Citation by Jonathan L. Payne, Stanford University
It is my great pleasure to recognize Dr. Kimberly (Kim) Lau for the Doris Curtis Outstanding Woman in Science Award. Kim combines non-traditional stable isotope systems with numerical models to study environmental change during critical transitions in the history of life. Each of her three dissertation chapters represents a major advance in understanding a critical interval in the history of animal life, the behavior of a novel, non-traditional isotope system in carbonate rocks, or both. In addition to having an immediate and major impact on her field, Kim is a stellar teacher and mentor now embarking on a faculty career at the University of Wyoming.
Kim has an exceptional eye for important problems and potential solutions. Early in her time at Stanford, Kim noted that the end-Permian mass extinction is associated with geochemical proxy evidence for major perturbations to ocean carbonate and redox chemistry. She further recognized that similar environmental conditions are hypothesized to have controlled the pattern and timing of biotic recovery during Early and Middle Triassic time but that appropriate geochemical proxy records had not yet been developed. Inspired by emerging evidence that uranium isotopes could be used as a global marine paleo-redox proxy, Kim set out to apply this system to the end-Permian mass extinction and its aftermath. She has now succeeded and has accomplished even more than what she set out to do.
In her first publication, Kim developed the first coupled record of uranium concentrations and uranium isotope ratios in shallow-marine rocks spanning the Permian-Triassic boundary interval and extending through the 15 million-year interval of biotic recovery during Early and Middle Triassic time. Kim’s data indicate a prolonged interval of extensive anoxia during Early Triassic time. By demonstrating correlative variations in both uranium concentrations and isotope ratios between China and Turkey, Kim has further ruled out local diagenetic processes as potential drivers of the coupled shifts in uranium concentrations and isotope compositions. This achievement alone was substantial, reflecting many hours of painstaking work in the lab. Kim substantially increased the impact of the paper by using a dynamic numerical model of the geological uranium cycle to interpret her data quantitatively. With this model, Kim showed that shifts in the concentration or isotope composition of uranium in source weathering regions cannot account for the rate and magnitude of observed shifts and was further able to quantify the extent of seafloor anoxia required to account for the observed record. She then went one step further, exploring the coupling between the uranium cycle, ocean redox conditions, and the carbon cycle to demonstrate how a steep redox gradient from oxygenated shallow waters (due to wind mixing with the atmosphere) to anoxic waters at a few hundred meters depth (implied by biomarker evidence and her uranium data) can account for the magnitude of Lower Triassic carbon isotope excursions. It is a provocative idea that could stand as a paper in its own right. Overall, this study epitomizes Kim’s unusual ability to combine detailed field and laboratory work with thoughtful analysis in the context of numerical models.
Kim’s second paper used uranium isotope stratigraphy again, this time to test the role of ocean oxygenation in the early evolution of animal life using samples from Cryogenian strata of Mongolia. Here, Kim found evidence for large and rapid changes in marine redox conditions during the Cryogenian interglacial time. In particular, she found strong uranium isotope evidence for substantial oxygenation of the ocean water column in the immediate aftermath of the Sturtian glaciation followed by deoxygenation associated with a large negative excursion in the carbon isotope record (the Taishir anomaly). This finding further highlights the utility of uranium isotopes for reconstructing large and rapid shifts in ocean oxygenation across geology time, the possible role of episodic oxygenation in triggering early phases of animal evolution, and the likely instability of ocean redox conditions during Neoproterozoic time. This study adds substantially to the emerging view that the Neoproterozoic was not a time of simple increase in surface oxygenation. Rather, it was a time of rapid variation in redox conditions that later stabilized with higher levels of oxygen in the oceans and atmosphere.
Kim has also made important contributions to the application of calcium isotopes to the interpretation of critical intervals in the history of animal life. She developed an extended record of Lower and Middle Triassic calcium isotopes. Like her uranium work, her calcium isotope dataset is by far the most extensive of its type for this event. And as part of this work, Kim discovered that she cannot correlate excursions among sections while honoring biostratigraphic and carbon isotope chemostratigraphic constraints. These observations forced her to consider other processes that may be responsible for calcium isotope variation. She demonstrated through numerical modeling that a combination of variation in the proportion of original mineralogy (aragonite versus calcite) along with subsequent water-rock interaction can account for the variability that she sees in her data. She further showed through reanalysis of published data that the same holds true for nearly all published calcium isotope records that have sufficient auxiliary information to test her hypothesis.
In addition to these major contributions, Kim has contributed and is contributing to many other projects on topics ranging from the silicate weathering feedback on climate during the Cenozoic to uranium isotope geochemistry of the end-Triassic mass extinction, carbon cycling across Phanerozoic time, and carbonate sedimentation following the end-Permian mass extinction. She is a young scientist with a broad vision and the ability to work across a broad range of topics with ease.
Kim’s skills and accomplishments as a teacher and mentor equal those as a researcher. During her time at Stanford, she taught and mentored grade school and high school students, undergraduates, and even her graduate student peers. Doris Curtis valued teaching and mentoring alongside research impact and Kim’s success in each of these areas make her an ideal candidate for the Doris Curtis Outstanding Woman in Science Award. Please join me in congratulating Kim for her accomplishments recognized by this award.
Response by Kimberly V. Lau
It is truly an honor to be selected as the Doris Curtis Outstanding Woman in Science. Thank you, Jon, for the kind words, for the nomination, and for your support since I began my geologic research career as an undergraduate. Your enthusiasm about the big questions made paleo research irresistible. I am also deeply grateful to Kate Maher, for her creativity and competitive spirit—and for her patience in teaching me the nuances of modeling and geochemistry which has immeasurably improved my science. Francis Macdonald introduced me to the Neoproterozoic world, and has been generous in including me on fascinating projects. Thanks also to Tim Lyons for his immediate belief in me when I arrived in his lab as a postdoc, for his fun conversation, and scientific inspiration.
My dissertation, and the path that led me to this point, would not have been accomplished without the mentorship and example of many women geoscientists. Particularly in the spirit of this award, I would be remiss in not thanking Elisabeth Vrba, Susan Butts, Karrie Weaver, Katja Meyer, Mary Droser, Marilyn Fogel, and again, Kate Maher. I hope I can emulate each of you as I strive to continue supporting young women in geoscience.
I am grateful for the support of many mentors, colleagues, co-authors, friends, and family. I would particularly like to thank Derek Briggs, Seth Finnegan, Kate Hewett, Dana Thomas, Cynthia McClain, Sam Ying, Dan Ibarra, Jeremy Caves Rugenstein, Matt Winnick, Adam Jost, Page Chamberlain, Andres Baresch, Hari Mix, Steve Bates, Steve Romaniello, Dan Gregory, Eddie Schwieterman, Leanne Hancock, Dalton Hardisty, Silke Severmann, and the members of the Maher, Payne, and Lyons research groups. My dissertation would not have been possible without the support from my family. Special thanks to my sister, Sabina, my parents, Stephen and Wanda. Thanks to my late uncle, Dr. Koon Lau, for being an early and inspiring example of scientific curiosity. My husband, Brian, is favorite my partner in all things science and fun. Last, sincere thanks to GSA for this honor.