Calcification intensity in planktonic Foraminifera reflects ambient conditions irrespective of environmental stress

Abstract

Planktonic Foraminifera are important marine calcifiers, and the ongoing change in the oceanic carbon system makes it essential to understand the influence of environmental factors on the biomineralisation of their shells. The amount of calcite deposited by planktonic Foraminifera during calcification has been hypothesized to reflect a range of environmental factors. However, it has never been assessed whether their calcification only passively responds to the conditions of the ambient seawater or whether it reflects changes in resource allocation due to physiological stress. To disentangle these two end-member scenarios, an experiment is required where the two processes are separated. A natural analogue to such an experiment occurred during the deposition of the Mediterranean sapropels, where large changes in surface water composition and stratification at the onset of the sapropel deposition were decoupled from local extinctions of planktonic Foraminifera species. We take advantage of this natural experiment and investigate the reaction of calcification intensity, expressed as size-normalized weight (SNW), of four species of planktonic Foraminifera to changing conditions during the onset of Sapropel S5 (126–121 ka) in a sediment core from the Levantine Basin. We observe a significant relationship between SNW and surface water properties, as reflected by stable isotopes in the calcite of Foraminifera shells, but we failed to observe any reaction of calcification intensity on ecological stress during times of decreasing abundance culminating in local extinction. The reaction of calcification intensity to surface water perturbation at the onset of the sapropel was observed only in surface dwelling species, but all species calcified more strongly prior to the sapropel deposition and less strongly within the sapropel than at comparable conditions during the present day. These results indicate that the high-salinity environment of the glacial Mediterranean Sea prior to sapropel deposition induced a more intense calcification, whereas the freshwater injection to the surface waters associated with sapropel deposition inhibited calcification. The results are robust to changes in carbonate preservation and collectively imply that changes in normalized shell weight in planktonic Foraminifera should reflect mainly abiotic forcing

Planktic Foraminiferal Test Size and Weight Response to the Late Pliocene Environment

“…Yet Weinkauf et al (, ) and de Moel et al () found that temperature, upwelling, productivity, and optimum growth conditions influence weight, regardless of changes in CO 2 3 − . Weinkauf et al () suggests that temperature and productivity control SNW in modern Gs.…”

“…This calcification response is more prominent in nonsymbiotic foraminifera than in symbiotic species, which are able to elevate the pH in surrounding waters due to photosynthetic CO 2 fixation (de Nooijer et al, ; Rink et al, ; Wolf‐Gladrow et al, ). The drivers of weight change in foraminifer are still heavily debated as some species and regions show no dependency on the carbonate system suggesting that temperature and productivity drive a change in calcification (Beer et al, ; Weinkauf et al, ; Weinkauf et al, ). For example, reduced salinity may inhibit calcification in some species of foraminifera (Beer et al, ; Bijma et al, ; Weinkauf et al, ).…”

“…The drivers of weight change in foraminifer are still heavily debated as some species and regions show no dependency on the carbonate system suggesting that temperature and productivity drive a change in calcification (Beer et al, ; Weinkauf et al, ; Weinkauf et al, ). For example, reduced salinity may inhibit calcification in some species of foraminifera (Beer et al, ; Bijma et al, ; Weinkauf et al, ).…”

Micro‐CT Scanning of Tests of Three Planktic Foraminiferal Species to Clarify DissolutionProcess and Progress

“…Based on calibration between SNW in core‐top sediments and bottom‐water Δ[CO 3 2− ] in the equatorial Pacific, size‐normalized test weights have served as a proxy for deep seawater [CO 3 2− ] (e.g., Broecker & Clark, ; Qin et al, ). In contrast, the test area density (μg μm −2 ) of foraminifera, which is the ratio of the weight of a test to its projected area, is a more rigorous size‐standardized proxy than SNW, and it is also employed as a proxy of calcification intensity controlled by sea surface conditions (e.g., Moy et al, ; Weinkauf et al, ; Zarkogiannis et al, ). Sea surface conditions where foraminifera calcify can influence the thickness of foraminiferal test walls (Marshall et al, ) and bulk density (Iwasaki et al, ), which implies that the initial weights of foraminiferal tests differ depending on growth conditions as suggested in Barker and Elderfield (); thus, the test weight proxies SNW and test area density may be affected by not only dissolution at the deep seafloor but also calcification at the sea surface.…”

Stable Oxygen Isotope Composition Is Biased by Shell Calcification Intensity in Planktonic Foraminifera

“…Marshall et al., 2013; Weinkauf et al., 2016). In this regard, shell calcification intensity has been mostly used as a proxy for dissolution (Broecker & Clark, 2001; Lohmann, 1995; Schiebel et al., 2007) and marine carbonate system variables (Bijma et al., 1999, 2002; de Moel et al., 2009; Davis et al., 2019; Osborne et al., 2016; Spero et al., 1997; Weinkauf et al., 2013). However, other studies could show that the picture is more complicated and shell calcification intensity is indeed influenced by a variety of environmental factors (Aldridge et al., 2012; Marshall et al., 2013; Mohan et al., 2015; Weinkauf et al., 2016), which may also have an influence on the shell's geochemical composition (e.g., water temperature and salinity; Davis et al., 2016; Gonzalez‐Mora et al., 2008; Zarkogiannis et al., 2019).…”