Geoscience Reference
In-Depth Information
the northwestern to southeastern), maintained by the survey team of the State Oceanic
Administration (SOA), China during 1976-2004. These data include physical (seawater
temperature (T) and salinity (S)) and chemical parameters (DO), phosphate (PO
4
-P),
silicate (SiO
3
-Si), DIN (including NO
3
-N, NO
2
-N and NH
4
-N)). The parameters of T,
S, and DO data collection started from 1976; and the nutrients data (PO
4
-P, SiO
3
-Si,
NO
3
-N, NO
2
-N, and NH
4
-N) collection started from 1989. Seawater samples were
collected using Nansen bottles from the surface, 5, 10, 15, 20, 25, 30, 35, 50, 75, 100,
150, and 200 m for T and S, and at the surface, 10, 20, 30, 50, 75, 100, 150, and 200
m for biogenic element determination. Seawater temperature was measured by using
a reversing thermometer attached to the Nansen bottle, and salinity was measured
using induction salinometer, according to SOAC (1975) and NBTS (1991). Nutrients
(nitrate, phosphate, and silicate) were analyzed by standard spectrophotometric method,
and DO was analyzed by the Winkler method (Strickland and Parsons, 1972). Photo-
synthetic pigments (Chl-
a
) were measured by the acetone extraction and fluorescence
method (Holm-Hansen et al., 1965).
Annual mean values were the average for winter and summer which were derived
from observations during February and August, respectively. The regional average
was the average value for the all stations illustrated in Figure 1. First, we took the
values at the sea surface (SS), the depth of 200 m and the average through the water
column for 0-200 m (integrated) for each parameter for each station, since at the depth
of 200 m concentrations of biogenic elements and other properties were relatively
stable and much less infl uenced by the upper layers. Second, the regional means for
each parameter on an annual scale were calculated. The average value for the water
column was computed, according to the following equation:
1
b
b
()
dz
(1)
∫
X
av
=
Xz
0
Where
X
is an environmental parameter; b is the water depth (200 m, or 2 m above
bottom if the water depth is shallower than 200 m) and z is the observation depth. In
order to show the interannual changes in environmental parameters in the nSCS, the
time series of various parameters was determined. The parameters include physical
parameters, such as SST, T
av
, T
200
m, SSS, S
av
, S
200
, and chemical parameters, such as
SSDO, DO
av
, DO
200
, SSP, P
av
, P
200
, SSSi, Si
av
, Si
200
, SSDIN, DIN
av
, DIN
200
, SSNO
2
-N,
NO
2
N
av
, NO
2
-N
200
, SSNO
3
-N, NO
3
-N
av
, NO
3
-N
200
, SSNH
4
N, NH
4
-N
av
, NH
4
-N
200
, and
the ratios of the chemical parameters SSN:SSP, N
av
:P
av
, N
200
:P
200
, SSSi:SSN, Si
av
:N
av
,
Si
200
:N
200
, where av = average for the whole water column and 200 = 200 m depth.
Statistical test and linear regression analyses were conducted on time series (Chen
and Ma, 1991) and climate trend coeffi cients (R
xt
) were estimated. The R
xt
was used
to assess whether there was a signifi cant linear climate-trend in a time series (Shi et
al., 1995). This coeffi cient was defi ned as the correlation coeffi cient between the time
series of an environmental parameter, {X
i
}, and the nature number {i}, i = 1, 2, 3..., n.
In this study, n is the total span of the years covered by the data. The coeffi cient was
computed from the following equation:
