Biomineralization in perforate foraminifera

In this paper, we review the current understanding of biomineralization in perforate foraminifera. Ideas on the mechanisms responsible for the flux of Ca2 + and inorganic carbon from seawater into the test were originally based on light and electron microscopic observations of calcifying foraminifera. From the 1980s onward, tracer experiments, fluorescent microscopy and high-resolution test geochemical analysis have added to existing calcification models. Despite recent insights, no general consensus on the physiological basis of foraminiferal biomineralization exists. Current models include seawater vacuolization, transmembrane ion transport, involvement of organic matrices and/or pH regulation, although the magnitude of these controls remain to be quantified. Disagreement between currently available models may be caused by the use of different foraminiferal species as subject for biomineralization experiments and/or lack of a more systematic approach to study (dis)similarities between taxa. In order to understand foraminiferal controls on element incorporation and isotope fractionation, and thereby improve the value of foraminifera as paleoceanographic proxies, it is necessary to identify key processes in foraminiferal biomineralization and formulate hypotheses regarding the involved physiological pathways to provide directions for future research

Impact of salinity on element incorporation in two benthic foraminiferal species with contrasting magnesium contents

Accurate reconstructions of seawater salinity could provide valuable constraints for studying past ocean circulation, the hydrological cycle and sea level change. Controlled growth experiments and field studies have shown the potential of foraminiferal Na ∕ Ca as a direct salinity proxy. Incorporation of minor and trace elements in foraminiferal shell carbonate varies, however, greatly between species and hence extrapolating calibrations to other species needs validation by additional (culturing) studies. Salinity is also known to impact other foraminiferal carbonate-based proxies, such as Mg ∕ Ca for temperature and Sr ∕ Ca for sea water carbonate chemistry. Better constraints on the role of salinity on these proxies will therefore improve their reliability. Using a controlled growth experiment spanning a salinity range of 20 units and analysis of element composition on single chambers using laser ablation-Q-ICP-MS, we show here that Na ∕ Ca correlates positively with salinity in two benthic foraminiferal species (<i>Ammonia tepida</i> and <i>Amphistegina lessonii</i>). The Na ∕ Ca values differ between the two species, with an approximately 2-fold higher Na ∕ Ca in <i>A. lessonii</i> than in <i>A. tepida</i>, coinciding with an offset in their Mg content ( ∼  35 mmol molM<super>−2</super> versus  ∼  2.5 mmol mol−<super>1</super> for <i>A. lessonii</i> and <i>A. tepida</i>, respectively). Despite the offset in average Na ∕ Ca values, the slopes of the Na ∕ Ca–salinity regressions are similar between these two species (0.077 versus 0.064 mmol mol<super>−1</super> change per salinity unit). In addition, Mg ∕ Ca and Sr ∕ Ca are positively correlated with salinity in cultured <i>A. tepida</i> but show no correlation with salinity for <i>A. lessonii</i>. Electron microprobe mapping of incorporated Na and Mg of the cultured specimens shows that within chamber walls of <i>A. lessonii</i>, Na ∕ Ca and Mg ∕ Ca occur in elevated bands in close proximity to the primary organic lining. Between species, Mg banding is relatively similar, even though Mg content is 10 times lower and that variation within the chamber wall is much less pronounced in <i>A. tepida</i>. In addition, Na banding is much less prominent in this species than it is in <i>A. lessonii</i>. Inter-species differences in element banding reported here are hypothesized to be caused by differences in biomineralization controls responsible for element uptake

Anti-cyclonic eddy imprint on calcite geochemistry of several planktonic foraminiferal species in the Mozambique Channel

Hydrographic conditions in the Mozambique Channel are dominated by the passing of large anticyclonic eddies, propagating poleward into the upstream Agulhas area. Further south, these eddies have been found to control the shedding of Agulhas rings into the Atlantic ocean, thereby playing a key role in Indo-Atlantic Ocean exchange. The element composition of several planktonic foraminifera species collected from sediment trap samples, was compared to in situ water column data from the Mozambique Channel. Single-chamber trace element composition of these foraminifera reveals a close coupling with hydrographic changes induced by anticyclonic eddies. Obtained Mg/Ca values for the surface dwelling Globigerinoides ruber as well as the thermocline dwelling Neogloboquadrina dutertrei follow temperature changes and reduced temperature stratification during eddy conditions. At greater depth, Globorotalia scitula and Pulleniatina obliquiloculata record stable temperatures and thus respond to hydrographic changes with a deepening in habitat depth. Furthermore, test Mn/Ca values indicate a close relationship between water column oxygenation and Mn incorporation in these planktonic foraminiferal specie

Effect of different seawater Mg²⁺ concentrations on calcification in two benthic foraminifers

Magnesium, incorporated in foraminiferal calcite (Mg/CaCC), is used intensively to reconstruct past seawater temperatures but, in addition to temperature, the Mg/CaCC of foraminiferal tests also depends on the ratio of Mg and Ca in seawater (Mg/CaSW). The physiological mechanisms responsible for these proxy relationships are still unknown. This culture study investigates the impact of different seawater [Mg2 +] on calcification in two benthic foraminiferal species precipitating contrasting Mg/CaCC: Ammonia aomoriensis, producing low-Mg calcite and Amphistegina lessonii, producing intermediate-Mg calcite. Foraminiferal growth and test thickness were determined and, Mg/Ca was analyzed using Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry (LA-ICP-MS). Results show that at present-day seawater Mg/CaSW of ~ 5, both species have highest growth rates, reflecting their adaptation to modern seawater element concentrations. Test thickness is not significantly affected by different Mg/CaSW. The relationship between Mg/CaSW and Mg/CaCC shows a distinct positive y-axis intercept, possibly reflecting at least two processes involved in foraminiferal biomineralization. The associated Mg partition (DMg) changes non-linearly with increasing Mg/CaSW, hence suggesting that the DMg is best described by an exponential function approaching an asymptot

Benthic foraminiferal Mn / Ca ratios reflect microhabitat preferences

The Mn / Ca of calcium carbonate tests of living (rose-Bengal-stained) benthic foraminifera (Elphidium batialis, Uvigerina spp., Bolivina spissa, Nonionellina labradorica and Chilostomellina fimbriata) were determined in relation to pore water manganese (Mn) concentrations for the first time along a bottom water oxygen gradient across the continental slope along the NE Japan margin (western Pacific). The local bottom water oxygen (BWO) gradient differs from previous field study sites focusing on foraminiferal Mn / Ca and redox chemistry, therefore allowing further resolution of previously observed trends. The Mn / Ca ratios were analysed using laser ablation inductively coupled plasma-mass spectrometer (ICP-MS), allowing single-chamber determination of Mn / Ca. The incorporation of Mn into the carbonate tests reflects environmental conditions and is not influenced by ontogeny. The inter-species variability in Mn / Ca reflected foraminiferal in-sediment habitat preferences and associated pore water chemistry but also showed large interspecific differences in Mn partitioning. At each station, Mn / Ca ratios were always lower in the shallow infaunal E. batialis, occupying relatively oxygenated sediments, compared to intermediate infaunal species, Uvigerina spp. and B. spissa, which were typically found at greater depth, under more reducing conditions. The highest Mn / Ca was always recorded by the deep infaunal species N. labradorica and C. fimbriata. Our results suggest that although partitioning differs, Mn / Ca ratios in the intermediate infaunal taxa are promising tools for palaeoceanographic reconstructions as their microhabitat exposes them to higher variability in pore water Mn, thereby making them relatively sensitive recorders of redox conditions and/or bottom water oxygenation.Peer reviewe

Shallow water benthic foraminifera as proxy for natural versus human-induced environmental change

Ecosystem composition and functioning is not only subjected to human-induced alterations, ecosystems also subjected to natural (e.g. climate-induced) variability. To quantify human impacts on ecosystems, these natural fluctuations must be accounted for. Since long-term biological monitoring programs are rare and usually do not include the pre-human state, we must rely on traces of past ecosystems found in the geologic record. Foraminifera (Protista) are close relatives of the amoeba, that live predominantly in the sea and have a unique feature that makes them popular proxies: many build a shell (a so-called test) of calciumcarbonate during their life. Since they are abundant in most marine environments and their tests are often preserved in sediments, they are widely used in paleoceanography and paleoclimatology. Besides two practical issues that are dealth with in this thesis, most chapters are concerned with developing proxies to reconstruct human influences on near-shore ecosystems by collecting living foraminifera from the North Sea and Dutch Wadden Sea. In the southern North Sea and Wadden Sea foraminiferal distributions did not appear to be limited by total food abundance or in-sediment oxygen concentrations. Additionally, foraminiferal community composition did not seem to be influenced by macrofaunal community composition (dominated by either filter feeders or burrowing species). We hypothesize that distribution of benthic foraminifera in the North Sea is mainly controlled by the type of food available (labile or refractory) and by the level of environmental variability. Different combinations of these two variables are found across habitats beneath tidal mixing fronts and therefore, benthic foraminifera in temperate, shallow seas are particularly suited to reconstruct hydrodynamic regimes. These conclusions were used to reconstruct the history of the western Wadden Sea. In this analysis, the interplay between anthropogenic and natural influences shows that the effects of human alterations had sudden and dramatic consequences for the functioning of this ecosystem

Shallow water benthic foraminifera as proxy for natural versus human-induced environmental change

Ecosystem composition and functioning is not only subjected to human-induced alterations, ecosystems also subjected to natural (e.g. climate-induced) variability. To quantify human impacts on ecosystems, these natural fluctuations must be accounted for. Since long-term biological monitoring programs are rare and usually do not include the pre-human state, we must rely on traces of past ecosystems found in the geologic record. Foraminifera (Protista) are close relatives of the amoeba, that live predominantly in the sea and have a unique feature that makes them popular proxies: many build a shell (a so-called test) of calciumcarbonate during their life. Since they are abundant in most marine environments and their tests are often preserved in sediments, they are widely used in paleoceanography and paleoclimatology. Besides two practical issues that are dealth with in this thesis, most chapters are concerned with developing proxies to reconstruct human influences on near-shore ecosystems by collecting living foraminifera from the North Sea and Dutch Wadden Sea. In the southern North Sea and Wadden Sea foraminiferal distributions did not appear to be limited by total food abundance or in-sediment oxygen concentrations. Additionally, foraminiferal community composition did not seem to be influenced by macrofaunal community composition (dominated by either filter feeders or burrowing species). We hypothesize that distribution of benthic foraminifera in the North Sea is mainly controlled by the type of food available (labile or refractory) and by the level of environmental variability. Different combinations of these two variables are found across habitats beneath tidal mixing fronts and therefore, benthic foraminifera in temperate, shallow seas are particularly suited to reconstruct hydrodynamic regimes. These conclusions were used to reconstruct the history of the western Wadden Sea. In this analysis, the interplay between anthropogenic and natural influences shows that the effects of human alterations had sudden and dramatic consequences for the functioning of this ecosystem

Data presented in the paper "In situ incubation of a coral patch for assessment of carbonate system dynamics"

Data belonging to the article "In situ incubation of a coral patch for assessment of carbonate system dynamics

Data presented in the paper "The impacts of seawater Mg/Ca and temperature on element incorporation in benthic foraminiferal calcite"

Laser ablation-ICP-MS data on single foraminiferal shells that were cultured at a range of seawater Mg/Ca and temperature