Deep-sea black carbon comes from hydrothermal vents

Hydrothermal vents have been identified as a previously undiscovered source of dissolved black carbon in the oceans, furthering the understanding of the role of oceans as a carbon sink.

The ocean is one of the largest dynamic carbon sinks in the world, and is susceptible to increased carbon emissions from human activities. There are even proposals to use the ocean to sequester carbon in an effort to reduce the carbon emissions. However, much of the processes by which the ocean functions as a carbon sink are not fully understood.

Associate Professor Youhei Yamashita and grad student Yutaro Mori at Hokkaido University, along with Professor Hiroshi Ogawa at AORI, The University of Tokyo, have revealed conclusive evidence that hydrothermal vents are a previously unknown source of dissolved black carbon in the deep ocean. Their discoveries were published in the journal Science Advances.

"One of the largest carbon pools on the Earth's surface is the dissolved organic carbon in the ocean," explains Ogawa. "We were interested in a portion of this pool, known as dissolved black carbon (DBC), which cannot be utilized by organisms. The source of DBC in the deep sea was unknown, although hydrothermal vents were suspected to be involved."

The researchers analyzed the distribution of DBC in the ocean basins of the North Pacific Ocean and Eastern South Pacific Ocean, and compared the data with previously reported concentrations of a helium isotope that is associated with hydrothermal vent emissions, as well as oxygen utilization in these areas.

Their findings showed that hydrothermal vents were an important source of DBC in the Pacific Ocean. This hydrothermal DBC is most likely formed due to the mixing of the hot fluids from hydrothermal vents with cold seawater, and is transported over long distances -- up to thousands of kilometers away.

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Shedding light on photosynthesis at sea

Plants that live on land, such as spinach, grow by using sunlight to perform photosynthesis. How, then, do algae photosynthesize in the deep sea, an environment where only a little light reaches them?

Land plants mainly absorb red and blue light from the sun and use it for photosynthesis. However, only weak blue-green light reaches the ocean floor. Therefore, macroalgae growing in the ocean have developed a protein, a so-called photosynthetic antenna, that efficiently utilizes this blue-green light. The photosynthetic antenna of marine macroalgae is very similar to that of land plants but differs in the structure of the pigments bound to it. Land plants have two types of pigments bound to their photosynthetic antennae, namely carotenoids and chlorophylls. In the marine green macroalga Codium fragile, the major carotenoids are substituted with siphonaxanthin while some chlorophyll a molecules are replaced by chlorophyll b molecules. Siphonaxanthin and chlorophyll b are known to contribute to increased absorption of green light and blue-green light, respectively, but the mechanism has not yet been fully understood.

Responding to this gap, a research team led by Associate Professor Ritsuko Fujii, from the Research Center for Artificial Photosynthesis (ReCAP) at Osaka Metropolitan University, and graduate student Soichiro Seki, from the Graduate School of Science at Osaka City University, used cryogenic electron microscopy to investigate the structures and binding environments of pigments bound to the photosynthetic antenna of C. fragile. The results allow for the elucidation of the molecular mechanism by which blue-green light -- the only light available in deep seawater -- is efficiently utilized for photosynthesis. Their findings were published in BBA Advances on November 11, 2022.

High-resolution analysis by cryogenic electron microscopy showed that siphonaxanthin in C. fragile is greatly distorted and forms hydrogen bonds with the surrounding protein at two locations. This structural feature is deemed a key factor in siphonaxanthin's ability to absorb green light. Additionally, the researchers successfully detected the difference between chlorophyll a and chlorophyll b, and they clarified several chlorophyll molecule substitution sites. When the substitution occurs, the adjacent region of chlorophyll b clusters becomes wider, enabling better absorption of blue-green light. In other words, the team was able to obtain information on the pigment coordinates, contributing to a better understanding of the mechanism of more efficient photosynthesis.

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A new species of deep-sea fish discovered in the Atacama Trench

A new small blue snailfish is changing our understanding of the world's deepest fishes.

In 2018, an international team of scientists studied the Atacama Trench, an expansive trench that runs along the west coast of South America as a deep underwater valley that mirrors the Andes Mountains. The team, including Newcastle University scientists, deployed free-falling landers to sample the sparse deep-sea creatures around cameras and traps with bait. Two lander systems from Newcastle University recorded three types of hadal snailfish and one of them was not like the others.

The small blue fish, seen from about 6,000 to 7,600 m deep, doesn't look like other hadal snailfish. With large eyes and striking colour, it resembles other species of snailfishes that are found living in much shallower waters. The team used a 3D x-ray technique called microcomputed tomography (micro-CT) and DNA barcoding to see where the new species fit within the snailfish family.

To the team's surprise, the new species appears to be a separate coloniser of the Atacama Trench. The new species belongs is a member of the genus Paraliparis. Species in this genus are particularly abundant in the Southern Ocean of the Antarctic and are rarely found deeper than 2,000 m. Significantly, this is the first time this genus has been found living in the hadal zone.

The team named the new species Paraliparis selti, meaning blue in the Kunza language of the indigenous peoples of the Atacama Desert. The description is published in the journal Marine Biodiversity.

Study lead author, Dr Thom Linley, a visiting researcher at Newcastle University said: "I find this family of fishes absolutely fascinating. They are not at all what we expect from a deep-sea fish and I love to show people that the world's deepest fishes are actually pretty cute.

"For me to get a camera down to where these animals live, it's made of inches thick stainless steel and sapphire glass. It then films these delicate and beautiful animals perfectly adapted to this extreme environment. With engineering-built force we can only clumsily visit these animals for a short time.

"We have been wondering for some time just what makes this type of fish so good at living deep. Maybe it was a series of lucky accidents, a chance fluke, that happened in one lineage. Finding this new species tells us that it's bigger than that. Lightning struck twice and there is something special about this Family.

"Paraliparis selti provides a fantastic opportunity to explore what allows fish to live so deep. If we only had a single lineage to study, we could never be sure which traits were just part of that lineage and which are the deep-sea secret sauce."

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New giant deep-sea isopod discovered in the Gulf of Mexico

Researchers have identified a new species of Bathonymus, the famed genera of deep-sea isopods whose viral internet fame has made them the most famous aquatic crustaceans since Sebastian of The Little Mermaid.

There are around 20 species of living Bathonymus, a mysterious and primitive group that inhabits the benthic zone of the ocean -- its deepest reaches, rarely explored in person. Isopod crustaceans are only distantly related to their better-known decapod relatives, the crabs, shrimp, and lobsters.

Publishing their findings in the peer-reviewed Journal of Natural History, a group of Taiwanese, Japanese, and Australian researchers reveal the latest creature to this list -- B. yucatanensis, a new species which is around 26cm long -- some 2,500% larger than the common woodlouse.

Deep sea isopods belong to the same group that contains the terrestrial isopods known variously as woodlice, pillbugs, and roly polys, which feed on decaying matter and are likely familiar to anyone who has lifted up a rock or dug around in the garden. Indeed, they look quite similar but for their extraordinary size -- the largest of them grow to nearly 50 centimeters. And, just like woodlouse, although they perhaps look a little scary, they are completely harmless to humans.

Their strange features and unusual dimensions have spawned endless memes and a range of products celebrating their endearing weirdness, from plush toys to phone cases.

This finding of B. yucatanensis adds another addition to the isopod pantheon and brings the total of known species of Bathonymus in the Gulf of Mexico to three -- B. giganteus was described in 1879 and B. maxeyorum was described in 2016.

It was initially thought to be a variation of B. giganteus, one of the largest of the deep-sea isopods. But closer examination of the specimen, which was captured in a baited trap in 2017 in the Gulf of Mexico off the Yucatán Peninsula at around 600 to 800 meters down, revealed an array of unique features.

"B. yucatanensis is morphologically distinct from both B. giganteus and B. maxeyorum," the authors claim.

Held by the Enoshima Aquarium in Japan, the individual studied was subtly different than its relatives. "Compared to B. giganteus, B. yucatanensis has more slender body proportions and is shorter in total length … and the pereopods [thoracic limbs] are more slender," the researchers observe. It also has longer antennae. The two species have the same number of pleotelson spines. These spines protrude from the tail end of the crustacean.

"Bathynomus giganteus was discovered over a century ago, and more than 1,000 specimens have been studied with no suggestion until now of a second species with the same number of pleotelsonic spines," they add. "Superficial examination, using only pleotelson spines, could easily result in specimens of B. yucatanensis being misidentified as B. giganteus."

"Compared with B. maxeyorum, the most distinctive feature is the number of pleotelson spines -- 11 spines in B. yucatanensis versus 7 in B. maxeyorum." The blotchy, creamy yellow coloration of the shell further distinguished it from its greyer relatives.

In order to be sure, the scientists conducted a molecular genetic analysis comparing B. giganteus and B. yucatanensis. "Due to the different sequences of the two genes (COI and 16S rRNA), coupled with differences in morphology, we identified it as a new species," they write. The phylogenetic tree they constructed showed B. yucatanensis as most closely related to B. giganteus.

"B. giganteus is indeed the species closest to B. yucatanensis," the authors assert. "This indicates that the two species likely had a common ancestor. Additionally, there may also be other undiscovered Bathynomus spp. in the tropical western Atlantic.

The paper also clarifies that specimens from the South China Sea identified as B. kensleyi are actually B. jamesi. B. kensleyi is restricted to the Coral Sea, off the coast of Australia.

"It is increasingly evident that species of Bathynomus may be exceedingly similar in overall appearance, and also that there is a long history of misidentification of species in the genus," the authors caution.

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