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  • Articles  (8)
  • Other Sources
  • Wiley  (8)
  • American Chemical Society
  • American Institute of Physics (AIP)
  • American Physical Society
  • National Academy of Sciences
  • Springer Nature
  • 2015-2019  (8)
  • 1985-1989
  • Global Biogeochemical Cycles  (8)
  • 7532
  • 1
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    Amazon forest response to repeated droughts (2016)
    T.R. Feldpausch, O.L. Phillips, R.J.W. Brienen, E. Gloor, J. Lloyd, G. Lopez-Gonzalez, A. Monteagudo-Mendoza, Y. Malhi, A. Alarcón, E. Álvarez Dávila, P. Alvarez-Loayza, A. Andrade, L.E.O.C. Aragao, L. Arroyo, G.A. Aymard C., T.R. Baker, C. Baraloto, J. Barroso, D. Bonal, W. Castro, V. Chama, J. Chave, T.F. Domingues, S. Fauset, N. Groot, E. Honorio C., S. Laurance, W.F. Laurance, S.L. Lewis, J.C. Licona, B.S. Marimon, B.H. Marimon-Junior, C. Mendoza Bautista, D.A. Neill, E.A. Oliveira, C. Oliveira dos Santos, N.C. Pallqui Camacho, G. Pardo-Molina, A. Prieto, C.A. Quesada, F. Ramírez, H. Ramírez-Angulo, M. Réjou-Méchain, A. Rudas, G. Saiz, R.P. Salomão, J.E. Silva-Espejo, M. Silveira, H. Steege, J. Stropp, J. Terborgh, R. Thomas-Caesar, G.M.F. Heijden, R. Vásquez Martinez, E. Vilanova, V.A. Vos
    Wiley
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    Publication Date: 2016-05-01
    Description: The Amazon Basin has experienced more variable climate over the last decade, with a severe and widespread drought in 2005 causing large basin-wide losses of biomass. A drought of similar climatological magnitude occurred again in 2010; however, there has been no basin-wide ground-based evaluation of effects on vegetation. We examine to what extent the 2010 drought affected forest dynamics using ground-based observations of mortality and growth utilizing data from an extensive forest plot network. We find that during the 2010 drought interval, forests did not gain biomass (net change: −0.43 Mg ha -1 , CI: −1.11, 0.19, n = 97), regardless of whether forests experienced precipitation deficit anomalies. This loss contrasted with a long-term biomass sink during the baseline pre-2010 drought period (1998 − pre-2010) of 1.33 Mg ha -1 yr -1 (CI: 0.90, 1.74, p  〈 0.01). The resulting net impact of the 2010 drought (i.e., reversal of the baseline net sink) was −1.95 Mg ha -1 yr -1 (CI:−2.77, −1.18; p  〈 0.001). This net biomass impact was driven by an increase in biomass mortality (1.45 Mg ha -1 yr -1 CI: 0.66, 2.25, p  〈 0.001), and a decline in biomass productivity (−0.50 Mg ha -1 yr -1 , CI:−0.78, −0.31; p  〈 0.001). Surprisingly, the magnitude of the losses through tree mortality was unrelated to estimated local precipitation anomalies, and was independent of estimated local pre-2010 drought history. Thus, there was no evidence that pre-2010 droughts compounded the effects of the 2010 drought. We detected a systematic basin-wide impact of drought on tree growth rates across Amazonia, with this suppression of productivity driven by moisture deficits in 2010, an impact which was not apparent during the 2005 event [ Phillips et al. , 2009]. Based on these ground data, both live biomass in trees and corresponding estimates of live biomass in roots, we estimate that intact forests in Amazonia were carbon neutral in 2010 (−0.07 PgC yr -1 CI:−0.42, 0.23), consistent with results from an independent analysis of airborne estimates of land-atmospheric fluxes during 2010 [ Gatti et al. , 2014]. Relative to the long-term mean, the 2010 drought resulted in a reduction in biomass carbon uptake of 1.1 PgC, compared to 1.6 PgC for the 2005 event [ Phillips et al . 2009].
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    Electronic ISSN: 1944-9224
    Topics: Biology , Chemistry and Pharmacology , Geography , Geosciences , Physics
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  • 2
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    Global oceanic emission of ammonia: constraints from seawater and atmospheric observations (2015)
    Wiley
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    Publication Date: 2015-07-19
    Description: Current global inventories of ammonia emissions identify the ocean as the largest natural source. This source depends on seawater pH, temperature, and the concentration of total seawater ammonia ( NH x ( sw )), which reflects a balance between remineralization of organic matter, uptake by plankton, and nitrification. Here, we compare [ NH x ( sw )] from two global ocean biogeochemical models (BEC and COBALT) against extensive ocean observations. Simulated [ NH x ( sw )] are generally biased high. Improved simulation can be achieved in COBALT by increasing the plankton affinity for NH x within observed ranges. The resulting global ocean emissions is 2.5 TgN a −1 , much lower than current literature values(7–23 TgN a −1 ), including the widely used GEIA inventory (8 TgN a −1 ). Such a weak ocean source implies that continental sources contribute more than half of atmospheric NH x over most of the ocean in the Northern hemisphere. Ammonia emitted from oceanic sources is insufficient to neutralize sulfate aerosol acidity, consistent with observations. There is evidence over the Equatorial Pacific for a missing source of atmospheric ammonia that could be due to photolysis of marine organic nitrogen at the ocean surface or in the atmosphere. Accommodating this possible missing source yields a global ocean emission of ammonia in the range 2–5 TgN a −1 , comparable in magnitude to other natural sources from open fires and soils.
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    Topics: Biology , Chemistry and Pharmacology , Geography , Geosciences , Physics
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  • 3
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    Partitioning N2O Emissions within the US Corn Belt using an Inverse Modeling Approach (2016)
    Wiley
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    Publication Date: 2016-08-09
    Description: Nitrous oxide (N 2 O) emissions within the US Corn Belt have been previously estimated to be 200-900% larger than predictions from emission inventories, implying that one or more source categories in bottom-up approaches are underestimated. Here we interpret hourly N 2 O concentrations measured during 2010 and 2011 at a tall tower using a time-inverted transport model and a scale factor Bayesian inverse method to simultaneously constrain direct and indirect agricultural emissions. The optimization revealed that both agricultural source categories were underestimated by the Intergovernmental Panel on Climate Change (IPCC) inventory approach. However, the magnitude of the discrepancies differed substantially, ranging from 42–58% and 200–525% for direct and indirect components, respectively. Optimized agricultural N 2 O budgets for the Corn Belt were 319 ± 184 (total), 188 ± 66 (direct), and 131 ± 118 Gg-N yr -1 (indirect) in 2010, versus 471 ± 326, 198 ± 80, and 273 ± 246 Gg-N yr -1 in 2011. We attribute the inter-annual differences to varying moisture conditions, with increased precipitation in 2011 amplifying emissions. We found that indirect emissions represented 41–58% of the total agricultural budget, a considerably larger portion than the 25–30% predicted in bottom-up inventories, further highlighting the need for improved constraints on this source category. These findings further support the hypothesis that indirect emissions are presently underestimated in bottom-up inventories. Based on our results, we suggest an indirect emission factor for runoff and leaching ranging from 0.014–0.035 for the Corn Belt, which represents an upward adjustment of 1.9–4.6 times relative to the IPCC and is in agreement with recent bottom-up field studies.
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    Topics: Biology , Chemistry and Pharmacology , Geography , Geosciences , Physics
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  • 4
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    Insights into the biogeochemical cycling of iron, nitrate and phosphate across a 5300 km South Pacific zonal section (153°E-150°W) (2018)
    Wiley
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    Publication Date: 2018-01-05
    Description: Iron, phosphate and nitrate are essential nutrients for phytoplankton growth and hence their supply into the surface ocean controls oceanic primary production. Here, we present a GEOTRACES zonal section (GP13; 30-33 o S, 153 o E-150 o W) extending eastwards from Australia to the oligotrophic South Pacific Ocean gyre outlining the concentrations of these key nutrients. Surface dissolved iron concentrations are elevated at 〉0.4 nmol L -1 near continental Australia (west of 165°E) and decreased eastward to ≤0.2 nmol L -1 (170 o W-150 o W). The supply of dissolved iron into the upper ocean (〈100m) from the atmosphere and vertical diffusivity averaged 11 ±10 nmol m -2 d -1 . In the remote South Pacific Ocean (170 o W-150 o W) atmospherically sourced iron is a significant contributor to the surface dissolved iron pool with average supply contribution of 23 ± 17% (range 3% to 55%). Surface-water nitrate concentrations averaged 5 ±4 nmol L -1 between 170 o W and 150 o W whilst surface-water phosphate concentrations averaged 58 ±30 nmol L -1 . The supply of nitrogen into the upper ocean is primarily from deeper waters (24-1647 μmol m -2 d -1 ) with atmospheric deposition and nitrogen fixation contributing 〈1% to the overall flux, in remote South Pacific waters. The deep water N:P ratio averaged 16 ±3 but declined to 〈1 above the deep chlorophyll maximum (DCM) indicating a high N:P assimilation ratio by phytoplankton leading to almost quantitative removal of nitrate. The supply stoichiometry for iron and nitrogen relative to phosphate at and above the DCM declines eastward leading to two biogeographical provinces: one with diazotroph production and the other without diazotroph production.
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  • 5
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    Recent Amazon Climate as background for possible ongoing and future changes of Amazon humid forests (2015)
    Wiley
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    Publication Date: 2015-07-23
    Description: Recent analyses of Amazon runoff and gridded precipitation data suggest an intensification of the hydrological cycle over the past few decades in the following sense: wet-season precipitation and peak river runoff (since ∼ 1980) as well as annual-mean precipitation (since ∼ 1990) have increased while dry-season precipitation and minimum runoff have slightly decreased. There has also been an increase in the frequency of anomalously severe floods and droughts. Here we extend and expand these analyses to characterize recent climate state and change, as a background for possible ongoing and future changes of these forests. The contrasting recent changes in wet and dry season precipitation have continued and are generally consistent with changes in catchment-level peak and minimum river runoff as well as a positive trend of water vapour inflow into the basin. Consistent with the river records the increased vapour inflow is concentrated to the wet season. Temperature has been rising by 0.7 ∘ C since 1980 with more pronounced warming during dry months. Suggestions for the cause of the observed changes of the hydrological cycle come from patterns in tropical sea surface temperatures (SST's). Tropical and North Atlantic SST's have increased rapidly and steadily since 1990, while Pacific SST's have shifted from a negative Pacific Decadal Oscillation (PDO) phase (approximately pre 1990) with warm eastern Pacific temperatures to a positive phase with cold eastern Pacific temperatures. These SST conditions have been shown to be associated with an increase in precipitation over most of the Amazon except the south and south-west. If ongoing changes continue we expect these to be generally beneficial for forests in those regions where there is an increase in precipitation with the exception of floodplain forests. An increase in flood-pulse height and duration could lead to increased mortality at higher levels of the floodplain and, over the long term, to a lateral shift of the zonally stratified floodplain forest communities. Negative effects on forests are mainly expected in the south-west and south, which have become slightly drier and hotter, consistent with tree mortality trends observed at the RAINFOR forest plot census network.
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    Topics: Biology , Chemistry and Pharmacology , Geography , Geosciences , Physics
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  • 6
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    Slow Sinking Particulate Organic Carbon in the Atlantic Ocean: magnitude, flux and potential controls (2017)
    Wiley
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    Publication Date: 2017-06-18
    Description: The remineralization depth of particulate organic carbon (POC) fluxes exported from the surface ocean exert a major control over atmospheric CO₂ levels. According to a long held paradigm most of the POC exported to depth is associated with large particles. However, recent lines of evidence suggest that slow sinking POC (SS POC ) may be an important contributor to this flux. Here we assess the circumstances under which this occurs. Our study uses samples collected using the Marine Snow Catcher throughout the Atlantic Ocean, from high latitudes to mid latitudes. We find median SS POC concentrations of 5.5 μg L -1 , 13 times smaller than suspended POC concentrations and 75 times higher than median fast sinking POC (FS POC ) concentrations (0.07 μg L -1 ). Export fluxes of SS POC generally exceed FS POC flux, with the exception being during a spring bloom sampled in the Southern Ocean. In the Southern Ocean SS POC fluxes often increase with depth relative to FS POC flux, likely due to midwater fragmentation of FS POC , a process which may contribute to shallow mineralization of POC and hence to reduced carbon storage. Biogeochemical models do not generally reproduce this behaviour, meaning that they likely overestimate long term ocean carbon storage.
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  • 7
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    A re-evaluation of the magnitude and impacts of anthropogenic atmospheric nitrogen inputs on the ocean (2017)
    Wiley
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    Publication Date: 2017-01-22
    Description: We report a new synthesis of best estimates of the inputs of fixed nitrogen to the world ocean via atmospheric deposition, and compare this to fluvial inputs and di-nitrogen fixation. We evaluate the scale of human perturbation of these fluxes. Fluvial inputs dominate inputs to the continental shelf, and we estimate about 75% of this fluvial nitrogen escapes from the shelf to the open ocean. Biological di-nitrogen fixation is the main external source of nitrogen to the open ocean, i.e. beyond the continental shelf. Atmospheric deposition is the primary mechanism by which land based nitrogen inputs, and hence human perturbations of the nitrogen cycle, reach the open ocean. We estimate that anthropogenic inputs are currently leading to an increase in overall ocean carbon sequestration of ~0.4% (equivalent to an uptake of 0.15 Pg C yr -1 and less than the Duce et al., 2008 estimate). The resulting reduction in climate change forcing from this ocean CO 2 uptake is offset to a small extent by an increase in ocean N 2 O emissions. We identify four important feedbacks in the ocean atmosphere nitrogen system that need to be better quantified to improve our understanding of the perturbation of ocean biogeochemistry by atmospheric nitrogen inputs. These feedbacks are recycling of (1) ammonia and (2) organic nitrogen from the ocean to the atmosphere and back, (3) the suppression of nitrogen fixation by increased nitrogen concentrations in surface waters from atmospheric deposition, and (4) increased loss of nitrogen from the ocean by denitrification due to increased productivity stimulated by atmospheric inputs.
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  • 8
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    Reassessing Southern Ocean air‐sea CO2 flux estimates with the addition of biogeochemical float observations (2019)
    Wiley
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    Publication Date: 2019
    Description: Abstract New estimates of pCO2 from profiling floats deployed by the Southern Ocean Carbon and Climate Observations and Modeling (SOCCOM) project have demonstrated the importance of wintertime outgassing south of the Polar Front, challenging the accepted magnitude of Southern Ocean carbon uptake (Gray et al. 2018). Here, we put 3.5 years of SOCCOM observations into broader context with the global surface carbon dioxide database (Surface Ocean CO2 Atlas, SOCAT) by using the two interpolation methods currently used to assess the ocean models in the Global Carbon Budget (Le Quéré et al. 2018) to create a ship‐only, a float‐weighted, and a combined estimate of Southern Ocean carbon fluxes (〈 35°S). In our ship‐only estimate, we calculate a mean uptake of ‐1.14 ± 0.19 Pg C yr‐1 for 2015‐2017, consistent with prior studies. The float‐weighted estimate yields a significantly lower Southern Ocean uptake of ‐0.35 ± 0.19 Pg C yr‐1. Subsampling of high‐resolution ocean biogeochemical process models indicates that some of the difference between float and ship‐only estimates of the Southern Ocean carbon flux can be explained by spatial and temporal sampling differences. The combined ship and float estimate minimizes the root mean square pCO2 difference between the mapped product and both datasets, giving a new Southern Ocean uptake of ‐0.75 ± 0.22 Pg C yr‐1, though with uncertainties that overlap the ship‐only estimate. An atmospheric inversion reveals that a shift of this magnitude in the contemporary Southern Ocean carbon flux must be compensated for by ocean or land sinks within the Southern Hemisphere.
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