It’s possible that I shall make an ass of myself. But in that case one can always get out of it with a little dialectic. I have, of course, so worded my proposition as to be right either way (K.Marx, Letter to F.Engels on the Indian Mutiny)
Thursday, September 26, 2024
OCEANOGRAPHY
‘Invisible forest’ of algae thrives as ocean warms
University of Exeter
image:
CTD rosette – a device equipped with sensors and bottles to collect water samples and measure different properties of the ocean at various depths
An “invisible forest” of phytoplankton is thriving in part of our warming ocean, new research shows.
Phytoplankton are tiny drifting organisms that do about half of the planet’s “primary production” (forming living cells by photosynthesis).
The new study, by the University of Exeter, examined phytoplankton at the ocean surface and the “subsurface” – a distinct layer of water beneath – to see how climate variability is affecting them.
Published in the journal Nature Climate Change, the findings show these two communities are reacting differently.
Over the last decade, the total “biomass” (living material) of subsurface phytoplankton has increased in response to warming.
Meanwhile, surface phytoplankton now has less chlorophyll – making it less green – but in fact total biomass has remained stable.
Based on 33 years of data from the Bermuda Atlantic Time-series Study (BATS) in the Sargasso Sea, the findings also suggest the depth of the “surface mixed-layer” (region of turbulence at the surface of the ocean) has shallowed as the ocean rapidly warmed in the last decade.
“It’s important to understand these trends because phytoplankton are the foundation of the marine food web, and play a key role in removing carbon dioxide from the atmosphere,” said Dr Johannes Viljoen, from the Department of Earth and Environmental Science at Exeter’s Penryn Campus in Cornwall.
“Our findings reveal that deep-living phytoplankton, which thrive in low-light conditions, respond differently to ocean warming and climate variability compared to surface phytoplankton.
“We typically rely on satellite observations to monitor phytoplankton, but the subsurface is hidden from satellite view.
“Our study highlights the limitations of satellite observations, and underscores the urgent need for improved global monitoring of phytoplankton below what satellites can see.”
Co-author Dr Bob Brewin added: “Changes at the base of the food web can have cascading effects on marine life, from tiny zooplankton to large fish and marine mammals.
“So the future of phytoplankton will have major implications for biodiversity, as well as climate change.”
Dr Viljoen added: “Continued monitoring of these deep-living phytoplankton will help scientists better understand ongoing changes in the ocean that might otherwise go unnoticed.”
The research of Dr Viljoen and co-authors Dr Brewin and Dr Xuerong Sun, all from the Centre for Geography and Environmental Science, is supported by a UKRI Future Leader Fellowship awarded to Dr Brewin.
The paper is entitled: “Climate variability shifts the vertical structure of phytoplankton in the Sargasso Sea.”
CTD rosette – a device equipped with sensors and bottles to collect water samples and measure different properties of the ocean at various depths
Credit
Dr Xuerong Sun
Journal
Nature Climate Change
Article Title
Climate variability shifts the vertical structure of phytoplankton in the Sargasso Sea
Article Publication Date
25-Sep-2024
New study: Deep-sea discovery shines light on life in the twilight zone
Unexpected findings expand our understanding of the impacts of climate change, including how and where the ocean stores carbon, said co-author and University of South Florida scholar Tim Conway
A conductivity, temperature and depth (CTD) rosette used to sample water from the ocean’s twilight zone during a GEOTRACES expedition in the Pacific Ocean.
TAMPA, Fla. (Sept. 23, 2024) – The ocean’s twilight zone is deep, dark, and — according to new research — iron deficient.
No sunlight reaches this region 200 to 1,000 meters below the sea surface, where levels of iron, a key micronutrient, are so low that the growth of bacteria is restricted. To compensate, these bacteria produce molecules called siderophores, which help the bacteria scavenge trace amounts of iron from the surrounding seawater.
The paper detailing these unexpected findings from the Pacific Ocean will publish on Wednesday, Sept. 25, at 11 a.m. ET (4 p.m. London Time) in Nature, and will be viewable at that time at this link. The study could change the way scientists view microbial processes in the deep ocean and offer new insight into the ocean’s capacity to absorb carbon.
“Understanding the organisms that facilitate carbon uptake in the ocean is important for understanding the impacts of climate change,” said Tim Conway, associate professor of chemical oceanography at the USF College of Marine Science, who co-authored the recent study. “When organic matter from the surface ocean descends to the deep ocean, it acts as a biological pump that removes carbon from the atmosphere and stores it in seawater and sediments. Measuring the rates and processes that influence this pump gives us insight into how and where the ocean stores carbon.”
To conduct the study, researchers collected water samples from the upper 1,000 meters of the water column during an expedition through the eastern Pacific Ocean from Alaska to Tahiti. What they found in the samples surprised them. Not only were concentrations of siderophores high in surface waters where iron is expected to be deficient, but they were also elevated in waters between 200 and 400 meters deep, where nutrient and iron concentrations were thought to have little impact on the growth of bacteria.
“Unlike in surface waters, we did not expect to find siderophores in the ocean’s twilight zone,” said Conway. “Our study shows that iron-deficiency is high for bacteria living in this region throughout much of the east Pacific Ocean, and that the bacteria use siderophores to increase their uptake of iron. This has a knock-on effect on the biological carbon pump, because these bacteria are responsible for the breakdown of organic matter as it sinks through the twilight zone.”
The recent discovery was part of GEOTRACES, an international effort to provide high-quality data for the study of climate-driven changes in ocean biogeochemistry.
The study of siderophores is still in the early stages. Researchers involved in GEOTRACES only recently developed reliable methods to measure these molecules in water samples, and they’re still working to understand where and when microbes use siderophores to acquire iron.
Although the research into siderophores is new, this study demonstrates their clear impact on the movement of nutrients in the ocean’s twilight zone.
“For a full picture of how nutrients shape marine biogeochemical cycles, future studies will need to take these findings into account,” said Daniel Repeta, senior scientist at Woods Hole Oceanographic Institution and co-author of the article. “In other words, experiments near the surface must expand to include the twilight zone.”
Click here for images and a PDF of the journal article
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About the University of South Florida
The University of South Florida, a high-impact research university dedicated to student success and committed to community engagement, generates an annual economic impact of more than $6 billion. With campuses in Tampa, St. Petersburg and Sarasota-Manatee, USF serves approximately 50,000 students who represent nearly 150 different countries. U.S. News & World Report has ranked USF as one of the nation’s top 50 public universities for five consecutive years, and this year USF earned its highest ranking ever among all universities public or private. In 2023, USF became the first public university in Florida in nearly 40 years to be invited to join the Association of American Universities, a prestigious group of the leading universities in the United States and Canada. Through hundreds of millions of dollars in research activity each year and as one of the top universities in the world for securing new patents, USF is a leader in solving global problems and improving lives. USF is a member of the American Athletic Conference. Learn more at www.usf.edu.
Left to right: CTD technician Kyle McQuiggan, Research Technician Keith Shadle and multi-talented Data Analyst Joseph Gum work together to repair the trace metal CTD rosette’s connection to the ship.
Co-chief Scientist Phoebe Lam of the University of California, Santa Cruz and others removed the pump’s damaged section of cable from the wi
Journal
Nature
Method of Research
Observational study
Subject of Research
Not applicable
Article Title
Microbial iron limitation in the ocean’s twilight zone
Article Publication Date
25-Sep-2024'
Nanostructures in the deep ocean floor hint at life’s origin
RIKEN
image:
a) Photograph of HV precipitates collected from the Shinkai Seep Field. b) Cross-polarized optical microscope images of precipitates in cross section. c,d) Scanning electron images showing layers within the precipitates. f) Magnification showing sublayers in the boxed area of d.
Researchers led by Ryuhei Nakamura at the RIKEN Center for Sustainable Resource Science (CSRS) in Japan and The Earth-Life Science Institute (ELSI) of Tokyo Institute of Technology have discovered inorganic nanostructures surrounding deep-ocean hydrothermal vents that are strikingly similar to molecules that make life as we know it possible. These nanostructures are self-organized and act as selective ion channels, which create energy that can be harnessed in the form of electricity. Published Sep. 25 in Nature Communications, the findings impact not only our understanding of how life began, but can also be applied to industrial blue-energy harvesting.
When seawater seeps way down into the Earth through cracks in the ocean floor, it gets heated by magma, rises back up to the surface, and is released back into the ocean through fissures called hydrothermal vents. The rising hot water contains dissolved minerals gained from its time deep in the Earth, and when it meets the cool ocean water, chemical reactions force the mineral ions out of the water where they form solid structures around the vent called precipitates.
Hydrothermal vents are thought to be the birthplace of life on Earth because they provide the necessary conditions: they are stable, rich in minerals, and contain sources of energy. Much of life on Earth relies on osmotic energy, which is created by ion gradients—the difference in salt and proton concentration—between the inside and outside of living cells. The RIKEN CSRS researchers were studying serpentinite-hosted hydrothermal vents because this kind of vent has mineral precipitates with a very complex layered structure formed from metal oxides, hydroxides, and carbonates. “Unexpectedly, we discovered that osmotic energy conversion, a vital function in modern plant, animal, and microbial life , can occur abiotically in a geological environment,” says Nakamura.
The researchers were studying samples collected from the Shinkai Seep Field, located in the Pacific Ocean’s Mariana Trench at a depth of 5743 m. The key sample was an 84-cm piece composed mostly of brucite. Optical microscopes and scans with micrometer-sized X-ray beams revealed that brucite crystals were arranged in continuous columns that acted as nano-channels for the vent fluid. The researchers noticed that the surface of the precipitate was electrically charged, and that the size and direction of the charge—positive or negative—varied across the surface. Knowing that structured nanopores with variable charge are the hallmarks of osmotic energy conversion, they next tested whether osmotic energy conversion was indeed occurring naturally in the inorganic deep-sea rock.
The team used an electrode to record the current-voltage of the samples. When the samples were exposed to high concentrations of potassium chloride, the conductance was proportional to the salt concentration at the surface of the nanopores. But at lower concentrations, the conductance was constant, not proportional, and was determined by the local electrical charge of the precipitate’s surface. This charge-governed ion transport is very similar to voltage-gated ion channels observed in living cells like neurons.
By testing the samples with chemical gradients that exist in the deep ocean from where they were extracted, the researchers were able to show that the nanopores act as selective ion channels. At locations with carbonate adhered to the surface, the nanopores allowed positive sodium ions to flow through. However, at nanopores with calcium adhered to the surface, the pores only allowed negative chloride ions to pass through.
“The spontaneous formation of ion channels discovered in deep-sea hydrothermal vents has direct implications for the origin of life on Earth and beyond,” says Nakamura. “In particular, our study shows how osmotic energy conversion, a vital function in modern life, can occur abiotically in a geological environment.”
Industrial power plants use salinity gradients between seawater and river water to generate energy, a process called blue-energy harvesting. According to Nakamura, understanding how nanopore structure is spontaneously generated in the hydrothermal vents could help engineers devise better synthetic methods for generating electrical energy from osmotic conversion.
Ionic transport by hydrothermal vent precipitates
Schematic showing osmotic power generation upon exposure to potassium chloride (KCl). Overlap of electric double layers within nanopores establishes a screening barrier that is permeable only to ions with specific charges.
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