A long‐term chlorophyll dataset reveals regime shift in North Sea phytoplankton biomass unconnected to nutrient levels

Abstract

During the 1980s, a rapid increase in the Phytoplankton Colour Index (PCI), a semiquantitative visual estimate of algal biomass, was observed in the North Sea as part of a regionwide regime shift. Two new data sets created from the relationship between the PCI and SeaWiFS chlorophyll a (Chl a) quantify differences in the previous and current regimes for both the anthropogenically affected coastal North Sea and the comparatively unaffected open North Sea. The new regime maintains a 13% higher Chl a concentration in the open North Sea and a 21% higher concentration in coastal North Sea waters. However, the current regime has lower total nitrogen and total phosphorus concentrations than the previous regime, although the molar N : P ratio in coastal waters is now well above the Redfield ratio and continually increasing. Besides becoming warmer, North Sea waters are also becoming clearer (i.e., less turbid), thereby allowing the normally light-limited coastal phytoplankton to more effectively utilize lower concentrations of nutrients. Linear regression analyses indicate that winter Secchi depth and sea surface temperature are the most important predictors of coastal Chl a, while Atlantic inflow is the best predictor of open Chl a; nutrient concentrations are not a significant predictor in either model. Thus, despite decreasing nutrient concentrations, Chl a continues to increase, suggesting that climatic variability and water transparency may be more important than nutrient concentrations to phytoplankton production at the scale of this study.

Deep ocean communities impacted by changing climate over 24 y in the abyssal northeast Pacific Ocean

“…Some studies based on satellite and in situ time-series measurements suggest that primary production in the ocean is increasing globally (2,22). Other studies indicate a reduction in primary production in mid to low latitudes because of increasing vertical stratification (3,23) and global reductions in primary production overall.…”

Is climate change the most likely driver of range expansion for a critically endangered top predator in northeast Atlantic waters?

“…While we do not dispute that UK and Irish records of Balearic shearwater has increased in recent years, this does not prove that the number of birds visiting the UK has increased. Following work by Bourne et al (1988) (McQuatters-Gollop et al 2007). Therefore the apparent increases could simply reflect a change in observer awareness.…”

Nutrient and chlorophyll a anomaly in red-tide periods of 2003–2008 in Sishili Bay, China

“…As a result, high nutrient and COD concentrations are still found near its estuary, even though the river has been dammed. In most marine environments, nitrogen appears to be the limiting factor of primary production; accordingly, the concentration of TIN, PO 4 -P and molar N/P ratio can control the pattern and function of the ecosystem of a bay, as well as alter the structure, production, and biomass of phytoplankton (Balode et al, 1998;Lenton and Watso, 2000;Leonardos and Geider, 2004;McQuatters-Gollop et al, 2007). However, more N than P entered Sishili Bay from terrestrial sources during rainfall events, as indicated by the increasing trend of TIN concentrations during precipitation.…”

“…However, phytoplankton blooms can be influenced by other factors in addition to nutrient concentrations, such as sea surface temperature (McQuatters-Gollop et al, 2007;Loebl et al, 2008). In Sishili Bay, the changing trend of chl-a lagged behind that of water temperature by one month, except in 2007, showing that high water temperature tends to increase the concentration of chl-a.…”