PI Sierra Petersen joined forces with Professor Kate Huntington (University of Washington) to author a review article on all things carbonate clumped isotope thermometry for Annual Reviews of Earth Sciences.
While writing this article, we envisioned it being used as the handbook you’d give to a new graduate student or collaborator to get them up to speed on the current state of the field and how it got here. For students in particular, we wrote a “Student Companion” supplement that goes into class-lecture-level detail on a number of foundational concepts of clumped isotope thermometry. We had never seen this type of information collected into one place before and had always struggled on how to onboard new students efficiently.
We hope this article will be useful to the clumped community – old and new members!
A new paper out of the SCIPP Lab investigates isotopic differences between the inner and outer shell layers of bivalve shells. In this paper, PhD student Allison Curley and coauthors show that differences between inner shell layer (ISL) and outer shell layer (OSL) carbonate is conserved within a species but differs between species. We suggest this ISL-OSL difference is a proxy for physiology of the organism – how it grows its shell.
These particular samples represent 6 extinct bivalve species from Seymour Island, Antarctica. Some species show one direction of isotopic offset (d18O and d13C higher in ISL and D47 lower in ISL than OSL), others show the opposite direction offset, and a third group show no difference between the ISL and OSL. Tantalizingly, of the 6 species studied, the two that survive the KPg mass extinction show the largest magnitude offsets, potentially indicating an ability to regulate their internal body chemistry, even in the face of adverse external conditions.
This paper defines a framework for how ISL-OSL differences could be interpreted in other species and opens the door to a wide range of new research directions. Very exciting!
PhD student Jade Zhang published her second paper, this one focusing on high-resolution clumped isotope sampling in bivalves.
High-resolution isotopic sampling along the direction of maximum growth of a mollusk (isotopic sclerochonology) has been done for many years using oxygen and carbon isotopes. This method can reveal seasonality of climate (via the d18O max, min, and range), mollusk growth rate, and more, but suffers from the same issues all oxygen isotope paleothermometry methods do – unknown d18Owater. Clumped isotope paleothermometry doesn’t have the same issues with uncertainty in d18Ow, but large historical sample size requirements have prevented much application of this powerful technique to mollusk sclerochronology.
With recent reductions in sample size, this new area of clumped isotope paleothermometry is increasingly being explored. In this study, Jade applies different subannual sampling methods (seasonally targeted vs. continuous sampling) to modern shells of the bivalve Lucina pensylvanica from sites around Florida and the Caribbean, testing which methods work best in higher (Florida) or lower (Caribbean) seasonality locations.
In the end, she proposes a trade-off between sampling resolution, sample size, machine precision with different sample sizes, and bivalve growth rate. This study both defines L. pensylvanica as a robust recorder of climate and also serves as a template for designing clumped isotope sclerochronology sampling strategies on other species.
The latest SCIPP-Lab paper comes from former SCIPP-lab postdoc Dr. Matt Jones (now at the Smithsonian Institute), publishing the work he did while at UM. Dr. Jones looked at fossil oysters from the Cretaceous Western Interior Seaway and used clumped isotope to reconstruct seaway temperatures during the time they lived.
We found that temperatures during the Cretaceous Thermal Maximum (Cenomanian-Turonian period, ~95 Million years ago) reached upper 20’s to lower 30’s Celsius in what is now modern day Utah and Wyoming. This is very hot! These water temperatures, which occurred in the mid-latitudes during the Cretaceous, are today only found in the warmest areas of the ocean like the Western Pacific Warm Pool. It makes you wonder how hot the tropics were if the mid-latitudes were >30C!! But that’s for another day…
Some Cenomanian-Turonian oyster fossils used in this studyShell cross section, showing growth banding (and some calcite veins).
SCIPP Lab members measuring section and collecting Plio-Pleistocene fossil shells
Four members of the SCIPP lab ventured to sunny, hot, humid (sooo humid so hot) Florida to gather shells from the Plio-Pleistocene for geochemical analysis. We spent 5 days in the Florida Shell and Fill quarry near Punta Gorda gathering as many fossils as we could. Graduate students Lucas Gomes, Allison Curley, and Jade Zhang accompanied Professor Sierra Petersen and collaborator Peter Riemersma (Grand Valley State University) for the week. Our local contact Roger Portell from the Florida Museum of Natural History joined the group for the first two days to help us get our bearings. A big shout out to the owners and operators of FL Shell – Joe, Jess, Marilyn, James, Ernesto!! Thank you for giving us access to this awesome site.
During the Plio-Pleistocene interval (around 0.1-3.5 Ma), the southern portion of Florida was underwater much of the time (excluding glacial intervals where seawater was trapped in ice sheets and sea level was lower). Studied formations (Ochape, Caloosahatchee, Bermont, and Fort Thompson) represent marine to shallow marine to beach environments. These formations are SO full of shells, it wasn’t a question of whether we would FIND any fossils, more like could we SAMPLE the right ones and keep track of where we found them. We got very picky about which were the “best” ones by the end of the week.
Grad Student Lucas Gomes describing the upper portion of the section. Grad student Jade Zhang points to an in-place coral we hope to date.
This site has an amazing diversity of shells. Literally hundreds of species. Some large, some small. We found everything from hand-span-sized scallops (Carolinapecten) to mm-sized micromollusks. Although larger shells appeared caked in mud and sand, when you wash them off, they’re actually filled with even smaller shells!
Fast growing scallop, Carolinapecten. Micromollusks washed out of a larger gastropod shell, inside a yogurt container for scale. Grad students Jade Zhang, Allison Curley, and Lucas Gomes organizing samples in the garage of our AirBNB in the evening. Great teamwork, great organization!
Whether it was the first real field work, or the first field work in a while, the grad student team did an amazing job with logistics, field sampling, and evening sample organization. Great job everyone! Very excited to see what science comes out of these (many many) samples. 🙂
SCIPP Lab is excited to announce that Sierra has been selected as a 2021 Sloan Research Fellowship.
Paraphrasing from the Sloan website…
The Sloan Research Fellowship seeks to stimulate fundamental research by early-career scientists and scholars of outstanding promise. These two-year, $75,000 fellowships are awarded yearly to 128 researchers in recognition of distinguished performance and a unique potential to make substantial contributions to their field. Their achievements and potential place them among the next generation of scientific leaders in the U.S. and Canada.
Sierra plans to use the funds to push forward our paleo-seasonality projects in the Pliocene and elsewhere.
Julia Kelson (collaborator and now postdoc in the SCIPP group) published a compilation study of all published paleosol clumped isotope data to investigate whether any patterns could emerge regarding seasonal timing of formation or temperature biases. She updated older data using the Brand/IUPAC parameters and culled out early data that didn’t meet current data collection standards.
She found that paleosol carbonates tend to show a warm season bias, and calculated d18Owater values are related to d18Oprecipiation values from the season of carbonate formation.
Our collaborator Benjamin Linzmeier just published a nice paper in Geology looking at calcium isotopes in fossil bivalves spanning the K-Pg boundary. The calcium isotopic composition (44Ca/40Ca) of carbonate is a proxy for carbonate saturation state and can indirectly indicate something about ocean acidification state. Ben analyzed shells from Seymour Island that were previously analyzed for their clumped isotopic composition in the SCIPP lab (Petersen et al., 2016; Nature Communications). We found that the ocean’s carbonate saturation state was highly variable leading into the KPg boundary, which we attribute to CO2 injection into the atmosphere from the massive Deccan Traps volcanic province.
Sierra wrapped up a community-wide effort to reprocess and update clumped isotope calibration data from 11 different laboratories, including over 1200 individual replicates, to bring it into the same framework. This involved updating the fundamental parameters R13_VPDB, R17_VSMOW, R18_VSMOW, and λ used to calculate raw D47, using a consistent and updated set of theoretical equilibrium values (D47_TE) to tie things into the absolute reference frame, and applying a single set of acid fractionation factors (D*90-25) across all studies. We found that agreement is quite good between labs, once all the data processing is done uniformly and the “two-slope” or “multi-slope” problem that plagued the clumped community in the early days has all but disappeared in more recent studies.
As part of this effort, we also developed a data template and began a relationship with the EarthChem database to house future clumped isotope datasets in a long-term storage location. For more information on that, see this page.
We welcomed in the new academic year with the arrival of four new lab members and the return of many others after a summer away. Sierra hosted the whole group at her house for a potluck dinner and the weather cooperated amazingly!
