A comprehensive estimate of recent carbon sinks in China using both top-down and bottom-up approaches

Atmospheric inversions use measurements of atmospheric CO2 gradients to constrain regional surface fluxes. Current inversions indicate a net terrestrial CO2 sink in China between 0.16 and 0.35 PgC/yr. The uncertainty of these estimates is as large as the mean because the atmospheric network historically contained only one high altitude station in China. Here, we revisit the calculation of the terrestrial CO2 flux in China, excluding emissions from fossil fuel burning and cement production, by using two inversions with three new CO2 monitoring stations in China as well as aircraft observations over Asia. We estimate a net terrestrial CO2 uptake of 0.39-0.51 PgC/yr with a mean of 0.45 PgC/yr in 2006-2009. After considering the lateral transport of carbon in air and water and international trade, the annual mean carbon sink is adjusted to 0.35 PgC/yr. To evaluate this top-down estimate, we constructed an independent bottom-up estimate based on ecosystem data, and giving a net land sink of 0.33 PgC/yr. This demonstrates closure between the top-down and bottom-up estimates. Both top-down and bottom-up estimates give a higher carbon sink than previous estimates made for the 1980s and 1990s, suggesting a trend towards increased uptake by land ecosystems in China.</p

Bias corrections of GOSAT SWIR XCO₂ and XCH₄ with TCCON data and their evaluation using aircraft measurement data

We describe a method for removing systematic biases of column-averaged dry air mole fractions of CO2 (XCO2) and CH4 (XCH4) derived from short-wavelength infrared (SWIR) spectra of the Greenhouse gases Observing SATellite (GOSAT). We conduct correlation analyses between the GOSAT biases and simultaneously retrieved auxiliary parameters. We use these correlations to bias correct the GOSAT data, removing these spurious correlations. Data from the Total Carbon Column Observing Network (TCCON) were used as reference values for this regression analysis. To evaluate the effectiveness of this correction method, the tnzuncorrected/corrected GOSAT data were compared to independent XCO2 and XCH4 data derived from aircraft measurements taken for the Comprehensive Observation Network for TRace gases by AIrLiner (CONTRAIL) project, the National Oceanic and Atmospheric Administration (NOAA), the US Department of Energy (DOE), the National Institute for Environmental Studies (NIES), the Japan Meteorological Agency (JMA), the HIAPER Pole-to-Pole observations (HIPPO) program, and the GOSAT validation aircraft observation campaign over Japan. These comparisons demonstrate that the empirically derived bias correction improves the agreement between GOSAT XCO2/XCH4 and the aircraft data. Finally, we present spatial distributions and temporal variations of the derived GOSAT biases

Source of organic matter in the sinking particles collected from the Pacific Sector of the Antarctic Ocean by sediment trap experiment

Sediment trap experiment was conducted at Stn. 3 (61°34.1′S, 150°23.3′E) in the Pacific Sector of the Antarctic Ocean for 23 days from December 20,1983 to January 13,1984. Sinking particles from 630,1430 and 3230m depths, suspended particles from 1,30,80 and 500m depths and bottom sediment were analyzed for hydrocarbons, which consisted of n-alkanes with the carbon atoms ranging from 14 to 32 (n-alkane, n-C_-C_), heneicosahexaene (n-C_), isoprenoid hydrocarbons and branched C_ and cyclic C_ alkenes (br-C_ and c-C_). Hydrocarbons were quantified by gas chromatography and identified and/or elucidated by combined gas chromatography and mass spectrometry. Isoprenoid hydrocarbons consisted of squalene, pristane and phytane, while branched C_ and C_ alkenes were composed of br-C_, br-C_, br-C_ (isomer of br-C_), c-C_ and c-C_. Hydrocarbon composition was characteristic to each of the particle and sediment samples. Thus, the hydrocarbon composition gives us a clue to clarify the source of organic matter in the sinking particles collected from the intermediate and deep waters. Heneicosahexaene widely occurring in diatoms and coccolithophores, was found in the suspended and sinking particles, indicating that organic matter in the sinking particles was derived from diatoms and/or coccolithophores living in the surface waters. br-C_ and C_ alkenes commonly found in the fecal pellets, were abundant in the sinking particles collected from the intermediate through deep waters. Thus, these findings indicate that large part of the organic materials in the sinking particles are derived from phytoplankton growing in the surface waters through fecal pellets of zooplankton. Occurrence of br-C_ and C_ alkenes even in the suspended particles of the euphotic layers indicates that these particles are contaminated by zooplankton fecal pellets and/or their debris. Further discussions will be conducted on the source materials of the sinking particles on the basis of the hydrocarbon compositions of the suspended and sinking particles

Distribution of the partial pressure of CO2 in surface water (pCO2w) between Japan and the Hawaiian Islands: pCO2wSST relationship in the winter and summer

On the basis of measurements of the partial pressure of carbon dioxide in surface seawater (pCO2w) between Japan and the Hawaiian Islands in winter and summer, we examined the relationship between the pCO2w and the sea surface temperature (SST) in the North Pacific Subtropical Gyre (NPSG). In winter, the pCO2w correlated well with the SST (0.14-0.24 %°C-1), suggesting a monotonous change in the carbonate system. However, in summer, five different pCO2w-SST relationships were found in the NPSG including the Kuroshio Extension due to changes in the relative contribution of ocean dynamics (upwelling, vertical mixing, and advection), the biological activity under the absence (very low level) of macro-nutrients, and thermodynamics. The increase in the pCO2w against the unit increase in the SST from January to July was low (<2.5%°C-1) west (leeward side) of the Hawaiian Islands (19-22˚N, 158-168˚W) and in the Kuroshio Extension (33-35ºN, 140-165ºE), and high (~3%°C-1) south of the Kuroshio Extension (25-30°N, 180-165°W) and the Hawaiian Islands (15-19°N, 157-162˚W). This suggested that the drawdown of dissolved inorganic carbon was affected by the enhanced biological activity due to upwelling events associated with eddies and/or the transport of dissolved nutrients from gyre edges to the interior

Relative contribution of transport/surface flux to the seasonal vertical synoptic CO2 variability in the troposphere over Narita

Frequent CO2 measurements obtained by commercial aircraft provide a unique, quasi-continuous record of free-tropospheric CO2 variability. Vertically-resolved synoptic-scale fluctuations of CO2 over Narita International Airport (lat 35.8&#x00B0;N, 140.4&#x00B0;E, 43&#x2009;m above sea-level) were investigated from November 2005 to March 2009, and combined with analyses of results from a transport model simulation for the year 2007 to retrieve information on sources contributing to the observed variability. The synoptic-scale variability of the observed CO2 mixing ratio, represented by the standard deviation (SD) from the fitted curves, increased in the upper troposphere in the spring, with a noticeable increase at all altitudes in the summer. This seasonal/altitudinal change of the observed SD was shown to be statistically significant throughout the observation period, and the model result agreed with the observation except for the underestimation of the summertime SD. Tagged simulations were conducted to evaluate the relative contribution of the regional fluxes to the synoptic-scale variability over Narita. The results indicate that the major contribution to the free troposphere (FT) variability was made by the fluxes in East Asia, while the Japanese fluxes contributed mostly to the variability in the planetary boundary layer (PBL). A sensitivity analysis was performed to evaluate the relative influence of transport and of flux magnitude on the CO2 SD over Narita for 2007. It was found that a change in the surface flux magnitude could affect the altitudinal distribution of the annual SD over Narita as follows: 41 and 3% at 9&#x2009;km, 61 and 4% at 5&#x2009;km, 19 and 83% at 0.5&#x2009;km when the fossil fuel flux from East Asia and Japan was doubled, respectively. These results are qualitative in nature (since SD is a non-linear function of concentration and flux), but do indicate that the CO2 SD over Narita is more sensitive to the fluctuation in the atmospheric transport (synoptic-scale meteorological variability) in the FT, while showing much more sensitivity to the magnitude of local fluxes in the PBL. The results also point to the fact that vertical profiles of atmospheric CO2 variability at the synoptic scale could potentially provide a useful additional constraint in the inversion analysis of regional CO2 fluxes