Lu Zunli

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Lu
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Zunli
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  • Dataset
    Geochemical concentrations (ppm) of six elements measured in Atlantic croaker otoliths
    (Biological and Chemical Oceanography Data Management Office (BCO-DMO). Contact: bco-dmo-data@whoi.edu, 2020-03-20) Walther, Benjamin ; Limburg, Karin ; Lu, Zunli
    Geochemical concentrations (ppm) of six elements measured in otoliths of Atlantic croaker sampled on board of the R/V Oregon II during the NOAA Seamap Fall Groundfish Survey of 2014 (Oct 10 to Nov 4) and 2015 (Oct 8 to Nov 22). For a complete list of measurements, refer to the full dataset description in the supplemental file 'Dataset_description.pdf'. The most current version of this dataset is available at: https://www.bco-dmo.org/dataset/784969
  • Article
    Upper ocean oxygenation dynamics from I/Ca ratios during the Cenomanian-Turonian OAE 2
    (John Wiley & Sons, 2015-05-13) Zhou, Xiaoli ; Jenkyns, Hugh C. ; Owens, Jeremy D. ; Junium, Christopher K. ; Zheng, Xin-Yuan ; Sageman, Bradley B. ; Hardisty, Dalton S. ; Lyons, Timothy W. ; Ridgwell, Andy ; Lu, Zunli
    Global warming lowers the solubility of gases in the ocean and drives an enhanced hydrological cycle with increased nutrient loads delivered to the oceans, leading to increases in organic production, the degradation of which causes a further decrease in dissolved oxygen. In extreme cases in the geological past, this trajectory has led to catastrophic marine oxygen depletion during the so-called oceanic anoxic events (OAEs). How the water column oscillated between generally oxic conditions and local/global anoxia remains a challenging question, exacerbated by a lack of sensitive redox proxies, especially for the suboxic window. To address this problem, we use bulk carbonate I/Ca to reconstruct subtle redox changes in the upper ocean water column at seven sites recording the Cretaceous OAE 2. In general, I/Ca ratios were relatively low preceding and during the OAE interval, indicating deep suboxic or anoxic waters exchanging directly with near-surface waters. However, individual sites display a wide range of initial values and excursions in I/Ca through the OAE interval, reflecting the importance of local controls and suggesting a high spatial variability in redox state. Both I/Ca and an Earth System Model suggest that the northeast proto-Atlantic had notably higher oxygen levels in the upper water column than the rest of the North Atlantic, indicating that anoxia was not global during OAE 2 and that important regional differences in redox conditions existed. A lack of correlation with calcium, lithium, and carbon isotope records suggests that neither enhanced global weathering nor carbon burial was a dominant control on the I/Ca proxy during OAE 2.
  • Preprint
    Perspectives on Proterozoic surface ocean redox from iodine contents in ancient and recent carbonate
    ( 2017-01) Hardisty, Dalton S. ; Lu, Zunli ; Bekker, Andrey ; Diamond, Charles W. ; Gill, Benjamin C. ; Jiang, Ganqing ; Kah, Linda ; Knoll, Andrew H. ; Loyd, Sean ; Osburn, Magdalena ; Planavsky, Noah J.
    The Proterozoic Eon hosted the emergence and initial recorded diversification of eukaryotes. Oxygen levels in the shallow marine settings critical to these events were lower than today’s, although how much lower is debated. Here, we use concentrations of iodate (the oxidized iodine species) in shallow-marine limestones and dolostones to generate the first comprehensive record of Proterozoic near-surface marine redox conditions. The iodine proxy is sensitive to both local oxygen availability and the relative proximity to anoxic waters. To assess the validity of our approach, Neogene-Quaternary carbonates are used to demonstrate that diagenesis most often decreases and is unlikely to increase carbonate-iodine contents. Despite the potential for diagenetic loss, maximum Proterozoic carbonate iodine levels are elevated relative to those of the Archean, particularly during the Lomagundi and Shuram carbon isotope excursions of the Paleo- and Neoproterozoic, respectively. For the Shuram anomaly, comparisons to Neogene-Quaternary carbonates suggest that diagenesis is not responsible for the observed iodine trends. The baseline low iodine levels in Proterozoic carbonates, relative to the Phanerozoic, are linked to a shallow oxic-anoxic interface. Oxygen concentrations in surface waters would have at least intermittently been above the threshold required to support eukaryotes. However, the diagnostically low iodine data from mid-Proterozoic shallow-water carbonates, relative to those of the bracketing time intervals, are consistent with a dynamic chemocline and anoxic waters that would have episodically mixed upward and laterally into the shallow oceans. This redox instability may have challenged early eukaryotic diversification and expansion, creating an evolutionary landscape unfavorable for the emergence of animals.
  • Preprint
    Organically bound iodine as a bottom-water redox proxy : preliminary validation and application
    ( 2017-03-15) Zhou, Xiaoli ; Jenkyns, Hugh C. ; Lu, Wanyi ; Hardisty, Dalton S. ; Owens, Jeremy D. ; Lyons, Timothy W. ; Lu, Zunli
    Carbonate-associated iodine (I/Ca) has been used as a proxy of local, upper-ocean redox conditions, and has successfully demonstrated highly dynamic spatial and temporal patterns across different time scales of Earth history. To further explore the utility of iodine as a paleo-environmental proxy, we present here a new method of extracting organically bound iodine (Iorg) from shale using volumes of samples on the order of tens of milligrams, thus offering the potential for high-resolution work across thin shale beds. The ratio of Iorg to total organic carbon (I/TOC) in modern surface and subsurface sediments decreases with decreasing bottom-water oxygen, which may be used to reconstruct paleo-redox changes. As a proof of concept, we evaluate the I/TOC proxy in Holocene sediments from the Baltic Sea, Landsort Deep (IODP 347) and discuss those data within a framework of additional independent redox proxies, e.g., iron speciation and [Mo]. The results imply that I/TOC may be sensitive to hypoxic–suboxic conditions, complementary to proxies sensitive to more reducing, anoxic–euxinic conditions. Then, we test the usage of I/TOC in sediments deposited during Late Cretaceous, Cenomanian–Turonian Oceanic Anoxic Event (OAE) 2 from ~ 94 million years ago (Ma). We generated I/TOC and Iorg records from six OAE 2 sections: Tarfaya (Morocco), Furlo (central Italy), Demerara Rise (western equatorial Atlantic), Cape Verde Basin (eastern equatorial Atlantic), South Ferriby (UK), and Kerguelen Plateau (southern Indian Ocean), which provide a broad spatial coverage. Generally, I/TOC decreases over the interval recorded by the positive carbon-isotope excursion, the global signature of OAE 2, suggesting an expansion of more reducing bottom-water conditions and consistent with independent constraints from iron speciation and redox-sensitive trace-metals (e.g., Mo). Relatively higher I/TOC values (thus more oxic conditions) are recorded at two high latitude sites for OAE 2, supporting previous model simulations (cGENIE) that indicated higher bottom water oxygen concentrations in these regions. Our results also indicate that organic-rich and oxygenated seafloors are likely a major sink of iodine and correspondingly influence its global seawater inventory.
  • Article
    Commentary: Planktic foraminifera iodine/calcium ratios from plankton tows
    (Frontiers Media, 2023-07-11) Lu, Zunli ; Thomas, Ellen ; Rickaby, Rosalind E. M. ; Lu, Wanyi ; Prow, Ashley N.
    I/Ca in planktic foraminiferal shells is one of the few proxies proposed for reconstructing past upper ocean oxygenation. Foraminiferal I/Ca values have been measured in globally distributed core-top samples, with low I/Ca values generally indicative of low-oxygen water (Lu et al., 2020a; Lu et al., 2020b). Winkelbauer et al. (2023) observed that “I/Ca values of plankton tow foraminifera from environments with well oxygenated subsurface waters, however, are an order of magnitude lower compared to core-tops from similarly well-oxygenated regions,” and concluded that “planktic foraminifera gain iodine post-mortem, either when sinking through the water column, or during burial.” These tow-derived low I/Ca values add to the information needed to mechanistically understand the planktic I/Ca proxy. However, we highlight the fact that tow-specimens do not represent the same populations as those present in core tops, and we think that further evidence is needed before reinterpreting the core-top and down-core planktic I/Ca records.