Freshwater fern Azolla in and around Arctic and Nordic seas

• Main Authors: Barke, Judith, van der Burgh, Johan, van Konijnenburg-van Cittert, Johanna H A, Collinson, Margaret E, Pearce, Martin A, Bujak, Jonathan, Heilmann-Clausen, Claus, Speelman, Eveline N, van Kempen, Monique M L, Reichart, Gert-Jan, Lotter, André F, Brinkhuis, Henk
• Format: Dataset
• Language: English
• Published: PANGAEA 2012
• Subjects: Integrated Ocean Drilling Program / International Ocean Discovery Program; IODP; Arctic; Arctic Ocean; Nordic Seas
• Online Access: https://doi.pangaea.de/10.1594/PANGAEA.787105; https://doi.org/10.1594/PANGAEA.787105

For a short time interval (c. 1.2 Myr) during the early middle Eocene (~49 Myr), the central Arctic Ocean was episodically densely covered by the freshwater fern Azolla, implying sustained freshening of surface waters. Coeval Azolla fossils in neighboring Nordic seas were thought to have been sourced from the Arctic. The recognition of a different Azolla species in the North Sea raised doubts about this hypothesis. Here we show that no less than five Azolla species had coeval blooms and spread in the Arctic and NW European regions. A likely trigger for these unexpected Azolla blooms is high precipitation prevailing by the end of the warmest climates of the Early Eocene Climatic Optimum (EECO).