Middleton Jennifer L.

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Last Name
Middleton
First Name
Jennifer L.
ORCID
0000-0001-7147-2388

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  • Article
    Trace metal evidence for deglacial ventilation of the abyssal Pacific and Southern Oceans
    (American Geophysical Union, 2021-08-17) Pavia, Frank ; Wang, Shouyi ; Middleton, Jennifer L. ; Murray, Richard W. ; Anderson, Robert F.
    The deep ocean has long been recognized as the reservoir that stores the carbon dioxide (CO2) removed from the atmosphere during Pleistocene glacial periods. The removal of glacial atmospheric CO2 into the ocean is likely modulated by an increase in the degree of utilization of macronutrients at the sea surface and enhanced storage of respired CO2 in the deep ocean, known as enhanced efficiency of the biological pump. Enhanced biological pump efficiency during glacial periods is most easily documented in the deep ocean using proxies for oxygen concentrations, which are directly linked to respiratory CO2 levels. We document the enhanced storage of respired CO2 during the Last Glacial Maximum (LGM) in the Pacific Southern Ocean and deepest Equatorial Pacific using records of deglacial authigenic manganese, which form as relict peaks during increases in bottom water oxygen (BWO) concentration. These peaks are found at depths and regions where other oxygenation histories have been ambiguous, due to diagenetic alteration of authigenic uranium, another proxy for BWO. Our results require that the entirety of the abyssal Pacific below approximately 1,000 m was enriched in respired CO2 and depleted in oxygen during the LGM. The presence of authigenic Mn enrichment in the deep Equatorial Pacific for each of the last five deglaciations suggests that the storage of respired CO2 in the deep ocean is a ubiquitous feature of late-Pleistocene ice ages.
  • Article
    230 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, Yuxin
    230Th 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).