Decrease in coccolithophore calcification and CO2 since the middle Miocene

Abstract

Marine algae are instrumental in carbon cycling and atmospheric carbon dioxide (CO2) regulation. One group, coccolithophores, uses carbon to photosynthesize and to calcify, covering their cells with chalk platelets (coccoliths). How ocean acidification influences coccolithophore calcification is strongly debated, and the effects of carbonate chemistry changes in the geological past are poorly understood. This paper relates degree of coccolith calcification to cellular calcification, and presents the first records of size-normalized coccolith thickness spanning the last 14 Myr from tropical oceans. Degree of calcification was highest in the low-pH, high-CO2 Miocene ocean, but decreased significantly between 6 and 4 Myr ago. Based on this and concurrent trends in a new alkenone ɛp record, we propose that decreasing CO2 partly drove the observed trend via reduced cellular bicarbonate allocation to calcification. This trend reversed in the late Pleistocene despite low CO2, suggesting an additional regulator of calcification such as alkalinity.

A Late Miocene Terrestrial Temperature History for the Northeastern Tibetan Plateau's Period of Tectonic Expansion

“…(f) shows the variance in changes in paleotemperature between the Xining Basin and SSTs at a similar latitude, as well as the differences in terrestrial paleotemperatures between tectonically active and stable areas by subtracting the 5‐point running mean curves in (b) and (c) from that in (a), respectively. (g) Reconstructed CO 2 data compiled after Ji et al (): foraminifera δ 11 B (Badger et al, ; Foster et al, ), stomata (Beerling et al, ; Kürschner et al, ; Retallack, ; Stults et al, ; Van Der Burgh et al, ; Y. Q. Wang et al, ), paleosols (Breecker & Retallack, ; Ji et al, ), pennate diatoms (Mejía et al, ), and haptophyte algae (using alkenones; Bolton et al, ; Pagani et al, , Seki et al, , Y. Zhang et al, ). The black and pink dotted arrows in (g) show two decreasing CO 2 trends based on paleosols and diatoms, respectively.…”

Size-dependent response of foraminiferal calcification to seawater carbonate chemistry

“…For example, coccolithophores were more heavily calcified during geological epochs characterised by higher CO 2 , and lower pH (e.g. Bolton et al, 2016), even if this result has not always been reproduced in culture (Riebesell et al, 2000;Langer et al, 2009). Additionally, despite observations of decreasing pH and [CO 2− 3 ] negatively impacting calcification in most planktonic and reef-dwelling foraminifera (e.g.…”

“…Diverse small benthic foraminifera assemblages have also been found living in highly undersaturated oligohaline conditions (Flako-Zaritsky et al, 2011). Indeed, while biomineralisation pathways clearly differ, recent work favours a similarly positive response of calcification to increased aqueous pCO 2 with lower pH in the much smaller coccolithophores (Bolton et al, 2016;McClelland et al, 2016).…”

Adaptive evolution in the coccolithophore Gephyrocapsa oceanica following 1,000 generations of selection under elevated CO2

“…Their calcite plates contribute to export of carbon from the sea surface to the ocean's interior by ballasting organic aggregates and accelerating their sinking to deeper waters. Like other calcifying organisms, most coccolithophores suffer from ocean acidification, with a response pattern of immediately decreased growth rates and calcification (Bolton et al., ; Liu et al., ; Riebesell et al., ). Other traits of coccolithophores such as cell size and elemental composition are also significantly influenced by ocean acidification (Feng et al., ; Schlüter et al., ).…”