Molecular‐Multiproxy Assessment of Land‐Derived Organic Matter Degradation Over Extensive Scales of the East Siberian Arctic Shelf Seas

Abstract

Global warming triggers permafrost thaw, which increases the release of terrigenous organic matter (terr-OM) to the Arctic Ocean by coastal erosion and rivers. Terrigenous OM degradation in the Arctic Ocean contributes to greenhouse gas emissions and severe ocean acidification, yet the vulnerability of different terr-OM components is poorly resolved. Here, terr-OM degradation dynamics are studied with unprecedented spatial coverage over the World's largest shelf sea system-the East Siberian Arctic Shelf (ESAS), using a multi-proxy molecular biomarker approach. Mineral-surface-area-normalized concentrations of terr-OM compounds in surface sediments decreases offshore. Differences between terr-OM compound classes (lignin phenols, high-molecular weight [HMW] n-alkanes, n-alkanoic acids and n-alkanols, sterols, 3,5-dihydroxybenzoic acids, cutin acids) reflect contrasting influence of sources, propensity to microbial degradation and association with sedimenting particles, with lignin phenols disappearing 3-times faster than total terr-OM, and twice faster than other biomarkers. Molecular degradation proxies support substantial terr-OM degradation across the ESAS, with clearest trends shown by: 3,5-dihydroxybenzoic acid/vanillyl phenol ratios, acid-to-aldehyde ratios of syringyl and vanillyl phenols, Carbon Preference Indices of HMW n-alkyl compounds and sitostanol/β-sitosterol. The combination of terr-OM biomarker data with δ 13 C/Δ 14 C-based source apportionment indicates that the more degraded state of lignin is influenced by the relative contribution of river-transported terr-OM from surface soils, while HMW n-alkanoic acids and stigmasterol are influenced by erosion-derived terr-OM from Ice Complex deposits. Our findings demonstrate differences in vulnerability to degradation between contrasting terr-OM pools, and underscore the need to consider molecular properties for understanding and modeling of large-scale biogeochemical processes of the permafrost carbon-climate feedback.Plain Language Summary Permafrost soils hold a huge amount of terrigenous organic matter (terr-OM) that is increasingly decomposed to greenhouse gases in a warming climate, possibly accelerating climate change. As part of this change, permafrost thaw is expected to also enhance the transport of terr-OM to the Arctic Ocean, through intensified coastal erosion and river transport. The translocated decomposition of terr-OM in the Arctic Ocean contributes to greenhouse gas emissions and strong ocean acidification, but the vulnerability of different terr-OM components to decomposition in the Arctic Ocean is poorly understood. We here investigate terr-OM degradation dynamics on the World's largest shelf sea system, the East Siberian Arctic Shelf, using a multi-proxy molecular approach to marine surface sediments. A range of terr-OM-specific biomarkers (e.g., lignin, high-molecular weight lipids), and molecular terr-OM degradation proxies were compared, and revealed substantial differences in sources, transport and degradation of different terr-OM...

The Role of Coastal Yedoma Deposits and Continental Shelf Sediments in the Arctic Ocean Silicon Cycle

“…Sediment δ 13 C followed previously reported trends and became less depleted further from river mouths, indicative of a shift from terrestrial to marine organic C sources (Bröder et al, 2018(Bröder et al, , 2019Martens et al, 2021Martens et al, , 2022Matsubara et al, 2022). However, we found no relationships between sediment ASi or TOC and distance from river mouths, possibly due to relatively low concentrations of both, indicative of rapid remineralization of organic material loaded on sediments in this region (Anderson et al, 2011).…”

“…Coastal erosion in this area is driven by the high frequency of Yedoma deposits along the coasts, that is, late‐Pleistocene permafrost deposits that are vulnerable to collapse due to their high ice content. Coastal erosion of Yedoma deposits is highest near the Buor Kaya Bay (Günther et al., 2013; Schirrmeister et al., 2017; Strauss et al., 2015), the Dmitri Laptev Strait, and the New Siberian Islands (Schirrmeister, Kunitsky, et al., 2011) and leads to significant loading of organic matter nearshore in the Laptev and East Siberian sea (Bröder et al., 2016; Matsubara et al., 2022).…”

“…Coastal erosion of Yedoma deposits is highest near the Buor Kaya Bay (Günther et al, 2013;Schirrmeister et al, 2017;Strauss et al, 2015), the Dmitri Laptev Strait, and the New Siberian Islands (Schirrmeister, Kunitsky, et al, 2011) and leads to significant loading of organic matter nearshore in the Laptev and East Siberian sea (Bröder et al, 2016;Matsubara et al, 2022).…”

Dynamics of the Seawater Carbonate System in the East Siberian Sea: The Diversity of Driving Forces

“…Therefore, the contribution of terrestrial organic carbon to particulate organic carbon reached 99% in the W-ESS, but accounts for as low as 1% in the E-ESS [38]. The waters of Pacific origin that also carried a labile OM fraction [38] were additionally modified on the ESS shelf owing to the interaction with the bottom sediments containing fresh autochthonous OM as well as relatively labile (compared to the western province) allochthonous OM [61]. Matsubara et al [61] showed that river-transported terrestrial OM from surface soils, which is less resistant to degradation compared to the erosion-derived terrestrial OM from ice complex deposits of the seashore and riverbank [29,30,62], prevails in the terrigenous component of the E-ESS bottom sediments.…”

“…The waters of Pacific origin that also carried a labile OM fraction [38] were additionally modified on the ESS shelf owing to the interaction with the bottom sediments containing fresh autochthonous OM as well as relatively labile (compared to the western province) allochthonous OM [61]. Matsubara et al [61] showed that river-transported terrestrial OM from surface soils, which is less resistant to degradation compared to the erosion-derived terrestrial OM from ice complex deposits of the seashore and riverbank [29,30,62], prevails in the terrigenous component of the E-ESS bottom sediments. For example, the degradation rate in the bottom sediments of lignin phenols coming to the shelf, mainly from seasonally melted soils, is three times as high as the degradation rate of the total sedimentary terrigenous OM pool [61].…”