‰ with larger seasonal variation. The main reasons might come from the micro-cracks, micro-pores or liquid inclusions existing in HS4, and organic materials in the speleothem might be another factor affecting the SIMS δ 18 O values, indicating that to obtain reliable speleothem SIMS δ 18 O values, both compaction and purity of samples are crucial.

A new Chinese national reference material (GBW04481) for calcite oxygen and carbon isotopic microanalysis

“…The 18 O/ 16 O and 13 C/ 12 C ratios are normalized by VPDB values ( 18 O/ 16 O = 0.0020672, 13 C/ 12 C = 0.0112372), 34 and the results are shown with δ notation. Detail analysis data can be found in Appendix S1.…”

“…Carbonate geochemistry and isotope compositions are the most important tracers for studies of paleoceanography, paleoenvironment and paleoclimate changes . Isotopic variations at micrometer scales are robust archives for reconstructing palaeoenvironment and paleoclimate changes at annual and seasonal resolution or even higher temporal resolution …”

“…[8][9][10][11] Isotopic variations at micrometer scales are robust archives for reconstructing palaeoenvironment and paleoclimate changes at annual and seasonal resolution or even higher temporal resolution. [12][13][14][15][16][17][18] SIMS (secondary ion mass spectrometer) is thought to be the most powerful technique for high-precision stable isotopic analysis at micrometer scales. However, matrix effects are demonstrated as the major limitations of SIMS carbonate isotopic microanalysis.…”

Comparison of δ18O analyses on individual planktic foraminifer (Orbulina universa) shells by SIMS and gas-source mass spectrometry

“…The inter-instrument differences reported in this study may arise from both GSMS analyses entailing acid digestion of whole shells and in situ SIMS analyses that subsample micrometer-scaled domains within an individual shell. Differences in paired SIMS-GSMS δ 18 O measurements of biogenic carbonates and speleothems have been previously reported, but the magnitude of the difference appears to vary with investigative procedures and the type of carbonate analyzed (Treble et al, 2007;Hanson et al, 2010;Allison et al, 2010;Orland, 2012;Liu et al, 2015;Orland et al, 2015). Such comparisons of SIMS and GSMS δ 18 O values have revealed correlations to mineralogy (calcite, aragonite), sample age, and OH/O (Orland et al, 2015).…”

“…The ultra-high spatial resolution (~1-10 μm) of SIMS analyses permits isolated measurement of δ 18 O in only the desired domain of an individual shell, and has been used to quantify the effects of diagenesis on the δ 18 O of fossil planktic foraminifer shells and delineate intra-shell δ 18 O signals that reflect experimentally induced geochemical bands in cultured planktic foraminifers (Vetter et al, 2013). SIMS has T likewise been used to interrogate micrometer-scale δ 18 O variability in carbonate materials as varied as corals (Rollion-Bard et al, 2007;Allison et al, 2010), nautiloids (Linzmeier et al, 2016), bivalves (Vihtakari et al, 2016), otoliths (Weidel et al, 2007;Hanson et al, 2010), and speleothems (Kolodny et al, 2003;Treble et al, 2007;Orland et al, 2009;Liu et al, 2015).…”