Micro‐CT Scanning of Tests of Three Planktic Foraminiferal Species to Clarify DissolutionProcess and Progress. (12th December 2019)

• Record Type: Journal Article
• Authors: Iwasaki, S.; Kimoto, K.; Okazaki, Y.; Ikehara, M.
• Is Part Of: Geochemistry, geophysics, geosystems. Volume 20:Number 12(2019)
• Page Start: 6051
• Page End: 6065
• Publication Date: 2019-12-12
• Subjects: planktic foraminifera -- X‐ray micro‐CT -- carbonate dissolution; Geochemistry -- Periodicals; Geophysics -- Periodicals; Earth sciences -- Periodicals; 550.5
• DOI: 10.1029/2019GC008456
• Languages: English
• ISSNs: 1525-2027

Abstract

Abstract: Evaluation of foraminiferal test dissolution in deep‐sea sediments facilitates reconstruction of seawater chemistry. Here we observed test dissolution processes of the planktic foraminifera Trilobatus sacculifer, Globigerinoides ruber, and Neogloboquadrina dutertrei from midlatitudes of the western North Pacific; in these three species, we tested the ability of a new dissolution index using data from X‐ray micro‐computed tomography scanning. Although the dissolution process of foraminiferal tests differed slightly among species, dissolution of all species was equally assessed by the calcite density distribution (%Low‐CT‐number calcite volume) calculated from the CT number histogram. In T. sacculifer and G. ruber, the test area density, a conventional proxy for assessing test condition based on weight measurement, is affected by variations in the thickness of the outermost chamber wall; thus, this conventional proxy can be affected by sea surface conditions during test calcification. In contrast, the relationship between the %Low‐CT‐number calcite volume of tests and the deep seawater calcite saturation state suggests that X‐ray micro‐computed tomography scanning is applicable for evaluating the intensity of foraminiferal test dissolution at the undersaturated deep seafloor in this area and is an invaluable proxy for detecting deep seawater carbonate ion concentration changes on glacial‐interglacial timescales. Key Points: Dissolution process of planktic foraminiferal tests was observed by X‐ray micro‐computed tomography Progression of test dissolution was assessed by using a new index based on X‐ray micro‐computed tomography‐number histograms The conventional proxy of test area density is considered to be controlled by factors other than deep seawater saturation state