scholarly journals Triple oxygen isotope constraints on atmospheric O2 and biological productivity during the mid-Proterozoic

2021 ◽  
Vol 118 (51) ◽  
pp. e2105074118
Author(s):  
Peng Liu ◽  
Jingjun Liu ◽  
Aoshuang Ji ◽  
Christopher T. Reinhard ◽  
Noah J. Planavsky ◽  
...  
Keyword(s):  
Atmospheric Oxygen ◽  
Gas Transfer ◽  
Atmospheric Methane ◽  
Biological Productivity ◽  
Transfer Rates ◽  
Physical Constraints ◽  
Fundamental Goal ◽  
History Of ◽  
Marine Productivity ◽  
Geologic Record

Reconstructing the history of biological productivity and atmospheric oxygen partial pressure (pO2) is a fundamental goal of geobiology. Recently, the mass-independent fractionation of oxygen isotopes (O-MIF) has been used as a tool for estimating pO2 and productivity during the Proterozoic. O-MIF, reported as Δ′17O, is produced during the formation of ozone and destroyed by isotopic exchange with water by biological and chemical processes. Atmospheric O-MIF can be preserved in the geologic record when pyrite (FeS2) is oxidized during weathering, and the sulfur is redeposited as sulfate. Here, sedimentary sulfates from the ∼1.4-Ga Sibley Formation are reanalyzed using a detailed one-dimensional photochemical model that includes physical constraints on air–sea gas exchange. Previous analyses of these data concluded that pO2 at that time was <1% PAL (times the present atmospheric level). Our model shows that the upper limit on pO2 is essentially unconstrained by these data. Indeed, pO2 levels below 0.8% PAL are possible only if atmospheric methane was more abundant than today (so that pCO2 could have been lower) or if the Sibley O-MIF data were diluted by reprocessing before the sulfates were deposited. Our model also shows that, contrary to previous assertions, marine productivity cannot be reliably constrained by the O-MIF data because the exchange of molecular oxygen (O2) between the atmosphere and surface ocean is controlled more by air–sea gas transfer rates than by biological productivity. Improved estimates of pCO2 and/or improved proxies for Δ′17O of atmospheric O2 would allow tighter constraints to be placed on mid-Proterozoic pO2.

Phanerozoic Oxygen

2017 ◽  
Author(s):  
Donald Eugene Canfield
Keyword(s):  
Oxygen Consumption ◽  
Organic Carbon ◽  
Sea Level ◽  
Time Scale ◽  
Atmospheric Oxygen ◽  
Sea Level Change ◽  
Oxygen Production ◽  
Level Change ◽  
History Of ◽  
Geologic Processes

This chapter discusses the modeling of the history of atmospheric oxygen. The most recently deposited sediments will also be the most prone to weathering through processes like sea-level change or uplift of the land. Thus, through rapid recycling, high rates of oxygen production through the burial of organic-rich sediments will quickly lead to high rates of oxygen consumption through the exposure of these organic-rich sediments to weathering. From a modeling perspective, rapid recycling helps to dampen oxygen changes. This is important because the fluxes of oxygen through the atmosphere during organic carbon and pyrite burial, and by weathering, are huge compared to the relatively small amounts of oxygen in the atmosphere. Thus, all of the oxygen in the present atmosphere is cycled through geologic processes of oxygen liberation (organic carbon and pyrite burial) and consumption (weathering) on a time scale of about 2 to 3 million years.

High Speed Packet Access Broadband Mobile Communications

2009 ◽  
pp. 595-604
Author(s):  
Athanassios C. Iossifides ◽  
Spiros Louvros
Keyword(s):  
Mobile Communications ◽  
Rural Areas ◽  
High Speed ◽  
Data Transfer ◽  
Mobile Wimax ◽  
Major Step ◽  
Transfer Rates ◽  
Mobile Broadband ◽  
History Of ◽  
Broadband Market

Mobile broadband communications systems have already become a fact during the last few years. The evolution of 3G Universal Mobile Telecommunications Systems (UMTS) towards HSDPA/HSUPA systems have already posed a forceful solution for mobile broadband and multimedia services in the market, making a major step ahead of the main competitive technology, that is, WiMax systems based on IEEE 802.16 standard. According to the latest analyses (GSM Association, 2007; Little, 2007), while WiMax has gained considerable attention the last few years, HSPA is expected to dominate the mobile broadband market. The main reasons behind this forecast are: • HSPA is already active in a significant number of operators and is going to be established for the majority of mobile broadband networks worldwide over the next five years, while commercial WiMax systems are only making their first steps. • Mobile WiMax is a competitive technology for selection by operators in only a limited number of circumstances where conditions are favourable. Future mobile WiMax systems may potentially achieve higher data transfer rates than HSPA, though cell coverage for these rates is expected to be substantially smaller. In addition, WiMax technology is less capable in terms of voice traffic capacity, thus limiting market size and corresponding revenues. • In order to overcome the aforementioned disadvantages, WiMax commercial launches are expected to introduce a relative CAPEX disadvantage of at least 20–50% comparing to HSPA, in favorable cases, while there are indications of an increase by up to 5–10 times when accounting for rural areas deployments. The short commercial history of HSDPA (based on Rel.5 specifications of 3GPP) started in December of 2005 (first wide scale launch by Cingular Wireless, closely followed by Manx Telecom and Telekom Austria). Bite Lietuva (Lithuania) was the first operator that launched 3.6 Mbps. HSUPA was first demonstrated by Mobilkom Austria in November 2006 and soon launched commercially in Italia by 3 in December 2006. Mobilkom Austria launched the combination of HSDPA at 7.2 Mbps and HSUPA in February 2007. By September of 2007, less than two years after the first commercial launch, 141 operators in 65 countries (24 out of 27 in EU) have already gone commercial with HSDPA with 38 operators among them supporting a 3.6 Mbps downlink. In addition, devices supporting HSDPA/HSUPA services are rapidly enriched. 311 devices from 79 suppliers have already been available by September 2007, including handsets, data cards, USB modems, notebooks, wireless routers, and embedded modules (http://hspa.gsmworld.com).

Effects of Continents and Supercontinents on Climate

2004 ◽  
Author(s):  
John J. W. Rogers ◽  
M. Santosh
Keyword(s):  
Global Climate ◽  
Climatic Conditions ◽  
Polar Regions ◽  
The North ◽  
Rock Types ◽  
Control Climate ◽  
The Earth ◽  
History Of ◽  
Earth’S Climate ◽  
Geologic Record

Continents affect the earth’s climate because they modify global wind patterns, control the paths of ocean currents, and absorb less heat than seawater. Throughout earth history the constant movement of continents and the episodic assembly of supercontinents has influenced both global climate and the climates of individual continents. In this chapter we discuss both present climate and the history of climate as far back in the geologic record as we can draw inferences. We concentrate on longterm changes that are affected by continental movements and omit discussion of processes with periodicities less than about 20,000 years. We refer readers to Clark et al. (1999) and Cronin (1999) if they are interested in such short-term processes as El Nino, periodic variations in solar irradiance, and Heinrich events. The chapter is divided into three sections. The first section describes the processes that control climate on the earth and includes a discussion of possible causes of glaciation that occurred over much of the earth at more than one time in the past. The second section investigates the types of evidence that geologists use to infer past climates. They include specific rock types that can form only under restricted climatic conditions, varieties of individual fossils, diversity of fossil populations, and information that the 18O/16O isotopic system can provide about temperatures of formation of ancient sediments. The third section recounts the history of the earth’s climate and relates changes to the growth and movement of continents. This history takes us from the Archean, when climates are virtually unknown, through various stages in the evolution of organic life, and ultimately to the causes of the present glaciation in both the north and the south polar regions. The earth’s climate is controlled both by processes that would operate even if continents did not exist and also by the positions and topographies of continents. We begin with the general controls, then discuss the specific effects of continents, and close with a brief discussion of processes that cause glaciation. The general climate of the earth is determined by the variation in the amount of sunshine received at different latitudes, by the earth’s rotation, and by the amount of arriving solar energy that is retained in the atmosphere.

Temperature Influence on Absorption and Stripping Processes

1987 ◽  
Vol 19 (5-6) ◽  
pp. 877-888
Author(s):  
Boris M. Khudenko ◽  
Alberto Garcia-Pastrana
Keyword(s):  
Simulation Analysis ◽  
Critical Energy ◽  
Temperature Correction ◽  
Gas Absorption ◽  
Gas Transfer ◽  
Distribution Law ◽  
Transfer Energy ◽  
Transfer Rates ◽  
Influence Of Temperature On ◽  
Transfer Apparatus

The influence of temperature on mass transfer rates in gas absorption and stripping processes has been evaluated. A computer simulation analysis has been used to identify fundamental reasons for variations among temperature correction factors published in the literature. A critical molecular transfer energy was postulated and the temperature correction factor was developed based on the Maxwell distribution law. The critical energy hypothesis was experimentally validated and the critical energy of molecules crossing the gas-liquid interface of 2.6.10−13 erg was determined for both methane and oxygen in the temperature range from 5° to 75°C. The critical energy was found to be a constant value for various hydrodynamic conditions and also for water with and without surfactants. The temperature correction expression derived based on the critical energy hypothesis was compared with several published relationships. The comparison has corroborated that the developed temperature correction relationship is applicable to various gas transfer apparatus and hydrodynamic regimes.

scholarly journals Feather duvet lung

2019 ◽  
Vol 12 (11) ◽  
pp. e231237 ◽  
Author(s):  
Patrick Liu-Shiu-Cheong ◽  
Chris RuiWen Kuo ◽  
Struan WA Wilkie ◽  
Owen Dempsey
Keyword(s):  
Lung Function ◽  
Hypersensitivity Pneumonitis ◽  
Oral Corticosteroid ◽  
Gas Transfer ◽  
Mosaic Pattern ◽  
Pet Birds ◽  
History Of ◽  
Function Testing ◽  
Oral Corticosteroid Therapy ◽  
Restrictive Pattern

A 43-year-old non-smoker was referred with a 3-month history of malaise, fatigue and breathlessness. Blood avian precipitins were strongly positive. Lung function testing confirmed a restrictive pattern with impaired gas transfer. A ‘ground glass’ mosaic pattern was seen on CT imaging, suggestive of hypersensitivity pneumonitis. Although he had no pet birds, on closer questioning he had recently acquired a duvet and pillows containing feathers. His symptoms, chest radiograph and lung function tests improved after removal of all feather bedding, and he was also started on oral corticosteroid therapy. Our case reinforces the importance of taking a meticulous exposure history and asking about domestic bedding in patients with unexplained breathlessness. Prompt recognition and cessation of antigen exposure may prevent the development of irreversible lung fibrosis.

scholarly journals Pyrogenic iron: The missing link to high iron solubility in aerosols

2019 ◽  
Vol 5 (5) ◽  
pp. eaau7671 ◽  
Author(s):  
Akinori Ito ◽  
Stelios Myriokefalitakis ◽  
Maria Kanakidou ◽  
Natalie M. Mahowald ◽  
Rachel A. Scanza ◽  
...  
Keyword(s):  
Statistical Analysis ◽  
Southern Ocean ◽  
Atmospheric Deposition ◽  
Field Data ◽  
Biological Productivity ◽  
Iron Solubility ◽  
Field Campaigns ◽  
Anthropogenic Perturbations ◽  
Marine Productivity ◽  
Multiple Field

Atmospheric deposition is a source of potentially bioavailable iron (Fe) and thus can partially control biological productivity in large parts of the ocean. However, the explanation of observed high aerosol Fe solubility compared to that in soil particles is still controversial, as several hypotheses have been proposed to explain this observation. Here, a statistical analysis of aerosol Fe solubility estimated from four models and observations compiled from multiple field campaigns suggests that pyrogenic aerosols are the main sources of aerosols with high Fe solubility at low concentration. Additionally, we find that field data over the Southern Ocean display a much wider range in aerosol Fe solubility compared to the models, which indicate an underestimation of labile Fe concentrations by a factor of 15. These findings suggest that pyrogenic Fe-containing aerosols are important sources of atmospheric bioavailable Fe to the open ocean and crucial for predicting anthropogenic perturbations to marine productivity.

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