Antony Gomez - Academia.edu (original) (raw)

Papers by Antony Gomez

Global Biogeochemical Cycles, 2001

We use the TM2 three-dimensional atmospheric tracer model with a methane source-sink budget based... more We use the TM2 three-dimensional atmospheric tracer model with a methane source-sink budget based on existing literature to simulate small spatial and temporal variations in the 13C/12C ratio of atmospheric methane. The results show that delta13C varies markedly with wind direction everywhere outside the extratropical Southern Hemisphere (ETSH). Within the ETSH, both methane mixing ratio and delta13C have regular seasonal cycles with differing and latitude-dependent phases. Phase diagrams constructed from these seasonal cycles, showing changes in delta13C versus changes in mixing ratio, have elliptical shapes. The slope of the major axis of these ellipses is determined by the kinetic isotope effect (KIE) of the single atmospheric methane removal process used in the model. The ellipse eccentricity is determined by seasonal variation in the source delta13CH4, which is dominated by the biomass burning source because of its isotopic enrichment relative to other sources. Comparison of the model results, for a KIE based on CH4+OH oxidation, with observations in the South Pacific region shows significant discrepancies in both the ellipse major axis slopes and eccentricities. We suggest that this is an indicator of an additional sink process that discriminates strongly against 13CH4. Such a sink could be active chlorine in the marine boundary layer.

The authors present and review the evidence for the declining growth rate in atmospheric methane ... more The authors present and review the evidence for the declining growth rate in atmospheric methane (CH{sub 4}) since ca 1992. The NOAA/CMDL records of methane concentration from a network of 28 sites implicate source reductions in the northern hemisphere, though an increase in the methane consumption rate cannot be ruled out. The New Zealand (NZ) NIWA laboratory has maintained since 1989 complementary concentration records at the NZ clean air site at Baring Head (41 S) and at Scott Base, Antarctica (78 S). These records show nearly identical features, and confirm a reduction in growth rate since early 1992, falling to less than 2 ppbv/yr in early 1994. In addition to the methane concentration record, the NIWA laboratory maintains a companion high precision time series of methane`s {sup 13}C/{sup 12}C isotope ratio. This broadens considerably the scope for identifying the origins of the reduction in methane growth rate. The main features of the isotope data are as follows. The isotope ...

IPCC AR4 multi-model ensemble maximum southern hemisphere wind stress

A wavelength-scanned cavity ring-down spectrometer (CRDS, available from PICARRO, Inc., Santa Cla... more A wavelength-scanned cavity ring-down spectrometer (CRDS, available from PICARRO, Inc., Santa Clara, CA) is a rapidly spreading observation instrument which can detect atmospheric CO2, CH4, and H2O simultaneously based on the principle of laser absorption technique (Crosson, 2008). Chen et al. (2010) made airborne observations of CO2 and CH4 over the Amazonian rain forest using a CRDS and evaluated its performance for CO2 measurement in comparison to NDIR. These investigators reported that CO2 mixing ratios from both CRDS and NDIR instruments showed good agreement, except that the CRDS measurements were affected by the variations in inert gaseous species (N2, O2, and Ar) due to pressure broadening effects on absorption spectrum of CO2 and CH4. However, the magnitudes of the pressure broadening effects were not tested. In this work we have evaluated the pressure broadening effects through laboratory experiments. Figure 1 shows pressure broadening effects of the inert gases on the mea...

Journal of Geophysical Research, 2010

This paper documents a global Bayesian variational inversion of CO 2 surface fluxes during the pe... more This paper documents a global Bayesian variational inversion of CO 2 surface fluxes during the period 1988-2008. Weekly fluxes are estimated on a 3.75°× 2.5°(longitudelatitude) grid throughout the 21 years. The assimilated observations include 128 station records from three large data sets of surface CO 2 mixing ratio measurements. A Monte Carlo approach rigorously quantifies the theoretical uncertainty of the inverted fluxes at various space and time scales, which is particularly important for proper interpretation of the inverted fluxes. Fluxes are evaluated indirectly against two independent CO 2 vertical profile data sets constructed from aircraft measurements in the boundary layer and in the free troposphere. The skill of the inversion is evaluated by the improvement brought over a simple benchmark flux estimation based on the observed atmospheric growth rate. Our error analysis indicates that the carbon budget from the inversion should be more accurate than the a priori carbon budget by 20% to 60% for terrestrial fluxes aggregated at the scale of subcontinental regions in the Northern Hemisphere and over a year, but the inversion cannot clearly distinguish between the regional carbon budgets within a continent. On the basis of the independent observations, the inversion is seen to improve the fluxes compared to the benchmark: the atmospheric simulation of CO 2 with the Bayesian inversion method is better by about 1 ppm than the benchmark in the free troposphere, despite possible systematic transport errors. The inversion achieves this improvement by changing the regional fluxes over land at the seasonal and at the interannual time scales.

Measurements of the mixing ratio and δ13C in methane (δ13CH4) are reported from large, clean air ... more Measurements of the mixing ratio and δ13C in methane (δ13CH4) are reported from large, clean air samples collected every 2.5° to 5° of latitude on four voyages across the Pacific between New Zealand and the West Coast of the United States in 1996 and 1997. The data show that the interhemispheric gradient for δ13CH4 was highly dependent on season and varied from 0.5‰ in November 1996 with an estimated annual mean of 0.2–0.3‰. The seasonal cycles in δ13CH4 reveal three distinct latitude bands differentiated by phase. Maxima occur in January-February for the extratropical Southern Hemisphere, in September-October for the tropics, and in June-July for the extratropical Northern Hemisphere. The data are compared with results from a three-dimensional transport and atmospheric chemistry model that simulates the observed latitudinal structure of either δ13CH4 or the methane mixing ratio well, but not both simultaneously. The requirement that a methane source-sink budget be consistent with b...

PLoS ONE, 2011

Ocean acidification is a well recognised threat to marine ecosystems. High latitude regions are p... more Ocean acidification is a well recognised threat to marine ecosystems. High latitude regions are predicted to be particularly affected due to cold waters and naturally low carbonate saturation levels. This is of concern for organisms utilising calcium carbonate (CaCO 3 ) to generate shells or skeletons. Studies of potential effects of future levels of pCO 2 on high latitude calcifiers are at present limited, and there is little understanding of their potential to acclimate to these changes. We describe a laboratory experiment to compare physiological and metabolic responses of a key benthic bivalve, Laternula elliptica, at pCO 2 levels of their natural environment (430 matm, pH 7.99; based on field measurements) with those predicted for 2100 (735 matm, pH 7.78) and glacial levels (187 matm, pH 8.32). Adult L. elliptica basal metabolism (oxygen consumption rates) and heat shock protein HSP70 gene expression levels increased in response both to lowering and elevation of pH. Expression of chitin synthase (CHS), a key enzyme involved in synthesis of bivalve shells, was significantly up-regulated in individuals at pH 7.78, indicating L. elliptica were working harder to calcify in seawater undersaturated in aragonite (V Ar = 0.71), the CaCO 3 polymorph of which their shells are comprised. The different response variables were influenced by pH in differing ways, highlighting the importance of assessing a variety of factors to determine the likely impact of pH change. In combination, the results indicate a negative effect of ocean acidification on whole-organism functioning of L. elliptica over relatively short terms (weeks-months) that may be energetically difficult to maintain over longer time periods. Importantly, however, the observed changes in L. elliptica CHS gene expression provides evidence for biological control over the shell formation process, which may enable some degree of adaptation or acclimation to future ocean acidification scenarios.

Journal of Geophysical Research, 2005

1] We present methane mixing ratio and d 13 C time series measured at Baring Head, New Zealand, a... more 1] We present methane mixing ratio and d 13 C time series measured at Baring Head, New Zealand, and Scott Base, Antarctica, over the years 1991-2003. These data demonstrate that the apparent kinetic isotope effect (KIE) of the methane atmospheric sink (derived from the amplitudes of the mixing ratio and d 13 C seasonal cycles) is generally much larger than would be expected if the sink were the hydroxyl radical alone and has changed significantly during the observation period on a timescale of 3years.WeshowusingaglobaltransportmodelthatthistechniqueforderivingtheKIEshouldbequiteaccurateforasingleatmosphericsinkandthatthechangewithtimeisunlikelytoarisefromElNino−SouthernOscillationtransporteffects.Weinferthatasinkinadditiontohydroxylisrequired.Astrongcandidateforthisextrasinkisatomicchlorineinthemarineboundarylayer(MBL).WederivetheamplitudeofthechlorineconcentrationseasonalcyclethatwouldfullyaccountfortheapparentKIE.Thisamplituderangesfrom3 years. We show using a global transport model that this technique for deriving the KIE should be quite accurate for a single atmospheric sink and that the change with time is unlikely to arise from El Niño-Southern Oscillation transport effects. We infer that a sink in addition to hydroxyl is required. A strong candidate for this extra sink is atomic chlorine in the marine boundary layer (MBL). We derive the amplitude of the chlorine concentration seasonal cycle that would fully account for the apparent KIE. This amplitude ranges from 3years.WeshowusingaglobaltransportmodelthatthistechniqueforderivingtheKIEshouldbequiteaccurateforasingleatmosphericsinkandthatthechangewithtimeisunlikelytoarisefromElNino−SouthernOscillationtransporteffects.Weinferthatasinkinadditiontohydroxylisrequired.Astrongcandidateforthisextrasinkisatomicchlorineinthemarineboundarylayer(MBL).WederivetheamplitudeofthechlorineconcentrationseasonalcyclethatwouldfullyaccountfortheapparentKIE.Thisamplituderangesfrom10 4 atom cm À3 in 1994-1996 to about 3 Â 10 3 atom cm À3 in 1998-2000. If the KIE is enhanced throughout the free troposphere, the seasonal mean concentrations of atomic chlorine required in the MBL would be about 3 Â 10 4 atom (2005), Interannual variation of 13 C in tropospheric methane: Implications for a possible atomic chlorine sink in the marine boundary layer,

Journal of Geophysical Research, 1994

Measurements of •3C in atmospheric methane made at Baring Head, New Zealand (41 øS), over the 4-y... more Measurements of •3C in atmospheric methane made at Baring Head, New Zealand (41 øS), over the 4-year period, 1989-1993, display a persistent but highly variable seasonal cycle. Values for •j•3C peak in summer at about -46.9%o and drop to around -47.5%o in the late winter. Methane concentration shows a similar cycle, with winter peaks and summer minima. Similar features are observed at the New Zealand Antarctic station, Scott Base, at 78øS. While the phase of the •jl3C cycle is consistent with a kinetic isotope effect that preferentially leaves methane enriched in •3C in the atmosphere after burden of methane has been attributed to growth in various agricultural and industrial sources [Ehhalt and Schmidt, 1978]. Recent reviews of budgets estimating methane source strengths have been published by Khalil and Rasmussen [1990] and by Lassey et al. [1992]. Isotopic determinations of methane in the atmosphere in conjunction with concentration measurements provide important constraints on estimates of the sources and sinks of the gas. For example, •4C determinations provide information on the role of fossil methane sources to the atmosphere [Lowe et at., 1988; Wahten et at., 1989; Manning et at., 1990; Quay et at., 1991], because such sources from coal mines and gas wells are devoid of •4C. Also, because biogenic methanogenesis under anaerobic conditions produces methane depleted in •3C, this isotope has been used to trace such sources [Tyler, 1989; Quay et at., 1991 ].

Journal of Geophysical Research, 1999

Measurefronts of the mixing ratio and õ•3C in methane (õ•3CHn) are reported from large, clean air... more Measurefronts of the mixing ratio and õ•3C in methane (õ•3CHn) are reported from large, clean air samples collected every 2.50 to 5 ø of latitude on four voyages across the Pacific between New Zealand and the West Coast of the United States in 1996 and 1997. The data

Chemosphere, 1993

We report data from the clean air monitoring station at Baring Head, New Zealand on concentration... more We report data from the clean air monitoring station at Baring Head, New Zealand on concentrations of atmospheric methane and its 13C/~2C and ~4C/12C ratios. The record for methane concentration features a recent (post-July 1991) and persistent elevation above expected levels. The 2-year 8~3C record shows a surprisingly large seasonal cycle (ca 0.3%o peak to peak) about a mean value of -47.14 + 0.03%o (2 standard deviations) with no discernible trend. The ~4C/'2C record is relatively featureless, corresponding to 119.7+0.7 percent modern carbon (pMC) in January 1990 with a small upward trend of 1.3 + 0.8 pMC/yr over the past three years. A simple model depicting the southern hemisphere atmosphere as a single methane reservoir with seasonally-modulated sources and sinks is used to examine methane dynamics in this hemisphere. According to this model, approximately half the methane in the southern hemisphere atmosphere is delivered from the northern hemisphere. The model can interpret the 8~3C seasonal cycle only as a large injection of isotopically heavy methane during the austral spring, such as might result from biomass burning.

Biogeochemistry, 2011

Measurements of near-sea-level tropospheric D 14

International Journal for Population Data Science

ABSTRACTObjectivesStatistics New Zealand’s Integrated Data Infrastructure (IDI) combines informat... more ABSTRACTObjectivesStatistics New Zealand’s Integrated Data Infrastructure (IDI) combines information from a range of government agencies (such as tax, health and education data) in order to provide the insights government needs to improve social and economic outcomes for New Zealanders. New Zealand has no national population register or unique identifier used in common across these multiple data sources, and probabilistic linkages are a feature of the IDI. A challenge for researchers is to understand the impact of linkage errors and coverage issues present in the linked data, and to develop the rules necessary to define their target population. We outline the statistical infrastructure Statistics New Zealand is developing to help researchers navigate these issues. ApproachA method has been developed to identify NZ residents at a given time from the much larger number of individuals present in the IDI. Census data linked to the IDI offers insight into the coverage of key population g...