Determination of weights of pteropod shells in samples from sediment traps obtained at the long-term observatory HAUSGARTEN and the calculation of pteropod contribution to the calcium carbonate sedimentation in Fram Strait

• Main Author: Seifert, Miriam
• Format: Thesis
• Language: unknown
• Published: 2015
• Subjects: Fram Strait; Limacina helicina
• Online Access: https://epic.awi.de/id/eprint/38843/; https://hdl.handle.net/10013/epic.46245

Pteropods are marine pelagic snails that form shells out of aragonite, a form of calcium carbonate (CaCO3). When CaCO3 precipitates, CO2 is set free and changes the chemistry of the surrounding water. As soon as pteropods die, the shells sink into deeper water layers and contribute to the marine carbonate flux. During the way through the water column, dissolution of the shells can occur which leads to a chemical bond of CO2. Thus, pteropods are, in addition to other calcifiers, an important part of the carbon storage system. Because aragonite is more soluble than calcite (which is formed by foraminifera and coccolithophorids) under the same physical and chemical conditions, the contribution of aragonite to the total carbonate flux is of special interest. The easiest way to determine this contribution is to multiply the amount of shells with an assumed shell weight. In this thesis, pteropods collected with sediment traps were investigated. The sediment traps are moored at the long-term deep-sea observatory HAUSGARTEN (operated by the Alfred Wegener Institute) in eastern Fram Strait. They sample the ambient particle flux in defined time periods during one year. Additionally, zooplankton can enter the traps. The samples examined in this thesis are from 2011/2012 and 2012/2013 from ~ 200 m and ~ 2500 m depth. In the Fram Strait two pteropod species, Limacina helicina and Limacina retroversa, are regularly recorded. To date, an average shell weight of 0.145 mg/shell was assumed to calculate the contribution of aragonite to the total carbonate flux. The aim of this thesis is to refine this guide value by investigating whether there is a difference in the shell weights of both species at both depths. Besides, it was tested if it is possible to consider the shell size in the calculation of the aragonite contribution. L. retroversa is the dominant pteropod species in the HAUSGARTEN area with a proportion of 90 % of the pteropod individuals. There is a significant difference in the shell weights of both species as well as ...