How the Subpolar gyre strength influences phytoplankton blooms dynamics in the North Atlantic

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Changes in the North Atlantic Subpolar gyre (NASPG) have been linked to the interannual variability of primary production. However, little is known about the mechanisms behind both environmental processes, and how the NASPG strength may extend its potential impacts to higher trophic levels, including early life stages of commercial fish species. We assess NASPG strength effect on North Atlantic phytoplankton bloom dynamics. We analysed time series (from 1998 to 2010) of chlorophyll α as a proxy of phytoplankton abundance, and the NASPG as a proxy for environmental variability. 17 regions were strategically chosen to characterize positions relative to the NASPG and its dynamics. It is hypothesized that a strong NASPG index will be associated with a low abundance, late phytoplankton bloom, possibly induced by higher heat losses, and thus lower temperatures. In general, across the entire North Atlantic, later blooms were observed in higher latitudes and for stronger NAPSG index (negative values). This pattern though has regional variations. In the eastern sectors, latitudinal timing differences are much stronger for strong NAPSG index than for weak index. Indications of a strong influence of NASPG index are related to areas within the NAPSG, which may have an impact in the ecosystem functioning. The results also suggest that physical forcing other than the strength of the NASPG influences primary production, particularly at regional scales.