Hengdi Liang

Hengdi Liang

Oceanographer. Modeler. Biogeochemist.

Research

Trace metal biogeochemistry

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Trace metals play crucial roles as micronutrients, influencing biological productivity and ecosystem dynamics, yet their distributions are controlled by a combination of physical, chemical, and biological processes. Biological uptake drives trace metal cycling, as phytoplankton assimilate essential metals like Fe, Zn, Cu, Ni, and Co in the surface ocean, which are subsequently regenerated through microbial decomposition and remineralization processes in the deep ocean. Organic complexation regulates the bioavailability of many trace metals, with strong ligand binding stabilizing dissolved species and extending their residence times. Scavenging onto sinking particles further removes trace metals from seawater, with rates influenced by particle composition and flux. Understanding and quantifying these processes is critical for predicting how marine ecosystems will respond to environmental changes. By integrating numerical modeling with observational datasets, I aim to unravel these interconnected mechanisms and their implications for ocean biogeochemistry, carbon cycling, and climate feedbacks.

Ocean carbon pumps

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Ocean carbon pumps play a crucial role in regulating atmospheric CO₂ by transporting carbon from the surface to the deep ocean. I am particularly interested in the biological carbon pump (BCP) and carbonate pump, which drive the cycling of organic and inorganic carbon in marine ecosystems. The biological pump facilitates carbon sequestration through the production, sinking, and remineralization of particulate organic carbon (POC), shaping nutrient distributions and deep ocean carbon storage. The carbonate pump, on the other hand, involves the formation and dissolution of calcium carbonate (CaCO₃) by marine organisms, influencing alkalinity and CO₂ exchange between the ocean and atmosphere. I use diverse numerical modeling tools to investigate the mechanisms controlling carbon transport and sequestration in the ocean, which are essential to ocean biogeochemistry and climate feedbacks. Understanding their sensitivity to environmental changes — such as ocean acidification and deoxygenation — is critical for predicting future carbon cycle dynamics.

Inverse modeling of ocean biogeochemical tracers and processes

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Forward and inverse models are two widely used methods for studying the ocean’s biogeochemical processes. Forward models use equations and physical parameters to simulate the ocean system’s behavior over time, while inverse models estimate unknown parameters by comparing observations with model output. I applied the inverse modeling method to global ocean tracer models, developing models within the framework of AWESOME OCIM (John et al., 2020) and optimizing the model parameters with global datasets like GEOTRACES and World Ocean Atlas.