Geoscience Reference
In-Depth Information
Chapter 11
X. Ning, C. Lin, Q. Hao, C. Liu, F. Le, and J. Shi
INTRODUCTION
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 dissolved inorganic nitrogen (DIN), seawater temperature (SST and
T
av
-average temperature of the water column), N:P ratio and salinity (S
av
and S
200
--
alinity at the 200 m layer) exhibited an increasing trend, while those of T
200
, dissolved
oxygen (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, . . . . . .n), were
0.38-0.89 and significant (p ≤ 0.01-0.05). Our results also showed that the ecosystem
has obviously been influenced by the positive trends of both sea surface temperature
(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
av
:P
av
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-a con-
centration, primary production (PP), phytoplankton abundance (PA), benthic biomass,
cephalopod catch (CC), and demersal trawl catch (DTC) have increased. But phospho-
rus depletion in upper layer may be related to the shift in the dominant species from
diatoms to dinofl agellates and cyanophytes. The ecosystem response was induced by
not only anthropogenic activities, but also global climate change, for example ENSO.
The effects of climate change on the nSCS were mainly through changes in the mon-
soon winds, and physical-biological oceanography coupling processes.
In this study physical-chemical parameters were systemic maintained, but the con-
temporaneous biological data were collected from various sources. Regional response
to global climate change is clearly a complicated issue, which is far from well under-
stood. This study was made an attempt to tackle this important issue. For the aim these
data were valuable.
The South China Sea (SCS) is the largest semi-enclosed marginal sea in Southeast
Asia with an area of about 3.5 × 10
6
km
2
. Our study area is the nSCS, bounded by the
mainland of China on the north and northwest sides, Taiwan Strait on the northeast,
Taiwan Island and Bashi Strait on the east side, and the Hainan Island on the west
