Japan Geoscience Union Meeting 2016

Presentation information


Symbol B (Biogeosciences) » B-PT Paleontology

[B-PT08] Evolution of Chemosynthetic Ecosystem in Earth History

Thu. May 26, 2016 1:45 PM - 3:15 PM 301A (3F)

Convener:*Robert Jenkins(School of Natural System, College of Science and Engineering, Kanazawa University), Hiromi WATANABE(Japan Agency for Marine-Earth Science and Technology), Takami Nobuhara(Science Education (Geology), Faculty of Education, Shizuoka University), Ryuichi Majima(Faculty of Education and Human Sciences, Yokohama National University), Chair:Robert Jenkins(School of Natural System, College of Science and Engineering, Kanazawa University), Hiromi Kayama WATANABE(Japan Agency for Marine-Earth Science and Technology)

2:15 PM - 2:30 PM

[BPT08-03] Influence of cold seep methane on the forming of echinoderm skeletons

*Moe Kato1, Tatsuo Oji2, Kotaro Shirai3, Tatsuya Unuma4 (1.Graduate School of Environmental Studies, Nagoya University, 2.Nagoya University Museum, 3.Atmosphere and Ocean Research Institute, The University of Tokyo, 4.Hokkaido National Fisheries Research Institute,Fisheries Research Agency)

Keywords:cold seep, echinoderms, chemosynthetic community, biomineralization

Recently, a few modern species of echinoderms have been reported as a member of the chemosynthetic community organisms, and at least two fossil species of echinoderms have been found from cold seep deposits (Pawson and Vance, 2004; Gaillard et al., 2011; Landman et al., 2012). In order to understand how these echinoderms from cold seep environment take carbon to form their skeletons, two analyses were done; 1) stable carbon isotope analysis of the fossil skeletons, and 2) stable carbon isotope analysis of a living sea urchins in aquaria under environments of controlled stable carbon isotope ratios (δ13C).
The fossil echinoderms have been collected and studied from two cold seep areas; the Upper Cretaceous (Campanian) in South Dakota, USA and the coeval formation in Hokkaido, Japan. The both crinoids from South Dakota and Hokkaido have clearly lower δ13C values than normal echinoderms, suggesting their skeletons were influenced by cold seep methane which has extremely low δ13C values (Kato and Oji, 2015). However, it was still unknown how these crinoids formed their skeletons with such low δ13C values.
A lot of marine organisms such as many mollusks, are considered to precipitate their skeletons in equilibrium with the ambient sea water in regards to their carbon isotope (Epstein et al., 1951). For example, bivalves shells from a chemosynthetic community show ±5‰ δ13C values (e.g. Mae et al., 2007). However, echinoderm skeletons, even from a normal (non-seep) environment, are known to be formed not in isotopic equilibrium, and the δ13C values of the echinoderms skeletons are different depending on the classes or species (e.g. Weber, 1968). Thus, in echinoderm biomineralization, an isotope fractionation due to vital effect or some carbon sources other than from sea water should be possible.
In order to clarify the cause of inequilibrium of the δ13C value in the skeletons of echinoderms and to estimate degree of isotope fractionation in forming skeletons, specimens of modern echinoid (Strongylocentrotus intermedius) have been raised in two experiments; 1) the echinoids has been raised under three types of sea water with differently controlled δ13C value of DIC (dissolved inorganic carbon), and 2) with two different types diets (a kelp (Saccharina longissima) and a land plant (Fallopia sachalinensis)) with different δ13C value.
Compared with the controlled case of culture with normal sea water with seaweed diet, δ13C value of the echinoid test changed in both cases (in waters with high δ13C value, and with different diets. Thus, it suggests that skeletons δ13C of this echinoid, are influenced by isotope ratio of both sea water and foods. This result clearly shows that the process of isotope fractionation and forming skeletons of echinoderms should be different from those of most of mollusks. It is thought that the echinoderms in cold seep environment depend on bacteria mat for their diet, or detritus that have low δ13C.