Human activity makes it harder for scientists to interpret the oceans’ past – Research News

NNew research shows that human activity is significantly changing the way marine organisms are preserved, with lasting effects that can either improve or degrade the fossil record.

“We don’t just change the environment; we are also changing the nature of the archive in which this information is archived,” said Michal Kowalewski, Thompson chair of invertebrate paleontology at the Florida Museum of Natural History. “These changes can be both good and bad. On the one hand, human activities can prevent the fossil record from preserving useful information about ongoing changes. In other situations, human actions can actually improve the quality of the currently formed fossil record, providing more information.”

If not properly taken into account, these effects on the fossil record can lead to misinterpretation of data critical to conservation efforts. Humans began changing ecosystems long before they began to study them systematically. In many places, scientists can only know what an ecosystem looked like before the arrival of humans by looking back at the recent fossil record.

“We use fossils in conservation to understand the transition from natural, pristine environments to the environments we have today,” says Kowalewski. If scientists know what a degraded ecosystem looked like before it was changed, they know what to look for when trying to restore it.

Kowalewski and his colleagues specialize in marine paleoecology and co-authored the study with a focus on fossil beds in the world’s oceans. In these environments, the authors say, there are several interrelated factors that influence fossils, including the rate at which sediment accumulates on the seafloor, the extent to which animals burrow through the sediment, the depth at which remains are buried and how quickly certain fossils are buried. disintegrate over time.

All these factors can and have been influenced by people. The practice of bottom trawling, which involves dragging a net across the seabed, mixes and churns sediment, infusing it with oxygen that breaks down organic residues.

On a global scale, it is estimated that bottom trawling pushes as much sediment into the water column as is deposited into the oceans from all the world’s rivers.

“When I worked on this study, I was surprised that the consequences of bottom trawling are so widespread,” says lead author Rafal Nawrot, a paleontologist at the University of Vienna. Nawrot studies changes in marine ecosystems that have occurred since the last ice age, an area where it is crucial to know the different factors that help or hinder the fossil record.

He talked about a study in which he and colleagues found a distinct lack of large shells from sediment cores drilled into the seafloor. “Given what we now know about the intensity of trawling in some of the areas we worked in, this pattern may merely be an artefact of its removal by nets dragged through the seabed.”

Changes in the fossil record can also be indirect. Local extinctions caused by human activity and the introduction of invasive species can both prevent and enhance the fossilization process. The authors give the example of red king crabs (Paralithodes camtschaticus), which were deliberately introduced into the Barents Sea between Russia and Finland in the 1960s. There they had few natural enemies and their population exploded. Red king crabs eat just about anything they can get their claws on and crush the shells of their prey. This caused a sharp reduction in the number of burrowing invertebrates, which oxygenate sediments.

Fewer burrowing organisms means less oxygen in the sediment, which means better preservation. But more crabs crushing shells means there are fewer shells to save. Without proper historical context, future paleontologists trying to unravel this sequence of events may walk away baffled.

It is unclear how plastics are changing the preservation of fossils, as their presence in the world’s oceans is a relatively new phenomenon. However, they will certainly change the chemical and structural properties of marine fossil beds.

Bottom trawls leave such distinctive marks on the seabed that they can be viewed from the water’s surface with a sonar array.

The introduction of invasive species, such as the case of king crabs in the Barents Sea, can significantly change the environment, the types of organisms that enter the fossil record and the rate at which they are preserved.

These and other human-induced changes can be particularly difficult to interpret because they mimic natural processes such as erosion or species migrations. In some cases, human activity can completely erase fossil records or confound research efforts by adding tons of foreign material to an environment.

“Certain processes do not occur naturally at all, such as beach nourishment,” says Kowalewski. When parts of a beach are washed away by hurricanes or rising sea levels, local authorities often pay for ships to transport sediment from deepwater environments—where natural erosion is negligible—to the shoreline, fossils and all.

In other cases, the fossils themselves are targeted for relocation.

“Oysters that lived hundreds of thousands of years ago could be removed from one area and added to the modern seabed of another area to facilitate the recovery of today’s oyster reefs,” Kowalewski said.

So how do scientists begin to untangle the various natural and human forces influencing the fossils? It’s complicated, Nawrot said. “It depends on the purpose of the research, but there are ways around these problems.”

One strategy that has become more feasible recently is radiocarbon dating. Scientists use this method to estimate the age of relatively young fossils, but until recently it could only be used sparingly due to the high cost. When analyzing a sediment core drilled from modern seafloors, in which organisms at the top may be thousands of years younger than those at the bottom, researchers typically select only a few fossils for radiocarbon dating. This provided reliable information but poor resolution, and if the sediment had been unknowingly mixed by bottom trawls the results could be misleading.

Exploration crews deploy sediment drills to extract a long vertical string of mud, sand and rock from the ocean floor.

Sediment cores preserve part of the seafloor in increasingly older periods as you go.

Sediment cores, such as these stored in the University of Oregon’s Marine and Geology Repository, allow scientists to reconstruct Earth’s past in great detail.

“You wouldn’t be aware of this problem unless you sampled multiple samples per layer, which is not a widespread approach. We believe it should be used much more often,” said Nawrot.

Researchers will also have to become more creative with the types of statistical analyzes they use to interpret data. These types of methods take time to develop and test, but they are slowly becoming more common and scientists are getting closer to a better understanding of how humans influence the historical record of life on Earth.

“Changes in the geological record can be fingerprints of human activity and can themselves reveal something about the history of an ecosystem,” Kowalewski said.

Martin Zuschin from the University of Vienna, Adam Tomašových from the Slovak Academy of Sciences and Daniele Scarponi from the Università di Bologna are also co-authors of the study.

Funding for the research was provided in part by the National Science Foundation (grant nos. EAR-1559196 and EAR-1922562); the Agentúra na Podporu Výskumu a Vývoja (grant no. APVV-22-0523); the Vedecká Grantová Agentúra MŠVVaŠ SR a SAV (grant no. 2/0106/23); and NextGenerationEU through the Italian Ministry of University and Research under PNRR – Mission 4 Component C2, Investments 1.1.

Sources: Michal Kowalewski, [email protected];
Rafal Nawrot, [email protected]
Media Contact: Jerald Pinson, [email protected], 352-294-0452