Long term changes in the ecosystem in the northern South China Sea during 1976–2004
Other literature type
Physical and chemical oceanographic data were obtained by
seasonal monitoring along a transect (Transect N) in the northern South
China Sea (nSCS) during 1976–2004. Fluctuations of DIN (dissolved inorganic
nitrogen), seawater temperature (SST and <I>T<sub>av</sub></I> – average temperature of
the water column), N:P ratio and salinity (<I>S<sub>av</sub></I> and <I>S</I><sub>200</sub> – salinity
at the 200 m layer) exhibited an increasing trend, while those of <I>T</I><sub>200</sub>,
DO, P, Si, Si:N and SSS exhibited a decreasing trend. The annual rates of
change in DIN, DO, T and S revealed pronounced changes, and the climate
trend coefficients, which was defined as the correlation coefficient
between the time series of an environmental parameter and the nature number
(namely 1,2,3,......<I>n</I>), were 0.38 to 0.89 and significant
(<I>p</I>≤0.01 to 0.05). Our results also
showed that the ecosystem has obviously been influenced by the positive
trends of both SST and DIN, and negative trends of both DO and P. For
example, before 1997, DIN concentrations in the upper layer were very low
and N:P ratios were less than half of the Redfield ratio of 16, indicating
potential N limitation. However after 1997, all Si:P ratios were >22 and
the N<sub><I>av</I></sub>:P<sub><I>av</I></sub> was close to the Redfield ratio, indicating potential
P limitation, and therefore N limitation has been reduced after 1997.
Ecological investigation shows that there have been some obvious responses
of the ecosystems to the long-term environmental changes in the nSCS.
Chlorophyll-<I>a</I> concentration, primary production, phytoplankton abundance,
benthic biomass, cephalopod catch and demersal trawl catch have increased.
But phosphorus depletion in upper layer may be related to the shift in the
dominant species from diatoms to dinoflagellates and cyanophytes. The
ecosystem response was induced by not only anthropogenic activities, but
also global climate change, e.g. ENSO. The effects of climate change on the
nSCS were mainly through changes in the monsoon winds, and
physical-biological oceanography coupling processes.
In this study physical-chemical parameters were systemic maintained, but the
contemporaneous biological data were collected from various sources.
Regional response to global climate change is clearly a complicated issue,
which is far from well understood. This study was made an attempt to tackle
this important issue. For the aim these data were valuable.