Clay mineral continental amplifier for marine carbon sequestration in a greenhouse ocean

Abstract

The majority of carbon sequestration at the Earth’s surface occurs in marine continental margin settings within fine-grained sediments whose mineral properties are a function of continental climatic conditions. We report very high mineral surface area (MSA) values of 300 and 570 m 2 g in Late Cretaceous black shales from Ocean Drilling Program site 959 of the Deep Ivorian Basin that vary on subcentennial time scales corresponding with abrupt increases from approximately 3 to approximately 18% total organic carbon (TOC). The observed MSA changes with TOC across multiple scales of variability and on a sample-by-sample basis (centimeter scale), provides a rigorous test of a hypothesized influence on organic carbon burial by detrital clay mineral controlled MSA. Changes in TOC also correspond with geochemical and sedimentological evidence for water column anoxia. Bioturbated intervals show a lower organic carbon loading on mineral surface area of 0.1 mg-OC m -2 when compared to 0.4 mg-OC m -2 for laminated and sulfidic sediments. Although either anoxia or mineral surface protection may be capable of producing TOC of < 5%, when brought together they produced the very high TOC (10–18%) apparent in these sediments. This nonlinear response in carbon burial resulted from minor precession-driven changes of continental climate influencing clay mineral properties and runoff from the African continent. This study identifies a previously unrecognized land–sea connection among continental weathering, clay mineral production, and anoxia and a nonlinear effect on marine carbon sequestration during the Coniacian-Santonian Oceanic Anoxic Event 3 in the tropical eastern Atlantic.

Small-scaled lateral variations of an organic-rich formation in a ramp-type depositional environment (the Late Jurassic of the Boulonnais, France): impact of the clastic supply

“…In clay-rich sediments, OM abundance is commonly correlated with smectite abundance. This correlation suggests that the expandable internal surface of smectite (i.e., interlayer region) can sequester large amounts of molecular-scaled OM (Keil and Mayer, 2014; Kennedy and Wagner, 2011; however, see discussion in Mahamat Ahmat et al, 2016). Indeed, it has been suggested that enhanced organic matter preservation in sediments is largely due to increased smectite abundance in sedimentary record through geological time (Kennedy et al, 2006): organic matter, once associated with smectite-rich sediments, would be physically protected against microbial oxidation (see details in Keil and Mayer, 2014;Mahamat Ahmat et al, 2016Zhang et al, 2014).…”

"OAE 3" – regional Atlantic organic carbon burial during the Coniacian–Santonian

“…Wagner et al (2004) and Beckmann et al (2005b) concluded that the chemical boundary conditions in the ocean have been as extreme as during OAE 2, but much more restricted in extent and duration, resulting in only brief intervals of lower photic zone euxinia. In addition, clay mineral composition, especially the presence of smectite, may have influenced the preservation of organic matter (Kennedy and Wagner, 2011).…”

Baseline biogeochemical data from Australia's continental margin links seabed sediments to water column characteristics

“…7a; Table 7). Recent studies have shown that clays can even bind reactive OM (including chlorins; Niggemann et al 2007) and shield it from degradation under anaerobic conditions (Kennedy and Wagner 2011;Lalonde et al 2012;Barber et al 2014). The WTS TSM results are a case in point because these rates varied inversely with Fe (Fig.…”