Small change, big impact
Researchers identify major ecological turnover occurred already before the largest warming event of the past 90 million years
MARUM - Center for Marine Environmental Sciences, University of Bremen
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Dr. Heather L. Jones examines tiny plankton fossils using a light microscope. Photo: MARUM – Center for Marine Environmental Sciences, University of Bremen; M. Toyos Simón
view moreCredit: MARUM – Center for Marine Environmental Sciences, University of Bremen; M. Toyos Simón
A large proportion of the carbon dioxide emissions that are currently being released into the atmosphere by human activities are absorbed by the surface ocean, making it more acidic. As a result, the tiny organisms (plankton), which lie at the base of the marine food web and make the surface ocean their home, are at risk. The fossil record can tell us how these plankton responded during ancient intervals of climatic change that were similarly associated with increased carbon dioxide emissions. One such event is the Paleocene-Eocene Thermal Maximum (PETM) around 56 million years ago, which can be used as a case study for near-future climate change if carbon dioxide emissions continue to increase (the so-called worst-case scenario). Hundreds of deep-sea sediment archives that span the PETM reveal global turnover in plankton communities due to sea surface warming and ocean acidification.
High-latitude phytoplankton particularly sensitive to climate change
A team of researchers from MARUM, University of Bremen have now investigated how high-latitude phytoplankton communities responded to PETM warming. Examining high-latitude communities is especially important because they are historically understudied and likely to be particularly sensitive to human-driven climate change. The focus of the study was on deep-sea sediment cores from the Campbell Plateau in the Southern Ocean, which were recovered during International Ocean Discovery Program (IODP) Expedition 378.
In their study, based on the fossilized remains of calcareous nannoplankton – microscopically small, single-celled algae that photosynthesize in the surface ocean and produce calcium carbonate (e.g., chalk) shells – the team was able to reconstruct changes in their community composition both before and during the PETM. “Certain nannoplankton species prefer to live in warmer waters with less nutrients, whilst others can only live in colder, higher nutrient waters. Therefore, major warming events like the PETM really affect which species thrive, and which don’t. This can be observed in the nannofossil record by counting how many of each species there are and how this changes through time,” explains first author Dr. Heather L. Jones.
Even small changes can have dramatic impacts on marine ecosystems
Somewhat surprisingly, the results from the research team’s study show that the PETM did not seem to affect nannoplankton communities as much as anticipated. They attribute this to a preceding, smaller warming event, which they propose had already destabilized nannoplankton communities approximately 200 thousand years before the PETM. “Most studies only focus on the PETM event itself and not the longer-term time before it,” explains Dr. Heather Jones. “However, examining these background intervals is absolutely critical in determining the extent to which warming events actually drove ecosystem change. In the case of our study, pre-event environmental conditions seem not to have been completely stable, which had a direct influence on how nannoplankton proceeded to respond to the PETM. It also highlights that even relatively small environmental changes can have dramatic impacts on marine ecosystems in certain locations, which has important implications for the current, highly regional effects of modern climate change.”
Archive of legacy deep-sea sediment cores will help with future studies
As the current study is the first to formally document this pre-PETM event, its global significance is uncertain. It therefore sets the stage for future studies to use the expansive archive of legacy deep-sea sediment cores – such as those housed at the Bremen Core Repository (BCR) in the MARUM – to identify this newly-described event in different ocean basins.
The first author, Dr. Heather L. Jones studied the calcareous nannofossils that led the team to the findings of their study, and is a topic that was investigated within the Cluster of Excellence “The Ocean Floor – Earth’s Uncharted Interface”, which is based at MARUM. One research focus of the cluster is how complex ecosystems react under changing environmental conditions.
MARUM produces fundamental scientific knowledge about the role of the ocean and the seafloor in the total Earth system. The dynamics of the oceans and the seabed significantly impact the entire Earth system through the interaction of geological, physical, biological and chemical processes. These influence both the climate and the global carbon cycle, resulting in the creation of unique biological systems. MARUM is committed to fundamental and unbiased research in the interests of society, the marine environment, and in accordance with the sustainability goals of the United Nations. It publishes its quality-assured scientific data to make it publicly available. MARUM informs the public about new discoveries in the marine environment and provides practical knowledge through its dialogue with society. MARUM cooperation with companies and industrial partners is carried out in accordance with its goal of protecting the marine environment.
Calcareous nannofossils from the SW Pacific Ocean show that plankton turnover occurred before the PETM. Image: MARUM – Center for Marine Environmental Sciences, University of Bremen; H. Jones.
Credit
MARUM – Center for Marine Environmental Sciences, University of Bremen; H. Jones.
Journal
Communications Earth & Environment
Article Title
Palaeoecological change preceded the Palaeocene-Eocene Thermal Maximum by 200 kyr in the high latitude south-west Pacific Ocean
