Yasuto Watanabe

Abstract Glacial cycles during the early Pleistocene are characterised by a dominant 41,000-year periodicity and amplitudes smaller than those of glacial cycles with ~100,000-year periodicity during the late Pleistocene. However, it remains unclear how the 41,000-year glacial cycles during the early Pleistocene respond to Earth’s astronomical forcings. Here we employ a three-dimensional ice-sheet model to simulate the glacial cycles at ~1.6–1.2 million years before present and analyse the phase

The advent of oxygenic photosynthesis represents the most prominent biological innovation in the evolutionary history of the Earth. The exact timing of the evolution of oxygenic photoautotrophic bacteria remains elusive, yet these bacteria profoundly altered the redox state of the ocean-atmosphere-biosphere system, ultimately causing the first major rise in atmospheric oxygen (O₂ )-the so-called Great Oxidation Event (GOE)-during the Paleoproterozoic (~2.5-2.2 Ga). However, it remains

Iron (Fe) is an essential element for life, and its geochemical cycle is intimately linked to the coupled history of life and Earth's environment. The accumulated geologic records indicate that ferruginous waters existed in the Precambrian oceans not only before the first major rise of atmospheric O₂ levels (Great Oxidation Event; GOE) during the Paleoproterozoic, but also during the rest of the Proterozoic. However, the interactive evolution of the biogeochemical cycles of O<sub>2</s

Abstract Oxygen is a potential biosignature for terrestrial Earth-like planets. The primary source of oxygen on Earth is oxygenic photosynthesis, which may be limited by the supply of riverine phosphorus. Therefore, phosphorus supply from the chemical weathering of continents is crucial for the evolution of p O 2 . Chemical weathering occurs on both the continents and seafloor and stabilizes the climate, but phosphorus is only supplied by continental weathering. The amount of continental weather

The Archean Earth was characterized by a persistent reducing atmosphere, while the occurrence of transient atmospheric oxygenation events—whiff of oxygen—has been suggested, the precise nature and causes of which remain elusive. Here we used a biogeochemical model, corroborating the eruption of large igneous provinces as a plausible mechanistic explanation for these transient oxygenation events. Our results show that biogeochemical dynamics induced by eruptions of large igneous provinces could h

Abstract Methane (CH 4 ) is a primarily biogenic greenhouse gas. As such, it represents an essential biosignature to search for life on exoplanets. Atmospheric CH 4 abundance on Earth-like inhabited exoplanets is likely controlled by marine biogenic production and atmospheric photochemical consumption. Such interactions have been previously examined for the case of the early Earth where primitive marine ecosystems supplied CH 4 to the atmosphere, showing that the atmospheric CH 4 response to bio

Abstract Understanding the oceanic phosphate concentration is critical for understanding marine productivity and oxygen evolution throughout Earth history. During the Archean, estimates of marine phosphate levels range from scarce to enriched conditions. However, biogeochemical conditions required for sustaining high phosphate concentrations while retaining an anoxic atmosphere during the Archean remain ambiguous. Here, we employ a biogeochemical model of the marine phosphate cycle to determine

(1) シイタケの炭水化物は大部分がいわゆるヘミセルローズであるが,炭水化物のシロネズミにおける消化率は約80%で,比較的大きいことを認めた. (2) 3種のシイタケヘミセルローズ,すなわちA(冷アルカリ可溶性), B(温アルカリ可溶性), C(温アルカリ不溶性)を,それぞれシイタケ無水物に対して13.6%, 3.3%, 26.9%の収率で得た. (3) これらの3つのヘミセルローズは,酸あるいは酵素によって加水分解を受ける程度がそれぞれ相違していたが,特にカタツムリの消化管に存在するヘミセルラーゼの作用によって加水分解される程度がA>B>Cの順であった.また稀鉱酸で加熱加水分解した場合の加水分解率はAおよびBはほぼ等しかったが, Cはこれらと比較して幾分小さかった. (4) 各ヘミセルローズを構成する糖類の種類にも相違があり,硫酸加水分解液中に検出された糖類は,Aではグルコーズ,マンノーズ,キシローズ,ウロン酸, Bではグルコーズ,キシローズ,ウロン酸, Cではグルコーズ,キシローズであった.またいずれのヘミセルローズも,グルコーズを主構成分としていることが認められた. (5) これ

Understanding the oceanic phosphate concentration is critical for understanding marine productivity and oxygen evolutions throughout Earth history. During the Archean, estimates of marine phosphate levels range from depleted to enriched conditions. However, biogeochemical conditions required for sustaining high phosphate concentrations while retaining an anoxic atmosphere during the Archean remain ambiguous. Here, we employ a biogeochemical model of the marine phosphate cycle to determine the co

Abstract. The climates of the mid-Holocene (MH) and Last Interglacial (LIG) are characterised by warm periods caused by astronomical forcing and climate feedback. One potential feedback is variation in the stratospheric ozone, the influence of which would extend down to the troposphere, potentially affecting the climate. However, understanding the role of changes in the stratospheric ozone during past warm interglacial periods is limited to MH conditions. Here, we employ MRI-ESM2.0, an Earth sys

<strong class="journal-contentHeaderColor">Abstract.</strong> The climates of the mid-Holocene (MH) and Last Interglacial (LIG) are characterised by warm periods caused by astronomical forcing and climate feedback. One potential feedback is variation in the stratospheric ozone, the influence of which would extend down to the troposphere, potentially affecting the climate. However, understanding the role of changes in the stratospheric ozone during past warm interglacial periods is limited to MH

<strong class="journal-contentHeaderColor">Abstract.</strong> The climates of the mid-Holocene (MH) and Last Interglacial (LIG) are characterised by warm periods caused by astronomical forcing and climate feedback. One potential feedback is variation in the stratospheric ozone, the influence of which would extend down to the troposphere, potentially affecting the climate. However, understanding the role of changes in the stratospheric ozone during past warm interglacial periods is limited to MH

Abstract. The climates of the mid-Holocene (MH) and Last Interglacial (LIG) are characterised by warm periods caused by astronomical forcing and climate feedback. One potential feedback is variation in the stratospheric ozone, the influence of which would extend down to the troposphere, potentially affecting the climate. However, little is known about the role of changes in the stratospheric ozone during past warm interglacial periods. Here, we employ MRI-ESM2.0, an Earth system model with an in