Abstract
Climate change is predicted to alter temperature, carbonate chemistry and oxygen availability in the oceans, which will affect individuals, populations and ecosystems. We use the fossil record of benthic foraminifers to assess developmental impacts in response to environmental changes during the Palaeocene–Eocene Thermal Maximum (PETM). Using an unprecedented number of µ-computed tomography scans, we determine the size of the proloculus (first chamber), the number of chambers and the final size of two benthic foraminiferal species which survived the extinction at sites 690 (Atlantic sector, Southern Ocean, palaeodepth 1900 m), 1210 (central equatorial Pacific, palaeodepth 2100 m) and 1135 (Indian Ocean sector, Southern Ocean, palaeodepth 600–1000 m). The population at the shallowest site, 1135, does not show a clear response to the PETM, whereas those at the other sites record reductions in diameter or proloculus size. Temperature was similar at all sites, thus it is not likely to be the reason for differences between sites. At site 1210, small size coincided with higher chamber numbers during the peak event, and may have been caused by a combination of low carbonate ion concentrations and low food supply. Dwarfing at site 690 occurred at lower chamber numbers, and may have been caused by decreasing carbonate saturation at sufficient food levels to reproduce. Proloculus size varied strongly between sites and through time, suggesting a large influence of environment on both microspheric and megalospheric forms without clear bimodality. The effect of the environmental changes during the PETM was more pronounced at deeper sites, possibly implicating carbonate saturation.This article is part of a discussion meeting issue ‘Hyperthermals: rapid and extreme global warming in our geological past’.
Highlights
The anthropogenic increase in atmospheric CO2 impacts the physical, chemical and biological properties of the ocean [1]
We use three-dimensional μ-computed tomography imaging to collect information on proloculus size, number of chambers and final size of two species of benthic foraminifera which survived the extinction at the Palaeocene–Eocene Thermal Maximum (PETM), at three locations, to quantify response by benthic foraminifers to the climatic and environmental perturbation
We focused on two species: the extant shallow infaunal [46,56,57] Oridorsalis umbonatus and the extinct, probably epifaunal N. truempyi
Summary
The anthropogenic increase in atmospheric CO2 impacts the physical, chemical and biological properties of the ocean [1]. Impacts of climate change in the fossil record have been assessed in terms of relative or absolute abundance of species, and their origination and extinction Such data show that the PETM resulted in a significant extinction of benthic foraminifera [21] and a transient faunal turnover [22], as well as migration to higher latitudes in planktic species [23,24]. We use three-dimensional μ-computed tomography imaging to collect information on proloculus size, number of chambers and final size of two species of benthic foraminifera which survived the extinction at the PETM, at three locations, to quantify response by benthic foraminifers to the climatic and environmental perturbation. The general picture was corroborated by a recent review of combined data and modelling results [15], which suggested increased oligotrophy at Shatsky Rise, and generally oligotrophic conditions but with short-term increases in the food supply at the onset of the CIE for the Southern Ocean sites. Number of chambers and size of proloculus were measured for individual specimens following Foster et al [26], in samples from before the CIE, in the core of the CIE, in the recovery interval and after the CIE (table 2)
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