Showing papers by "Andrew J. Watson published in 2010"

The Give and Take of Alcohol Activation

Abstract: Alcohols are relatively common starting materials for chemical reactions, even though they are quite unreactive. For example, reactions that would substitute another functional group (a nucleophile) for OH often fail because the hydroxide group (HO−) is difficult to displace—it is a poor leaving group. Alcohols are usually activated by turning the hydroxide into a better leaving group, either by protonating the alcohol or by converting it into a sulfonate or halide. However, both of these activation methods have some disadvantages ( 1 ). The acidic environment required for protonating the alcohol also protonates and deactivates the incoming nucleophile, especially amines. Conversion of the alcohol into a sulfonate or halide can lead to toxicity problems; many alkyl halides and alkyl sulfonates are mutagenic.

Meridional density gradients do not control the Atlantic overturning circulation

Abstract: A wide body of modeling and theoretical scaling studies support the concept that changes to the Atlantic meridional overturning circulation (AMOC), whether forced by winds or buoyancy fluxes, can be understood in terms of a simple causative relation between the AMOC and an appropriately defined meridional density gradient (MDG). The MDG is supposed to translate directly into a meridional pressure gradient. Here two sets of experiments are performed using a modular ocean model coupled to an energy‐moisture balance model in which the positive AMOC‐MDG relation breaks down. In the first suite of seven model integrations it is found that increasing winds in the Southern Ocean cause an increase in overturning while the surface density difference between the equator and North Atlantic drops. In the second suite of eight model integrations the equation of state is manipulated so that the density is calculated at the model temperature plus an artificial increment DT that ranges from 238 to 98C. (An increase in DT results in increased sensitivity of density to temperature gradients.) The AMOC in these model integrations drops as the MDG increases regardless of whether the density difference is computed at the surface or averaged over the upper ocean. Traditional scaling analysis can only produce this weaker AMOC if the scale depth decreases enough to compensate for the stronger MDG. Five estimates of the depth scale are evaluated and it is found that the changes in the AMOC can be derived from scaling analysis when using the depth of the maximum overturning circulation or estimates thereof but not from the pycnocline depth. These two depth scales are commonly assumed to be the same in theoretical models of the AMOC. It is suggested that the correlation between the MDG and AMOC breaks down in these model integrations because the depth and strength of the AMOC is influenced strongly by remote forcing such as Southern Ocean winds and Antarctic Bottom Water formation.

A global sea surface carbon observing system: assessment of changing sea surface CO 2 and air-sea CO 2 fluxes

Abstract: (1) Ocean Systems & Climate Group, CSIR (Council for Scientific and Industrial Research), Stellenbosch 7599, South Africa, Email: pmonteir@csir.co.za (2) School of Environment Sciences, University of East Anglia, University Drive, Norwich, NR4 7TJ UK, Email: u.schuster@uea.ac.uk (3) IOCCP (International Ocean Carbon Coordination Project), IOC UNESCO (Intergovernmental Oceanographic Commission of United Nations Educational, Scientific and Cultural Organization) 1 rue Miollis 75732, Paris, France, Email: maria.hood@ioccp.org (4) CSIRO (Commonwealth Scientific and Industrial Research Organisation) Marine & Atmospheric Research, Castray Esplanade, Hobart Tas 7000, Australia, Email: andrew.lenton@csiro.au; bronte.tilbrook@csiro.au (5) LOCEAN-IPSL (Laboratoire d'Oceanographie et du Climat: Experimentations et approches numeriques-Institut Pierre Simon Laplace), CNRS (Centre national de la recherche scientifique), Universite P. et M. Curie Case 100, 4, place Jussieu 75252 Paris Cedex 5, France, Email: nicolas.metzl@upmc.fr (6) Bjerknes Center for Climate Research, Allegaten 55 5007 Bergen, Norway Email: are.olsen@gfi.uib.no (7) AOS (Atmospheric and Oceanic Sciences) Program, Princeton University, 300 Forrestal Road, Sayre Hall, Princeton, NJ 08544 USA, Email: krodgers@princeton.edu (8) NOAA (National Oceanic and Atmospheric Administration) Pacific Marine Environmental Laboratory, 7600 Sand Point Way NE, Seattle, WA 98115, USA Email: chris.Sabine@noaa.gov (9) Lamont-Doherty Earth Observatory – Columbia University, Palisades NY 10964-8000 USA Email: taka@ldeo.columbia.edu (10) Woods Hole Oceanographic Institution, 266 Woods Hole Road, Woods Hole, MA 02543, USA Email: jyoder@whoi.edu (11) NOAA (National Oceanic and Atmospheric Administration)/AOML 4301 Rickenbacker Causeway Miami, FL 33149 Email: rik.wanninkhof@noaa.gov

Anthropogenic carbon accumulation in the subtropical North Atlantic

Abstract: [1] Recent data suggest the accumulation of anthropogenic carbon dioxide (ΔCanth) in the subtropical North Atlantic is not occurring at a steady rate throughout the water column. Carbon measurements from three transatlantic cruises along 24.5°N in 1992, 1998, and 2004 were investigated for changes in Canth using both a back-calculation shortcut technique and extended multiple linear regression. For three time periods (1992–1998, 1998–2004, and 1992–2004) we observed spatial and vertical changes in Canth storage, along with a general increase in total concentration. In the surface layers, total dissolved inorganic carbon (TCO2) and Canth concentrations increased in line with atmospheric CO2 levels: TCO2 +8.8 ± 0.5 μmol kg−1 for 1992–1998 and +8.6 ± 0.5 μmol kg−1 for 1998–2004 and Canth +8.0 ± 0.2 μmol kg−1 for 1992–1998 and +6.8 ± 0.3 μmol kg−1 for 1998–2004. In deeper waters, ΔCanth was significantly different than zero for all depths above 5000 dbar between 1992 and 2004, while on a subdecadal timescale, significant variability was observed for ΔCanth at a depth range of 800–1000 dbar. Evidence is presented for the arrival at 24.5°N at depth of freshly ventilated Labrador Sea Water from the subpolar North Atlantic between 1992 and 1998, as well as consistent smaller ΔCanth signals alongside the Mid-Atlantic Ridge. This is in addition to low-level, stable increases identified in the deep eastern basin between 1992 and 2004, the first time that ΔCanth has been detected and confirmed by new measurements of carbon tetrachloride and CFC-11 from 2004. These results highlight the importance of the subtropics as a site for long-term Canth storage away from the surface.

Rapid changes in surface water carbonate chemistry during Antarctic sea ice melt

Abstract: The effect of sea ice melt on the carbonate chemistry of surface waters in the Weddell–Scotia Confluence, Southern Ocean, was investigated during January 2008. Contrasting concentrations of dissolved inorganic carbon (DIC), total alkalinity (TA) and the fugacity of carbon dioxide ( f CO 2 ) were observed in and around the receding sea ice edge. The precipitation of carbonate minerals such as ikaite (CaCO 3 ·6H 2 O) in sea ice brine has the net effect of decreasing DIC and TA and increasing the f CO 2 in the brine. Deficits in DIC up to 12 ± 3 μmol kg -1 in the marginal ice zone (MIZ) were consistent with the release of DIC-poor brines to surface waters during sea ice melt. Biological utilization of carbon was the dominant processes and accounted for 41 ± 1 μmol kg -1 of the summer DIC deficit. The data suggest that the combined effects of biological carbon uptake and the precipitation of carbonates created substantial undersaturation in f CO 2 of 95 μatm in the MIZ during summer sea ice melt. Further work is required to improve the understanding of ikaite chemistry in Antarctic sea ice and its importance for the sea ice carbon pump. DOI: 10.1111/j.1600-0889.2010.00496.x

A multi-variable box model approach to the soft tissue carbon pump

Abstract: . The canonical question of which physical, chemical or biological mechanisms were responsible for oceanic uptake of atmospheric CO2 during the last glacial is yet unanswered. Insight from paleo-proxies has led to a multitude of hypotheses but none so far have been convincingly supported in three dimensional numerical modelling experiments. The processes that influence the CO2 uptake and export production are inter-related and too complex to solve conceptually while complex numerical models are time consuming and expensive to run which severely limits the combinations of mechanisms that can be explored. Instead, an intermediate inverse box model approach of the soft tissue pump is used here in which the whole parameter space is explored. The glacial circulation and biological production states are derived from these using proxies of glacial export production and the need to draw down CO2 into the ocean. We find that circulation patterns which explain glacial observations include reduced Antarctic Bottom Water formation and high latitude upwelling and mixing of deep water and to a lesser extent reduced equatorial upwelling. The proposed mechanism of CO2 uptake by an increase of eddies in the Southern Ocean, leading to a reduced residual circulation, is not supported. Regarding biological mechanisms, an increase in the nutrient utilization in either the equatorial regions or the northern polar latitudes can reduce atmospheric CO2 and satisfy proxies of glacial export production. Consistent with previous studies, CO2 is drawn down more easily through increased productivity in the Antarctic region than the sub-Antarctic, but that violates observations of lower export production there. The glacial states are more sensitive to changes in the circulation and less sensitive to changes in nutrient utilization rates than the interglacial states.

A comprehensive, multi-process box-model approach to glacial-interglacial carbon cycling

Abstract: The canonical question of which physical, chemical or biological mechanisms were responsible for oceanic uptake of atmospheric CO2 during the last glacial is yet unanswered. Insight from paleo proxies has led to a multitude of hypotheses but none so far have been convincingly supported in three dimensional numerical modelling experiments. The processes that influence the CO2 uptake and export production are inter-related and too complex to solve conceptually while complex numerical models are time consuming and expensive to run which severely limits the combinations of mechanisms that can be explored. Instead, an intermediate inverse box model approach is used here in which the whole parameter space is explored. The glacial circulation and biological production states are derived from these using proxies of glacial export production and the need to draw down CO2 into the ocean. We find that circulation patterns which explain glacial observations include reduced Antarctic Bottom Water formation and high latitude mixing and to a lesser extent reduced equatorial upwelling. The proposed mechanism of CO2 uptake by an increase of eddies in the Southern Ocean, leading to a reduced residual circulation, is not supported. Regarding biological mechanisms, an increase in the nutrient utilization in either the equatorial regions or the northern polar latitudes can reduce atmospheric CO2 and satisfy proxies of glacial export production. Consistent with previous studies, CO2 is drawn down more easily through increased productivity in the Antarctic region than the sub-Antarctic, but that violates observations of lower export production there.

Correction: Predicting Visibility of Aircraft

Abstract: There is an error in the authors' affiliation. The Affiliation should be: NASA Ames Research Center, Moffett Field, California, United States of America

Eliminating End Effects for Theoretical Panel Buckling with FEM

Abstract: VICONOPT assumes an infinitely long panel, and while FEM can be used to predict both buckling and postbuckling performance of finite sized panels. The authors were unable to find published instances of boundary condition calculations or a method that could be used to verify VICONOPT’s theoretical determinations with an infinite length panel that was able to predict all possible buckling modes; without additional invalid buckling modes. And they were unable to find a program that was able to predict mode jumping in the post-buckling range. This paper presents three FEM models for the finite element modelling of the buckling and post-buckling performance of infinite length thin walled stiffened panels; a single bay, a double half-bay and a quad half-bay model. The quad half bay model is shown to be the ideal model as all wavelengths of buckling are permitted and thus enables the calculation of buckling performance of theoretical panels accurately using FEM, and the accurate post-buckling and collapse performance, including mode jumping.