Identifying disruptions to the ecological balance of nature: a foraminiferal example across the initiation of the Paleocene–Eocene thermal maximum

Abstract

Deriving ecological and evolutionary descriptions of, and implications from, faunal assemblage patterns is commonly addressed by observation and a variety of exploratory techniques (scaling and clustering), along with qualitative evaluations of species occurrences and relative abundances. We argue that interpretations of faunal patterns, especially those documented by the fossil record, should be based upon the composition and structure of entire communities to provide strong conclusions and replicable results.As an example, we use benthic foraminiferal data at high resolution (1–2 cm, corresponding to 300–1400 yr) over a section corresponding to about 20 kyr across the beginning of the Paleocene–Eocene thermal maximum (PETM). The PETM was an episode of rapid global warming about 55.5 Ma, associated with ocean acidification and lowered open oceanic productivity and deoxygenation and marked by severe turnover in benthic foraminiferal assemblages. Here we provide a stand-alone approach applicable to any dynamic faunal system, perturbation detection analysis (PDA), to recognize and identify community disruption evidenced as either positive growth or negative decline, and we use this methodical approach to obtain new information on foraminiferal communities before, during, and after the initiation of the PETM.We conclude that the late Paleocene benthic foraminiferal community (FCOM1) was in a growth stage of positive increasing diversity, suggestive of favorable environmental conditions. This stage continued through the initial changes at the onset of the PETM, when disruption through environmental stress led to this community's termination. A second community (FCOM2) formed with declining diversity and high variability, showing a lack of adaptation to changing conditions. Knowledge of total assemblage status under both adverse and advantageous conditions is necessary, but not recognized by methods that rely upon analysis of single samples only: individual samples cannot be used to recognize disruptive changes in a community's structure, but these are easily identified using PDA.

Benthic foraminiferal turnover across the Dan-C2 event in the eastern South Atlantic Ocean (ODP Site 1262)

“…Biotic turnover across the largest hyperthermal event, the PETM, has been extensively described, especially of deep-sea benthic foraminifera which underwent their largest extinction of the Late Cretaceous-Cenozoic (Tjalsma and Lohmann, 1983;Miller et al, 1987;Katz and Miller, 1991;Thomas, 1989Thomas, , 1990aThomas, , b, 1998Thomas, , 2007Alegret et al, 2009aAlegret et al, , b, 2018Hayek et al, 2019). Other marine and terrestrial groups show diversification, evolution of short-lived taxa, and/or migration to higher latitudes (e.g., McInerney and Wing, 2011;Speijer et al, 2012).…”

Benthic Foraminiferal Community Changes Across the Miocene Climatic Optimum Identified by Shebi Analysis (She Analysis for Biozone Identification), Calvert Cliffs, Maryland, USA

“…This differs from the Paleocene Eocene Thermal Maximum (PETM) event that has been studied using SHE analysis. Hayek et al (2019) developed and used a new Perturbation Detection Analysis, which incorporated a SHE analysis of 29 subsamples of benthic foraminiferal assemblage data from the onset of the PETM at ODP Site 690 to recognize benthic foraminiferal communities, before determining whether communities were in decline, growth, or stasis. SHE analysis recognized two communities, one immediately before the PETM carbon isotope excursion (CIE) and another during the CIE (Hayek et al, 2019).…”

Planktic Foraminiferal Resilience to Environmental Change Associated With the PETM

“…Benthic foraminifers experienced a significant PETM extinction, with 30%–50% of species lost (Speijer et al., 2012; Thomas, 2007; Thomas & Shackleton, 1996). This extinction has often been attributed to hypoxic deep‐water, a shoaling of the carbonate compensation depth, decreased food availability, or a combination of these (Griffith et al., 2021; Hayek et al., 2019; Stassen et al., 2015; Thomas, 2007; Zhou et al., 2016). However, the response of benthic foraminifers also shows regional modulations which suggest that temperature was not the main driver but that food and saturation impacted benthic foraminiferal growth (Schmidt et al., 2018).…”