Appearance of the Pacific diatom Neodenticula seminae in the northern Nordic Seas — An indication of changes in Arctic sea ice and ocean circulation

The marine diatom Neodenticula seminae belongs to the present day planktonic assemblage of the subarctic North Pacific and its high-latitude marginal seas. In the middle and high-latitude North Atlantic, N. seminae occurred from the middle Pleistocene to the early–middle Pleistocene transition when it became locally extinct. After a long absence of 0.84 Ma, it was found again in the North Atlantic in the late 1990s (Reid et al. 2007). e show from sediment samples taken in 2006, 2007 and 2008 that N. seminae now has appeared in the Nordic Seas for the first time in geologic history, and it already has a widespread modern distribution in the northern Nordic Seas. The appearance of N. seminae in the Nordic Seas coincides with an increased influence of Pacific water via the Arctic Ocean due to diminished sea ice and/or changed ocean circulation in the Arctic Ocean. Our results show that trans-Arctic exchanges, which were first observed in the North Atlantic in the late 1990ʹs are still in motion, or possibly even accelerated during recent years. The appearance of N. seminae in the Nordic Seas might even suggest initiation of a unique climatic transition of the scale seen during the mid-Pleistocene transition. More trans-Arctic exchanges can be expected in the near future if the modern warming trend and reduction of sea ice continues in the Arctic.