Our study suggests that a combination of physical processes and sediment oxygen consumption determine the spatial extent and temporal dynamics of hypoxia on the Louisiana shelf. In summer, stratification isolates oxygen-rich surface waters from hypoxic bottom waters; oxygen outgasses to the atmosphere at this time. A large fraction of primary production occurs below the pycnocline in summer, but this primary production does not strongly affect the spatial extent of hypoxic bottom waters.

Seawater sulfate concentrations are closely related to the oxygenation history of Earth's surface environment. We develop two approaches for quantification of ancient seawater sulfate concentrations based on the sulfur isotopic composition of pyrite and carbonate-associated sulfur (CAS). Our analysis indicates low seawater sulfate (<5mM) at 635 million years ago, rising in a stepwise manner to near-modern levels (~20-30mM) by about 250 million years ago.

A culture study with the benthic foraminifer Amphistegina lessonii was conducted at varying seawater [Ca2+] and constant [Mg2+]. Results showed optimum growth rates and test thickness at ambient seawater Mg/Ca and a calcite Mg/Ca which is controlled by the relative seawater ratio. Results support the conceptual biomineralization model by Nehrke et al. (2013); however, our refined flux-based model suggests transmembrane transport fractionation that is slightly weaker than expected.

The ratio of simple optical properties measured from underwater autonomous platforms, such as floats and gliders, is used as a new tool for studying phytoplankton distribution in the North Atlantic Ocean. The resolution that optical instruments carried by autonomous platforms provide allows us to study phytoplankton patchiness and its drivers in the oceanic systems.

Climatic warming is affecting permafrost, including decomposition of organic matter (OM). However, quantitative data for the quality of OM and its availability for decomposition is limited. We analyzed the quality of OM in late Pleistocene (Yedoma) and Holocene (thermokarst) deposits. A lack of depth trends reveals a constant quality of OM showing that permafrost acts like a freezer, preserving OM quality. This OM will be susceptible to decomposition under climatic warming.