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Schulz H.,Holderlinstr. 12 | Luckge A.,Federal Institute for Geosciences and Natural Resources | Emeis K.-C.,Institute for Biogeochemistry and Marine Chemistry | Mackensen A.,Alfred Wegener Institute for Polar and Marine Research
Marine Geology

Large rivers on continental margins play an important role as interfaces between land and ocean sedimentation. In many cases the modes and history of sediment dispersal, and the final deposition of the impressive volumes of terrigenous matter in the deep ocean remain poorly constrained by detailed sedimentary observations. The Zambezi River, by far the largest river of southeast Africa, discharges into the narrow, funnel-shaped Mozambique Strait between Africa and Madagascar. Here, we study the distribution of lithic grain sizes and major bulk fractions of biogenic and abiogenic components in core tops and long sediment cores off the Zambezi River, spanning the past ~. 60,000. years of the central and northern Mozambique continental margin. Due to the particular current regime, the modern Mozambique margin shows distinct sedimentation patterns not seen off most rivers of comparable size. Deposition is largely free of hiatuses, with high accumulation rates of fine-grained material, and only minor signs of erosion or sediment winnowing. Zambezi riverine detritus dominates the sedimentary facies between 20°S and 17°S from below the shelf break down to 2000. m water depth. However, a considerable fraction at present high sea level is deposited not directly downstream the Zambezi River mouth, but is dispersed to the northeast by along-shore transport, opposite to the mean flow within the Mozambique Strait. As a consequence, downslope transport today is highly unfocused and a canyon system at the upper slope is only poorly developed. We suggest that most of the riverine matter leaves the continental shelf ~. 200. km to the northeast of the present river mouth. Sediments took a more direct, chanellized path during the last glacial period of lowered sea level, which was confirmed by the reconstruction of Holocene and Late Glacial sedimentation rates in the area. In this regard, the Zambezi River-Margin sedimentary system stands for a margin with considerable temporal and spatial variabilities in downslope deposition on glacial-to-interglacial timescales. © 2011 Elsevier B.V. Source

Valentini R.,University of Tuscia | Valentini R.,Euro Mediterranean Center on Climate Change | Arneth A.,Karlsruhe Institute of Technology | Bombelli A.,Euro Mediterranean Center on Climate Change | And 26 more authors.

This paper, developed under the framework of the RECCAP initiative, aims at providing improved estimates of the carbon and GHG (CO2, CH4 and N2O) balance of continental Africa. The various components and processes of the African carbon and GHG budget are considered, existing data reviewed, and new data from different methodologies (inventories, ecosystem flux measurements, models, and atmospheric inversions) presented. Uncertainties are quantified and current gaps and weaknesses in knowledge and monitoring systems described in order to guide future requirements. The majority of results agree that Africa is a small sink of carbon on an annual scale, with an average value of -0.61 ± 0.58 Pg C yr-1. Nevertheless, the emissions of CH4 and N2O may turn Africa into a net source of radiative forcing in CO2 equivalent terms. At sub-regional level, there is significant spatial variability in both sources and sinks, due to the diversity of biomes represented and differences in the degree of anthropic impacts. Southern Africa is the main source region; while central Africa, with its evergreen tropical forests, is the main sink. Emissions from land-use change in Africa are significant (around 0.32 ± 0.05 Pg C yr-1), even higher than the fossil fuel emissions: this is a unique feature among all the continents. There could be significant carbon losses from forest land even without deforestation, resulting from the impact of selective logging. Fires play a significant role in the African carbon cycle, with 1.03 ± 0.22 Pg C yr-1 of carbon emissions, and 90% originating in savannas and dry woodlands. A large portion of the wild fire emissions are compensated by CO2 uptake during the growing season, but an uncertain fraction of the emission from wood harvested for domestic use is not. Most of these fluxes have large interannual variability, on the order of ±0.5 Pg C yr-1 in standard deviation, accounting for around 25% of the year-to-year variation in the global carbon budget.

Despite the high uncertainty, the estimates provided in this paper show the important role that Africa plays in the global carbon cycle, both in terms of absolute contribution, and as a key source of interannual variability. © Author(s) 2014. CC Attribution 3.0 License. Source

Patra P.K.,Japan Agency for Marine - Earth Science and Technology | Canadell J.G.,CSIRO | Houghton R.A.,Woods Hole Oceanographic Institution | Piao S.L.,Peeking University | And 14 more authors.

The source and sinks of carbon dioxide (CO2) and methane (CH4) due to anthropogenic and natural biospheric activities were estimated for the South Asian region (Bangladesh, Bhutan, India, Nepal, Pakistan and Sri Lanka). Flux estimates were based on top-down methods that use inversions of atmospheric data, and bottom-up methods that use field observations, satellite data, and terrestrial ecosystem models. Based on atmospheric CO2 inversions, the net biospheric CO2 flux in South Asia (equivalent to the Net Biome Productivity, NBP) was a sink, estimated at -104 ± 150 Tg C yr−1 during 2007-2008. Based on the bottom-up approach, the net biospheric CO2 flux is estimated to be -191 ± 193 Tg C yr−1 during the period of 2000-2009. This last net flux results from the following flux components: (1) the Net Ecosystem Productivity, NEP (net primary production minus heterotrophic respiration) of -220 ± 186 Tg C yr−1 (2) the annual net carbon flux from land-use change of -14 ± 50 Tg C yr−1, which resulted from a sink of -16 Tg C yr−1 due to the establishment of tree plantations and wood harvest, and a source of 2 Tg C yr−1 due to the expansion of croplands; (3) the riverine export flux from terrestrial ecosystems to the coastal oceans of +42.9 Tg C yr−1; and (4) the net CO2 emission due to biomass burning of +44.1 ± 13.7 Tg C yr−1. Including the emissions from the combustion of fossil fuels of 444 Tg C yr−1 for the 2000s, we estimate a net CO2 land-atmosphere flux of 297 Tg C yr−1. In addition to CO2, a fraction of the sequestered carbon in terrestrial ecosystems is released to the atmosphere as CH4. Based on bottom-up and top-down estimates, and chemistry-transport modeling, we estimate that 37 ± 3.7 Tg C yr−1 were released to atmosphere from South Asia during the 2000s. Taking all CO2 and CH4 fluxes together, our best estimate of the net land-atmosphere CO2-equivalent flux is a net source of 334 Tg C yr−1 for the South Asian region during the 2000s. If CH4 emissions are weighted by radiative forcing of molecular CH4, the total CO2-equivalent flux increases to 1148 Tg C yr−1 suggesting there is great potential of reducing CH4 emissions for stabilizing greenhouse gases concentrations. © Author(s) 2013. Source

Regnier P.,Free University of Colombia | Friedlingstein P.,University of Exeter | Ciais P.,French Climate and Environment Sciences Laboratory | Mackenzie F.T.,University of Hawaii at Manoa | And 28 more authors.
Nature Geoscience

A substantial amount of the atmospheric carbon taken up on land through photosynthesis and chemical weathering is transported laterally along the aquatic continuum from upland terrestrial ecosystems to the ocean. So far, global carbon budget estimates have implicitly assumed that the transformation and lateral transport of carbon along this aquatic continuum has remained unchanged since pre-industrial times. A synthesis of published work reveals the magnitude of present-day lateral carbon fluxes from land to ocean, and the extent to which human activities have altered these fluxes. We show that anthropogenic perturbation may have increased the flux of carbon to inland waters by as much as 1.0 Pg C yr -1 since pre-industrial times, mainly owing to enhanced carbon export from soils. Most of this additional carbon input to upstream rivers is either emitted back to the atmosphere as carbon dioxide (∼0.4 Pg C yr -1) or sequestered in sediments (∼0.5 Pg C yr -1) along the continuum of freshwater bodies, estuaries and coastal waters, leaving only a perturbation carbon input of ∼0.1 Pg C yr -1 to the open ocean. According to our analysis, terrestrial ecosystems store ∼0.9 Pg C yr -1 at present, which is in agreement with results from forest inventories but significantly differs from the figure of 1.5 Pg C yr -1 previously estimated when ignoring changes in lateral carbon fluxes. We suggest that carbon fluxes along the land-ocean aquatic continuum need to be included in global carbon dioxide budgets. Source

Bahlmann E.,Institute for Biogeochemistry and Marine Chemistry | Weinberg I.,Institute for Biogeochemistry and Marine Chemistry | Seifert R.,Institute for Biogeochemistry and Marine Chemistry | Tubbesing C.,Institute for Biogeochemistry and Marine Chemistry | Michaelis W.,Institute for Biogeochemistry and Marine Chemistry
Atmospheric Measurement Techniques

The isotopic composition of volatile organic compounds (VOCs) can provide valuable information on their sources and fate not deducible from mixing ratios alone. In particular the reported carbon stable isotope ratios of chloromethane and bromomethane from different sources cover a δ 13C-range of almost 100‰ making isotope ratios a very promising tool for studying the biogeochemistry of these compounds. So far, the determination of the isotopic composition of C 1 and C 2 halocarbons others than chloromethane is hampered by their low mixing ratios. In order to determine the carbon isotopic composition of C 1 and C 2 halocarbons with mixing ratios as low as 1 pptv (i) a field suitable cryogenic high volume sampling system and (ii) a chromatographic set up for processing these samples have been developed and validated. The sampling system was tested at two different sampling sites, an urban and a coastal location in Northern Germany. The average δ 13C-values for bromomethane at the urban site were -42.9 ± 1.1‰ and agreed well with previously published results. But at the coastal site bromomethane was substantially enriched in 13C by almost 10‰. Less pronounced differences were observed for chlorodifluoromethane, 1,1,1-trichloroethane and chloromethane. We suggest that these differences are related to the turnover of these compounds in ocean surface waters. Furthermore we report first carbon isotope ratios for iodomethane (-40.4‰ to -79.8‰), bromoform (-13.8‰ to 22.9‰), and other halocarbons. © Author(s) 2011. Source

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