Radiocarbon‐based carbon source quantification of anomalous isotopic foraminifera in last glacial sediments in the western North Pacific

摘要: A previous study interpreted extremely 13C-depleted excursions of planktonic and benthic foraminifera in last glacial sediments (17,500 to 25,400 cal years B.P.) the core retrieved from off Shimokita Peninsula Hokkaido, Japan, as evidence for periodic releases methane, arising dissociation methane hydrate. To better understand formation process excursions, we conducted high-resolution natural radiocarbon measurements biogeochemical analyses. We found highly depleted 13C ranging −10.2‰ −1.6‰ −6.8‰ foraminifera, respectively. Most foraminiferal tests these horizons were brown, most likely a result postdepositional alteration, reflecting authigenic carbonate on surface tests. These alterations also supported by high levels Mg-calcite acid-leaching test anomalous foraminifera. evaluate carbon sources altered tests, quantified relative contributions 14C-free methane-derived carbonates with using coupled mass balance isotopic model (14C/C 13C/12C). The ages both approximately 600 2000 older than those normal nearby horizons. derived oxidizing reached ∼22 wt% ∼15 δ13C values calculated between −29‰ −68‰ −40‰ −108‰ consistent reported thermogenic abiogenic global hydrate reservoirs. data consistently suggest that methane-related drastic environmental change occurred included anomalies. This provides important information interpreting geological records instability associated climate.