Abstract
The North Atlantic with its spring-bloom ecosystem has its particular responses to climate change, many of them different from the other parts of the world’s oceans. The system is strongly influenced by anthropogenic climate change as well as to strong decadal to multidecadal natural climate variability. In particular, the northernmost part of the system and the Arctic is exposed to higher increase in temperature than any other ocean region. The most pronounced examples of poleward migration of marine species are found in the North Atlantic, and comprise the recent warming phase after the 1970s. The latitudinal asymmetric position of the Arctic Front and its nature of change result in a considerably larger migration distance and migration speed of species in the Northeast Atlantic part of the system. However, we here hypothesize that there is a limit to the future extent of poleward migration of species constrained by the latitudinal region adjacent the Polar Circle. We define this region the critical latitudes. This is because the seasonal light cycle at high latitudes sets particular demands on the life cycle of planktivore species. Presently, boreal planktivore species at high latitudes deposit lipids during the short spring bloom period and overwinter when phytoplankton production is insufficient for feeding. Unless invading temperate species from farther south are able to adapt by developing a similar life cycle future poleward migration of such species will be unlikely.
Highlights
Specialty section: This article was submitted to Global Change and the Future Ocean, a section of the journal Frontiers in Marine Science
If temperate zooplankton species would not adapt to the high-latitude light cycle by developing lipid deposition and overwintering, nor that the boreal lipid-depositing zooplankton species adapt to the higher temperatures under future climate change, the high latitude northeast Atlantic region between the North Atlantic Current and the Arctic could become a region with low and decreasing ecosystem productivity
The region contains the most comprehensive biological and hydrographic time series of the world oceans, some of them extending back to the beginning of the twentieth century. This implies that it is possible to distinguish between twentieth century anthropogenic temperature change and multidecadal climate signals like the Atlantic Multidecadal Oscillation (AMO)
Summary
The North Atlantic spring-bloom ecosystem extends from the northern rim of the North Atlantic subtropical gyre at about 30◦N to the Arctic ecosystems of the Davis Strait between Canada and Greenland, across the Fram Strait between the Norwegian Sea and the Polar Basin and along the northernmost part of the Barents Sea at 80◦N (Hoegh-Guldberg et al, 2014). In the southern part of the biome winter primary production can be high enough to sustain autumn and winter spawning behavior, but at higher latitudes, to the north of 60◦N, marine organisms are increasingly forced into the spring-spawning cycle (e.g., Ellertsen et al, 1989) because of nearly complete absence of primary production during the dark winter time This high-latitude seasonal light cycle has developed herbivore copepods with the particular attribute of very efficient feeding during the short phytoplankton production season and deposition of large stores of lipids for overwintering at deeper depths during winter (Falk-Petersen et al, 2009). Northward migration of lower-latitude temperate species induced by climate change may become constrained due to lack of adaptation to the needed lipid deposition and overwintering
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