My research group studies geologic records of environmental changes to understand how the Earth system responds to natural and anthropogenic forcings on  millennial time scales. We focus on lake sediments from Alaska, geochronology, and proxy climate syntheses.

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David Hopkins & DK, Seward Peninsula, ca. 1984

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Research

Jon & Hannah, Tokin Lake

To understand environmental change and its current trajectory requires a long-term perspective of the natural variability in the Earth system. My group studies lake and glacial deposits that provide an archive of long-term climate variability. Our field-oriented projects are mainly in Alaska where past environmental changes have been pronounced and future changes are anticipated to be greatest. In the lab, we analyze the physical properties of lake sediments, particularly those from glaciated basins, and apply amino acid geochronology to resolve Quaternary paleoclimatic and geochronological problems.

Lake Sediments from Alaska

Anne & Dave, sediment core from Andrew Lake, Adak Island

Sediments that accumulate in lakes contain a wealth of information about past and present environmental changes. My group collects sediment cores from lakes and analyzes them for a variety of physical and biological properties. In addition to the analytical equipment in the Sedimentary Records of Environmental Change Lab at NAU, we collaborate with the National Lacustrine Core Facility and other laboratories for various analyses.

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Al & Scott assemble weather station, Long Lake, Copper R basin

In southern Alaska we are using annually bedded sediment from glacier-fed lakes and isotopes and productivity indicators from non-glacial lakes to interpret climatic changes and glacier fluctuations.

In Arctic Alaska and elsewhere  we are monitoring the rivers and lakes, along with the weather, to inform our interpretations of the sedimentary sequences stored by the lakes.

We integrate our studies into larger international syntheses of  lacustrine-based paleoenvironmental records internationally.


Quaternary Geochronology

Volcanic ash in a sediment core

Because knowing the ages of sedimentary sequences and their constituents is essential to understanding the timing, rate, and regional extent of past environmental changes, my group has a strong emphasis in geochronology. Specialties include:

  • amino acid geochronology
  • radiocarbon
  • tephrochronology

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Amino acid geochronology

Snails, Pleistocene Lake Bonneville

The technique is used to determine the approximate ages of carbonate-based fossils as old as several million years. Recent applications in the Amino Acid Geochronology Laboratory include conservation paleobiology, time-averaging of the fossil record, tectonic geomorphology, as well as methodological advancements.

Radiocarbon
We use radiocarbon extensively to date our lake sediment cores, sometimes in combination of tephras, and to calibrate the rate of amino acid reactions. Along with the AMS facility at UC Irvine, we are helping to develop the rapid AMS procedure for dating carbonates.

Tephrochronology

Aniakchak tephra

All of the lakes that we study in Alaska contain volcanic ash layers from frequent eruptions of Aleutian Arc volcanoes. We collaborate with tephra specialists at University of Alberta and elsewhere to document the regional tephra sequences and have used tephra to validate the accuracy of radiocarbon-based age models, including their error estimates.


Paleoclimate Data Syntheses

PAGES 2k paleotemperature sites

My group is involved in large collaborative projects that assemble proxy climate records to study past global climate changes. These synthesis studies are used to place recent changes in a long-term context, to evaluate climate model performance, and they give insights into natural climate variability. Developing the large datasets for these projects requires a major effort in data stewardship.

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The Arctic Holocene Transitions project generated a major database of Arctic Holocene proxy climate records. We used the dataset to reconstruct Holocene climate changes across the western Arctic including Alaska and Yukon, Canada and Greenland, and the North Atlantic and Scandinavia.

Bear Lake GSA Speical Paper cover

We collaborate with colleagues internationally through the Past Global Changes (PAGES) program to generate global multi-proxy data sets of temperature over the past 2000 years, and to reconstruct temperatures for each continent, and the Arctic.

We worked with the USGS Powell Center on a paleoclimate synthesis of hydroclimate of North America over the past 2000 years.

In Utah, we collaborated with the US Geological Survey in a broad-ranging investigation of the paleo environments of Bear Lake and its catchment.


 

Opportunities

Students Wanted

I am seeking graduate (MS and PhD levels) and undergraduate students to join my research group. I have current and pending funding for research projects in Alaska and elsewhere.

Financial support: All students who are accepted to the graduate program are funded as either Teaching or Research Assistants. Undergraduate assistants are frequently needed for the lab and the field.

Graduate degrees: My students pursue their Master’s degree in either Geology or in the Paleoenvironments Emphasis of Environmental Sciences & Policy, and their PhD degree in Earth Sciences & Environmental Sustainability with an emphasis in either Climate & Environmental Change or Earth Systems.

Subbottom stratigraphy, Emerald Lake

For more information: Please contact me or any of my graduate students for information about the graduate programs at Northern Arizona University. NAU has a great deal to offer students, and Flagstaff is a wonderful town in an attractive, high-elevation, American West setting.

Career paths: Since 1995, I have served as the primary faculty advisor for 29 successful MS students. Almost all of the MS theses have led to publications in scientific journals. My students have gone on to professional careers in: geoscience consultants (6), government- and university-based scientists (5), university professors (PhD level; 6), college instructors (MS level; 4), small business owners (3)

Facilities: Students are trained in both field and laboratory procedures. The laboratory combines techniques in sediment analyses and  geochronology, with daily operations overseen by a laboratory manager.

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Kevin preparing samples for biogenic Si analysis

Field equipment: lake coring platform, percussion corer, Uwitec surface corer, automated sediment traps, logging sensors for hydrological and meteorological parameters, conductivity-temperature-depth loggers (CTDs), recording sonar

Sediment lab equipment: particle size analyzer, hyperspectral core scanner, magnetic susceptibility, thermogravimetric analyzer, onsite cold room, microscopes, microbalance, sonicators, drying ovens

Sediment lab procedures: radiocarbon sample preparation, ABA treatment, diatom purification, cryptotephra separation, biogenic silica content, loss on ignition

Amino acid geochronology lab equipment: high performance liquid chromatographs, high precision ovens, laminar flow hood

Megan & Dave preparing water samples

Collaborating labs at NAU:
Paleoclimate Dynamics Lab
Laboratory of Paleoecology
Colorado Plateau Stable Isotope Lab
Schuur Radiocarbon Lab
Environmental Analysis Lab

People

SES Faculty; Where’s DK?

My students and I work closely with others in the Past and Present Climate Change research area in the School of Earth & Sustainability, including professors Nick McKay, Scott AndersonCody Routson and postdoc Michael Erb. We collaborate with the Center for Ecosystem Science and Society, and with many specialists in the US and internationally.

 

Darrell Kaufman
Darrell is a Regents’ Professor in the School of Earth and Sustainability. He has been studying the Quaternary geology and paleoclimatology of Alaska for over 30 years, and has been coring lakes there for more than two decades. He has a special interest in geochronology and in facilitating large collaborative science synthesis projects.

Brief CV
Google Scholar

Current Graduate Students

Ellie Broadman
Ellie is a PhD student in Earth Sciences and Environmental Sustainability. She is analyzing  oxygen isotopes in diatoms from lake sediments to reconstruct Holocene changes in hydrological conditions in both the Kenai lowlands and the northeastern Brooks Range. Ellie worked at the US Geological Survey in Menlo Park, CA after receiving her B.A. in Geography from UC Berkeley.

 

Annie Wong
Annie is a Master’s candidate in Environmental Science & Policy. Her research focuses uses lake sediment from Pothole Lake to determining the timing of glacial sediment aggradation in the Skilak River outwash plain on the Kenai Peninsula in southern Alaska. Annie received her B.A. degrees in Biology and Geology from Mount Holyoke College.

Laboratory Manager

Katherine Whitacre
Katherine is a Senior Research Specialist and the laboratory manager since 2010. Previously she served as a research assistant at the Oak Ridge National Laboratory in Tennesse, and for the Department of Agriculture, University of California, as well as the Merriam-Powell Center for Environmental Research at NAU. She received her BS in Biological Sciences from NAU in 2005, and her MS in Environmental and Soil Science from the University of Tennessee in 2010.

 

Completed Graduate Students
(with their current positions)

Rebecca Ellerbroek, 2018, Three-component hydrograph separation for the glaciated Lake Peters catchment, Arctic Alaska (Instructor, Northern Arizona University)

Chris Benson, 2018, 16,000 years of paleoenvironmental change from the Lake Peters- Schrader area, northeastern Brooks Range, Alaska

Douglas Steen, 2016, Late Quaternary paleomagnetism and environmental magnetism at Cascade and Shainin Lakes, north-central Brooks Range, Alaska (Environmental consulting, Houston, TX)

Paul Zander, 2015, Tephrochronology and paleoenvironmental change during the past 15,000 years at Whitshed Lakes, south-central Alaska (PhD student University Bern, Switzerland)

Taylor LaBrecque, 2014, Holocene glacier fluctuations inferred from proglacial-lacustrine sediment cores from Emerald Lake, Kachemak Bay, Alaska (Environmental consulting, Maine)

Brandon Boldt, 2013, A multi-proxy approach to reconstructing Holocene climate variability at Kurupa River valley, Arctic Alaska (Brewmeister, Denver, CO)

Anne Krawiec (Hamblin), 2013, Holocene tephrochronology and storminess inferred from two lakes on Adak Island, Alaska (Consulting Geologist, Denver, CO)

David Vaillencourt, 2013, Five-thousand years of hydroclimate variability on Adak Island, Alaska inferred from dD of n-alkanoic acids (Orion GMP Solutions, Organic chemistry, Colorado Springs, CO)

Chris Kassel, 2009, Lacustrine evidence from Mother Goose Lake of Holocene geothermal activity at Mount Chiginagak, Alaska Peninsula (Geologist, Arcadis Consultancy, Syracuse, NY)

Heidi Roop, 2009, Climate influence on varve sedimentation at Cascade Lake, Ahklun Mountains, southwestern Alaska (Science communication, Climate Impacts, University of Washington, WA)

Caleb Schiff, 2007, Late Holocene storm-trajectory changes inferred from the oxygen isotope composition of lake diatoms (Restaurant owner, Pizzicletta, Flagstaff, AZ)

Nicholas McKay, 2007, Late Holocene climate at Hallet and Greyling Lakes, central Chugach Range, south-central Alaska (Professor, Northern Arizona University)

Thomas Daigle, 2006, Late Holocene climate change at Goat Lake, Kenai Mountains, south-central Alaska (Consulting Geologist, Denver, CO)

Kasey Kathan, 2006, Late Holocene climate fluctuations at cascade Lake, northeastern Ahklun Mountains, southwestern Alaska

Janelle Sikorski, 2004, Little Ice Age glacier fluctuations and winter precipitation, Brooks Range, Alaska (Instructor, University Alaska, Anchorage, AK)

Christian deFontaine, 2004, Holocene tephrochronology, Cook Inlet, Alaska (Environmental Scientist, U.S. Geological Survey)

Nicholas Balascio, 2003, Late Wisconsin equilibrium-line altitudes, Brooks Range, Alaska (Professor, William & Mary College, Williamsburg, VA)

Jordon Bright, 2003, Oxygen isotopes and ostracodes in a 250,000-year-long core from, Bear Lake, Utah/Idaho (PhD student, University of Arizona)

Laura Levy, 2002, Late Holocene glacier fluctuations, Ahklun Mountains, SW Alaska (Professor, Humbolt State University, CA)

Gary O’Brien, 2002, Oxygen isotope composition of banded Quaternary travertine, Grand Canyon National Park, Arizona (Research Associate, Utah State University, Logan, UT)

Benjamin Laabs, 2001, Quaternary lake-level and tectonic geomorphology, Bear Lake Valley, Utah/Idaho (Professor, North Dakota State University, Fargo)

Yarrow Axford, 2000, Late Quaternary glacier fluctuations and vegetation change in the northwestern Ahklun Mountains, SW Alaska (Professor, Northwestern University, Chicago, IL)

Kathy Lemke, 2000, Holocene tephrochronology of the Homer area, Cook Inlet, Alaska (Lecturer, Puget Sound Community College, WA)

Jason Briner, 1999, Late Wisconsin glacial chronology of the western Ahklun Mountains, SW Alaska (Professor, University of Buffalo, New York)

Jeffrey Bigelow, 1998, Amino acid geochronology of the Lahontan basin, Nevada (Consultant, Parsons, Salt Lake City, UT)

David Bouchard, 1997, Quaternary Bear River paleohydrogeography reconstructed from the 87Sr/86Sr composition of lacustrine fossils

Amy Hochberg, 1996, Aminostratigraphy of Thatcher Basin, SE Idaho–Reassessment of Pleistocene lakes (Geology Instructor, Utah State University, Logan, UT)

Caleb Thompson, 1996, Pre-late Wisconsin glacial history of the Naknek River valley, SW Alaska (Database developer, MongoDB, New York)

Karen Stilwell (Miller), 1995, Late Quaternary glacial geology, shoreline morphology, and tephrochronology of the Iliamna/Naknek/Brooks Lake area, SW Alaska (President, M2 Resource Consulting)