Experimental evidence for foraminiferal calcification under anoxia

Abstract

Abstract. Benthic foraminiferal tests are widely used for paleoceanographic reconstructions from a range of different environments with varying dissolved oxygen concentrations in the bottom water. There is ample evidence that foraminifera can live in anoxic sediments. For some species, this is explained by a switch to facultative anaerobic metabolism (i.e. denitrification). Here we show for the first time that adult specimens of three benthic foraminiferal species are not only able to survive, but are also able to calcify under anoxic conditions, at various depths in the sediment, and with or without nitrates. In fact, several specimens of Ammonia tepida (1–4%), Bulimina marginata (8–24%) and Cassidulina laevigata (16–23%) were able to calcify at different redox fronts of sediment cores, under laboratory conditions. This demonstrates ongoing metabolic processes, even in micro-environments where denitrification is not possible. Earlier observations suggest that the disappearance of foraminiferal communities after prolonged anoxia is not due to instantaneous or strongly increased adult mortality. Here we show that it cannot be explained by an inhibition of growth through chamber addition either. Our observations of ongoing calcification under anoxic conditions mean that geochemical proxy data obtained from benthic foraminifera in settings experiencing intermittent anoxia have to be reconsidered. The analysis of whole single specimens or of their successive chambers may provide essential information about short-term environmental variability and/or the causes of anoxia.

Mn∕Ca intra- and inter-test variability in the benthic foraminifer <i>Ammonia tepida</i>

“…In Lake Grevelingen, A. tepida is almost exclusively represented by the T6 genotype. Ammonia tepida is abundant in coastal areas of temperate climate zones, tolerating diverse biological and environmental stress factors, including low-oxygen conditions (Moodley and Hess, 1992;Sen Gupta et al, 1996;Geslin et al, 2014;Nardelli et al, 2014;Thibault de Chanvalon et al, 2015;Cesbron et al, 2016). The salty bottom waters of Lake Grevelingen, an artificial lake created after the closure of a branch of the Rhine-Meuse-Scheldt estuary, are characterized by seasonal hypoxia ([O 2 ] < 63 µM) and anoxia ([O 2 ] < detection limit of 1 µM) (Hagens et al, 2015;Seitaj et al, 2017).…”

Technical Note: Towards resolving in situ, centimeter-scale location and timing of biomineralization in calcareous meiobenthos – the calcein–osmotic pump method

“…For foraminiferal calcite labeling, a calcein concentration of 10 mg L −1 has been typically used previously Denoyelle et al, 2012;Nardelli et al, 2014;Filipsson et al, 2010) although concentrations as low as 5 mg L −1 reportedly also labeled foraminiferal calcite (Dissard et al, 2009;Kurtarkar et al, 2015). The maximum possible calcein concentration in overlying waters of our foraminiferal incubations was less than 1 mg L −1 .…”

“…The foraminiferal species known to autofluoresce lacks a carbonate test, so it cannot be confused with our calcein-labeling approach. If there are calcareous foraminifera with similarly autofluorescent cytoplasm, distinguishing between cytoplasmic fluorescence (from viability indicators reliant on similar excitation and emission wavelengths) and carbonate fluorescence is not difficult if one considers the patterns and shapes of the signal (Nardelli et al, 2014).…”

“…was used to reconstruct bottom-water oxygen concentration (Hoogakker et al, 2015), an approach that could be further improved by this method. Foraminiferal-based ecology studies under shifting environmental conditions, such as varying water oxygen concentration (Nardelli et al, 2014) or pH conditions would also benefit from our calcein-osmotic pump method. Of course, our method should be considered a first step given that most paleoceanographically relevant foraminifera presumably are able to migrate within the sediment column.…”

“…The method employs commercially available osmotic pumps to deliver calcein, which is a fluorescent compound that binds to calcium in biomineralized structures as it is precipitated (e.g., Medeiros-Bergen and Ebert, 1995;Monaghan, 1993;Moran, 2000;Collin and Voltzow, 1998;Hernaman et al, 2000). Using full immersion incubations, calcein has been used to mark bivalves (e.g., Kaehler and McQuaid, 1999;Moran and Marko, 2005;van der Geest et al, 2011) and in laboratory studies regarding foraminiferal calcification Denoyelle et al, 2012;Dissard et al, 2009;Filipsson et al, 2010;Kurtarkar et al, 2015;Nardelli et al, 2014). In this contribution, we describe a novel point-source calcein dispensation method and show proof of concept for quahog (hard clam) bivalves and benthic foraminifera.…”