Plankton has not been the same since the Industrial Revolution | Science

As scientists struggle to understand how ocean warming will affect the world's marine ecosystems, from bleaching coral reefs to modified migration routes, one of the most ubiquitous organisms in the sea is helping researchers measure changes. already occurred. Centuries of fossil recordings and live animal catch data show that some marine plankton populations reflect a distinct shift in response to human industrialization and warming oceans, which is the largest in the world. accompany.

The researchers found distinct differences between communities of planktonic foraminifers – tiny unicellular creatures floating in ocean waters – before and after the start of the industrial age, some 170 years ago, according to a study published this week in Nature. The proportion of plankton species in these communities has changed in proportion to changes in sea temperature, indicating that ocean warming has profoundly altered these populations and their larger marine ecosystems.

Although the idea that climate change is affecting marine life is not new, the plankton study incorporates an exceptionally comprehensive set of data spanning the globe and penetrating deeply into past centuries to reaffirm the impact of climate change. humanity on the oceans.

Planktonic foraminifers provide a comprehensive database of fossils, as their hard calcite shell is well preserved in sediments at the bottom of the ocean, says lead author Lukas Jonkers, paleontological oceanographer at the University of California. 39, University of Bremen, Germany. The organisms also populate the waters all over the world. Although rare in the surface oceans, planktonic foraminifers are abundant at greater depths, and in some places they cover entire areas of the seabed, says Jonkers.

"We can really very well compare the distribution of the species in the modern world. [era] with the past, "says Jonkers. "There are not so many zooplankton groups where the fossil record is as well preserved. In fact, I do not think there is any.

To understand the state of these communities before the start of the industrial era, Jonkers and his team analyzed more than 3,700 samples previously taken from layers of sediments located at the bottom of the ocean. According to scientists, scientists have estimated that the top layer of sediment nuclei – essentially "mud cylinders" drawn from the bottom of the ocean, would contain centuries-old fossils, Jonkers explains. before the industrial revolution.

The team then compared these pre-industrial samples to more recent data collected using sediment traps, funnels docked at the bottom of the sea that capture anything that falls from the upper layers of the ocean (including drifting plankton). in water). Using information collected from 1978 to 2013, the researchers found that communities of planktonic foraminifers had changed considerably between the deposition of bottom-living fossils and organisms captured in sediment traps.

The offset, measured by comparing the relative abundances of dozens of plankton species in the samples, does not appear to be random. The amount of change in plankton communities correlated with the degree of temperature change documented in the surrounding waters. The leadership of the changing communities has also been largely aligned with models of ocean temperature change, as the authors have found by mapping the seabed fossils with their closest analogues in the world. modern communities.

With data showing a correspondence in the degree and direction of change, Jonkers is confident that temperature is driving changes in planktonic foraminiferal populations.

"I was expecting to see a difference and an effect of global change," says Jonkers. "But I did not expect the signal to be so clear."

The new study replicates on a global scale what other researchers have discovered in specific fields, says David Field, marine science scientist at Hawaii Pacific University, who has done research on planktonic foraminifers but did not participate in this study. Although scientists have not yet understood why plankton communities are evolving, the results of this study and others clearly indicate that ocean warming is the likely cause, whether as a direct or indirect influence. other aspects of the underwater environment, Field says.

Comparing sediment trap samples with seabed fossils may not be a perfect analogy – differences in conservation may affect the data – but the evidence provided by the authors convincingly confirms enormous influence of ocean warming on marine species.

"This indicates that warming has begun to affect marine ecosystems long ago, even before we had good results," said Field. "We can expect much more impact of ocean warming on ecosystems in the future. The oceans will continue to change in a way we have never seen before. "

Planktonic foraminifers may not be as majestic as whales or sea stars, but the extent of their fossil record provides a useful baseline for confirming a broader trend of changing ocean life in response to human activity. Changes in plankton communities are a worrying indicator of the "global vision" of marine ecosystems as ocean temperatures continue to grow at an ever faster rate, says Jonkers.

"The question is, what will happen with the progression of climate change?", States Jonkers. "Even to a degree [of temperature change]we are already seeing great changes in planktonic foraminifers, and probably also in other marine biota. This means that all these species have to adapt and for the moment we do not know if they can, or if they can do it fast enough. "

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