News

Four seniors completed senior theses in the group this year. They also presented their work orally during a special session of the Michigan Geophysical Union conference for senior theses students.

Cecilie Philips – Temperature Dependent Growth Shutoffs in the Bivalve Mercenaria as determined by d18O of Interglacial Aged Shells

Jon Portinga – Scallops as High-Resolution Recorders of Pleistocene Climate

Eric Water – Gradualism in the Face of Extinction: a Test Case in the Bivalve Chione sp. in Plio-Pleistocene Florida (*awarded highest honors*)

Kailey Koshorek – Morphometric variation in the clam genus Mercenaria and their relation to environment

Congratulations Seniors!

Undergraduate student Jon Hoffman published his senior thesis as a first-author paper in P3, in a special issue on sclerochronology.

Jon conducted high resolution d18O and D47 to reconstruct seasonality in temperature in the Western Interior Seaway. He found highly seasonal temperature and d18Ow, suggesting subannual shifts in circulation and/or terrestrial runoff within the seaway. These are the first-ever estimates of absolute temperature seasonality in the seaway. This study also demonstrates that D47-paleothermometry is vital for reconstructing seasonality in the WIS due to variable d18Ow values.

Link to Paper: https://www.sciencedirect.com/science/article/pii/S003101822500063X

PhD student Lucas Gomes published his first paper (congrats!!) in Journal of Sedimentary Research. This stems from our field work in 2022 to a new site called Florida Shell Quarry near Punta Gorda Florida.

Lucas documents in detail the 4 geologic formations present at this quarry and uses sedimentological and faunal evidence to describe the fluctuating paleoenvironment in this location. These formations include key intervals in the molluscan mass extinction that has been documented in Florida and along the East Coast.

Describing new sites in Florida is especially important because each study location is only accessible for a year to a handful of years. Once quarrying work is done, each pit is flooded and turned into a lake. Lucas links this new site to those described elsewhere in seminal work from decades ago. With Lucas’s nice paper, future workers will be able to similarly link new sites to Florida Shell Quarry, even after it’s no long accessible.

This is the first of many more papers to come looking at Florida Shell, as we collected 100s of lbs of fossils we plan to study for paleoclimate purposes. Laying the stratigraphic framework is critical for these future paleothermometry studies.

Link to Paper: https://pubs.geoscienceworld.org/sepm/jsedres/article/95/2/367/653487/Plio-Pleistocene-stratigraphy-paleoenvironments

At this year’s awards dinner, students from the SCIPP Lab (and friends) won lots of awards!

Eric Waters – “Undergraduate Excellence Award for best senior”

Yunhan Fang – “Undergraduate Excellence Award for best junior”

Lucas Gomes – “Outstanding Graduate Student Instructor Award”

Friend of the lab Sydney Gable was also awarded the Rackham Outstanding GSI award for her work with revamping Intro Oceanography.

Lucas Gomes was also awarded the Rackham Pre-Doctoral Fellowship which covers his stipend and tuition for his final PhD year. This is a big honor!

PhD student Allison Curley publishes her second paper, this time in EPSL.

During the Late Cretaceous, North America was split in two by the Western Interior Seaway. To the west, mountains were rising to become today’s Rocky Mountain range. Major river systems drained from these mountains, across plains and into the seaway, influencing coastal salinity and seaway chemistry.

Previous work analyzing the d18O composition of mollusks living in these freshwater environments has documented two different clusters of data, reflecting high-altitude rivers draining from the mountains vs. low-altitude rivers and ponds. However, how much of this difference in d18O was due to the temperature of the water as opposed to the d18O composition of the water remained unknown. Allison here measures these freshwater mollusks for their clumped isotope composition and separates the influences of temperature and d18Ow.

Temperature estimates from multiple sites document a similar latitudinal temperature gradient as has been found in previous studies. Spatial patterns of d18Ow are consistent with a Campanian Proto-North American Monsoon and the lowest d18Ow values are consistent with a paleoelevation of >3500 m in the Proto-Cordillera.

She also analyzed 87Sr/86Sr in the hopes of using a two-end-member mixing model with d18Ow to estimate the freshwater influence in coastal regions and back out seaway salinity. However, 87Sr/86Sr was too spatially variable to accomplish this.

Link to Paper: https://www.sciencedirect.com/science/article/pii/S0012821X24006125

Former MS Student Serena Scholz published her second paper, this one focusing on high-resolution d18O profiles in the marine Turritellid gastropods and their ability to accurately record paleo-seasonality.

High-resolution oxygen isotopic sampling along the direction of maximum growth of a mollusk (isotopic sclerochonology) has been used to reconstruct paleo-seasonality. Carbonate d18O is controlled by growth temperature and the isotopic composition of the growth fluid (d18Ow). By assuming d18Ow is fixed and that all d18O variations are due to temperature variations, high-res d18O profiles can be converted to seasonal temperature profiles. However, if d18Ow is not in fact constant, the inferred magnitude of the seasonal temperature cycle may be incorrect in either to “too big” or “too small” direction.

Serena shows that shallow-dwelling gastropods like Turritellids may be susceptible to this problem due to their habitat. Nearshore, shallow coastal areas experience freshwater runoff from land, which can be constant or seasonally variable. In locations with high seasonality of rainfall (e.g. a heavy rainy season), periods of enhanced runoff may cause seasonal variations in d18Ow and salinity in the waters Turritellids inhabit. Depending on the phasing of this rainfall with seasons (e.g. rainy winter vs. rainy summer), this can add to the apparent d18O amplitude or decrease it.

Serena compares modern climate data with high resolution d18O profiles from Turritellid gastropods from many locations. She shows that using high-res d18O to reconstruct paleo-seasonality using Turritellids may lead to inaccurate results. However, if seasonality is known to be low (e.g. tropics), the amplitude of the d18O signal can then tell you something about the seasonality of rainfall and freshwater delivery to the coastal regions.

LINK TO PAPER: https://www.sciencedirect.com/science/article/pii/S003101822400542X

The SCIPP Lab welcomes new MS student Erin Kim. Erin joins us from University of Massachusetts Amherst, where she worked with Mark Leckie and became a devout lover of foraminifera. Although her project in the SCIPP Lab will not involve forams, it will involved water masses and paleo-ocean circulation. Erin will be working on changes in climate and Gulf Stream position over the Miocene-modern of the US East Coast, with a particular focus on the Yorktown Formation.

Welcome Erin!

We also welcome a new cohort of undergrads through the new Research Course Sierra is running (Earth 296). This SCIPPx, or SCIPP Lab extension group, will be working on fossils from Florida Shell Quarry, applying isotopic and trace elemental methods, as well as some morphometrics, to help answer the question “How did climate changes in Florida from the Pliocene to today”. We are hoping that after the fall semester is over, some of these students will continue to work in the group in winter!

Our projects in Bermuda continue with two new papers by PhD student Jade Zhang and collaborators Lillian Minnebo and Ian Winkelstern (Grand Valley State Univ.).

In previous work we showed that during the Last Interglacial, d18Ow values along the South Shore of Bermuda fluctuated subannually. We inferred that this was related to submarine groundwater discharge from an underground aquifer. Now, in her new paper, Jade presents >100 water samples from modern Bermuda documenting this unexpected variability in coastal seawater d18Ow, specifically along the South Shore. She links this to well water samples showing the composition of the freshwater lens underground central Bermuda.

Link to Paper: https://www.frontiersin.org/journals/marine-science/articles/10.3389/fmars.2024.1441113/full

In related work, Lillian continues our efforts to reconstruct Last Interglacial climate in Bermuda, this time using samples from within the Great Sound. These should be well away from any submarine groundwater discharge influence. In contrast to Zhang et al 2021 who found cooler-than-modern conditions, Lillian finds that the Last Interglacial was the same to slightly warmer than present day. Future work should disentangle whether these disparate results are due to 1) different taxa used or 2) outcrops representing different moments in time within the LIG.

Link to Paper: https://www.sciencedirect.com/science/article/pii/S0031018224001846

In May, Sierra was officially awarded tenure by a confirmation vote of the UM Regents. Out of all faculty newly receiving tenure at UM, Sierra was one of three faculty selected by the Provost to be highlighted individually at the Regents meeting.

This would not have been possible without the hard work of all of the past and present members of the SCIPP Lab! Thanks everyone!

The brand new Dr. Allison Curley passed her thesis defense with the combination of rigor and dry humor we know and love. She nicely presented her thesis work on Biologicaly-Derived Isotopic Fractionations (BioDIFs) in modern and fossil bivalves and it’s potential link to precipitation mechanisms and paleophysiology. A wide audience of friends and colleagues attended virtually and in person.

Dr. Curley leaves the group shortly to join the Fiebig Group at Goethe University in Frankfurt, Germany where she will further her work on BioDIFs using dual clumped isotope paleothermometry. Auf Wiedersehen Allison!