Marine algae inform past calving rates of a tide water glacier in western Greenland.

Coralline algae are ubiquitous in marine environments worldwide. They are ecosystem engineers, cementing reefs together and providing habitat for local communities with the 3D structure of their calcified thallus material. The calcified thallus make corallines a resource of environmental data as well, providing information on the scale of 10s-100s of years. Free living coralline algae, or maerl, dominate local habitats along the coasts and in fjord systems of western Greenland. Using the long lived maerl species, Lithothamnion glaciale, we present multi-proxy data sets for the large fjord system adjacent to the Kangiata Nunta Sermia (KNS) glacier. This information provides a record of glacial movement (advance and retreat) and calving from the Medieval Warm Period through the Little Ice Age to the present day. The KNS glacier is one of the largest tidewater glaciers in western Greenland and contributes to the mass transfer of glaciers and ice sheets into the world oceans. The present data combined with terrestrial proxies will help inform policy and models focusing on future climate conditions.