Earth’s oceanic oxygen history from Phanerozoic to Pleistocene glacial cycles: insights from the carbonate iodine-to-calcium proxy

Oxygen in the oceans is an important part of the significant and complex evolution of Earth’s climate, with great significance for the evolution of life in the oceans. My PhD research has been primarily driven by three major questions: (1) How can we reliably reconstruct oxygen levels in ancient oceans? (2) How did oceanic oxygen levels evolve throughout Earth’s history? (3) How did oceanic oxygen levels affect habitability of the Earth? Most studies of the Earth’s oxygen history have focused on the atmosphere and deep oceans, but in contrast, I focused on the upper ocean (the top tens to a few hundred meters in the water column) where we see the oxygen minimum zones in the present oceans. This is a critical zone where animals have diversified most dramatically in Phanerozoic (542 million years ago (Ma) to present day) and where geologists have the best fossil record for biology/environment comparison. I used a novel proxy, the iodine-to-calcium ratio (I/Ca) in carbonate rocks and planktic microfossils, which can track oxygen changes over a range of values where most modern marine animals are sensitive, i.e., at higher oxygen levels rather than euxinia (containing H2S) or anoxia (no O2). Four major projects in my dissertation are: 1) Phanerozoic upper ocean oxygenation history and its coevolution with life. When and how oceanic oxygen had evolved to modern-like levels has remained elusive in Earth’s oxygen history, because few redox proxies can track secular variations in dissolved oxygen concentrations around threshold values for metazoan survival in the upper ocean. To address this question, we measured I/Ca in an extensive Phanerozoic collection of shallow marine carbonates and simulated marine iodine cycle in an Earth system model. We found that (1) I/Ca spiked during the Devonian, supporting a major rise in atmospheric O2 at ~400 Ma. (2) a step change in the oxygenation of the upper ocean to relatively sustainable near-modern conditions at ~200 Ma, likely driven by a shift in organic matter remineralization to greater depths, which may be due to increasing size and biomineralization of eukaryotic plankton. 2) Planktic foraminiferal I/Ca proxy in the Southeast Atlantic Ocean. Planktic foraminiferal I/Ca is a promising tool to reconstruct the extent of past upper ocean oxygenation, but a thorough assessment is necessary to evaluate both its potential and its limitations. We used foraminifers from Holocene core-tops (Southeast Atlantic Ocean) to document planktic I/Ca across a range of oceanographic conditions. We found that low planktic I/Ca can be used empirically to indicate hypoxia (O2 \u3c 70–100 µmol/kg) in the upper water column. At a site located in the Benguela Upwelling System, down-core I/Ca records suggested that only small changes occurred in upper ocean oxygenation during the past 240 ka, probably related to strong upwelling dynamics in this region. 3) Bottom water oxygen changes in the glacial oceans and their driving mechanisms. Reliable, quantitative paleo-O2 data is needed to test whether climate models can replicate past climate conditions in order to improve the forecast of future oceanic oxygenation changes under possible global warming. To address this question, we developed I/Ca in the benthic foraminiferal Cibicidoides spp. as a novel semi-quantitative bottom water oxygen proxy. We then applied this proxy to five ocean drilling cores to reconstruct the bottom water oxygen levels in the glacial-interglacial oceans. Using a multi-proxy approach, we found that low-O2 water (\u3c 50 µmol/kg) may have been more extensive in the glacial Atlantic and Pacific Oceans compared to modern/Holocene, and the driving mechanisms for glacial deoxygenation may vary by ocean basin. 4) Direct comparison of benthic foraminiferal surface porosity and I/Ca proxies. Benthic foraminiferal surface porosity (the mean percentage of surface area covered by pores; higher porosity: lower oxygenation) and I/Ca (higher I/Ca: higher oxygenation) are both promising paleoceanographic proxies that need testing in down-core studies. Here we report the first down-core comparison (~45 kyr) of these proxies in a core from a cold seep site on the southern Brazilian margin (26°40′S, 46°26′W, 475 m water depth). The two proxies are overall consistent, with porosity values generally low (\u3c 10%) and I/Ca ranges between ~4 and ~6 µmol/mol throughout the core, suggesting that bottom water oxygen concentrations at the site remained above 50 µmol/kg during the last 45 kyr. Potential seafloor methane release during the last glacial period (40-20 ka), as indicated by anomalously negative δ13C values in foraminifera, apparently had limited impact on bottom water oxygenation, and interactions between competing processes potentially affecting bottom water oxygenation (i.e., water column stratification and productivity) may have limited the magnitude of changes in bottom water oxygen levels at the core site

Devonian Upper Ocean Redox Trends Across Laurussia: Testing Potential Influences of Marine Carbonate Lithology on Bulk Rock I/Ca Signals

The Devonian is characterized by major changes in ocean-atmosphere O2 concentrations, colonialization of continents by plants and animals, and widespread marine anoxic events associated with rapid d13C excursions and biotic crises. However, the long-term upper ocean redox trend for the Devonian is still not well understood. This study presents new I/Ca data from well-dated Lower Devonian through Upper Devonian limestone sections from the Great Basin (western Laurussia) and the Illinois Basin (central Laurussia). In addition, to better address potential influences of lithology and stratigraphy on I/Ca redox signals, I/Ca data are reported here as carbonate lithology-specific. Results indicate that lithologic changes do not exert a dominant control on bulk carbonate I/Ca trends, but the effects of some diagenetic overprints cannot be ruled out. For the Illinois Basin, low I/Ca values (more reducing) are recorded during the Pragian to Emsian and increased but fluctuating values are recorded during the Eifelian to Givetian. The Great Basin I/Ca trends suggest local upper oceans were more reducing in the Lochkovian, more oxic in the Pragian- Emsian, return to more reducing in the Eifelian, then to increasingly more oxic, but fluctuating in the Givetian-Frasnian. The local I/Ca variations at Great Basin likely share more similarity with global upper ocean condition (compared to the Illinois Basin) based on its position adjacent to the Panthalassic Ocean and its temporal co-variation with global environmental volatility trends. The overall reducing and variable redox conditions of local upper ocean (if not a diagenetic signal) during the Middle and Late Devonian of Great Basin coincide with evidence of increased global environmental volatility suggesting seawater redox may have been an important part of environmental instability at this time

Surface climate signals transmitted rapidly to deep North Atlantic throughout last millennium

Instrumental observations of subsurface ocean warming imply that ocean heat uptake has slowed 20th-century surface warming. We present high-resolution records from subpolar North Atlantic sediments that are consistent with instrumental observations of surface and deep warming/freshening and in addition reconstruct the surface-deep relation of the last 1200 years. Sites from ~1300 meters and deeper suggest an ~0.5 degrees celsius cooling across the Medieval Climate Anomaly to Little Ice Age transition that began ~1350 ± 50 common era (CE), whereas surface records suggest asynchronous cooling onset spanning ~600 years. These data suggest that ocean circulation integrates surface variability that is transmitted rapidly to depth by the Atlantic Meridional Ocean Circulation, implying that the ocean moderated Earth’s surface temperature throughout the last millennium as it does today

Folding graft copolymer with pendant drug segments for co-delivery of anticancer drugs

A graft copolymer with pendant drug segment can fold into nanostructures in a protein folding-like manner. The graft copolymer is constructed by directly polymerizing γ-camptothecin-glutamate N-carboxyanhydride (Glu(CPT)-NCA) on multiple sites of poly(ethylene glycol) (PEG)-based main chain via the ring open polymerization (ROP). The “purely” conjugated anticancer agent camptothecin (CPT) is hydrophobic and serves as the principal driving force during the folding process. When exposed to water, the obtained copolymer, together with doxorubicin (Dox), another anticancer agent, can fold into monodispersed nanocarriers (with a diameter of around 50 nm) for dual-drug delivery. Equipped with a PEG shell, the nanocarriers displayed good stability and can be internalized by a variety of cancer cell lines via the lipid raft and clathrin-mediated endocytotic pathway without premature leakage, which showed a high synergetic activity of CPT and Dox toward various cancer cells. In vivo study validated that the nanocarriers exhibited strong accumulation in tumor sites and showed a prominent anticancer activity against the lung cancer xenograft mice model compared with free drugs

Endoscopic rhizotomy for chronic lumbar zygapophysial joint pain.

BACKGROUND: Chronic lumbar zygapophysial joint pain is a common cause of chronic low back pain. Percutaneous radiofrequency ablation (RFA) is one of the effective management options; however, the results from the traditional RFA need to be improved in certain cases. The aim of this study is to investigate the effect of percutaneous radiofrequency ablation under endoscopic guidance (ERFA) for chronic low back pain secondary to facet joint arthritis. METHODS: This is a prospective study enrolled 60 patients. The cases were randomized into two groups: 30 patients in the control group underwent traditional percutaneous radiofrequency ablation, others underwent ERFA. The lumbar visual analog scale (VAS), MacNab score, and postoperative complications were used to evaluate the outcomes. All outcome assessments were performed at postoperative 1 day, 1 month, 3 months, 6 months, and 12 months. RESULTS: There was no difference between the two groups in preoperative VAS (P \u3e 0.05). VAS scores, except the postoperative first day, in all other postoperative time points were significantly lower than preoperative values each in both groups (P \u3c 0.05). There was no significant difference between the two groups in VAS at 1 day, 1 month, and 3 months after surgery (P \u3e 0.05). However, the EFRA demonstrated significant benefits at the time points of 3 months and 6 months (P \u3e 0.05). The MacNab scores of 1-year follow-up in the ERFA group were higher than that in the control group (P \u3c 0.05). The incidence of complications in the ERFA group was significantly less than that in the control group (P \u3c 0.05). CONCLUSIONS: ERFA may achieve more accurate and definite denervation on the nerves, which leads to longer lasting pain relief

Oxygen depletion recorded in upper waters of the glacial Southern Ocean

Oxygen depletion in the upper ocean is commonly associated with poor ventilation and storage of respired carbon, potentially linked to atmospheric CO2 levels. Iodine to calcium ratios (I/Ca) in recent planktonic foraminifera suggest that values less than ~2.5 μmol mol−1 indicate the presence of O2-depleted water. Here we apply this proxy to estimate past dissolved oxygen concentrations in the near surface waters of the currently well-oxygenated Southern Ocean, which played a critical role in carbon sequestration during glacial times. A down-core planktonic I/Ca record from south of the Antarctic Polar Front (APF) suggests that minimum O2 concentrations in the upper ocean fell below 70 μmol kg−1 during the last two glacial periods, indicating persistent glacial O2 depletion at the heart of the carbon engine of the Earth’s climate system. These new estimates of past ocean oxygenation variability may assist in resolving mechanisms responsible for the much-debated ice-age atmospheric CO2 decline

Secondary Production of Gaseous Nitrated Phenols in Polluted Urban Environments

Nitrated phenols (NPs) are important atmospheric pollutants that affect air quality, radiation, and health. The recent development of the time-of-flight chemical ionization mass spectrometer (ToF-CIMS) allows quantitative online measurements of NPs for a better understanding of their sources and environmental impacts. Herein, we deployed nitrate ions as reagent ions in the ToF-CIMS and quantified six classes of gaseous NPs in Beijing. The concentrations of NPs are in the range of 1 to 520 ng m(-3). Nitrophenol (NPh) has the greatest mean concentration. Dinitrophenol (DNP) shows the greatest haze-to-clean concentration ratio, which may be associated with aqueous production. The high concentrations and distinct diurnal profiles of NPs indicate a strong secondary formation to overweigh losses, driven by high emissions of precursors, strong oxidative capacity, and high NOx levels. The budget analysis on the basis of our measurements and box-model calculations suggest a minor role of the photolysis of NPs (Peer reviewe

Self-folded redox/acid dual-responsive nanocarriers for anticancer drug delivery

Self-folded redox/acid dual-responsive nanocarriers (RAD-NCs) are developed for physiologically triggered delivery of anticancer drug. The evidenced redox/acid responsiveness, facile decoration of ligands, and active tumor-targeting capability of RAD-NCs suggest their potential as a promising formulation for tumor-targeted chemotherapy