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Abstract Details

(2020) Uranium Isotope Constraints on the Dynamics of Global Carbon Cycle Perturbations

Romaniello SJ

https://doi.org/10.46427/gold2020.2220

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14b: Plenary Hall, Monday 22nd June 22:03 - 22:06

Listed below are questions that have been submitted by the community that the author will try and cover in their presentation. To submit a question, ensure you are signed in to the website. Authors or session conveners approve questions before they are displayed here.

Submitted by Elizabeth Swanner on Sunday 21st June 19:18
This seems like a great idea, but harder going deeper in time. Specifically, the paleogeographic reconstruction becomes much more difficult, and very few lines of evidence about ocean currents, etc. that would heavily influence mixing. I am curious how you envision a global model accounting for such huge uncertainties.
Thanks, Betsy! This a great question and certainly a hard problem. Published 3D models of ocean circulation have been constructed back to the Cambrian with correspondingly larger uncertainties. Digital paleogeographic continental reconstructions are now available nearly continuously over the Phanerozoic and people like Andy Ridgwell are exploring configuring models like Genie to automatically ingest those data and produce 3D paleobathymetry every 10 Ma or so over the Phanerozoic to simplify ease of use. There’s no doubt that Deep Time geoscience requires a "high tolerance for ambiguity," but I think incorporation of thoughtfully-constructed 3D models can only help rather than hinder our ability to quantitatively and qualitatively synthesize different ocean proxies into one spatially- and temporally-consistent reconstruction of Earth system processes.

Submitted by Torsten Vennemann on Monday 22nd June 12:48
A question on where the phosphorous data is from ? Is it from the same profiles as the Sr, U, etc. or a compilation from different localities? If so, are these localities fully marine or rather shallow water locations ? (Torsten Vennemann).
Hi Torsten! I think you are asking about the PO4 data on Slide 12. These plots are the output of an ocean PO4 box model where we tied PO4 inputs to the riverine Sr flux estimated from the 87Sr/86Sr data and assumed that the residence time of PO4 followed a sigmoidal relationship with the area of anoxic seafloor (after Payne and Kump, 2007). This removal function assumes that P is more efficiently buried under oxic conditions due to Fe/Mn trapping at the sediment-water interface. These PO4 data would mostly closely correspond to open water, deepwater PO4 concentrations, as we were using a 1-box ocean model. You can find more details about the model in the Supplement for Zhang et al. 2018 (Sci Advances) here: https://advances.sciencemag.org/highwire/filestream/203180/field_highwire_adjunct_files/1/1602921_SM.pdf. I would be happy to discuss it at length with you one-on-one if you like.

Submitted by Kimberly Lau on Monday 22nd June 17:47
Thanks for the great talk and discussion points. I'm looking forward to hearing your ideas on how to build community between geochemists and paleontologists!
Thanks Kim! I'm pretty sure the answer involves beer and dozens of sketches on bar napkins. We're working on an app that replicates this experience.

Submitted by Stephen Romaniello on Monday 22nd June 17:57
Hi Torsten! I think you are asking about the PO4 data on Slide 12. These plots are the output of an ocean PO4 box model where we tied PO4 inputs to the riverine Sr flux estimated from the 87Sr/86Sr data and assumed that the residence time of PO4 followed a sigmoidal relationship with the area of anoxic seafloor (after Payne and Kump, 2007). This removal function assumes that P is more efficiently buried under oxic conditions due to Fe/Mn trapping at the sediment-water interface. These PO4 data would mostly closely correspond to open water, deepwater PO4 concentrations, as we were using a 1-box ocean model. You can find more details about the model in the Supplement for Zhang et al. 2018 (Sci Advances) here: https://advances.sciencemag.org/highwire/filestream/203180/field_highwire_adjunct_files/1/1602921_SM.pdf. I would be happy to discuss it at length with you one-on-one if you like.


Submitted by Georgina Lukoczki on Monday 22nd June 20:39
Very good points! I also would like to join in to increase more awareness of petrographic analysis of thin sections being performed on samples corresponding to geochemical data. It would greatly help identify diagenetic alterations and avoid misleading interpretations.
Hi Georgina, I agree completely. The more perspectives we can bring to bear on these data, the better. One of the biggest challenges in interpreting multiproxy data is that few, if any, of the proxy records are truly pristine, and each proxy is subject to its own pattern and degree of alteration which makes it a hard problem.

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