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In this study, we analysed the interannual variability of sea surface temperature (SST), sea surface wind (SSW), and sea level anomaly (SLA) in the South China Sea (SCS) during 1985–2016 using monthly reanalysis and satellite datasets. An empirical orthogonal function (EOF) analysis was performed to evaluate the interannual variability of each variable. The warming rate of SST was 0.18 ± 0.26°C decade−1 in the SCS. The first EOF of SST was characterized by basin-wide warming, with the highest anomalies in the northern deep basin. The first temporal coefficient of SST was negatively correlated with the Niño 3.4 index, with a lag of 6 mo. The mean rising rate of SLA was 7.6 cm decade−1, with the greatest trend in the coastal water of Vietnam, which exhibited a similar spatial pattern with the first EOF of SLA. The temporal coefficient of SLA was negatively correlated with that of SST, with a lag of 5 mo. The trend of SSW was around 0.8 m s−1 decade−1 over the SCS. The first EOF of SSW was characterized by an anticyclonic pattern. The temporal coefficient was correlated with that of SST, with a lead of 2 mo. Wavelet coherence was used to investigate the cross-correlation relationship between SST and other variables. SST and SLA had a strong negative correlation in the 8–16-mo (1–1.5 yr) band. The high positive wavelet coherencies between SST and SSW and Niño 3.4 were mainly in the 32–64 mo (3–5 yr) band in the SCS. [ABSTRACT FROM AUTHOR]

A time series of satellite data on Chlorophyll-a concentration (Chl-a) that used ocean color was studied to determine mechanisms of phytoplankton variation in recent decade in the Yellow Sea, China during 2003–2015. The variability patterns on seasonal and inter-annual oscillation periods were confirmed using the Empirical Orthogonal Function (EOF), and Morlet wavelet transform analyses, respectively. The first EOF mode for Chl-a was dominated by obvious spring and fall blooms in a spatial pattern that was related to the strong mixing of the water masses from the Yellow Sea Cold Warm Mass (YSCWM) and the Yellow Sea Warm Current (YSWC) in winter. The second EOF mode for Chl-a showed an opposite spatial pattern between the northern and southern regions. The temporal coefficient showed differences in the timing of blooms. On an inter-annual scale, Chl-a indicated variation at periods of 2–4 years during 2003–2015. Chl-a showed a significantly negative correlation with the sea surface temperature (r = -0.21, p<0.01), with time lags of 4 months (Chl-a ahead). Chl-a was coupled with El Niño Southern Oscillation (ENSO) events, with a positive correlation (r = 0.46, p<0.01) at a lag of 3–5 months (ENSO ahead). The present study demonstrated that the variation in phytoplankton biomass was controlled primarily by water mass seasonally, and it was influenced by ENSO events on an inter-annual scale. [ABSTRACT FROM AUTHOR]

The impact of tropical cyclones (TCs) on the CO2 partial pressure at the sea surface (pCO2sea) and air‐sea CO2 flux (FCO2) in the Bay of Bengal (BoB) was quantified based on satellite data and in situ observations between November 2013 and January 2017. The in situ observations were made at the BoB Ocean Acidification mooring buoy. A weak time‐mean net source of 55.78 ± 11.16 mmol CO2 m−2 year−1 at the BoB Ocean Acidification site was estimated during this period. A wide range in increases of pCO2sea (1.0–14.8 μatm) induced by TCs occurred in postmonsoon (October–December), and large decreases of pCO2sea (−14.0 μatm) occurred in premonsoon (March–May). Large vertical differences in the ratio of dissolved inorganic carbon (DIC) to total alkalinity (TA) in the upper layer (ΔDIC/TA) were responsible for increasing pCO2sea in postmonsoon. Relatively small values of ΔDIC/TA were responsible for decreasing pCO2sea in premonsoon. Five TCs (Hudhud, Five, Kyant, Vardah, and Roanu) were considered. Hudhud significantly enhanced CO2 efflux (18.49 ± 3.70 mmol CO2/m2) in oversaturated areas due to the wind effect during the storm and wind‐pump effects after the storm. Vardah insignificantly changed FCO2 (1.22 ± 0.24 mmol CO2/m2) in undersaturated areas because of the counteraction of these two effects. Roanu significantly enhanced CO2 efflux (19.08 ± 3.82 mmol CO2/m2) in highly oversaturated conditions (ΔpCO2 > 20 μatm) since the wind effect greatly exceeded the wind‐pump effects. These five TCs were estimated to account for 55 ± 23% of the annual‐mean CO2 annual efflux, suggesting that TCs have significant impacts on the carbon cycle in the BoB. Plain Language Summary: We examined the impact by five tropical cyclones on the sea surface pCO2 and air‐sea CO2 exchange using Bay of Bengal Ocean Acidification moored buoy measurements over the Bay of Bengal. To our knowledge, this is the first study on the different effects of tropical cyclones and vertical differences in the ratio of dissolved inorganic carbon to total alkalinity in the upper layer on the sea surface pCO2 and local air‐sea CO2 flux. Key Points: TCs tended to increase the pCO2sea in the postmonsoon and to decrease the pCO2sea in the premonsoon in the Bay of BengalLarge vertical differences in the ratio of DIC to TA in the upper layer were responsible for increasing pCO2sea induced by TCsTCs were estimated to account for 55 ± 23% of the annual‐mean CO2 annual efflux [ABSTRACT FROM AUTHOR]

This study investigates the processes of occasional sea surface temperature (SST) fronts and their impacts on chlorophyll-a concentration (chl-a) in the South China Sea (SCS), based on satellite remote sensing and in situ observations in 2009-2013. The SST fronts were detected by an entropy-based edge detection algorithm method from satellite-derived SST images with a 0.011° grid size. Three offshore SST front case studies (S1, S2 and S3) at the peripheries of eddies in the northern SCS were studied. In case S1 in September 2013, two SST fronts were detected with gradient magnitudes (GMs) greater than 0.06°C km-1 in the cyclonic eddy and 0.08°C km-1 in the periphery waters, and the fronts only existed for one and two days, respectively. After three and seven days, the high chl-a was found in the strong SST front waters which were about 51 and 54% higher than the concentration in the surrounding waters. The depth of the maximum chl-a elevated from the subsurface (50 m) to the surface. In case S2 in August 2013, two SST fronts were detected at the periphery of an anti-cyclonic eddy with GM stronger than 0.06°C km-1 and only existed for one day. After two days, the chl-a in the SST front waters was about 40% higher than the levels in the surrounding waters. In case S3 in June 2009, the GM of the eddy-feature SST front was stronger than 0.12°C km-1 and existed for three days, which was generated by tropical cyclone Linfa. The chl-a in the eddy-feature phytoplankton bloom was 6 times higher than in the surrounding waters. The results show that, in general, occasional offshore SST fronts at peripheries of eddies have stronger influence on surface chl-a, comparing to those seasonal coastal and permanent offshore SST fronts, via ‘Wind Pump’ effects. [ABSTRACT FROM AUTHOR]

A massive bloom of green macroalgaeUlva proliferaoccurred in June 2008 in the Yellow Sea, resulting in perhaps the largest “green tide” event in the history of bloom research. The covered area is about 1,200 km2and the impacted area reached 40,000 km2on 31 May. This also occurred in the following two years, 2009 and 2010. We analyzed the satellite data from MODIS and the results showed that sea surface temperature increased 1–3°C inU. proliferabloom locations. The macroalgae in the water may have been the cause of the increase of sea surface temperatures. Rapid increases ofU. proliferabiomass during the blooms may have increased radiation absorption of the water, and thus enhanced the rate of heating at the sea surface. The present study represents a preliminary observation, which is an important step for understanding influences of macroalgae on ocean surface conditions. [ABSTRACT FROM AUTHOR]

The China-France Oceanography SATellite (CFOSAT), launched on 29 October 2018, is a joint mission developed by China and France. To evaluate the CFOSAT wind product, L2B swath data with a spatial resolution of 25 × 25 km were compared with in situ measurements between December 2018 and December 2020. The in situ measurements were collected from 217 buoys. All buoy winds were adjusted to 10 m height using a simple logarithmic correction method. The temporal and spatial separations between the CFOSAT and in situ measurements were restricted to less than 30 min and 0.25°. The results indicate that the CFOSAT wind retrievals agree well with the buoy measurements. The root mean square errors (RMSEs) of wind vectors were 1.39 m s−1 and 34.32° and negligible biases were found. In the near shore under rain-free conditions, the RMSEs were enhanced to 1.42 m s−1 and 33.43°. Similarly, the RMSEs were reduced to 1.16 m s−1 and 30.41° offshore after the rain effect was removed. After winds less than 4 m s−1 were removed, the RMSE of wind directions was reduced to 19.69°. The effects of significant wave height, air-sea temperature difference, sea surface temperature, atmospheric pressure and ocean surface current on the wind residuals were assessed. The performance of wind retrievals under the passage of tropical cyclones was evaluated. The evaluation results show that the CFOSAT wind retrievals satisfy the accuracy requirements of scientific research, although some improvements are needed to enhance the performance. [ABSTRACT FROM AUTHOR]

Abstract: It is well known that tropical cyclones can cause upwelling, decrease of sea surface temperature, increase of chlorophyll-a (Chl-a) concentration and enhancement of primary production. But little is known about the response of dissolved oxygen (DO) concentration to a typhoon in the open ocean. This paper investigates the impact of a typhoon on DO concentration and related ecological parameters using in situ and remote sensing data. The in situ data were collected 1week after the passage of the super-typhoon Nanmadol in the northern South China Sea in 2011. An increase in DO concentration, accompanied by a decrease in water temperature and an increase in salinity and Chl-a concentration, was measured at sampling stations close to the typhoon track. At these stations, maximum DO concentration was found at a depth of around 5m and maximum Chl-a concentration at depths between 50 and 75m. The layer of high DO concentration extends from the surface to a depth of 35m and the concentrations stay almost constant down to this depth. Due to the passage of the typhoon, also a large sea level anomaly (21.6cm) and a high value of Ekman pumping velocity (4.0×10−4 ms−1) are observed, indicating upwelling phenomenon. At the same time, also intrusion of Kuroshio waters in the form of a loop current into the South China Sea (SCS) was observed. We attribute the increase of DO concentration after the passage of the typhoon to three effects: (1) entrainment of oxygen from the air into the upper water layer and strong vertical mixing of the water body due to the typhoon winds, (2) upwelling of cold nutrient-rich water which stimulates photosynthesis of phytoplankton and thus the generation of oxygen, which also increases the DO concentration due to cold water since the solubility of oxygen increase with decreasing water temperature, and, possibly, (3) transport of DO enriched waters from the Western Pacific to the SCS via the intrusion of Kuroshio waters. [Copyright &y& Elsevier]