Geoscience Reference
In-Depth Information
n
∑
x
i
−
x
(
)
()
x
i
−
x
i
−
t
R
xt
=
i
=
1
(2)
n
∑
n
∑
(
)
2
()
2
i
−
t
i
=
1
i
=
1
where t = (n + 1)/2. Its signifi cance level is determined from the Student t-test. A
positive/negative value of R
xt
indicates that the time series, {X
i
}, has a linear positive/
negative trend. In order to compare the environmental change rates between coastal/
shelf waters with the slope/open sea, data for water depths <200 and >200 m, respec-
tively, were analyzed.
Biological oceanography data, such as chlorophyll-a, PA, PP, zooplankton bio-
mass (ZB), benthos biomass (BB), CC, etc. were obtained during the period by marine
ecosystem surveys conducted by the South China Sea Fisheries Research Institute
(SCSFRI), the SCS Institute of Oceanography, Chinese Academy of Sciences and the
Second Institute of Oceanography, SOA. For the observational methods, Chl-a was
determined by acetone extraction fl uorescence method (Holm-Hansen et al., 1965)
and often calibrated by spectrophotometry. Primary productivity was measured us-
ing the 14C tracer method established by Steemann-Nielsen (1952) and modifi ed for
scintillation counting by Wolfe and Schelske (1967). Phytoplankton samples were col-
lected by vertical haul using a Judy net with a mesh size of 76 μm. The samples were
preserved with Lugol's solution, and the species identifi cation and cell counts were
made using a microscope to get PA (Sournia, 1978). Zooplankton samples were col-
lected by vertical haul using plankton net with a mesh size of 505 μm, and the samples
were preserved with neutral formaldehyde solution (5%). The species identifi cation
and individual counts were made using a stereo microscope, and the wet weight bio-
mass (ZB) was measured by an electronic balance after removing the body surface
water in the lab, according to SOAC (1975) and NBTS (1991). Benthic macrofauna
samples were collected by using a grab with a sampling area of 0.1 m
2
, and the ani-
mals were sorted after removing the mud by elutriation. The species identifi cation and
individual counts were made using a stereo microscope, and the wet weight biomass
(BB) was measured gravimetrically after removing the body surface water in the lab
(NBTS, 1991; SOAC, 1975). The nekton samples were collected by using a cystoids
net with a mesh size of 20 mm, towed by a pair of boats at a speed of 3-4 km for 1 hr
at each station (NBTS, 1991; SOAC, 1975).
DISCUSSION
Increasing Trends and the Response of the Ecosystem
The positive increasing trends in SST and T
av
in the nSCS during 1976-2004 are con-
sistent with the increasing trends in the mean air temperature (AT) observed through-
out the Northern Hemisphere (Fu et al., 2006; Houghton et al., 1996), South China
(Chen et al., 1998, 1999; Zhai and Ren, 1997) and the annual means of AT and SST
observed along the coast of the SCS (He et al., 2003; Martin and Arun, 2003). The
increasing trends were also in phase with the changes in SST observed along the coast
of the Yellow Sea and Bohai Sea (Lin et al., 2001, 2005). However, these annual rates
