Micro‐CT Scanning of Tests of Three Planktic Foraminiferal Species to Clarify DissolutionProcess and Progress

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 glacialinterglacial timescales.

Calcification, Dissolution and Test Properties of Modern Planktonic Foraminifera From the Central Atlantic Ocean

“…Overall, although the shells were found to be best preserved below the subtropical gyres, the overall preservation of the scanned specimens was found to be good. This is also manifested by the mild bimodality of the CT number histograms (Iwasaki et al, 2015;Iwasaki et al, 2019) from samples where the highest CTX was recorded (Figures 9C, D). Dissolution primarily affects foraminifera test integrity rather than its outer geometry.…”

X-ray tomographic data of planktonic foraminifera species Globigerina bulloides from the Eastern Tropical Atlantic across Termination II

“…Apart from studies that uses CT analysis to examine biometrical foraminifera parameters [9,10,16] there are studies that can use the pixel's grey levels to extract geochemical environmental information [6] or information about the shell's corrosion state [17]. Knowledge of the degree of shell dissolution is of key importance in the study of foraminifera shell mass CT information is particularly useful in the study of foraminifera shell mass since in order to conclude about the cause behind shell mass changes in the paleoceanographic record it is important to have foraminifera biometric information (cell volumes) and information about the quantity of calcite mass loss to dissolution [13] as well as the degree of contamination due to sediment infilling of chambers, which as shown in the recent study [4] can produce considerable artifact yields.…”

Evidence for late glacial oceanic carbon redistribution and discharge from the Pacific Southern Ocean

“…Here, we employ a new proxy approach to derive [CO 3 2− ] based on the dissolution of planktic foraminiferal tests of Globigerina bulloides (G. bulloides), using the test density analyzed by X-ray micro-CT scanning (XMCT). This new proxy overcomes weaknesses of conventional dissolution proxies [30][31][32] , while showing signi cant correlation with deep-water Δ[CO 3 2− ] 33 . We apply this new method to reconstruct [CO 3 2− ] change in the subantarctic SE Paci c from the LGM across the deglaciation (10-21 ka BP).…”