Abstract
Widely regarded as an imminent threat to our oceans, ocean acidification has been documented in all oceanic basins. Projected changes in seawater chemistry will have catastrophic biotic effects due to ocean acidification hindering biogenic carbonate production, which will in turn lead to substantial changes in marine ecosystems. However, previous attempts to quantify the effect of acidification on planktonic calcifying organisms has relied on laboratory based studies with substantial methodological limitations. This has been overcome by comparing historic plankton tows from the seminal HMS Challenger Expedition (1872–1876) with the recent Tara Oceans expedition material (2009–2016). Nano CT-scans of selected equatorial Pacific Ocean planktonic foraminifera, have revealed that all modern specimens had up to 76% thinner shells than their historic counterparts. The “Challenger Revisited” project highlights the potential of historic ocean collections as a tool to investigate ocean acidification since the early Industrial Revolution. Further analyses of such biotic archives will enable researchers to quantify the effects of anthropogenic climate change across the globe.
Highlights
The HMS Challenger expedition from 1872 to 1876 can claim to be the foundation of modern oceanographic studies
We test the utility of these collections for modern climate change studies by comparing specimens of planktonic foraminifera collected in tow nets from HMS Challenger Station 272 (1875) (Fig. 1) with Tara expedition (2011)[21] stations 127 and 128, in the eastern Pacific Ocean; a region that is recognized as being vulnerable to deoxygenation and surface warming in the wake of anthropogenic climate change[20]
Tow samples that had been stored in ethanol immediately after collecting were analysed under light microscope and picked for planktonic foraminifera, with selected specimens imaged using a scanning electron microscope (SEM) to test for any visible signs of dissolution (Fig. 2)
Summary
The HMS Challenger expedition from 1872 to 1876 can claim to be the foundation of modern oceanographic studies This historic voyage was the first to gather data on a broad range of ocean features, including ocean temperatures, seawater chemistry, currents, marine life, and the geology of the seafloor[1,2]. In 2022 scientists will celebrate 150 years since the HMS Challenger first left port to begin this ground-breaking oceanographic expedition During this time scientific and technological methods have advanced substantially, but the wealth of knowledge associated with the modern ocean systems is in stark contrast to the fundamental lack of baseline ocean data from the Industrial Revolution onwards[3]. One centimeter depth of deep sea sediment may represent 100’s of years of Earth’s history[18], this method inevitably incorporates a mix of specimens from a large window of geological time, leading to potential circularity when comparing data from these sediments to modern sediment traps or plankton tows
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