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Abstract: Foraminifera are unicellular organisms that inhabit the oceans. They play an important role in the global carbon cycle and record valuable paleoclimate information through the uptake of trace elements such as strontium into their calcitic shells. Understanding how foraminifera control their internal fluid composition to make calcite is important for predicting their response to ocean acidification and for reliably interpreting the chemical and isotopic compositions of their shells. Here, we model foraminiferal calcification and strontium partitioning in the benthic foraminifera Cibicides wuellerstorfi and Cibicidoides mundulus based on insights from inorganic calcite experiments. The numerical model reconciles inter-ocean and taxonomic differences in benthic foraminifer strontium partitioning relationships and enables us to reconstruct the composition of the calcifying fluid. We find that strontium partitioning and mineral growth rates of foraminiferal calcite are not strongly affected by changes in external seawater pH (within 7.8–8.1) and dissolved inorganic carbon (DIC, within 2100–2300 μmol/kg) due to a regulated calcite saturation state at the site of shell formation.

The authors regret that in the original article, the kinetic fractionation factors (KFFs) related to the CO2 hydroxylation reaction (CO2(aq) + OH– → HCO3–) were calculated using atmospheric δ18OCO2 values of 0.0 ± 0.5 ‰ (VPDB) while the correct values are 10.25 ± 0.5 ‰ (VPDB). We erroneously employed the atmospheric δ18OCO2 values from the NOAA CO2 global network (Trolier et al., 1996) by not converting atmospheric δ18OCO2 from the VPDB-CO2 scale to the VPDB scale through the following expression (e.g. Srivastava and Verkouteren, 2018): [Formula presented] This correction affects the reported oxygen isotope KFFs for CO2 hydroxylation to form HCO3– prior to CaCO3 precipitation. We have corrected Table 7 and Fig. 13 accordingly (see below). The composition of atmospheric CO2 was also incorrectly plotted on the VPDB scale in Figs. 1, 8 and 15 of our original manuscript based on previous works (Fig. 8 in Clark and Fontes, 1990; Fig. 2 in Clark et al., 1992). Importantly, the modelling outputs and main conclusions of the original article are not affected by these corrections. Nevertheless, the updated KFFs resolve an apparent discrepancy between the laboratory and field studies in our original article. Moreover, the oxygen isotope KFF for CO2 hydroxylation now displays a positive temperature dependence over the 4–28 °C range, which was not statistically significant in the original article (Fig. 13c, r2 = 0.86, n = 10, p-value

The Cedars ultramafic block hosts alkaline springs (pH > 11) in which calcium carbonate forms upon uptake of atmospheric CO2 and at times via mixing with surface water. These processes lead to distinct carbonate morphologies with “floes” forming at the atmosphere-water interface, “snow” of fine particles accumulating at the bottom of pools and terraced constructions of travertine. Floe material is mainly composed of aragonite needles despite CaCO3 precipitation occurring in waters with low Mg/Ca (

Kinetic calcium isotope effects can be used as growth-rate proxies for volcanic and subvolcanic minerals. Here, we analyze Ca isotopic compositions in experimental and natural samples and confirm that large kinetic effects (>2‰) can occur during magmatic plagioclase crystallization. Experiments confirm theoretical predictions that disequilibrium isotope effects depend mainly on the rates for crystal growth relative to liquid phase Ca diffusivity (R/D). Plagioclase phenocrysts from the 1915 Mount Lassen rhyodacite eruption, the ∼650-y-old Deadman Creek Dome eruption, and several mafic subvolcanic orbicules and plagioclase comb layers from Northern California have disequilibrium Ca isotopic compositions that suggest rapid crystal growth rates (>1 cm/y to 15 cm/y). The Ca isotope results, combined with complementary crystal-size distribution analyses, suggest that magmatic rejuvenation (and eruption) events, as reflected in crystal growth times, can be as short as ∼10-3 y. Although mafic systems are predicted to have shorter magmatic rejuvenation periods, we find similarly short timescales in both mafic and silicic systems. These results are consistent with a growing body of evidence suggesting that dominantly crystalline volcanic magma reservoirs can be rapidly reactivated by the injection of fresh magma prior to eruption. By focusing on a common mineral such as plagioclase, this approach can be applied across all major magmatic compositions, suggesting that Ca isotopes can be used as a tool for investigating the dynamics and timing of volcanic eruptions.

Size spectra analysis (SSA) is used to detect changes in food webs by simplifying complex community structures through abundance-versus-biomass considerations. We applied SSA to 10 years (2006-2015) of data on Great Lakes organisms ranging in size from picoplankton to macrozooplankton. Summer pelagic size spectra slopes were near the theoretical value of -1.0, but spring slopes were steeper, reflecting seasonal differences in abundance of small and large individuals. Pelagic size spectra slopes were relatively stable over the time period we examined. Height (the predicted number of organisms at the spectra midpoint) varied among lakes and was slightly higher in summer than spring in more productive basins. Including benthic data led to shallower slopes when combined with pelagic data, suggesting benthic organisms may increase food web efficiency; height was less affected by benthic data. Benthic data are not routinely included in SSA, but our results suggest they affect slopes and therefore SSA-based predictions of fish abundance. The ability of SSA to track changes in trophic energy transfer makes it a valuable ecosystem monitoring tool. L'analyse des spectres de taille (AST) est utilisee pour detecter des changements dans les reseaux trophiques en simplifiant la structure de communautes complexes sur la base de considerations concernant l'abondance et la biomasse. Nous avons applique l'AST a 10 annees (2006-2015) de donnees sur des organismes des Grands Lacs de tailles allant du picoplancton au macrozooplancton. Les pentes des spectres de taille pelagiques estivaux s'approchent de la valeur theorique de -1,0, mais les pentes des spectres printaniers sont plus fortes, refletant des variations saisonnieres de l'abondance des petits et grands individus. Les pentes des spectres de taille pelagiques sont relativement stables durant la periode etudiee. La hauteur (le nombre predit d'organismes au point median du spectre) varie d'un lac a l'autre et est legerement plus grande en ete qu'au printemps dans les bassins plus productifs. L'inclusion de donnees benthiques produit des pentes plus faibles quand elles sont combinees aux donnees pelagiques, ce qui donne a penser que les organismes benthiques pourraient accroitre l'efficacite du reseau trophique; l'incidence des donnees benthiques sur la hauteur est moins importante. Des donnees benthiques ne sont pas systematiquement incluses dans les AST, mais nos resultats indiqueraient qu'elles ont une incidence sur les pentes et donc sur les predictions de l'abondance des poissons issues de l'AST. La capacite de l'AST de faire ressortir les variations des transferts energetiques trophiques en fait un bon outil de surveillance des ecosystemes. [Traduit par la Redaction], Introduction Understanding and predicting ecosystem productivity requires knowledge about the current state of the ecosystem and how it influences production of different organisms. However, ecosystem modeling is challenging because food [...]