Understanding natural and anthropogenic climate and environmental change, particularly from the perspective of atmospheric composition and chemistry.
Ice Cores Audio Slideshow | Field Photos
Changes in atmospheric composition and chemistry can be powerful drivers of the Earth's climate, as we are witnessing today with the human-caused increase in greenhouse gases and the resulting gradual warming of our planet.
There is a great need for an improved understanding of the Earth's climate system and how it responds to various forcings. For example, we know with certainty that the anthropogenic increase in greenhouse gas concentrations is causing the Earth to warm, and will continue to do so. But there is uncertainty in how much and how fast the planet would warm for a given increase in carbon dioxide concentrations. The Earth's climate system is vast and relatively slow-responding, so it's not feasible to study it by direct experimentation (as you would with a smaller system in a lab setting). One of the best ways we can gain understanding about the Earth's climate system is to examine the geologic record of past climate. In this way we can improve our understanding of how the Earth's environmental conditions (e.g., temperature) respond to changing climate forcings (e.g., carbon dioxide concentration).
My research uses records from ancient glacial ice to answer questions about the Earth's climate system. The oldest ice on Earth is contained in the Greenland (over 100,000 years old) and Antarctic (over 800,000 years old) ice caps. As this ice accumulated slowly (from fallen snow in places where it's too cold to ever melt) year after year, it recorded environmental conditions such as temperature (in oxygen and hydrogen isotopes) and windiness (in the amount and grain size of dust particles). One very special attribute of glacial ice as a geologic record is that it also records past atmospheric composition. When snow gets transformed to ice in a glacier (via slow recrystallization under pressure of overlying snow), some of the air present in the snow gets trapped in bubbles in the ice. Because of this trapped ancient air, we now know how greenhouse gases have varied in the atmosphere for the last 800,000 years.
One main direction of my current research is reconstructing past carbon monoxide (CO) concentrations and stable isotopic composition. CO is a highly reactive gas and is a major sink of atmospheric hydroxyl radicals (OH), which serve as the "cleansing agent" of the atmosphere. Through its impact on OH, CO concentration in the atmosphere can have a profound influence on the lifetimes of other gases and on atmospheric chemistry in general. For example, increasing CO may cause a drop in OH. OH is what removes methane (CH4) from the atmosphere, so increasing CO may cause an accompanying increase in atmospheric CH4, which is a powerful greenhouse gas. CO stable isotopes help with understanding the changes in the individual sources and sinks of CO.
Another main direction of my research is using carbon-14 of ancient atmospheric CH4 to understand past changes in the global CH4 budget. Carbon-14 is an excellent tracer for distinguishing between biospheric (e.g., wetlands, animals) and geologic (clathrates, natural gas seeps) CH4 emissions. My recent work using ancient ice samples from the Greenland ice sheet margin showed that a large and rapid increase in atmospheric CH4 concentration which happened about 11,600 years ago in association with a large and rapid warming event was likely due to increased CH4 emissions from wetlands in response to the warming.
I am also interested in cosmogenic production of carbon-14 in glacial ice. Carbon-14 is produced in glacial ice by secondary cosmic ray particles (e.g., fast neutrons, muons) from oxygen-16. Cosmogenic carbon-14 content in glacial ice can tell us about ice flow history and ablation rate, and may contain information about past variations in solar activity.
Courses Offered (subject to change)
- EES 105
INTRODUCTION TO CLIMATE CHANGE
- EES 218/418
- EES 265/465
- EES 266/466
ICE CORE RECORDS OF CLIMATE AND ENVIRONMENTAL CHANGE
- Petrenko, V.V., P. Martinerie,
P. Novelli, D. M. Etheridge, I. Levin, Z. Wang, G. Petron, T. Blunier, J.
Chappellaz, J. Kaiser, P. Lang, L. P. Steele, F. Vogel, M. A. Leist, J. Mak, R.
L. Langenfelds, J. Schwander, J. P. Severinghaus, G. Forster, W. Sturges, M.
Rubino, J.W.C. White. 2013. A 60 yr record of atmospheric
carbon monoxide reconstructed from Greenland firn air. Atmospheric
Chemistry and Physics, 13, 7567 - 7585.
Core Records: Ice Margin Sites. 2013. In Encyclopedia
of Quaternary Science, 2nd ed. S.A. Elias, ed. Elsevier. Vol 2,
416 – 430.
- Petrenko, V.V.. J. Severinghaus, A.M. Smith, K.
Riedel, D. Baggenstos, C. Harth, A. Orsi, Q. Hua, P. Franz, Y. Takeshita, G.
Brailsford, R.F. Weiss, C. Buizert, A. Dickson, and H. Schaefer. High-precision 14C measurements
demonstrate production of in situ cosmogenic 14CH4 and
rapid loss of in situ cosmogenic 14CO in shallow
2013. Earth and Planetary Science Letters, 365, 190-197.
Etheridge, R.F. Weiss, E.J. Brook, H. Schaefer, J.P. Severinghaus, A.M. Smith,
D. Lowe, Q. Hua, K. Riedel. 2010. Methane from the East Siberian Arctic Shelf. Science, 329 (5996), 1146–1147.
Smith, J.P. Severinghaus, E.J. Brook, D. Lowe, K. Riedel, G. Brailsford, Q.
Hua, H. Schaefer, N. Reeh, R.F. Weiss and D. Etheridge. 2009. 14CH4
measurements in Greenland ice: investigating last glacial termination CH4
sources. Science, 324 (5926), 506-508.
Severinghaus, E.J. Brook, N. Reeh, and H. Schaefer. 2006. Gas records from the
West Greenland ice margin covering the Last Glacial Termination: a horizontal
ice core. Quaternary Science Reviews,
25 (9-10), 865-875.
- Schaefer, H., M.J. Whiticar, E.J.
Brook, V.V. Petrenko, D.F. Ferretti,
and J.P. Severinghaus. 2006. Ice record of delta C-13 for atmospheric CH4
across the Younger Dryas-Preboreal transition. Science, 313 (5790),