Title
Tracing external sources of nutrients in the East China Sea and evaluating theircontributions to primary production

Members’ names and affiliations
NameInstitution
Departmentand Employmentposition

College of Oceanic
Shizuo FengandAtmospheric Professor

Sciences,

Ocean

University of China
Faculty member of Professor
Xinyu Guo

LaMer

Aim
The research aims to apply the new tracking technique to the multi-source nutrientsin the East China Sea (ECS), evaluate their roles in the primary productions over thecontinental shelf of the ECS and explore the corresponding dynamic mechanism.

Procedure
The technique has been applied into the physical-biological coupled model for theECS. The model domain is shown in Fig. 1 and the area of interest in this study is thecontinental shelf of the ECS is indicated by dark blue. We first analyzed the distribution
characteristics and the seasonal variations of the nutrients and primary production in theECS; then found the dynamic mechanism for the distribution of nutrients from different
sources; finally evaluated the contribution of each source of nutrients to the nutrient
inventory and primary production over the ECS shelf.

Fig. 1 Bathymetric map of the East China Sea. The study area of interest is shaded indark blue. Contour lines in black represent the 50-m, 100-m, and 200-m isobaths. The1 / 4

blue dots denote the positions of inflow from rivers. The blue line shows the position oftwo sections.

ResultUsing the physical-biological coupled model and a tracking module, we
examined the distributions of DIN with different origins and the corresponding primary
production in four seasons over the ECS, and evaluated the roles of DIN with different
origins in primary production in the inner, middle, outer and entire shelves of the ECS.
Both physical and biological processes affect the distributions of nutrients with different
origins. Physical processes regulate the distribution of the nutrients, mainly throughtransport and mixing. For example, the dominant areas of each source nutrient in theinventory of nutrients generally follow distributions of the water masses. On the otherhand, biological processes likely contribute to change the concentrations of nutrients
locally, which rely closely on local temperature and light intensity. This appears as
different distributions of DIN from the same source, which are determined only bybiological processes.
The DIN from rivers (DINR), the atmosphere (DINA), the Kuroshio (DINK), andthe Taiwan Strait (DINT) play different roles in different areas (Table. 1). In the innershelf, the DINR (mainly the Changjiang) shares more than half of DIN inventory andsupports more than half of primary production. The DINA is the secondary source(>20%) while those from the Kuroshio and Taiwan Strait both share only ~10% of DIN
inventory and support ~10% of primary production in the inner shelf. In the middle
shelf, the DINK shares ~40% of DIN inventory and supports ~40% of primaryproduction. The DINT and DINA have a similar ratio (~20%) in the DIN inventory andprimary production and the DINR share the residual 10% in both DIN inventory andprimary production in the middle shelf. In the outer shelf, the DINK shares >90% ofDIN inventory and supports ~80% of primary production. Therefore, the Kuroshio is adominant source for the nutrients inventory and primary production.
Considering the ECS as a whole, DINK are the largest contributor in the nutrient
inventory and primary production. The DIN from the Taiwan Strait, rivers andatmosphere shares equal contributions in nutrient inventory and primary production.
Primary production supported by each source is a direct criterion, while neither input
flux nor inventory of nutrient is a good index to represent the contribution of nutrientsfrom different sources to primary production. The production efficiency of each sourceof DIN is a way to understand the relation among these evaluation methods. The
Kuroshio shows a leading role in input flux, nutrient inventory, and primary production,
but its DIN has low production efficiency because a large amount of them distribute
below the euphotic layer. The DINR has a dominant role in coastal area, but its
production efficiency is also low due to local limitations of DIP and high turbidity. TheDINT is efficient but has no advantage in terms of input flux, inventory of nutrient, or2 / 4

primary production. The DINA from atmosphere are also efficient because they enter thesea from the surface.
Table 1. Inventory (TN, 107 kmol), primary production (N-IPP, kmol s-1), andproduction efficiency (EPC) of DIN from rivers, the Kuroshio, the Taiwan Strait and theatmosphere. Production efficiency is defined as the ratio of N-IPP to TN. The ‘Total’column shows the situation of the total DIN, sum of the DIN with different sources. The
numbers in parentheses are the corresponding percentages.
RiversKuroshio

TaiwanStraitAtmosphereTotal

2.5 (58%)

0.4 (9%)0.4 (9%)1.0 (23%)

4.3

4.1 (56%)

0.8 (11%)0.8 (11%)

1.6 (22%)

7.3

1/71

1/58

1/58

1/72

1/68

TN

0.9 (12%)3.1 (42%)1.6 (22%)

1.7 (23%)

7.3

N-IPP1.7 (11%)

5.8 (38%)

4.4 (29%)

3.5 (23%)

15.4

EPC

1/61

1/62

1/42

1/56

1/55

TN

0.1 (0.6%)

8.1 (92%)

0.4 (5%)0.3 (3%)

8.9

N-IPP

0.2 (1%)13.5 (78%)

1.6 (9%)1.9 (11%)

17.2

EPC

1/29

1/69

1/29

1/18

1/60

TN

3.5 (17%)

11.6 (57%)

2.4 (12%)3.0 (15%)

20.5

N-IPP

6.0 (15%)

20.1 (50%)

6.8 (17%)7.0 (18%)

39.9

EPC

1/67

1/67

1/41

1/50

1/59

TN
7Inner shelf(0-50 m)(10 kmol)
N-IPP(kmol s-1)
EPC
(day-1)

Middle shelf(50-100 m)

Outer shelf(100-200 m)

The
entire shelf(0-200 m)

Publication/conference presentation
Zhang, J., Guo, X., Zhao, L. Tracing external sources of nutrients in the East China Sea
and evaluating their contributions to primary production. Progress in Oceanography, in
2nd revision.

Perspectives in future
The production efficiency was proposed to evaluate the roles of DIN from different
sources in primary production over the ECS. But the influence factors for thespatiotemporal variations of production efficiency need further examinations. The
primary production consists of two parts: new production and regenerated production. It

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is assumed that DIN with more regeneration times is more efficient. So, we are planning
to apply this tracing model to separate the new and regenerated DIN.

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