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  • Amazon  (3)
  • Weathering  (2)
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  • 1
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    Dual isotope evidence for sedimentary integration of plant wax biomarkers across an Andes-Amazon elevation transect (2018)
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © The Author(s), 2018. This is the author's version of the work. It is posted here under a nonexclusive, irrevocable, paid-up, worldwide license granted to WHOI. It is made available for personal use, not for redistribution. The definitive version was published in Geochimica et Cosmochimica Acta 242 (2018): 64-81, doi:10.1016/j.gca.2018.09.007.
    Description: Tropical montane regions tend to have high rates of precipitation, biological production, erosion, and sediment export, which together move material off the landscape and toward sedimentary deposits downstream. Plant wax biomarkers can be used to investigate sourcing of organic matter and are often used as proxies to reconstruct past climate and environment in sedimentary deposits. To understand how plant waxes are sourced within a wet, tropical montane catchment, we measure the stable C and H isotope composition (δ13C and δD) of n-alkanes and n-alkanoic acids in soils along an elevation transect and from sediments within the Madre de Dios River network along the eastern flank of the Peruvian Andes, draining an area of 75,400 km2 and 6 km of elevation. Soils yield systematic trends in plant wax δ13C (+1.75 and +1.31‰ km−1, for the C29n-alkanes and C30n-alkanoic acids respectively in the mineral horizon) and δD values (−10 and −12‰ km−1, respectively) across a 3.5 km elevation transect, which approximates trends previously reported from canopy leaves, though we find offsets between δ13C values in plants and soils. River suspended sediments generally follow soil isotopic gradients defined by catchment elevations (δ13C: +1.03 and +0.99‰ km−1 and δD: −10 to −7‰ km−1, for the C29n-alkanes and C30n-alkanoic acids respectively) in the wet season, with a lowering in the dry season that is less well-constrained. In a few river suspended sediments, petrogenic contributions and depth-sorting influence the n-alkane δ13C signal. Our dual isotope, dual compound class and seasonal sampling approach reveals no Andean-dominance in plant wax export, and instead that the sourcing of plant waxes in this very wet, forested catchment approximates that expected for spatial integration of the upstream catchment, thus with a lowland dominance on areal basis, guiding paleoenvironmental reconstructions in tropical montane regions. The dual isotope approach provides a cross-check on the altitudinal signals and can resolve ambiguity such as might be associated with vegetation change or aridity in paleoclimate records. Further, the altitude effect encoded within plant waxes presents a novel dual-isotope biomarker approach to paleoaltimetry.
    Description: This material is based upon work supported by the US National Science Foundation under Grant No. EAR-1227192 to A.J.W and S.J.F for the river work.
    Keywords: Plant wax ; Leaf wax ; Biomarker ; Hydrogen isotope ; Carbon isotope ; Andes ; Amazon ; Paleoaltimetry ; Source-to-sink
    Repository Name: Woods Hole Open Access Server
    Type: Preprint
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  • 2
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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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  • 3
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    Source to sink : evolution of lignin composition in the Madre de Dios River system with connection to the Amazon basin and offshore (2016)
    John Wiley & Sons
    Details
    Publication Date: 2022-05-26
    Description: Author Posting. © American Geophysical Union, 2016. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Biogeosciences 121 (2016): 1316–1338, doi:10.1002/2016JG003323.
    Description: While lignin geochemistry has been extensively investigated in the Amazon River, little is known about lignin distribution and dynamics within deep, stratified river channels or its transformations within soils prior to delivery to rivers. We characterized lignin phenols in soils, river particulate organic matter (POM), and dissolved organic matter (DOM) across a 4 km elevation gradient in the Madre de Dios River system, Peru, as well as in marine sediments to investigate the source-to-sink evolution of lignin. In soils, we found more oxidized lignin in organic horizons relative to mineral horizons. The oxidized lignin signature was maintained during transfer into rivers, and lignin was a relatively constant fraction of bulk organic carbon in soils and riverine POM. Lignin in DOM became increasingly oxidized downstream, indicating active transformation of dissolved lignin during transport, especially in the dry season. In contrast, POM accumulated undegraded lignin downstream during the wet season, suggesting that terrestrial input exceeded in-river degradation. We discovered high concentrations of relatively undegraded lignin in POM at depth in the lower Madre de Dios River in both seasons, revealing a woody undercurrent for its transfer within these deep rivers. Our study of lignin evolution in the soil-river-ocean continuum highlights important seasonal and depth variations of river carbon components and their connection to soil carbon pools, providing new insights into fluvial carbon dynamics associated with the transfer of lignin biomarkers from source to sink.
    Description: U.S. National Science Foundation Grant Number: 1227192; National Program on Key Basic Research Project Grant Number: 2015CB954201; National Natural Science Foundation of China Grant Number: 41422304; Natural Environment Research Council NE/F002149/1 Grant Number: FT110100457; European Union Marie Curie Fellowship Grant Number: FP7-2012-329360; NSF Grant Number: OCE-0934073
    Description: 2016-11-21
    Keywords: Lignin phenols ; Dissolved organic matter (DOM) ; Particulate organic matter (POM) ; Andes ; Amazon ; Depth profile
    Repository Name: Woods Hole Open Access Server
    Type: Article
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  • 4
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    Leaf wax biomarkers in transit record river catchment composition (2014)
    John Wiley & Sons
    Details
    Publication Date: 2022-05-26
    Description: Author Posting. © American Geophysical Union, 2014. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 41 (2014): 6420–6427, doi:10.1002/2014GL061328.
    Description: Rivers carry organic molecules derived from terrestrial vegetation to sedimentary deposits in lakes and oceans, storing information about past climate and erosion, as well as representing a component of the carbon cycle. It is anticipated that sourcing of organic matter may not be uniform across catchments with substantial environmental variability in topography, vegetation zones, and climate. Here we analyze plant leaf wax biomarkers in transit in the Madre de Dios River (Peru), which drains a forested catchment across 4.5 km of elevation from the tropical montane forests of the Andes down into the rainforests of Amazonia. We find that the hydrogen isotopic composition of leaf wax molecules (specifically the C28 n-alkanoic acid) carried by this tropical mountain river largely records the elevation gradient defined by the isotopic composition of precipitation, and this supports the general interpretation of these biomarkers as proxy recorders of catchment conditions. However, we also find that leaf wax isotopic composition varies with river flow regime over storm and seasonal timescales, which could in some cases be quantitatively significant relative to changes in the isotopic composition of precipitation in the past. Our results inform on the sourcing and transport of material by a major tributary of the Amazon River and contribute to the spatial interpretation of sedimentary records of past climate using the leaf wax proxy.
    Description: This work was supported by funding from the U.S. National Science Foundation award 1227192 to A.J.W. and S.J.F. V.G. was supported by the U.S. National Science Foundation award OCE-0928582.
    Description: 2015-03-23
    Keywords: Hydrogen isotopes ; Biomarkers ; Fluvial transport ; Erosion ; Paleoclimate ; Amazon
    Repository Name: Woods Hole Open Access Server
    Type: Article
    Format: text/richtext
    Format: application/pdf
    Format: application/vnd.ms-excel
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  • 5
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    Isotopic evidence for sources of dissolved carbon and the role of organic matter respiration in the Fraser River basin, Canada (2022)
    Springer
    Details
    Publication Date: 2022-11-04
    Description: © The Author(s), 2022. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Voss, B., Eglinton, T., Peucker-Ehrenbrink, B., Galy, V., Lang, S., McIntyre, C., Spencer, R., Bulygina, E., Wang, Z., & Guay, K. Isotopic evidence for sources of dissolved carbon and the role of organic matter respiration in the Fraser River basin, Canada. Biogeochemistry. (2022), https://doi.org/10.1007/s10533-022-00945-5.
    Description: Sources of dissolved and particulate carbon to the Fraser River system vary significantly in space and time. Tributaries in the northern interior of the basin consistently deliver higher concentrations of dissolved organic carbon (DOC) to the main stem than other tributaries. Based on samples collected near the Fraser River mouth throughout 2013, the radiocarbon age of DOC exported from the Fraser River does not change significantly across seasons despite a spike in DOC concentration during the freshet, suggesting modulation of heterogeneous upstream chemical and isotopic signals during transit through the river basin. Dissolved inorganic carbon (DIC) concentrations are highest in the Rocky Mountain headwater region where carbonate weathering is evident, but also in tributaries with high DOC concentrations, suggesting that DOC respiration may be responsible for a significant portion of DIC in this basin. Using an isotope and major ion mass balance approach to constrain the contributions of carbonate and silicate weathering and DOC respiration, we estimate that up to 33 ± 11% of DIC is derived from DOC respiration in some parts of the Fraser River basin. Overall, these results indicate close coupling between the cycling of DOC and DIC, and that carbon is actively processed and transformed during transport through the river network.
    Description: Open Access funding provided by the MIT Libraries. This work was supported by the WHOI Academic Programs Office, the MIT EAPS Department Student Assistance Fund, and the PAOC Houghton Fund to BMV; NSF-ETBC grants OCE-0851015 to BPE, VG, and TIE and OCE-0851101 to RGMS; NSF grant EAR-1226818 to BPE; NSF grant OCE-0928582 to TIE and VG; and a WHOI Arctic Research Initiative grant to ZAW.
    Keywords: River ; Carbon isotopes ; Radiocarbon ; Weathering ; Carbon cycle
    Repository Name: Woods Hole Open Access Server
    Type: Article
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