The North Atlantic Spring-Bloom System—Where the Changing Climate Meets the Winter Dark

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 planktivorous species. Presently, boreal planktivorous 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.

Responses of Marine Organisms to Climate Change across Oceans

“…Light regime thresholds likely trigger events such as reproduction and migration (Davenport et al, 2005), in addition to temperature thresholds. Thus, temperature-driven shifts in distribution and phenology of species can be constrained by the influence of the seasonality of light on photoperiod, particularly at high latitudes (Figure 4; Saikkonen et al, 2012;Sundby et al, 2016). For example, in polar oceans, extreme light seasonality results in a short annual window of primary productivity and therefore food availability, thus restricting the potential for temperature-driven invasion of the high Arctic waters by species from lower latitudes (Kaartvedt, 2008).…”

Oogenesis and reproductive investment of Atlantic herring are functions of not only present but long-ago environmental influences as well

“…2A, respectively). Hence, the tactical pattern of small eggs in autumn spawners and large eggs in spring spawners of this species (26) was firmly confirmed, divergences thought to be related to spatiotemporal differences in zooplankton type and size (25). In contrast to general expectations of increased specific reproductive costs with growing body size (17), present RF P,S of NSSH appeared unrelated to TL (P = 0.659) (Fig.…”

“…S3). The annual cycle of zooplankton (prey) production in the North Sea and in the Norwegian Sea is illustrated (green bar) (25).…”

Are fish outside their usual ranges early indicators of climate‐driven range shifts?

“…First sightings from polar regions were very rare (only three observations), which may reflect sampling constraints at extreme latitudes. However, the movement of temperate and subpolar species into higher latitudes is likely to be limited by the high seasonality of light and primary production in these high-latitude waters, and the adaptations required to thrive in such extreme seasonal environments Sundby et al, 2016). However, impacts on biodiversity are anticipated, particularly towards boreal fringes of polar regions.…”