Link between light-triggered Mg-banding and chamber formation in the planktic foraminifera Neogloboquadrina dutertrei

Abstract

The relationship between seawater temperature and the average Mg/Ca ratios in planktic foraminifera is well established, providing an essential tool for reconstructing past ocean temperatures. However, many species display alternating high and low Mg-bands within their shell walls that cannot be explained by temperature alone. Recent experiments demonstrate that intrashell Mg variability in Orbulina universa, which forms a spherical terminal shell, is paced by the diurnal light/dark cycle. Whether Mg-heterogeneity is also diurnally paced in species with more complex shell morphologies is unknown. Here we show that high Mg/Ca-calcite forms at night in cultured specimens of the multi-chambered species Neogloboquadrina dutertrei. Our results demonstrate that N. dutertrei adds a significant amount of calcite, and nearly all Mg-bands, after the final chamber forms. These results have implications for interpreting patterns of calcification in N. dutertrei and suggest that diurnal Mg-banding is an intrinsic component of biomineralization in planktic foraminifera.

Size-dependent response of foraminiferal calcification to seawater carbonate chemistry

“…In a practical sense, however, we suspect the conceptualisation of shell thickening chosen is not likely to greatly impact our conclusions, for two reasons. Firstly, even with observed end-stage thickening in N. dutertrei, older chambers are often more heavily thickened than later chambers (Fehrenbacher et al, 2017), which could in a post hoc sense result in similarly thickened older chambers as in the models we use here, even if the ontogenetic pathway to achieving this differs. Secondly, and perhaps more crucially, our model ontogenies are screened against size-weight relationships in towed foraminifera, and so by necessity our modelled ontogenetic trends must approximate true physiology.…”

“…Other species appear to secondarily thicken their tests following precipitation of their final chamber and some may form a crust (e.g. Srinivasan and Kennett, 1974;Spero et al, 2015;Fehrenbacher et al, 2017), although this…”

“…Emerging findings from species such as Neogloboquadrina dutertrei (e.g. Fehrenbacher et al, 2017) suggest that at least some foraminifera may first add chambers until they reach a final test size, and then subsequently thicken all chambers continually over some days prior to gametogenesis. Note that this is distinct from concepts such gametogenic calcite addition or encrustation, and refers specifically to ontogenetic thickening.…”

Relationships Between Temperature, pH, and Crusting on Mg/Ca Ratios in Laboratory‐Grown Neogloboquadrina Foraminifera

“…dutertrei (Fehrenbacher et al, ). A crust is added later, if at all, with some shells acquiring a crusted texture several days prior to gametogenesis (Fehrenbacher et al, ; von Langen, ). Encrusted fossil foraminifera are characterized by a thicker shell, a distinct euhedral texture, low δ 18 O, and a relatively low‐Mg/Ca ratio (Arikawa, ; Bolton & Marr, ; Kozdon, Ushikubo, et al, ; Sadekov et al, ).…”

Mg / Ca and δ<sup>18</sup>O in living planktic foraminifers from the Caribbean, Gulf of Mexico and Florida Straits

“…Here, the high Mgheterogeneity in single chambers (cf. Fehrenbacher et al, 2017) probably caused the large offset between the two measuring techniques (see above). However, the average derived Mg/Ca-temperature of plankton bulk samples (~26.3 °C) at station 221 is in good agreement with the in situ temperature of the seawater at this station (~26.5 °C) (Fig.…”