Alkaline leaching characteristics of biogenic opal in Eocene sediments from the central Arctic Ocean: a case study in the ACEX cores
Accurate knowledge of the extent of biogenic opal preservation in marine sediment cores is important for paleoceanographic reconstructions. The alkaline leaching method is widely employed for %biogenic opal analysis due to its ease and speed. In this study, a revised method for measuring %biogenic opal in sediment from arctic coring expedition samples was suggested. The studied middle Eocene sediments from the central Arctic Ocean presented a problem in insufficiently leaching biogenic opal with a Na2CO3 solution. Based on XRD analysis, it was suggested that such an alkaline resistance results from slight diagenesis of biogenic opal. In order to solve this problem, an alkaline leaching method utilizing a 2 M NaOH solution was suggested for the accurate measurement of %biogenic opal in the Eocene sediments from the central Arctic. Furthermore, dissolution rates from lithogenic matter by NaOH solution were measured in order to correct the %biogenic opal values.
KeywordsBiogenic opal Arctic Ocean Eocene Alkaline extraction Opal-CT Diagenesis IODP expedition 302 Marine sediments
We thank Co-Chief Scientists Jan Backman and Kate Moran for leading the ACEX with success. We also thank the ACEX fellow scientists, Captains, and crew on board R/V Oden, D/V Vidar Viking, and I/B Sovietsky Soyuz. This work has benefited from the following funding: MEXT Grants-in-Aid-for Scientific Research B1 Project No. 13440152, B2 Project No. 15310001, and JSPS B Project No. 17310009.
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