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The sedimentary total organic carbon (TOC) in mangrove ecosystems plays an essential role in the global carbon storage. Nevertheless, little information is available about the pattern of TOC in sediments varying from bare and flat to those beneath mangroves. To find out the roles of new-developing mangroves in sedimentary TOC accumulation, a serials of sediment samples were collected from the creek mudflat zone (CMZ) through the fringe mangrove zone (FMZ) to the interior mangrove zone (IMZ) in young mangrove system of Nanliu River Delta in China. Sediment compositions, TOC, total nitrogen (TN), molar C/N ratios, and carbon stable isotopes (δ13C) were analyzed to examine the accumulation processes. The results revealed the distinct differences in the sedimentary TOC values, with an obvious increasing trend from the CMZ and FMZ to the IMZ. We quantified that terrestrials, marine-derived and mangrove-derived sources contributed 39.2-74.1%, 24.7-63.1% and 0.9-6.9%, respectively, to the sedimentary TOC in the mangrove ecosystems. The organic carbon accumulation rates ranged from 2.59 to 269.60 g•m-2•a-1, with values of 8.77 ± 19.87, 24.78 ± 12.53, 167.19 ± 57.79 g•m-2•a-1 for CMZ, FMZ and IMZ. Our work highlights information showing that young mangrove forests of the tropical delta have important potential for carbon storage. [ABSTRACT FROM AUTHOR]

We investigated spatial and temporal changes in accumulation rate and source of organic carbon on a gradient along the Lysefjord and the more coastal Høgsfjord, Western Norway. This was achieved through analysis of total organic carbon and nitrogen content of sediment cores, which were radiometrically dated to the early 19th and 20th centuries for the Høgsfjord and Lysefjord, respectively. Benthic foraminifera (protists) were utilized to determine changes in organic carbon supply and Ecological Quality Status (EcoQS) by their accumulation rate (benthic foraminiferal accumulation rate (BFAR)), assemblage composition, species diversity, individual species responses and the composition of stable carbon isotopes of the tests (shells) of Cassidulina laevigata, Hyalinea balthica and Melonis barleeanus. Organic carbon accumulation rates were greatest closest to the river Lyse at the head of the Lysefjord (83-171 g C m-2 yr-1). The organic carbon at the head of the fjord is mainly terrestrial in origin, and this terrestrial influence becomes progressively less seaward. The d13C in H. balthica tests as well as the benthic foraminiferal assemblage composition also showed a clear fjord to coast gradient. Organic carbon accumulation rates were lower and less variable at the seaward study sites (13-61 g C m-2 yr-1). We observe no temporal trend in organic carbon, carbon isotopes, EcoQS or foraminiferal assemblage composition in the Lysefjord. In contrast, in the Høgsfjord, there seems to have been an increase in organic carbon accumulation rates during the 1940s. Subsequent accumulation rates are stable. The foraminiferal assemblages in the surface sediments reflect a recent transition from good/moderate to moderate/bad EcoQS. [ABSTRACT FROM AUTHOR]

Organic carbon (OC) accumulation and storage in lake sediments is considered to be an important component of global C cycling. However, the storage of OC in Chinese lakes is not well constrained, and its role in future global change processes has rarely been considered. Here, we analyzed the OC burial and its correlation with lake catchment properties in Chinese lakes that have experienced heavy anthropogenic influence over the last ∼150 years. We compiled OC data from sixty-four lakes from the literature. The results showed that organic carbon accumulation rates (OCARs) in Chinese lakes ranged between 1.4 and 259.5 g m −2 yr −1 , with a mean of 22 g m -2 yr −1 over the past ∼150 years, consistent with the global estimate of the carbon burial rate in lake sediments (11–26 g m −2 yr −1 ). Extrapolated to the whole country, a total of 269.5 Tg OC (ranging from 138.9 to 690.4 Tg C) was stored in Chinese lakes over the past 150 years. Spearman analysis revealed that OCARs strongly depended on lake and catchment size, precipitation, temperature, longitude, altitude and anthropogenic activities. Moreover, OCARs showed an increasing trend, especially after the 1950s, coinciding with land use changes and lake nutrient level shifts. [ABSTRACT FROM AUTHOR]

Abstract: Changes in marine primary productivity following the latest Permian mass extinction (LPME) have been debated at length, with little resolution to date owing to a paucity of quantitative data. Herein, we report total organic carbon (TOC) concentrations and organic carbon accumulation rates (OCAR) for 40 Permian–Triassic boundary (PTB) sections with a near-global distribution and consider their implications for changes in marine productivity during the boundary crisis. Many sections in South China exhibit abrupt declines in TOC and OCAR from the Changhsingian (latest Permian) to the Griesbachian (earliest Triassic), a pattern not observed for sections in other regions. This pattern cannot be explained through secular changes in sedimentation rates, sedimentary facies, or redox conditions, all of which would have favored higher (rather than lower) TOCs and OCARs during the Griesbachian. Further, back-calculation of OC fluxes demonstrate that this pattern cannot be attributed to diagenetic loss of OC in the sediment or, possibly, to OC remineralization in the water column. The most likely explanation is a collapse of marine primary productivity across the South China region concurrently with the LPME and continuing for an extended interval into the Early Triassic. The productivity crash as well as the coeval decimation of benthic marine fauna coincided with deposition of the “boundary clay” at Meishan D, suggesting that both events were related to a large explosive volcanic eruption of uncertain provenance. In other PTB sections having a wide geographic distribution, OCARs increased on average by a factor of ~4× across the LPME, largely owing to a concurrent increase in bulk accumulation rates (BARs). Radiometric dating uncertainties can account at most for only a fraction of the secular change in BARs, which are likely to reflect an increase in subaerial weathering rates and elevated fluxes of detrital material to Early Triassic marine systems. Intensification of chemical weathering relative to physical weathering may have increased the flux of nutrients to the Early Triassic ocean, enhancing marine productivity and contributing to the widespread development of marine dysoxia–anoxia. [Copyright &y& Elsevier]