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.
Highlights
Oxygen depletion is one of the most severe environmental stressors in marine ecosystems
Many foraminiferal species are known to be able to survive short to long periods of hypoxic or even anoxic conditions (Bernhard, 1993; Bernhard and Alve, 1996; Moodley et al, 1997; Langlet et al, 2013; Geslin et al, 2014), it is still an open question as to whether benthic foraminifera are able to calcify under anoxia
The discovery of a facultative anaerobic metabolism by certain foraminiferal species, and the hypothesis of other possible anaerobic pathways suggested by several authors (e.g. Bernhard and Alve, 1996; Bernhard and Bowser, 2008), allowing them to survive and potentially be active in the absence of oxygen, suggested that calcification could eventually take place under anoxia
Summary
Oxygen depletion is one of the most severe environmental stressors in marine ecosystems. Many foraminiferal species are known to be able to survive short to long periods of hypoxic or even anoxic conditions (Bernhard, 1993; Bernhard and Alve, 1996; Moodley et al, 1997; Langlet et al, 2013; Geslin et al, 2014), it is still an open question as to whether benthic foraminifera are able to calcify under anoxia. The discovery of a facultative anaerobic metabolism (i.e. denitrification; Risgaard-Petersen et al, 2006) by certain foraminiferal species, and the hypothesis of other possible anaerobic pathways suggested by several authors (e.g. Bernhard and Alve, 1996; Bernhard and Bowser, 2008), allowing them to survive and potentially be active in the absence of oxygen, suggested that calcification could eventually take place under anoxia. Two experiments were carried out using three benthic foraminiferal species: (1) Ammonia tepida (coastal species), and (2) Bulimina marginata and (3) Cassidulina laevigata (shelf to deep-sea species)
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