As human activities continue to alter Earth’s climate, it becomes increasingly important to look to the past to better understand the future.
I am a paleoceanographer, studying large-scale changes in ocean circulation and biogeochemistry that occur over timescales ranging from a few years to millions of years. Major variations in ocean circulation, from the surface to abyssal depths, have influenced climate via the transport and storage of heat. The oceans also exert control over atmospheric levels of carbon dioxide, an important greenhouse gas. Such changes are reflected in the physical and chemical properties of seawater, including temperature, salinity, carbonate chemistry, radiocarbon age, and the concentrations of various nutrients. I use the chemistry of marine calcifiers, mainly foraminifera, as recorders of these properties.
I grew up in the geologically fascinating state of Connecticut, and was the first member of my family to attend college. Since collecting minerals and fossils were favorite hobbies of my youth, I decided to major in geology at Yale University. I did undergraduate research with geochemist Karl Turekian and micropaleontologist Kuo-Yen Wei. It was only natural to combine these two fields in my pursuit of a PhD in the MIT–Woods Hole Oceanographic Institution Joint Program. My principal advisors there were paleoceanographers Bill Curry and Delia Oppo, and Ed Boyle was also an important mentor. I then spent a bit over three years at the Lamont-Doherty Earth Observatory, working with a tremendous group of scientists that included my post-doctoral advisor Jean Lynch-Stieglitz, Lex van Geen, Peter deMenocal, Gerard Bond, Sidney Hemming, and Wally Broecker. I have been teaching at CU Boulder since 2003.
- PhD: Marine Geology and Geophysics, MIT-Woods Hole Oceanographic Institution Joint Program, 1999
- BS: Geology and Geophysics, Yale University, 1994
- College Scholar Award, University of Colorado Boulder, 2017
- Kavli Frontiers of Science Fellow, National Academy of Sciences, 2013
- Provost's Faculty Achievement Award, University of Colorado Boulder, 2008
Past abrupt climate change, ocean circulation, ocean biogeochemistry, marine carbon cycle, trace and minor elements in biogenic calcium carbonates, biomineralization
Below are some of my current research projects. I am also continually collaborating on multiple paleoceanographic studies spanning from the Pliocene to the Anthropocene.
Timing and Paleoceanographic Impacts of the Onset of Arctic-Baffin Bay Throughflow
PI: Anne Jennings; co-PIs: John Andrews, Alex Jahn, Tom Marchitto, Julio Sepulveda; Postdocs: Lineke Woelders, Hannah Zanowski
We are using numerical modeling and multi-proxy analyses of sediment cores from northern Baffin Bay to discover the timing and consequences of the Holocene (post-glacial) opening of the western gateway for Arctic freshwater to the Labrador Sea. We hypothesize that the establishment of this connection through the Canadian archipelago was important for the Atlantic meridional overturning circulation (AMOC) and the development of the North Water Polynya. Supported by NSF OPP Arctic Natural Sciences (2018-2021).
Fertilizing the North Atlantic: How Greenland's Icebergs Raft Sediments into the Ocean
PI: Irina Overeem; co-PI: Tom Marchitto; PhD student: Ethan Pierce
The rapidly changing Greenland Ice Sheet supplies about 8% of the global riverine sediment flux to the ocean. Sediments rafted by icebergs might be an even greater flux, but constraints are poor. We are using field work, laboratory analysis, and numerical modeling to improve quantitative estimates of the modern fluxes of sediments and soluble iron (an important micronutrient) from Greenland icebergs. Supported by CU Boulder Research & Innovation Seed Grant (2018-2021).
Collaborative PIs: Edgar Lobaton, Tom Marchitto; co-PI: Michael Daniele
We are developing an autonomous sorting system for foraminifera, which will be accessible (in terms of usability and cost) to the scientific community. The automated identification of forams to the species level is accomplished using machine learning, developed under our prior NSF grant "A Visual System for Autonomous Foraminifera Identification." The current system makes use of micromanipulation and microfluidics to facilitate the transport of forams from a hopper to their sorted receptacles. Supported by NSF OCE Ocean Technology and Interdisciplinary Coordination (2016-2018 & 2019-2021).
Development of Individual Foraminiferal Mg/Ca to Reconstruct Past ENSO Variability
PI: Tom Marchitto; PhD student: Brigitta Rongstad
Since planktic foraminifera only live for a few weeks, each shell provides a monthly-scale snapshot of upper ocean conditions. By measuring the paleotemperature proxy Mg/Ca in a population of individual shells, we can probe questions about past climate variance, such as seasonality and interannual variability. We are using tropical Pacific core tops to show that this method is valid, by constraining the impacts of partial dissolution, and by comparing fossil population statistics to upper ocean instrumental temperatures. We then apply the approach to infer ENSO variance during the Last Glacial Maximum. Supported by NSF OCE Paleo Perspectives on Climate Change (2016-2018).
- GEOL 4270/5270: Marine Chemistry and Geochemistry (alternate Falls)
- Examines the chemical, biological, geological, and physical processes affecting (and affected by) the chemistry of the oceans. Topics include: chemical speciation in seawater; the marine carbon cycle and its long-term control on atmospheric CO2; the large-scale interdependence of nutrient distributions and biological productivity; chemical tracers of ocean circulation; and the chemistry of marine sediments, including early diagenesis. Prereq., introductory geology and/or oceanography; CHEM 1111 General Chemistry or equivalent; comfort with algebra and calculus (differentials).
- GEOL 3070: Introduction to Oceanography (every Spring)
- Explores Earth's dynamic oceans. The course is roughly divided amongst the four main disciplines of oceanography: marine geology, marine chemistry, physical oceanography (i.e., circulation), and marine biology. Students will learn that there is much overlap and interdependence between these disciplines. Specific topics include seafloor spreading, marine sediments, salinity, biogeochemical cycles, ocean structure, currents, waves, tides, primary production, marine ecology, climate change, and much more.
- GEOL 5420: Quaternary Dating Methods (Spring 2011)
- In-depth survey of standard and experimental dating methods that provide absolute ages for events of the last two million years of Earth history. Includes theory and application of radiocarbon, uranium series, amino acid, thermo-luminescence, fission track, potassium/argon, hydration, light stable isotopes, and other radioactive techniques. Prerequisites: Restricted to graduate students only.
- GEOL 5430: Paleoceanography and Paleoclimatology (alternate Falls)
- Examines scientific tools, data, and theories related to the dramatically varied past climate of the Earth. Focus will be on marine records of climate change and ocean circulation, but ice core and other continental archives will also be discussed. Course will cover the Cretaceous Period to the present, with particular emphasis on the past 150,000 years (the last ice age cycle). Prereq., intro geology or equivalent. Recommended prereq., intro oceanography or atmospheric science.
- GEOL 5701: Super-Problems in Quaternary Climate (Fall 2008, Spring 2010, Spring 2014)
- Investigates major problems in the study and understanding of Quaternary climate variation, in seminar format. Each year one major topic will be addressed, such as: the physics and chemistry of the ice age ocean circulation; the theory and mechanics of glacial/interglacial atmospheric CO2 change; or the origins of the 20, 40, and 100 kyr orbital (Milankovitch) climate cycles.
- GEOL 5705: Seminar in Paleoclimate (every Spring)
- Investigates major problems in the study and understanding of past climate variations as preserved in the geologic record. Course format is a seminar-style critical reading and discussion of journal articles in paleoclimatology and paleoceanography. Topical focus varies from year to year.
- Jody Wycech, CIRES Visiting Postdoctoral Fellow 2017-2019 (co-advisors: Peter Molnar and Balaji Rajagopalan)
- USGS Central Energy Resource Science Center, Lakewood
- Lineke Woelders, ATOC & NSF Postdoc 2018-2019
- Western Water Assessment, CU Boulder
- Ritayan Mitra, NSF Postdoc 2016-2017
- Assistant Professor, Indian Institute of Technology, Bombay
- Kirstin Werner, German Academic Exchange Service Postdoctoral Fellow 2012-2013
- AWI Helmholtz Centre for Polar and Marine Research
Former graduate students
- Emily Roeder, MS 2021
- Brigitta Rongstad, PhD 2020
- CIRES Education & Outreach, CU Boulder
- Colin Lindsay, Postdoctoral Investigator, 2016-2018; PhD 2016 (co-advisor: Scott Lehman)
- Whitney Doss, PhD 2014
- US DOE Office of Energy Efficiency and Renewable Energy, Golden
- Ursula Quillmann, PhD 2014 (co-advisor: Anne Jennings)
- Associate Professor, Colorado State University
- Hannah Grist, MS 2014
- US Forest Service, John Day, Oregon
- Sean Bryan, MS 2007, PhD 2010 (co-advisor: Scott Lehman)
- Senior Instructor, Colorado State University
Former undergraduate honors thesis students
- Baylee Sergent, Honors BA 2020
- Andrew Parker, Honors BA 2011
- Dan Lopez, Honors BA 2007
American Journal of Science
Annual Review of E&PS
Climate of the Past
Deep Sea Research I
Deep Sea Research II
Earth and Planetary Science Letters
Geochimica et Cosmochimica Acta
Geophysical Research Letters
Global Biogeochemical Cycles
Journal of Climate
Journal of Physical Oceanography
Journal of Quaternary Science
Progress in Oceanography
Quaternary Science Reviews