Harry McClelland
Postdoc
Stable isotope ratios are widely used to investigate the nature of life and environment when it cannot be observed directly. Examples include: Earth’s geologic past; metabolism at the scale of individual cells; and in locations that are impossible to reach, such as the deep subsurface and even other planets. However, extracting meaningful information about life or environment with isotopes, requires a quantitative understanding of the filter through which we are observing it. My research centers on mechanistically understanding this filter in various scenarios, using experiments and simple mathematical models. My with Itay includes an investigation into the effect of microbial mat metabolism on geochemical compositions preserved in the geological record, and an investigation into carbon isotope fractionation during photosynthetic carbon fixation at the level of cellular metabolism. My wider interests include paleoclimate proxies for temperature and pCO2, life in the deep subsurface, population dynamics in bacteria and phytoplankton, and the interface between phenotypic plasticity and evolutionary adaptation across all spatial and temporal scales.

Ichiko Sugiyama
PhD student
Green rust is a metastable iron hydroxysalt, which may have played a role in the early iron cycle and the genesis of iron formations. Studies have shown that green rust strongly interacts with several transition metals and major nutrients. However, the interaction of green rust with compounds of geochemical and geobiological importance has not been systematically explored. Furthermore, the fate of the nutrients and metals upon transformation of green rust to stable minerals is unknown. In a set of experiments, I investigate the interaction of green rust with various trace metals and nutrients. The findings have implications for our understanding of biological productivity and evolution, and for the use of trace metals as proxies for Earth's surface oxidation state.

Jonathan Gropp
PhD student
Methane, a major greenhouse gas, is produced anaerobically by microorganisms in anoxic environments. During the formation of methane, these microorganisms often preferentially utilize the lighter stable isotopes of carbon and hydrogen to a varying degree, thereby creating an isotopic signature of the methane that can be traced in both natural and laboratory culture setups. In my research I develop a bio-isotopic model that aims to decipher the mechanisms that govern the isotopic signals in methane, by combining various biochemical and geochemical modeling approaches.

Michal Sela-Adler
Postdoc
My main interest is in redox cycling and biogeochemical processes in sediments, using geochemical, isotopic and microbiological methods. My research in Itay's group involves the investigation of mineral-water oxygen isotopic fractionation in synthetic and microbially-mediated goethite precipitation and its dependence on the temperature and composition of aqueous solutions. In addition, I'm investigating the retention or release of trace elements upon Fe(II)-catalyzed transformation of ferrihydrite to goethite and hematite.

Nir Galili
PhD student
I am working to construct a long-term record of oxygen isotope ratios in iron oxides of marine origin. With this record we hope to address the longstanding question of whether a secular increase of 10-20 permil in 18O/16O of marine carbonates and cherts since the early Archean is due to a much hotter early climate, or a more 18O-depleted ocean. My research combines fieldwork, lab experiments, petrography, and high-resolution in situ geochemical analyses. In several related projects I aim to gain as broad an understanding as possible of the emerging record and its long term implications.

Peter Crockford
Postdoc
The overarching focus of my research to date has entailed a combined field-lab-modeling approach to probe the Earth surface environment over critical intervals of Earth history. Such intervals include Cryogenian Snowball Earth glaciations, Earth’s Great Oxidation Event, and the colloquially named ‘boring billion’ that captures the time period when Earth’s first eukaryotic organisms evolved. To gain insight into Earth’s past surface conditions I employ a wide range of isotopic tools that can track processes from stratospheric photochemistry to microbial remineralization of organic matter in ancient sediments. My work with Itay is focused on better understanding carbonate records as recorders of the ancient carbon cycle, with particular attention to Earth’s first and second major rises in atmospheric oxygen across the Proterozoic.

Roy Naor
PhD student
The nature of many geological depressions observed on the surface of Mars over the last several decades remains unknown. Studying their formation mechanism can lead to a better understanding of Mars’ subsurface environment, past climate and hydrology. Despite the occasional occurrence of these geomorphological features in regions rich in evaporite deposits, geochemical void-forming mechanisms, such as dissolution or dehydration of salts, are largely unexplored. I study a terrestrial analog to collapse of basalt into underlying voids in sedimentary rocks in the Levantine volcanic plateau of Harrat A-Sham. In this terrestrial analog site, I work to develop the conceptual coupling between subsurface void generation, surface observations and regional geological context. By so doing, I hope to place new constraints on the processes that formed the Martian and analog geological depressions and on climatic and hydrological implications.

Shahar Hegyi
MSc student
I am developing a 2D model of carbon, iron and sulfur diagenesis in marine sediments, using lattice Boltzmann methods. The model will account for the processes that drive sulfur cycling in marine sediments, including microbial sulfate reduction, sulfide oxidation, pyrite formation and organic matter sulfurization. The objective of my work is to understand bulk and spatial patterns of the sulfur isotope composition of pyrite and organic sulfur compounds, and the information they hold on past depositional environments and pyrite formation mechanisms.

Shlomit Sharoni
PhD student
Phytoplankton are the dominant single-celled autotrophs driving marine primary production. As they form organic biomass from inorganic substrates, the elemental stoichiometry of phytoplankton dictates the amount of nutrients transferred to higher trophic levels, and the amount of carbon that is sequestered to the ocean's interior via the biological pump. My research focuses on understanding the processes that govern variability in the elemental composition of phytoplankton, such as evolutionary adaptation and community composition. I investigate the climatic and ecological effects of this variation on biogeochemical cycles. My research combines data analysis, mathematical modeling, and physiological experiments, and it will hopefully foster a better understanding of the response of the marine biosphere to past, as well as future global change.

Virgil Pasquier
Postdoc
I am working to understand the influence of the physical parameters of marine depositional environments on the sulfur isotope composition of pyrite. The sulfur isotope composition of pyrite in modern marine sediments and in sedimentary rocks has seen wide use for reconstruction of events and processes in the global sulfur cycle, with linkages to the carbon and oxygen cycles, and global climate. However, there is increasing evidence that local depositional parameters exert a strong influence on the isotopic composition of pyrite preserved in marine sediments. I study sedimentary successions, in which we have a good understanding of temporal variations in the physical parameters of the depositional environment, to constrain the effect of such variations on pyrite sulfur isotopes. For this purpose, I combine multiple sulfur isotope analyses of pyrite in marine sediment cores and diagenetic models.

Yigal Barkan
PhD student
Sulfate incorporated into marine carbonates (Carbonate Associated Sulfate, CAS) is increasingly used as a proxy for the sulfur isotope composition of seawater sulfate, especially during times in which sulfate evaporites are absent from the sedimentary record. However, the fractionation of sulfur isotopes upon incorporation of sulfate into carbonate minerals has not been systematically investigated in experiments. I synthesize carbonate minerals in the lab, in the presence of sulfate, and study the effect of sulfate incorporation on sulfur isotopes. We find fractionations of several permil, which depend on the CAS concentration, and more weakly on the carbonate minerals' precipitation rate.

Ziv Sade
PhD student
Information on past environments is commonly reconstructed from carbonate minerals precipitated in (or close to) equilibrium. However, isotopic equilibrium is a unique and rare state, and disequilibrium isotopic compositions in carbonate minerals are abundant in the geologic record. I investigate kinetic isotope effects in carbon and oxygen during the reactions involved in carbonate mineral formation. The findings contribute to a better understanding of disequilibrium isotopic compositions in carbonate minerals, and will hopefully help to unlock paleoclimatic and paleohydrological information in speleothems, spring deposits, soil carbonates and cryogenic calcite, among other carbonate repositories.

ALUMNI

Dr. Masha Alesker Postdoc (currently a staff scientist at Bar-Ilan University)
Itamar Benisti Undergraduate (currently a PhD student at the Technion)
Dr. Or Bialik Postdoc (currently a postdoc at the University of Haifa)
Dr. Natella Mirzoyan Postdoc (currently teaching at the University of Armenia)
Dr. Nataly Ozak Postdoc (currently a postdoc at the University of Leuven)
Yonatan Sadeh MSc student
Dr. Caroline Thaler Postdoc (currently a postdoc at the Museum National d'Histoire Naturelle, Paris)
Dr. Christine Wenk Postdoc (currently a staff scientist at the University of Basel)
Dr. Yael Schuster Senior intern (Founder of "The KnowItAlls")


Dept. of Earth & Planetary Sciences / Weizmann Institute of Science / Rehovot 76100 / Israel
Telephone: +972 8 934 6987 / Fax: +972 8 934 4124 / E-mail: itay.halevy@weizmann.ac.il