A ten-year time series from Monterey Bay,
California: Seasonal, interannual and long-term patterns
I N T E R A N N U A L V A R I A B I L I T Y
4. Anomalies from the mean annual cycle for upwelling index, winds and currents, SST,
temperature at 60 m, sea surface salinity, sigma-t, surface nitrate, nitrate at 60 m,
surface chlorophyll, integrated primary production, centric diatoms, pennate diatoms,
dinoflagellates, and small phytoplankton (less than 5 ĩm).
Winds and Currents
The El Niņo signal is not clearly represented in the wind and current
records. In general there are weaker upwelling indices and weaker northwesterly winds
during the 1992-93 and 1997-98 El Niņo but there are non-El Niņo years, like 1995, that
display similar, if not stronger anomalies (Fig 4). During the 1992-93 El Niņo there is
an indication of increased equatorward flow throughout the water but that same signal is
not as clearly represented during 1997-98, if at all (Fig 4).
Temperature and salinity
The El Niņo signal in SST is evident (Fig 4). The magnitude of the
anomalies is about a °C warmer for the 1997-98 El Niņo than the 1992-93 El Niņo. The
positive anomalies lasted longer for the 1992-93 El Niņo but the 1997-98 El Niņo had a
broader peak of anomalies >0.5°C that lasted from mid-1997 to mid-1998. The magnitude
of the subsurface anomalies was much larger for 1997-98 when compared to 1992-93 (Fig 4).
The interannual signal in salinity is not as clear. There is a clear freshening during
1992-93; during 1997 but was strong during 1998. 1995 was also a fresh year (Fig 4).
The interannual variability in nitrate is very similar to temperature.
There are substantial negative nitrate anomalies during El Niņo and the strongest
anomalies are observed during 1997-98 (Fig 4).
Chlorophyll and primary production
Primary production and chlorophyll are reduced during the El Niņo
years of 1992-93 and 1997-98. There are differences between the onset of the effects on
chlorophyll and primary production (Fig 4). The SeaWiFS imagery collected during 1998
shows that a narrow near-coastal band of high chlorophyll water is maintained during the
El Niņo months of January-May. As El Niņo waned the area of high chlorophyll broadened
in the fall (Fig 6).
Phytoplankton taxonomic groups
Centric diatoms are the phytoplankton that seem most affected by El
Niņo. None of the groups presented seems favored during El Niņo. Dinoflagellates were
favored during 1995 when winds were light and waters stratified but nitrate levels were
not as low as during El Niņo (Fig 4).
Next: Long-term Trends