Long-term and regional variability of phytoplankton biomass in the Northeast Atlantic (1960-1995)

Long-term regional changes in phytoplankton biomass in the Northeast Atlantic and North Sea are investigated using data from the Continuous Plankton Recorder survey. During the last decade there have been large changes in the long-term variation in phytoplankton biomass in the Northeast Atlantic and North Sea. Most regions, particularly in the North Sea, have shown a considerable increase in phytoplankton biomass while the opposite pattern was seen in the northern oceanic region of the Northeast Atlantic. These different spatial responses show similar patterns of change to the decadal variability in sea surface temperature influenced by the North Atlantic Oscillation index. Two rare oceanographic events and their relationship to the interannual changes in phytoplankton biomass are discussed. The results highlight the importance of maintaining long-term biological monitoring programmes to assess the biological responses to slow oceanic/atmospheric processes and to rare or episodic physical events.

Regional climate change and harmful algal blooms in the northeast Atlantic

We investigated long-term spatial variability in a number of Harmful Algal Blooms (HABs) in the northeast Atlantic and North Sea using data from the Continuous Plankton Recorder. Over the last four decades, some dinoflagellate taxa showed pronounced variation in the south and east of the North Sea, with the most significant increases being restricted to the adjacent waters off Norway. There was also a general decrease along the eastern coast of the United Kingdom. The most prominent feature in the interannual bloom frequencies over the last four decades was the anomalously high values recorded in the late 1980s in the northern and central North Sea areas. The only mesoscale area in the northeast Atlantic to show a significant increase in bloom formation over the last decade was the Norwegian coastal region. The changing spatial patterns of HAB taxa and the frequency of bloom formation are discussed in relation to regional climate change, in particular, changes in temperature, salinity, and the North Atlantic Oscillation (NAO). Areas highly vulnerable to the effects of regional climate change on HABs are Norwegian coastal waters and the Skagerrak. Other vulnerable areas include Danish coastal waters, and to a lesser extent, the German and Dutch Bight and the northern Irish Sea. Quite apart from eutrophication, our results give a preview of what might happen to certain HAB genera under changing climatic conditions in temperate environments and their responses to variability of climate oscillations such as the NAO.

Coccolithophore bloom size variation in response to the regional environment of the subarctic North Atlantic

Several environmental/physical variables derived from satellite and in situ data sets were used to understand the variability of coccolithophore abundance in the subarctic North Atlantic. The 7-yr (1997–2004) time-series analysis showed that the combined effects of high solar radiation, shallow mixed layer depth (<20 m), and increased temperatures explained >89% of the coccolithophore variation. The June 1998 bloom, which was associated with high light intensity, unusually high sea-surface temperature, and a very shallow mixed layer, was found to be one of the most extensive (>995,000 km2) blooms ever recorded. There was a pronounced sea-surface temperature shift in the mid-1990s with a peak in 1998, suggesting that exceptionally large blooms are caused by pronounced environmental conditions and the variability of the physical environment strongly affects the spatial extent of these blooms. Consequently, if the physical environment varies, the effects of these blooms on the atmospheric and oceanic environment will vary as well.