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  • 1
    Publication Date: 2016-07-21
    Description: Stratigraphy provides insights into the evolution and dynamics of the Earth System over its long history. With recent developments in Earth System science, changes in Earth System dynamics can now be observed directly and projected into the near future. An integration of the two approaches provides powerful insights into the nature and significance of contemporary changes to Earth. From both perspectives, the Earth has been pushed out of the Holocene Epoch by human activities, with the mid-20 th century a strong candidate for the start date of the Anthropocene, the proposed new epoch in Earth history. Here we explore two contrasting scenarios for the future of the Anthropocene, recognizing that the Earth System has already undergone a substantial transition away from the Holocene state. A rapid shift of societies towards the UN Sustainable Development Goals could stabilize the Earth System in a state with more intense interglacial conditions than in the late Quaternary climate regime and with little further biospheric change. In contrast, a continuation of the present Anthropocene trajectory of growing human pressures will likely lead to biotic impoverishment and a much warmer climate with a significant loss of polar ice.
    Electronic ISSN: 2328-4277
    Topics: Geosciences
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  • 2
    Publication Date: 2016-02-04
    Description: Biospheric relationships between production and consumption of biomass have been resilient to changes in the Earth system over billions of years. This relationship has increased in its complexity, from localised ecosystems predicated on anaerobic microbial production and consumption, to a global biosphere founded on primary production from oxygenic photoautotrophs, through the evolution of Eukarya, metazoans, and the complexly networked ecosystems of microbes, animals, fungi and plants that characterise the Phanerozoic Eon (the last ~541 million years of Earth history). At present, one species, Homo sapiens , is refashioning this relationship between consumption and production in the biosphere with unknown consequences. This has left a distinctive stratigraphy of the production and consumption of biomass, of natural resources, and of produced goods. This can be traced through stone tool technologies and geochemical signals, later unfolding into a diachronous signal of technofossils and human bioturbation across the planet, leading to stratigraphically almost isochronous signals developing by the mid-20 th century. These latter signals may provide an invaluable resource for informing and constraining a formal Anthropocene chronostratigraphy, but are perhaps yet more important as tracers of a biosphere state that is characterised by a geologically unprecedented pattern of global energy flow that is now pervasively influenced and mediated by humans, and which is necessary for maintaining the complexity of modern human societies.
    Electronic ISSN: 2328-4277
    Topics: Geosciences
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  • 3
    Publication Date: 2016-04-13
    Description: There is increasing emphasis from funding agencies on transdisciplinary approaches to integrate science and end-users. However, transdisciplinary research can be laborious and costly and knowledge of effective collaborative processes in these endeavors is incomplete. More guidance grounded in actual project experiences is needed. Thus, this paper describes and examines the collaborative process of the Ecological Effects of Sea Level Rise in the Northern Gulf of Mexico (EESLR-NGOM) transdisciplinary research project, including its development, implementation, and evaluation. Reflections, considerations, and lessons learned from firsthand experience are shared, supported with examples, and connected to relevant scholarly literature.
    Electronic ISSN: 2328-4277
    Topics: Geosciences
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  • 4
    Publication Date: 2017-12-01
    Description: Changing frequencies of extreme weather events and shifting fire seasons call for enhanced capability to forecast where and when forested landscapes switch from a non-flammable (i.e. wet fuel) state to the highly flammable (i.e. dry fuel) state required for catastrophic forest fires. Current forest fire danger indices used in Europe, North America and Australia rate potential fire behaviour by combining numerical indices of fuel moisture content, potential rate of fire spread, and fire intensity. These numerical rating systems lack the physical basis required to reliably quantify forest flammability outside the environments of their development or under novel climate conditions. Here, we argue that exceedance of critical forest flammability thresholds is a prerequisite for major forest fires and therefore early warning systems should be based on a reliable prediction of fuel moisture content plus a regionally calibrated model of how forest fire activity responds to variation in fuel moisture content. We demonstrate the potential of this approach through a case study in Portugal. We use a physically-based fuel moisture model with historical weather and fire records to identify critical fuel moisture thresholds for forest fire activity and then show that the catastrophic June 2017 forest fires in central Portugal erupted shortly after fuels in the region dried out to historically unprecedented levels.
    Electronic ISSN: 2328-4277
    Topics: Geosciences
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  • 5
    Publication Date: 2017-04-27
    Description: The changing Arctic sea ice cover is likely to impact the trans-border exchange of sea ice between the exclusive economic zones (EEZs) of the Arctic nations, affecting the risk of ice-rafted contamination. We apply the Lagrangian Ice Tracking System (LITS) to identify sea ice formation events and track sea ice to its melt locations. Most ice (52%) melts within 100 km of where it is formed; circa 21% escapes from its EEZ. Thus most contaminants will be released within an ice parcel's originating EEZ, while over 1,000,000 km 2 of ice—an area larger than France and Germany combined, to other nations’ waters. Between the periods 1988–1999 and 2000–2014, sea ice formation increased by ~17% (roughly 6 million km 2 vs 5 million km 2 annually). Melting peaks earlier; freeze-up begins later; and the central Arctic Ocean is more prominent in both formation and melt in the later period. The total area of ice transported between EEZs increased, while transit times decreased: for example, Russian ice reached melt locations in other nations’ EEZs an average of 46% faster while North American ice reached destinations in Eurasian waters an average of 37% faster. Increased trans-border exchange is mainly a result of increased speed (~14% per decade), allowing first year ice to escape the summer melt front, even as the front extends further north. Increased trans-border exchange over shorter times is bringing the EEZs of the Arctic nations closer together, which should be taken into account in policy development—including establishment of marine protected areas.
    Electronic ISSN: 2328-4277
    Topics: Geosciences
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  • 6
    Publication Date: 2016-12-27
    Description: Rising global temperature has put increasing pressure on understanding the linkage between atmospheric warming and the occurrence of natural hazards. While the Paris Agreement has set the ambitious target to limiting global warming to 1.5°C compared to pre-industrial levels, scientists are urged to explore scenarios for different warming thresholds and quantify ranges of socio-economic impact. In this work, we present a framework to estimate the economic damage and population affected by river floods at global scale. It is based on a modeling cascade involving hydrological, hydraulic and socio-economic impact simulations, and makes use of state-of-the-art global layers of hazard, exposure and vulnerability at 1 km grid resolution. An ensemble of seven high-resolution global climate projections based on Representative Concentration Pathways (RCP) 8.5 is used to derive streamflow simulations in the present and in the future climate. Those were analyzed to assess the frequency and magnitude of river floods and their impacts under scenarios corresponding to 1.5°C, 2°C, and 4°C global warming. Results indicate a clear positive correlation between atmospheric warming and future flood risk at global scale. At 4°C global warming, countries representing more than 70% of the global population and global GDP will face increases in flood risk in excess of 500%. Changes in flood risk are unevenly distributed, with the largest increases in Asia, America and Europe. In contrast, changes are statistically not significant in most countries in Africa and Oceania for all considered warming levels.
    Electronic ISSN: 2328-4277
    Topics: Geosciences
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  • 7
    Publication Date: 2017-12-14
    Description: Mechanisms such as ice-shelf hydrofracturing and ice-cliff collapse may rapidly increase discharge from marine-based ice sheets. Here, we link a probabilistic framework for sea-level projections to a small ensemble of Antarctic ice-sheet (AIS) simulations incorporating these physical processes to explore their influence on global-mean sea-level (GMSL) and relative sea-level (RSL). We compare the new projections to past results using expert assessment and structured expert elicitation about AIS changes. Under high greenhouse gas emissions (Representative Concentration Pathway [RCP] 8.5), median projected 21st century GMSL rise increases from 79 to 146 cm. Without protective measures, revised median RSL projections would by 2100 submerge land currently home to 153 million people, an increase of 44 million. The use of a physical model, rather than simple parameterizations assuming constant acceleration of ice loss, increases forcing sensitivity: overlap between the central 90% of simulations for 2100 for RCP 8.5 (93–243 cm) and RCP 2.6 (26–98 cm) is minimal. By 2300, the gap between median GMSL estimates for RCP 8.5 and RCP 2.6 reaches 〉10 m, with median RSL projections for RCP 8.5 jeopardizing land now occupied by 950 million people (vs. 167 million for RCP 2.6). The minimal correlation between the contribution of AIS to GMSL by 2050 and that in 2100 and beyond implies current sea-level observations cannot exclude future extreme outcomes. The sensitivity of post-2050 projections to deeply uncertain physics highlights the need for robust decision and adaptive management frameworks.
    Electronic ISSN: 2328-4277
    Topics: Geosciences
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  • 8
    Publication Date: 2020-07-30
    Description: Dimethylsulfide (DMS) atmospheric and oceanic concentrations and eddy covariance air/sea fluxes were measured over the N. Atlantic Ocean during July 2007 from Iceland to Woods Hole, MA, USA. Seawater DMS levels north of 55 degrees N ranged from 3 to 17 nM, with variability related to the satellite-derived distributions of coccoliths and to a lesser extent, chlorophyll. For the most intense bloom region southwest of Iceland, DMS air/sea fluxes were as high as 300 mu mol m(-2) d(-1), larger than current model estimates. The observations imply that gas exchange coefficients in this region are significantly greater than those estimated using most gas transfer parameterizations. South of 55 degrees N, DMS levels were lower and the gas transfer coefficients were similar to those observed in other regions of the ocean. The data suggest that DMS emissions from the bloom region may be significantly larger than current estimates. The anomalous gas exchange coefficients likely reflect strong near-surface, water column DMS gradients influenced by physical and biological processes
    Type: Article , PeerReviewed
    Format: text
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  • 9
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    American Geophysical Union (AGU)
    In:  Geophysical Research Letters, 36 . L15816.
    Publication Date: 2020-07-30
    Description: We report the first simultaneous eddy covariance flux measurements of CO2 and dimethylsulfide (DMS) over the open ocean for two North Atlantic cruises. After normalization for Schmidt number, the two gases give essentially identical gas transfer coefficients and wind speed dependences for the wind speed range 2–10 ms−1. The data indicate a linear relationship between the gas transfer coefficient and mean wind speed, with measured gas transfer coefficients slightly above the Wanninkhof (1992) parameterization, particularly at low wind speeds.
    Type: Article , PeerReviewed
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  • 10
    Publication Date: 2023-03-31
    Description: Coeval changes in atmospheric CO2 and 14C contents during the last deglaciation are often attributed to ocean circulation changes that released carbon stored in the deep ocean during the Last Glacial Maximum (LGM). Work is being done to generate records that allow for the identification of the exact mechanisms leading to the accumulation and release of carbon from the oceanic reservoir, but these mechanisms are still the subject of debate. Here we present foraminifera 14C data from five cores in a transect across the Chilean continental margin between ~540 and ~3,100 m depth spanning the last 20,000 years. Our data reveal that during the LGM, waters at ~2,000 m were 50% to 80% more depleted in Δ14C than waters at ~1,500 m when compared to modern values, consistent with the hypothesis of a glacial deep ocean carbon reservoir that was isolated from the atmosphere. During the deglaciation, our intermediate water records reveal homogenization in the Δ14C values between ~800 and ~1,500 m from ~16.5–14.5 ka cal BP to ~14–12 ka cal BP, which we interpret as deeper penetration of Antarctic Intermediate Water. While many questions still remain, this process could aid the ventilation of the deep ocean at the beginning of the deglaciation, contributing to the observed ~40 ppm rise in atmospheric pCO2.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , peerRev
    Format: application/pdf
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