Below are themes and information from some ongoing research projects. Graduate students and postdocs working in the lab will have the opportunity to expand on these projects, but also to branch out and lead independent research related to or beyond that already ongoing at MSU.
Top: Rosette for collection of seawater onboard the RV Atlantic Explorer in Sept. 2018 in the Sargasso Sea. The seawater is being used for incubations to track iodine oxidation.
Bottom: Seawater incubations onboard the RV Falkor at the oxygen minimum zone off the coast of Mexico in July 2018. This ongoing study is aimed at understanding iodine reduction.

Tracers in modern systems

Our group currently has an NSF-funded research project focused on placing chemical constraints on the modern iodine cycle. Multiple fields rely on an understanding of marine iodine chemistry, but many of the fundamentals are still unknown. For example, seawater iodate can be tracked in carbonate sediment and used as a tracer of oxygen availability in ancient seawater, but gaps in our understanding of iodate formation limit this application. Iodine also plays a key role in tropospheric ozone cycling, and tying ozone models to marine iodine chemistry remains a challenge. Tracking the fate of radioactive isotopes of iodine emitted from nuclear facilities also requires quantitative constraints on the biological and chemical cycling of iodine in seawater. 

The main question: how and where does iodate, the oxidized form of iodine, form in the ocean? What processes drive iodine oxidation and reduction in seawater? Can we close the marine iodine mass balance? These currently missing fundamentals act a bottleneck for multiple research fields. Determination of reaction mechanisms and kinetics for the marine iodine cycle will be a major contribution to the above listed and other applications.

The project features a collaboration with Woods Hole Oceanographic Institution, multi-collector ICP-MS application, and experiments aboard multiple research vessels. Using subsamples collected from shipboard seawater tracer experiments, we use MC-ICP-MS to measure the iodine isotopic composition of specific iodine chemical species and reconstruct chemical reaction pathways and rates. To date, this has involved the study of oxidative iodine cycling in the Atlantic onboard the RV Endeavor and RV Atlantic Explorer and the study of reductive cycling in Pacific oxygen minimum zones onboard the RV Falkor. 

Though our lab currently has a large focus on iodine, we ultimately plan to expand our tracer work to other redox-sensitive elements whose seawater abundance can be reconstructed from the rock record, but are similarly missing fundamental modern constraints.

​Marine chemical budgets

​Caption: Photos taken from HOV Alvin during a cruise targeting samples from hydrothermal fluids and resulting plumes at the East Pacific Rise 9°N in Dec. 2018.
As complimentary constraints to our tracer experiments examining chemical reactions of redox-sensitive elements in seawater, we are also striving to better constrain the chemical budgets of these same elements. As part of that effort, Hardisty traveled to the East Pacific Rise in Dec. 2018 in an effort to characterize the marine input flux of redox-sensitive elements, most prominently iodine, and their isotope compositions in hydrothermal vent fluids and resulting plumes. The research project is part of Hardisty's involvement in an NSF chief-scientist training cruise onboard the RV Atlantis. The cruise scientists will deploy the Human Occupied Vehicle Alvin to directly sample from the hydrothermal vent sites. This video link and this video link show highlights from one of the DSV Alvin dives from our cruise to  the EPR. We'll keep you updated!
Caption: From Lu et al., 2108. I/Ca ratios in carbonate rocks are a tracer for ambient dissolved iodate concentrations in the ocean. I/Ca ratios can be linked to ancient oxygen availability.

Tracers of ancient seawater oxygen

The distribution of redox-sensitive elements, those whose speciation in part depends on ambient oxygen availability, in sedimentary minerals are commonly applied to reconstruct oxygen availability in ancient seawater. Hardisty's group is engaged in a number of these applications, with a focus on understanding seawater oxygen concentrations and distribution during the early evolution of marine eukaryotes and animals. Our past and ongoing work  has focused on the application of iodine in carbonate rocks to track past seawater iodate concentrations. Recent findings culminating from these works (left, Lu et al., 2018, Science) reveal that well-oxygenated ocean's similar to today may not have become characteristic until as early as 200 million years ago.

Work to fill in gaps in the record, provide independent constraints from other redox proxies, understand the role of diagenesis on the carbonate iodine record, and better constrain the modern iodine cycle are the next steps. Using MSU's new clean lab, laser ablation, and ICP-MS, our research group has active plans to utilize additional concentration and isotope-based tracers to constrain ocean chemistry on a range of timescales through Earth history.
 Caption: Fossilized coral (Pleistocene age) at Windley Key State Park in the Florida Keys. Understanding the ongoing chemical and mineralogical transitions that occur after deposition in carbonate from the Keys and Bahamas are pivotal to interpreting carbonate geochemistry in the ancient record.

Carbonate diagenesis

As a contributor to collaborations with the University of North Carolina, Yale University, Georgia Tech, and Arizona State University, we are actively seeking to understand the post-depositional, or diagenetic, influences on a range carbonate-hosted paleoredox proxies. We are evaluating paleoredox proxies (I/Ca, Ce anomaly, U isotopes, among others) in the same well-characterized carbonate samples from the Great Bahamas Bank to recognize influences beyond primary seawater chemistry on the elemental and isotopic compositions we view today. The ultimate goal is to make applications to less-constrained ancient carbonates more quantitative through the use of multiple proxies whose relationships are well known in analogous modern rock types.