Geoscience Reference
In-Depth Information
CONCLUSION
The fluctuations in environmental parameters in the nSCS during 1976-2004 dis-
played different patterns, that is temperature (SST and T av ), salinity (S av and S 200 ),
DIN and N:P annual rates increased, while DO, P, Si, Si:N, SSS, and T 200 annual rates
decreased. The climate trend coefficients, R xt of these time series were all over 0.38
(n = 29) or 0.50 (n = 16), and highly significant (p ≤ 0.05), except for the time series
of P and Si.
The increasing trends in SST and T av were consistent with the rise of the mean
AT in the northern Hemisphere and southern China. The increase in SST and T av and
decrease in SSS in the nSCS led to strengthening of the thermocline and halocline,
less mixing of deep water to the surface and thus a decrease in the P supply from deep
waters. The increasing trend in DIN may have been infl uenced by the Pearl River
discharge, and atmospheric dry and wet deposition, (which are related to anthropo-
genic activities), coastal upwelling and cyclonic eddies. The nSCS always experienced
limitation of N before 1997, but the situation in the upper layer sea water has been
mitigated since 1998, due to the increase in N concentration and decrease in P, which
resulted in not only the positive trends in N:P ratios which are now close to the Red-
fi eld ratio, but also the decreasing trend in Si:N ratios, indicating of potential P limi-
tation. The decrease in DO concentration may be linked to the increase in seawater
temperature and the increase in the concentration of organic matter inputs mainly from
the Pearl River and phytoplankton blooms, particularly since the 1990s. Chlorophyll-
a, PP, PA, BB, CC, and DTC have increased, and zooplankton abundance decreased.
These ecosystem responses resulted from environmental changes were induced by not
only climate change, but also anthropogenic activities. After 1998, phosphorus deple-
tion in upper layer may be associated with a shift from diatoms to dinofl agellates and
cyanophytes domination.
Pronounced responses of the environmental parameters to ENSO were observed.
The effects of climate change on the nSCS were mainly through changes in monsoon
and its causative links, monsoon circulation nutrients PP.
It must be pointed out that although the data set we adopted in the present analysis
is large and from various sources. As such the quality of data might vary throughout
the long period of observation. But these data were valuable for studying the long term
changes in environmental conditions and the responses of the ecosystem in this region.
And using these data we can still fi nd and understand some regulations on the response
of the ecosystems to the environmental changes in the SCS. This regional response of
SCS to global climate change was investigated the fi rst which is far from well under-
stood. The evolving nutrient environment may be related to the observed ecosystem
changes in the nSCS such as increase in biological productivity. More long-time series
observations on the structure and function of ecosystems and the relationships with
environmental changes are needed in the SCS in the future.
 
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