@article {2474, title = {Erosion of modern terrestrial organic matter as a major component of sediments in fjords}, journal = {Geophysical Research Letters}, volume = {442824441945245112168105110293225215662639493436151675187268234320723424507431438414191121427211539259}, year = {2017}, month = {Apr-02-2018}, pages = {1457 - 1465}, abstract = {Fjords have recently been recognized as {\textquotedblleft}hot spots{\textquotedblright} of carbon burial. In this study, we investigated organic carbon (OC) and biomarker radiocarbon values in fjord sediments from New Zealand. Our results showed that OC was mostly modern with the most aged OC in middle reaches of fjords, likely related to hydrodynamic sorting and inputs along adjacent slopes. Radiocarbon ages of sedimentary OC increased from north-to-south, consistent with the Fiordland regional gradients of lower fjord slopes and less rainfall. Our biomarker results suggested that lignin and long-chain fatty acids were preferentially linked with fresh terrestrial debris and degraded soil, respectively, likely due to their chemical and physical properties. Finally, we propose that fjords are a significant sink of modern OC, in contrast to large lowland coastal systems as a major sink of preaged OC. Overall, this study indicated that radiocarbon techniques are critical in investigating carbon dynamics in coastal systems.}, doi = {10.1002/2016GL072260}, url = {http://doi.wiley.com/10.1002/2016GL072260http://onlinelibrary.wiley.com/wol1/doi/10.1002/2016GL072260/fullpdfhttps://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1002\%2F2016GL072260}, author = {Cui, Xingqian and Bianchi, Thomas S. and Savage, Candida} } @article {2697, title = {The experimental flow to the Colorado River delta: Effects on carbon mobilization in a dry watercourse}, journal = {Journal of Geophysical Research: Biogeosciences}, volume = {122}, year = {2017}, month = {Jan-03-2017}, pages = {607 - 627}, abstract = {Here we report on the effects of an experimental flood on the carbon cycling dynamics in the dry watercourse of the Colorado River in Mexico. We observed post-flood differences in the degree of decay, age, and concentration of dissolved organic carbon (DOC), as well as dissolved CH4 and CO2 concentrations throughout the study site. Our results indicate that this flooded waterway was a limited source of CH4 and CO2 to the atmosphere during the event and that DOC age increased with time of flooding. Based on our findings, we suggest that the interplay between storage and mobilization of carbon and greenhouse gases in arid and semiarid regions is potentially sensitive to changing climate conditions, particularly hydrologic variability. Changes in the radiocarbon age of DOC throughout the flooding event suggest that organic matter (OM) that had been stored for long periods (e.g., millennial) was mobilized by the flooding event along with CO2. The OM residing in the dry riverbed that was mobilized into floodwaters had a signature reflective of degraded vascular plant OM and microbial biomass. Whether this microbial OM was living or dead, our findings support previous work in soils and natural waters showing that microbial OM can remain stable and stored in ecosystems for long time periods. As human appropriation of water resources continues to increase, the episodic drying and rewetting of once natural riverbeds and deltas may fundamentally alter the processing and storage of carbon in such systems.}, keywords = {carbon cycling, Colorado River, dry watercourse, flooding, greenhouse gases, mobilization}, doi = {10.1002/2016JG003555}, url = {https://agupubs.onlinelibrary.wiley.com/doi/10.1002/2016JG003555}, author = {Bianchi, Thomas S. and Butman, David and Raymond, Peter A. and Ward, Nicholas D. and Kates, Rory J. S. and Flessa, Karl W. and Zamora, Hector and Arellano, Ana R. and Ramirez, Jorge and Rodriguez, Eliana} } @article {2698, title = {Permafrost Organic Carbon Mobilization From the Watershed to the Colville River Delta: Evidence From 14C Ramped Pyrolysis and Lignin Biomarkers}, journal = {Geophysical Research Letters}, volume = {44}, year = {2017}, month = {Apr-11-2019}, pages = {11,491 - 11,500}, abstract = {The deposition of terrestrial-derived permafrost particulate organic carbon (POC) has been recorded in major Arctic river deltas. However, associated transport pathways of permafrost POC from the watershed to the coast have not been well constrained. Here we utilized a combination of ramped pyrolysis-oxidation radiocarbon analysis (RPO 14C) along with lignin biomarkers, to track the linkages between soils and river and delta sediments. Surface and deep soils showed distinct RPO thermographs which may be related to degradation and organo-mineral interaction. Soil material in the bed load of the river channel was mostly derived from deep old permafrost. Both surface and deep soils were transported and deposited to the coast. Hydrodynamic sorting and barrier island protection played important roles in terrestrial-derived permafrost POC deposition near the coast. On a large scale, ice processes (e.g., ice gauging and strudel scour) and ocean currents controlled the transport and distribution of permafrost POC on the Beaufort Shelf.}, keywords = {Arctic, carbon cycling, Colville River, Lignin, permafrost, pyrolysis}, issn = {0094-8276}, doi = {10.1002/grl.v44.2210.1002/2017GL075543}, url = {https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/2017GL075543}, author = {Zhang, Xiaowen and Bianchi, Thomas S. and Cui, Xingqian and Rosenheim, Brad E. and Ping, Chien-Lu and Hanna, Andrea J. M. and Kanevskiy, Mikhail and Schreiner, Kathryn M. and Allison, Mead A.} } @article {2457, title = {Comparison of eastern tropical Pacific TEX 86 and Globigerinoides ruber Mg/Ca derived sea surface temperatures: Insights from the Holocene and Last Glacial Maximum}, journal = {Earth and Planetary Science Letters}, volume = {434}, year = {2016}, month = {Jan-01-2016}, pages = {320 - 332}, abstract = {The use of the TEX86TEX86 temperature proxy has thus far come to differing results as to whether TEX86TEX86 temperatures are representative of surface or subsurface conditions. In addition, although TEX86TEX86 temperatures might reflect sea surface temperatures based on core-top (Holocene) values, this relationship might not hold further back in time. Here, we investigate the TEX86TEX86 temperature proxy by comparing TEX86TEX86 temperatures to Mg/Ca temperatures of multiple species of planktonic foraminifera for two sites in the eastern tropical Pacific (on the Cocos and Carnegie Ridges) across the Holocene and Last Glacial Maximum. Core-top and Holocene View the MathML sourceTEX86H temperatures at both study regions agree well, within error, with the Mg/Ca temperatures of Globigerinoides ruber , a surface dwelling planktonic foraminifera. However, during the Last Glacial Maximum, View the MathML sourceTEX86H temperatures are more representative of upper thermocline temperatures, and are offset from G. ruber Mg/Ca temperatures by 5.8 {\textdegree}C and 2.9 {\textdegree}C on the Cocos Ridge and Carnegie Ridge, respectively. This offset between proxies cannot be reconciled by using different TEX86TEX86 temperature calibrations, and instead, we suggest that the offset is due to a deeper export depth of GDGTs at the LGM. We also compare the degree of glacial cooling at both sites based on both temperature proxies, and find that View the MathML sourceTEX86H temperatures greatly overestimate glacial cooling, especially on the Cocos Ridge. This study has important implications for applying the TEX86TEX86 paleothermometer in the eastern tropical Pacific.}, keywords = {Foraminifera, Holocene, LGM; Pacific Ocean, Mg/Ca, TEX86TEX86}, issn = {0012821X}, doi = {10.1016/j.epsl.2015.11.050}, url = {http://linkinghub.elsevier.com/retrieve/pii/S0012821X15007542http://api.elsevier.com/content/article/PII:S0012821X15007542?httpAccept=text/xmlhttp://api.elsevier.com/content/article/PII:S0012821X15007542?httpAccept=text/plain}, author = {Hertzberg, Jennifer E. and Schmidt, Matthew W. and Bianchi, Thomas S. and Smith, Richard W. and Shields, Michael R. and Marcantonio, Franco} } @article {59, title = {Late Holocene sedimentation in a high Arctic coastal setting: Simpson Lagoon and Colville Delta, Alaska}, journal = {Continental Shelf Research}, volume = {74}, year = {2014}, pages = {11-24}, abstract = {Arctic coastal environments near major river outfalls, like Simpson Lagoon, Alaska and the adjacent Colville River Delta, potentially contain high-resolution sediment records useful in elucidating late Holocene Arctic sediment transport pathways and coupled terrestrial-ocean evidence of paleoclimate variability. This study utilizes a multi-tracer geochronology approach (137Cs, 239,240Pu, and 14C) tailored for high-latitude environments to determine the age models for cores collected from Simpson Lagoon, and to date seismic boundaries in shallow acoustic reflection data (CHIRP) to examine late Holocene infill patterns. Modern (~100 y) sediment accumulation rates range from 5 m of late Holocene interbedded sediments, likely derived primarily from the Colville River, with onset of accumulation occurring prior to ~3500 y BP. A paleo-high in central Simpson Lagoon, separating the two depocenters, was subaerially exposed prior to ~600 y BP. The millimeters-per-year sedimentation rates across the lagoon, coupled with the undisturbed, interbedded sediment record, indicate that these settings hold great potential to develop new Arctic paleoenvironmental records.}, issn = {0278-4343}, doi = {10.1016/j.csr.2013.11.026}, url = {http://www.sciencedirect.com/science/article/pii/S0278434313004056}, author = {Hanna, Andrea J. M. and Allison, Mead A. and Bianchi, Thomas S. and Marcantonio, Franco and Goff, John A.} } @article {2455, title = {A 28-ka history of sea surface temperature, primary productivity and planktonic community variability in the western Arabian Sea}, journal = {Paleoceanography}, volume = {22}, year = {2007}, month = {Jan-12-2007}, pages = {n/a - n/a}, abstract = {Uranium series radionuclides and organic biomarkers, which represent major groups of planktonic organisms, were measured in western Arabian Sea sediments that span the past 28 ka. Variability in the past strength of the southwest and northeast monsoons and its influence on primary productivity, sea surface temperature (SST), and planktonic community structure were investigated. The average alkenone-derived SST for the last glacial period was \~{}3{\textdegree}C lower than that measured for the Holocene. Prior to the deglacial, the lowest SSTs coincide with the highest measured fluxes of organic biomarkers, which represent primarily a planktonic suite of diatoms, coccolithophorids, dinoflagellates, and zooplankton. We propose that intensification of winter northeast monsoon winds during the last glacial period resulted in deep convective mixing, cold SSTs and enhanced primary productivity. In contrast, postdeglacial (<17 ka) SSTs are warmer during times in which biomarker fluxes are high. Associated with this transition is a planktonic community structure change, in which the ratio of the average cumulative flux of diatom biomarkers to the cumulative flux of coccolithophorid biomarkers is twice as high during the deglacial and Holocene than the average ratio during the last glacial period. We suggest that this temporal transition represents a shift from a winter northeast monsoon-dominated (pre-17 ka) to a summer southwest monsoon-dominated (post-17 ka) wind system.}, doi = {10.1029/2007PA001502}, url = {http://doi.wiley.com/10.1029/2007PA001502https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1029\%2F2007PA001502}, author = {Pourmand, Ali and Marcantonio, Franco and Bianchi, Thomas S. and Canuel, Elizabeth A. and Waterson, Elizabeth J.} }