Jacobel
Allison W.
Jacobel
Allison W.
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ArticleGlobal ocean sediment composition and burial flux in the deep sea(American Geophysical Union, 2021-03-21) Hayes, Christopher T. ; Costa, Kassandra M. ; Anderson, Robert F. ; Calvo, Eva ; Chase, Zanna ; Demina, Ludmila L. ; Dutay, Jean-Claude ; German, Christopher R. ; Heimbürger, Lars-Eric ; Jaccard, Samuel L. ; Jacobel, Allison W. ; Kohfeld, Karen E. ; Kravchishina, Marina ; Lippold, Jörg ; Mekik, Figen ; Missiaen, Lise ; Pavia, Frank ; Paytan, Adina ; Pedrosa-Pamies, Rut ; Petrova, Mariia V. ; Rahman, Shaily ; Robinson, Laura F. ; Roy-Barman, Matthieu ; Sanchez-Vidal, Anna ; Shiller, Alan M. ; Tagliabue, Alessandro ; Tessin, Allyson C. ; van Hulten, Marco ; Zhang, JingQuantitative knowledge about the burial of sedimentary components at the seafloor has wide-ranging implications in ocean science, from global climate to continental weathering. The use of 230Th-normalized fluxes reduces uncertainties that many prior studies faced by accounting for the effects of sediment redistribution by bottom currents and minimizing the impact of age model uncertainty. Here we employ a recently compiled global data set of 230Th-normalized fluxes with an updated database of seafloor surface sediment composition to derive atlases of the deep-sea burial flux of calcium carbonate, biogenic opal, total organic carbon (TOC), nonbiogenic material, iron, mercury, and excess barium (Baxs). The spatial patterns of major component burial are mainly consistent with prior work, but the new quantitative estimates allow evaluations of deep-sea budgets. Our integrated deep-sea burial fluxes are 136 Tg C/yr CaCO3, 153 Tg Si/yr opal, 20Tg C/yr TOC, 220 Mg Hg/yr, and 2.6 Tg Baxs/yr. This opal flux is roughly a factor of 2 increase over previous estimates, with important implications for the global Si cycle. Sedimentary Fe fluxes reflect a mixture of sources including lithogenic material, hydrothermal inputs and authigenic phases. The fluxes of some commonly used paleo-productivity proxies (TOC, biogenic opal, and Baxs) are not well-correlated geographically with satellite-based productivity estimates. Our new compilation of sedimentary fluxes provides detailed regional and global information, which will help refine the understanding of sediment preservation.
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Article230 Th normalization: new insights on an essential tool for quantifying sedimentary fluxes in the modern and quaternary ocean(John Wiley & Sons, 2020-01-27) Costa, Kassandra M. ; Hayes, Christopher T. ; Anderson, Robert F. ; Pavia, Frank ; Bausch, Alexandra ; Deng, Feifei ; Dutay, Jean-Claude ; Geibert, Walter ; Heinze, Christoph ; Henderson, Gideon M. ; Hillaire‐Marcel, Claude ; Hoffmann, Sharon S. ; Jaccard, Samuel L. ; Jacobel, Allison W. ; Kienast, Stephanie S. ; Kipp, Lauren ; Lerner, Paul ; Lippold, Jörg ; Lund, David C. ; Marcantonio, Franco ; McGee, David ; McManus, Jerry F. ; Mekik, Figen ; Middleton, Jennifer L. ; Missiaen, Lise ; Not, Christelle ; Pichat, Sylvain ; Robinson, Laura F. ; Rowland, George H. ; Roy-Barman, Matthieu ; Tagliabue, Alessandro ; Torfstein, Adi ; Winckler, Gisela ; Zhou, Yuxin230Th normalization is a valuable paleoceanographic tool for reconstructing high‐resolution sediment fluxes during the late Pleistocene (last ~500,000 years). As its application has expanded to ever more diverse marine environments, the nuances of 230Th systematics, with regard to particle type, particle size, lateral advective/diffusive redistribution, and other processes, have emerged. We synthesized over 1000 sedimentary records of 230Th from across the global ocean at two time slices, the late Holocene (0–5,000 years ago, or 0–5 ka) and the Last Glacial Maximum (18.5–23.5 ka), and investigated the spatial structure of 230Th‐normalized mass fluxes. On a global scale, sedimentary mass fluxes were significantly higher during the Last Glacial Maximum (1.79–2.17 g/cm2kyr, 95% confidence) relative to the Holocene (1.48–1.68 g/cm2kyr, 95% confidence). We then examined the potential confounding influences of boundary scavenging, nepheloid layers, hydrothermal scavenging, size‐dependent sediment fractionation, and carbonate dissolution on the efficacy of 230Th as a constant flux proxy. Anomalous 230Th behavior is sometimes observed proximal to hydrothermal ridges and in continental margins where high particle fluxes and steep continental slopes can lead to the combined effects of boundary scavenging and nepheloid interference. Notwithstanding these limitations, we found that 230Th normalization is a robust tool for determining sediment mass accumulation rates in the majority of pelagic marine settings (>1,000 m water depth).
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ArticleMarine sedimentary uranium to barium ratios as a potential quantitative proxy for Pleistocene bottom water oxygen concentrations(Elsevier, 2023-02-15) Costa, Kassandra M. ; Nielsen, Sune G. ; Wang, Yi ; Lu, Wanyi ; Hines, Sophia K.V. ; Jacobel, Allison W. ; Oppo, Delia W.Oxygen is essential for marine ecosystems, and it is linked by respiration to carbon storage in the deep ocean. Reconstructing oxygen concentrations in the past has been limited by the absence of quantitative, rather than qualitative, proxies, but several new (semi-) quantitative oxygen proxies have recently been developed. In this study we explore the possibility of adding bulk sedimentary uranium (U) to this list by normalizing it to barium (Ba). First, U/Ba and bottom water oxygen concentrations are compared on a global scale, using a core top database, in pelagic environments greater than 200 m water depth. Then, the relationships between U/Ba and bottom water oxygen are examined on smaller spatial scales: within each ocean basin and regionally within the Eastern Equatorial Pacific, the Arabian Sea, and Western Equatorial Atlantic. At this regional scale, where secondary influences on the behavior of both U and Ba may be more spatially uniform, empirical piecewise linear calibrations are developed and subsequently tested on downcore records. U/Ba-based oxygen reconstructions generally agree with those derived from previously published alkenone preservation and benthic foraminiferal surface porosity records. Several limitations to the utility of U/Ba as a proxy for oxygen have also been identified. The proxy should only be applied in the uppermost sedimentary intervals that contain porewater sulfate to minimize barite diagenesis, and phosphorus contents should be monitored for the potential influence of apatite on uranium content. U/Ba is more successful at recording oxygen concentrations during mean glacial and interglacial periods than during climate transitions, when the timing and amplitude may be more sensitive to burndown and smoothing. Conservative errors on the calibrations result in the greatest utility of U/Ba in regions with relatively high oxygen concentrations (e.g., >50 μmol/kg) and large oxygen variability (±10 s of μmol/kg). Even with these caveats, U/Ba is only one of two quantitative oxygen proxies potentially capable of recording variability above 50 μmol/kg, and further investigation into its functionality in different environmental settings is worthwhile in the endeavor to reconstruct the full marine range of oxygen concentrations in the past. All data are available in Supplementary Data 1 and 2.