An Abrupt Aging of Dissolved Organic Carbon in Large Arctic Rivers

Schwab, Melissa Sophia; Hilton, Robert; Raymond, Peter A.; Haghipour, Negar; Amos, Edwin; Tank, Suzanne E.; Holmes, Robert M.; Tipper, Edward T.; Eglinton, T. I.

doi:10.1029/2020gl088823

Cited by 43 publications

(34 citation statements)

References 108 publications

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“…Spring freshet also had the highest Δ 14 C-DOC values, while winter baseflow had the lowest values (radiocarbon ages from 1,533 years before present (ybp) to >modern and 2,371 ybp to >modern, respectively; Table 1; Figure 2d; Kruskal-Wallis test: p < 0.0001). This pattern of modern DOC during spring freshet and older DOC during winter has been well documented previously for large Arctic rivers (Raymond et al, 2007;Wild et al, 2019), though some aged DOC has been seen in spring in large Arctic rivers as well (Schwab et al, 2020).…”

Section: Seasonal Synchrony and The Latent High-energy Spring Subsidysupporting

confidence: 83%

Pan‐Arctic Riverine Dissolved Organic Matter: Synchronous Molecular Stability, Shifting Sources and Subsidies

Behnke

McClelland²,

Tank

et al. 2021

Global Biogeochemical Cycles

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Climate change is dramatically altering Arctic ecosystems, leading to shifts in the sources, composition, and eventual fate of riverine dissolved organic matter (DOM) in the Arctic Ocean. Here we examine a 6-year DOM compositional record from the six major Arctic rivers using Fourier-transform ion cyclotron resonance mass spectrometry paired with dissolved organic carbon isotope data (Δ 14 C, δ 13 C) to investigate how seasonality and permafrost influence DOM, and how DOM export may change with warming. Across the pan-Arctic, DOM molecular composition demonstrates synchrony and stability. Spring freshet brings recently leached terrestrial DOM with a latent high-energy and potentially bioavailable subsidy, reconciling the historical paradox between freshet DOM's terrestrial bulk signatures and high biolability. Winter features undiluted baseflow DOM sourced from old, microbially degraded groundwater DOM. A stable core Arctic riverine fingerprint (CARF) is present in all samples and may contribute to the potential carbon sink of persistent, aged DOM in the global ocean. Future warming may lead to shifting sources of DOM and export through: (1) flattening Arctic hydrographs and earlier melt modifying the timing and role of the spring high-energy subsidy; (2) increasing groundwater discharge resulting in a greater fraction of DOM export to the ocean occurring as stable and aged molecules; and(3) increasing contribution of nitrogen/sulfur-containing DOM from microbial degradation caused by increased connectivity between groundwater and surface waters due to permafrost thaw. Our findings suggest the ubiquitous CARF (which may contribute to oceanic carbon sequestration) underlies predictable variations in riverine DOM composition caused by seasonality and permafrost extent.

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Section: Seasonal Synchrony and The Latent High-energy Spring Subsidysupporting

confidence: 83%

Pan‐Arctic Riverine Dissolved Organic Matter: Synchronous Molecular Stability, Shifting Sources and Subsidies

Behnke

McClelland²,

Tank

et al. 2021

Global Biogeochemical Cycles

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“…This is particularly true for Shallow Bay for which the Q-tDOC merged relationship is the strongest (r = 0.79) even compared to the Q-tDOC in situ relationship (r = 0.59). There is growing evidence that tDOC concentrations and quality vary in the course of the main channels of the Mackenzie Delta (Emmerton et al, 2008b;Griffin et al, 2018;Kipp et al, 2020;Schwab et al, 2020). The use of satellite tDOC retrieved in nearshore waters in the very close vicinity of the delta outlets allows for the effect of regional biogeochemical signatures to be considered in the estimated landto-sea fluxes of tDOC.…”

Section: A Complex Land-to-sea Interfacementioning

confidence: 99%

Merging Satellite and in situ Data to Assess the Flux of Terrestrial Dissolved Organic Carbon From the Mackenzie River to the Coastal Beaufort Sea

et al. 2022

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In response to global warming, the Arctic is undergoing rapid and unprecedented changes that alter the land-to-sea forcing in large Arctic rivers. Improving our knowledge of terrestrial dissolved organic carbon (tDOC) flux to the coastal Arctic Ocean (AO) is thus critical and timely as these changes strongly alter the biogeochemical cycles on AO shelves. In this study, we merged riverine in situ tDOC concentrations with satellite ocean-color estimates retrieved at the land-marine interface of the Mackenzie Delta to make a first assessment of the tDOC export from its main outlets to the shelf. We combined tDOC and river discharge data to develop a regression model that simulated tDOC concentrations and fluxes from daily to interannual (2003–2017) time scales. We then compared the simulated satellite-derived estimates to those simulated by the model constrained by in situ tDOC data only. As the satellite tDOC estimates reflect the delta effect in terms of tDOC enrichment and removal, our results inform us of how much tDOC can potentially leave the delta to reach the ocean (1.44 ± 0.14 TgC.yr−1). The chemodynamic relationships and the model suggest contrasting patterns between Shallow Bay and the two easternmost delta outlets, which can be explained by the variability in their geomorphological settings. At the seasonal scale and for all outlets, the satellite-derived tDOC export departs from the estimate based on in situ tDOC data only. During the river freshet in May, the satellite-derived tDOC export is, on average, ∼15% (Shallow Bay) to ∼20% (Beluga Bay) lower than the in situ-derived estimate. This difference was the highest (−60%) in 2005 and exceeds 30% over most of the last decade, and can be explained by qualitative and quantitative differences between the tDOCin situ and tDOCsat datasets in a period when the freshet is highly variable. In contrast, in summer and fall, the satellite-derived tDOC export is higher than the in situ-derived estimate. The temporal difference between the satellite and in situ-derived export estimates suggests that predicting seasonal tDOC concentrations and fluxes from remote Arctic deltas to the coastal AO remains a challenge for assessing their impact on already changing carbon fluxes.

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“…There is evidence that ancient DOC decomposes quickly following thaw, so a large fraction of DOC released by active layer thickening may mineralize near the source (Drake et al, 2015;Vonk et al, 2015a). In the few instances where radiocarbon ages have been measured on surface water DOC exported from permafrost terrain, aged DOC is detectable, particularly late in the thaw season (Neff et al, 2006;Striegl et al, 2007) but the signal is small and likely to diminish quickly due to high biolability (Vonk et al, 2013;Wickland et al, 2018) and/or dilution by modern C sources (Aiken et al, 2014;Dean et al, 2020;Schwab et al, 2020; Table 2, C1). Studies in northern permafrost regions indicate a mixed response in DOC riverine export to active layer thickening (Vonk et al, 2015b; Table 2, C2).…”

Section: Response To Active Layer Thickeningmentioning

confidence: 99%

“…Dissolved C transport through lateral taliks could help explain the large observed soil carbon losses. Likewise, Schwab et al (2020) attribute a pulse of aged DOC, determined by radiocarbon activity in DOC, in the northern Mackenzie River basin of Canada, to lateral transport of thawed permafrost C through newly developed supra-permafrost taliks following several warm summer and winter seasons. The coupled hydrologic and biogeochemical role of lateral taliks remains poorly quantified and is likely to increase in importance with time and continued subsurface warming (Vonk et al, 2019;Walvoord et al, 2019).…”

Section: Response To Supra-permafrost Talik Developmentmentioning

confidence: 99%

Complex Vulnerabilities of the Water and Aquatic Carbon Cycles to Permafrost Thaw

Walvoord

Striegl

2021

Front. Clim.

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The spatial distribution and depth of permafrost are changing in response to warming and landscape disturbance across northern Arctic and boreal regions. This alters the infiltration, flow, surface and subsurface distribution, and hydrologic connectivity of inland waters. Such changes in the water cycle consequently alter the source, transport, and biogeochemical cycling of aquatic carbon (C), its role in the production and emission of greenhouse gases, and C delivery to inland waters and the Arctic Ocean. Responses to permafrost thaw across heterogeneous boreal landscapes will be neither spatially uniform nor synchronous, thus giving rise to expressions of low to medium confidence in predicting hydrologic and aquatic C response despite very high confidence in projections of widespread near-surface permafrost disappearance as described in the 2019 Intergovernmental Panel on Climate Change Special Report on the Ocean and Cryosphere in a Changing Climate: Polar Regions. Here, we describe the state of the science regarding mechanisms and factors that influence aquatic C and hydrologic responses to permafrost thaw. Through synthesis of recent topical field and modeling studies and evaluation of influential landscape characteristics, we present a framework for assessing vulnerabilities of northern permafrost landscapes to specific modes of thaw affecting local to regional hydrology and aquatic C biogeochemistry and transport. Lastly, we discuss scaling challenges relevant to model prediction of these impacts in heterogeneous permafrost landscapes.

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An Abrupt Aging of Dissolved Organic Carbon in Large Arctic Rivers

Cited by 43 publications

References 108 publications

Pan‐Arctic Riverine Dissolved Organic Matter: Synchronous Molecular Stability, Shifting Sources and Subsidies

Pan‐Arctic Riverine Dissolved Organic Matter: Synchronous Molecular Stability, Shifting Sources and Subsidies

Merging Satellite and in situ Data to Assess the Flux of Terrestrial Dissolved Organic Carbon From the Mackenzie River to the Coastal Beaufort Sea

Complex Vulnerabilities of the Water and Aquatic Carbon Cycles to Permafrost Thaw

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