Publications

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2014
Thompson, RL, Patra PK, Ishijima K, Saikawa E, Corazza M, Karstens U, Wilson C, Bergamaschi P, Dlugokencky E, Sweeney C, Prinn RG, Weiss RF, O'Doherty S, Fraser PJ, Steele LP, Krummel PB, Saunois M, Chipperfield M, Bousquet P.  2014.  TransCom N2O model inter-comparison - Part 1: Assessing the influence of transport and surface fluxes on tropospheric N2O variability. Atmospheric Chemistry and Physics. 14:4349-4368.   10.5194/acp-14-4349-2014   AbstractWebsite

We present a comparison of chemistry-transport models (TransCom-N2O) to examine the importance of atmospheric transport and surface fluxes on the variability of N2O mixing ratios in the troposphere. Six different models and two model variants participated in the inter-comparison and simulations were made for the period 2006 to 2009. In addition to N2O, simulations of CFC-12 and SF6 were made by a subset of four of the models to provide information on the models' proficiency in stratosphere-troposphere exchange (STE) and meridional transport, respectively. The same prior emissions were used by all models to restrict differences among models to transport and chemistry alone. Four different N2O flux scenarios totalling between 14 and 17 TgN yr(-1) (for 2005) globally were also compared. The modelled N2O mixing ratios were assessed against observations from in situ stations, discrete air sampling networks and aircraft. All models adequately captured the large-scale patterns of N2O and the vertical gradient from the troposphere to the stratosphere and most models also adequately captured the N2O tropospheric growth rate. However, all models underestimated the inter-hemispheric N2O gradient by at least 0.33 parts per billion (ppb), equivalent to 1.5 TgN, which, even after accounting for an overestimate of emissions in the Southern Ocean of circa 1.0 TgN, points to a likely underestimate of the Northern Hemisphere source by up to 0.5 TgN and/or an overestimate of STE in the Northern Hemisphere. Comparison with aircraft data reveal that the models over-estimate the amplitude of the N2O seasonal cycle at Hawaii (21 degrees N, 158 degrees W) below circa 6000 m, suggesting an overestimate of the importance of stratosphere to troposphere transport in the lower troposphere at this latitude. In the Northern Hemisphere, most of the models that provided CFC-12 simulations captured the phase of the CFC-12, seasonal cycle, indicating a reasonable representation of the timing of STE. However, for N2O all models simulated a too early minimum by 2 to 3 months owing to errors in the seasonal cycle in the prior soil emissions, which was not adequately represented by the terrestrial biosphere model. In the Southern Hemisphere, most models failed to capture the N2O and CFC-12 seasonality at Cape Grim, Tasmania, and all failed at the South Pole, whereas for SF6, all models could capture the seasonality at all sites, suggesting that there are large errors in modelled vertical transport in high southern latitudes.

2001
Alexander, B, Vollmer MK, Jackson T, Weiss RF, Thiemens MH.  2001.  Stratospheric CO2 isotopic anomalies and SF6 and CFC tracer concentrations in the Arctic polar vortex. Geophysical Research Letters. 28:4103-4106.   10.1029/2001gl013692   AbstractWebsite

Isotopic measurements (delta O-17 and delta O-18) Of CO2 along with concentration measurements of SF6, CC1(3)F (CFC-11), CC1(2)F(2) (CFC-12) and CC1(2)FCC1F(2) (CFC-113) in stratospheric samples collected within the Arctic polar vortex are reported. These are the first simultaneous measurements of the concentration of fluorinated compounds and the complete oxygen isotopic composition Of CO2 in the middle atmosphere. A mass-independent anomaly in the oxygen isotopic composition Of CO2 is observed that arises from isotopic exchange with stratospheric O(D-1) derived from O-3 photolysis. The data exhibit a strong anti-correlation between the Delta O-17 (the degree of the mass-independent anomaly) and molecular tracer concentrations. The potential ability of tl-ris isotopic proxy to trace mesospheric and stratospheric transport is discussed.

1998
Murphy, PP, Harrison DE, Feely RA, Takahashi T, Weiss RF, Gammon RH.  1998.  Variability of Δ pCO2 in the subarctic North Pacific. A comparison of results from four expeditions. Tellus Series B-Chemical and Physical Meteorology. 50:185-204.   10.1034/j.1600-0889.1998.t01-1-00006.x   AbstractWebsite

Time-space variability of surface seawater pCO(2) is examined over the region (150 degrees W-180 degrees, 46 degrees N-50 degrees N) of the subarctic North Pacific where large meridional gradients of temperature and nutrient concentrations exist. The data were collected during four trans-Pacific expeditions in three different years (1985-1987), but within the same 30-day period of the year (August-September). Systematic measurement differences between the four data sets are estimated as <10 mu atm. The inter-expedition comparison suggests that surface seawater pCO(2) in the study area is quite variable, with mean differences of up to 25 mu atm and local differences up to 60 mu atm. Spatial and interannual variability of surface seawater pCO(2) were found to contribute significant uncertainty to estimates of the mean Delta pCO(2) for the study area. Fluxes were calculated using Delta pCO(2) values from the four expeditions combined with gas exchange coefficients calculated from four different wind fields giving a range of -0.94 to +4.1 mmol CO2 m(-2) d(-1). The range of fluxes from the study area is scaled to a larger area of the North Pacific to address how this variability can translate into uncertainties in basin-wide carbon air-sea exchange fluxes.

1997
Takahashi, T, Feely RA, Weiss RF, Wanninkhof RH, Chipman DW, Sutherland SC, Takahashi TT.  1997.  Global air-sea flux of CO2: An estimate based on measurements of sea-air pCO2 difference. Proceedings of the National Academy of Sciences of the United States of America. 94:8292-8299.   10.1073/pnas.94.16.8292   AbstractWebsite

Approximately 250,000 measurements made for the pCO(2) difference between surface water and the marine atmosphere, Delta pCO(2), have been assembled for the global oceans. Observations made in the equatorial Pacific during El Nine events have been excluded from the data set, These observations are mapped on the global 4 degrees x 5 degrees grid for a single virtual calendar year (chosen arbitrarily to be 1990) representing a non-El Nino year. Monthly global distributions of Delta pCO(2) have been constructed using an interpolation method based on a lateral advection-diffusion transport equation. The net flux of CO2 across the sea surface has been computed using Delta pCO(2) distributions and CO2 gas transfer coefficients across sea surface. The annual net uptake flux of CO2 by the global oceans thus estimated ranges from 0.60 to 1.34 Gt-C.yr(-1) depending on different formulations used for wind speed dependence on the gas transfer coefficient, These estimates;Ire subject to an error of up to 75% resulting from the numerical interpolation method used to estimate the distribution of Delta pCO(2) over the global oceans, Temperate and polar oceans of the both hemispheres are the major sinks for atmospheric CO2, whereas the equatorial oceans are the major sources for CO2. The Atlantic Ocean is the most important CO2 sink, providing about 60% of the global ocean uptake, while the Pacific Ocean is neutral because of its equatorial source flux being balanced by the sink flux of the temperate oceans, The Indian and Southern Oceans take up about 20% each.

1996
Landrum, LL, Gammon RH, Feely RA, Murphy PP, Kelly KC, Cosca CE, Weiss RF.  1996.  North Pacific Ocean CO2 disequilibrium for spring through summer, 1985-1989. Journal of Geophysical Research-Oceans. 101:28539-28555.   10.1029/96jc02100   AbstractWebsite

Extensive measurements of CO2 fugacity in the North Pacific surface ocean and overlying atmosphere during the years 1985-1989 are synthesized and interpreted to yield a basin-wide estimate of Delta fCO(2). The observations, taken from February through early September, suggest that the subtropical and subarctic North Pacific is a small sink for atmospheric CO2 (0.07 to 0.2 Gton C (half year)(-1) for the region north of 15 degrees N). Objective analysis techniques are used to estimate uncertainty fields resulting from constructing basin-wide contours of oceanic fCO(2) on the basis of individual cruise transects. The uncertainties are significant and imply that future sampling programs need to recognize that estimating oceanic uptake of anthropogenic CO2 from ship-transect observations of oceanic fCO(2) alone will require very extensive sampling.