Kalkskjell

Kalkskjell is a term used to describe shells that are primarily composed of calcium carbonate (CaCO3). The concept refers to the shells of many marine organisms, including mollusks such as snails and clams, as well as brachiopods, foraminifera, corals and certain bryozoans. The calcium carbonate in kalkskjell can crystallize as calcite or aragonite, and the shells may have nacreous (mother-of-pearl) or prismatic microstructures created through biomineralization processes guided by organic matrices.

Kalkskjell play a key role in marine ecosystems by providing protection and structural support for the organisms that produce them. They also contribute to the carbon cycle, as calcium carbonate formation stores carbon in solid form. The fossil record of kalkskjell is extensive, making them important in paleontological studies and reconstructions of past environmental conditions, such as seawater chemistry and climate.

Environmental factors influence kalkskjell formation. Ocean acidification, driven by increased atmospheric CO2, reduces the concentration of carbonate ions in seawater and lowers pH, which can hinder calcification and, in some cases, lead to dissolution of shells. Temperature, food availability, and water chemistry also affect growth rates and shell integrity across different species.

Kalkskjell are distributed worldwide in marine environments, from shallow coastal waters to deeper regions, with variations among taxa in shell composition and structure. They are of interest to biology, geology and environmental science for understanding biogenic calcium carbonate and its responses to changing ocean conditions.