Hardisty
Dalton S.
Hardisty
Dalton S.
No Thumbnail Available
Search Results
Now showing
1 - 9 of 9
-
PreprintTrace elements at the intersection of marine biological and geochemical evolution( 2016-10) Robbins, Leslie J. ; Lalonde, Stefan V. ; Planavsky, Noah J. ; Partin, Camille A. ; Reinhard, Christopher T. ; Kendall, Brian ; Scott, Clint ; Hardisty, Dalton S. ; Gill, Benjamin C. ; Alessi, Daniel S. ; Dupont, Christopher L. ; Saito, Mak A. ; Crowe, Sean A. ; Poulton, Simon W. ; Bekker, Andrey ; Lyons, Timothy W. ; Konhauser, Kurt O.Life requires a wide variety of bioessential trace elements to act as structural components and reactive centers in metalloenzymes. These requirements differ between organisms and have evolved over geological time, likely guided in some part by environmental conditions. Until recently, most of what was understood regarding trace element concentrations in the Precambrian oceans was inferred by extrapolation, geochemical modeling, and/or genomic studies. However, in the past decade, the increasing availability of trace element and isotopic data for sedimentary rocks of all ages have yielded new, and potentially more direct, insights into secular changes in seawater composition – and ultimately the evolution of the marine biosphere. Compiled records of many bioessential trace elements (including Ni, Mo, P, Zn, Co, Cr, Se, and I) provide new insight into how trace element abundance in Earth’s ancient oceans may have been linked to biological evolution. Several of these trace elements display redox-sensitive behavior, while others are redox-sensitive but not bioessential (e.g., Cr, U). Their temporal trends in sedimentary archives provide useful constraints on changes in atmosphere-ocean redox conditions that are linked to biological evolution, for example, the activity of oxygen-producing, photosynthetic cyanobacteria. In this review, we summarize available Precambrian trace element proxy data, and discuss how temporal trends in the seawater concentrations of specific trace elements may be linked to the evolution of both simple and complex life. We also examine several biologically relevant and/or redox-sensitive trace elements that have yet to be fully examined in the sedimentary rock record (e.g., Cu, Cd, W) and suggest several directions for future studies.
-
PreprintAn evaluation of sedimentary molybdenum and iron as proxies for pore fluid paleoredox conditions( 2018-04) Hardisty, Dalton S. ; Lyons, Timothy W. ; Riedinger, Natascha ; Isson, Terry T. ; Owens, Jeremy D. ; Aller, Robert C. ; Rye, Danny ; Planavsky, Noah J. ; Reinhard, Christopher T. ; Gill, Benjamin C. ; Masterson, Andrew L. ; Asael, Dan ; Johnston, David T.Iron speciation and trace metal proxies are commonly applied together in efforts to identify anoxic settings marked by the presence of free sulfide (euxinia) or dissolved iron (ferruginous) in the water column. Here, we use a literature compilation from modern localities to provide a new empirical evaluation of coupled Fe speciation and Mo concentrations as a proxy for pore water sulfide accumulation at non-euxinic localities. We also present new Fe speciation, Mo concentration, and S isotope data from the Friends of Anoxic Mud (FOAM) site in Long Island Sound, which is marked by pore water sulfide accumulation of up to 3 mM beneath oxygen-containing bottom waters. For the operationally defined Fe speciation scheme, ‘highly reactive’ Fe (FeHR) is the sum of pyritized Fe (Fepy) and Fe dominantly present in oxide phases that is available to react with pore water sulfide to form pyrite. Observations from FOAM and elsewhere confirm that Fepy/FeHR from non-euxinic sites is a generally reliable indicator of pore fluid redox, particularly the presence of pore water sulfide. Molybdenum (Mo) concentration data for anoxic continental margin sediments underlying oxic waters but with sulfidic pore fluids typically show authigenic Mo enrichments (2-25 ppm) that are elevated relative to the upper crust (1-2 ppm). However, compilations of Mo concentrations comparing sediments with and without sulfidic pore fluids underlying oxic and low oxygen (non-euxinic) water columns expose non-unique ranges for each, exposing false positives and false negatives. False positives are most frequently found in sediments from low oxygen water columns (for example, Peru Margin), where Mo concentration ranges can also overlap with values commonly found in modern euxinic settings. FOAM represents an example of a false negative, where, despite elevated pore water sulfide concentrations and evidence for active Fe and Mn redox cycling in FOAM sediments, sedimentary Mo concentrations show a homogenous vertical profile across 50 cm depth at 1-2 ppm. A diagenetic model for Mo provides evidence that muted authigenic enrichments are derived from elevated sedimentation rates. Consideration of a range of additional parameters, most prominently pore water Mo concentration, can replicate the ranges of most sedimentary Mo concentrations observed in modern non-euxinic settings. Together, the modern Mo and Fe data compilations and diagenetic model provide a framework for identifying paleo-pore water sulfide accumulation in ancient settings and linked processes regulating seawater Mo and sulfate concentrations and delivery to sediments. Among other utilities, identifying ancient accumulation of sulfide in pore waters, particularly beneath oxic bottom waters, constrains the likelihood that those settings could have hosted organisms and ecosystems with thiotrophy at their foundations.
-
PreprintIron formations: A global record of Neoarchaean to Palaeoproterozoic environmental history( 2017-06-25) Konhauser, Kurt O. ; Planavsky, Noah J. ; Hardisty, Dalton S. ; Robbins, Leslie J. ; Warchola, Tyler J. ; Haugaard, Rasmus ; Lalonde, Stefan V. ; Partin, Camille A. ; Oonk, Paul B. H. ; Tsikos, Harilaos ; Lyons, Timothy W. ; Bekker, Andrey ; Johnson, Clark M.Iron formations (IF) represent an iron-rich rock type that typifies many Archaean and Proterozoic supracrustal successions and are chemical archives of Precambrian seawater chemistry and postdepositional iron cycling. Given that IF accumulated on the seafloor for over two billion years of Earth’s early history, changes in their chemical, mineralogical, and isotopic compositions offer a unique glimpse into environmental changes that took place on the evolving Earth. Perhaps one of the most significant events was the transition from an anoxic planet to one where oxygen was persistently present within the marine water column and atmosphere. Linked to this progressive global oxygenation was the evolution of aerobic microbial metabolisms that fundamentally influenced continental weathering processes, the supply of nutrients to the oceans, and, ultimately, diversification of the biosphere and complex life forms. Many of the key recent innovations in understanding IF genesis are linked to geobiology, since biologically assisted Fe(II) oxidation, either directly through photoferrotrophy, or indirectly through oxygenic photosynthesis, provides a process for IF deposition from mineral precursors. The abundance and isotope composition of Fe(II)-bearing minerals in IF additionally suggests microbial Fe(III) reduction, a metabolism that is deeply rooted in the Archaea and Bacteria. Linkages among geobiology, hydrothermal systems, and deposition of IF have been traditionally overlooked, but now form a coherent model for this unique rock type. This paper reviews the defining features of IF and their distribution through the Neoarchaean and Palaeoproterozoic. This paper is an update of previous reviews by Bekker et al. (2010, 2014) that will improve the quantitative framework we use to interpret IF deposition. In this work, we also discuss how recent discoveries have provided new insights into the processes underpinning the global rise in atmospheric oxygen and the geochemical evolution of the oceans.
-
PreprintUncovering the spatial heterogeneity of Ediacaran carbon cycling( 2016-12) Li, Chao ; Hardisty, Dalton S. ; Luo, Genming ; Huang, Junhua ; Algeo, Thomas J. ; Cheng, Meng ; Shi, Wei ; An, Zhihui ; Tong, Jinnan ; Xie, Shucheng ; Jiao, Nianzhi ; Lyons, Timothy W.Records of the Ediacaran carbon cycle (635 to 541 million years ago) include the Shuram excursion (SE), the largest negative carbonate-carbon isotope excursion in Earth history (down to -12 ‰). The nature of this excursion remains enigmatic given the difficulties of interpreting a perceived extreme global decrease in the δ13C of seawater dissolved inorganic carbon (DIC). Here, we present carbonate and organic carbon isotope (δ13Ccarb and δ13Corg) records from the Ediacaran Doushantuo Formation along a proximal-to-distal transect across the Yangtze Platform of South China as a test of the spatial variation of the SE. Contrary to expectations, our results show that the magnitude and morphology of this excursion and its relationship with coexisting δ13Corg are highly heterogeneous across the platform. Integrated geochemical, mineralogical, petrographic, and stratigraphic evidence indicates that the SE is a primary marine signature. Data compilations demonstrate that the SE was also accompanied globally by parallel negative shifts of δ34S of carbonate-associated sulfate (CAS) and increased 87Sr/86Sr ratio and coastal CAS concentration, suggesting elevated continental weathering and coastal marine sulfate concentration during the SE. In light of these observations, we propose a heterogeneous oxidation model to explain the high spatial heterogeneity of the SE and coexisting δ13Corg records of the Doushantuo, with likely relevance to the SE in other regions. In this model, we infer continued marine redox stratification through the SE but with increased availability of oxidants (e.g., O2 and sulfate) limited to marginal near-surface marine environments. Oxidation of limited spatiotemporal extent provides a mechanism to drive heterogeneous oxidation of subsurface reduced carbon mostly in shelf areas. Regardless of the mechanism driving the SE, future models must consider the evidence for spatial heterogeneity in δ13C presented in this study.
-
ArticleUpper 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, ZunliGlobal 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.
-
PreprintPerspectives 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.
-
PreprintOrganically 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, ZunliCarbonate-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.
-
ArticleIodine-to-calcium ratios in deep-sea scleractinian and bamboo corals(Frontiers Media, 2023-11-06) Sun, Yun-Ju ; Robinson, Laura F. ; Parkinson, Ian J. ; Stewart, Joseph A. ; Lu, Wanyi ; Hardisty, Dalton S. ; Liu, Qian ; Kershaw, James ; LaVigne, Michele ; Horner, Tristan J.The distribution of dissolved iodine in seawater is sensitive to multiple biogeochemical cycles, including those of nitrogen and oxygen. The iodine-to-calcium ratio (I/Ca) of marine carbonates, such as bulk carbonate or foraminifera, has emerged as a potential proxy for changes in past seawater oxygenation. However, the utility of the I/Ca proxy in deep-sea corals, natural archives of seawater chemistry with wide spatial coverage and radiometric dating potential, remains unexplored. Here, we present the first I/Ca data obtained from modern deep-sea corals, specifically scleractinian and bamboo corals, collected from the Atlantic, Eastern Pacific, and Southern Oceans, encompassing a wide range of seawater oxygen concentrations (10–280 μmol/kg). In contrast to thermodynamic predictions, we observe higher I/Ca ratios in aragonitic corals (scleractinian) compared to calcitic corals (bamboo). This observation suggests a strong biological control during iodate incorporation into deep-sea coral skeletons. For the majority of scleractinian corals, I/Ca exhibits a covariation with local seawater iodate concentrations, which is closely related to seawater oxygen content. Scleractinian corals also exhibit notably lower I/Ca below a seawater oxygen threshold of approximately 160 μmol/kg. In contrast, no significant differences in I/Ca are found among bamboo corals across the range of oxygen concentrations encountered (15–240 μmol/kg). In the North Atlantic, several hydrographic factors, such as temperature and/or salinity, may additionally affect coral I/Ca. Our results highlight the potential of I/Ca ratios in deep-sea scleractinian corals to serve as an indicator of past seawater iodate concentrations, providing valuable insights into historical seawater oxygen levels.
-
ArticleRates and pathways of iodine speciation transformations at the Bermuda Atlantic Time Series(Frontiers Media, 2024-01-08) Schnur, Alexi A. ; Sutherland, Kevin M. ; Hansel, Colleen M. ; Hardisty, Dalton S.The distribution of iodine in the surface ocean – of which iodide-iodine is a large destructor of tropospheric ozone (O3) – can be attributed to both in situ (i.e., biological) and ex situ (i.e., mixing) drivers. Currently, uncertainty regarding the rates and mechanisms of iodide (I-) oxidation render it difficult to distinguish the importance of in situ reactions vs ex situ mixing in driving iodine’s distribution, thus leading to uncertainty in climatological ozone atmospheric models. It has been hypothesized that reactive oxygen species (ROS), such as superoxide (O2•−) or hydrogen peroxide (H2O2), may be needed for I- oxidation to occur at the sea surface, but this has yet to be demonstrated in natural marine waters. To test the role of ROS in iodine redox transformations, shipboard isotope tracer incubations were conducted as part of the Bermuda Atlantic Time Series (BATS) in the Sargasso Sea in September of 2018. Incubation trials evaluated the effects of ROS (O2•−, H2O2) on iodine redox transformations over time and at euphotic and sub-photic depths. Rates of I- oxidation were assessed using a 129I- tracer (t1/2 ~15.7 Myr) added to all incubations, and 129I/127I ratios of individual iodine species (I-, IO3-). Our results show a lack of I- oxidation to IO3- within the resolution of our tracer approach – i.e., <2.99 nM/day, or <1091.4 nM/yr. In addition, we present new ROS data from BATS and compare our iodine speciation profiles to that from two previous studies conducted at BATS, which demonstrate long-term iodine stability. These results indicate that ex situ processes, such as vertical mixing, may play an important role in broader iodine species’ distribution in this and similar regions.