What We Do
Our work is inspired by the rich history of heavy elements, the mysteries surrounding non-traditional stable isotope fractionation, and the fascinating world of planktonic organisms.
Mercury and sulfur have captivated scientists and philosophers alike since the Middle Ages. The early studies of mercury-sulfur mixtures by alchemists can even be interpreted as the earliest descriptions of a chemical bond. Over 2000 years later, we remain fascinated by the chemistry of these elements. In my group, we also delve into the chemistry of actinides and lanthanides.
Our goal is to uncover the chemical principles hidden in nature, using stable isotopes to address questions that span the continuum from theoretical chemistry to biological oceanography. Our approach integrates quantum chemical modeling, laboratory experiments with both planktonic and abiotic systems, and seagoing fieldwork.
Current Projects
Theoretical
Over 20 years ago, experiments on MeHg photochemistry revealed that Hg isotopes can undergo magnetic isotope effects (MIE). Subsequently, we demonstrated that phytoplankton mediate similar MIE reactions, a process we termed photomicrobial. However, according to photochemistry, Hg compounds should not exhibit MIE. The observed Hg isotope signals in marine organisms challenge existing chemical theories. We have a project dedicated to developing quantum methodologies to explain MIE Hg signals in ecosystems. MIE has been proposed as a testing ground for biological processes, and our work could improve the investigation of these processes.
Experimental
MeHg photolysis is considered the main pathway for reducing the pool of MeHg by dissolved organic matter (DOM). However, this process may have limited impact on the bioavailable MeHg to phytoplankton cells. This raises a critical question: Could phytoplankton intracellular biochemistry play an active role in controlling MeHg photolysis, rather than merely serving as a storage for Hg? This possibility challenges the conventional emphasis on MeHg-DOM photolysis.
ANALYTICAL
Theoretical or laboratory experiments are not perfect representations of the complex ocean. It is critical to determine whether the proposed mechanisms for MeHg are active in the ocean. This is where the use of Hg stable isotopes offers a significant advantage, as the isotopic composition of Hg in marine organisms records the chemistry of MeHg.
The unique bioaccumulation and trophic transfer of MeHg, along with the elimination of inorganic Hg within marine food webs, will allow us to use Hg stable isotopes as inert tracers to map the food web structure from phytoplankton to forage fish. Shedding light on some of the more intricate aspects of the microbial loop that cannot be accessed using traditional carbon and nitrogen stable isotopes.