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  • Amazon river  (2)
  • River  (2)
  • Weathering
  • American Geophysical Union  (4)
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  • 1
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    Land2Sea database of river drainage basin sizes, annual water discharges, and suspended sediment fluxes (2010)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2009. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geochemistry Geophysics Geosystems 10 (2009): Q06014, doi:10.1029/2008GC002356.
    Description: The Land2Sea database contains data on the sizes of 1519 exorheic river drainage basins (79% of the exorheic land area), annual suspended sediment fluxes (593 rivers, 63% of the exorheic land area), and water discharges (1272 rivers, 76% of the exorheic land area) that have been compiled from a variety of sources. The database extends earlier compilations, such as GEMS/GLORI. The river basins are grouped into 19 large-scale drainage regions to investigate the regional variability in freshwater and sediment fluxes to various ocean basins. The annual suspended sediment flux to the coastal ocean (~18.5 × 109 tons) is dominated by east Asia (6.1 × 109 tons); Arabia, India, and southeast Asia (4.3 × 109 tons); and eastern South America (2.4 × 109 tons). Small topical islands of Oceania support the highest annual sediment fluxes per drainage area (~9650 t km−2 a−1). Annual freshwater discharge to the coastal ocean (~38,857 km3) is dominated by runoff from eastern South America (11,199 km3); east Asia (7114 km3); and Arabia, India, and southeast Asia (4384 km3). The empirical data agree well with results from global models (ART and BQART) that have been trained on a subset of the data compiled here.
    Description: The Woods Hole Oceanographic Institution, the U.S. National Science Foundation (grants EAR-0519387 and OCE-0851015), and the French CNRS (Observatoire Midi- Pyre´ne´es in Toulouse, France) funded this work.
    Keywords: River ; Database ; Water discharge ; Runoff ; Suspended sediment ; Drainage basin area
    Repository Name: Woods Hole Open Access Server
    Type: Article
    Format: text/plain
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  • 2
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    Continental bedrock and riverine fluxes of strontium and neodymium isotopes to the oceans (2010)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2010. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geochemistry Geophysics Geosystems 11 (2010): Q03016, doi:10.1029/2009GC002869.
    Description: Realistic models of past climate and ocean chemistry depend on reconstructions of the Earth's surface environments in the geologic past. Among the critical parameters is the geologic makeup of continental drainage. Here we show, for the present, that the isotope composition of dissolved strontium in rivers increases linearly with the age of bedrock in drainage basins, with the notable exception of the drainage area of Arabia, India, and Southeast Asia that is affected by unusually radiogenic dissolved Sr from the Himalaya. We also demonstrate that the neodymium isotope compositions of suspended matter in rivers as well as clastic sediments deposited along the ocean margins decrease linearly with the bedrock ages of river drainage basins and large-scale continental drainage regions, as determined from digital geologic maps. These correlations are used to calculate the present-day input of dissolved Sr (4.7 × 1010 mol yr−1, 87Sr/86Sr of ∼0.7111) and particulate Nd isotopes (ɛNd of approximately −7.3 ± 2.2) to the oceans. The fact that the regionally averaged ɛNd of the global detrital input to the global coastal ocean is identical to globally averaged seawater (ɛNd of −7.2 ± 0.5) lends credence to the importance of “boundary exchange” for the Nd isotope composition of water masses. Regional biases in source areas of detrital matter and runoff are reflected by the observation that the average age of global bedrock, weighted according to the riverine suspended sediment flux, is significantly younger (∼336 Myr) than the age of global bedrock weighted according to water discharge (394 Myr), which is younger than the average bedrock age of the nonglaciated, exorheic portions of the continents (453 Myr). The observation that the bedrock age weighted according to Sr flux is younger (339 Myr) than that weighted according to water flux reflects the disproportionate contribution from young sedimentary and volcanic rocks to the dissolved Sr load. Neither the isotope composition of the dissolved nor the particulate continental inputs to the ocean provide unbiased perspectives of the lithologic makeup of the Earth's surface. Temporal changes in bedrock geology as well as the shifting focal points of physical erosion and water discharge will undoubtedly have exerted strong controls on temporal and spatial changes in the isotope chemistry of past global runoff and thus seawater.
    Description: NSF grants EAR‐ 0125873, EAR‐0519387, and OCE‐0851015 to B.P.‐E. and a CNRS‐funded “poste rouge” position for B.P.‐E. at the Observatoire Midi‐Pyrénées in Toulouse supported this work.
    Keywords: Seawater ; River ; Strontium ; Neodymium ; Isotope ; Continental runoff
    Repository Name: Woods Hole Open Access Server
    Type: Article
    Format: application/pdf
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    Format: application/vnd.ms-excel
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  • 3
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    The pulse of the Amazon: fluxes of dissolved organic carbon, nutrients, and ions from the world's largest river (2021)
    American Geophysical Union
    Details
    Publication Date: 2022-10-26
    Description: Author Posting. © American Geophysical Union, 2021. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Global Biogeochemical Cycles 35(4), (2021): e2020GB006895, https://doi.org/10.1029/2020GB006895.
    Description: The Amazon River drains a diverse tropical landscape greater than 6 million km2, culminating in the world's largest export of freshwater and dissolved constituents to the ocean. Here, we present dissolved organic carbon (DOC), organic and inorganic nitrogen (DON, DIN), orthophosphate (PO43−), and major and trace ion concentrations and fluxes from the Amazon River using 26 samples collected over three annual hydrographs. Concentrations and fluxes were predominantly controlled by the annual wet season flood pulse. Average DOC, DON, DIN, and PO43− fluxes (±1 s.d.) were 25.5 (±1.0), 1.14 (±0.05), 0.82 (±0.03), and 0.063 (±0.003) Tg yr−1, respectively. Chromophoric dissolved organic matter absorption (at 350 nm) was strongly correlated with DOC concentrations, resulting in a flux of 74.8 × 106 m−2 yr−1. DOC and DON concentrations positively correlated with discharge while nitrate + nitrite concentrations negatively correlated, suggesting mobilization and dilution responses, respectively. Ammonium, PO43−, and silica concentrations displayed chemostatic responses to discharge. Major and trace ion concentrations displayed clockwise hysteresis (except for chloride, sodium, and rubidium) and exhibited either dilution or chemostatic responses. The sources of weathered cations also displayed seasonality, with the highest proportion of carbonate- and silicate-derived cations occurring during peak and baseflow, respectively. Finally, our seasonally resolved weathering model resulted in an average CO2 consumption yield of (3.55 ± 0.11) × 105 mol CO2 km−2 yr−1. These results represent an updated and temporally refined quantification of dissolved fluxes that highlight the strong seasonality of export from the world's largest river and set a robust baseline against which to gauge future change.
    Description: This work was supported by a grant from the Harbourton Foundation to R. G. M. Spencer and R. M. Holmes. T. W. Drake was supported by ETH Zurich core funding to J. Six. R. G. M. Spencer was additionally supported by NSF OCE-1333157.
    Description: 2021-09-15
    Keywords: Amazon river ; Dissolved organic carbon ; Fluxes ; Weathering ; Geochemistry
    Repository Name: Woods Hole Open Access Server
    Type: Article
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  • 4
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    Drivers of organic molecular signatures in the Amazon River (2021)
    American Geophysical Union
    Details
    Publication Date: 2022-05-27
    Description: Author Posting. © American Geophysical Union, 2021. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Global Biogeochemical Cycles 35(6), (2021): e2021GB006938, https://doi.org/10.1029/2021GB006938.
    Description: As climate-driven El Niño Southern Oscillation (ENSO) events are projected to increase in frequency and severity, much attention has focused on impacts regarding ecosystem productivity and carbon balance in Amazonian rainforests, with comparatively little attention given to carbon dynamics in fluvial ecosystems. In this study, we compared the wet 2012 La Niña period to the following normal hydrologic period in the Amazon River. Elevated water flux during the La Niña period was accompanied by dilution of inorganic ion concentrations. Furthermore, the La Niña period exported 2.77 Tg C yr−1 more dissolved organic carbon (DOC) than the normal period, an increase greater than the annual amount of DOC exported by the Mississippi River. Using ultra-high-resolution mass spectrometry, we detected both intra- and interannual differences in dissolved organic matter (DOM) composition, revealing that DOM exported during the dry season and the normal period was more aliphatic, whereas compounds in the wet season and following the La Niña event were more aromatic, with ramifications for its environmental role. Furthermore, as this study has the highest temporal resolution DOM compositional data for the Amazon River to-date we showed that compounds were highly correlated to a 6-month lag in Pacific temperature and pressure anomalies, suggesting that ENSO events could impact DOM composition exported to the Atlantic Ocean. Therefore, as ENSO events increase in frequency and severity into the future it seems likely that there will be downstream consequences for the fate of Amazon Basin-derived DOM concurrent with lag periods as described here.
    Description: This work was partially supported by National Science Foundation grant OCE-1464396 to Robert G. M. Spencer and funding from the Harbourton Foundation to Robert G. M. Spencer, R. Max Holmes, and Bernhard Peucker-Ehrenbrink.
    Description: 2021-12-11
    Keywords: Amazon river ; carbon cycling ; dissolved organic carbon ; dissolved organic matter ; ENSO ; FT-ICR MS
    Repository Name: Woods Hole Open Access Server
    Type: Article
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