3D morphological variability in foraminifera unravel environmental changes in the Baltic Sea entrance over the last 200 years

Abstract

Human activities in coastal areas have intensified over the last 200 years, impacting also high-latitude regions such as the Baltic Sea. Benthic foraminifera, protists often with calcite shells (tests), are typically well preserved in marine sediments and known to record past bottom-water conditions. Morphological analyses of marine shells acquired by microcomputed tomography (µCT) have made significant progress toward a better understanding of recent environmental changes. However, limited access to data processing and a lack of guidelines persist when using open-source software adaptable to different microfossil shapes. This study provides a post-data routine to analyze the entire test parameters: average thickness, calcite volume, calcite surface area, number of pores, pore density, and calcite surface area/volume ratio. A case study was used to illustrate this method: 3D time series (i.e., 4D) of Elphidium clavatum specimens recording environmental conditions in the Baltic Sea entrance from the period early industrial (the 1800s) to present-day (the 2010 s). Long-term morphological trends in the foraminiferal record revealed that modern specimens have ∼28% thinner tests and ∼91% more pores than their historic counterparts. However, morphological variability between specimens and the BFAR (specimens cm−2 yr−1) in E. clavatum were not always synchronous. While the BFAR remained unchanged, morphological variability was linked to natural environmental fluctuations in the early industrial period and the consequences of anthropogenic climate change in the 21st century. During the period 1940–2000 s, the variations in BFAR were synchronous with morphological variability, revealing both the effects of the increase in human activities and major hydrographic changes. Finally, our interpretations, based on E. clavatum morphological variations, highlight environmental changes in the Baltic Sea area, supporting those documented by the foraminiferal assemblages.

Reviews and syntheses: Review of proxies for low-oxygen paleoceanographic reconstructions

“…While interest in studying foraminiferal morphology in 3D emerged in the mid-20th century (Bé et al, 1969;Schmidt, 1952), quantifications and paleoclimatic reconstructions using such methods have become possible only recently. Since the pioneering µCT work of Speijer et al (2008), the number of studies dealing with 3D reconstructions of foraminiferal tests is increasing towards a variety of ends such as taxonomy and ontogeny (e.g., Briguglio et al, 2011, Görog et al, 2012, Schmidt et al, 2013, Caromel et al, 2016, 2017Burke et al, 2020), ocean acidification and test dissolution processes (e.g., Johnstone et al, 2010, Iwasaki et al, 2015, Prazeres et al, 2015, Ofstad et al, 2021, Charrieau et al, 2022, Choquel et al, 2023, effects of temperature (e.g., Kinoshita et al, 2021, Titelboim et al, 2021, and paleoclimate reconstruction (e.g., Fox et al, 2020, Zarkogiannis et al, 2021, Todd et al, 2020, Schmidt et al, 2018. These studies have been focused mainly on planktic and tropical larger benthic foraminifera, with a recent study by Choquel et al (2023) expanding this research to benthic foraminifera.…”

“…To date "conventional" µCT scanners have primarily been used, supplemented with particle accelerator facilities, and Atomic Force Microscopy (AFM). Studies using 3D foraminifera constructions with scanner-based or synchrotron light-based µCT were reviewed in Choquel et al (2023). Most studies reconstructing foraminifera in 3D are performed with costly software such as Avizo (e.g., Fox et al, 2020), Amira (e.g., Schmidt et al, 2013), Molcer Plus and ConeCT express (e.g., Iwasaki et al, 2015).…”

Virtual Paleobiology – Advances in X-Ray Computed Microtomography and 3D Visualization of Fossils

“…Our contribution focuses on the morphology of one of the most important calcitic microorganisms in the oceans-the foraminifera. Since the pioneering work of Speijer et al (2008), the number of studies dealing with 3D reconstructions of foraminiferal shells (tests) is increasing, reaching in 2022 an estimated cumulative number of ~4,000 scanned specimens (Figure 1A). Foraminiferal 3D reconstructions have allowed various topics to be addressed such as taxonomy and ontogeny studies, effects of ocean acidification, effects of temperatures, and micropaleontological time series (see review in Supplementary Table S1).…”

“…The geology of the area around Okoshizawa is detailed in Ehiro et al (2008) and Muto et al (2023) (Figure 2). The pelagic deep-sea sedimentary rocks in Okoshizawa mostly comprise bedded chert and siliceous claystone of the Otori Unit of Takahashi et al (2016) (revised by Muto et al, 2023).…”

“…In lateral view, a large hole is present in the vomerine dorsal septum (Figures 6A, B) and is likely due to postmortem damage. However, Ivakhnenko (2008) reported the presence of a large foramen in some therapsids in the same area of the internasal septum. In ventral view, the ventral plate of the vomer is excavated by a deep midline groove bordered by two sharp lateral ridges (Figure 6D).…”