Evaluating controls on planktonic foraminiferal geochemistry in the Eastern Tropical North Pacific
To explore relationships between water column hydrography and foraminiferal geochemistry in the Eastern Tropical North Pacific, we present δO18 and Mg/Ca records from three species of planktonic foraminifera, Globigerinoides ruber, Globigerina bulloides, and Globorotalia menardii, collected from a s...
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ftcdlib:oai:escholarship.org/ark:/13030/qt69r3r0pv 2023-05-15T18:01:12+02:00 Evaluating controls on planktonic foraminiferal geochemistry in the Eastern Tropical North Pacific Gibson, KA Thunell, RC Machain-Castillo, ML Fehrenbacher, J Spero, HJ Wejnert, K Nava-Fernández, X Tappa, EJ 2016-10-15 application/pdf https://escholarship.org/uc/item/69r3r0pv unknown eScholarship, University of California qt69r3r0pv https://escholarship.org/uc/item/69r3r0pv public foraminiferal geochemistry Mg/Ca Eastern Tropical North Pacific water column hydrography secondary calcite pH/[CO32-] Geochemistry & Geophysics Physical Sciences Earth Sciences article 2016 ftcdlib 2021-06-28T17:06:36Z To explore relationships between water column hydrography and foraminiferal geochemistry in the Eastern Tropical North Pacific, we present δO18 and Mg/Ca records from three species of planktonic foraminifera, Globigerinoides ruber, Globigerina bulloides, and Globorotalia menardii, collected from a sediment trap mooring maintained in the Gulf of Tehuantepec from 2006–2012. Differences in δO18 between mixed-layer species G. ruber and G. bulloides and thermocline-dweller G. menardii track seasonal changes in upwelling. The records suggest an increase in upwelling during the peak positive phase of El Niño, and an overall reduction in stratification over the six-year period. For all three species, Mg/Ca ratios are higher than what has been reported in previous studies, and show poor correlations to calcification temperature. We suggest that low pH (7.6–8.0) and [CO32−] values (∼70–120 μmol/kg) in the mixed layer contribute to an overall trend of higher Mg/Ca ratios in this region. Laser Ablation Inductively Coupled Mass Spectrometry analyses of G. bulloides with high Mg/Ca ratios (>9 mmol/mol) reveal the presence of a secondary coating of inorganic calcite that has Mg/Ca and Mn/Ca ratios up to an order of magnitude higher than these elemental ratios in the primary calcite, along with elevated Sr/Ca and Ba/Ca ratios. Some of the samples with abnormally high Mg/Ca are found during periods of high primary productivity, suggesting the alteration may be related to changes in carbonate saturation resulting from remineralization of organic matter in oxygen-poor waters in the water column. Although similar shell layering has been observed on fossil foraminifera, this is the first time such alteration has been studied in shells collected from the water column. Our results suggest a role for seawater carbonate chemistry in influencing foraminiferal calcite trace element:calcium ratios prior to deposition on the seafloor, particularly in high-productivity, low-oxygen environments. Article in Journal/Newspaper Planktonic foraminifera University of California: eScholarship Pacific |
institution |
Open Polar |
collection |
University of California: eScholarship |
op_collection_id |
ftcdlib |
language |
unknown |
topic |
foraminiferal geochemistry Mg/Ca Eastern Tropical North Pacific water column hydrography secondary calcite pH/[CO32-] Geochemistry & Geophysics Physical Sciences Earth Sciences |
spellingShingle |
foraminiferal geochemistry Mg/Ca Eastern Tropical North Pacific water column hydrography secondary calcite pH/[CO32-] Geochemistry & Geophysics Physical Sciences Earth Sciences Gibson, KA Thunell, RC Machain-Castillo, ML Fehrenbacher, J Spero, HJ Wejnert, K Nava-Fernández, X Tappa, EJ Evaluating controls on planktonic foraminiferal geochemistry in the Eastern Tropical North Pacific |
topic_facet |
foraminiferal geochemistry Mg/Ca Eastern Tropical North Pacific water column hydrography secondary calcite pH/[CO32-] Geochemistry & Geophysics Physical Sciences Earth Sciences |
description |
To explore relationships between water column hydrography and foraminiferal geochemistry in the Eastern Tropical North Pacific, we present δO18 and Mg/Ca records from three species of planktonic foraminifera, Globigerinoides ruber, Globigerina bulloides, and Globorotalia menardii, collected from a sediment trap mooring maintained in the Gulf of Tehuantepec from 2006–2012. Differences in δO18 between mixed-layer species G. ruber and G. bulloides and thermocline-dweller G. menardii track seasonal changes in upwelling. The records suggest an increase in upwelling during the peak positive phase of El Niño, and an overall reduction in stratification over the six-year period. For all three species, Mg/Ca ratios are higher than what has been reported in previous studies, and show poor correlations to calcification temperature. We suggest that low pH (7.6–8.0) and [CO32−] values (∼70–120 μmol/kg) in the mixed layer contribute to an overall trend of higher Mg/Ca ratios in this region. Laser Ablation Inductively Coupled Mass Spectrometry analyses of G. bulloides with high Mg/Ca ratios (>9 mmol/mol) reveal the presence of a secondary coating of inorganic calcite that has Mg/Ca and Mn/Ca ratios up to an order of magnitude higher than these elemental ratios in the primary calcite, along with elevated Sr/Ca and Ba/Ca ratios. Some of the samples with abnormally high Mg/Ca are found during periods of high primary productivity, suggesting the alteration may be related to changes in carbonate saturation resulting from remineralization of organic matter in oxygen-poor waters in the water column. Although similar shell layering has been observed on fossil foraminifera, this is the first time such alteration has been studied in shells collected from the water column. Our results suggest a role for seawater carbonate chemistry in influencing foraminiferal calcite trace element:calcium ratios prior to deposition on the seafloor, particularly in high-productivity, low-oxygen environments. |
format |
Article in Journal/Newspaper |
author |
Gibson, KA Thunell, RC Machain-Castillo, ML Fehrenbacher, J Spero, HJ Wejnert, K Nava-Fernández, X Tappa, EJ |
author_facet |
Gibson, KA Thunell, RC Machain-Castillo, ML Fehrenbacher, J Spero, HJ Wejnert, K Nava-Fernández, X Tappa, EJ |
author_sort |
Gibson, KA |
title |
Evaluating controls on planktonic foraminiferal geochemistry in the Eastern Tropical North Pacific |
title_short |
Evaluating controls on planktonic foraminiferal geochemistry in the Eastern Tropical North Pacific |
title_full |
Evaluating controls on planktonic foraminiferal geochemistry in the Eastern Tropical North Pacific |
title_fullStr |
Evaluating controls on planktonic foraminiferal geochemistry in the Eastern Tropical North Pacific |
title_full_unstemmed |
Evaluating controls on planktonic foraminiferal geochemistry in the Eastern Tropical North Pacific |
title_sort |
evaluating controls on planktonic foraminiferal geochemistry in the eastern tropical north pacific |
publisher |
eScholarship, University of California |
publishDate |
2016 |
url |
https://escholarship.org/uc/item/69r3r0pv |
geographic |
Pacific |
geographic_facet |
Pacific |
genre |
Planktonic foraminifera |
genre_facet |
Planktonic foraminifera |
op_relation |
qt69r3r0pv https://escholarship.org/uc/item/69r3r0pv |
op_rights |
public |
_version_ |
1766170575574663168 |