Trace element proxies for surface ocean conditions: A synthesis of culture calibrations with planktic foraminifera

Allen, Katherine A.; Hönisch, Bärbel; Eggins, Stephen; Haynes, L.; Rosenthal, Yair; Yu, Jimin

doi:10.1016/j.gca.2016.08.015

Cited by 129 publications

(330 citation statements)

References 107 publications

(201 reference statements)

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“…The highest growth rates are observed in foraminifers from the PR culture season (8.1–11.5 μg d −1 ), as well as at high pH (9.0 ± 1.5 μg d −1 ). These rates are similar to those found by Allen et al [] in O. universa (6.0 μg d −1 on average). However, growth rate only reached 7.5 μg d −1 in that study at high pH, where [CO 3 2− ] = 300 μmol kg −1 , compared to values of up to 9.0 μg d −1 in our high pH experiments where [CO 3 2− ] was lower (240 μmol kg −1 ).…”

Section: Resultssupporting

confidence: 91%

“…However, because Ω calcite also significantly covaries with [B(OH) 4 − ]/DIC and [B(OH) 4 − ]/[HCO 3 − ], we thus cannot rule out a [B(OH) 4 − ]/DIC or a [B(OH) 4 − ]/[HCO 3 − ] control on B/Ca in their data set. Curiously, the results of Salmon et al [], who used test area density as a proxy for shell thickness (in μg/μm 2 calcite) and thus growth rate, directly conflict with the culture results of Allen et al [], who estimated average growth rates in μg d −1 . Salmon et al [] found that test area density was higher in G. ruber compared to O. universa , while Allen et al [] found the opposite trend.…”

Section: Discussionmentioning

confidence: 97%

“…In addition, the slopes of the B/Ca response to DIC between both O. universa (this study) and T. sacculifer [ Allen et al , ] are nearly indistinguishable (Figure b). This may further suggest that the response to DIC is more inorganically driven by the competition of B(OH) 4 − and DIC ions, as average shell growth rate has been found to be greater in cultured O. universa compared to T. sacculifer [ Allen et al , ] and would likely impose a species‐dependent effect if it was a major determinant of B/Ca.…”

Section: Discussionmentioning

confidence: 99%

“…Allen et al [] suggest that area‐normalized foraminiferal growth rates appear to fall below the range where B/Ca in inorganic calcites is strongly affected by rate [ Uchikawa et al , ]. We also plot our area‐normalized growth rate estimates (Table S2) versus Uchikawa et al 's [] proposed controlling parameter, K D = [B/Ca]/[[B] T /DIC].…”

Section: Discussionmentioning

confidence: 99%

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Calibration of the B/Ca proxy in the planktic foraminifer Orbulina universa to Paleocene seawater conditions

et al. 2017

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The B/Ca ratio of planktic foraminiferal calcite, a proxy for the surface ocean carbonate system, displays large negative excursions during the Paleocene‐Eocene Thermal Maximum (PETM, 55.9 Ma), consistent with rapid ocean acidification at that time. However, the B/Ca excursion measured at the PETM exceeds a magnitude that modern pH calibrations can explain. Numerous other controls on the proxy have been suggested, including foraminiferal growth rate and the total concentration of dissolved inorganic carbon (DIC). Here we present new calibrations for B/Ca versus the combined effects of pH and DIC in the symbiont‐bearing planktic foraminifer Orbulina universa, grown in culture solutions with simulated Paleocene seawater elemental composition (high [Ca], low [Mg], and low total boron concentration ([B]T). We also investigate the isolated effects of low seawater [B]T, high [Ca], reduced symbiont photosynthetic activity, and average shell growth rate on O. universa B/Ca in order to further understand the proxy systematics and to determine other possible influences on the PETM records. We find that average shell growth rate does not appear to determine B/Ca in high calcite saturation experiments. In addition, our “Paleocene” calibration shows higher sensitivity than the modern calibration at low [B(OH)4−]/DIC. Given a large DIC pulse at the PETM, this amplification of the B/Ca response can more fully explain the PETM B/Ca excursion. However, further calibrations with other foraminifer species are needed to determine the range of foraminifer species‐specific proxy sensitivities under these conditions for quantitative reconstruction of large carbon cycle perturbations.

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Section: Resultssupporting

confidence: 91%

Section: Discussionmentioning

confidence: 97%

Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

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Calibration of the B/Ca proxy in the planktic foraminifer Orbulina universa to Paleocene seawater conditions

et al. 2017

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“…The Mg/Ca‐temperature relationship is typically calibrated using foraminifera preserved in recent core‐top sediments (Dekens et al, ; Elderfield & Ganssen, ), collected in sediment traps or plankton tows (Anand et al, ; Martínez‐Botí et al, ; McConnell & Thunell, ), or reared in culture experiments (Allen et al, ; Kısakürek et al, ; Lea et al, ). Most calibrations consider Mg/Ca to be a univariate exponential function of temperature, but it has long been suggested that additional variables may also have an appreciable effect on Mg/Ca.…”

Section: Introductionmentioning

confidence: 99%

Calibration and Validation of Environmental Controls on Planktic Foraminifera Mg/Ca Using Global Core‐Top Data

Saenger

Evans

2019

Paleoceanog and Paleoclimatol

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The Mg/Ca of planktic foraminifera is commonly assumed to be a univariate function of ocean temperature, but recent work suggests that nonthermal variables may have a secondary effect, thereby complicating an inverse approach for paleotemperature reconstructions. However, the significance of secondary variables has not been independently validated, and their inclusion may reflect statistical overfitting. Here we evaluate the significance of seven predictive variables on a global compilation (n = 1,124) of core‐top planktic foraminifera Mg/Ca spanning five species. An additive approach was used to construct models that included only variables with significant validation skill. Optimal models support the use of Mg/Ca as a paleothermometer but also find evidence for nonthermal variables: (a) Mg/Ca (N. pachy+incompta) = 0.186 ± 0.001 · exp(0.095 ± 0.002 · T) + 2.95E‐3 ± 5.4E‐6 · size; (b) Mg/Ca (G. ruber) = 0.685 ± 0.005 · exp(0.058 ± 0.001 · T) + 0.928 ± 0.02 · Omega(deep); (c); Mg/Ca (G. inflata) = 1.737 ± 0.007 · exp(0.065 ± 0.001 · T) · Omega(shallow)^‐0.734 ± 0.003; and (d) Mg/Ca (G. bulloides) = 0.623 ± 0.007 · exp(0.079 ± 0.001 · T) + 0.548 ± 0.007 · Omega(deep). Results highlight the importance of independent validation and suggest that Ω and size dependences may complicate univariate inversions for paleotemperature in some species. This is particularly true over timescales when secondary terms cannot be considered constant. Forward modeling is an attractive alternative, and improved Mg/Ca models may reduce bias in paleoceanographic data assimilation efforts. Salinity is absent from all relationships, suggesting that it may have a smaller influence than previously thought or may not vary sufficiently to be resolved at core‐top sites. The stepwise approach illustrated in this study is widely applicable, and validation exercises should be applied to the calibration of other paleoceanographic proxies.

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Salinity controls on Na incorporation in Red Sea planktonic foraminifera

et al. 2016

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Whereas several well‐established proxies are available for reconstructing past temperatures, salinity remains challenging to assess. Reconstructions based on the combination of (in)organic temperature proxies and foraminiferal stable oxygen isotopes result in relatively large uncertainties, which may be reduced by application of a direct salinity proxy. Cultured benthic and planktonic foraminifera showed that Na incorporation in foraminiferal shell calcite provides a potential independent proxy for salinity. Here we present the first field calibration of such a potential proxy. Living planktonic foraminiferal specimens from the Red Sea surface waters were collected and analyzed for their Na/Ca content using laser ablation quadrupole inductively coupled plasma mass spectrometry. Using the Red Sea as a natural laboratory, the calibration covers a broad range of salinities over a steep gradient within the same water mass. For both Globigerinoides ruber and Globigerinoides sacculifer calcite Na/Ca increases with salinity, albeit with a relatively large intraspecimen and interspecimen variability. The field‐based calibration is similar for both species from a salinity of ~36.8 up to ~39.6, while values for G. sacculifer deviate from this trend in the northernmost transect. It is hypothesized that the foraminifera in the northernmost part of the Red Sea are (partly) expatriated and hence should be excluded from the Na/Ca‐salinity calibration. Incorporation of Na in foraminiferal calcite therefore provides a potential proxy for salinity, although species‐specific calibrations are still required and more research on the effect of temperature is needed.

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Trace element proxies for surface ocean conditions: A synthesis of culture calibrations with planktic foraminifera

Cited by 129 publications

References 107 publications

Calibration of the B/Ca proxy in the planktic foraminifer Orbulina universa to Paleocene seawater conditions

Calibration of the B/Ca proxy in the planktic foraminifer Orbulina universa to Paleocene seawater conditions

Calibration and Validation of Environmental Controls on Planktic Foraminifera Mg/Ca Using Global Core‐Top Data

Salinity controls on Na incorporation in Red Sea planktonic foraminifera

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