Journal: Global Biogeochemical Cycles

Abbreviation

Glob. biogeochem. cycles

Publisher

Wiley

Journal Volumes

ISSN

0886-6236
1944-9224

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2018 - 201952020 - 202410
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Publications 1 - 10 of 15
  • Integrative Crop-Soil-Management Modeling to Assess Global Phosphorus Losses from Major Crop Cultivations
    Item type: Journal Article
    Liu, Wenfeng; Yang, Hong; Ciais, Philippe; et al. (2018)
    Global Biogeochemical Cycles
  • Negligible Quantities of Particulate Low-Temperature Pyrogenic Carbon Reach the Atlantic Ocean via the Amazon River
    Item type: Journal Article
    Häggi, Christoph; Hopmans, Ellen; Schefuß, Enno; et al. (2021)
    Global Biogeochemical Cycles
    Particulate pyrogenic carbon (PyC) transported by rivers and aerosols, and deposited in marine sediments, is an important part of the carbon cycle. The chemical composition of PyC is temperature dependent and levoglucosan is a source-specific burning marker used to trace low-temperature PyC. Levoglucosan associated to particulate material has been shown to be preserved during riverine transport and marine deposition in high- and mid-latitudes, but it is yet unknown if this is also the case for (sub)tropical areas, where 90% of global PyC is produced. Here, we investigate transport and deposition of levoglucosan in suspended and riverbed sediments from the Amazon River system and adjacent marine deposition areas. We show that the Amazon River exports negligible amounts of levoglucosan and that concentrations in sediments from the main Amazon tributaries are not related to long-term mean catchment-wide fire activity. Levoglucosan concentrations in marine sediments offshore the Amazon Estuary are positively correlated to total organic content regardless of terrestrial or marine origin, supporting the notion that association of suspended or dissolved PyC to biogenic particles is critical in the preservation of PyC. We estimate that 0.5–10 × 106 g yr−1 of levoglucosan is exported by the Amazon River. This represents only 0.5–10 ppm of the total exported PyC and thereby an insignificant fraction, indicating that riverine derived levoglucosan and low-temperature PyC in the tropics are almost completely degraded before deposition. Hence, we suggest caution in using levoglucosan as tracer for past fire activity in tropical settings near rivers.
  • An Assessment of CO₂ Storage and Sea-Air Fluxes for the Atlantic Ocean and Mediterranean Sea Between 1985 and 2018
    Item type: Journal Article
    Pérez, Fíz F.; Becker, Meike; Goris, Nadine; et al. (2024)
    Global Biogeochemical Cycles
  • Magnitude, Trends, and Variability of the Global Ocean Carbon Sink From 1985 to 2018
    Item type: Journal Article
    DeVries, Tim; Yamamoto, Kana; Wanninkhof, Rik; et al. (2023)
    Global Biogeochemical Cycles
    This contribution to the RECCAP2 (REgional Carbon Cycle Assessment and Processes) assessment analyzes the processes that determine the global ocean carbon sink, and its trends and variability over the period 1985–2018, using a combination of models and observation-based products. The mean sea-air CO₂ flux from 1985 to 2018 is −1.6 ± 0.2 PgC yr⁻¹ based on an ensemble of reconstructions of the history of sea surface pCO₂ (pCO₂ products). Models indicate that the dominant component of this flux is the net oceanic uptake of anthropogenic CO₂, which is estimated at −2.1 ± 0.3 PgC yr⁻¹ by an ensemble of ocean biogeochemical models, and −2.4 ± 0.1 PgC yr−1 by two ocean circulation inverse models. The ocean also degasses about 0.65 ± 0.3 PgC yr⁻¹ of terrestrially derived CO₂, but this process is not fully resolved by any of the models used here. From 2001 to 2018, the pCO₂ products reconstruct a trend in the ocean carbon sink of −0.61 ± 0.12 PgC yr⁻¹ decade⁻¹, while biogeochemical models and inverse models diagnose an anthropogenic CO₂-driven trend of −0.34 ± 0.06 and −0.41 ± 0.03 PgC yr⁻¹ decade⁻¹, respectively. This implies a climate-forced acceleration of the ocean carbon sink in recent decades, but there are still large uncertainties on the magnitude and cause of this trend. The interannual to decadal variability of the global carbon sink is mainly driven by climate variability, with the climate-driven variability exceeding the CO₂-forced variability by 2–3 times. These results suggest that anthropogenic CO₂ dominates the ocean CO₂ sink, while climate-driven variability is potentially large but highly uncertain and not consistently captured across different methods.
  • The Impact of the Amazon on the Biological Pump and the Air-Sea CO2 Balance of the Western Tropical Atlantic
    Item type: Journal Article
    Louchard, Domitille; Gruber, Nicolas; Münnich, Matthias (2021)
    Global Biogeochemical Cycles
    The Amazon River strongly modifies the biogeochemistry of the Western Tropical Atlantic (WTA). To disentangle the different mechanisms driving these modifications, we conduct a series of modeling experiments with a high-resolution regional ocean model (ROMS) coupled to a biogeochemical/ecological model (BEC) that we augmented to include Diatom-Diazotroph-Assemblages (DDAs). In our model, the Amazon River increases net primary production (NPP) in the WTA by almost 10%, exceeding the stimulation expected from the supplied inorganic nitrogen and phosphorus by a factor of two. This amplification is fueled by new nitrogen stemming from DDA-driven N2 fixation in the plume region, supported, in part, by the consumption of riverine dissolved organic phosphorus. The vertical export of organic carbon is enhanced by a shift of the phytoplankton community toward diatoms induced by the large amount of Si(OH)4 delivered by the Amazon. These changes in NPP and export production induce a strong uptake of atmospheric CO2. In contrast, the remineralization of the river-delivered terrestrial organic matter leads to a release of CO2 over the WTA, which is partially offset by a net uptake induced by the riverine dissolved inorganic carbon and alkalinity. Overall, the Amazon reduces the strong outgassing of the WTA in our simulations by more than 50%. Our study demonstrates how rivers modify the marine biological pump and the air-sea CO2 fluxes in the downstream ocean through a myriad of cascading effects, highlighting the need to fully consider the land-ocean aquatic continuum in the modeling of the Earth System.
  • On the Role of the Amazon River for N2 Fixation in the Western Tropical Atlantic
    Item type: Journal Article
    Louchard, Domitille; Münnich, Matthias; Gruber, Nicolas (2023)
    Global Biogeochemical Cycles
    The high rates of N2 fixation observed in the Western Tropical Atlantic Ocean are powered, at least in parts, by large influx of nutrients from the Amazon River. To disentangle the impact of the Amazon on different factors controlling N2 fixation in the region, we use a high-resolution regional model (Regional Oceanic Modeling System-Biogeochemical Elemental Cycling model) that includes two diazotrophic phytoplankton classes (Trichodesmium and Diatom-Diazotroph-Assemblages, DDAs). In our simulations, the Amazon enhances marine N2 fixation by 74% (3.8 Tg N yr−1), with most of the enhancement driven by DDAs that represent 90% of the diazotrophic community in plume waters. To determine how the Amazon creates the conditions in which DDAs thrive, we analyze bottom-up and top-down controls on phytoplankton along the plume pathway and how the phytoplankton competition is disrupted by the delivery of nutrients by the river. Along the entire plume pathway, DDAs out-compete Trichodesmium as their higher maximum growth makes them more efficient in building biomass. Nevertheless, DDAs never account for more than 25% of the total phytoplankton biomass as they face the competition of other non-diazotrophic phytoplankton types in the use of the riverine nutrients. Overall, DDAs thrive in the offshore plume region where their nutrient uptake advantages (N-fixation, DOP uptake) is concomitant with a relaxed grazing pressure.
  • A Synthesis of Global Coastal Ocean Greenhouse Gas Fluxes
    Item type: Journal Article
    Resplandy, Laure; Hogikyan, Allison; Müller, Jens Daniel; et al. (2024)
    Global Biogeochemical Cycles
    The coastal ocean contributes to regulating atmospheric greenhouse gas concentrations by taking up carbon dioxide (CO2) and releasing nitrous oxide (N2O) and methane (CH4). In this second phase of the Regional Carbon Cycle Assessment and Processes (RECCAP2), we quantify global coastal ocean fluxes of CO2, N2O and CH4 using an ensemble of global gap-filled observation-based products and ocean biogeochemical models. The global coastal ocean is a net sink of CO2 in both observational products and models, but the magnitude of the median net global coastal uptake is ∼60% larger in models (−0.72 vs. −0.44 PgC year−1, 1998–2018, coastal ocean extending to 300 km offshore or 1,000 m isobath with area of 77 million km2). We attribute most of this model-product difference to the seasonality in sea surface CO2 partial pressure at mid- and high-latitudes, where models simulate stronger winter CO2 uptake. The coastal ocean CO2 sink has increased in the past decades but the available time-resolving observation-based products and models show large discrepancies in the magnitude of this increase. The global coastal ocean is a major source of N2O (+0.70 PgCO2-e year−1 in observational product and +0.54 PgCO2-e year−1 in model median) and CH4 (+0.21 PgCO2-e year−1 in observational product), which offsets a substantial proportion of the coastal CO2 uptake in the net radiative balance (30%–60% in CO2-equivalents), highlighting the importance of considering the three greenhouse gases when examining the influence of the coastal ocean on climate.
  • Community‐Level Responses to Iron Availability in Open Ocean Plankton Ecosystems
    Item type: Journal Article
    Caputi, Luigi; Carradec, Quentin; Eveillard, Damien; et al. (2019)
    Global Biogeochemical Cycles
  • A Mechanistic Model of Microbially Mediated Soil Biogeochemical Processes: A Reality Check
    Item type: Journal Article
    Fatichi, Simone; Manzoni, Stefano; Or, Dani; et al. (2019)
    Global Biogeochemical Cycles
Publications 1 - 10 of 15