Name: Takuro Nunoura

Email: takuron@jamstec.go.jp

Author: 1Takuro Nunoura,2Michinari Sunamura, 1Junichi Miyazaki, 3Akiko Makabe, 3Kazuhiro Inoue, 1, 4Tohru Kikuchi, 1Osamu Koide, 5Yuichiro Ueno, 1Ken Takai

Author affiliation: 1Extremobiosphere Research Program, Japan Agency for Marine-Earth Science & Technology, 2Department of Earth & Planetary Science, School of Science, The Universityof Tokyo, 3Department of Environmental Science and Technology, Interdisciplinary Graduate School of Science and Engineering Tokyo Institute of Technology, 4International College of Arts & Sciences, Yokohama City University, 5Global Edge Institute, Tokyo Institute of Technology

Abstract title: Viral abundance and distribution in Challenger Deep waters of the Mariana Trough

Absstract:

The Challenger Deep is the deepest ocean on the earth. Viral abundance in hadopelagic waters (below 6000 m depth) has not been investigated yet. Vertical profiles of virus like particle (VLP) and prokaryote abundance were investigated from the surface to in proximity of the bottom (10257 m depth) in the Challenger Deep. Sampling was carried out using ROV ABISMO during the JAMSTEC KR08-05 cruise (the R/V Kairei) on June 2008. Profiles of CTD data and geochemical parameters (O2, NO3-, NH4+, SO42- and CH4) indicated that the water column in the Challenger Deep consisted of 4 water masses; epipelagic waters (0 - 200 m depth), mesopelagic and bathypelagic waters (200 - 2000 m depth), abyssopelagic waters (2000 - 6000 m depth), and hadopelagic waters (6000 m depth to the bottom). Prokaryotic cell abundance generally decreased with increasing depth, and ranged 5.5 x 10^3 to 6.3 x 10^5 cells ml^-1. The maximum VLP abundance occurred in epipelagic waters and the minimum was observed at a depth of 1500 m. VLP abundance increased at a depth of 2000 m and those below 2000 m depth did not show significant changes. Significant correlation between VLP and prokaryote abundance was observed at the depths between 150 and 1500 m. Significant semilogarithmic correlation between VLP to prokaryote abundance ratio (VPR) and depth observed in epipelagic, mesopelagic and bathypelagic, and abyssopelagic waters, and VPR in epipelagic and abyssopelagic waters increased with increasing depth. Notable prokaryotic cell size changes also occurred in water mass interfaces, and good correlations between cell size and depth were observed in each water mass. These data suggest that hadopelagic waters represent a own ecosystem that have not been pointed out, and water mass interfaces have major impacts on prokaryote activity and viral abundance.