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Philosophical Transactions. Series A, Mathematical, Physical, and Engineering Sciences

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https://www.readbyqxmd.com/read/28784716/climate-change-and-ocean-deoxygenation-within-intensified-surface-driven-upwelling-circulations
#1
REVIEW
Andrew Bakun
Ocean deoxygenation often takes place in proximity to zones of intense upwelling. Associated concerns about amplified ocean deoxygenation arise from an arguable likelihood that coastal upwelling systems in the world's oceans may further intensify as anthropogenic climate change proceeds. Comparative examples discussed include the uniquely intense seasonal Somali Current upwelling, the massive upwelling that occurs quasi-continuously off Namibia and the recently appearing and now annually recurring 'dead zone' off the US State of Oregon...
September 13, 2017: Philosophical Transactions. Series A, Mathematical, Physical, and Engineering Sciences
https://www.readbyqxmd.com/read/28784715/patterns-of-deoxygenation-sensitivity-to-natural-and-anthropogenic-drivers
#2
REVIEW
Andreas Oschlies, Olaf Duteil, Julia Getzlaff, Wolfgang Koeve, Angela Landolfi, Sunke Schmidtko
Observational estimates and numerical models both indicate a significant overall decline in marine oxygen levels over the past few decades. Spatial patterns of oxygen change, however, differ considerably between observed and modelled estimates. Particularly in the tropical thermocline that hosts open-ocean oxygen minimum zones, observations indicate a general oxygen decline, whereas most of the state-of-the-art models simulate increasing oxygen levels. Possible reasons for the apparent model-data discrepancies are examined...
September 13, 2017: Philosophical Transactions. Series A, Mathematical, Physical, and Engineering Sciences
https://www.readbyqxmd.com/read/28784714/high-latitude-ocean-ventilation-and-its-role-in-earth-s-climate-transitions
#3
Alberto C Naveira Garabato, Graeme A MacGilchrist, Peter J Brown, D Gwyn Evans, Andrew J S Meijers, Jan D Zika
The processes regulating ocean ventilation at high latitudes are re-examined based on a range of observations spanning all scales of ocean circulation, from the centimetre scales of turbulence to the basin scales of gyres. It is argued that high-latitude ocean ventilation is controlled by mechanisms that differ in fundamental ways from those that set the overturning circulation. This is contrary to the assumption of broad equivalence between the two that is commonly adopted in interpreting the role of the high-latitude oceans in Earth's climate transitions...
September 13, 2017: Philosophical Transactions. Series A, Mathematical, Physical, and Engineering Sciences
https://www.readbyqxmd.com/read/28784713/ocean-de-oxygenation-from-the-last-glacial-maximum-to-the-twenty-first-century-insights-from-earth-system-models
#4
L Bopp, L Resplandy, A Untersee, P Le Mezo, M Kageyama
All Earth System models project a consistent decrease in the oxygen content of oceans for the coming decades because of ocean warming, reduced ventilation and increased stratification. But large uncertainties for these future projections of ocean deoxygenation remain for the subsurface tropical oceans where the major oxygen minimum zones are located. Here, we combine global warming projections, model-based estimates of natural short-term variability, as well as data and model estimates of the Last Glacial Maximum (LGM) ocean oxygenation to gain some insights into the major mechanisms of oxygenation changes across these different time scales...
September 13, 2017: Philosophical Transactions. Series A, Mathematical, Physical, and Engineering Sciences
https://www.readbyqxmd.com/read/28784712/physiological-and-ecological-implications-of-ocean-deoxygenation-for-vision-in-marine-organisms
#5
REVIEW
Lillian R McCormick, Lisa A Levin
Climate change has induced ocean deoxygenation and exacerbated eutrophication-driven hypoxia in recent decades, affecting the physiology, behaviour and ecology of marine organisms. The high oxygen demand of visual tissues and the known inhibitory effects of hypoxia on human vision raise the questions if and how ocean deoxygenation alters vision in marine organisms. This is particularly important given the rapid loss of oxygen and strong vertical gradients in oxygen concentration in many areas of the ocean. This review evaluates the potential effects of low oxygen (hypoxia) on visual function in marine animals and their implications for marine biota under current and future ocean deoxygenation based on evidence from terrestrial and a few marine organisms...
September 13, 2017: Philosophical Transactions. Series A, Mathematical, Physical, and Engineering Sciences
https://www.readbyqxmd.com/read/28784711/ventilation-variability-of-labrador-sea-water-and-its-impact-on-oxygen-and-anthropogenic-carbon-a-review
#6
Monika Rhein, Reiner Steinfeldt, Dagmar Kieke, Ilaria Stendardo, Igor Yashayaev
Ventilation of Labrador Sea Water (LSW) receives ample attention because of its potential relation to the strength of the Atlantic Meridional Overturning Circulation (AMOC). Here, we provide an overview of the changes of LSW from observations in the Labrador Sea and from the southern boundary of the subpolar gyre at 47° N. A strong winter-time atmospheric cooling over the Labrador Sea led to intense and deep convection, producing a thick and dense LSW layer as, for instance, in the early to mid-1990s. The weaker convection in the following years mostly ventilated less dense LSW vintages and also reduced the supply of oxygen...
September 13, 2017: Philosophical Transactions. Series A, Mathematical, Physical, and Engineering Sciences
https://www.readbyqxmd.com/read/28784710/depth-perception-the-need-to-report-ocean-biogeochemical-rates-as-functions-of-temperature-not-depth
#7
Peter G Brewer, Edward T Peltzer
For over 50 years, ocean scientists have oddly represented ocean oxygen consumption rates as a function of depth but not temperature in most biogeochemical models. This unique tradition or tactic inhibits useful discussion of climate change impacts, where specific and fundamental temperature-dependent terms are required. Tracer-based determinations of oxygen consumption rates in the deep sea are nearly universally reported as a function of depth in spite of their well-known microbial basis. In recent work, we have shown that a carefully determined profile of oxygen consumption rates in the Sargasso Sea can be well represented by a classical Arrhenius function with an activation energy of 86...
September 13, 2017: Philosophical Transactions. Series A, Mathematical, Physical, and Engineering Sciences
https://www.readbyqxmd.com/read/28784709/ocean-deoxygenation-the-global-phosphorus-cycle-and-the-possibility-of-human-caused-large-scale-ocean-anoxia
#8
Andrew J Watson, Timothy M Lenton, Benjamin J W Mills
The major biogeochemical cycles that keep the present-day Earth habitable are linked by a network of feedbacks, which has led to a broadly stable chemical composition of the oceans and atmosphere over hundreds of millions of years. This includes the processes that control both the atmospheric and oceanic concentrations of oxygen. However, one notable exception to the generally well-behaved dynamics of this system is the propensity for episodes of ocean anoxia to occur and to persist for 10(5)-10(6) years, these ocean anoxic events (OAEs) being particularly associated with warm 'greenhouse' climates...
September 13, 2017: Philosophical Transactions. Series A, Mathematical, Physical, and Engineering Sciences
https://www.readbyqxmd.com/read/28784708/ocean-ventilation-and-deoxygenation-in-a-warming-world-posters
#9
John G Shepherd, Peter G Brewer, Andreas Oschlies, Andrew J Watson
No abstract text is available yet for this article.
September 13, 2017: Philosophical Transactions. Series A, Mathematical, Physical, and Engineering Sciences
https://www.readbyqxmd.com/read/28784707/ocean-ventilation-and-deoxygenation-in-a-warming-world-introduction-and-overview
#10
John G Shepherd, Peter G Brewer, Andreas Oschlies, Andrew J Watson
Changes of ocean ventilation rates and deoxygenation are two of the less obvious but important indirect impacts expected as a result of climate change on the oceans. They are expected to occur because of (i) the effects of increased stratification on ocean circulation and hence its ventilation, due to reduced upwelling, deep-water formation and turbulent mixing, (ii) reduced oxygenation through decreased oxygen solubility at higher surface temperature, and (iii) the effects of warming on biological production, respiration and remineralization...
September 13, 2017: Philosophical Transactions. Series A, Mathematical, Physical, and Engineering Sciences
https://www.readbyqxmd.com/read/28784706/photosynthetic-oxygen-production-in-a-warmer-ocean-the-sargasso-sea-as-a-case-study
#11
Katherine Richardson, Jørgen Bendtsen
Photosynthetic O2 production can be an important source of oxygen in sub-surface ocean waters especially in permanently stratified oligotrophic regions of the ocean where O2 produced in deep chlorophyll maxima (DCM) is not likely to be outgassed. Today, permanently stratified regions extend across approximately 40% of the global ocean and their extent is expected to increase in a warmer ocean. Thus, predicting future ocean oxygen conditions requires a better understanding of the potential response of photosynthetic oxygen production to a warmer ocean...
September 13, 2017: Philosophical Transactions. Series A, Mathematical, Physical, and Engineering Sciences
https://www.readbyqxmd.com/read/28784705/biogeochemical-modelling-of-dissolved-oxygen-in-a-changing-ocean
#12
Oliver Andrews, Erik Buitenhuis, Corinne Le Quéré, Parvadha Suntharalingam
Secular decreases in dissolved oxygen concentration have been observed within the tropical oxygen minimum zones (OMZs) and at mid- to high latitudes over the last approximately 50 years. Earth system model projections indicate that a reduction in the oxygen inventory of the global ocean, termed ocean deoxygenation, is a likely consequence of on-going anthropogenic warming. Current models are, however, unable to consistently reproduce the observed trends and variability of recent decades, particularly within the established tropical OMZs...
September 13, 2017: Philosophical Transactions. Series A, Mathematical, Physical, and Engineering Sciences
https://www.readbyqxmd.com/read/28739971/frustrated-lewis-pair-chemistry
#13
Douglas W Stephan, Gerhard Erker
No abstract text is available yet for this article.
August 28, 2017: Philosophical Transactions. Series A, Mathematical, Physical, and Engineering Sciences
https://www.readbyqxmd.com/read/28739970/design-and-reactions-of-a-carbon-lewis-base-boron-lewis-acid-frustrated-lewis-pair
#14
Jennifer Möricke, Birgit Wibbeling, Constantin G Daniliuc, Gerald Kehr, Gerhard Erker
The conjugated dienamine 4 selectively adds Piers' borane [HB(C6F5)2] to give the enamine/borane system 5, which features a boratirane structure by internal enamine carbon Lewis base to boron Lewis acid interaction. Compound 5 behaves as a C/B frustrated Lewis pair and undergoes typical addition reactions to benzaldehyde, several nitriles and to sulfur dioxide.This article is part of the themed issue 'Frustrated Lewis pair chemistry'.
August 28, 2017: Philosophical Transactions. Series A, Mathematical, Physical, and Engineering Sciences
https://www.readbyqxmd.com/read/28739969/halogenated-triphenylgallium-and-indium-in-frustrated-lewis-pair-activations-and-hydrogenation-catalysis
#15
Maotong Xu, Josephine Possart, Alexander E Waked, Julie Roy, Werner Uhl, Douglas W Stephan
The Lewis acids Ga(C6F5)3, In(C6F5)3 and Ga(C6Cl5)3 are prepared and their Lewis acidity has been probed experimentally and computationally. The species Ga(C6F5)3 and In(C6F5)3 in conjunction with phosphine donors are shown to heterolytically split H2 and catalyse the hydrogenation of an imine. In addition, frustrated Lewis pairs (FLPs) derived from Ga(C6F5)3 and In(C6F5)3 and phosphines react with diphenyldisulfide to phosphoniumgallates or indates of the form [tBu3PSPh][PhSE(C6F5)3] and [tBu3PSPh][(μ-SPh)(E(C6F5)3)2] (E = Ga, In)...
August 28, 2017: Philosophical Transactions. Series A, Mathematical, Physical, and Engineering Sciences
https://www.readbyqxmd.com/read/28739967/reactions-of-biologically-inspired-hydride-sources-with-b-c6f5-3
#16
Lewis C Wilkins, Nicolò Santi, Louis Y P Luk, Rebecca L Melen
The combination of 1-benzyl-1,4-dihydropyridines with the strong Lewis acid, B(C6F5)3, generates a stable pyridinium borohydride species in high yields (94%) in as little as 10 min. This use of biologically inspired hydride sources further builds on the recent work of new hydride donors in the formation of borohydrides. When functionalizing the dihydropyridine with an amide or carboxylic acid moiety, a disproportionation reaction composed of a series of protonation/reduction steps is observed upon the addition of B(C6F5)3 As a result, one equivalent of dihydropyridine undergoes net hydrogenation, whereas the other is dehydrogenated yielding the pyridinium counterpart in a transfer hydrogenation-type mechanism...
August 28, 2017: Philosophical Transactions. Series A, Mathematical, Physical, and Engineering Sciences
https://www.readbyqxmd.com/read/28739966/hydrogen-activation-using-a-novel-tribenzyltin-lewis-acid
#17
Robert T Cooper, Joshua S Sapsford, Roland C Turnell-Ritson, Dong-Hun Hyon, Andrew J P White, Andrew E Ashley
Over the last decade there has been an explosion in the reactivity and applications of frustrated Lewis pair (FLP) chemistry. Despite this, the Lewis acids (LAs) in these transformations are often boranes, with heavier p-block elements receiving surprisingly little attention. The novel LA Bn3SnOTf (1) has been synthesized from simple, inexpensive starting materials and has been spectroscopically and structurally characterized. Subtle modulation of the electronics at the tin centre has led to an increase in its Lewis acidity in comparison with previously reported R3SnOTf LAs, and has facilitated low temperature hydrogen activation and imine hydrogenation...
August 28, 2017: Philosophical Transactions. Series A, Mathematical, Physical, and Engineering Sciences
https://www.readbyqxmd.com/read/28739965/attempted-synthesis-of-ortho-phenylene-phosphino-tritylium-cations
#18
Kantapat Chansaenpak, Mengxi Yang, François P Gabbaï
With the synthesis of ortho-phenylene phosphino-tritylium cations as an objective, we generated (2-lithiophenyl)diphenylphosphine and (2-lithiophenyl)di-isopropylphosphine and allowed these organolithium reagents to react with benzophenone. The resulting phosphino-triarylcarbinols were allowed to react with HBF4 in the presence of trifluoroacetic anhydride in order to generate the corresponding cations. Instead of the targeted ortho-phenylene phosphino-tritylium, the cations formed in these reactions were identified as the four-membered phosphonium species 7,7-bis(phenyl)-8,8-bis(phenyl)-7-phosphoniabicyclo[4...
August 28, 2017: Philosophical Transactions. Series A, Mathematical, Physical, and Engineering Sciences
https://www.readbyqxmd.com/read/28739964/on-the-hydrogen-activation-by-frustrated-lewis-pairs-in-the-solid-state-benchmark-studies-and-theoretical-insights
#19
Lei Liu, Jan Gerit Brandenburg, Stefan Grimme
Recently, the concept of small molecule activation by frustrated Lewis pairs (FLPs) has been expanded to the solid state showing a variety of interesting reactivities. Therefore, there is a need to establish a computational protocol to investigate such systems theoretically. In the present study, we selected several FLPs and applied multiple levels of theory, ranging from a semi-empirical tight-binding Hamiltonian to dispersion corrected hybrid density functionals. Their performance is benchmarked for the computation of crystal geometries, thermostatistical contributions, and reaction energies...
August 28, 2017: Philosophical Transactions. Series A, Mathematical, Physical, and Engineering Sciences
https://www.readbyqxmd.com/read/28739963/on-the-concept-of-frustrated-lewis-pairs
#20
REVIEW
Frédéric-Georges Fontaine, Douglas W Stephan
In this concept article, we consider the notion of 'frustrated Lewis pairs' (FLPs). While the original use of the term referred to steric inhibition of dative bond formation in a Lewis pair, work in the intervening decade demonstrates the limitation of this simplistic view. Analogies to known transition metal chemistry and the applications in other areas of chemistry are considered. In the light of these findings, we present reflections on the criteria for a definition of the term 'frustrated Lewis pair'. Segregation of the Lewis acid and base and the kinetic nature of FLP reactivity are discussed...
August 28, 2017: Philosophical Transactions. Series A, Mathematical, Physical, and Engineering Sciences
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