The Sigman Lab at Princeton University

FACULTY

Daniel Sigman is Dusenbury Professor of Geological and Geoophysical Sciences at Princeton University. He studies the global cycles of biologically active elements, in particular, nitrogen and carbon, and he is active in the development of analytical techniques for studying nitrogen in the environment. He also investigates the history of these cycles in order to understand the causes of past changes in the atmospheric concentration of carbon dioxide, the role of this greenhouse gas in the waxing and waning of ice ages, and the ocean’s response to climate change. Sigman received a B.S. from Stanford University in 1991 and a Ph.D. from the Massachusetts Institute of Technology/Woods Hole Oceanographic Joint Program in Oceanography in 1997. His honors include the Macelwane Medal of the American Geophysical Union (2004), the Bessel Award of the Humboldt Foundation (2004) , a MacArthur Fellowship (2009) , and the Science Innovation Award of the European Association of Geochemistry (2012).

MASS SPEC MANAGER

Sergey has always been fascinated by the mechanical workings of things surrounding him - clocks, toys, pianos… His desire to know how the world is constructed brought him to the Russian chemical-technological university in Moscow, where he discovered the amazing power of the mass spectrometer to investigate the world. Sergey obtained his PhD from Moscow State University, and has been working in mass spectrometry for more then 25 years. His scientific interests are wide and are united by the use of stable isotopes as markers of natural processes.

LAB MANAGER

ASSOCIATE RESEARCH SCHOLAR

Katye started her postdoctoral work as a NOAA Climate and Global Change Postdoctoral Fellow working jointly with Danny Sigman and Meredith Hastings at Brown University. For the 2012-2013 academic year, she is a Visiting Fellow in the Department of Geological Sciences at Brown, while also continuing on as an Associate Research Scholar at Princeton. Katye studies atmospheric biogeochemistry and her research seeks to improve our understanding of how atmospheric chemistry influences the composition of nitrogen-containing compounds as they are transported through the land-atmosphere-ocean system. Anthropogenic activities are altering this chemistry, rendering it a challenge to differentiate the natural cycling of the marine atmosphere from the impacts of air pollution on remote marine ecosystems. Her postdoctoral work focuses on characterizing the sources, composition, and interrelationships among inorganic and organic nitrogen species in rainwater and aerosols deposited in the subtropical North Atlantic surface ocean. Katye conducts her fieldwork on the small island of Bermuda, which is ideally located for such a study; it is 1000 km off the coast of South Carolina and receives ~ 6 months of polluted air masses from North America and ~ 6 months of clean, marine air masses. The rainwater and aerosols collected on the island are analyzed by 1) ultra-high resolution mass spectrometry, which characterizes the complex mixture of organic nitrogen-containing molecules, and 2) isotope ratio mass spectrometry, which measures the isotopic composition of ammonium and nitrate, providing information on the sources and atmospheric-formation mechanisms of these inorganic nitrogen species. Ultimately, the goal of this research is to better understand both the natural and human-impacted atmospheric nitrogen cycle and its links to the ocean.

Sarah is broadly interested in understanding the complex relationships between nitrogen (N) fluxes and primary productivity in the ocean, which has implications for past and future climate, ecosystem function, and global biogeochemical cycles. Sarah received her Ph.D. in 2012 from Princeton University, in collaboration with the Bermuda Institute of Ocean Sciences. Her dissertation research was conducted at the Bermuda Atlantic Time-series Study (BATS) site, located at the northwestern margin of the North Atlantic Subtropical Gyre (the “Sargasso Sea”). In this region of the ocean, intense surface stratification limits the nitrate supply from below such that regenerated N is assumed to fuel most phytoplankton growth. In such N-poor systems (> 50% of the global ocean area) the N acquisition strategies of different phytoplankton taxa have proven difficult to study and quantify. As a graduate student, Sarah developed a method for characterizing the N source preferences of different phytoplankton groups: the coupling of flow cytometry with N isotope analysis. This work has shown that the least abundant phytoplankton (the eukaryotes) specialize in the acquisition of nitrate supplied from the ocean interior, and also seem to be disproportionately more important to organic matter export than their abundance implies; thus, eukaryotic phytoplankton drive the subtropical ocean’s biological pump. Applying the coupled flow cytometry-N isotope approach to the summer-to-fall progression at BATS has revealed a counterintuitive relationship between upper ocean stratification and phytoplankton N uptake: nitrate assimilation tends to be greater when the mixed layer is shallowest (i.e., in the summer), which may help explain the surprisingly high export production in the subtropical and tropical ocean.

As a postdoc, Sarah is building on the approach described above to address questions of N cycling in the subpolar North Atlantic, where the relatively predictable spring phytoplankton bloom is so large that it has biogeochemical consequences for the global ocean, as well as in the Southern Ocean, where the efficiency of the biological pump is currently limited by incomplete consumption of nitrate in surface waters.

François Fripiat is a visiting Post-doctoral research scholar in the Sigman group. He obtained his Ph.D. at the Royal Museum for Central Africa (Belgium) and started a Post-doctoral project at the University of Brussels (Belgium) in collaboration with the Sigman group.

Fripiat's research interest is focused on biogeochemical cycles in the polar open-oceans and in Sea Ice, using the natural isotopic composition of silicon, nitrogen and oxygen (respectively δ30Si, δ15N, and δ18O). The δ30Si and δ15N of particulate matter in sediments provide a view of nutrient consumption:supply ratio in past oceans and are used to formulate and test hypotheses on Southern Ocean productivity and fluctuations in atmospheric pCO2 over glacial cycles. His present work aims at (1) developing a mechanistic understanding of the processes controlling the origin and fate of the isotopic compositions and (2) using the different sensitivities of the mass and isotopic balances as a constraint of the modern elemental cycling.

Fripiat's is also involved in the utilisation of isotopic tracer incubation experiments (30Si, 15N, and 13C), both in the ocean and in Sea Ice, in order to better constrain the rate of biogeochemical processes.

GRADUATE STUDENT

GRADUATE STUDENT

Farhan is a first year graduate student in the Geosciences department at Princeton, and he is working on developing a new method for measuring nitrogen isotopes.
 

Tony Wang received his B.S.in Geochemistry in 2010 from Nanjing University, China. After that, he came to Princeton University to continue his graduate studies. Wang's current research is focused on interpreting nitrogen isotopes of organic matter within biogenic minerals (surface coral, deep-sea coral, foraminifera, shark teeth, etc.) as a climate proxy or a biogeochemical indicator. Any biogenic minerals trapped a tiny amount of organic matter during the mineralization process because it is much easier for the organisms to do the mineralization job with organic matter serving as the crystal nucleus. Based on the very sensitive technique developed in the Sigman lab, they are able to measure the nitrogen isotopes of that tiny amount of organic matter within the minerals. Wang's main application of this technique is to understand the Glacial-Interglacial marine nitrogen cycle change and its feedbacks to the carbon cycle and climate system.

FACULTY ASSISTANT