Wednesday, December 1

Undeveloped Submarine Resources — Forefront of Research on “Undersea Manganese Deposits”

Did you know that Japan, which lacks terrestrial mineral resources and energy, relies on imports from abroad for most of it? However, in recent years, it has become clear from the results of a survey of Japan’s exclusive economic zone that a large amount of marine resources such as “methane hydrate” and “iron manganese crust” exist. If these can be put into practical use commercially, they may support the future industrial economy of Japan. In the “Marine Energy and Mineral Resources Development Plan” formulated by the Ministry of Economy, Trade and Industry, for example, “iron manganese crust” is planned to be commercialized by a private company by 2028. Surveys of these marine resources have been in full swing since 2011, but their properties, distribution, and formation process are often unknown. For commercialization, it is essential to establish a low-cost and efficient collection method and a research method to clarify the area where it can be collected, but in order to reach that point, basic research on these marine resources is first required. .. The Japan Agency for Marine-Earth Science and Technology (JAMSTEC) holds a report meeting on the results of marine resource research on different resources every year, and uses this meeting as a place for discussions with industry for future commercial utilization.

We interviewed the results report meeting “Undersea Manganese Deposit-Forefront of Cobalt Rich Crust Research and Potential as a Resource” held on September 6th. In this article, we will briefly explain marine resources such as submarine manganese deposits, and then introduce the presentations of the four speakers.

Undersea resources around Japan

First, I would like to introduce some energy resources and mineral resources distributed on the seabed around Japan.One of them is a submarine hydrothermal vent that operates on the deep sea floor. At the submarine hydrothermal vent, hot water of 300 degrees or higher that springs up from below the seabed is ejected from a chimney-like “Chimney” (columnar outlet). Chimneys consist of sulfides such as copper, zinc, lead and silver and can be metal deposits of rare metals.

Figure 1. A hydrothermal vent on the seafloor in the southern part of the Central Indian Ridge. This is a spout that emits black hot water and is also called a
Figure 1. A hydrothermal vent on the seafloor in the southern part of the Central Indian Ridge. This is a spout that emits black hot water and is also called a “black smoker.” White shrimp can be seen in the surrounding area (Courtesy: JAMSTEC)

The second is methane hydrate, which is a water molecule that takes in methane molecules and solidifies into ice under low-temperature and high-pressure conditions under the seabed. There are two types of methane, one is produced by thermal decomposition of organic matter under the seabed and the other is produced by microbial activity. While it is expected to be a next-generation energy resource to replace fossil fuels such as coal and petroleum, it is feared that methane gas can become a greenhouse gas in the air.

Figure 2. Methane hydrate exposed on the seafloor off the coast of the Sea of ​​Japan (courtesy of JAMSTEC)
Figure 2. Methane hydrate exposed on the seafloor off the coast of the Sea of ​​Japan (courtesy of JAMSTEC)

The third is the iron manganese crust reported this time (hereinafter referred to as manganese crust). Manganese crust is mainly composed of iron and manganese oxide, and exists so as to cover the slopes and tops of seamounts. Also includes rare metals such as cobalt and platinum, and rare earths. In particular, those containing a large amount of cobalt are called “cobalt-rich crusts”. Manganese-rich heavy metal oxide deposits, including manganese crusts and cobalt-rich crusts, are called “manganese deposits” and are the main theme of this results report meeting.

In January of this year, a survey with the unmanned explorer “Kaikou Mk-IV” succeeded in sampling the cobalt lick crust, which extends to the deepest water depth of 5,500 meters, and provided a stepping stone to greatly advance the research. (See related links).

Figures 3 and 4. The photo above is a pillow-shaped manganese crust taken in the Shikoku Basin (courtesy of JAMSTEC). The photo below is the manganese crust exhibited at the venue.
Figure 3. Pillow-shaped manganese crust photographed in the Shikoku Basin (courtesy of JAMSTEC).
Figures 3 and 4. The photo above is a pillow-shaped manganese crust taken in the Shikoku Basin (courtesy of JAMSTEC). The photo below is the manganese crust exhibited at the venue.
Figure 4. The manganese crust exhibited at the venue.
Figure 5. Distribution of submarine resources near Japan. It can be seen that all the red points indicating the manganese crust are distributed on the summits and slopes of seamounts (courtesy of JAMSTEC).
Figure 5. Distribution of submarine resources near Japan. It can be seen that all the red points indicating the manganese crust are distributed on the summits and slopes of seamounts (courtesy of JAMSTEC).

From the announcement of four researchers

At the debriefing session, each of the four researchers will discuss 1. Summary of current findings of seafloor manganese deposits, origin of seafloor manganese deposits, 2. Formation model on ancient Earth, 3. Chemical approach, 4. Biological approach. Announced the research results of.

● How much do you know about the actual condition of submarine manganese deposits?

Akira Usui is a specially appointed professor at the Center for Marine Core Research, Kochi University, who has been conducting research on seafloor manganese deposits for more than 40 years since the first research on the development of marine resources. According to Usui, exploration research on submarine manganese deposits has made great strides between 2011 and 2014 due to the acceleration of technological development such as sonar (sound wave) exploration in recent years. The latest survey found that the distribution in the northwestern Pacific extends from west of Hawaii to off Kyushu, with a depth of more than 1,000 to 6,000 meters, and the area and depth are wider than expected at the beginning of the study. Since the seafloor manganese deposit contains iron and metals such as manganese and cobalt in a ratio close to that of onshore ore, it means that a huge amount of resources comparable to those on land are sleeping.

The submarine manganese deposit is said to be a “living deposit” that grows at a rate of a few millimeters to a few centimeters over millions of years and continues to form in an ongoing manner through a steady material cycle. Found on the deep sea floor of the world, the main sources of metals are believed to be weathering and volcanic activity of crustal material. However, the process of how iron and manganese are oxidized and concentrated is not yet clear. The ultra-slow formation speed makes it difficult to elucidate.

In 2001, Mr. Usui conducted an “on-site deposition experiment of manganese oxide” on the manned submersible research vehicle “Shinkai 6500”. This is to sink the core plate of manganese oxide crystals into the deep sea floor and see how the metal concentrates in seawater. In 2014, when the submerged plate was taken out and analyzed, it was found that metal crystals such as rare earths, nickel, and copper were formed around the plate. Usui suspects this is a primary substance of manganese crust. The plate is still on the deep sea floor, and we look forward to the next recovery and analysis. He also introduced his latest achievement, which shows a correlation between water depth and metal concentration.

● Undersea manganese deposits

Katsuhiko Suzuki, Deputy Director of JAMSTEC Submarine Resources Research and Development Center, introduced research to estimate the formation process of submarine manganese deposits, using onshore manganese deposits as hints. In the 4.6 billion year history of the earth, it is said that there were two “snowball earths” that freeze the entire earth, but there is a glacier deposit “diamicton” under the largest Kalahari manganese deposit (South Africa) on land. It is deposited and is known to have formed in the first Snowball Earth (2.4-2.2 billion years ago) sea. It is also known that oxygen in the atmosphere rose at that time.

Figure 6. A diagram showing the history of the earth. It can be seen that the time when the Kalahari manganese deposit was formed (red bar in the center of the lower frame) coincides with the time of the first Snowball Earth (global freeze) (from Suzuki's slide. Courtesy of JAMSTEC).
Figure 6. A diagram showing the history of the earth. It can be seen that the time when the Kalahari manganese deposit was formed (red bar in the center of the lower frame) coincides with the time of the first Snowball Earth (global freeze) (from Suzuki’s slide. Courtesy of JAMSTEC).

As mentioned above, manganese deposits are mainly composed of iron and manganese oxide. In other words, it is thought that it was created in an era when there was abundant oxygen enough to oxidize metal ions in the sea. Here is the scenario in which the Kalahari manganese deposit was created. In the days of Snowball Earth, where the earth’s surface was covered with ice, land and sea surfaces were frozen, but liquid water was trapped in the sea. Therefore, manganese ions in seawater increased due to underwater volcanic activity. Eventually, when that era ended and cyanobacteria * in the sea proliferated, oxygen in seawater increased. This oxidizes manganese ions and precipitates them on the seafloor, forming manganese deposits.

* Cyanobacteria / blue-colored algae that breed in water and glaciers. It is thought that 2.7 billion years ago, as a result of the large breeding of cyanobacteria, a large amount of oxygen was produced on the earth by photosynthesis, creating the current oxygen-rich atmosphere.

To confirm this scenario, Suzuki et al. Investigated past changes in the Earth’s oxygen concentration using “Os (osmium. Platinum group) isotopes”. Osmium has isotopes such as 187Os and 188Os, and terrestrial rocks have more 187Os than 188Os. The higher the oxygen concentration, the higher the proportion of 187Os in seawater because 187Os flows out from land into the sea. In other words, it can be said that changes in the osmium isotope ratio directly represent changes in the oxygen concentration of the Earth’s atmosphere in the past. Examining this change revealed that at the end of the Snowball Earth era, there was a large supply of 187Os to the ocean. In other words, it is evidence that oxygen was abundant in the sea, which is consistent with the scenario proposed by Suzuki et al.

At the end of the lecture, Mr. Suzuki emphasized that manganese deposits are scientifically very valuable as a medium for storing information such as the components and temperature of the sea from ancient times.

● Micro process of enormous resources

Teruhiko Kashiwabara, a researcher at the JAMSTEC Center’s Resource Generation Research Group, noted that manganese deposits concentrate various elements such as iron and manganese, as well as rare metals, which are expected to be resources, and their chemistry. Trying to clarify the process. So far, X-ray analysis with SPring-8 etc. has been carried out in order to clarify where and how other elements are incorporated in iron-manganese oxide.

It is known that a rare metal called “Te (tellurium)” is specifically concentrated in the manganese crust on the seabed. Kashiwara et al. Found that this is because the tellurium molecule is very similar in shape to the iron molecule. Tellurium is not only adsorbed on the surface of the iron-manganese oxide, but also incorporated into its structure, which is why tellurium is concentrated. In addition, when we analyzed elements that behave similarly chemically, such as molybdenum and tungsten, more elements that form strong chemical bonds with the solid phase (solid) are concentrated, and those that are electrically attracted are relative. It was found that the degree of concentration was small.

In the future, we will clarify the difference in the concentration mechanism of each element, predict which element will behave and what kind of behavior when microorganisms are involved, and think that it may be possible to control the concentration process. .. That way, not only can you find out where the deposits that contain more of the metal you want are, but you may also be able to get the metal you want without having to go deep into the sea.

● Microorganisms that swarm on seafloor manganese deposits

Shingo Kato A specially appointed researcher in the Resource Generation Research Group of JAMSTEC is studying what kind of microorganisms inhabit manganese crusts and what they are doing. For example, in our mouth, microorganisms dissolve teeth to create cavities and deposit secretions to create tartar. It is no wonder that microorganisms interact with various elements in the ocean, and Kato thinks that they may be involved in the origin of manganese crusts. In addition to being difficult to obtain because the sample is on the deep sea floor, it is difficult to collect and manage it so that it does not mix with microorganisms on the surface of the earth. I moved forward.

Using the “next-generation DNA sequencer”, we comprehensively analyzed the DNA extracted from the manganese crust and estimated that there are more than 25,000 types of microorganisms in the manganese crust. 99% of them are unknown microorganisms and it is unknown what kind of function they have. It was found that these microorganisms inhabit only the surface of the crust and hardly inhabit the inside. It was also found that a large number of microorganisms of a specific strain group inhabit regardless of the water depth. It is not yet clear how these microorganisms are involved in the formation of manganese crusts, but on the crust surface, pH drops due to metabolic activity and sticky substances are produced, at least some chemical changes. It is said that it may be causing.

Figure 7. Electron micrograph of microorganisms on the surface of manganese crust.  A rod-shaped organism of about 1 micrometer can be confirmed, and it can be seen that nano-level fibrous secretions are spread around it (from the summary of the results report meeting, provided by JAMSTEC).
Figure 7. Electron micrograph of microorganisms on the surface of manganese crust. A rod-shaped organism of about 1 micrometer can be confirmed, and it can be seen that nano-level fibrous secretions are spread around it (from the summary of the results report meeting, provided by JAMSTEC).

Mr. Kato said that ammonia in seawater may not be the food for microorganisms, or that the adhesive substance produced by metabolism may adsorb iron-manganese oxide particles, or that iron-manganese oxide is produced by dissolution precipitation. It is said that it will clarify the function of microorganisms with a view to various possibilities such as whether it is. Mr. Kato’s team has also succeeded in culturing microorganisms in samples collected from the deep sea for two years to produce manganese oxide, and will explore the relationship with other elements in the future. By elucidating the origin of manganese crust, it seems possible to know the relationship between microorganisms and elements that we did not know.

Great potential, but still in the middle of research

After the reports of the four researchers, in the panel discussion, the researchers and those involved in resource development exchanged opinions. In Japan, rare earths, germanium, cobalt, antimony, tungsten, magnesium, etc. are highly dependent on foreign countries and are valuable. Since manganese crust contains various metal elements, it is a resource that can respond to this plight, and excavation of manganese crust in the deep sea is more costly than on land, but the value of the resource itself is high and the amount is enormous. Therefore, it was confirmed that commercialization is possible if an efficient method is established.

How are manganese crusts and other undersea resources produced and what metals are given? If we cannot solve this mystery, we will not be able to make the best use of the resources that remain asleep in the sea. I look forward to the steady progress of research to make undersea resources a “treasure that saves Japan.”

(Science writer Moeko Tabata)

Top page and list page photos: Submarine manganese ore exhibited at the results report meeting of this article (Photo by the author: JAMSTEC)