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Spatial-temporal variations in net primary productivity in the Arctic from 2003 to 2016
Haili Li, Changqing Ke, Qinghui Zhu, Su Shu
doi: 10.1007/s13131-018-1274-5
The area of Arctic sea ice has dramatically decreased, and the length of the open water season has increased; these patterns have been observed by satellite remote sensing since the 1970s. In this paper, we calculate the net primary productivity (NPP, calculated by carbon) from 2003 to 2016 based on sea ice concentration products, chlorophyll a (Chl a) concentration, photosynthetically active radiation (PAR), sea surface temperature (SST), and sunshine duration data. We then analyse the spatiotemporal changes in the Chl a concentration and NPP and further investigate the relations among NPP, the open water area, and the length of the open water season. The results indicate that (1) the Chl a concentration increased by 0.025 mg/m3 per year; (2) the NPP increased by 4.29 mg/(m2·d) per year, reaching a maximum of 525.74 mg/(m2·d) in 2016; and (3) the Arctic open water area increased by 57.23×103 km2/a, with a growth rate of 1.53 d/a for the length of the open water season. The annual NPP was significantly positively related to the open water area, the length of the open water season and the SST. The daily NPP was also found to have a lag correlation with the open water area, with a lag time of two months. With global warming, NPP has maintained an increasing trend, with the most significant increase occurring in the Kara Sea. In summary, this study provides a macroscopic understanding of the distribution of phytoplankton in the Arctic, which is valuable information for the evaluation and management of marine ecological environments.
key words: sea ice, open water area, chlorophyll a, net primary productivity, Arctic
Classification and 3-D distribution of upper layer water masses in the northern South China Sea
Jia Zhu, Quanan Zheng, Jianyu Hu, Hongyang Lin, Dewen Chen, Zhaozhang Chen, Zhenyu Sun, Liyan Li, Hao Kong
doi: 10.1007/s13131-019-1418-2
Using the fuzzy cluster analysis and the temperature-salinity (T-S) similarity number analysis of cruise conductivity-temperature-depth (CTD) data in the upper layer (0–300 m) of the northern South China Sea (NSCS), we classify the upper layer water of the NSCS into six water masses: diluted water (D), surface water (SS), the SCS subsurface water mass (US), the Pacific Ocean subsurface water mass (UP), surface-subsurface mixed water (SU) and subsurface-intermediate mixed water (UI). A new stacked stereogram is used to illustrate the water mass distribution, and to examine the source and the distribution of UP, combining with the sea surface height data and geostrophic current field. The results show that water mass UP exists in all four seasons with the maximum range in spring and the minimum range in summer. In spring and winter, the UP intrudes into the Luzon Strait and the southwest of Taiwan Island via the northern Luzon Strait in the form of nonlinear Rossby eddies, and forms a high temperature and high salinity zone east of the Dongsha Islands. In summer, the UP is sporadically distributed in the study area. In autumn, the UP is located in the upper 200 m layer east of Hainan Island.
key words: water mass classification, northern South China Sea, fuzzy cluster analysis, T-S similarity number

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