Lina Cai, Ruohao Xin, Xiaomin Ye, Rong Tang, Jie Yin, Leichao Cheng. Remote sensing monitoring for impact of island on chlorophyll a in the water near the Diaoyu Island and its affiliated islands, China[J]. Acta Oceanologica Sinica. doi: 10.1007/s13131-024-2371-2
Citation:
Lina Cai, Ruohao Xin, Xiaomin Ye, Rong Tang, Jie Yin, Leichao Cheng. Remote sensing monitoring for impact of island on chlorophyll a in the water near the Diaoyu Island and its affiliated islands, China[J]. Acta Oceanologica Sinica. doi: 10.1007/s13131-024-2371-2
Lina Cai, Ruohao Xin, Xiaomin Ye, Rong Tang, Jie Yin, Leichao Cheng. Remote sensing monitoring for impact of island on chlorophyll a in the water near the Diaoyu Island and its affiliated islands, China[J]. Acta Oceanologica Sinica. doi: 10.1007/s13131-024-2371-2
Citation:
Lina Cai, Ruohao Xin, Xiaomin Ye, Rong Tang, Jie Yin, Leichao Cheng. Remote sensing monitoring for impact of island on chlorophyll a in the water near the Diaoyu Island and its affiliated islands, China[J]. Acta Oceanologica Sinica. doi: 10.1007/s13131-024-2371-2
Marine Science and Technology College, Zhejiang Ocean University, Zhoushan 316022, China
2.
National Satellite Ocean Application Service, Beijing 100081, China
Funds:
The Basic Public Welfare Research Program of Zhejiang Province under contract No. LGF21D010004; the Key R&D Projects in Zhejiang Province under contract No. 2023C03120.
The Diaoyu Island and its affiliated islands (DAA) have abundant fishery resources, and chlorophyll a (Chl a) concentration is an important marine color element and an important indicator of primary productivity in the ocean. Therefore, it is meaningful to understand the distribution and variation characteristics of Chl a concentration in the waters near the DAA. The distribution details of Chl a concentration in the adjacent waters of DAA were revealed by high-resolution satellite GF-1 Wide Field View (WFV) data with 16 m spatial resolution. This paper found that: (1) The Chl a concentration is between 0.06 and 0.38 μg/L throughout the year and the concentration of Chl a in the northeast and east directions of the island (downstream) is significantly higher than that in the west (upstream), and there are observed vortexes with high Chl a concentration in the downstream of DAA. This phenomenon continues to persist in the waters surrounding the DAA all year. (2) The vortex induced by the interaction between the current and island results in the vorticity change of water, inducing the replenishment of a large number of nutrients to the surface, thereby promoting the growth of plankton in the downstream of DAA on the east. In addition, the DAA also plays a significant role in regulating the downstream mix layer depth (MLD). The MLD in the northeast downstream is considerably deeper than the upstream in winter and spring; it is deeper in the east downstream in summer and autumn, and the range of influence for the MLD is greatly larger than the size of the island itself. This shows that the disruption of the DAA on the current is substantial. In addition, the combined effects of SST, and wind also play a significant role in modifying Chla. (3) Based on the analysis above, this paper proposes the conception of building fishing pastures downstream of the DAA, and proposes a general migration plan in different seasons to scientifically and rationally utilize and protect the surrounding waters of DAA.
Figure 1. Location map around the waters of the Diaoyu Island. a, b and c. The elevation maps of the surrounding larger-scale areas (a) and smaller-scale areas (b) and (c). The region circled by blue rectangle in (a) implies the (b) and (c) area. d. Topographic map of the area around DAA from a three-dimensional perspective, and the DAA circled by elliptical.
Figure 2. The distribution of climatology seasonal Chl a concentration from MODIS data in the sea around DAA. The location of the DAA is marked by a black circle.
Figure 3. The seasonal distribution and concentration of Chl a in the DAA sea from 2014 to 2021. The column from top to bottom represents spring, summer, autumn, and winter. The real line in the figure represents the isoline of the corresponding value. The location of the general study area is shown in the last subplot by red rectangle. The location of the DAA is marked by a black circle.
Figure 4. High-resolution Chl a concentration around the DAA obtained from the GF-1 Black patch: DAA. The color and labels on the color bar represent the qualitative description of Chl a concentration in a specific time and space range of the image display, indicating only the relative change degree of Chl a concentration. R-low represents relatively low and R-high relatively high. The solid elliptical area marks the IME area, and the dotted elliptical area marked the low values area in the front of DAA. U represents upstream, D downstream, and arrow the direction of the current.
Figure 5. The seasonal average distribution map of SST from 2002 to 2022 at 24°-28°N (a, the black ellipse area is the sea around DAA) and the annual average temperature distribution of the DAA from 2015 to 2020 (b, the black ellipse area is the sea around DAA).
Figure 6. The current of DAA. The left panel shows the flow field at a depth of 0.5 m below the sea surface. The middle panel shows the flow field at a depth of 34.5 m below the sea surface. The right panel shows the flow field at a depth of 55.8 m below the sea surface. Every column from top to bottom is the average data for January, April, July, and October, representing winter, spring, summer, and autumn respectively. The DAA is located at the solid ellipse mark in the figure. Red arrow means the direction of current.
Figure 7. The DAA’s monthly average wind field intensity and direction distribution in 2021. The DAA is located at the solid ellipse mark in the figure.
Figure 8. The MLD contribution map of the DAA sea. Upper four rows represent the monthly average MLD data of the from a to l, and the lower graph (m) shows the corresponding water depth map in the same geographic extent. The location of the DAA on the map is marked by solid ellipses.
DownLoad:
