Surviving rapid climate change in the deep sea during the Paleogene hyperthermals

Abstract

Predicting the impact of ongoing anthropogenic CO 2 emissions on calcifying marine organisms is complex, owing to the synergy between direct changes (acidification) and indirect changes through climate change (e.g., warming, changes in ocean circulation, and deoxygenation). Laboratory experiments, particularly on longer-lived organisms, tend to be too short to reveal the potential of organisms to acclimatize, adapt, or evolve and usually do not incorporate multiple stressors. We studied two examples of rapid carbon release in the geological record, Eocene Thermal Maximum 2 (∼53.2 Ma) and the Paleocene Eocene Thermal Maximum (PETM, ∼55.5 Ma), the best analogs over the last 65 Ma for future ocean acidification related to high atmospheric CO 2 levels. We use benthic foraminifers, which suffered severe extinction during the PETM, as a model group. Using synchrotron radiation X-ray tomographic microscopy, we reconstruct the calcification response of survivor species and find, contrary to expectations, that calcification significantly increased during the PETM. In contrast, there was no significant response to the smaller Eocene Thermal Maximum 2, which was associated with a minor change in diversity only. These observations suggest that there is a response threshold for extinction and calcification response, while highlighting the utility of the geological record in helping constrain the sensitivity of biotic response to environmental change. marine calcifiers | greenhouse gases | ecosystem stress response

Size-dependent response of foraminiferal calcification to seawater carbonate chemistry

“…6b). Our models similarly reveal a strong size dependency in volumenormalised approaches, such as that used by Foster et al (2013) across the PETM. All model runs predict that the foraminiferal calcite volume / total volume ratio exhibits a strong dependence on test size (Fig.…”

“…While there are as yet few data from smaller species of planktonic foraminifera and early ontogenetic stage individuals of larger planktonic foraminiferal species, there are some lines of evidence from small benthic foraminifera that could support the inverse calcification response that we propose. Foster et al (2013) found that small benthic foraminifera became more heavily calcified during the PETM, when ocean pH was lower (Penman et al, 2014). By contrast, during the high pH "carbonate overshoot" in the aftermath of the event (Penman et al, 2016), these foraminifera displayed thinner walls .…”

“…Aldridge et al, 2012;Weinkauf et al, 2016). Furthermore, other studies have observed an inverse response of SNW to carbonate system change in some species (Beer et al, 2010b;Foster et al, 2013) -that is, a greater test thickness at lower pH and/or ]. It is possible that at least some of the discrepancies described above may stem from methodological differences, since foraminiferal SNW has been quantified in a number of different ways (see Beer et al, 2010a;Aldridge et al, 2012;Marshall et al, 2013, for further discussion).…”

Determining climate change impacts on ecosystems: the role of palaeontology

“…Those benthic foraminiferal species surviving the PETM had the ability to enhance their calcification relative to body volume (Foster et al . ). Intriguingly, deep sea ostracods show highly variable responses, some of which suggest that the climate change impacted the assemblages negatively (Steineck & Thomas ) while others suggest little change (Webb et al .…”

“…; PETM: (Foster et al . ). While there was extinction during the PETM (Thomas ), there is currently no evidence for climate‐related extinction in the marine record.…”