The seeding of ice algal blooms in Arctic pack ice: The multiyear ice seed repository hypothesis

摘要

During the Norwegian young sea ICE expedition (N-ICE2015) from January to June 2015 the packice in the Arctic Ocean north of Svalbard was studied during four drifts between 83° and 80°N. This pack iceconsisted of a mix of second year,first year, and young ice. The physical properties and ice algal communitycomposition was investigated in the three different ice types during the winter-spring-summer transition.Our results indicate that algae remaining in sea ice that survived the summer melt season are subsequentlytrapped in the upper layers of the ice column during winter and may function as an algal seed repository.Once the connectivity in the entire ice column is established, as a result of temperature-driven increase in iceporosity during spring, algae in the upper parts of the ice are able to migrate toward the bottom and initiatethe ice algal spring bloom. Furthermore, this algal repository might seed the bloom in younger ice formedin adjacent leads. This mechanism was studied in detail for the dominant ice diatomNitzschia frigida. Theproposed seeding mechanism may be compromised due to the disappearance of older ice in the anticipatedregime shift toward a seasonally ice-free Arctic Ocean.