G02_01

Recent changes in ocean DI¹⁴C and implications for ocean circulation

Lester J¹,  Graven H¹, Khatiwala S², Key R³, McNichol A⁴

¹Imperial College London, London, United Kingdom, ²University of Oxford, Oxford, United Kingdom, ³Princeton University, , USA, ⁴Woods Hole Oceanographic Institution, , USA

Anthropogenic perturbations from fossil fuel burning and nuclear bomb testing have created a useful transient tracer of ocean circulation from measurements and modelling of dissolved ¹⁴C. The atmospheric ¹⁴C/C ratio (∆¹⁴C) peaked in the early 1960s and has decreased now to nearly pre-bomb levels. We present the first analysis of a new decade of observations from 2007 to 2016 which gives a comprehensive overview of the changes in ocean ∆¹⁴C since the 1990s. Surface ocean ∆¹⁴C decreased from the 2000s to 2010s at a similar rate as from the 1990s to 2000s (20‰/decade). In contrast to the period from the 1990s to the 2000s when denser waters gained ¹⁴C from the continued downward ventilation of bomb ¹⁴C, the extent of positive ∆¹⁴C between the 2000s to 2010s is much reduced. Comparison to two ocean models, the Community Earth System Model v2 (CESM2) and the Estimating the Climate and Circulation of the Ocean v4 (ECCOv4), shows evidence from ∆¹⁴C of decadal variability in the ventilation of Southern Ocean intermediate waters. The decrease in surface tracers from the 2000s to the 2010s is consistently stronger in observations than in these models, which may result from a reduction in vertical transport and mixing due to stratification.

G02_02

Evolution of radiocarbon in the North Atlantic during 1990s-2020 inferred from in-situ observations and model simulations

Castrillejo M^1,2,  Wacker L², Lester J¹, Graven H¹

¹Department of Physics, Imperial College London, London, United Kingdom, ²Laboratory of Ion Beam Physics, ETH-Zurich, Zurich, Switzerland

Radiocarbon in dissolved inorganic carbon (DI¹⁴C) is an important tracer of the carbon cycle and of the processes involved in its uptake and redistribution such as the ocean circulation. In this work, we assess the spatial and temporal evolution of DI¹⁴C in the North Atlantic to better understand the processes driving its distribution in the water column. To that end, we use new Δ¹⁴C observations and model simulations obtained from the ‘Nucleus for European Modelling of the Ocean’ model, as well as other model outputs from the Coupled Model Intercomparison Project Phase 6. We focus on GO-SHIP A25 and A05 lines that cover the subpolar gates to the Arctic Sea and subtropical latitudes, respectively. The region between the two oceanic sections hosts major water mass transformation processes involved in the shallow to deep sequestration of climate properties. We collected 400 seawater samples in 2018-2020 to determine DI¹⁴C using the new ETH-LIP analytical method. The new Δ¹⁴C data are used to infer the water masses involved in major radiocarbon changes since the 1990s by comparison to previously reported data available in GLODAPv2 and CCHDO. Then Δ¹⁴C observations are compared to model outputs sampled at nearby geographical locations to identify the strengths and weaknesses of the various models in simulating Δ14C. Some model simulations were conducted using different wind forcing and atmospheric Δ¹⁴C and CO₂ boundary conditions, therefore allowing us to evaluate the role of ocean circulation (stationary vs time variable) and bomb-¹⁴C in shaping the water column distribution of DI¹⁴C.

G02_04

Climate induced thermocline aging and ventilation south of the Azores front over the last 32,000 years

Beisel E¹,  Frank N¹, Lausecker M¹, Friedrich R², Therre S¹, Schröder-Ritzrau A¹, Butzin M³

¹Institute of Environmental Physics, Heidelberg University, Heidelberg, Germany, ²Curt-Engelhorn-Center Archaeometry, Mannheim, Germany, ³MARUM-Center for Marine Environmental Sciences, University of Bremen, Bremen, Germany

The radiocarbon analysis of uranium-thorium-dated cold-water corals (CWC) provides an excellent opportunity for qualitative reconstruction of past ocean circulation and water mass aging. While mid-depth water mass aging has been studied in the Atlantic Ocean, the evolution of the thermocline, tightly coupled to the atmosphere, remains largely unknown. Here we present a high-resolution dataset of combined ¹⁴C and U/Th data obtained from thermocline-dwelling CWCs at various sites in the Atlantic Ocean, directly compared to simulation results of the ¹⁴C-equipped Large Scale Geostrophic ocean general circulation model for the last 32 ka. CWCs off Angola provide the link between previous records from the equatorial Atlantic and Southern Ocean at greater depths, opening the possibility of a unified southern ¹⁴C signal in the Last Glacial Maximum (LGM). In contrast to the South Atlantic and to modeling results, North Atlantic CWCs show strong variations of a well-ventilated water mass near the Azores Front. Our results confirm previous observations of enhanced ventilation during the Bølling-Allerød interstadial (B/A), both shallower and deeper water layers exhibit the same radiocarbon signal. We conclude that the North and South Atlantic must be considered as separately acting reservoirs during the LGM, subsequent deglaciation and B/A. Respired carbon is stored in the dynamic mid-depth to deep Atlantic south of the Azores Front, while the subpolar North Atlantic waters remain a persistent well-ventilated ocean. Consequently, CWC-¹⁴C records from the South Atlantic and Southern Ocean provide the opportunity to determine a high-precision calibration curve for the radiocarbon content of the thermocline.

G02_05

Dissolved inorganic radiocarbon (DI¹⁴C) constraints on the biogeochemistry of marine dissolved organic matter (DOM)

Beaupre S¹,  Walker B², Druffel E³

¹School of Marine and Atmospheric Sciences, Stony Brook University, Stony Brook, United States, ²Department of Earth and Environmental Science, University of Ottawa, Ottawa, Canada, ³Department of Earth System Science, University of California Irvine, Irvine, United States

Marine dissolved organic matter (DOM) comprises all organic substances smaller than ~1 μm in seawater, with myriad physical properties, chemical reactivities, and biogeochemical lifetimes ranging from seconds to millennia.  Yet, global DOM concentrations and Δ¹⁴C values have remarkably predictable vertical distributions.  This may be due, in part, to DOM’s shared propensity for transport predominantly as solutes in moving currents.  Dissolved inorganic carbon (DIC) is both a tracer of ocean circulation and the ultimate source of most DOM carbon atoms (DOC). In this way, DIC Δ¹⁴C can also be used as a tool to constrain the biogeochemistry of DOM.  Analyses of the concentrations and fractionation-corrected ¹⁴C atom abundances (¹⁴C*) of DOC and DIC in contemporaneous profiles show consistency with the simple two-component mixing model and yet, simultaneously, reveal readily distinguishable depths exerting unique biogeochemical controls on DOM.  Variability in DOM concentrations and Δ¹⁴C values are dominated by net imbalances of in situ production and loss processes in the upper ocean, and by transport in the deeper ocean.  In addition, profiles of Z-scores of DOC and DIC concentrations and ¹⁴C abundances are identical throughout the deeper ocean at Station M in the eastern North Pacific, demonstrating that their biogeochemical sources and sinks are tightly coupled.  Collectively, DIC and conservation of mass may be useful tools for constraining the net reactivity of DOC in the deep sea, and for predicting and interpreting the global distribution of DOC Δ¹⁴C values.

G02_06

From the Southern Ocean to the Bering Sea: using radiocarbon to investigate dissolved organic carbon aging in the Pacific

Schlagenhauff S¹,  Bercovici S³, Grotheer H¹, Niggemann J³, Dittmar T³, Mollenhauer G^1,2

¹Alfred Wegener Institute, Bremerhaven, Germany, ²Marum Center for Marine Environmental Research and Department of Geosciences, Bremen, Germany, ³Institute for Chemistry and Biology of the Marine Environment, Oldenburg, Germany

Although marine dissolved organic matter (DOM) mainly forms from primary production at the surface, from sources with young Δ¹⁴C values, DOM from deep water samples is significantly older (4000-6300 years) and is either supplemented by an older source or persists on millennial timescales. Understanding how DOM endures in the ocean is key to predicting future DOM fluctuations. This project presents the Δ¹⁴C values of marine DOM from a Pacific transect collected on the RV Sonne in 2016 and 2017. The transect runs from 58.9°N along the 180°E longitudinal meridian to 52.1°S and provides an unprecedented dataset of Δ¹⁴C values of Pacific DOM. The samples were solid phase extracted and then isotopically analyzed on the MICADAS mini-carbon dating system. At the surface (upper 100 m), Δ¹⁴C values ranged from -302 ‰ in the subtropics to a more depleted value of -466 ‰ in the Southern Ocean, likely influenced by upwelling deep waters via the Antarctic Circumpolar Current. In deeper waters across the transect (3000 – 6000 m) the average Δ¹⁴C value was -548 ± 25 ‰ with a minimum value of -603 ‰ in the Bering Sea. The northern stations also revealed local areas of old DOM input to the ocean, likely from the Bering Sea. The Δ¹⁴C values generally align well with known water mass gradients across the Pacific and decrease with depth. These findings provide evidence for (1) a stable pool of aged DOM in the deep ocean and (2) localized processes adding autochthonous DOM to the system.

G02_07

Seawater dissolved organic carbon is rapidly removed in ultramafic hydrothermal systems and replaced by ¹⁴C-free labile organics

Lang S^1,2,  Benitez-Nelson B², Vincent M², Mau A², Simpson A³, Kock F³, Lysak D³, Soong R³

¹Woods Hole Oceanographic Institution, Woods Hole, United States, ²University of South Carolina, Columbia, United States, ³University of Toronto, Tronto, Canada

Large volumes of water have passed through the hot, rocky subseafloor throughout Earth’s history. This circulation of fluids through oceanic rocks is sufficiently large to impact the cycling of marine dissolved organic carbon (DOC) and to sequester oceanic carbon in the subseafloor over geologic timescales. While the fate of DOC in numerous mafic systems has been examined, there have been no previous reports on the less studied but still abundant ultramafic systems. We analyzed the concentration and composition of DOC from two systems hosted on ultramafic rocks, the Lost City hydrothermal field (30°N, Mid-Atlantic Ridge) and the Von Damm hydrothermal system (Mid-Cayman Rise). We show that per liter of seawater, more DOC is removed and at an >700 time faster rate than in mafic ridge flank systems. Simultaneously, labile ¹⁴C-free organics are exported from the system in concentrations up to 20 times higher than deep seawater. Early in Earth’s history, similar sequestration could have served to concentrate organic molecules for further prebiotic geochemical reactions, in the lead up to early life.

G02_08

Bridging marine biosphere and geosphere using compound-specific radiocarbon analysis of amino acids in fish muscle

Ishikawa N^1,2,  Blattmann T^1,2, Haghipour N², Ogawa N¹, Eglinton T², Ohkouchi N¹

¹Biogeochemistry Research Center, Yokosuka, Japan, ²Geological Institute, Zürich, Switzerland

The Earth surface is a dynamic environment of carbon exchange among different pools. Of these, the linkage between biosphere and geosphere is of key importance for understanding the global carbon cycle. In this presentation, we test a hypothesis that amino acid-specific radiocarbon signatures reflect the exchange of carbon between the marine biosphere and geosphere. To this end, we employed compound-specific radiocarbon analysis of amino acids in fish muscle using High-Performance Liquid Chromatography followed by Elemental-Analyzer Accelerator Mass Spectrometry, which allows us to downsize the final target compounds of > 20 μgC (Ishikawa et al. 2018; Haghipour et al. 2019). Most amino acids did not show Δ¹⁴C values significantly different from those of their expected carbon source (i.e., seawater dissolved inorganic carbon: DIC). However, some amino acids exhibited remarkably low Δ¹⁴C values, suggesting that their carbon skeleton is derived from other carbon sources with signatures different from seawater DIC. The results will not only revise the current picture of carbon cycling in connection with the biosphere, but also open up a new frontier of amino acid biogeochemistry.

References:

Ishikawa, N. F., Itahashi, Y., Blattmann, T. M., Takano, Y., Ogawa, N. O., Yamane, M., Yokoyama, Y., Nagata, T., Yoneda, M., Haghipour, N., Eglinton, T. I., & Ohkouchi, N. (2018). Analytical Chemistry, 90(20), 12035-12041.

Haghipour, N., Ausín, B., Usman, M. O., Ishikawa, N., Wacker, L., Welte, C., Ueda, K., & Eglinton, T. I. (2018). Analytical Chemistry, 91(3), 2042-2049.

G02_09

Sedimentary organic carbon ¹⁴C age and D¹⁴CTOC variations in a 200-yr core from Santa Barbara Basin: Anthropogenic and climatic influences

Li H¹,  Chang H¹, Shen T¹

¹Department of geosciences, National Taiwan University, Taipei, Taiwan

We have done 210Pb dating, varve counting, AMS ¹⁴C dating and scanning XRF and acid (0.5N HCl) leachate elemental (ALE) contents on a 51-cm core from the depo-center of Santa Barbara Basin (SBB). The core contains a depositional history during 1815-2011 CE. A total of 89 AMS ¹⁴C measurements on samples from 66 horizons show apparent ¹⁴C ages between 500 and 4000 yr BP. Among these AMS dates, 78 TOC ¹⁴C dates from 62 horizons provide high-resolution D¹⁴C variations ranging from -64.3‰ to -383.8‰. The ¹⁴CTOC is influenced by the input of terrigenous sediments, changes in ocean circulation, biological input and carbon remineralization as well as anthropogenic impacts. Three strong old ¹⁴CTOC excursions at 1964~69, 1884~87 and 1819~21 CE caused by some unusual events (e.g., oil spill and extraction, flood event and earthquake). The D¹⁴CTOC shifts in three zones were mainly caused by changes in fossil carbon emission from the seafloor and the atmospheric nuclear bomb ¹⁴C input. On interannual scales, variations of D¹⁴CTOC correspond to ENSO and PDO effects. During the La Niña period (and cold PDO phase), stronger upwelling and northerly California Current bring nutrient-enriched water into SBB and lead to higher productivity. The organic carbon and carbonate enriched sediment layers contain lower scanning XRF K and Ti but higher ALE with higher D¹⁴CTOC during La Niña period. During the El Niño period, the phenomena are opposite. Spectrum analyses of the SOI and the D¹⁴CTOC and their comparison support our scenarios.

G02_P01

Radiocarbon geochemistry of amino acids in marine sediments

Blattmann T^1,2,  Ishikawa N², Keil R³, Yokoyama Y⁴, Ogawa N², Haghipour N^1,5, Sun Y^2,4,6, Neibauer J³, Duffy M³, Suga H², Miyairi Y⁴, Eglinton T¹, Takano Y², Ohkouchi N²

¹ETH Zurich, Zurich, Switzerland, ²Biogeochemistry Research Center, JAMSTEC, Yokosuka, Japan, ³School of Oceanography, Seattle, USA, ⁴Atmosphere and Ocean Research Institute, The University of Tokyo, Kashiwa, Japan, ⁵Laboratory of Ion Beam Physics, ETH Zurich, Zurich, Switzerland, ⁶Department of Earth and Planetary Science, The University of Tokyo, Tokyo, Japan

The “building blocks of life” occur ubiquitously on Earth’s surface in the form of proteins, peptides, and single amino acids. To shed light on amino acid sources, cycling, and preservation, we have conducted amino acid-specific radiocarbon analysis on surficial marine sediment from the North American west coast. As the main goal for these investigations, we test a hypothesis that amino acid-specific radiocarbon signatures reflect the interactions of organic matter with mineral surfaces on a molecular level. This hypothesis was inspired by laboratory-based sorption experiments showing strong differences in the partitioning of different amino acids between dissolved and clay mineral adsorbed states (Blattmann & Ishikawa, 2020). We employed high-performance liquid chromatography described in Blattmann et al. (2020) to isolate individual amino acids extracted from marine sediment which were vetted for their purity via chromatography and elemental composition. Isolated amino acids were measured on accelerator mass spectrometers as gas and graphite samples at ETH Zurich and the University of Tokyo, respectively. Amino acids showed multiple centuries age difference demonstrating differential turnover within this compound class in marine surface sediments. The results highlight the role of clay minerals in modulating the preservation of amino acids in the sedimentary record.

References:

Blattmann, T.M. & Ishikawa, N.F. (2020) Theoretical amino acid-specific radiocarbon content in the environment: Hypotheses to be tested and opportunities to be taken. Frontiers in Marine Science 7.

Blattmann, T.M. et al. (2020) Liquid chromatographic isolation of individual amino acids extracted from sediments for radiocarbon analysis. Frontiers in Marine Science 7.

G02_P02

Ensuring comparability of radiocarbon measurements in dissolved inorganic carbon of seawater between ETH-Zurich and NOSAMS

Castrillejo M^1,2,  Hansman R³, Wacker L², Lester J¹, Graven H¹

¹Department of Physics, Imperial College London, London, United Kingdom, ²Laboratory of Ion Beam Physics, ETH-Zurich, Zurich, Switzerland, ³Woods Hole Oceanographic Institution - National Ocean Sciences Accelerator Mass Spectrometry Facility, Woods Hole, USA

Radiocarbon observations provide useful information about carbon cycling and ocean circulation of the real ocean and of model simulations. In an effort to provide high-quality radiocarbon observations, the Laboratory of Ion Beam Physics (LIP) developed the ETH-LIP analytical method allowing the rapid and precise analysis of radiocarbon in small seawater samples. The performance of this method is continuously assessed by following several internal quality controls. Yet, further steps have been taken to ensure the comparability of the data produced at ETH to previously existing observations.

In the absence of standards or reference materials of seawater, comparability can be assessed through inter-laboratory comparisons. To that end, an inter-comparison exercise was conducted in 2021 between ETH and the National Ocean Sciences Accelerator Mass Spectrometry (NOSAMS) Facility at Woods Hole Oceanographic Institution. In February 2020, duplicate seawater samples were collected from 14 depths and geographical locations distributed along the GO-SHIP A05 line in the subtropical North Atlantic (~ 24.5° N). This work presents the results reported from the two laboratories, which overall showed a very good agreement. We further discuss important aspects related to the different sample collection, preservations and storage techniques used to collect the seawater for NOSAMS and ETH.

G02_P03

AMS ¹⁴C dating and stable isotope analysis on an 8-kyr oyster shell from Taipei Basin: Sea level and SST changes

Chou C¹,  Kang S¹, Liu T¹, Li H¹

¹Department Of Geosciences, NTU, Taipei, Taiwan

A giant oyster shell ( 42 cm long), Crassostrea gigas, was uncovered from an oyster reef on the ancient shore of eastern Taipei Basin in 2002. The oyster reef was 14.9 m below the ground surface which has an elevation of 10 m a.s.l. Eight AMS ¹⁴C dates along the growth axis of the shell are from 8130±200 yr BP to 8435±155 yr BP, indicating that the shell was formed and deposited about 8300 years ago during the high sea level stand of middle Holocene. A plancenta shell collected 5 m above the oyster reef shows a ¹⁴C age of 7640±60 yr BP, indicating that Taipei Basin was covered by ocean water during 7640±60 ~ 8435±155 yr BP. A total of 79 stable isotope samples were collected in a 5.5-cm section from the oldest part of the shell, giving δ¹⁸O range of -6.03‰ ~ -1.33‰ and δ¹³C range of -2.21‰ ~ -0.31‰ (VPDB). These δ¹⁸O and δ¹³C profiles show clear seasonal cycles, indicating a 4-year growth in the 5.5-cm section. Both δ¹⁸O and δ¹³C values illustrate that the oyster grew in a saline environment. Compared with the δ¹⁸O profiles of modern oyster shells in Taiwan, the ancient oyster grew in a much warmer shoreline water environment. According to the studying section, the oyster reef had an elevation of 0 m at 8300 yr BP, and the Plancenta shell had 3-5 m a.s.l. at 7600 yr BP.

Key words: Taipei Basin, early-Mid Holocene, oyster shell, ¹⁴C dating, stable isotopes

G02_P04

Tracking the ¹⁴C bomb peak recorded in Arctica Islandica across the North Sea and Northeast Atlantic Ocean

Christiane Y¹, Christl M¹,  Witbaard R², Wacker L¹, Hattendorf B³, Welte C^1,4, Synal H¹

¹ETH Zurich, Laboratory of Ion Beam Physics, Zurich, Switzerland, ²Royal Netherlands Institute for Sea Research, Texel,, , ³ETH Zurich, Trace Element and Microanalysis, Zurich, Switzerland, ⁴ETH Zurich, Biogeosciences, Zurich, Switzerland

Spatially resolved radiocarbon profiles were recorded using Laser Ablation AMS (LA-AMS) from six Arctica Islandica shells collected at different locations in the North Sea and Northern Norway. The profiles were combined with independently derived chronologies from counting the growth bands of the bivalves to reconstruct spatial and temporal differences in the marine ¹⁴C bomb pulse. Shells were sampled from a range of water depths, i.e., 15 to 150 m, with growth rates varying between 3 and <0.1 mm/yr. For ¹⁴C sampling, the shells were moved under the laser with a speed of 10-25 μm/s with an integration time of 10 s. The recorded ¹⁴C profiles were further integrated to reduce noise and scatter of the data resulting in a final sampling resolution between 1 and 10 yrs. Comparison of the LA-AMS derived data with graphite measurements from earlier studies was very good.

The ¹⁴C bomb peak was identified in all samples, but with different timing and amplitude compared to the modeled marine mixed layer (MMML) calibration curve. The maximum of the ¹⁴C signal in the shells correlates inversely with water depth, while the delay of the peak increases with greater water depth. Both observations consistently indicate a dampening of the atmospheric signal with water depth due to the increased influence of Atlantic deep waters. The presented profiles show the potential of LA-AMS to map the spatiotemporal variation of the marine bomb pulse, providing valuable information on local deviations from the MMML and constraining simulations of the marine bomb peak.

G02_P05

Radiocarbon in the ocean: ensuring high quality results

Hansman R¹,  Key R², McNichol A¹, Sonnerup R³

¹Woods Hole Oceanographic Institution, Woods Hole, United States, ²Princeton University, Princeton, United States, ³University of Washington, Seattle, United States

Repeat open ocean radiocarbon measurements of dissolved inorganic carbon (DIC) have led to a better understanding of key ocean processes such as mixing, ventilation rates, air-sea gas exchange, and ocean biogeochemistry.  Until recently, only a few laboratories had the ability to make the precise ¹⁴C analyses necessary to document ocean circulation and the oceanic uptake of anthropogenic CO₂, but technological advances have reduced sample size requirements, brought new methods online, and made it easier for more laboratories to collect and analyze DI¹⁴C in the ocean.  However, as there are presently no recognized standards or reference materials for radiocarbon in seawater, it is critical to ensure the quality and data comparability of these measurements across laboratories and over time.  To this end, a three-day virtual workshop sponsored by the Ocean Carbon & Biogeochemistry program was held in November 2021 to discuss best practices for the measurement, data handling, and reporting of carbon isotopes in the ocean.  While the workshop included the analysis of both DI¹³C and DI¹⁴C, an immediate need for an inter-laboratory comparison exercise of radiocarbon in seawater DIC was determined.  We will present a summary of the workshop discussion and outcomes, including imminent plans for this DI¹⁴C inter-comparison, as well as work towards establishing reference materials for the community.

G02_P06

Long Term Time Series of Surface Water Dissolved Inorganic Carbon Isotopes from the Southern California Bight

Hauksson N¹,  Griffin S¹, Xu X¹, Martinez H¹, Pedron S¹, Druffel E¹

¹University Of California, Irvine, Irvine, United States

The Southern California Bight is an oceanographically complex region in a Mediterranean climate, strong upwelling, and limited rainfall. The health of kelp forests and marine protected areas in these waters depend on the balance of waters from wind-driven upwelling, the California current, and the California counter-current. Water mass tracers, such as carbon isotopes, inform the movement of water masses in this region. We report dissolved inorganic carbon (DIC) ∆¹⁴C and 𝛅¹³C values in seawater collected from the Newport Beach Pier in Orange County, California from 2011 to 2022. The ∆¹⁴C values decrease over this period, consistent with depletion of the ¹⁴C generated by thermonuclear weapons testing and dilution of ¹⁴C-free CO₂ from fossil fuel combustion. We analyze the relationship of these isotopes with the environmental conditions during this time series.

G02_P07

The chronology of the sedimentation in the Danube abyssal fan records the major episodes of the late-Holocene Black Sea evolution

Ilie M^1,2,  Sava T¹, Vespremeanu-Stroe A³, Duliu O², Cristea G⁴, Ion G⁵, Olteanu D^1,3, Haliuc A⁶, Manailescu C¹, Sava G¹

¹RoAMS Laboratory, Horia Hulubei National Institute For R&D In Physics And Nuclear Engineering (IFIN-HH), Magurele, Ilfov, Romania, ²University of Bucharest, Faculty of Physics, Magurele, Romania, ³GEODAR Research Center for Geomorphology, Geoarchaeology and Paleo-environments, Faculty of Geography, University of Bucharest, Bucharest, Romania, ⁴Department of Mass Spectrometry, Chromatography and Applied Physics, National Institute for Research and Development of Isotopic and Molecular Technologies, Cluj-Napoca, Romania, ⁵National Institute of Marine Geology and Geo-Ecology (GeoEcoMar), Bucharest, Romania, ⁶Romanian Academy, Institute of Speleology, Cluj-Napoca, Romania

The construction for the high-resolution Bayesian sedimentation model spanning the last 5500 years based on 25 AMS radiocarbon dated sediments of bulk organic matter (OM) sampled from the NW Black Sea anoxic waters of the continental slope is presented in this paperwork. The corrections for the ¹⁴C ages due to marine reservoir effect (MRE) and detritus organic carbon are correlated with exogenous information such as 210Pb dating, metallurgy pollution and human-induced soil erosion, highlighting the Danube influence on the geochemistry and chronology of the NW Black Sea sediments through the input of terrigenous organic matter.

The results show excellent agreement with some of the previous studies, supporting a total age offset for the bulk OM of 60 years as MRE and 580 years as detritus organic carbon influence. The revisited chronology pinpoints the first and second invasion of the coccolitho-phores Emiliania huxleyi at 2524 ± 87 and 625 ± 65 years cal. BP. The sedimentation rate shows an increase of about three times with the starting of the late Medieval, which corresponds to the highest observed sediment discharge of the Danube as are considered the last 500-300 years.

This type of high-resolution sedimentation model is an important step for constructing the carbon budget in bottom waters of variable oxygen concentration.

G02_P08

Organic carbon cycling in the deep ocean: Implications from radiocarbon

Kim M^1,2,3,  Hwang J², Haghipour N^3,4, Eglinton T³

¹Kyungpook National University, Daegu, South Korea, ²School of Earth and Environmental Sciences/Research Institute of Oceanography, Seoul National University, Seoul, South Korea, ³Geological Institute, Swiss Federal Institute of Technology in Zürich (ETHZ), Zurich, Switzerland, ⁴Laboratory of Ion Beam Physics, ETH Zürich, Zurich, Switzerland

The transport of carbon from surface waters to the deep ocean via primary production and subsequent export of POC, known as the biological carbon pump, is a crucial process for sequestration of atmospheric CO₂. Large-scale sediment trap studies have advanced our understanding of material fluxes during vertical transit from surface to deep waters. However, despite the potential importance in the oceanic carbon cycle, the global feature of lateral supply of aged organic matter hosted on lithogenic particles derived from sediment resuspension has not been systematically examined.

Here I summarize the results of previous studies that have insights on the lateral transport of aged organic matter: Amundsen Sea, East/Japan Sea, deep abyssal Pacific, and the Northwest Atlantic. Especially in Kim et al. (2020), we compiled concentrations and fluxes of lithogenic material in the ocean on a global-scale by using literature data of sediment trap studies to understand the contribution of resuspended sediment to sinking particulate matter. Examination of Δ¹⁴C values of sinking POC revealed strong relationships with parameters that represent contribution of resuspended sediment. We then derive estimates for the contribution of aged POC from sediment resuspension to sinking POC based on these relationships and global lithogenic material flux data. Based on this relationship, and the global mean of lithogenic content of sinking particulate matter, we calculate that aged POC from sediment resuspension comprises 3~5 % of sinking POC intercepted by sediment traps.

G02_P09

Tracing bomb radiocarbon in sinking particulate organic carbon in the deep Sargasso Sea

Schnepper C¹,  Pedrosa-Pamies R², Conte M², Gruber N¹, Haghipour N¹, Eglinton T¹

¹Geological Institute, ETH , Zürich, Switzerland, ² Marine Biological Laboratory, WHOI, Woods Hole, USA

The imprint of bomb radiocarbon on sinking particulate organic carbon (PO¹⁴C) intercepted by sediment traps, together with flux and compositional data, provides information about the origin and dynamics of oceanic particles (Hwang et al., 2010). Of particular interest is the question of whether the intercepted POC in the deep ocean stems from overlying primary production, i.e., as part of the “extrinsic“ biological pump, or whether the POC additionally originates from advection and subsequent aggregation of resuspended sedimentary carbon originating from continental margins and other far-away sources (“intrinsic” flux). Measurements by Kim et al. (2020) revealed significant variability in PO¹⁴C, however the processes driving this variability remain poorly understood. To quantify the intra- and inter-annual variability in PO¹⁴C, an in-depth study was initiated at the Ocean Flux Program site in the Sargasso Sea. This sediment trap time-series has generated (bi-)weekly samples and resulting information on particle fluxes and flux compositions at three water depths (500, 1500, 3200 m) since 1978. Preliminary data reveal intra-annual variations in PO¹⁴C with an amplitude of ca. 100 ‰. Seasonal Δ¹⁴C variations are paralleled by shifts in the POC/Lithogenic ratio. This supports the notion that POC with high Δ¹⁴C values, high POC/Lithogenic ratio and POC flux reflects supply of particles that originate via the “extrinsic“ biological pump, while lower Δ¹⁴C values and POC/Lithogenic ratios may reflect the “intrinsic” flux including resuspended sediments with higher lithogenic content emanating from continental margins. A nascent global PO¹⁴C database will allow to assess the broader relevance of our findings.

G02_P10

Age offsets between marine-derived lipid biomarkers, TOC, and foraminifera during cross shelf-slope lateral transport revealed by compound-specific radiocarbon dating

UCHIDA M¹,   Eglinton T², Coppola L³, Gustafsson Ö⁴, Mollenhauer G⁵, Hayes J^6,8, Ahagon N⁷, Harada N⁷

¹Earth System Division, National Institute For Environmental Studies, Tsukuba, Japan, ²Geological Institute, ETH, Zurich, Switzerland, ³Villefranche-sur-mer, Alpes Maritimes, France, ⁴Institute of Applied Environmental Research, Stockholm University, Stockholm, Sweden, ⁵Alfred Wegener Institute for Polar and Marine Research, Bremerhaven, Germany, ⁶National Ocean Sciences Accelerator Mass Spectrometry facility, Woods Hole Oceanographic Institution, Woods Hole, U.S.A., ⁷Japan Agency for Marine-Earth Science and Technology, Yokosuka, Japan, ⁸Deceased 3 February 2017, ,

Compound-specific radiocarbon analysis was performed on bulk sediments and different grain-size fractions (>250μm, 150-250μm, 63-150μm,38-63μm, <38μm) of shelf-slope surface sediments (0-2cm, outer shelf of 150m water depth and upper slope of 600m water depth) from Washington Margin to examine their relationships between hydrodynamic sorting of sediments and timescales and preservation of organic carbon. Here we obtained datasets of radiocarbon ages of alkenone, low molecular weight fatty acids (LMW-FAs, C₁₄, C₁₆, and C₁₈), high molecular weight fatty acids (HMW-FAs, C₂₄, C₂₆, and C₂₈), total organic carbon and planktic foraminifera. These results were also discussed with previous reported lateral transport times of organic carbon (Bao et al., 2019). Age offsets between planktonic foraminifera, LMW-FAs, and alkenone in bulk phase sediments were significantly large in shelf compared with slope. On the other hand, age offsets between size fractions were not likely observed between LMW-FAs and alkenone except for large fractions(>250μm). Ages of LMW-FAs for both shelf and slope were younger than those of alkenone in all fractions including bulk-phase sediments. Moreover, we obtained radiocarbon ages of marine-derived compounds (alkenone, LMW-FAs), plant wax-derived compounds(HMW-FAs), planktic foraminifera, and total organic carbon from the last deglaciation- Holocene covered-marginal sediments from western North Pacific (1366m water depth, N41°) and Okhotsk Sea (1225m water depth, N44°). We discuss with palaeoceanographic interpretation on sedimentary records such as alkenone temperatures and ventilation.

G02_P11

Carbon isotopic constraints on the sources and preservation of organic compounds in sediment of the South China Sea

Wang F^1,2, Fu W¹, Ren P², Zhang H¹, Luo C¹, Wang X^1,2

¹Ocean University Of China, Qingdao, China, ²Qingdao National Laboratory of Marine Science and Technology, Qingdao, China

Organic matter (OM) preservation in marine sediments is an important sink of carbon cycle and provides useful information on the sources, biodegradation and transformation of organic carbon during early diagenesis.  The South China Sea (SCS), as one of the largest semi-enclosed marginal sea in the western North Pacific Ocean, receives large amount of organic carbon fluxes from river input and land erosion, especially in its northern shelf and slope regions. The burial of organic compounds in sediment of the SCS, however, has not been well studied. Here, we present the first data set of radiocarbon combined with stable carbon isotope measurements of total organic carbon (TOC), hydrolysable amino acids (THAA), total lipids, humic acids (HA), and acid-base insoluble OM in four sediment cores collected from the northern slope of the SCS. Distinct differences in both ¹³C and ¹⁴C values were found among these compound classes. The δ¹³C values are more depleted for total lipids and HA (-23.1‰ to -30.2‰) than the THAA and the acid-base insoluble OM (-15.3‰ to -20.6‰). The D¹⁴C values ranged from -632‰ to -194‰ in TOC, -331‰ to -66‰ in THAA, -574‰ to -253‰ in total lipids, -569‰ to -168‰ in HA, and -848‰ to -458‰ in acid-base insoluble OM, respectively. The acid-base insoluble OM has the oldest ¹⁴C ages (mean 7800 years) among the compound classes in the sediments. These distinct isotopic signatures provide new insight and reveal the selective decomposition, transformation and preservation mechanisms of OM derived from different sources in marine sediment.

G02_P12

Bomb-pulse radiocarbon record for a well-dated Caribbean coral core

Winkler S^1,2,  Steier P², Carilli J³

¹Helmholtz-zentrum Dresden-Rossendorf, Dresden, Germany, ²Universität Wien, Wien, Austria, ³ University of California San Diego, La Jolla , USA

The radiocarbon bomb-pulse created by nuclear weapons testing in the 1950s and 1960s has created a massive spike of atmospheric ¹⁴C, which has been used in the study of the global carbon cycle in many subsystems including the marine environment. Coral records of bomb-pulse era ¹⁴C have been studied over the past decades to gain insight into the uptake and mixing of atmospheric CO₂ in the ocean. The ¹⁴C level seen in surface waters is specific to the origin of the water masses and ocean-atmosphere exchange of CO₂.

We present results for radiocarbon levels in coral aragonite with yearly resolution for a coral core from Belize. The core has a well-established stratigraphy, stretching from the onset of atmospheric testing of thermonuclear devices to 2007. The core has previously been analyzed for and trace metal content in relation to environmental impacts and the bomb-pulse of ²³⁶U. We compare the results with existing results and model expectations for the Caribbean Sea. We further discuss the close agreement for the prior results in terms of feasibility and the achievable accuracy of cross-dating of cores using the rise of radiocarbon by the atmospheric bomb-pulse.