Systematic change of foraminiferal Mg/Ca ratios across a strong salinity gradient
The Mg/Ca ratio of foraminiferal calcite is an important proxy for estimating past ocean temperatures. Used in conjunction with δ18O of foraminiferal calcite it allows deconvolution of temperature and ice-volume signals to infer past ocean temperatures and salinities (assuming the relationship betwe...
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ftcdlib:oai:escholarship.org/ark:/13030/qt8w1481s1 2023-05-15T18:01:05+02:00 Systematic change of foraminiferal Mg/Ca ratios across a strong salinity gradient Ferguson, JE Henderson, GM Kucera, M Rickaby, REM 153 - 166 2008-01-15 application/pdf https://escholarship.org/uc/item/8w1481s1 unknown eScholarship, University of California qt8w1481s1 https://escholarship.org/uc/item/8w1481s1 CC-BY CC-BY Earth and Planetary Science Letters, vol 265, iss 1-2 Geochemistry & Geophysics Physical Sciences Earth Sciences article 2008 ftcdlib 2021-06-28T17:06:59Z The Mg/Ca ratio of foraminiferal calcite is an important proxy for estimating past ocean temperatures. Used in conjunction with δ18O of foraminiferal calcite it allows deconvolution of temperature and ice-volume signals to infer past ocean temperatures and salinities (assuming the relationship between seawater δ18O and salinity is known). Such work assumes that temperature is the only, or at least the dominant, environmental controller of foraminiferal Mg/Ca. The semi-enclosed Mediterranean Sea, where salinity varies from 36 to 40psu over a seasonal temperature range of between only 5°C to 8°C, provides a relevant setting to test this assumption outside the laboratory. In this study, planktonic foraminifera (O. universa, G. siphonifera, G. bulloides and G. ruber (white) and (pink)) were picked from 11 box core tops spanning the Mediterranean salinity gradient and analysed for their trace-element concentrations. Mg/Ca ratios are higher, for the associated calcification temperatures, than in other regions where calibrations have been conducted and correlate poorly with calcification temperature. Mg/Ca ratios are particularly high for samples from the Eastern Mediterranean where salinity is unusually high. Correlations of Mg/Ca with the calcification salinity are statistically significant with Mg/Ca changing by 15-59% per psu, suggesting that salinity may act as a control on Mg/Ca ratios in addition to the dominant temperature control. We show that contamination by non-carbonate material and diagenetic high-Mg carbonate overgrowths cannot account for the observed trend of increasing Mg/Ca with salinity. A relationship between Mg/Ca and salinity is also suggested by re-analysis of calibrations from open-ocean settings. These new Mediterranean results are from a region with unusually high salinity but suggest that the effects of salinity on the Mg/Ca palaeothermometer should be considered even in open-ocean settings, particularly where large salinity changes occurred in the past. © 2007 Elsevier B.V. All rights reserved. Article in Journal/Newspaper Planktonic foraminifera University of California: eScholarship |
institution |
Open Polar |
collection |
University of California: eScholarship |
op_collection_id |
ftcdlib |
language |
unknown |
topic |
Geochemistry & Geophysics Physical Sciences Earth Sciences |
spellingShingle |
Geochemistry & Geophysics Physical Sciences Earth Sciences Ferguson, JE Henderson, GM Kucera, M Rickaby, REM Systematic change of foraminiferal Mg/Ca ratios across a strong salinity gradient |
topic_facet |
Geochemistry & Geophysics Physical Sciences Earth Sciences |
description |
The Mg/Ca ratio of foraminiferal calcite is an important proxy for estimating past ocean temperatures. Used in conjunction with δ18O of foraminiferal calcite it allows deconvolution of temperature and ice-volume signals to infer past ocean temperatures and salinities (assuming the relationship between seawater δ18O and salinity is known). Such work assumes that temperature is the only, or at least the dominant, environmental controller of foraminiferal Mg/Ca. The semi-enclosed Mediterranean Sea, where salinity varies from 36 to 40psu over a seasonal temperature range of between only 5°C to 8°C, provides a relevant setting to test this assumption outside the laboratory. In this study, planktonic foraminifera (O. universa, G. siphonifera, G. bulloides and G. ruber (white) and (pink)) were picked from 11 box core tops spanning the Mediterranean salinity gradient and analysed for their trace-element concentrations. Mg/Ca ratios are higher, for the associated calcification temperatures, than in other regions where calibrations have been conducted and correlate poorly with calcification temperature. Mg/Ca ratios are particularly high for samples from the Eastern Mediterranean where salinity is unusually high. Correlations of Mg/Ca with the calcification salinity are statistically significant with Mg/Ca changing by 15-59% per psu, suggesting that salinity may act as a control on Mg/Ca ratios in addition to the dominant temperature control. We show that contamination by non-carbonate material and diagenetic high-Mg carbonate overgrowths cannot account for the observed trend of increasing Mg/Ca with salinity. A relationship between Mg/Ca and salinity is also suggested by re-analysis of calibrations from open-ocean settings. These new Mediterranean results are from a region with unusually high salinity but suggest that the effects of salinity on the Mg/Ca palaeothermometer should be considered even in open-ocean settings, particularly where large salinity changes occurred in the past. © 2007 Elsevier B.V. All rights reserved. |
format |
Article in Journal/Newspaper |
author |
Ferguson, JE Henderson, GM Kucera, M Rickaby, REM |
author_facet |
Ferguson, JE Henderson, GM Kucera, M Rickaby, REM |
author_sort |
Ferguson, JE |
title |
Systematic change of foraminiferal Mg/Ca ratios across a strong salinity gradient |
title_short |
Systematic change of foraminiferal Mg/Ca ratios across a strong salinity gradient |
title_full |
Systematic change of foraminiferal Mg/Ca ratios across a strong salinity gradient |
title_fullStr |
Systematic change of foraminiferal Mg/Ca ratios across a strong salinity gradient |
title_full_unstemmed |
Systematic change of foraminiferal Mg/Ca ratios across a strong salinity gradient |
title_sort |
systematic change of foraminiferal mg/ca ratios across a strong salinity gradient |
publisher |
eScholarship, University of California |
publishDate |
2008 |
url |
https://escholarship.org/uc/item/8w1481s1 |
op_coverage |
153 - 166 |
genre |
Planktonic foraminifera |
genre_facet |
Planktonic foraminifera |
op_source |
Earth and Planetary Science Letters, vol 265, iss 1-2 |
op_relation |
qt8w1481s1 https://escholarship.org/uc/item/8w1481s1 |
op_rights |
CC-BY |
op_rightsnorm |
CC-BY |
_version_ |
1766170431267536896 |