Compaction of Modern Soft Sediments during Core Sampling—An In Situ Investigation at an Estuary Site

Graduate School of Arts and Sciences, The University of Tokyo, Komaba 3-8-1, Meguro-Ku, Tokyo 153-8902, Japan

Dr. Guodong Zheng is a postdoctoral research fellow in the Department of General Systems Studies at the University of Tokyo. He received a B.Sc. in geology from Lanzhou University, China in 1983 and a Ph.D. in multidisciplinary sciences from the University of Tokyo, Japan in 2001. He also studied geochemistry at Masaryk University, Czech Republic during 1992–1994. He was a research associate for petroleum geology and geochemistry at the Lanzhou Institute of Geology, Chinese Academy of Sciences for over 10 years. His current research interests focus on chemical speciation of S, Se, As, Fe, and heavy metals in aquatic sediments and soils and their isotopic fractionation in geological processes and environmental problems.

Dr. Bokuichiro Takano is professor of chemistry at the University of Tokyo, Graduate School of Arts and Sciences. He is a life member of the Penn State Alumni Association. His research interests are focused on the geochemistry of aquatic environments, especially active crater lakes in Kamchatka, Indonesia, Costa Rica, and New Zealand. Another of his interests is the geochemistry of the 16th group elements in aquatic sediments.

Motoyuki Matsuo is an associate professor of chemistry at the Graduate School of Arts and Sciences, University of Tokyo. He received a Doctorate of Science from the University of Tokyo in 1983. He trained as a Ramsay Memorial Fellow at the Department of Inorganic and Structural Chemistry, University of Leeds, England (1987–1989). Dr. Matsuo’s research interests are the environmental evaluation by the state analysis of elements. His attention has been paid to chemical states of iron (oxidation states, coordination, magnetic properties, etc.) that are involved in various environmental or geochemical samples using Mössbauer spectroscopy and XAFS.

Yuto Tanaka received a Master’s degree in multidisciplinary sciences from the University of Tokyo in 2002. His major was environmental chemistry and he is now interested in the study of geochemical behavior of certain elements in estuary sediments, particularly in urban areas such as metropolitan Tokyo. His favorite techniques include instrumental neutron activation analysis and Mössbauer spectroscopy.

ABSTRACT

The vertical compaction of unconsolidated subsurface sediment was investigated at the Tama river estuary in Tokyo, Japan. The cores were taken by hand using polybutyrate tubes with different inner diameters, and core compaction ratios were measured in situ. Percent compaction varied with depth within the same core and with the inner diameter of a coring tube as well as its wall thickness. These results strongly suggest that vertical compaction of soft sediments during coring should be well documented in published articles relevant to the time-dependent analysis of sedimentary environments. Otherwise, comparison of one core with another could be misleading in discussions focused on modern soft sediment.