TY - JOUR
T1 - Foraminifera Iodine to Calcium Ratios
T2 - Approach and Cleaning
AU - Winkelbauer, Helge
AU - Cordova-Rodriguez, Kathy
AU - Reyes-Macaya, Dharma
AU - Scott, Jennifer
AU - Glock, Nicolaas
AU - Lu, Zunli
AU - Hamilton, Elliott
AU - Chenery, Simon
AU - Holdship, Phil
AU - Dormon, Charlotte
AU - Hoogakker, Babette
N1 - Funding Information:
This research used samples provided by the Ocean Drilling Program (ODP). ODP was sponsored by the US National Science Foundation and participating countries (Natural Environment Research Council in the UK) under the management of Joint Oceanographic Institutions (JOI). The authors thank the crews and scientific team of the R/V Meteor cruise M77/1 and RRS Discovery cruise 184 for help with the sample acquisition. This work was supported by a James Watt Scholarship awarded to H. A. Winkelbauer. D. Reyes-Macaya was supported by a PhD joint grant of Becas Chile (17342817-0) and DAAD (57144001). Additional thanks to the National Fund for Scientific, Technological Development and Technological Innovation (FONDECYT) in Peru for funding the 3 months internship at the Lyell Centre granted to K. Cordova-Rodriguez. GLOMAR and IMPULSE programs from the University of Bremen in Germany support 3 months internship of D. Reyes-Macaya at the Lyell Centre. B. A. A. Hoogakker acknowledges support from UKRI Future Leaders Grant MR/S034293/1 and UK Natural Environment Research Council (NERC) grant NE/I020563/1. Z. Lu acknowledges support from National Science Foundation (NSF) grants OCE-1232620 and OCE-1736542. N. Glock acknowledges support from the German Research Foundation (DFG) grants GL 999/3-1 und SFB754.
Funding Information:
This research used samples provided by the Ocean Drilling Program (ODP). ODP was sponsored by the US National Science Foundation and participating countries (Natural Environment Research Council in the UK) under the management of Joint Oceanographic Institutions (JOI). The authors thank the crews and scientific team of the R/V cruise M77/1 and RRS cruise 184 for help with the sample acquisition. This work was supported by a James Watt Scholarship awarded to H. A. Winkelbauer. D. Reyes‐Macaya was supported by a PhD joint grant of Becas Chile (17342817‐0) and DAAD (57144001). Additional thanks to the National Fund for Scientific, Technological Development and Technological Innovation (FONDECYT) in Peru for funding the 3 months internship at the Lyell Centre granted to K. Cordova‐Rodriguez. GLOMAR and IMPULSE programs from the University of Bremen in Germany support 3 months internship of D. Reyes‐Macaya at the Lyell Centre. B. A. A. Hoogakker acknowledges support from UKRI Future Leaders Grant MR/S034293/1 and UK Natural Environment Research Council (NERC) grant NE/I020563/1. Z. Lu acknowledges support from National Science Foundation (NSF) grants OCE‐1232620 and OCE‐1736542. N. Glock acknowledges support from the German Research Foundation (DFG) grants GL 999/3‐1 und SFB754. Meteor Discovery
Publisher Copyright:
© 2021. The Authors.
PY - 2021/11
Y1 - 2021/11
N2 - Planktic and benthic foraminiferal iodine (I) to calcium (Ca) molar ratios have been proposed as an exciting new proxy to assess subsurface and bottom water oxygenation in the past. Compared to trace metals, the analysis of iodine in foraminiferal calcite is more challenging, as iodine is volatile in acid solution. Here, we compare previous analyses that use tertiary amine with alternative analyses using tetramethylammonium hydroxide (TMAH) and ammonium hydroxide (NH4OH) to stabilize iodine in solution. In addition, we assess the effect of sample size and cleaning on planktic and benthic foraminiferal I/Ca. Our stabilization experiments with TMAH and NH4OH show similar trends as those using tertiary amine, giving relatively low I/Ca ratios for planktic and benthic foraminifera samples from poorly oxygenated waters, and high ratios for well-oxygenated waters. This suggests that both alternative methods are suitable to stabilize iodine initially dissolved in acid. Samples that contain 5–10 specimens show a wide spread in I/Ca. Samples containing 20 specimens or more show more centered I/Ca values, indicating that a larger sample size is more representative of the average planktic foraminifera community. The impact of cleaning on planktic and benthic foraminifera I/Ca ratios is very similar to Mg/Ca, with the largest effect occurring during the clay removal step. The largest iodine contaminations were recorded at locations characterized by moderate to high organic carbon contents. In those circumstances, we recommend doubling the oxidative cleaning steps (4 instead of 2 repetitions) to ensure that all organic material is removed.
AB - Planktic and benthic foraminiferal iodine (I) to calcium (Ca) molar ratios have been proposed as an exciting new proxy to assess subsurface and bottom water oxygenation in the past. Compared to trace metals, the analysis of iodine in foraminiferal calcite is more challenging, as iodine is volatile in acid solution. Here, we compare previous analyses that use tertiary amine with alternative analyses using tetramethylammonium hydroxide (TMAH) and ammonium hydroxide (NH4OH) to stabilize iodine in solution. In addition, we assess the effect of sample size and cleaning on planktic and benthic foraminiferal I/Ca. Our stabilization experiments with TMAH and NH4OH show similar trends as those using tertiary amine, giving relatively low I/Ca ratios for planktic and benthic foraminifera samples from poorly oxygenated waters, and high ratios for well-oxygenated waters. This suggests that both alternative methods are suitable to stabilize iodine initially dissolved in acid. Samples that contain 5–10 specimens show a wide spread in I/Ca. Samples containing 20 specimens or more show more centered I/Ca values, indicating that a larger sample size is more representative of the average planktic foraminifera community. The impact of cleaning on planktic and benthic foraminifera I/Ca ratios is very similar to Mg/Ca, with the largest effect occurring during the clay removal step. The largest iodine contaminations were recorded at locations characterized by moderate to high organic carbon contents. In those circumstances, we recommend doubling the oxidative cleaning steps (4 instead of 2 repetitions) to ensure that all organic material is removed.
KW - benthic and planktic foraminifera I/Ca
KW - cleaning method
KW - iodine stabilization
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U2 - 10.1029/2021GC009811
DO - 10.1029/2021GC009811
M3 - Article
AN - SCOPUS:85119837085
SN - 1525-2027
VL - 22
JO - Geochemistry, Geophysics, Geosystems
JF - Geochemistry, Geophysics, Geosystems
IS - 11
M1 - e2021GC009811
ER -