This protistan grazing, which is a key mechanism for carbon transport and recycling in microbial food webs, exerts a higher predation pressure at hydrothermal vent sites than in the surrounding deep-sea environment, a new paper finds.

“Our findings provide a first estimate of protistan grazing pressure within hydrothermal vent food webs, highlighting the important role that diverse deep-sea protistan communities play in deep-sea carbon cycling,” according to the paper, Protistan grazing impacts microbial communities and carbon cycling ad deep-sea hydrothermal vents published in the Proceedings of the National Academy of Sciences (PNAS).

Protists serve as a link between primary producers and higher trophic levels, and their grazing is a key mechanism for carbon transport and recycling in microbial food webs, the paper states.

The research found that protists consume 28-62% of the daily stock of bacteria and archaea biomass within discharging hydrothermal vent fluids from the Gorda Ridge, which is located about 200 kilometers off the coast of southern Oregon. In addition, researchers estimate that protistan grazing could account for consuming or transferring up to 22% or carbon that is fixed by the chemosynthetic population in the discharging vent fluids. Though the fate of all of that carbon is unclear, “protistan grazing will release a portion of the organic carbon into the microbial loop as a result of excretion, egestion, and sloppy feeding,” and some of the carbon will be taken up by larger organisms that consume protistan cells, the paper states.

After collecting vent fluid samples from the Sea Cliff and Apollo hydrothermal vent fields in the Gorda Ridge, researchers conducted grazing experiments, which presented some technical challenges that needed to be overcome. For instance, “prepping a quality meal for these protists is very difficult,” said lead author Sarah Hu, a postdoctoral investigator in the Marine Chemistry and Geochemistry Department at the Woods Hole Oceanographic Institution (WHOI).

“Being able to do this research at a deep-sea vent site was really exciting because the food web there is so fascinating, and it’s powered by what’s happening at this discharging vent fluid,” said Hu, who was onboard the E/V Nautilus during the May-June 2019 cruise. “There is this whole microbial system and community that’s operating there below the euphotic zone outside of the reach of sunlight. I was excited to expand what we know about the microbial communities at these vents.”

Hu and co-author Julie Huber said that quantitative measurements are important to understand how food webs operate at pristine and undisturbed vent sites.

“The ocean provides us with a number of ecosystem services that many people are familiar with, such as seafood and carbon sinks. Yet, when we think about microbial ecosystem services, especially in the deep sea, we just don’t have that much data about how those food webs work,” said Huber, associate scientist in WHOI’s Marine Chemistry and Geochemistry Department.

Obtaining baseline measurements “is increasingly important as these habitats are being looked at for deep-sea mining or carbon sequestration. How might that impact how much carbon is produced, exported, or recycled?” she said.

“We need to understand these habitats and the ecosystems they support,” Huber said. “This research is connecting some new dots that we weren’t able to connect before.”

The research was supported by NASA, the National Oceanic and Atmospheric Administration, Ocean Exploration Trust, the National Science Foundation, and WHOI.

Investigating how climate affects intense rainstorms across Europe, climate experts have shown there will be a significant future increase in the occurrence of slow-moving intense rainstorms. The scientists estimate that these slow-moving storms may be 14 times more frequent across land by the end of the century. It is these slow-moving storms that have the potential for very high precipitation accumulations, with devastating impacts, as we saw in Germany and Belgium.

Led by Dr Abdullah Kahraman, of Newcastle University’s School of Engineering, the researchers used very detailed climate model simulations at the UK Met Office Hadley Centre. They found that slower storm movement acts to increase the amount of rainfall that accumulates locally, increasing the risk of flash floods across Europe beyond what has been expected based on previous studies.

Published in the journal Geophysical Research Letters, the study results show that storms producing intense rain may move slower with climate change, increasing the duration of exposure to these extremes.

Dr Abdullah Kahraman, who is also a visiting scientist at the Met Office, said: “With recent advances in supercomputer power, we now have pan-European climate simulations resolving the atmosphere in high detail as short-range weather forecasting models do. These models have grid spacing of approximately 2 km, which allows them to simulate storm systems much better, resulting in better representation of extremes.

“Using these state-of-the-art climate simulations, we have developed metrics to extract potential cases for heavy rainfall, and a smaller, almost-stationary subset of these cases with the potential for high rainfall accumulations. These metrics provide a holistic view of the problem, and help us understand which factors of the atmosphere contribute to heavy rainfall changes.

“This is one of the first studies to explore changes in the speed of such heavy rainfall systems — an important aspect contributing to flood risk. Currently, we are also investigating other extreme weather types by examining the climate simulations data with a severe weather forecaster’s perspective.”

Professor Hayley Fowler, of Newcastle University’s School of Engineering, added: “Governments across the world have been too slow in reducing greenhouse gas emissions and global warming continues apace. This study suggests that changes to extreme storms will be significant and cause an increase in the frequency of devastating flooding across Europe. This, alongside the current floods in Europe, is the wake-up call we need to produce improved emergency warning and management systems, as well as implementing climate change safety factors into our infrastructure designs to make them more robust to these severe weather events.”

Professor Lizzie Kendon, Science Fellow at the Met Office and Professor at Bristol University, said: “This study shows that in addition to the intensification of rainfall with global warming, we can also expect a big increase in slow-moving storms which have the potential for high rainfall accumulations. This is very relevant to the recent flooding seen in Germany and Belgium, which highlights the devastating impacts of slow-moving storms.

“Our finding that slow-moving intense rainstorms could be 14 times more frequent by the end of the century under the high emissions RCP8.5 scenario, shows the serious impacts that we may expect across Europe if we do not curb our emissions of greenhouse gases.”

The study findings are relevant to climate mitigation and adaptation policy in Europe, with specific implications for future flooding impacts, the design of infrastructure systems, and the management of water resources.

Currently, almost stationary intense rainstorms are uncommon in Europe and happen rarely over parts of the Mediterranean Sea. Accurate predictions of future changes in intense rainfall events are key to putting effective adaptation and mitigation plans in place to limit the adverse impacts of climate change.

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“One of the dirty tricks of climate change is that local pollution has far-reaching consequences,” says former Aquarium Chief Scientist Dr. Kyle Van Houtan, who led the study during his tenure. “When we burn fossil fuels like coal, oil, and gas locally, we mix them in the experimental chamber pot of our planet’s atmosphere. The result is that their warming impacts are often exported to far away locations.”

The study reinforces that, while people living near refinery, drilling, and manufacturing facilities experience localized health and environmental impacts, emissions from a relatively small area are raising temperatures in communities and ecosystems around the world.

To reach these conclusions, the study charts discharges of the top four heat-trapping agents, which make up 92 percent of all greenhouse emissions, from 1970 to 2018: carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O) and black carbon (sometimes referred to as PM2.5). The authors compared the sources of those emissions to global temperature projections over the entire surface of the planet.

They confirmed that, while the source of emissions causing climate change are concentrated, the impacts are widespread. Remarkably, 90 percent of all greenhouse emissions are generated from human activities across eight percent of Earth’s surface area — yet more than half of Earth’s landmass will experience extreme warming by the end of the 21st century.

The study also mapped the economic disparities that are inherent with climate change. The researchers showed how more developed and industrialized regions such as western Europe, northeastern North America and the Arabian gulf states emit more extreme amounts of heat-trapping emissions but will experience relatively fewer climate impacts. Countries in Africa and across Central Asia, which produce some of the lowest amounts of these emissions, will experience the most disruption from the impacts of burning of fossil fuels.

The disparities illustrated on the global map can also be found within individual countries. For example, most greenhouse emissions within the United States originate in the more industrialized northeastern region (New Jersey, Connecticut, Pennsylvania). Warming, though, is more likely to happen in the west — most notably in Alaska, South Dakota, Idaho, and Montana.

This study helps visualize the outsized role the ocean plays in absorbing emissions-driven warming. While it is estimated that the ocean takes in about 93 percent of the excess heat that is a consequence of these emissions, the researchers calculated that over 95 percent of the greenhouse emissions measured originated on land.

In serving this role, the ocean mitigates the worst impacts of climate change for all humankind.

“Our findings offer a stark rendering of what the ocean does for us,” says Dr. Van Houtan. “Covering 72 percent of our planet, the global ocean serves as the heart of our climate system, regulating weather patterns and transferring heat and water around the planet. But we can’t take the ocean for granted. We need to protect ocean health so that it continues to play this vital role for all people on Earth. We need to focus on drastically reducing greenhouse emissions and adapting to climate impacts so that we can protect and maintain the ecosystem services we all depend on for survival.”

Study authors say the warming projections reinforce the urgent need for global collective action to avoid the 1.5 degrees C above pre-industrial levels by the end of the century. It underscores the need for data visualization and science communications to facilitate productive public dialogue about equitable climate solutions. It also highlights the outsized role the ocean plays in mitigating against the worst impacts for all humankind.

“When we listen to the scientific consensus — and to the people suffering most from climate disruption — we see that only a broad, international collaboration to stabilize our planet’s climate will work,” says Dr. Van Houtan. “And by working together today to reduce our reliance on fossil fuels, we can protect the global ocean and living world that sustains all life on Earth.”