Nobuki Takamatsu

Color change of lake water at the active crater lake of Aso volcano, Yudamari, Japan: is it in response to change in water quality induced by volcanic activity?

One feature of volcanic lakes influenced by subaqueous fumaroles existing at lake bottoms (called active crater lakes) is the remarkable color of their waters: turquoise or emerald green. The active crater lake named Yudamari at Mt. Nakadake of Aso volcano, Japan, takes on a milky pale blue-green. The particular blue component of the lake water color results from Rayleigh scattering of sunlight by very fine aqueous colloidal sulfur particles; the green component is attributable to absorption of sunlight by dissolved ferrous ions. An objective color observation conducted during 2000–2007 revealed that the lake water color changed from blue-green to solid green. The disappearance of the blue ingredient of the water color will result in diminution of aqueous colloidal sulfur from chemical analyses of lake waters sampled simultaneously. The aqueous sulfur is produced by the reaction of sulfur dioxide and hydrogen sulfide supplied from subaqueous fumaroles. However, its production efficiency decreases by domination of sulfur dioxide in the subaqueous fumarolic sulfur gas species with increasing subaqueous fumarolic temperature. The disappearance of blue ingredients from the blue-green color of the lake water may be attributed to activation of subaqueous fumarole activity.

Rayleigh scattering by aqueous colloidal silica as a cause for the blue color of hydrothermal water

Abstract Thermal waters in hydrothermal ponds, bathing pools and the brines of geothermal electric power plants commonly have a characteristic blue color. Although many researchers have assumed that the blue color is due to a colloidal suspension and/or absorption by dissolved ferrous iron or by water itself, there has been no specific effort to identify the physical nature of this phenomenon. We have tested, in synthetic and natural solutions, whether aqueous colloidal silica is responsible for the blue color. Aqueous colloidal silica is formed by silica polymerization in thermal waters of the neutral-chloride type which contain initially monomeric silica in concentrations up to three times above the solubilities of amorphous silica. The hue of the blue thermal waters in the pools tested agrees with that of a synthesized colloidal silica solution. Grain-size analyses of aqueous colloidal silica in the blue-colored thermal waters demonstrate that the color is caused by Rayleigh scattering from aqueous colloidal silica particles with diameters (0.1–0.45 μm) smaller than the wavelengths of visible radiation.

Paleoenvironmental Changes in the Eurasian Continental Interior during the Last 12 Million Years Derived from Organic Components in Sediment Cores (BDP-96 and BDP-98) from Lake Baikal

Organic components in combined sediment cores (BDP-96 and BDP-98) of BDP-96-1 and -2 (200 m) and BDP-98-1 and -2 (600 m) from Academician Ridge in Lake Baikal, in south-central Siberia, were studied to clarify the biological production, sources of organic matter, and paleoenvironmental changes during the last 12 million years (Myr) in the Eurasian continental interior as well as in the world. Total organic carbon (TOC) contents ranging from 0.13% to 2.8%, with an average of 0.93% (n = 7710), were fairly low, and were similar to those found in some oligotrophic lakes. TOC and total nitrogen (TN) contents had decreased by about half from 12 Myr ago to the present as a result of global climate cooling. Higher biological production periods are mainly attributed to the contribution of vascular plants.

The origin of salts in water bodies of the McMurdo Dry Valleys

Lithium distributions in lake and pond waters of the McMurdo Dry Valleys of southern Victoria Land, Antarctica were studied to elucidate the origin of dissolved salts and the evolutionary history of the lakes and ponds. The Ef Li [(Li/Cl)sample/(Li/Cl)seawater] values of the bottom waters in Lakes Bonney and Fryxell were higher than unity (Ef Li =4–7), indicating that the salts originated from sea salts (probably relict seawater) and have been subsequently modified by the contribution of meltwaters containing atmospheric fallout and/or rock and soil weathering products. In contrast, extremely high Li concentrations with high Ef Li values in the Don Juan Pond water (Ef Li = 180) and the bottom waters of Lake Vanda (Ef Li = 40) suggest that the salts originated from deep groundwaters influenced mainly by saline water-rock interactions, as supported by the dissolution experiments of granite in NaCl solution. The low Li concentrations of pond waters with high Ef Li values in the Labyrinth indicate that the salts are derived from atmospheric fallout. The decrease of the Ef Li values with the increase of Cl concentrations can be explained by the repeated cycles of the migration of Li into the ice phase and subsequent ablation of surface ice, as indicated by seawater freezing experiments.

Orbital signals found in physical and chemical properties of bottom sediments from Lake Baikal

Physical and chemical properties of two 100 m sediment cores (BDP-93-1, 93-2) obtained from the Buguldeika saddle of Lake Baikal in the eastern Siberia and a 14C-based age scale for the core show that the core bottom is about 400 000 years ago and that the changes in the sedimentological environment of the area during the interval were that comparatively coarse and high C/N ratio sediments accumulated in the lake during interglacial periods, and fine material and low C/N ratio during glacial periods. The tentative age scale suggests that the first excursion in the earths magnetic field at about 26 m (BDP-93-1 and 93-2) from the sediment surface corresponds to the Blake event. Statistical analyses of the data-sets for the some properties show that the fluctuations have distinct periods; 20000 years, 40000 years and 100000 years, that are related to the Milankovitch parameters and support that the tentative age scale is approximately acceptable.

Paleoenvironmental changes in the Eurasian continent interior inferred from chemical elements in sediment cores (BDP96/1, BDP96/2) from Lake Baikal

Publisher Summary This chapter presents a study to estimate the paleoenvironmental changes in the Eurasian continent interior during the past 5.2 million years (My) from the levels of inorganic chemical elements in the B DP96/1 core, and to examine the relative contribution of the frequency of precession, obliquity, and eccentricity by spectral analysis of K distribution in the BDP96/2 core. The chemical elements in sediment cores (BDP96/1, BDP96/2) are studied and the terrigenous element content (A1, Ti, and K, etc.) is inversely correlated with diatom abundance, which is a proxy for paleoclimate change. Principal component analysis of data sets for 28 element/aluminum weight ratios in the BDP96/1 core showed that the first principal component scores increased abruptly at 3.4 Ma. The inorganic element content of the BDP96/1 core indicated significant climate change at 2.5 Ma (onset of Northern Hemisphere cooling) and at 3.5 Ma (onset of the aridification of Asia) in the Eurasian continent interior. Spectral analysis of K distribution in the BDP96/2 core showed that the relative variance of the frequency of eccentricity increased from 2.5 Ma to the present. The contributions of frequency of precession and obliquity in the Eurasian continent interior are much greater than those of marine climate records (SPECMAP).

Paleoenvironmental record of Lake Hovsgol (Mongolia) in northeast Eurasia

Studies on paleoenvironmental changes are important to estimate future global warming induced by human activity. Information on paleoenvironmental changes in the northeast Eurasia has been collected by Baikal Drilling Project (BAIKAL DRILLING PROJECT GRouP 2000). Lake Hovsgol is located in the Lake Baikal basin at an altitude of 1667 m a.s.l. in the subarctic zone and is approximately 1200m higher than Lake Baikal (GouLDEN et al. 2006). Mean annual air temperatures of the lake area during the glacial period are assumed to have been lower than -15 oe; thus, it is possible that not only the lake surface was covered with perennial ice, but also that higher land plants almost disappeared during the glacial period. Organic components in lake sediments are chemical fossils of paleoenvironmental changes in the drainage basin and are extensively used as biomarkers to evaluate sources and sedimentary conditions of organic matter in various environments (MEYERS & ISHIWATARI 1993, MATSUMOTO et al. 2003). Here we report organic components in HDP04 sediment core from Lake Hovsgol to elucidate biological production, sources of organic matter, and paleoenvironmental changes during the last 1030 ka in the northeast Eurasia. These results are compared with Lake Baikal sediment core signals.

Abstracts from the Japanese Journal of Limnology

The Japanese Journal of Limnology is another official publication of the Japanese Society of Limnology. The original papers in the journal were peer-reviewed by a few authorized referees, and appeared in Japanese with English abstracts.

Paleoenvironmental Changes during the Last 12 Million Years in the Eurasian Continental Interior Estimated by Chemical Elements in Sediment Cores (BDP-96 and BDP-98) from Lake Baikal

The content of 29 chemical elements (Na, K, Mg, Ca, Al, Fe, Li, Be, Sc, Ti, V, Cr, Mn, Co, Ni, Cu, Zn, Ga, Ge, As, Rb, Sr, Mo, Cs, Ba, W, Pb, Th, and U) in 589 subsamples of BD-P96 cores and 703 subsamples of BDP-98 cores from the Academician Ridge of Lake Baikal were determined using inductively coupled plasma-mass spectromety (ICP-MS) in order to estimate paleoenvironmental changes during the last 12 million years in the Eurasian continental interior. The content of terrigenous elements (Na, K, Mg, Ca, Al, Ti, etc.) increased gradually from about 6 Ma BP to the present, with repeated major fluctuations after 3.6 Ma BP, indicating a significant climate change at 3.6Ma BP in the Eurasian continental interior. The abrupt change may be mainly associated with the uplift of the Tibetan plateau and Himalayas. This result corresponds with the rapid increase in the eolian dust accumulation rate in the central north Pacific sediment core (Rea et al. 1998). The data from BDP98 cores indicated that some big changes in the sources of chemical elements occurred at about 7 Ma BP, when the sedimentation rate in the core suddenly increased. We also estimated from the chemical index of alteration (CIA) that the variation in the climate from 8 to 12 Ma BP was small, and the rapid climate change started at 3.6 Ma BP.