Description: Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution September 1986

Description: A study of the remineralization of organic carbon was conducted in the organic-rich sediments of Buzzards Bay, MA. Major processes affecting the carbon chemistry in sediments are reflected by changes in the stable carbon isotope ratios of dissolved inorganic carbon (ΣCO2) in sediment pore water. Six cores were collected seasonally over a period of two years. The following species were measured in the pore waters: ΣCO2, δ13C-ΣCO2, PO4, ΣH2S, Alk, DOC, and Ca. Measurements of pore water collected seasonally show large gradients with depth, which are larger in summer than in winter. The δ13C (PDB) of ΣCO2 varies from 1.3 o/oo in the bottom water to approximately -10 o/oo at 30 cm. During all seasons, there was a trend towards more negative values with depth in the upper 8 cm due to the remineralization of organic matter. There was a trend toward more positive values below 8 cm, most likely due to biological irrigation of sediments with bottom water. Below 16-20 cm, a negative gradient was re-established which indicates a return to remineralization as the main process affecting pore water chemistry. Using the ΣCO2 depth profile, it was estimated that 67-85 gC/m2 are oxidized annually and 5 gC/m2-yr are buried. The amount of carbon oxidized represented remineralization occurring within the sediments. This estimate indicated that approximately 20% of the annual primary productivity reached the sediments. The calculated remineralization rates varied seasonally with the high of 7.5 x 10-9 mol/L-sec observed in August 84 and the low (0.6 x 10-9) in December 83. The calculated remineralization rates were dependent on the amount of irrigation in the sediments; if the irrigation parameter is known to ±20%, then the remineralization rates are known to this certainty also. The amount of irrigation in the sediments was estimated using the results of a seasonal study of 222Rn/22R6a disequilibria at the same study site (Martin, 1985). Estimates of the annual remineralization in the sediments using solid-phase data indicated that the solid-phase profiles were not at steady-state concentrations. The isotopic signature of ΣCO2 was used as an indicator of the processes affecting ΣCO2 in pore water. During every month, the oxidation of organic carbon to CO2 provided over half of the carbon added to the ΣCO2 pool. However, in every month, the δ13C of ΣCO2 added to the pore water in the surface sediments was greater than -15 o/oo, significantly greater than the δ13C of solid-phase organic carbon in the sediments (-20.6 o/oo). The δ13C of ΣCO2 added to the pore water in the sediments deeper than 7 cm was between -20 and -21 o/oo, similar to the organic carbon in the sediments. Possible explanations of the 13C-enrichment observed in the surface sediments were: a) significant dissolution of CaC0, (δ13C = + 1.7 o/oo), b) the addition of significant amounts of carbonate ion from bottom water to pore water, c) an isotopic difference between the carbon oxidized in the sediments and that remaining in the sediments. The effect of CaCO3 dissolution was quantified using measured dissolved Ca profiles and was not large enough to explain the observed isotopic enrichment. An additional source of 13C-enriched carbon was bottom water carbonate ion. In every month studied, there was a net flux of ΣCO2 from pore water to bottom water. The flux of pore water ΣCO2 to bottom water ranged from a minimum of 10 x 10-12 mol/cm2-sec in December 83 to a maximum of 50 x 10-12 mol/cm2-sec in August 84. However, because the pH of bottom water was about 8 while that of the pore water was less than or equal to 7, the relative proportion of the different species of inorganic carbon (H2CO*3, HCO-3, CO2-3 was very different in bottom water and pore water. Thus, while there was a net flux of ΣCO2 from pore water to bottom water, there was a flux of carbonate ion from bottom water to pore water. Because bottom water ΣCO2 was more 13C-enriched than pore water ΣCO2, the transfer of bottom water carbonate ion to pore water was a source of 13C-enriched carbon to the pore water. If the δ13C of CO2 added to the pore water from the oxidation of organic carbon was -20.6 o/oo, then the flux of Co2-3 from bottom water to pore water must have been 10-30% of the total flux of ΣCO2 from pore water to bottom water. This is consistent with the amount calculated from the observed gradient in carbonate ion. Laboratory experiments were conducted to determine whether the δ13C of CO2 produced from the oxidation of organic carbon (δ13C-OCox) was different from the δ13C of organic carbon in the sediments (δ13C-SOC). In the laboratory experiments, mud from the sampling site was incubated at a constant temperature. Three depths were studied (0-3, 10-15, and 20-25 cm). For the first study (IE1), sediment was stirred to homogenize it before packing into centrifuge tubes for incubation. For the second study (IE2), sediment was introduced directly into glass incubation tubes by subcoring. The second procedure greatly reduced disturbance to the sediment. Rates of CO2 production were calculated from the concentrations of ΣCO2 measured over up to 46 days. In both studies, the values of Rc in the deeper intervals were about 10% of the surface values. This was consistent with the field results, although the rates decreased more rapidly in the field. In all cases, the remineralization rates during the beginning of IE1 were much greater than those at the beginning of IE2. The sediment for IE1 was collected in February 84. The measured value of Rc in the surface sediment of the laboratory experiment (24 x 10-9 mol/L-sec) was much greater than the value of Rc observed in the field in another winter month, December 83 (.62 x 10-9). The sediment for IE2 was collected in August 85. The measured values of Rc in the surface sediment (6.6-12 x 10-9 mol/L-sec) were consistent with the field values from August 84 (7.5 x 10-9). The ΣCO2 results indicated that IE2 reproduced field conditions more accurately than IE1 did. The isotopic results from the experiments strongly suggested that δ13C-OCox in the surface sediments (-17.8 o/oo ± 1.9 o/oo) was greater than δ13C-SOC (-20.6 ± 0.2 o/oo). The magnitude of the observed fractionation was small enough that the observed values of δ13C-ΣCO2 in the pore waters could be explained by fractionated oxidation coupled with the diffusion of carbonate ion from bottom water to pore water. The observed fractionation was most likely due to the multiple sources of organic carbon to coastal sediments. A study of the natural levels of radiocarbon In these sediments indicated that the carbon preserved in the sediments is approximately 30% terrestrial while the rest is from phytoplankton.

Description: Financial support was provided by the Education Office of the Massachusetts Institute of Technology/Woods Hole Oceanographic Institution Joint Program In Oceanography, by an Andrew W. Mellon Foundation grant to the Coastal Research Center, WHOI, and by the National Science foundation under grant NSF OCE83-15412.

Description: Author Posting. © American Geophysical Union, 2013. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Paleoceanography 28 (2013): 227–236, doi:10.1002/palo.20023.

Description: During the past 40,000 years, global climate has moved into and out of a full glacial period, with the deglaciation marked by several millennial-scale rapid climate change events. Here we investigate the ecological response of deep-sea coral communities to both glaciation and these rapid climate change events. We find that the deep-sea coral populations of Desmophyllum dianthus in both the North Atlantic and the Tasmanian seamounts expand at times of rapid climate change. However, during the more stable Last Glacial Maximum, the coral population globally retreats to a more restricted depth range. Holocene populations show regional patterns that provide some insight into what causes these dramatic changes in population structure. The most important factors are likely responses to climatically driven changes in productivity, [O2] and [CO32–].

Description: 2013-11-30

Description: Author Posting. © American Geophysical Union, 2017. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 44 (2017): 2407–2415, doi:10.1002/2016GL071348.

Description: We present concentration and isotopic profiles of total, size, and polarity fractionated dissolved organic carbon (DOC) from Station ALOHA (A Long-term Oligotrophic Habitat Assessment), an oligotrophic site in the North Pacific Ocean. The data show that, between the surface and 3500 m, low molecular weight (LMW) hydrophilic DOC, LMW hydrophobic DOC, and high molecular weight (HMW) DOC constitute 22–33%, 45–52%, and 23–35% of DOC, respectively. LMW hydrophilic DOC is more isotopically depleted (δ13C of −23.9‰ to −31.5‰ and Δ14C of −304‰ to −795‰; mean age of 2850 to 15000 years) than the LMW hydrophobic DOC (δ13C of −22‰ to −23‰ and Δ14C of −270‰ to −568‰; 2470 to 6680 years) and HMW DOC (δ13C of ~−21‰ and Δ14C of −24‰ to −294‰; 135–2700 years). Our analyses suggest that a large fraction of DOC may be derived from allochthonous sources such as terrestrial and hydrothermal DOC and cycle on much longer time scales of 〉10000 years or enter the ocean as preaged carbon.

Description: NSF Cooperative Agreement for the Operation of a National Ocean Sciences Accelerator Mass Spectrometry Facility Grant Number: OCE-0753487; Gordon and Betty Moore Foundation Grant Numbers: GBMF3298, GBMF3794; Simons Foundation Grant Number: 329108

Description: 2017-09-07

Description: © The Author(s), 2021. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Schwestermann, T., Eglinton, T., I., Haghipour, N., McNichol, A. P., Ikehara, K., & Strasser, M. Event-dominated transport, provenance, and burial of organic carbon in the Japan Trench. Earth and Planetary Science Letters, 563, (2021): 116870, https://doi.org/10.1016/j.epsl.2021.116870.

Description: The delivery of organic carbon (OC) to the ocean's deepest trenches in the hadal zone is poorly understood, but may be important for the carbon cycle, contain crucial information on sediment provenance and event-related transport processes, and provide age constraints on stratigraphic sequences in this terminal sink. In this study, we systematically characterize bulk organic matter (OM) and OC signatures (TOC/TN, C, 14C), as well as those from application of serial thermal oxidation (ramped pyrolysis/oxidation) of sediment cores recovered along an entire hadal trench encompassing high stratigraphic resolution records spanning nearly 2000 years of deposition. We analyze two cores from the southern and northern Japan Trench, where submarine canyon systems link shelf with trench. We compare results with previously published data from the central Japan Trench, where canyon systems are absent. Our analyses enable refined dating of the stratigraphic record and indicate that event deposits arise from remobilization of relatively surficial sediment coupled with deeper erosion along turbidity current pathways in the southern and central study site and from canyon flushing events in the northern study site. Furthermore, our findings indicate deposition of predominantly marine OC within hemipelagic background sediment as well as associated with event deposits along the entire trench axis. This implies that canyon systems flanking the Japan Trench do not serve as a short-circuit for injection of terrestrial OC to the hadal zone, and that tropical cyclones are not major agents for sediment and carbon transfer into this trench system. These findings further support previous Japan Trench studies interpreting that event deposits originate from the landward trench slope and are earthquake-triggered. The very low terrestrial OC input into the Japan Trench can be explained by the significant distance between trench and hinterland (〉180 km), and the physiography of the canyons that do not connect to coast and river systems. We suggest that detailed analyzes of long sedimentary records are essential to understand OC transfer, deposition and burial in hadal trenches.

Description: The cruise was supported by the German Bundesministerium für Bildung und Forschung (BMBF 03G0251A) and the Deutsche Forschungsgemeinschaft. We acknowledge the Kochi core repository for additional surface samples of Japanese Cruises. Al Gagnon and Mary Lardie are thanked for their great help and technical assistance with the RPO instrument at NOSAMS. APM and the NOSAMS work were supported by the National Science Foundation Cooperative Agreement OCE-1239667. We appreciate the assistance from members of the Laboratory of Ion Beam Physics for the AMS measurements. Rui Bao is acknowledged for helpful discussions. A special thank you goes to Madalina Jaggi for her technical assistance for the C analysis of rinsed samples. This study was supported by the Austrian Science Fund (FWF P29678-N28) and a postgraduate grant by the International Association of Sedimentologists (IAS). We also acknowledge constructive support by the two reviewers (Jordon Hemingway and an anonymous). The authors declare no conflict of interests. The bathymetric data used in figure 1 is available at JAMSTEC-DARWIN database (http://www.godac.jamstec.go.jp/darwin/e) and Bundesamt für Seeschifffahrt und Hydrographie (https://www.bsh.de/DE/DATEN/Ozeanographisches_Datenzentrum/Vermessungsdaten/Nordpazifischer_Ozean/nordpazifik_node.html). Data of carbon analyses are displayed in the supporting information and also available from the corresponding author on reasonable request.

Description: Author Posting. © American Geophysical Union, 2021. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 48(2), (2021): e2020GL090287, https://doi.org/10.1029/2020GL090287.

Description: Salt marsh survival with sea‐level rise (SLR) increasingly relies on soil organic carbon (SOC) accumulation and preservation. Using a novel combination of geochemical approaches, we characterized fine SOC (≤1 mm) supporting marsh elevation maintenance. Overlaying thermal reactivity, source (δ13C), and age (F14C) information demonstrates several processes contributing to soil development: marsh grass production, redeposition of eroded material, and microbial reworking. Redeposition of old carbon, likely from creekbanks, represented ∼9%–17% of shallow SOC (≤26 cm). Soils stored marsh grass‐derived compounds with a range of reactivities that were reworked over centuries‐to‐millennia. Decomposition decreases SOC thermal reactivity throughout the soil column while the decades‐long disturbance of ponding accelerated this shift in surface horizons. Empirically derived estimates of SOC turnover based on geochemical composition spanned a wide range (640–9,951 years) and have the potential to inform predictions of marsh ecosystem evolution.

Description: This work was supported by NSF (OCE1233678) and NOAA (NA14OAR4170104 and NA14NOS4190145) grants to ACS, USGS Coastal & Marine Geology Program, and PIE‐LTER (NSF OCE1238212 and OCE1637630).

Description: 2021-06-11

Description: Author Posting. © American Geophysical Union, 2021. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 48(10), (2021): e2021GL092904, https://doi.org/10.1029/2021GL092904.

Description: We report marine dissolved organic carbon (DOC) concentrations, and DOC Δ14C and δ13C values in seawater collected from the Southern Ocean and eastern Pacific GOSHIP cruise P18 in 2016/2017. The aging of 14C in DOC in circumpolar deep water northward from 69°S to 20°N was similar to that measured in dissolved inorganic carbon in the same samples, indicating that the transport of deep waters northward is the primary control of 14C in DIC and DOC. Low DOC ∆14C and δ13C measurements between 1,200 and 3,400 m depth may be evidence of a source of DOC produced in nearby hydrothermal ridge systems (East Pacific Rise).

Description: This work was supported by NSF (OCE-1458941 and OCE-1951073 to Ellen R. M. Druffel), Fred Kavli Foundation, Keck Carbon Cycle AMS Laboratory, NSF/NOAA funded GO-SHIP Program, Canada Research Chairs program (to Brett D. Walker) and American Chemical Society Petroleum Research Fund New Directions (55,430-ND2 to Ellen R. M. Druffel and Brett D. Walker).

Description: 2021-11-24

Description: Author Posting. © American Geophysical Union, 2011. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Paleoceanography 26 (2011): PA4212, doi:10.1029/2011PA002174.

Description: Radiocarbon analyses of carbonate materials provide critical information for understanding the last glacial cycle, recent climate history and paleoceanography. Methods that reduce the time and cost of radiocarbon (14C) analysis are highly desirable for large sample sets and reconnaissance type studies. We have developed a method for rapid radiocarbon analysis of carbonates using a novel continuous-flow accelerator mass spectrometry (CFAMS) system. We analyzed a suite of deep-sea coral samples and compared the results with those obtained using a conventional AMS system. Measurement uncertainty is 〈0.02 Fm or 160 Ryr for a modern sample and the mean background was 37,800 Ryr. Radiocarbon values were repeatable and in good agreement with those from the conventional AMS system. Sample handling and preparation is relatively simple and the method offered a significant increase in speed and cost effectiveness. We applied the method to coral samples from the Eastern Pacific Ocean to obtain an age distribution and identify samples for further analysis. This paper is intended to update the paleoceanographic community on the status of this new method and demonstrate its feasibility as a choice for rapid and affordable radiocarbon analysis.

Description: This work was performed under NSF Cooperative Agreement OCE‐0753487, and also NSF‐OPP awards 0636787 and 0944474.