Management of microanalytical data


QGIS_Map_Layers

Work at WiscSIMS involves correlation of multiple types of data from optical microscopy, to scanning electron imaging, to point geochemical analyses. Management and effecient integration of these data facilitates good science and communication of results. A group of graduate students and research scientists developed a workflow to better integrate data through all steps of analysis using the freely available geographic information systems software, QGIS. You can read an overview of this workflow here . A short tutorial website can be found here .

Development of this project is ongoing and will lead to increases in efficency of data collection and reduction of a variety of microanalytical datasets. Stay tuned for updates.


Ocean acidification and proxy calibration


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Rapid injection of CO2 into the atmosphere drives marine pH lower which disrupts the growth of shells in a

To determine if Deccan Traps volcanism influenced carbonate saturation state in the ocean before the K-Pg extinction, we measured the δ44/40Ca of well-preserved mollusk shell from Seymour Island, Antarctica. Shell values are distinctly different than carbonate cements and show excursions that align with new radiometric dates of Deccan volcanic flows. Simple box modeling of ocean δ44/40Ca suggests it can not vary on these timescales due to the abundance of calcium. We infer that the way bivalves change δ44/40Ca of their shells must change with marine chemistry on these timescales. Take a look at the paper here.

After making this observation in bivalves from the Cretaceous, we are doing more work on modern mollusks to investigate how much change in δ44/40Ca can be found with differing carbonate chemistry conditions. We are currently analyzing wild-collected historical Arctica islandica and aquarium-reared Giant Clams. We hope to add additional samples in the future.


Using geochemistry to understand behavior

NautilusMigration

The Nautilus has been a model organism for understanding the ecology and life history of ammonites and extinct nautiloids because it is the last living externally shelled cephalopod. Slow reproductive rates and fishing pressures from the shell trade have recently prompted CITES lisiting for all Nautilus species. The genus is a scavenger in steep forereef environments, where it swims around slowly smelling for food. Radiotracking studies have shown Nautilus to be active swimmers that cross hundreds of meteres a day across a large range of temperatures.

Because of its status as a model organism and its swimming behavior, I hypothesized that this behavior could be recorded in the δ18O of the shell. I used the WiscSIMS Cameca IMS-1280 to measure δ18O values of shell grown in less than 24 hours and found variability indicative of depth migration behavior. The paper communicating these results is here . These findings are a modern test for the preservation of sub-daily behavior in the mineralized parts of cephalopods in deep time.


Environment of ammonite hatchling development

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Ammonoids were a major component of marine ecosystems from their first appearance in the Devonian until their ultimate extinction in the early Paleogene. Unlike living Nautilus that has large benthic eggs, ammonoids likely had many small eggs. Because modern cephalopods that have small eggs generally have planktic hatchlings, it has been hypothesized that ammonites had at least a short window of time with a planktic mode of life.

To test this, I used δ18O measured from the thin walls of hatchling ammonites collected from rocks of the Cretaceous Western Interior Seaway and compared these data to similar data from obligate benthic bivalves to constrain vertical position in the water column due to the temperature gradient. I found that pre-hatching values are more similar to bivalves, suggesting a benthic egg laying and that values reflect warmer or fresher water indicating shallower habitat after hatching. Variability between five different individuals in the same concretion suggests seasonally protracted spawning. To read more about this, take a look at the paper.