TY - JOUR T1 - Temporal constraints on lateral organic matter transport along a coastal mud belt JF - Organic Geochemistry Y1 - 2019 A1 - Bao, Rui A1 - Zhao, Meixun A1 - McNichol, Ann A1 - Galy, Valier A1 - McIntyre, Cameron A1 - Haghipour, Negar A1 - Eglinton, Timothy I. KW - 14C aging KW - Continental shelf seas KW - East China Sea KW - Mud belt KW - organic matter KW - Sediment resuspension AB - Constraints on timescales of lateral transport of sedimentary organic carbon (OC) over continental shelves and associated influences on the distribution and abundance of OC remain sparse. Preferential degradation of labile, young OC during lateral transport results in apparent “diagenetic aging” of OC. Additionally, sediment translocation can also result in “transport time-associated aging” of associated organic matter (OM) as a function of the lateral transport time (LTT). Here, we use a coupled thermal decomposition and radiocarbon (14C) approach to constrain timescales of lateral transport and concomitant loss of OC associated with different grain size fractions of sediments collected from two locations ∼275 km apart along a dispersal pathway on the inner shelf of the East China Sea. The 14C age contrasts between corresponding thermal fractions are used to distinguish these two components of sedimentary OM “aging”. To minimize interferences from hydrodynamic sorting and diagenetic aging of OC accompanying lateral transport, we assess 14C age differences of decomposition products from the most thermally-refractory OC components associated with specific grain size fractions between locations. We show that LTTs vary among different grain size fractions, and examine relationships between LTTs and sedimentary OC loss in order to assess the decomposition of OC as a consequence of lateral transport. We suggest that the decomposition of OC associated with protracted lateral transport exerts a strong influence on OC burial efficiency, with broad implications for carbon cycling over continental shelves. VL - 128 UR - https://www.sciencedirect.com/science/article/pii/S0146638019300075 ER - TY - JOUR T1 - Temporal deconvolution of vascular plant-derived fatty acids exported from terrestrial watersheds JF - Geochimica et Cosmochimica Acta Y1 - 2019 A1 - Vonk, Jorien E. A1 - Drenzek, Nicholas J. A1 - Hughen, Konrad A. A1 - Stanley, Rachel H.R. A1 - McIntyre, Cameron A1 - çon, Daniel B. A1 - Giosan, Liviu A1 - Southon, John R. A1 - Santos, Guaciara M. A1 - Druffel, Ellen R.M. A1 - Andersson, August A. A1 - öld, Martin A1 - Eglinton, Timothy I. KW - british-columbia KW - CARIACO BASIN KW - compound-specific radiocarbon KW - MACKENZIE DELTA KW - marine-sediments KW - odp leg 169s KW - saanich inlet KW - SANTA-MONICA BASIN KW - SOIL ORGANIC-MATTER KW - TROPICAL VEGETATION AB - Relatively little is known about the amount of time that lapses between the photosynthetic fixation of carbon by vascular land plants and its incorporation into the marine sedimentary record, yet the dynamics of terrestrial carbon sequestration have important implications for the carbon cycle. Vascular plant carbon may encounter multiple potential intermediate storage pools and transport trajectories, and the age of vascular plant carbon accumulating in marine sediments will reflect these different pre-depositional histories. Here, we examine down-core C-14 profiles of higher plant leaf wax-derived fatty acids isolated from high fidelity sedimentary sequences spanning the so-called "bomb-spike", and encompassing a ca. 60-degree latitudinal gradient from tropical (Cariaco Basin), temperate (Saanich Inlet), and polar (Mackenzie Delta) watersheds to constrain integrated vascular plant carbon storage/transport times ("residence times"). Using a modeling framework, we find that, in addition to a "young" (conditionally defined as < 50 y) carbon pool, an old pool of compounds comprises 49 to 78 % of the fractional contribution of organic carbon (OC) and exhibits variable ages reflective of the environmental setting. For the Mackenzie Delta sediments, we find a mean age of the old pool of 28 ky (+/- 9.4, standard deviation), indicating extensive pre-aging in permafrost soils, whereas the old pools in Saanich Inlet and Cariaco Basin sediments are younger, 7.9 (+/- 5.0) and 2.4 (+/- 0.50) to 3.2 (+/- 0.54) ky, respectively, indicating less protracted storage in terrestrial reservoirs. The "young" pool showed clear annual contributions for Saanich Inlet and Mackenzie Delta sediments (comprising 24% and 16% of this pool, respectively), likely reflecting episodic transport of OC from steep hillside slopes surrounding Saanich Inlet and annual spring flood deposition in the Mackenzie Delta, respectively. Contributions of 5-10 year old OC to the Cariaco Basin show a short delay of OC inflow, potentially related to transport time to the offshore basin. Modeling results also indicate that the Mackenzie Delta has an influx of young but decadal material (20-30 years of age), pointing to the presence of an intermediate reservoir. Overall, these results show that a significant fraction of vascular plant C undergoes pre-aging in terrestrial reservoirs prior to accumulation in deltaic and marine sediments. The age distribution, reflecting both storage and transport times, likely depends on landscape-specific factors such as local topography, hydrographic characteristics, and mean annual temperature of the catchment, all of which affect the degree of soil buildup and preservation. We show that catchment-specific carbon residence times across landscapes can vary by an order of magnitude, with important implications both for carbon cycle studies and for the interpretation of molecular terrestrial paleoclimate records preserved in sedimentary sequences. VL - 244 UR - https://linkinghub.elsevier.com/retrieve/pii/S0016703718305702https://api.elsevier.com/content/article/PII:S0016703718305702?httpAccept=text/xmlhttps://api.elsevier.com/content/article/PII:S0016703718305702?httpAccept=text/plain ER - TY - JOUR T1 - Tectonically-triggered sediment and carbon export to the Hadal zone JF - Nature Communications Y1 - 2018 A1 - Bao, Rui A1 - Strasser, Michael A1 - McNichol, Ann P. A1 - Haghipour, Negar A1 - McIntyre, Cameron A1 - Wefer, Gerold A1 - Eglinton, Timothy I. AB - Sediments in deep ocean trenches may contain crucial information on past earthquake history and constitute important sites of carbon burial. Here we present 14C data on bulk organic carbon (OC) and its thermal decomposition fractions produced by ramped pyrolysis/oxidation for a core retrieved from the >7.5 km-deep Japan Trench. High-resolution 14C measurements, coupled with distinctive thermogram characteristics of OC, reveal hemipelagic sedimentation interrupted by episodic deposition of pre-aged OC in the trench. Low δ13C values and diverse 14C ages of thermal fractions imply that the latter material originates from the adjacent margin, and the co-occurrence of pre-aged OC with intervals corresponding to known earthquake events implies tectonically triggered, gravity-flow-driven supply. We show that 14C ages of thermal fractions can yield valuable chronological constraints on sedimentary sequences. Our findings shed new light on links between tectonically driven sedimentological processes and marine carbon cycling, with implications for carbon dynamics in hadal environments. VL - 9 UR - http://www.nature.com/articles/s41467-017-02504-1http://www.nature.com/articles/s41467-017-02504-1.pdfhttp://www.nature.com/articles/s41467-017-02504-1.pdfhttp://www.nature.com/articles/s41467-017-02504-1 IS - 1 ER - TY - JOUR T1 - Hydrologic controls on seasonal and inter-annual variability of Congo River particulate organic matter source and reservoir age JF - Chemical Geology Y1 - 2017 A1 - Hemingway, Jordon D. A1 - Schefuß, Enno A1 - Spencer, Robert G.M. A1 - Dinga, Bienvenu Jean A1 - Eglinton, Timothy I. A1 - McIntyre, Cameron A1 - Galy, Valier V. KW - biomarkers KW - Congo River KW - GDGTs KW - Particulate organic matter KW - radiocarbon AB - We present dissolved organic carbon (DOC) concentrations, particulate organic matter (POM) composition (δ13C, δ15N, ∆14C, N/C), and particulate glycerol dialkyl glycerol tetraether (GDGT) distributions from a 34-month time-series near the mouth of the Congo River. An end-member mixing model using δ13C and N/C indicates that exported POM is consistently dominated by C3 rainforest soil sources, with increasing contribution from C3 vegetation and decreasing contribution from phytoplankton at high discharge. Large C4 inputs are never observed despite covering ≈ 13% of the catchment. Low and variable ∆14C values during 2011 [annual mean = (− 148 ± 82) ‰], when discharge from left-bank tributaries located in the southern hemisphere reached record lows, likely reflect a bias toward pre-aged POM derived from the Cuvette Congolaise swamp forest. In contrast, ∆14C values were stable near − 50‰ between January and June 2013, when left-bank discharge was highest. We suggest that headwater POM is replaced and/or diluted by C3 vegetation and pre-aged soils during transit through the Cuvette Congolaise, whereas left-bank tributaries export significantly less pre-aged material. GDGT distributions provide further evidence for seasonal and inter-annual variability in soil provenance. The cyclization of branched tetraethers and the GDGT-0 to crenarchaeol ratio are positively correlated with discharge (r ≥ 0.70; p-value ≤ 4.3 × 10− 5) due to the incorporation of swamp-forest soils when discharge from right-bank tributaries located in the northern hemisphere is high. Both metrics reach record lows during 2013, supporting our interpretation of increased left-bank contribution at this time. We conclude that hydrologic variability is a major control of POM provenance in the Congo River Basin and that tropical wetlands can be a significant POM source despite their small geographic coverage. VL - 466 UR - https://linkinghub.elsevier.com/retrieve/pii/S0009254117303935 ER -