My Research
Controlling factor of atmospheric CO2 concentration
The Earth’s climate has alternated between glacial and interglacial periods in 100 kyrs cycles. Human civilization developed highly during the last several thousand years; today, it greatly impacts the global environment. However, today’s highly developed civilization has never experienced a glacial period, which is different from today’s climate mode. Can we sustain the current scale of civilization under different climate modes? To answer this question, the investigation of paleoclimate and the mechanism of climate change is very important.
The atmospheric carbon dioxide (CO2) concentration change showed a similar pattern to global climate change. This suggests that CO2 concentration is one of the important controlling factors of climate change. However, there is no consensus about how have atmospheric CO2 concentrations changed, where did CO2 come from, and where did it go? A clue to the questions is in the ocean. Seawater contains a large amount of CO2 dissolved in it, and it has been considered as a major carbon reservoir, which controls the atmospheric CO2 concentration. Therefore, my research aims to answer the following questions: How did the ocean uptake CO2 from the atmosphere? Where and how much CO2 was stored in the ocean during the glacial period? How did the ocean release CO2 into the atmosphere?
Microfossil: a recorder of the past environment
Micro fossil of marine plankton preserved in deep seafloor sediment enables us to reconstruct the paleoceanic environment. The shells of marine plankton provide various information about ambient seawater conditions regarding the process of growth at the sea surface, settlement in the water column from the sea surface to the sea floor, and burial into the sediment. Furthermore, there are various methods to evaluate the condition of micro-fossil, such as identifying species, assessing the shape of the shell, and analyzing the geochemical characteristics of the shell. Using these various tools and methods, I am studying marine microfossils preserved in deep seafloor sediment to reconstruct the variation of the ocean carbon cycle. The followings are topics of my previous research.
- Biogenic productivity change in the sea surface on the glacial-interglacial time scale
- Development of paleo-deep seawater [CO32–] proxy using planktonic foraminiferal shell
- Reconstruction of deep ocean carbon storage variations during glacial and interglacial periods
- Influence of ocean acidification to carbonate organism (foraminifera and coral).
Ongoing Project 1: Deep seawater carbon storage assessment in the South Pacific
History of carbon storage variability in the deep Pacific Southern Ocean
The ocean has a carbon storage capacity about 50 times greater than that of the atmosphere. Therefore, glacial-interglacial changes in atmospheric CO2 concentrations appear to be caused by CO2 storage in the deep ocean, which is an important process in regulating atmospheric CO2 concentrations. However, where and how much carbon were stored in the deep ocean is not well understood. The Pacific Southern Ocean (off Chile area) is a node of the major deep-water masses (Pacific Deep Water: PDW, Antarctic Bottom Water: AABW, North Atlantic Deep Water: NADW). Using sediment cores from different depths belonging to different water masses in this area, we reconstruct the carbonate ion concentrations in deep seawater during the last glaciation. The results tell us ‘Which deep water masses effectively stored carbon and how much carbon is there during the glacial period'. For this purpose, we use planktonic foraminiferal shells preserved in the sediment cores. Because the dissolution of foraminiferal shells is controlled by the deep seawater carbonate ion concentration, it is possible to reconstruct past deep-water carbonate ion concentrations by measuring the dissolution intensity of foraminiferal shells. In this study, we use the 3D physical measurements of shells using microfocus X-ray CT as a quantitative indicator of shell dissolution intensity, allowing us to assess the distribution of carbon storage in the deep ocean during the last glaciation with unprecedented temporal and spatial resolution.
Ongoing Project 2: Assessing the impact of global warming
Impact of the Arctic Ocean acidification on foraminiferal shell formation
Since the Industrial Revolution, which began about 200 years ago, we have released amount of CO2 into the atmosphere, and increased atmospheric pCO2 approximately 1.5 times. The Arctic Ocean is particularly strongly affected by the global warming. Ocean acidification due to increasing atmospheric pCO2 and decreasing salinity caused by sea-ice melting is a particular concern in the Arctic Ocean, which may result in the negative effect on the calcification of organisms such as foraminifera. Foraminifera are important as food for local ecosystems, but they are also key organisms that drive the marine carbon cycle through the processes of carbonate production, transport, dissolution and burial. Therefore, to understand the impact of global warming on the marine carbon cycle, it is essential to assess the variation in foraminiferal shell properties (shell size, shape, density, etc.) under conditions of active environmental change since the Industrial Revolution. Here we investigate the impact of ocean acidification on foraminiferal shell by evaluating the physical properties of shells preserved in sediment cores from the Beaufort Sea coast of the Arctic Ocean, which have been continuously recorded at high temporal resolution for the last 300 years. What is occurring now in the Arctic Ocean could occur in other ocean in the future. Therefore, this project is also concerning the future of global ocean.
My Publication
•Shinya Iwasaki, Katsunori Kimoto, Michal Kucera, Development of a deep-water carbonate ion concentration proxy based on preservation of planktonic foraminifera shells quantified by X-ray CT scanning, Paleoceanography and Paleoclimatology, https://doi.org/10.1029/2022PA004601, 2023. Journal page
•Shinya Iwasaki, Lester Lembke-Jene, Kana Nagashima, Helge Arz, Naomi Harada, Katsunori Kimoto, Frank Lamy, Evidence for late glacial oceanic carbon redistribution and discharge from the Pacific Southern Ocean, Nature Communications, https://doi.org/10.21203/rs.3.rs-1199164/v1, 2022. Journal page
•Stergios D. Zarkogiannis, Shinya Iwasaki, James William Buchanan Rae, Matthew W. Schmidt, P. Graham Mortyn, George Kontakiotis, Jennifer E. Hertzberg, Rosalind E. M. Rickaby, Calcification, Dissolution and Test Properties of Modern Planktonic Foraminifera from the Central Atlantic Ocean, Front. Mar. Sci. 9:864801. doi: 10.3389/fmars.2022.864801, 2022. Journal page
•Hiroto Kajita, Yuki Ota, Toshihiro Yoshimura, Daisuke Araoka, Takuya Manaka, Ouyang Ziyu, Shinya Iwasaki, Takuya Yanase, Akihiko Inamura, Etsuo Uchida, Hongbo Zheng, Qing Yang, Ke Wang, Atsushi Suzuki, Hodaka Kawahata, Seasonal and Spatial Variations of Chemical Weathering in the Mekong Basin: From the Headwaters to the Lower Reaches, Aquatic Geochemistry, https://doi.org/10.1007/s10498-020-09374-y, 2020. Journal page
•Shinya Iwasaki, Katsunori Kimoto, Yusuke Okazaki, Minoru Ikehara, X-ray micro-CT scanning of tests of three planktic foraminiferal species to clarify dissolution process and progress, Geochemistry, Geophysics, Geosystems, DOI:10.1029/2019GC008456, 2019. Journal page
•Shinya Iwasaki, Katsunori Kimoto, Osamu Sasaki, Harumasa Kano, Hiroshi Uchida, Sensitivity of planktic foraminiferal test bulk density to ocean acidification, Scientific Reports, https://doi.org/10.1038/s41598-019-46041-x, 2019. Journal page
•Shinya Iwasaki, Atsushi Suzuki, Akira Iguchi, Osamu Sasaki, Harumasa Kano, Yoshikazu Ohno, Koichiro Enomoto, Effect of seawater turbulence on formation of coral primary polyp skeletons, Coral Reefs, 37(3), 939-944, 2018. Journal page
•Shinya Iwasaki, Katsunori Kimoto, Azumi Kuroyanagi, Hodaka Kawahata, Horizontal and vertical distributions of planktic foraminifera in the subarctic Pacific, Marine Micropaleontology, 130, 1-14, 2017. Journal page
•Shinya Iwasaki, Mayuri Inoue, Atsushi Suzuki, Osamu Sasaki, Harumasa Kano, Akira Iguchi, Kazuhiko Sakai, Hodaka Kawahata, The role of symbiotic algae in the formation of the coral polyp skeleton: 3-D morphological study based on X-ray micro-computed tomography, Geochemistry, Geophysics, Geosystems, 17, doi:10.1002/2016GC006536. 2016. Journal page
•Shinya Iwasaki, Kozo Takahashi, Yoshiyuki Kanematsu, Hirofumi Asahi, Jonaotaro Onodera, A. C. Ravelo, Paleoproductivity and paleoceanography of the last 4.3 Myrs at IODP Expedition 323 Site U1341 in the Bering Sea based on biogenic opal content, Deep Sea Research II, 125–126, 145–154, 2016. Journal page
•Shinya Iwasaki, Katsunori Kimoto, Osamu Sasaki, Harumasa Kano, Makio C. Honda, Yusuke Okazaki, Observation of the dissolution process of Globigerina bulloides tests (planktic foraminifera) by X-ray micro-computed tomography, Paleoceanography, 30, 317–331, 2015. Journal page
•Shinya Iwasaki, Kozo Takahashi, Yusuke Ogawa, Seiichiro Uehara, Christoph Vogt, Alkaline leaching characteristics of biogenic opal in Eocene sediments from the central Arctic Ocean: a case study in the ACEX cores, Journal of Oceanography, Springer, DOI 10.1007/s10872-014-0227-7, 2014. Journal page
•Shinya Iwasaki, Kozo Takahashi, Takuya Maesawa, Tatsuhiko Sakamoto, Saburo Sakai, Koichi Iijima, Paleoceanography of the last 500 kyrs in the central Okhotsk Sea based on geochemistry, Deep-Sea Research II, Elsevier, 61-64, pp. 50-62, 2012. Journal page
Latest News
East Hokkaido sampling trip
07.2023
The sampling trip to the East-Hokkaido area. We drilled peat sediment cores at marsh. The peat sediment of this area records an environmental history of more than 10,000 years. The blue sky, green land, and people eagerly drilling peat only for science...Beautiful!
Jingisukan (BBQ) party
07.2023
The Jingisukan (BBQ) party was held at the beginning of summer. It was my first Jingisukan party "Jin-Pa" in Hokkaido. Good oppotunity to see everybody in our institute.
IODP Exp.383 Post Cruise Meeting
05.2023
The post-cruise meeting was held at the Lamont-Doherty Earth Observatory in New York for three days from 2 May. It was my first visit to this institute, and it was a lovely place surrounded by forest.
Hello, Sapporo!
04.2023
I started my new position at Hokkaido University, Sapporo, JAPAN. You are very welcome to visit me. Let's have a cup of coffee.
Tschüss, Bremen!
03.2023
It was very happy and exciting days for me. See you again soon everybody. And see you soon Bremer Grünkohl. I am missing you!
