Ocean life may adapt to climate change, but with hidden costs

Copepods are small crustaceans found in nearly every freshwater and marine habitat—and they may be the most abundant animals in the ocean. UVM scientists studied one species of them—Acartia tonsa, shown here—to test how they would respond to climate change. Credit: UVM/Pespeni Lab

Suppose that we could watch twenty generations of whales or sharks adapting to climate change—measuring how they evolve and how their biology changes as temperatures and carbon dioxide levels rise. That could tell us a lot about how resilient life in the oceans might be to a warmer world. But it would also take hundreds of years—not very useful to scientists or policymakers trying to understand our warming world today.

Instead, consider the life of the Acartia tonsa, a tiny and humble sea creature near the bottom of the food web. It reproduces, matures, and creates a new generation in about twenty days. Twenty copepod generations pass in about one year.

A team of six scientists, led by University of Vermont (UVM) biologist Melissa Pespeni and postdoctoral scientist Reid Brennan, did just that: In a first-of-its kind laboratory experiment, they exposed thousands of copepods to the high temperatures and high levels that are predicted for the future of the oceans. And watched as twenty generations passed. Then they took some of the copepods and returned them to the baseline conditions—the temperature and CO2 levels that the first started in, which are like conditions today. And then they kept watching as three more generations passed.

The results, published in the journal Nature Communications, “show that there is hope,” Pespeni says, “but also complexity in how life responds to .”

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Hexbyte Glen Cove Ocean acidification and warming disrupts fish shoals

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Caesio teres in Fiji by Nick Hobgood. Credit: Creative Commons

Researchers from the University of Adelaide have found that the way fish interact in groups is being upset by ocean acidification and global warming.

“Fish show gregarious behavior and cluster in shoals which helps them to acquire food and for protection against predators,” said project leader Professor Ivan Nagelkerken from the University of Adelaide’s Environment Institute and Southern Seas Ecology Laboratories.

“Many gregarious are shifting poleward under current ocean warming and interacting in new ways with fish in more temperate areas.”

Under controlled laboratory conditions the researchers evaluated how species interacted and behaved in new ways with changing temperature and acidification.

The rising concentration of carbon dioxide in the atmosphere is driving up ocean surface temperatures and causing . Although warming and acidification are different phenomena, they interact to the detriment of marine ecosystems.

“We found that tropical and temperate fish species tend to move to the right when coordinating together in a shoal especially when spooked by a predator, but this bias significantly diminished under acidification,” said University of Adelaide Ph.D. student Angus Mitchell who performed the experiments.

“Mixed shoals of tropical and temperate species became less cohesive under future climate conditions and showed slower escape responses from potential threats.”

Professor David Booth from the University of Technology, Sydney collaborated on the study.

“Our findings highlight the direct effect of climate stressors on fish behavior and the interplay with the indirect effects of new species interactions,” he said.

The team of researchers published their findings in the journal Global Change Biology.

“Strong shoal cohesion and coordinated movement affect the survival of a species: whether to acquire food or evade predators,” said Professor Nagelkerken.

“If the ability for to work together is detrimentally affected it could determine the survival of particular species in the oceans of the future. Tropical may initially fare poorly when moving into new temperate areas.”



More information:
Ocean warming and acidification degrade shoaling performance and lateralization of novel tropical–temperate fish shoals, Global Change Biology (2021). DOI: 10.1111/gcb.16022

Citation:
Ocean acidification and warming disrupts fish shoals (2021, December 17)
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Hexbyte Glen Cove Arctic Ocean started getting warmer decades earlier than we thought, study finds

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An international group of researchers reconstructed the recent history of ocean warming at the gateway to the Arctic Ocean in a region called the Fram Strait, between Greenland and Svalbard, and found that the Arctic Ocean has been warming for much longer than earlier records have suggested. Credit: Sara Giansiracusa

The Arctic Ocean has been getting warmer since the beginning of the 20th century—decades earlier than records suggest—due to warmer water flowing into the delicate polar ecosystem from the Atlantic Ocean.

An international group of researchers reconstructed the recent history of at the gateway to the Arctic Ocean in a region called the Fram Strait, between Greenland and Svalbard.

Using the chemical signatures found in marine microorganisms, the researchers found that the Arctic Ocean began warming rapidly at the beginning of the last century as warmer and saltier waters flowed in from the Atlantic—a phenomenon called Atlantification—and that this change likely preceeded the warming documented by modern instrumental measurements. Since 1900, the has risen by approximately 2 degrees Celsius, while sea ice has retreated and salinity has increased.

The results, reported in the journal Science Advances, provide the first historical perspective on Atlantification of the Arctic Ocean and reveal a connection with the North Atlantic that is much stronger than previously thought. The connection is capable of shaping Arctic climate variability, which could have important implications for sea-ice retreat and global sea level rise as the polar ice sheets continue to melt.

All of the world’s oceans are warming due to climate change, but the Arctic Ocean, the smallest and shallowest of the world’s oceans, is warming fastest of all.

“The rate of warming in the Arctic is more than double the global average, due to feedback mechanisms,” said co-lead author Dr. Francesco Muschitiello from Cambridge’s Department of Geography. “Based on satellite measurements, we know that the Arctic Ocean has been steadily warming, in particular over the past 20 years, but we wanted to place the recent warming into a longer context.”

Atlantification is one of the causes of warming in the Arctic, however instrumental records capable of monitoring this process, such as satellites, only go back about 40 years.

Using the chemical signatures found in marine microorganisms, researchers have found that the Arctic Ocean began warming rapidly at the beginning of the last century as warmer and saltier waters flowed in from the Atlantic – a phenomenon called Atlantification. Credit: Sara Giansiracusa

As the Arctic Ocean gets warmer, it causes the ice in the polar region to melt, which in turn affects global sea levels. As the ice melts, it exposes more of the ocean’s surface to the sun, releasing heat and raising air temperatures. As the Arctic continues to warm, it will melt the permafrost, which stores huge amounts of methane, a far more damaging greenhouse gas than .

The researchers used geochemical and ecological data from ocean sediments to reconstruct the change in water column properties over the past 800 years. They precisely dated sediments using a combination of methods and looked for diagnostic signs of Atlantification, like change in temperature and salinity.

“When we looked at the whole 800-year timescale, our temperature and salinity records look pretty constant,” said co-lead author Dr. Tesi Tommaso from the Institute of Polar Sciences of the National Research Council in Bologna. “But all of a sudden at the start of the 20th century, you get this marked change in temperature and salinity—it really sticks out.”

“The reason for this rapid Atlantification of at the gate of the Arctic Ocean is intriguing,” said Muschitiello. “We compared our results with the ocean circulation at lower latitudes and found there is a strong correlation with the slowdown of dense water formation in the Labrador Sea. In a future warming scenario, the deep circulation in this subpolar region is expected to further decrease because of the thawing of the Greenland ice sheet. Our results imply that we might expect further Arctic Atlantification in the future because of climate change.”

The researchers say that their results also expose a possible flaw in climate models, because they do not reproduce this early Atlantification at the beginning of the last century.

“Climate simulations generally do not reproduce this kind of warming in the Arctic Ocean, meaning there’s an incomplete understanding of the mechanisms driving Atlantification,” said Tommaso. “We rely on these simulations to project future , but the lack of any signs of an early warming in the Arctic Ocean is a missing piece of the puzzle.”



More information:
Tommaso Tesi, Rapid Atlantification along the Fram Strait at the beginning of the 20th century, Science Advances (2021). DOI: 10.1126/sciadv.abj2946. www.science.org/doi/10.1126/sciadv.abj2946

Citation:
Arctic Ocean started getting warmer decades earlier than we thought, study finds (2021, November 24)
retrieved 25 November 2021
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Hexbyte Glen Cove Ocean currents predicted on Enceladus thumbnail

Hexbyte Glen Cove Ocean currents predicted on Enceladus

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Encased in an icy shell, the ocean on Enceladus appears to be churning. Credit: California Institute of Technology

Buried beneath 20 kilometers of ice, the subsurface ocean of Enceladus—one of Saturn’s moons—appears to be churning with currents akin to those on Earth.

The theory, derived from the shape of Enceladus’s , challenges the current thinking that the moon’s is homogenous, apart from some vertical mixing driven by the warmth of the moon’s core.

Enceladus, a tiny frozen ball about 500 kilometers in diameter (about 1/7th the diameter of Earth’s moon), is the sixth largest moon of Saturn. Despite its , Enceladus attracted the attention of scientists in 2014 when a flyby of the Cassini spacecraft discovered evidence of its large subsurface ocean and sampled water from geyser-like eruptions that occur through fissures in the ice at the . It is one of the few locations in the solar system with (another is Jupiter’s moon Europa), making it a target of interest for astrobiologists searching for signs of life.

The ocean on Enceladus is almost entirely unlike Earth’s. Earth’s ocean is relatively shallow (an average of 3.6 km deep), covers three-quarters of the planet’s surface, is warmer at the top from the sun’s rays and colder in the depths near the seafloor, and has currents that are affected by wind; Enceladus, meanwhile, appears to have a globe-spanning and completely subsurface ocean that is at least 30 km deep and is cooled at the top near the ice shell and warmed at the bottom by heat from the moon’s core.

Despite their differences, Caltech graduate student Ana Lobo (MS ’17) suggests that oceans on Enceladus have currents akin to those on Earth. The work builds on measurements by Cassini as well as the research of Andrew Thompson, professor of environmental science and engineering, who has been studying the way that ice and water interact to drive ocean mixing around Antarctica.

The oceans of Enceladus and Earth share one important characteristic: they are salty. And as shown by findings published in Nature Geoscience on March 25, variations in salinity could serve as drivers of the ocean circulation on Enceladus, much as they do in Earth’s Southern Ocean, which surrounds Antarctica.

Lobo and Thompson collaborated on the work with Steven Vance and Saikiran Tharimena of JPL, which Caltech manages for NASA.

Gravitational measurements and heat calculations from Cassini had already revealed that the ice shell is thinner at the poles than at the equator. Regions of thin ice at the poles are likely associated with melting and regions of thick ice at the equator with freezing, Thompson says. This affects the ocean currents because when salty water freezes, it releases the salts and makes the surrounding water heavier, causing it to sink. The opposite happens in regions of melt.

“Knowing the distribution of ice allows us to place constraints on circulation patterns,” Lobo explains. An idealized computer model, based on Thompson’s studies of Antarctica, suggests that the regions of freezing and melting, identified by the ice structure, would be connected by the ocean currents. This would create a pole-to-equator circulation that influences the distribution of heat and nutrients.

“Understanding which regions of the subsurface might be the most hospitable to life as we know it could one day inform efforts to search for signs of life,” Thompson says.



More information:
A pole-to-equator ocean overturning circulation on Enceladus, Nature Geoscience (2021). DOI: 10.1038/s41561-021-00706-3

Citation:
Ocean currents predicted on Enceladus (2021, March 25)
retrieved 26 March 2021
from https://phys.org/news/2021-03-ocean-currents-enceladus.html

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Hexbyte Glen Cove Oil in the ocean photooxidizes within hours to days, new study finds thumbnail

Hexbyte Glen Cove Oil in the ocean photooxidizes within hours to days, new study finds

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Satellite image taken on May 9, 2010 of the Deepwater Horizon oil spill site in the Gulf of Mexico. Credit: MODIS on NASA’s AQUA satellite, 9 May 2010 @ 190848 UTC. Downlink and processed at the UM Rosenstiel School’s Center for Southeastern Tropical Advanced Remote Sensing (CSTARS)

A new study led by scientists at the University of Miami (UM) Rosenstiel School of Marine and Atmospheric Science demonstrates that under realistic environmental conditions oil drifting in the ocean after the DWH oil spill photooxidized into persistent compounds within hours to days, instead over long periods of time as was thought during the 2010 Deepwater Horizon oil spill. This is the first model results to support the new paradigm of photooxidation that emerged from laboratory research.

After an oil , oil droplets on the ocean surface can be transformed by a weathering process known as photooxidation, which results in the degradation of crude oil from exposure to light and oxygen into new by-products over time. Tar, a by-product of this weathering process, can remain in coastal areas for decades after a spill. Despite the significant consequences of this weathering pathway, photooxidation was not taken into account in oil spill models or the oil budget calculations during the Deepwater Horizon spill.

The UM Rosenstiel School research team developed the first oil-spill model algorithm that tracks the dose of solar radiation oil droplets receive as they rise from the deep sea and are transported at the ocean surface. The authors found that the weathering of oil droplets by solar light occurred within hours to days, and that roughly 75 percent of the photooxidation during the Deepwater Horizon oil spill occurred on the same areas where chemical dispersants were sprayed from aircraft. Photooxidized oil is known to reduce the effectiveness of aerial dispersants.

“Understanding the timing and location of this weathering process is highly consequential. said Claire Paris, a UM Rosenstiel School faculty and senior author of the study. “It helps directing efforts and resources on fresh oil while avoiding stressing the environment with chemical dispersants on oil that cannot be dispersed.”

“Photooxidized compounds like tar persist longer in the environment, so modeling the likelihood of photooxidation is critically important not only for guiding first response decisions during an oil spill and restoration efforts afterwards, but it also needs to be taken into account on risk assessments before exploration activities” added Ana Carolina Vaz, assistant scientist at UM’s Cooperative Institute for Marine and Atmospheric Studies and lead author of the study.

The study, titled “A Coupled Lagrangian-Earth System Model for Predicting Oil Photooxidation,” was published online on Feb 19, 2021 in the journal Frontiers in Marine Science. The authors of the paper include: Ana Carolina Vaz, Claire Beatrix Paris and Robin Faillettaz.



More information:
Ana C. Vaz et al, A Coupled Lagrangian-Earth System Model for Predicting Oil Photooxidation, Frontiers in Marine Science (2021). DOI: 10.3389/fmars.2021.576747

Citation:
Oil in the ocean photooxidizes within hours to days, new study finds (2021, March 13)
retrieved 15 March 2021
from https://phys.org/news/2021-03-oil-ocean-photooxides-hours-days.html

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