Ninety years of data shows global warming impacts on foundation of marine ecosystems

Ninety years of data shows global warming impacts on foundation of marine ecosystems
Based on one of the longest time series of phytoplankton in the Southern Hemisphere, Australian researchers have found a significant warming signature in the phytoplankton community overtime. Credit: P. Ajani

Understanding the impacts of global warming on phytoplankton- the foundation of marine ecosystems -is critical to predicting changes in future biodiversity, ocean productivity, and ultimately fisheries production.


Based on one of the longest time series of phytoplankton in the Southern Hemisphere, Australian researchers have found a significant warming signature in the phytoplankton community overtime.

The data set was collected over almost 90 years from 1931-2019 from a Pacific Ocean coastal station offshore from Sydney.

The University of Technology Sydney (UTS) led research, published in Frontiers in Marine Science, provides insights into the potential traits that may determine the adaptive capacity or survivability of species under climate change.

Lead author, Dr. Penelope Ajani, said environmental data showed ocean temperature had risen 1.8°C over 90 years in south eastern Australia, one of the greatest warming regions in the world.

“We examined the phytoplankton community response to this long-term ocean warming using the Community Temperature Index (CTI), “Dr. Ajani said.

The CTI is an index of the preferred temperature of a phytoplankton community.

“We found a significant increase in the CTI overtime which suggests that the relative proportion of warm-water to cold-water species has increased,” Dr. Ajani said.

The researchers say that an almost 40% increase in the chain-forming diatom species Leptocylindrus danicus may provide a glimpse of the functional traits necessary to be a “winner” under climate change.

“This species does well in warmer water, reproduces rapidly and can survive in a wide temperature range. Together with the formation of resting spores and a high degree of variability in size, shape and physiology, these traits may point to the adaptive capacity or survivability of species under climate change, ” Dr. Ajani said.


Algae declines in the water off Sydney


More information:
Penelope A. Ajani et al, Global Warming Impacts Micro-Phytoplankton at a Long-Term Pacific Ocean Coastal Station, Frontiers in Marine Science (2020). DOI: 10.3389/fmars.2020.576011
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University of Technology, Sydney

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Ninety years of data shows global warming impacts on foundation of marine ecosystems (2020, November 2)
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Soot particles influence global warming more than previously assumed

Soot particles influence global warming more than previously assumed
Credit: Shutterstock

A team of researchers from ETH Zurich has for the first time used simulations on the CSCS supercomputer Piz Daint to investigate how certain aging mechanisms of soot particles in the atmosphere affect cloud formation. The results show that the influence of ozone and sulfuric acid on soot aging alters cloud formation and, ultimately, the climate.


Burning wood, petroleum products or other organic materials releases soot particles into the atmosphere that consist mainly of carbon. This soot is considered the second most important anthropogenic climate forcing agent after carbon dioxide. In the atmosphere or as deposits on snow and ice surfaces, soot particles absorb the short-wave radiation of the sun and thus contribute to global warming.

In the atmosphere, soot particles also have an indirect effect on the climate by altering the formation, development and properties of clouds. A research team led by Ulrike Lohmann, professor at the Institute for Atmosphere and Climate at ETH Zurich, has now for the first time investigated how two specific types of soot particles influence clouds and, in turn, the climate: on the one hand, soot aerosols that age due to ozone and, on the other, those that age due to sulfuric acid.

Soot chemistry changes cloud formation

“Until now, it was assumed that these two types of soot aging had little effect on cloud formation and climate,” says David Neubauer, scientific programmer in Lohmann’s research group. However, the results of the simulations now carried out on the CSCS supercomputer Piz Daint paint a different picture.

Soot particles influence global warming more than previously assumed
The impact of aged soot particles acting as cloud condensation nuclei (CCN) and ice nucleating particles (INPs) on cloud properties and the climate (equilibrium climate sensitivity (ECS). Credit: Fabian Mahrt/ETH Zurich

When soot particles combine with ozone or sulfuric acid, their physical and chemical properties change, write the researchers in their study recently published in the journal Nature Geoscience. Soot particles aged by ozone form condensation nuclei in lower layers of the atmosphere, which help clouds to form. In higher layers of the atmosphere, however, the soot particles aged by sulfuric acid act as ice nuclei and help cirrus clouds to form.

The team simulated how the differently aging soot particles influence cloud formation, and consequently the climate, from pre-industrial times to the future. In these simulations, the development of the aerosol particles is coupled to the physics of cloud formation in an interactive computation. This is complex and requires more computing time than conventional climate simulations.

The researchers made clearly defined assumptions for their calculations by describing the aging state of the soot particles, depending on temperature and ozone concentration. Both factors have a significant influence on aging: For soot to age rapidly through ozone, the temperature and ozone concentration must be high. For the ability of soot to act as an ice nuclei by sulfuric acid aging, a low temperature plays the decisive role.

Changed cloud formation leads to warming

Simulations of ozone-aged soot show that when the carbon dioxide content of the

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Mixed-phase clouds slow down global warming, but only up to a certain point

cloud
Credit: CC0 Public Domain

As the ice in the clouds melts into droplets, they reflect more sunlight. But in the end there is no more ice left to melt.


Clouds that contain both water droplets and ice crystals, calledmixed-phase clouds, have a slowing effect on global warming. This is because the clouds reflect more and more sunlight as ice turns to water.

But what happens when all the ice crystals have turned into droplets?

Doctoral Research Fellow Jenny Bjordal and Professor Trude Storelvmo at the Department of Geosciences at the University of Oslo have tried to figure it out.

“What we have found, is exciting, but also scary,” Storelvmo says to Titan.uio.no.

The results were published today in the scientific journal Nature Geoscience.

Clouds of ice and water

The clouds they have studied are in areas of the atmosphere with temperatures between 0 and 38 degrees below zero.

“The area where we find most of them is across the Southern Ocean. They are also found elsewhere, but that is where most of them are,” Bjordal says.

As climate scientists, they do not look at individual clouds and how they change or move. They study how the clouds change in an area over a long period of time—and whether they move in height, for example.

“These clouds consist of a mixture of ice crystals and drops,” Storelvmo says.

“When the climate gets warmer, more of the ice crystals will melt,” Bjordal explains.

Each small ice crystal turns into many even smaller droplets which gives an overall larger surface.

“Then the clouds reflect more sunlight,” Bjordal says.

“In that sense, those clouds have helped us a little. They have curbed the warming so far,” Storelvmo says.

Feedback effect

What happens to these clouds is an example of what is calledfeedback effects. Higher temperatures on Earth lead to changes in the clouds, which in turn affect the temperature.

Feedback effects can be both positive and negative. What the researchers call a positive feedback, means that the temperature will be even higher. Negative for the climate, that is, but positive in the calculations.

Mixed-phase clouds have a negative feedback. When it gets warmer, they reflect more light. They prevent sunlight from hitting the earth. Positive for the climate, but a minus in the figures.

“This means that we get a smaller temperature rise than we would have had without this effect,” Bjordal says.

The hotter it gets, the more ice will melt. This effect will increase as the temperature rise and keep it in check a bit. It does not stop it, but slows it down.

But only up to a certain point.

What happens when all the ice is melted?

At some point, there will be no more ice left. The clouds will still reflect sunlight, but the effect will not be able to increase and become even greater.

“As long as you have ice that can melt, the clouds will constantly reflect more and more. But eventually it will reach a

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