Wildfires and fossil fuel combustion produce large amounts of charred pyrogenic organic materials, including black carbon (BC). Pyrogenic carbon is chemically heterogenous and is described as a continuum from charcoal to soot. Black carbon is an incomplete combustion byproduct that could be a sink for fixed carbon, especially when deposited to pelagic sediments or long-term cycling in the oceans. In the atmosphere, BC is a key driver of global climate change; yet it’s feedbacks are not included in Earth System Models. Omitting BC production from assessments of fire impacts leads to an overestimation of the strength of positive feedbacks caused by wildfires. There is a general assumption that rivers deliver most or all BC to the ocean. Yet the sources, transport and transformation of BC are not well constrained in intermediate reservoirs or in atmospheric and ocean circulation models. For example, few BC flux measurements are available in remote ocean sediments to understand this transfer of BC. Once deposited to the ocean, some BC is buried in sediments, and can account for significant fractions of the organic matter preserved in sediments. Dissolved BC, in contrast, cycles in the oceans on millennial timescales. A better understanding of the carbon cycle thus depends on working at the interface of numerous disciplines, including oceanography, paleography, atmospheric science, biogeochemistry, and analytical chemistry. The proposed ASLO session is thus relevant and timely to further expand our understanding of the cycling of pyrogenic carbon, as well as BC components, which is key to understanding carbon mitigation and negative feedback strategies with continued climate change.
Lead Organizer: Rainer Lohmann, University of Rhode Island (rlohmann@uri.edu)
Co-organizers:
Sasha Wagner, Rensselaer Polytechnic Institute (wagnes3@rpi.edu)
Alysha Coppola, ETH Zurich (acoppola@ethz.ch)
Presentations
06:30 PM
MOLECULAR COMPOSITION OF DISSOLVED PYROGENIC ORGANIC MATTER CONVERGES ACROSS VEGETATION TYPES WITH INCREASING BURN SEVERITY (5588)
Primary Presenter: Alan Roebuck, Pacific Northwest National Laboratory (alan.roebuck@pnnl.gov)
Wildfires significantly alter terrestrial carbon pools through the production of pyrogenic organic matter (PyOM), with a complex chemical makeup thought to determine its fate in aquatic systems. Our current molecular level understanding of dissolved-phase PyOM chemistry is rooted in experiments specifically linked to burn temperature (e.g., Heat Temperature Treatments), which in the environment can be heterogenous and is not directly linked to field assessments of burn severity. In this study, we seek to understand the relationship between PyOM production and vegetation burn severity through a comprehensive characterization of dissolved PyOM generated along a burn severity continuum. We used a combination of optical techniques, ultra-high resolution mass spectrometry, and benzene polycarboxylic acids to characterize leachates from chars generated in open-air conditions at varying degrees of burn severity with vegetation representative of Pacific Northwest land cover types. We highlight an independence in PyOM molecular signatures across vegetation types from raw and lower burn severities that ultimately converge at higher severities into uniform signatures characteristic of degraded, aromatic DOM with enriched nitrogen containing functionality. The results of this study improve our understanding of the production of PyOM across burn severities that will enhance our understanding of wildfire impacts on ecosystem processes and our predictive understanding of wildfire impacts on terrestrial and aquatic biogeochemical cycles.
06:30 PM
LATITUDINAL VARIABILITY IN DISSOLVED BLACK CARBON ISOTOPIC COMPOSITION IN ATLANTIC SURFACE WATERS COMPARED TO ATMOSPHERIC PYROGENIC CARBON INPUTS (5755)
Primary Presenter: Nina Davtian, Universitat Autònoma de Barcelona (UAB) (nina.davtian@uab.cat)
The main sources of pyrogenic carbon (PyC) to the ocean are rivers and aerosols. The Atlantic Ocean not only receives substantial riverine inputs but also substantial atmospheric PyC inputs from massive grassland wildfires. The Atlantic Ocean thus constitutes an ideal test bench to assess the impact of atmospheric PyC inputs on the dissolved black carbon (DBC) concentration and isotopic composition in open ocean surface waters. Here we show the DBC distribution in surface waters along a latitudinal transect across the Atlantic Ocean. This latitudinal transect includes areas subject to large inputs of atmospheric PyC from Africa. We quantified and characterized the stable carbon isotopic composition of DBC using the benzene polycarboxylic acid (B6CA and B5CA) method and compared the observed results with satellite estimates of PyC to assess the contribution of aeolian inputs to the oceanic DBC.
06:30 PM
Black Carbon transport through the Mackenzie River-Beaufort Sea system (6636)
Primary Presenter: Alysha Coppola, ETH Zurich (acoppola@ethz.ch)
Biomass burning and fossil fuel combustion releases large amounts of carbon into the atmosphere that are changing Earth’s climate. Up to 27% and 0.2% of carbon from biomass burning and fossil fuel combustion, respectively, is retained as black carbon (BC), a byproduct from incomplete combustion, rather than emitted as greenhouse gases. In addition to affecting radiative budgets, BC also influences biogeochemical processes, and plays an key - yet currently poorly quantified - role in the global carbon cycle. Our understanding of the role of BC in the regional and global-scale carbon cycle is hindered in large part due to limited constraints on the riverine export and fate of BC in the ocean. Here, we use the Mackenzie River- Beaufort Sea system in the Arctic to assess the magnitude and nature of BC transfer across the river-to-ocean aquatic continuum. We focus on this system due to the disproportionally large terrestrial influence on this semi-enclosed marine basin, and because of the rapid pace of change that this system is experiencing. We report the first high resolution production input of BC by fires on a regional level across 6 sub-basins of the Mackenzie River using the Arctic Boreal Vulnerability Experiment Fire Emissions Database (ABoVE-FED) and ratios of production to carbon emissions. We compile black carbon stocks and fluxes, D14C values, as well as qualitative information on BC composition across the entire aquatic continuum, with the goal of shedding new light on the dynamics of this important yet enigmatic component of the carbon cycle, as well as its sensitivity to, and influence on past and future environmental change.
06:30 PM
Fate of fire-altered carbon along an arctic river-to-ocean continuum (4914)
Primary Presenter: Linn Speidel, ETH Zürich (lspeidel@ethz.ch)
Climate change is amplified in arctic and boreal regions, with one consequence of higher average temperatures and less precipitation in the summer months being longer wildfire seasons, severity, frequency and areal extent. This increases the release of carbon into the atmosphere as greenhouse gases and aerosols, amplifying climate change even further. Black carbon (BC), resulting from the incomplete combustion of biomass and fossil fuels, is produced on land, but a fraction of BC is exported by rivers to the oceans as both dissolved BC (DBC) and particulate BC, where it may be sequestered for millennia. Its fate along the river-to-ocean continuum determines the role of BC as a carbon sink. It is thus important to understand sources, transformations and fate of BC in the arctic given the increased prevalence of fires in this climatically vulnerable region. Here, we examine the sources, characteristics and fate of riverine DBC carried by the Mackenzie River to the adjacent Beaufort Sea. DBC concentrations in ocean water and corresponding d14C values were determined for samples collected on two cruises covering the outflow of the Mackenzie River and its mixing with the Beaufort Sea in 2021 and 2022 covering the outflow of the Mackenzie River. We use the concentration and 14C characteristics of specific DBC marker compounds to resolve the sources, transport pathways and fate of DBC in the Mackenzie River/Arctic Ocean system.
06:30 PM
Sedimentary Accumulation of Black Carbon on the East Coast of The United States (7250)
Primary Presenter: Ita Wulandari, National Research and Innovation Agency - BRIN (itaw001@brin.go.id)
The occurrence, trends and sources of soot black carbon (BC) in coastal sediments are poorly understood, particularly during the Anthropocene. Two sediment cores, covering the last ~100 years from the US East Coast, off North Carolina and in the Florida Straits, were analyzed for organic carbon (OC), BC fluxes and BC sources. BC fluxes were 0.1 g cm−2 year−1 at both sites and accounted for 8-22% of total OC. Carbon stable isotope values indicated OC to be of marine origin, while the BC was mostly terrestrially derived, C3-plant material. Radiocarbon values revealed BC originating mostly from fossil fuels or pre-aged carbon (fraction modern of 14−31%) at North Carolina, while in the Florida Strait the BC was mostly derived from biomass burning (fraction modern of 70−74%), in-line with continental (NC) or marine (FS) air mass origins. Ratios of polycyclic aromatic hydrocarbons broadly supported different BC sources at the two sites.
SS041P Transport, Transformation and Trends of Pyrogenic Carbon in the Aquatic Environment
Description
Time: 6:30 PM
Date: 7/6/2023
Room: Mezzanine