Rivers across the Siberian Arctic unearth the patterns of carbon release from thawing permafrost

Abstract

Climate warming is expected to mobilize northern permafrost and peat organic carbon (PP-C), yet magnitudes and system specifics of even current releases are poorly constrained. While part of the PP-C will degrade at point of thaw to CO2 and CH4 to directly amplify global warming, another part will enter the fluvial network, potentially providing a window to observe large-scale PP-C remobilization patterns. Here, we employ a decade-long, high-temporal resolution record of 14C in dissolved and particulate organic carbon (DOC and POC, respectively) to deconvolute PP-C release in the large drainage basins of rivers across Siberia: Ob, Yenisey, Lena, and Kolyma. The 14C-constrained estimate of export specifically from PP-C corresponds to only 17 ± 8% of total fluvial organic carbon and serves as a benchmark for monitoring changes to fluvial PP-C remobilization in a warming Arctic. Whereas DOC was dominated by recent organic carbon and poorly traced PP-C (12 ± 8%), POC carried a much stronger signature of PP-C (63 ± 10%) and represents the best window to detect spatial and temporal dynamics of PP-C release. Distinct seasonal patterns suggest that while DOC primarily stems from gradual leaching of surface soils, POC reflects abrupt collapse of deeper deposits. Higher dissolved PP-C export by Ob and Yenisey aligns with discontinuous permafrost that facilitates leaching, whereas higher particulate PP-C export by Lena and Kolyma likely echoes the thermokarst-induced collapse of Pleistocene deposits. Quantitative 14C-based fingerprinting of fluvial organic carbon thus provides an opportunity to elucidate large-scale dynamics of PP-C remobilization in response to Arctic warming.

Particulate Organic Matter Dynamics in a Permafrost Headwater Stream and the Kolyma River Mainstem

“…Ice‐complex deposit permafrost soils of Northeast Siberia store large amounts of OM from the Pleistocene (e.g., Zimov et al, ), resulting in an endmember 14 C value that is almost radiocarbon‐dead (Δ 14 C = −940 ± 84‰, Vonk et al, ). Recent terrestrial and aquatic vegetation, on the other hand, incorporates mostly modern carbon from the atmosphere, potentially even carrying elevated levels of 14 C affected by nuclear weapons testing during the 1960s and 1970s (Δ 14 C = +97 ± 125‰, Wild et al, ).…”

“…Dual‐carbon isotope signatures of potential POM sources (i.e., endmembers), comprising recent vegetation, active layer soil OM, Holocene, and Pleistocene permafrost soil OM, have been compiled in a recent study (Wild et al, ; Figure c). Their Δ 14 C values range from +97 ± 125‰ for recently formed vegetation to −955 ± 66‰ Pleistocene permafrost deposits along river banks and coastlines and thus cover the entire range of the samples from Kolyma and Y3.…”

“…Corresponding δ 13 C values, however, span only from −27.7 ± 1.3‰ for recent vegetation to −26 ± 3‰ for Holocene permafrost deposits, while the majority of the Kolyma‐ and Y3‐POM samples are more depleted than these endmembers. This may reflect aquatic production, which is fueled by terrigenous OM and results in lower δ 13 C values through additional fractionation effects (Finlay, ; Wild et al, ). This assumption appears to be supported by biomarker data (see Figure b and discussion there).…”

“…Suspended particulate OM (POM) is operationally defined as the OM fraction that is collected on a filter (common cut‐off 0.7 μm pore size), while the dissolved OM (DOM) fraction passes through the filter. In arctic rivers, POM is on average older than DOM, and may thus be used as a tracer for OM originating from a permafrost thaw source (e.g., Guo et al, ; Wild et al, ). Ancient DOM released from ice‐rich Yedoma deposits (Pleistocene ice‐ and OM‐rich loess deposits, Zimov et al, ) has been shown to readily degrade upon thaw (Spencer et al, ; Vonk et al, ).…”

Seasonal source variability of carbonaceous aerosols at the Rwanda Climate Observatory

“…However, the level of scientific understanding of the overall health and climate impact of aerosols is still low, owing to the complex aerosol life cycle during which emissions, transformations, and sinks are associated with large uncertainties, in particular given their vast physical and chemical complexity. A major limiting factor regarding improving our understanding of these effects in SSA is the limited number of in situ observations (Williams et al, 2007;Cais et al, 2011;Kulmala, 2018;López-Ballesteros et al, 2018).…”