Research

Manganese oxides are great scavengers of trace metals in the waters. How trace metals get removed from the water via sorption and whether there is fractionation occurring in this process play an important role in their marine mass balance. The various kinds of Mn oxide minerals in the natural environments also mean that metal sorption and isotope fraction behavior could vary significantly with Mn oxide mineralogy. We are using various lab synthesized Mn oxide minerals to investigate how Tl gets removed and (not) fractionated on the mineral surface (supported by NASA funding).

Relevant publications:

• R. F. Phillips*, Y. Wang, F. Klein, G. Farfan, C. M. Ostrander, H. Gadol, C. M. Hansel, and S. G. Nielsen. The role of manganese oxide mineralogy in thallium isotopic fractionation upon sorption, 2023. Geochimica et Cosmochimica Acta, 356, 83-92, doi: 10.1016/j.gca.2023.07.011. (* student mentee).

With new modern calibration of thallium isotopes, we have applied this proxy in multiple paleo-scenarios (Last Glacial Maximum, Oceanic Anoxic Event, to Mesoproterozoic). Newly funded NSF project will focus on the Penultimate Glacial Cycle, which aims to reconstruct both local and global ocean oxygen responses to glacial-glacial climate change. Other opportunities include Cenozoic sediments from the recent IODP 390/393 cruise.

Funding:

NSF-OCE 2310174, PIs: Yi Wang (lead), Sune Nielsen, and Kassandra Costa, From local to global: deciphering oceanic oxygenation responses through the Penultimate Glacial Cycle ($688,078) 

Post-Expedition Award for IODP 390: Lessons from past warm periods: preliminary study on oxygenation responses to climate change in Cenozoic ($19,938)

Relevant publications:

• Y. Wang, K. M. Costa, W. Lu, Sophia K.V. Hines, and S. G. Nielsen. Global oceanic oxygenation controlled by the Southern Ocean through the last deglaciation (in review, Science Advances).

• A. Heard**, Y. Wang**, C. M. Ostrander, M. Auro, D. Canfield, S. Zhang, H. Wang, X. Wang, and S. Nielsen. Coupled vanadium and thallium isotope constraints on Mesoproterozoic ocean oxygenation around 1.38-1.39 Ga, 2023. Earth & Planetary Science Letters, 616, doi: 10.1016/j.epsl.2023.118127. (**co-first author)

• Y. Wang, S. Bodin, J. S. Blusztajn, C. Ullmann, and S. G. Nielsen, 2022. Orbitally paced global oceanic deoxygenation decoupled from volcanic CO2 emission during the middle Cretaceous Oceanic Anoxic Event 1b (Aptian-Albian transition), Geology, doi: 10.1130/G50553.1.

To investigate atmospheric teleconnections and oceanic oxygenation responses, we investigated the Holocene oxygenation using redox-sensitive trace metal records, which suggests much lower DO in the early to mid Holocene (before ~6 ka) than post-Industrial Revolution values. 

After comparing the DO record with climate parameters (e.g., sea surface temperatures) and productivity, we attribute this much larger natural variability of DO to oxygen changes in the North Pacific Intermediate Water that forms in the northwest Pacific and propagates to the east. This is also corroborated by state-of-the-art model (Community Earth System Model 1.2) results, as sea ice brine rejection was weakened owing to early Holocene atmospheric circulation patterns (e.g., weakened Aleutian Low). We thus suggest a coupled oceanic response in North Pacific (e.g., mid-depth ventilation) to atmospheric circulation changes in Holocene.

Relevant publications:

• Y. Wang, I. Hendy, and J. Zhu. Extreme low-oxygen conditions in the early-to mid- Holocene associated with ventilation shifts in the Northeast Pacific, Quaternary Science Reviews, 238, doi:10.1016/j.quascirev.2020.106326. 

To identify appropriate redox proxies that minimize possible post-depositional overprints, modern proxy validation is required.

Fe speciation that measures readily reduced reactive Fe and redox-sensitive pyrite has been widely used as a redox proxy. We revisited some caveats of Fe speciation with magnetic analyses that characterize magnetic Fe minerals. We confirmed that instantaneous depositional events (e.g., flood and turbidite layers) could initiate post-depositional pyrite formation, and thus result in ‘false-positive’ sulfidic (HS- presence, complete absence of oxygen) water columns, compromising redox reconstructions.

Relevant publications:

• Y. Wang, I. Hendy, J. C. Latimer, D. Bilardello. Diagenesis and iron paleo-redox proxies: new perspectives from magnetic and iron speciation analyses in the Santa Barbara Basin, Chemical Geology, 519, 95-109, DOI: 10.1016/j.chemgeo.2019.04.018.

• Y. Wang. Post-deposition diagenesis indicated by mineralogy shifts from magnetic measurements. The IRM Quarterly, 27(1). 

Intrigued by longer time scale variability (multicentennial to millennial), we explored a Common Era core (~2-5 year resolution) in SBB to resolve natural magnitude of DO variability. Bulk sedimentary δ15N and total organic carbon were analyzed, which revealed competing tropical and subarctic water masses that transport nitrate to Southern California. We confirmed more tropical water influences during the Medieval Climate Anomaly (~1000-1100 CE) yet stronger connections with the subarctic water transport during the Little Ice Age (1670-1840 CE), which suggests responses of oceanic nitrogen cycling to remote atmospheric forcing driven by climate shifts. 

Relevant publications:

• Y.Wang, I. Hendy, and R. Thunell. Local and remote forcing of denitrification in the Northeast Pacific for the last 2000 years. Paleoceanography and Paleoclimatology, 34, doi:10.1029/2019PA003577

When extracting O2 shifts from redox records, it is necessary to apply an integrated approach that investigates the knobs controlling oceanic O2 inventory (O2 supply and consumption) including climate parameters (e.g., temperature, wind field, sea ice) and biological activities (e.g., productivity).

Post-Industrial Revolution oxygenation history was constructed from a trace metal record from the Santa Barbara Basin (SBB) in Southern California. We demonstrated that decreased oxygen concentrations since the 20th century is associated with the anthropogenic warming trend. Additionally, El Niño is shown to control advection of the dense and oxygenated intermediate water into the SBB. 

Relevant publications:

• Y. Wang, I. Hendy, and T. Napier. Climate and anthropogenic controls of coastal deoxygenation on interannual to centennial timescales, Geophysical Research Letters. 44, 11,528–11,536, DOI: 10.1002/2017GL075443