Xuan Lu, Qibin Lao, Fajin Chen, Guangzhe Jin, Chunqing Chen, Qingmei Zhu. The impact of typhoons on the biogeochemistry of dissolved organic matter in eutrophic bays in northwestern South China Sea[J]. Acta Oceanologica Sinica. doi: 10.1007/s13131-023-2283-6
Citation:
Xuan Lu, Qibin Lao, Fajin Chen, Guangzhe Jin, Chunqing Chen, Qingmei Zhu. The impact of typhoons on the biogeochemistry of dissolved organic matter in eutrophic bays in northwestern South China Sea[J]. Acta Oceanologica Sinica. doi: 10.1007/s13131-023-2283-6
Xuan Lu, Qibin Lao, Fajin Chen, Guangzhe Jin, Chunqing Chen, Qingmei Zhu. The impact of typhoons on the biogeochemistry of dissolved organic matter in eutrophic bays in northwestern South China Sea[J]. Acta Oceanologica Sinica. doi: 10.1007/s13131-023-2283-6
Citation:
Xuan Lu, Qibin Lao, Fajin Chen, Guangzhe Jin, Chunqing Chen, Qingmei Zhu. The impact of typhoons on the biogeochemistry of dissolved organic matter in eutrophic bays in northwestern South China Sea[J]. Acta Oceanologica Sinica. doi: 10.1007/s13131-023-2283-6
College of Ocean and Meteorology, Guangdong Ocean University, Zhanjiang 524088, China
2.
Polar and Marine Research Institute, College of Harbor and Coastal Engineering, Jimei University, Xiamen, 361021, China
3.
Key Laboratory for Coastal Ocean Variation and Disaster Prediction, Guangdong Ocean University, Zhanjiang 524088, China
4.
Key Laboratory of Climate, Resources and Environment in Continental Shelf Sea and Deep Sea of Department of Education of Guangdong Province, Guangdong Ocean University, Zhanjiang 524088, China
Highly productive estuaries facilitate intense decomposition of dissolved organic matter (DOM) as a carbon source. However, the specific impacts of typhoons on DOM decomposition in eutrophic bays remain unclear. To address this issue, we investigated the spectral characteristics of DOM before and after Typhoon “Ewiniar” in Zhanjiang Bay, a eutrophic semi-enclosed bay in the northwestern South China Sea. The results revealed that intense microbial decomposition of DOM occurred during the pre-typhoon period because high nutrient inputs facilitated the mobilization of DOM in the bay. However, the intrusion of external seawater induced by the typhoon diluted the nutrient levels in Zhanjiang Bay, reducing the impact of microbial decomposition on DOM during the post-typhoon period. Nevertheless, the net addition of DOM occurred in Zhanjiang Bay during the post-typhoon period, possibly because of the decomposition of particulate organic matter (POM) and desorption of particulate matter. In addition, an increase in apparent oxygen utilization, a decrease in DO saturation and the reduced level of Chl a indicated that organic matter (OM) decomposition was enhanced and OM decomposition shifted to POM decomposition in Zhanjiang Bay after the typhoon. Overall, our study highlighted the shift in the intense OM decomposition from DOM to POM decomposition before and after typhoons in eutrophic bays, providing new insights into the response of typhoons to biogeochemistry.
Figure 1. Map of the passage and intensity (wind speed) of Typhoon Ewiniar, and the sampling stations in Zhanjiang Bay, northwestern South China Sea, during the pre- and post-typhoon periods.
Figure 2. The rainfall and wind-stress during the typhoon Ewiniar. (a) and (b) are accumulated rainfall before (May 01-14) and during and after (June 07–20) typhoon passage (https://disc.gsfc.nasa.gov/datasets/TRMM_3B42_Daily_7/summary). (c) is the numerical model results and (d) is the satellite observations. The daily data of numerical models are obtained from Global Ocean Hourly Reprocessed Sea Surface Wind and Stress from Scatterometer and Model (https://data.marine.copernicus.eu/product/WIND_GLO_PHY_L4_MY_012_006/ description). The daily data of satellite observations are obtained from Global Ocean Daily Gridded Sea Surface Winds from Scatterometer (https://data.marine.copernicus.eu/product/WIND_GLO_WIND_L3_NRT_OBSERVATIONS_012_002/description).
Figure 3. Surface distribution of temperature, salinity, DO, DO%, and AOU in the Zhanjiang Bay during pre- and post-typhoon periods.
Figure 4. Surface distribution of Chl a, DIN (NH4++ NO2−+ NO3−), PO43−, and SiO32− in the Zhanjiang Bay during pre- and post-typhoon periods.
Figure 5. Surface distribution of a254, a325, and S275-295in the Zhanjiang Bay during pre- and post-typhoon periods.
Figure 6. Surface and bottom distribution of C1, C2, C3, HIX, BIX and FI in the Zhanjiang Bay during pre- and post-typhoon periods.
Figure 7. Variations of a254 (m−1) (a, b), a325 (m−1) (c, d), C1 (10−2 RU) (e, f), C2 (10−2 RU) (g, h), C3 (10 −2 RU) (i, j) along with salinity in the water of Zhanjiang Bay during the pre-typhoon and post-typhoon. The red stars denote the low-salinity and high-salinity end-members used in this study.
Figure 8. Transect distribution of S275-295, Δa254, Δa325, ΔC1, ΔC2, and ΔC3 in the Zhanjiang Bay during pre- and post-typhoon periods.
Figure 9. Simplified schematic sketch summarizing the decomposition of OM in Zhanjiang Bay, northwestern South China Sea, during the pre- and post-typhoon periods.
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