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Research Group Division of GeoEnvironmental Science

 

Paleo-Environment change Research Group

•Professor Yasuhumi Iryu,
•Professor (of Tohoku University Museum) Hiroshi Nishi, specializing in micropaleontology
•Assoc. Professor (of Tohoku University Museum) Reishi Takashima, Geology and Stratigraphy
•Asst. Professor Tsutomu Yamada, specializing in Isotope Geochemistry, Carbonate Geochemistry
•Asst. Professor Noritoshi Suzuki, specializing in Micropaleobiology, and Ocean Plankton
•Asst. Professor Hideko Takayanagi,
•Asst. Professor (of Tohoku University Museum) Azumi Kuroyanagi,
 
 

Understanding Marine Environment Change History with
Integrated Ocean Drilling Program (IODP)

Understanding Marine Environment Change History with IODP (Integrated Ocean Drilling Program) The 70% of the earth surface is covered by the ocean. The current and existing oceanic crust was made 150 million years ago and later, and the geoenvironmental changes during this period are recorded in the sedimentary layer on the bottom of deep sea. To read and understand all the records, the Integrated Ocean Drilling Program (IODP) has been conducted as international collaboration work. To accomplish that work, Japan took the initiative and built a state-of-the-art deep-sea drilling vessel, “Chikyu” of 210 m length. (For further details of “Chikyu”, please see the Web page of the Japan Agency for Marine-Earth Science and Technology (JAMSTEC).) The Division of Geoenvironmental Science is a member of the IODP; it is striving to achieve good research performance by contributing further to deep-sea drilling programs.

 

The ocean is home to such unicellular micro-creatures as foraminifera and nanoplankton, which are covered with a calcium carbonate shells, and radiolaria and diatoms, which are covered with silicon-based shells. Micro-creatures of these types change independently, responding sensitively to such environmental factors as water temperature, salt, dissolved oxygen, and nutrient salts. Because the dead bodies of plankton accumulate on the deep-sea bottom, we can analyze fossil assemblages in sediments, and thereby know of changes occurring in marine environments. Research work for restoring marine environment changes that have been made from the past and determining the geological era based on the full use of the fossils (microfossils) of such unicellular creatures is a particularly strong capability of the Geoenvironmental Science Division. Its Professors––Nishi, Kaiho, and Suzuki––are striving aggressively to advance this area of research.
We can introduce one example of studies undertaken to restore marine environment changes of the past using samples obtained from the deep-sea bottom and collected from the various places throughout the world. Foraminifera (benthic foraminifera) of several kinds live on the sea bottom. Their community composition depends closely on the ocean floor environment. Professor Kaiho and others obtained fossils of benthic foraminifera from samples drilled from the deep-sea bottom; then they analyzed them. Among their reported results, they described their discovery that the deep-sea bottom happened to show shortages of oxygen twice––once 93 million years ago and once again in 55 million years ago––so that the size of foraminifera decreased once, but recovered and increased rapidly after that.

 

Understanding the past, the present, and the future comprehensively is an important strategy. We are studying the community composition of plankton including floating foraminifera and other microbiota in the Pacific Ocean making sediment-trap fixed-point observations and using a plankton net. Recently, we ascertained changes in the way the plankton gather for each of El Niño and La Nina when they occurred.
 
 

Continental-area environmental changes examined at Lake Baikal

The environmental systems of the ocean and of the continent are mutually linked. The group including Prof. Minoura and others is proceeding with an internationally organized plan to drill Lake Baikal and Lake Khubsugul with the cooperation of Japan, America, Russia, and the EU. Based on the sediments available on the lake bottom, they are undertaking work to elucidate and then clarify the history of environmental changes on the Eurasian continent over the last 12 million years. The analytical results of the sediments on the bottom of Lake Baikal portray the primary production of creatures conforming to weather changes that occurred during the glacial and interglacial periods, the earth’s crust weathering around the water area, and the prosperity and decline of the Siberian Taiga.
 
 

Examining coral reefs in a South Seas Paradise using high-resolution
environmental history

Looking at the coral reefs in the South Seas Paradise with a high resolution of environmental history During this past 60 years or so since the marine environment started being recorded using scientific measuring devices, some environmental changes have been recognized such as El Niño, La Nina, and the “Pacific Ocean changes occurring in the past several decades”. To clarify those changes, whether they are of a semi-cyclic type or merely chaotic, we require contiguous data of high resolution in terms of time for hundreds of years of the past. Associate Professor Nakamori and Assistant Professor Yamada, and others analyzed the isotope ratios of carbon to oxygen for the annual growing rings of the skeletal structures of corals and giant clam shells, and restored the temperature, the salt level, and the hours of sunlight of the past with precision from the daily change level to the seasonal change level. Applying this technique to samples obtained by drilling into coral reefs, they are attempting to understand the environmental changes that have been occurring over the past tens of thousands of years.

 

This study group––choosing the islands of Okinawa, part of the “South Seas Paradise”, as its main activity field––is investigating the ecological system of the coral reefs there with its associated materials cycle, the formation of coral reefs during the Quaternary period of weather changes, and the changes of carbonate rocks to dolomites. Additionally, they are attempting to restore the biogeochemical cycle of the past 100 million years based on data available from carbonate platform sediments.