The Phanerozoic Eon marks the beginning of the biogenic carbonate fossil record providing information about the evolution of life, the land-ocean interaction and long term climate change. The varying chemical composition of Phanerozoic seawater also contributed to the extinction of many marine species during minor and in particular the largest five mass-extinction events. Proxy information necessary to extract quantitative information is gained mainly from major and trace element ratios as well as isotopic compositions in shells and tests of calcifying organisms like brachiopods, belemnites, bivalves, corals, foraminifera and others. However, the quality and reliability of these Phanerozoic records critically depends on the ability to recover original signals which have been in thermodynamic equilibrium with the surrounding Phanerozoic seawater. This goal cannot simply be achieved because species dependent vital effects and time dependent chemical alteration among other processes superimpose the original water signal to a certain extend making time series of trace element and isotope signals difficult to interpret. Therefore the improvement of existing and the development of new technical approaches and methods are highly desirable to improve and refine our existing knowledge on the history of the chemical composition of Phanerozoic seawater. Similar important are laboratory based culturing experiments in order to decipher the pathways and processes of trace elements from seawater to the site of calcification. In this regard we invite contributions about new and refined data and/or model based information about trace element and isotope compositions and cycling in Phanerozoic seawater. A special focus is on the marine biogeochemistry around the big five mass extension events and other important transitions characterizing changing in seawater composition. Welcome are also culturing studies on those calcifying organisms serving as archives for Phanerozoic seawater proxies. Furthermore, contributions emphasizing diagenetic processes or contributions introducing improved analytical techniques and methods for a better reconstruction of Phanerozoic seawater data are also highly welcome.