Novel Method to Image and Quantify Cogwheel Structures in Foraminiferal Shells

Abstract

Most studies designed to better understand biomineralization by foraminifera focus mainly on their shell chemistry in order to retrace processes responsible for element uptake and shell formation. Still, shell formation is a combination of not only chemical and biological processes, but is also limited by structural features. Since the processes involved in the formation of the foraminifera shell remains elusive, new focus has been put on potential structural constraints during shell formation. Revealing structural details of shells of foraminifera might increase our mechanistic understanding of foraminifera calcification, and even explain species-specific differences in element incorporation. Recently, shell structures have been studied in increasingly higher resolution and detail. This paper aims to provide new insights on the structural features on foraminifera shells, so-called cogwheels, which can be observed in the shell wall and at its surface. Here, we present a novel method to image and quantify these cogwheel structures, using field specimens from different environments and ecological groups, including benthic and planktonic species. Application of this method allows for comparing shell structures at specimen and species level, to unravel potential drivers of shell formation.

Fast and pervasive diagenetic isotope exchange in foraminifera tests is species-dependent

“…3 – 5 ). In addition to chamber walls of variable thickness, tests of different foraminifera species have different cogwheel structures in terms of size, distribution, and density 43 , as is the case for the species studied here (Fig. 2 ).…”

“…The test wall is further divided into domains that resemble interlocking cogwheels when observed on the outer wall surface, or in the interior of the wall in sections cut parallel to the wall surface (Fig. 2d–i ) 42 , 43 . The cogwheel-like domains are 3-dimensional structures that extend throughout the thickness of the wall (Fig.…”

“…Organic linings and cogwheel structures are fundamental structural features in the tests of both benthic and planktonic foraminifera 43 , and can become the main pathways for H 2 O penetration and hence also induce isotopic exchange after the (partial) degradation of the organic matter (Figs. 3 – 5 ).…”

“…The surface density of the cogwheel interfaces was calculated for all three species of foraminifera used in this study (Supplementary Fig. 11 , Supplementary Table 2 ) using the methodology described in van Dijk et al 43 . Ammonia sp.…”

“…Cogwheel interface densities were calculated using the ImageJ macro from van Dijk et al 43 . Secondary electron SEM images at ×5000 magnification were taken of the outer surface of the second to the last chamber of tests from all three species studied here.…”