Deconvolving the Fate of Carbon in Coastal Sediments

Abstract

Coastal oceans play a crucial role in the global carbon cycle, and are increasingly affected by anthropogenic forcing. Understanding carbon cycling in coastal environments is hindered by convoluted sources and myriad processes that vary over a range of spatial and temporal scales. In this study, we deconvolve the complex mosaic of organic carbon manifested in Chinese Marginal Sea (CMS) sediments using a novel numerical clustering algorithm based on 14 C and total OC content. Results reveal five regions that encompass geographically distinct depositional settings. Complementary statistical analyses reveal contrasting region-dependent controls on carbon dynamics and composition. Overall, clustering is shown to be highly effective in demarcating areas of distinct organic facies by disentangling intertwined organic geochemical patterns resulting from superimposed effects of OC provenance, reworking and deposition on a shelf region exhibiting pronounced spatial heterogeneity. This information will aid in constraining region-specific budgets of carbon burial and carbon cycle processes. Plain Language SummaryIn the context on ongoing climate change, it is crucial to understand how and where carbon is buried. Coastal oceans are very important areas for carbon burial globally, even though they only form a small part of the total ocean surface. These areas are very complex because there is carbon coming both from the land as well as the sea. By understanding where thecarbon from land and where the carbon from the sea ends up, we can better estimate carbon storage. This paper presents a clustering approach which uses the large dataset of carbon age and concentration in the Chinese marginal seas. The clustering approach shows where the carbon from land goes and how it is buried, which areas lose carbon and which areas bury carbon. This approach could also be used in the future on other datasets such as the Arctic Seas.

Influence of Hydrodynamic Processes on the Fate of Sedimentary Organic Matter on Continental Margins

“…Marginal sea systems are highly dynamic and heterogeneous, with spatially diverse sediment transport processes as well as OC inputs that influence the distribution and composition of sedimentary OM (Bao et al, 2016;Bianchi et al, 2018). Significant gaps remain in our understanding of relationships between transport processes and OM characteristics; spatially comprehensive investigations are needed to deconvolve the intertwined influences of carbon sources and transport processes on the composition and distribution of OM accumulating in continental shelf sediments (e.g., van der Voort et al, 2018).…”

The Role of Reactive Iron in the Preservation of Terrestrial Organic Carbon in Estuarine Sediments

“…In fact, large inputs of Fe oxides, coupled with frequent physical reworking, result in rapid Fe + redox cycling (reduction and reoxidation) which is largely responsible for the loss of SOC in ECS mobile muds (Ma et al, ; Yao et al, ; Zhao et al, ; Zhu et al, ). Protracted sediment entrainment in cyclic resuspension‐deposition processes can change the properties of SOC, resulting in much lower Δ 14 C values (−274‰ to −682‰) on the ECS inner shelf than in suspended OC (−103‰ to −129‰) from the Changjiang Estuary and middle/outer ECS shelf (−174‰ to −280‰; Bao et al, ; Van der Voort et al, ; Wang et al, ). Redox oscillations and transient diagenesis, induced by resuspension in mobile muds, effectively enhance remineralization of SOC; these muds are commonly known as suboxic fluidized‐bed reactors (Abril et al, ; Aller, , ; Audry et al, ).…”

Radiocarbonscapes of Sedimentary Organic Carbon in the East Asian Seas

“…For example, particulate OM from the Yellow River contains a higher percentage of aged OC (Tao et al, 2015(Tao et al, , 2016Yu et al, 2019); hence, the corresponding deltaic area shows lower 14 C content than elsewhere in the Bohai Sea (Bao et al, 2016; Figure 1A). Similarly, based on cluster analysis of combined sedimentary OC content and its 14 C concentration across the vast expanses of the East China Sea, the radiocarbonscape emanating from the Yangtze River reflects heavy terrestrial influence (Van der Voort et al, 2018). An extreme case of provenance-dominated oceanic radiocarbonscape is exemplified by the export of 14 C-free OC of petrogenic origin (i.e., kerogen) (Kao and Liu, 1996;Hilton et al, 2008;Lin et al, 2020).…”