Alysha I. Coppola

Aged black carbon in marine sediments and sinking particles

PUBLICATIONS Geophysical Research Letters RESEARCH LETTER 10.1002/2013GL059068 Key Points: • Multipool black carbon data set of Δ C values, BC/OC%, and BPCA abundances • A significant fraction of biomass-derived BC is transported to sediments by particulate organic carbon • Our BC flux estimate represents ~8–16% of the global OC burial flux to sediments Supporting Information: • Readme • Figure S1 • Table S1 • Table S2 • Equation S1 Correspondence to: A. I. Coppola, acoppola@uci.edu Aged black carbon in marine sediments and sinking particles Alysha I. Coppola 1 , Lori A. Ziolkowski 2 , Caroline A. Masiello 3 , and Ellen R. M. Druffel 1 Department of Earth System Science, University of California, Irvine, California, USA, 2 Marine Science Program and Department of Earth and Ocean Sciences, University of South Carolina, Columbia, South Carolina, USA, 3 Department of Earth Science and Department of Chemistry, Rice University, Houston, Texas, USA Abstract We report measurements of oceanic black carbon (BC) to determine the sources of BC to abyssal marine sediments in the northeast Pacific Ocean. We find that the average 14 C age of BC is older (by 6200 ± 2200 14 C years) than that of the concurrently deposited non-BC sedimentary organic carbon. We investigate sources of aged BC to sediments by measuring a sample of sinking particulate organic carbon (POC) and find that POC may provide the main transport mechanism of BC to sediments. We suggest that aged BC is incorporated into POC from a combination of resuspended sediments and sorption of ancient dissolved organic carbon BC onto POC. Our BC flux estimate represents ~8–16% of the global burial flux of organic carbon to abyssal sediments and constitutes a minimum long-term removal estimate of 6–32% of biomass-derived BC using the present day emission flux. 1. Introduction Citation: Coppola, A. I., L. A. Ziolkowski, C. A. Masiello, and E. R. M. Druffel (2014), Aged black carbon in marine sediments and sinking particles, Geophys. Res. Lett., 41, doi:10.1002/2013GL059068. Received 18 DEC 2013 Accepted 3 FEB 2014 Accepted article online 5 FEB 2014 Black carbon (BC), formed by incomplete combustion of organic matter, cycles on annual to millennial time scales [Masiello and Druffel, 1998; Middelburg et al., 1999]. Black carbon is defined as a continuum from slightly charred plant material to highly graphitized soot [Goldberg, 1985; Schmidt and Noack, 2000; Masiello, 2004]. Char BC is produced by the incomplete combustion of biomass, coals, and other materials, while soot BC is formed from the condensation of combustion gases. Black carbon has been found in marine dissolved organic carbon (DOC) [Dittmar, 2008; Ziolkowski and Druffel, 2010a], particulate organic carbon (POC) [Lohmann et al., 2009; Zigah et al., 2012; Flores-Cervantes et al., 2010], and sedimentary organic carbon (SOC) [Goldberg, 1985; Masiello and Druffel, 2003; Ohkouchi and Eglinton, 2006]. Black carbon enters the ocean by rivers and atmospheric deposition. Modern biomass-derived BC is mainly transported by surface erosion of soils and rivers, delivered to watersheds, and then to the ocean [Foereid et al., 2011; Major et al., 2010; Rumpel et al., 2006; Hockaday et al., 2007; Jaffe et al., 2013]. Because of its submicron size, soot BC can travel long distances before it is deposited into the ocean [Lohmann et al., 2009; Posfai and Buseck, 2010; Gustafsson and Gschwend, 1998; Ohkouchi and Eglinton, 2006]. Once BC enters the ocean’s DOC pool, its chemical and isotopic composition (as measured in ultrafiltered, high molecular weight DOC) dramatically changes between coastal and open ocean regions, suggesting that there are BC loss processes from the marine DOC pool [Ziolkowski and Druffel, 2010a, 2010b; Ward et al., 2014]. Two proposed loss processes are photochemical oxidation in the sea surface [Stubbins et al., 2012] and transport to sediments via sorption to POC [Flores-Cervantes et al., 2010; Zigah et al., 2012]. Marine sediments contain a significant amount of BC in organic carbon, with BC/OC% values ranging from 15 ± 2% to 21 ± 6% in abyssal sediments and up to 50 ± 40% in coastal sediments [Verardo and Ruddiman, 1996; Masiello and Druffel, 1998, 2003; Gustafsson and Gschwend, 1998; Middelburg et al., 1999; Lohmann et al., 2009]. The variability of sediment BC/OC% values is partly due to differences in methods used to quantify BC and to environmental transformations not accounted for by the analytical method used [Hammes et al., 2007; Currie et al., 2002]. Masiello and Druffel [1998] measured 15 ± 2% BC/OC in sediment (0–50 cm) from the northeast Pacific, with 14 C ages of the SOC BC 2400 ± 120 to 5400 ± 520 14 C years older than concurrently deposited non-BC SOC. This suggested that BC is preaged for thousands of years prior to deposition in the sediments. Here we report that BC is removed from seawater via sorption to marine POC and subsequently transported to sediments. We compare BC concentration, 14 C analyses, and qualitative BC structural information to COPPOLA ET AL. ©2014. American Geophysical Union. All Rights Reserved.

Cycling of black carbon in the ocean

Black carbon (BC) is a by-product of combustion from wildfires and fossil fuels and is a slow-cycling component of the carbon cycle. Whether BC accumulates and ages on millennial time scales in the world oceans has remained unknown. Here we quantified dissolved BC (DBC) in marine dissolved organic carbon isolated by solid phase extraction at several sites in the world ocean. We find that DBC in the Atlantic, Pacific, and Arctic oceans ranges from 1.4 to 2.6 μM in the surface and is 1.2 ± 0.1 μM in the deep Atlantic. The average 14C age of surface DBC is 4800 ± 620 14C years and much older in a deep water sample (23,000 ± 3000 14C years). The range of DBC structures and 14C ages indicates that DBC is not homogeneous in the ocean. We show that there are at least two distinct pools of marine DBC, a younger pool that cycles on centennial time scales and an ancient pool that cycles on >105 year time scales.

Radiocarbon in dissolved organic carbon of the Atlantic Ocean

PUBLICATIONS Geophysical Research Letters RESEARCH LETTER 10.1002/2016GL068746 Key Points: • More than 10% of DOC in the deep North Atlantic contains bomb C • DOC decreases in concentration and increases in C age along the deep ocean conveyor • DOC in the deep ocean is surprisingly dynamic both temporally and spatially Supporting Information: • Supporting Information S1 • Movie S1 Correspondence to: E. R. M. Druffel, edruffel@uci.edu Citation: Druffel, E. R. M., S. Griffin, A. I. Coppola, and B. D. Walker (2016), Radiocarbon in dissolved organic carbon of the Atlantic Ocean, Geophys. Res. Lett., 43, 5279–5286, doi:10.1002/2016GL068746. Received 6 JAN 2016 Accepted 12 MAY 2016 Accepted article online 16 MAY 2016 Published online 31 MAY 2016 Radiocarbon in dissolved organic carbon of the Atlantic Ocean E. R. M. Druffel 1 , S. Griffin 1 , A. I. Coppola 1,2 , and B. D. Walker 1 Department of Earth System Science, University of California, Irvine, Irvine, California, USA, 2 Department of Geography, University of Zurich, Zurich, Switzerland Abstract Marine dissolved organic carbon (DOC) is produced in the surface ocean though its radiocarbon ( 14 C) age in the deep ocean is thousands of years old. Here we show that ≥10% of the DOC in the deep North Atlantic is of postbomb origin and that the 14 C age of the prebomb DOC is ≥4900 14 C year, ~900 14 C year older than previous estimates. We report 14 C ages of DOC in the deep South Atlantic that are intermediate between values in the North Atlantic and the Southern Ocean. Finally, we conclude that prebomb DOC 14 C ages are older and a portion of deep DOC is more dynamic than previously reported. 1. Introduction Marine DOC is the largest pool of reduced carbon (C) in the oceans, about equal to the atmospheric CO 2 reservoir. Though most DOC is produced from photosynthetic uptake of modern DIC in the surface ocean, estimates of the bulk 14 C ages in deep open ocean DOC ranged from 4000 14 C years in the Sargasso Sea to 6000 14 C years in the North and South Pacific [Druffel and Griffin, 2015; Druffel et al., 1992; Williams and Druffel, 1987]. Previous work suggested that the average 14 C age of DOC in the deep Southern Ocean (5600 14 C years) was much closer to that in the deep Pacific, suggesting that the deep North Atlantic DOC contained bomb 14 C, that there was a source of old DOC to the Southern Ocean [Druffel and Bauer, 2000] or that there were diverse isotopic sources of DOC [Follett et al., 2014; Loh et al., 2004; McCarthy et al., 2011; Walker et al., 2011; Ziolkowski and Druffel, 2010]. In the ocean margins, there is evidence of inputs of old DOC in the deep northeast Pacific and the mid-Atlantic Bight off the U.S. coast [Bauer and Druffel, 1998; Ziolkowski and Druffel, 2010] and young DOC to the deep subpolar North Pacific [Tanaka et al., 2010]. Terrestrially derived DOC was found in the deep Arctic Ocean [Griffith et al., 2012]. We find here that the DOC Δ 14 C values in the deep Sargasso Sea in 2012 are lower than those in 1989, indicating that bomb 14 C levels have decreased over a period of two decades, similar to the decrease of surface dissolved inor- ganic C (DIC). Implications for the C cycle in the ocean include the presence of a labile pool of DOC in deep water. 2. Setting and Methods Water samples were collected from the North and South Atlantic Ocean during the Repeat Hydrography Climate Variability and Predictability program. Sampling included surface and subsurface water, northward Antarctic Intermediate Water (AAIW ~700–1200 m, low salinity, high silica) and Upper Circumpolar Deep Water (1000–2000 m), southward North Atlantic Deep Water (NADW 1500–4000 m, high oxygen, low silica), and Antarctic Bottom Water (within a few hundred meters of the bottom, cold and dense) [Jenkins et al., 2015a; Reid, 1989]. A data-constrained, ocean circulation model was used to show that in the South Atlantic, Antarctic water penetrates the NADW in volume-weighted averages that vary from 20 to 40% [DeVries and Primeau, 2011]. Radiocarbon in DOC was measured in seawater samples collected from three stations along 32°S on the A10 cruise in October 2011, four stations along 20°W on the A16N cruise in July/August 2013, and four stations along 65°W on the A22 cruise in March/April 2012 (Figure 1 and Table S1 in the supporting information). Samples shallower than 400 m were filtered using precombusted glass fiber (0.7 μM) filters, and all samples were collected in 1 L Amber Boston Round glass bottles and frozen at 20°C at an angle to avoid breakage until analysis at University of California, Irvine (UCI). Samples were diluted with 18.2 MΩ Milli-Q water (DOC concentration 0.5–0.9 μM), acidified to pH 2 with 85% phosphoric acid, purged with ultra high purity helium gas and UV-oxidized (UVox) [Beaupre et al., 2007; Druffel et al., 2013; Griffin et al., 2010]. Samples for DIC Δ 14 C analyses were prepared according to standard methods [McNichol et al., 1994]. ©2016. American Geophysical Union. All Rights Reserved. DRUFFEL ET AL. The resultant CO 2 from UVox was converted to graphite on iron catalyst for 14 C analysis at the Keck carbon cycle accelerator mass spectrometry (AMS) laboratory at UCI [Southon et al., 2004; Xu et al., 2007]. Total uncertainties for RADIOCARBON IN DOC OF THE ATLANTIC