Hilton Robert G.

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Robert G.

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  • Preprint
    Erosion of organic carbon in the Arctic as a geological carbon dioxide sink
    ( 2015-05-12) Hilton, Robert G. ; Galy, Valier ; Gaillardet, Jerome ; Dellinger, Mathieu ; Bryant, Charlotte ; O'Regan, Matt ; Grocke, Darren R. ; Coxall, Helen ; Bouchez, Julien ; Calmels, Damien
    Soils of the northern high latitudes store carbon over millennial timescales (103 yrs) and contain approximately double the carbon stock of the atmosphere1-3. Warming and associated permafrost thaw can expose soil organic carbon and result in mineralisation and carbon dioxide (CO2) release4-6. However, some of this soil organic carbon may be eroded and transferred to rivers7-9. If it escapes degradation during river transport and is buried in marine sediments, then it can contribute to a longer-term (>104 yrs), geological CO2 sink8-10. Despite this recognition, the erosional flux and fate of particulate organic carbon (POC) in large rivers at high latitudes remains poorly constrained. Here, we quantify POC source in the Mackenzie River, the main sediment supplier to the Arctic Ocean11,12 and assess its flux and fate. We combine measurements of radiocarbon, stable carbon isotopes and element ratios 26 to correct for rock-derived POC10,13,14. Our samples reveal that the eroded biospheric POC has resided in the basin for millennia, with a mean radiocarbon age of 5800±800 yr, much older than large tropical rivers13,14. Based on the measured biospheric POC content and variability in annual sediment yield15, we calculate a biospheric POC flux of 𝟐. 𝟐𝟐−𝟎𝟎.𝟗𝟗 +𝟏𝟏.𝟑𝟑 TgC yr-1 from the Mackenzie River, three times the CO2 drawdown by silicate weathering16. Offshore we find evidence for efficient terrestrial organic carbon burial over the Holocene, suggesting that erosion of organic carbon-rich, high latitude soils may result in a significant geological CO2 sink.
  • Article
    Turbidity currents can dictate organic carbon fluxes across river‐fed fjords: an example from Bute Inlet (BC, Canada)
    (American Geophysical Union, 2022-05-25) Hage, Sophie ; Galy, Valier ; Cartigny, Matthieu J. B. ; Heerema, Catharina ; Heijnen, Maarten S. ; Acikalin, Sanem ; Clare‬, Michael A. ; Giesbrecht, Ian J. W. ; Grocke, Darren R. ; Hendry, A. ; Hilton, Robert G. ; Hubbard, Stephen M. ; Hunt, James E. ; Lintern, D. Gwyn ; McGhee, Claire A. ; Parsons, Daniel R. ; Pope, Edward L. ; Stacey, Cooper David ; Sumner, Esther J. ; Tank, Suzanne E. ; Talling, Peter J.
    The delivery and burial of terrestrial particulate organic carbon (OC) in marine sediments is important to quantify, because this OC is a food resource for benthic communities, and if buried it may lower the concentrations of atmospheric CO2 over geologic timescales. Analysis of sediment cores has previously shown that fjords are hotspots for OC burial. Fjords can contain complex networks of submarine channels formed by seafloor sediment flows, called turbidity currents. However, the burial efficiency and distribution of OC by turbidity currents in river-fed fjords had not been investigated previously. Here, we determine OC distribution and burial efficiency across a turbidity current system within Bute Inlet, a fjord in western Canada. We show that 62% ± 10% of the OC supplied by the two river sources is buried across the fjord surficial (30–200 cm) sediment. The sandy subenvironments (channel and lobe) contain 63% ± 14% of the annual terrestrial OC burial in the fjord. In contrast, the muddy subenvironments (overbank and distal basin) contain the remaining 37% ± 14%. OC in the channel, lobe, and overbank exclusively comprises terrestrial OC sourced from rivers. When normalized by the fjord’s surface area, at least 3 times more terrestrial OC is buried in Bute Inlet, compared to the muddy parts of other fjords previously studied. Although the long-term (>100 years) preservation of this OC is still to be fully understood, turbidity currents in fjords appear to be efficient at storing OC supplied by rivers in their near-surface deposits.
  • Article
    Efficient preservation of young terrestrial organic carbon in sandy turbidity-current deposits
    (Hage, S., Galy, V. V., Cartigny, M. J. B., Acikalin, S., Clare, M. A., Grocke, D. R., Hilton, R. G., Hunt, J. E., Lintern, D. G., McGhee, C. A., Parsons, D. R., Stacey, C. D., Sumner, E. J., & Talling, P. J. (2020). Efficient preservation of young terrestrial organic carbon in sandy turbidity-current deposits. Geology, 48(9), 882-887., 2020-05-29) Hage, Sophie ; Galy, Valier ; Cartigny, Matthieu J. B. ; Acikalin, Sanem ; Clare‬, Michael A. ; Grocke, Darren R. ; Hilton, Robert G. ; Hunt, James E. ; Lintern, D. Gwyn ; McGhee, Claire A. ; Parsons, Daniel R. ; Stacey, Cooper David ; Sumner, Esther J. ; Talling, Peter J.
    Burial of terrestrial biospheric particulate organic carbon in marine sediments removes CO2 from the atmosphere, regulating climate over geologic time scales. Rivers deliver terrestrial organic carbon to the sea, while turbidity currents transport river sediment further offshore. Previous studies have suggested that most organic carbon resides in muddy marine sediment. However, turbidity currents can carry a significant component of coarser sediment, which is commonly assumed to be organic carbon poor. Here, using data from a Canadian fjord, we show that young woody debris can be rapidly buried in sandy layers of turbidity current deposits (turbidites). These layers have organic carbon contents 10× higher than the overlying mud layer, and overall, woody debris makes up >70% of the organic carbon preserved in the deposits. Burial of woody debris in sands overlain by mud caps reduces their exposure to oxygen, increasing organic carbon burial efficiency. Sandy turbidity current channels are common in fjords and the deep sea; hence we suggest that previous global organic carbon burial budgets may have been underestimated.
  • Preprint
    Microbial oxidation of lithospheric organic carbon in rapidly eroding tropical mountain soils
    ( 2018-02-15) Hemingway, Jordon D. ; Hilton, Robert G. ; Hovius, Niels ; Eglinton, Timothy I. ; Haghipour, Negar ; Wacker, Lukas ; Chen, Meng-Chiang ; Galy, Valier
    Lithospheric organic carbon (“petrogenic”; OCpetro) is oxidized during exhumation and subsequent erosion within mountain ranges. This process is a significant source of CO2 to the atmosphere over geologic timescales, but the mechanisms that govern oxidation rates in mountain landscapes remain poorly constrained. We demonstrate that, on average, 67 ± 11 % of OCpetro initially present in bedrock exhumed from the tropical, rapidly eroding Central Range of Taiwan is oxidized within soils, leading to CO2 emissions of 6.1 – 18.6 t C km-2 yr-1. The molecular and isotopic evolution of bulk OC and lipid biomarkers during soil formation reveals that OCpetro remineralization is microbially mediated. Rapid oxidation in mountain soils drives CO2 emissions fluxes that increase with erosion rate, thereby counteracting CO2 drawdown by silicate weathering and biospheric OC burial.
  • Article
    Global patterns of radiocarbon depletion in subsoil linked to rock-derived organic carbon
    (European Association of Geochemistry, 2023-04-19) Grant, Katherine E. ; Hilton, Robert G. ; Galy, Valier V.
    Organic matter stored in sedimentary rocks is one of the largest stocks of carbon at Earth’s surface. The fate of this rock organic carbon (OCpetro) during weathering in soils influences the geological carbon cycle, and impacts soil radiocarbon content that is used to quantify soil carbon turnover. Here, we assess the potential contribution of OCpetro to soils, using a mixing model generated by a global dataset of soil radiocarbon measurements (14C). Soils developed on sedimentary rocks (rather than on igneous substrate) have a paired OC content and 14C values consistent with OCpetro input, giving rise to apparent increase in soil residence time. We call for renewed assessment of OCpetro input to soils, in terms of its impact on soil radiocarbon inventories, and its potential to release carbon dioxide.