Abstract The ongoing oceanic oxygen loss will have a profound impact on the distribution and density of life on Earth. However, drivers of the initiation and termination of global oceanic deoxygenation are poorly understood. Here we present a thallium isotope record that reveals three rapid (50 k.y.) global deoxygenation intervals during the mid-Cretaceous that postdate massive volcanism by at least 1 m.y. New strontium isotope data reveal gradually enhanced continental weathering under a warmer climate following volcanism. However, global deoxygenation occurred only under the combined influences of a long-term increase in weathering rates in a warmer climate and short-term orbital modulation that led to atmospheric-circulation reorganization. Interactions of multiple drivers are consistent with the abrupt termination of each deoxygenation interval. Dynamic oxygenation responses in the mid-Cretaceous highlight the role of these processes for understanding the consequences and potential termination of the current oceanic deoxygenation.
Land use in urban areas is crucial for urban land management decision-making,environment monitoring and urban planning.According to the landscape ecology concept that the landscape patterns within the same land use type are similar,this paper presents a new land use classification approach which integrates landscape characteristics and high-spatial resolution remote sensing data.Some key landscape metrics were selected to quantify the landscape patterns of different land uses.Then,the integration of SPOT image and landscape characteristics was applied to land use classification within the 5th Ring Road of Beijing.The overall land use classification accuracy was 85.9% with Kappa parameter being 71.1%.The results show that the specific landscape patterns of different land use types would significantly contribute to improving land use classification,and could potentially be applied to other urban areas.
The significant hydrocarbon discoveries have been found during the past few years in Middle Jurassic Xishanyao Formation in Southeastern Xiayan Rise, Junggar Basin. The braided delta front deposits and shore‐shallow lacustrine deposits are well preserved in Xishanyao Formation, their history being documented by integrated analysis of seismic volumes and borehole datasets (wireline logs, cores, grain size etc). The results reveal that five sedimentary microfacies are identified. Among them, the braided delta front deposits include subaqueous distributary channel, inter‐distributary channel and mouth bar, while shore‐shallow lacustrine deposits consist of lacustrine mud and swamp. In addition, depositional evolution of braided delta front deposits and shore‐shallow lacustrine deposits from bottom to top in Xishanyao Formation is characterized by retrogradation and progradation during depositional period. The depositional evolution during depositional period of Xishanyao Formation is controlled by interactions of the source and distribution of provenance, the catchments, the lacustrine fluctuations and the climates.
Abstract. A growing body of observations reveals rapid changes in both the total inventory and distribution of marine oxygen over the later half of the 21st century, leading to increased interest in extending oxygenation records into the past. Use of paleo-oxygen proxies have the potential to extend the spatial and temporal range of current records, bound pre-anthropogenic baselines, provide datasets necessary to test climate models under different boundary conditions, and ultimately understand how ocean oxygenation responds beyond decadal scale changes. This review seeks to summarize the current state-of-knowledge about proxies for reconstructing Cenozoic marine oxygen: sedimentary features, sedimentary redox-sensitive trace elements and isotopes, biomarkers, nitrogen isotopes, foraminiferal trace elements, foraminifera assemblages, foraminifera morphometrics, and benthic foraminifera carbon isotope gradients. Taking stock of each proxy reveals some common limitations in that the majority of proxies function best at low-oxygen concentrations and many reflect multiple environmental drivers. We also highlight recent breakthroughs in geochemistry and proxy approaches for constraining pelagic (in addition to benthic) oxygenation that are rapidly advancing the field. In light of both the emergence of new proxies and the persistent multiple driver problem, the need for multi-proxy approaches and FAIR data storage and sharing is emphasized. Continued refinement of proxy approaches and both proxy-proxy and proxy-model comparisons are likely to support the growing needs of both oceanographer and paleoceanographers interested in paleo-oxygenation records.
Abstract The magnitude of natural oceanic dissolved oxygen (DO) variability remains poorly understood due to the short duration of the observational record. Here we present a high‐resolution (4–9 years) reconstruction of the Southern California oxygen minimum zone (OMZ) through the Common Era using redox‐sensitive metals. Rapid OMZ intensification on multidecadal timescales reveals greater DO variability than observed in instrumental records. An anomalous interval of intensified OMZ between 1600–1750 CE contradicts the expectation of better‐ventilated mid‐depth North Pacific during cool climates. Although the influence of low‐DO Equatorial Pacific Intermediate Water on the Southern California Margin was likely weaker during this interval, we attribute the observed rapid deoxygenation to reduced North Pacific Intermediate Water (NPIW) ventilation. NPIW ventilation thus appears very sensitive to atmospheric circulation reorganization (e.g., a weakened Siberian High and Aleutian Low). In addition to temperature‐induced gas solubility, atmospheric forcing under future anthropogenic influences could amplify OMZ variability.
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