Figure 8 Contour plots of
monthly phytoplankton
colour during 1948—1995
for the Central North Sea,
central northeast Atlantic
and northern northeast
Atlantic.
(Figure 8). Zooplankton abundance also increased (lagged 1 year), as did horse
mackerel catches (lagged two years) (Figure 9). It is now believed that these are
indicators of a major regime shift that affected the North Atlantic around 1988.
Alterations in the centre of deep water convection from the Greenland Sea to the
Labrador Sea after 1988, and increases in the flow of oceanic water into the
North Sea through the Shelf Edge Current appear to be the main drivers for
these changes. A similar shift may have also been observed after 1996, extending
further north the habitat of tropical fish species west of Europe. It is unclear
whether these shifts are indicative of long-term global change or short-term
stochastic variability, but indicate the potential for specific atmospheric physical
forcings to dramatically influence the structure and productivity of the North
Atlantic ecosystem.
Non-linear responses to physical forcing have also been observed in this
region. For example, the NAO index and the abundance of the copepod Calanus
finmarchicus in the North East Atlantic were negatively correlated from 1958 to
1995, although positively correlated in the Northwest Atlantic. When the
NAO reversed to negative values in 1996—97, the abundance of C. finmarchicus in
the Northeast Atlantic remained low (Figure 10) and is yet to recover. It is now
believed that the reversal of the NAO did not result in any immediate increase in
the supply of Norwegian Sea Deep Water (NSDW) to the Faroe—Shetland
channel bottom water. In consequence, the supply of copepods has remained at a
low level, despite the more favourable climatic conditions. It has been postulated
that it would take several years of persistent deep convection in the Greenland
J.-C. Quero, M. H. Du Buit and J. J. Vayne, Oceanol. Acta, 1998, 21, 345—351.
J. M. Fromentin and B. Planque, Mar. Ecol. Prog. Ser., 1996, 134, 111—118.
B. Planque and P. C. Reid, J. Mar. Biol. Assoc. UK, 1998, 78, 1015—1018.
M. Barange
68
monthly phytoplankton
colour during 1948—1995
for the Central North Sea,
central northeast Atlantic
and northern northeast
Atlantic.
(Figure 8). Zooplankton abundance also increased (lagged 1 year), as did horse
mackerel catches (lagged two years) (Figure 9). It is now believed that these are
indicators of a major regime shift that affected the North Atlantic around 1988.
Alterations in the centre of deep water convection from the Greenland Sea to the
Labrador Sea after 1988, and increases in the flow of oceanic water into the
North Sea through the Shelf Edge Current appear to be the main drivers for
these changes. A similar shift may have also been observed after 1996, extending
further north the habitat of tropical fish species west of Europe. It is unclear
whether these shifts are indicative of long-term global change or short-term
stochastic variability, but indicate the potential for specific atmospheric physical
forcings to dramatically influence the structure and productivity of the North
Atlantic ecosystem.
Non-linear responses to physical forcing have also been observed in this
region. For example, the NAO index and the abundance of the copepod Calanus
finmarchicus in the North East Atlantic were negatively correlated from 1958 to
1995, although positively correlated in the Northwest Atlantic. When the
NAO reversed to negative values in 1996—97, the abundance of C. finmarchicus in
the Northeast Atlantic remained low (Figure 10) and is yet to recover. It is now
believed that the reversal of the NAO did not result in any immediate increase in
the supply of Norwegian Sea Deep Water (NSDW) to the Faroe—Shetland
channel bottom water. In consequence, the supply of copepods has remained at a
low level, despite the more favourable climatic conditions. It has been postulated
that it would take several years of persistent deep convection in the Greenland
J.-C. Quero, M. H. Du Buit and J. J. Vayne, Oceanol. Acta, 1998, 21, 345—351.
J. M. Fromentin and B. Planque, Mar. Ecol. Prog. Ser., 1996, 134, 111—118.
B. Planque and P. C. Reid, J. Mar. Biol. Assoc. UK, 1998, 78, 1015—1018.
M. Barange
68