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Abstract Details

(2020) Processes that Impact the Composition of FeMn Crusts from the Pacific Ocean and their Use in Refining Permissive Criteria

Mizell K, Hein JR, Lam PJ, Koppers AAP & Staudigel H

https://doi.org/10.46427/gold2020.1819

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08m: Room 3, Tuesday 23rd June 22:45 - 22:48

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 Daniel Gregory on Friday 19th June 04:53
Thank you for the very interesting presentation. Can you suggest why the Co and Ni are enriched in the shallow, low O2 areas?


Submitted by Daniel Gregory on Friday 19th June 05:04
Thank you for the very interesting presentation. Can you suggest why the Co and Ni are enriched in the shallow, low O2 areas?
Thank you for the question, Daniel. Cobalt and Ni are enriched in the shallow, low O2 regions for two reasons. First, both are associated with the Mn-oxide mineral phase of ferromanganese crusts, and Mn-oxide formation is elevated under these conditions due to increased supply of Mn2+ from the oxygen-depleted waters (aka OMZ). Cobalt and Ni enrichment is also typically related to slow growth rates of ferromanganese crusts which occur at shallow depths due to low oxygen conditions and less detrital input.

Submitted by Akira Usui on Tuesday 23rd June 13:20
Thank you, Kira for a comprehensive summary in the CPB crusts with plenty of on-site and in-lab data. Please let us know your assumption for your model in understanding latitudinal, water-depth, and secular variability. 1) Do you assume higher or lower rate (MAR or flux) of Mn in OMZ?, 2) Do you assume similar growth rates or variable in the water depth ranges btw 1&6km? 3) Is it reasonable to correlate your variable chemistry and areal patterns to modern oceanographic conditions? In our cases in the NW Pacific seamounts, Mn flux have been almost constant and continuous between OMZ and deepsea basins, we found no significant variable changes in growth rate between 1-6km, the correlation between compositional diversity with modern ocean parameter is not always successful. Akira at Kochi.
Thank you for the questions, Akira. We do assume higher flux of Mn from the relatively strong and established OMZ in the northern equatorial Pacific for this study. For this statistical study, we did not measure growth rates using any isotopic systems. However, we did calculate the cobalt chronometer dates, and these estimated growth rates increase as water depth increases. We recognize that for our sample set, the changes with depth are concurrent with large changes in latitude and therefore may be more dramatic than changes observed with depth within a single seamount. We recognized that your 2017 paper did not see these large changes in growth rate with depth, but our data show that for very large regional-scale changes in oxygen concentration, the correlations of higher Mn, Co, and Ni with slower growth rates and shallower depths is evident. We only measured the composition of the upper 15 mm or less for of each of the 57 crusts in this study, which we think is reasonable to correlate with modern oceanographic conditions; however, we acknowledge that it is not a perfect scenario and the paleoceanographic changes in oceanographic and geographic conditions should be considered for even more robust models.

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