Petrology and geochemistry of Quaternary tephras of the Izu-Bonin Arc

Quaternary marine tephras in the Izu-Bonin Arc offer significant information about explosive volcanic activities of the arc. Visual core descriptions, petrographic examinations, and chemical and grain-size analyses were conducted on tephras of backarc, arc, and forearc origin. Tephras are black and white and occur in simple and multiple modes with mixed and nonmixed ashes of black and white glass shards. The grain size distributions of the tephras are classified into three categories: coarse, white pumiceous, and fine white and black well-sorted types. The frequency of occurrence of the white and black tephras differs within the tectonic settings of the arc. Chemically, the Quaternary tephras in this region belong to low-alkali tholeiitic series with lower K2O and TiO2 than normal ordinary arc volcanic materials. Several tephras from different sites along the forearc correlate with each other and with tephras in the Shikoku Basin site and with Aogashima volcanics. These volcanic ashes resemble those in other backarc rifting areas, such as in the Fiji, Okinawa (Ryukyu), and Mariana regions.

Isotopic composition of bottom and interstitial waters in the area of gas plumes, Sea of Okhotsk

Data on isotopic composition of interstitial and bottom waters collected in an area of gas hydrate occurrence in the Sea of Okhotsk are presented. Investigations indicate that heavy isotopes of oxygen and hydrogen are used in generation of gas hydrate, so that isotopic composition of its water of constitution is: d18O = +1.9 per mil, d2H = +23 per mil (relative to SMOW). Production of authigenic carbonates results in isotopic exchange with interstitial water, which in turn alters its isotopic composition by an increase in d18O. Bottom waters are isotopically light relative to the SMOW standard and to the average isotopic composition of interstitial waters in the area of gas hydrate occurrence in study.

Tomographic measurements of O. umbonatus and N. truempyi during the PETM and ETM-2 at ODP Sites 208-1262 and 208-1263

Predicting the impact of ongoing anthropogenic CO2 emissions on calcifying marine organisms is complex, owing to the synergy between direct changes (acidification) and indirect changes through climate change (e.g., warming, changes in ocean circulation, and deoxygenation). Laboratory experiments, particularly on longer-lived organisms, tend to be too short to reveal the potential of organisms to acclimatize, adapt, or evolve and usually do not incorporate multiple stressors. We studied two examples of rapid carbon release in the geological record, Eocene Thermal Maximum 2 (~53.2 Ma) and the Paleocene Eocene Thermal Maximum (PETM, ~55.5 Ma), the best analogs over the last 65 Ma for future ocean acidification related to high atmospheric CO2 levels. We use benthic foraminifers, which suffered severe extinction during the PETM, as a model group. Using synchrotron radiation X-ray tomographic microscopy, we reconstruct the calcification response of survivor species and find, contrary to expectations, that calcification significantly increased during the PETM. In contrast, there was no significant response to the smaller Eocene Thermal Maximum 2, which was associated with a minor change in diversity only. These observations suggest that there is a response threshold for extinction and calcification response, while highlighting the utility of the geological record in helping constrain the sensitivity of biotic response to environmental change.