Open or closed: pH modulation and calcification by foraminifera

Area of Science:

• Marine Biology
• Biogeochemistry
• Geochemistry

Background:

• Marine calcifying organisms precipitate shells through biological control or in equilibrium with seawater.
• Elemental signatures in shells, such as Mg/Ca ratios, vary significantly among species.
• Understanding the mechanisms controlling shell composition is crucial for paleoceanography and marine ecology.

Purpose of the Study:

• To investigate the relationship between ion transport, biological control, and shell elemental signatures in marine calcifying organisms.
• To elucidate the role of transmembrane transporters and mitochondria in regulating calcification.
• To explain species-specific elemental signatures in foraminifera shells.

Main Methods:

• Comparative analysis of "closed" and "open" calcification systems in marine organisms.
• Investigation of ion fluxes (H+, Ca2+) and their relationship to calcification rates.
• Localization and density analysis of mitochondria at calcification sites.

Main Results:

• Marine calcification exists on a spectrum from "closed" to "open" systems.
• Closed systems exhibit high ion fluxes, leading to Mg/Ca dilution and low Mg/Ca calcite.
• Open systems show lower ion fluxes and higher seawater exchange, resulting in high Mg/Ca foraminifera.
• Mitochondrial density correlates with ion pumping rates at calcification sites.

Conclusions:

• Transmembrane transporters and mitochondria play critical roles in regulating foraminifera calcification.
• The degree of system openness or closure explains species-specific Mg/Ca elemental signatures.
• These findings provide a framework for understanding biomineralization and its environmental implications.