Trace Metal Biogeochemistry Laboratory

Welcome to the Twining Laboratory! We conduct interdisciplinary research on the biogeochemistry of metals in marine and aquatic systems. Our research is focused on the interactions between trace metals and aquatic organisms that have biogeochemical, ecological, or toxicological implications. Our work takes many forms and includes laboratory investigations with cultured phytoplankton and protists, as well as field work to collect and study planktonic organisms in natural systems.

Many of our projects focus on the elemental composition of plankton. Planktonic organisms influence the distribution and geochemical fate of many important elements (including carbon) in the ocean, and we strive to understand the factors which affect elemental stoichiometries in marine protists. Plankton also form the base of most aquatic food webs, and contaminants such as cadmium, selenium, silver, and mercury can become concentrated in plankton and passed to higher organisms. We are interested in the determining the occurrence and understanding the implications of metal accumulation in marine organisms.

The growth of phytoplankton in several large ocean regions is limited by the availability of iron, and much of our work is specifically focused on understanding iron cycling and biogeochemistry. Projects investigating iron accumulation and cycling are ongoing in the equatorial Pacific Ocean, the Weddell Sea, the Sargasso Sea, and in coastal waters off New Zealand. We are particularly interested in quantifying the amount of iron accumulated by cells of varying taxonomic and functional groups, in order to better understand iron acquisition mechanisms in natural plankton communities.

We apply a number of analytical tools to study metals in plankton. We are actively developing novel approaches to analyze the composition of individual cells using microanalytical techniques. Foremost amongst these is synchrotron x-ray fluorescence microscopy, or SXRF. This technique enables us to quantify the elemental contents (typically of elements between silicon and zinc) of each target cell while also generating maps of element distributions. We also utilize inductively-coupled plasma mass spectrometry (ICP-MS) to measure element concentrations in natural particle assemblages and plankton cultures, and we have begun to incorporate flow cytometry and electron microscopy techniques, as well.

Finally, metal bioavailability in natural waters is influenced by chemical speciation, and plankton can influence the speciation and bioavailability of metals in their environment through direct and indirect production of organic ligands. We are interested in the relationship between metal speciation and bioavailability in a variety of biogeochemically important organisms and systems. In particular, we are studying iron redox cycling and complexation using flow-injection chemiluminescence and electrochemical techniques.

A 3-D Look Inside a Microscopic Cell

Senior Research Scientist Dr. Ben Twining is part of a research team that has captured the inner world of the aquatic diatom Cyclotella meneghiania through the use of a technological advance in microscopy called X-ray fluorescence microtomography. The group has successfully created three-dimensional maps that show the structure and distribution of trace metals essential in the life cycle of this single-celled freshwater phytoplankton species. Applying this technology to marine phytoplankton will give researchers new insights about ocean biogeochemistry and the global carbon cycle. The team includes scientists from Stony Brook University, the Georgia Institute of Technology, the Argonne National Laboratory, and the Australian Synchrotron. Their work has been published in the Proceedings of the National Academy of Sciences of the United States of America (Quantitative 3D elemental microtomography of Cyclotella meneghiniana at 400-nm resolution,PNAS September 7, 2010 vol. 107 no. 36 .15676-15680)