Size-dependent response of foraminiferal calcification to seawater carbonate chemistry

Abstract

The response of the marine carbon cycle to changes in atmospheric CO 2 concentrations will be determined, in part, by the relative response of calcifying and non-calcifying organisms to global change. Planktonic foraminifera are responsible for a quarter or more of global carbonate production, therefore understanding the sensitivity of calcification in these organisms to environmental change is critical. Despite this, there remains little consensus as to whether, or to what extent, chemical and 5 physical factors affect foraminiferal calcification. To address this, we directly test the effect of multiple controls on calcification in culture experiments and core-top measurements of Globigerinoides ruber. We find that two factors, body size and the carbonate system, strongly influence calcification intensity in life, but that exposure to corrosive bottom waters can overprint this signal post mortem. Using a simple model for the addition of calcite through ontogeny, we show that variable body size between and within datasets could complicate studies that examine environmental controls on foraminiferal shell weight. 10In addition, we suggest that size could ultimately play a role in determining whether calcification will increase or decrease with acidification. Our models highlight that knowledge of the specific morphological and physiological mechanisms driving ontogenetic change in calcification in different species will be critical in predicting the response of foraminiferal calcification to future change in atmospheric pCO 2 .

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

“…In both modern and geological field studies of a variety of species, multiple drivers of weight change are indicated. In general, calcification is energetically more difficult outside optimum CO 2 conditions for each species (de Nooijer et al, ; Foster et al, ; Henehan et al, ) and at lower carbonate ion concentrations (Kroeker et al, ). In laboratory experiments, a clear reduction of weight in response to lower carbonate ion changes is documented (Beer et al, ; Bijma et al, ; Bijma et al, ; Henehan et al, ; Lombard et al, ; Russel et al, ).…”

“…Marine calcifying organisms play a fundamental role in the inorganic carbon cycle (Boyce et al, ; Henehan et al, ). Carbonate production in the ocean is roughly equally divided between the shelf and the open ocean (Cartapanis et al, ).…”

“…Other than size, foraminiferal weight is a fundamental indicator of foraminiferal carbonate production. Planktic foraminifera in general respond to changes in lower pH, carbonate ion concentration, and saturation with thinner tests and reduction in test size (Barker & Elderfield, ; Bijma et al, ; Henehan et al, ; Naik et al, ; Spero et al, ). 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, ).…”

Did Photosymbiont Bleaching Lead to the Demise of Planktic ForaminiferMorozovellaat the Early Eocene Climatic Optimum?

“…Changes in ocean chemistry also may have affected morozovellid calcification and explain to some extent the observed test size reduction. Recent culturing and open ocean observations suggest that acidification can affect variably sized foraminifera differently, such that larger planktic foraminifera preferentially reduce their calcification (Henehan et al, ). We cannot exclude that morozovellids may have decreased their maximum size as a consequence of a drop in pH, because there are several short‐term negative CIEs within the EECO probably signifying addition of CO 2 to the ocean and atmosphere (e.g., Dickens et al, ; Zeebe et al, ).…”

Reconstructing 800 Years of Carbonate Ion Concentration in the Cariaco Basin Using the Area Density of Planktonic Foraminifera Shells

“…The highly significant relationship between size and weight also shows that factors such as secondary precipitation, dissolution, or sediment infilling were minimal or consistent through time. However, scatter within this relationship does demonstrate variability in the size and weight relationship for any given individual foraminifera, such as the influence of body size on response to carbonate chemistry (Henehan et al, ) or the influence of temperature and nutrients during an individual's lifetime. Moreover, no significant relationship was found between sample average area density and average area ( p value = 0.24), indicating that size normalization of weights was effective in limiting bias due to size change.…”