Research

Much of our research relies on measurements of stable isotope distributions in a variety of natural materials (teeth, carbonates, water etc).

We’re in the midst of re-establishing the lab at the University of Michigan, building on what we did at Hopkins and expanding it so we can work in a greater range of systems. We don’t have a lab website up and running yet but until we do you can check out the site for the lab at Johns Hopkins to get sense for the kinds of things we do.

And take a look at the photos on the ISO PALEO LAB Instagram account to see the latest lab activity.

 

Triple oxygen isotopes in the hydrosphere and applications to the geologic record

17Otap_LialGCASmall variations in the relationship between δ18O and δ17O values of natural waters has become an emerging field ever since Barkan and Luz (2005) demonstrated that such deviations could be measured precisely in waters. These deviations, termed Δ17O, in waters, rocks and plants hold promise to provide new windows into natural systems. Shuning Li, who finished her PhD in 2015 in the lab at JHU, has generated a Δ17O ‘isoscape’ of North American tap waters (see Shuning’s 2015 GCA paper). Shuning has also generated a Δ17O leaf water dataset from Mpala, Kenya (Li et al. 2017, EPSL) which provides important insights into Δ17O in plant waters and the relationships between Δ17O and d-excess when evaporation is the primary driver of oxygen and hydrogen isotope fractionation in waters.

Δ17O in precipitation
We have also measured Δ17O in samples from the United States Network for Isotopes in Precipitation (USNIP) in collaboration with Jeff Welker at the University of Alaska Anchorage, from precipitation and river water samples collected by Renée Brooks at the EPA, and from precipitation and river waters collected locally in Baltimore. Preliminary results from this work were presented at the Goldschmidt Conference in Florence, Italy, August 2013 and at the 2014 AGU Fall meeting in San Francisco, CA. This research was funded by the American Chemical Society.

We’re building on this existing to work to expand the geographic range and resolution of sampling to develop a better understanding for how Δ17O in waters tracks with hydrology, climate and geography.  Some of this work is piggy-backing on existing research at UM EARTH, like Phoebe Aron and Chris Poulsen’s work on the isotopic composition of precipitation in Peru. Phoebe will present the initial results at AGU 2018.

Crowdsource Δ17O project
The water Δ17O work continues to grow.  In May 2018, we asked members of the UM EARTH community  to collect waters during their summer travels.  The response was huge. Over 60 people have collected more than 500 water samples from 5 continents and 27 countries. UM EARTH grad student Phoebe Aron is taking the lead on this project. Her first step is to measure the δ18O and δD values of these waters in the Poulsen Lab, and then we’ll next analyze a subset of these waters to determine their Δ17O values. Sample collection is still on going and are still recruiting people to collect waters for those who are interested in helping. Click here for more information about the crowdsource #17Owatermap project.

Δ17O in the geologic record
The work on Δ17O in waters is being conducted in parallel with efforts led by Ben Passey to measure Δ17O in carbonates. There was a big push to polish off a slew of datasets on lake carbonates, teeth, eggshells, soil carbonates and waters in the JHU lab before we shut it down in May 2016. Here are some abstracts from AGU and GSA that describe some of this work, including our initial Δ17O results from Lake Junin, Peru, work by postdoc Jessica Moerman on the constraining hydroclimate of southern Kenya in the last 500 kyr using Δ17O, and work by former student Sophie Lehmann (PhD 2016) on using Δ17O in teeth to reconstruct paleoaridity. Postdoc, Emily Beverly is working on understanding Δ17O variation in soil carbonates in eastern Africa, figuring out how it works in modern soils from the Serengeti, Tanzania) and applying what she learns to the record of soil carbonates from the Omo-Turkana basin in Ethiopia and Kenya. Emily will be presenting this work at GSA 2018.

Stay tuned for the resulting publications.

Studies involving triple oxygen isotope variations in waters, carbonates, silicates and oxides is a big focus of the group’s current and future research.

Environmental Change in the Southern Kenya Rift

IMG_2446-300x225Our work in the southern Kenya Rift involves developing stable isotope records from outcrop and drillcores to reconstruct hydroclimate and ecological change in the region over the last one million years. This work is done as part of efforts led by the Smithsonian Human Origins group. We are currently focusing on outcrop samples from Olorgesailie and drillcore samples from the Olorgesailie Drilling Project. Among our many collaborators on these projects are Rick Potts and Kay Behrensmeyer, who are both at the Smithsonian National Museum of Natural History. Jessica Moerman’s postdoctoral research is focusing on developing triple oxygen isotope and clumped isotope records from both outcrop and core carbonates.

Woranso-Mille, Afar Region, Ethiopia

IMG_3026Woranso-Mille is a Pliocene paleontological site in the Afar region of Ethiopia known for its fossil record of the hominin Australopithecus. I work on this project with a group of paleontologists and geologists with the aim of reconstructing the sedimentological, tectonic and environmental histories in this area. My work specifically involves generating stable isotopic records from fossil teeth and soil carbonates. Some of this work has been published in a PNAS paper that focuses on diets of hominins and monkeys from the early Pliocene. You can find more publications and more about the project here. This work is in collaboration with Yohannes Haile-Selassie, Beverly Saylor, Mulugeta Alene, Al Deino and Luis Gibert Beotas. The project has been funded by the National Science Foundation. Naomi is recruiting students to work on this project.

Isotopic Composition of Waters from Eastern Africa

DSCN0835The stable isotopic composition of waters offers an opportunity to use isotopic distributions today as frameworks for interpreting oxygen isotopes archived in the geologic record. Former JHU post-doc Zelalem Bedaso is leading an effort to document isotopic variation in precipitation in Ethiopia and has deployed daily, weekly and monthly precipitation collectors at 4 weather stations in Ethiopia, in collaboration with the National Meteorological Agency of Ethiopia. Zelalem presented the initial results from these collections at the 2013 AGU Fall Meeting and the analysis of samples from the 16-month long sample collection campaign is currently in the works. Nikki DeLuca will present an update on results from this work at the 2016 AGU Fall meeting.

Elandsfontein, Western Cape, South Africa

IMG_0380Work at Elandsfontein, a middle Pleistocene paleontological and archaeological site in the Western Cape of South Africa, is in collaboration with David Braun at George Washington University. My involvement in this project is centered on establishing the stratigraphic and paleoenvironmental context of the fossil and artifact finds at Elandsfontein. Active dune fields that bury the Pleistocene sediments have forced us to make our own outcrop by digging pits and auger holes so that we can actually see the stratigraphy. By taking a look at what’s beneath the modern dunes, we have been able to correlate many of the artifact and fossil localities. See Braun et al. (2013) for a description of the geologic work that we’ve done at Elandsfontein.

DSCN3738The Elandsfontein work also involves isotopic analysis of materials from Elandsfontein (including fossil teeth) with the goal of building detailed isotopic records of mid-Pleistocene environmental and climatic change for the Western Cape.

This work was the focus of Sophie Lehmann’s dissertation work  – Sophie is just finishing her PhD (at JHU) on the sedimentological and tooth enamel isotopic records at Elandsfontein. See recent papers led by Sophie Lehmann, David Patterson and David Braun with results from our recent work at Elandsfontein. This work is funded by the National Science Foundation.

Gona, Afar Region, Ethiopia

RFB_NEL_BusidimaGona is best known for archaeological sites that contain the oldest evidence for stone tools in the world, however there is also a rich hominid fossil record that spans the late Miocene through the Pleistocene. In addition to paleoanthropological, archaeological, and paleontological resources, Gona contains an excellent sedimentary archive of >6 million years of environmental change in an active rift basin.

I have worked as geologist on the Gona Research Project since 2001. My work at Gona includes stratigraphy, mapping, and isotopic studies of soil carbonates, fossil teeth and mollusks. These studies are part of an initiative to build a complete paleoenvironmental story at Gona, that provides an environmental context for human evolution and an anchor point for characterizing local terrestrial responses to regional climate change in eastern Africa since the late Miocene. My work at Gona is primarily in collaboration with Sileshi Semaw, Scott Simpson, Dan Peppe, Jay Quade and Stephen Frost, although there are many other scientists who contribute to the research at Gona. All of our work is done with the help of the Afar people. The work was recently funded by the National Geographic Society.

Turkana Basin, Kenya

OmoGroupMap2The Turkana Basin, in northern Kenya and southern Ethiopia, contains extensive exposures of Pliocene and Pleistocene sediments (the Omo Group) that fill a depression where the Main Ethiopian and East African rift systems meet. The Turkana Basin is best known for substantial number of hominid fossil remains that have been recovered from the Omo Group deposits, however the ~5,000 km2 of sediment exposures also provide an excellent opportunity to examine environmental variability in a large basin through time. My work in the Turkana Basin primarily focuses on using carbon and oxygen isotope ratios of pedogenic carbonates and fossil teeth to study this variability and link it to regional and global climate change during the Pliocene and Pleistocene. This isotopic work is in collaboration with Frank Brown, Thure Cerling, John Harris, Meave Leakey, Kay Behrensmeyer, and David Braun.