Pleistocene surface-ocean changes across the Southern subtropical front recorded by cryptic species of Orbulina universa

ABSTRACT Porosity in planktonic foraminifers (the proportion of the shell surface covered by pores) is a conspicuous quantitative trait, well preserved in fossil shells and implicated as a source of environmental information. Despite its potential, the functional importance of porosity remains poorly understood. It is likely that pores are important in gas exchange, and differences in shell porosity among species or within species may reflect differences in metabolic rates or ambient oxygen concentration. Theoretically, porosity also affects the weight of the shell; and differences in porosity may reflect an adaptation to the specific density of the seawater or differences in allocation of resources to calcification (shell calcification intensity). Finally, there is evidence that porosity may differ between closely related cryptic species. Here we analyzed the potential role of porosity as a regulator of calcification intensity in Orbulina universa by combining biometric measurements based on sediment surface samples from the western Atlantic with a modelling approach. Specimens of O. universa were analyzed concerning their shell size, shell thickness, and shell porosity under light and scanning electron microscopy, and weighed using a microbalance. The resulting empirically derived model shows an effect size of shell thickness that is 7.5 times larger than the effect of shell porosity on the overall shell calcification intensity. This indicates that porosity is unlikely to be used by this species to regulate calcification intensity. By implementing the model on literature data which analyzed calcification intensity in O. universa, we also show that porosity differences among cryptic species in O. universa are unlikely to explain the observed differences in calcification intensity within the species. These findings indicate that functional explanations for differences in porosity in planktonic foraminifers have to be sought outside of calcification or density regulation and, conversely, that the observed differences in calcification intensity are likely driven by shell thickness and their relationship with environmental forcing can be applied without correction for porosity.

Download Full-text

Decoupled carbonate chemistry controls on the incorporation of boron into <i>Orbulina universa</i>.

10.5194/bg-2016-90 ◽

2016 ◽

Cited By ~ 1

Author(s):

E. L. Howes ◽

K. Kaczmarek ◽

M. Raitzsch ◽

A. Mewes ◽

N. Bijma ◽

...

Keyword(s):

Culture Media ◽

Isotope Composition ◽

Planktonic Foraminifera ◽

Femtosecond Laser Ablation ◽

Natural Systems ◽

Surface Ocean ◽

Constant Ph ◽

Icp Ms ◽

Effects Of Ph ◽

Orbulina Universa

Abstract. In order to fully constrain paleo-carbonate systems, proxies for two out of seven parameters, plus temperature and salinity are required. The boron isotopic composition (δ11B) of planktonic foraminifera shells is a powerful tool to reconstruct changes in past surface ocean pH. As B(OH)4− is substituted into the biogenic calcite lattice in place of CO32−, it has been suggested that B/Ca ratios in biogenic calcite are a possible proxy for [CO32−]. However, differentiating between the effects of pH and [CO32−] is problematic, as they co-vary closely in natural systems, and so the major control on boron incorporation remains unclear. To deconvolve the effects of pH and [CO32−] on the B/Ca ratio and to test whether δ11B remains constant at constant pH, but under changing [CO32−] (pH 8.05 with 238, 285 and 532 µmol kg−1 CO32−) and vice versa, we decoupled pH and [CO32−] (276 ± 19.5 µmol kg−1 CO32− with pH 7.7, 7.9 and 8.05) and grew the planktonic foraminifer Orbulina universa in these manipulated culture media. Measurements of the isotope composition of boron and the B/Ca ratio were performed simultaneously using a femtosecond laser ablation system coupled to an MC ICP-MS. Results show that δ11B is controlled by pH and does not respond to changes in [CO32−]. On the other hand, the B/Ca ratio is driven by [HCO3−] independently of pH. This suggests that B/Ca ratios in foraminiferal calcite may be used as a second, independent, proxy for paleo-carbonate system reconstructions.

Download Full-text

Boron proxy constraints on the magnitude of surface ocean acidification during the Paleocene-Eocene Thermal Maximum

Rendiconti online della Società Geologica Italiana ◽

10.3301/rol.2014.106 ◽

2014 ◽

Vol 31 ◽

pp. 173-174

Author(s):

Donald E. Penman

Keyword(s):

Ocean Acidification ◽

Surface Ocean ◽

Thermal Maximum

Download Full-text

High-resolution paleotemperature record of the surface ocean from the Eocene-Oligocene boundary of the South Australian Coast

Rendiconti online della Società Geologica Italiana ◽

10.3301/rol.2014.98 ◽

2014 ◽

Vol 31 ◽

pp. 157-158

Author(s):

Bradley N. Opdyke

Keyword(s):

High Resolution ◽

The South ◽

Surface Ocean

Download Full-text

Identification of sibling species in the genus Eucyclops from water-bodies of Ukraine and Russia using crossbreeding studies

Ecology and Noospherology ◽

10.15421/031406 ◽

2014 ◽

Vol 25 (1-2) ◽

pp. 61-68 ◽

Cited By ~ 1

Author(s):

V. I. Monchenko ◽

L. P. Gaponova ◽

V. R. Alekseev

Keyword(s):

Cryptic Species ◽

River Basin ◽

Black Sea ◽

Species Complex ◽

River Basins ◽

Water Bodies ◽

Similar Species ◽

Basin Water ◽

Different Populations ◽

Baltic Sea Basin

Crossbreeding experiments were used to estimate cryptic species in water bodies of Ukraine and Russia because the most useful criterion in species independence is reproductive isolation. The problem of cryptic species in the genus Eucyclops was examined using interpopulation crosses of populations collected from Baltic Sea basin (pond of Strelka river basin) and Black Sea basin (water-reservoires of Dnieper, Dniester and Danube rivers basins). The results of reciprocal crosses in Eucyclops serrulatus-group are shown that E. serrulatus from different populations but from water bodies belonging to the same river basin crossed each others successfully. The interpopulation crosses of E. serrulatus populations collected from different river basins (Dnipro, Danube and Dniester river basins) were sterile. In this group of experiments we assigned evidence of sterility to four categories: 1) incomplete copulation or absence of copulation; 2) nonviable eggs; 3) absence of egg membranes or egg sacs 4) empty egg membranes. These crossbreeding studies suggest the presence of cryptic species in the E. serrulatus inhabiting ecologically different populations in many parts of its range. The same crossbreeding experiments were carries out between Eucyclops serrulatus and morphological similar species – Eucyclops macruroides from Baltic and Black Sea basins. The reciprocal crossings between these two species were sterile. Thus taxonomic heterogeneity among species of genus Eucyclops lower in E. macruroides than in E. serrulatus. The interpopulation crosses of E. macruroides populations collected from distant part of range were fertile. These crossbreeding studies suggest that E. macruroides species complex was evaluated as more stable than E. serrulatus species complex.

Download Full-text