Satellite-derived phytoplankton pigment absorption (a_ph) has been used as a key predictor of phytoplankton photosynthetic efficiency to estimate global ocean net primary production (NPP). In this study, an a_ph-based NPP model (AbPM) with four input parameters including the photosynthetically available radiation (PAR), diffuse attenuation at 490 nm (K_d(490)), euphotic zone depth (Z_eu) and the phytoplankton pigment absorption coefficient (a_ph) is compared with the chlorophyll-based model and carbon-based model. It is found that the AbPM has significant advantages on the ocean NPP estimation compared with the chlorophyll-based model and carbon-based model. For example, AbPM greatly outperformed the other two models at most monitoring sites and had the best accuracy, including the smallest values of RMSD and bias for the NPP estimate, and the best correlation between the observations and the modeled NPPs. In order to ensure the robustness of the model, the uncertainty in NPP estimates of the AbPM was assessed using a Monte Carlo simulation. At first, the frequency histograms of simple difference (δ), and logarithmic difference (δ^LOG) between model estimates and in situ data confirm that the two input parameters (Z_eu and PAR) approximate the Normal Distribution, and another two input parameters (a_ph and K_d(490)) approximate the logarithmic Normal Distribution. Second, the uncertainty in NPP estimates in the AbPM was assessed by using the Monte Carlo simulation. Here both the PB (percentage bias), defined as the ratio of ΔNPP to the retrieved NPP, and the CV (coefficient of variation), defined as the ratio of the standard deviation to the mean are used to indicate the uncertainty in the NPP brought by input parameter to AbPM model. The uncertainty related to magnitude is denoted by PB and the uncertainty related to scatter range is denoted by CV. Our investigations demonstrate that PB of NPP uncertainty brought by all parameters with an annual mean of 5.5% covered a range of –5%–15% for the global ocean. The PB uncertainty of AbPM model was mainly caused by a_ph; the PB of NPP uncertainty brought by a_ph had an annual mean of 4.1% for the global ocean. The CV brought by all the parameters with an annual mean of 105% covered a range of 98%–134% for global ocean. For the coastal zone of Antarctica with higher productivity, the PB and CV of NPP uncertainty brought by all parameters had annual means of 7.1% and 121%, respectively, which are significantly larger than those obtained in the global ocean. This study suggests that the NPPs estimated by AbPM model are more accurate than others, but the magnitude and scatter range of NPP errors brought by input parameter to AbPM model could not be neglected, especially in the coastal area with high productivity. So the improving accuracy of satellite retrieval of input parameters should be necessary. The investigation also confirmed that the SST related correction is effective for improving the model accuracy in low temperature condition.

On the basis of the latest version of a U.S. Navy generalized digital environment model (GDEM-V3.0) and World Ocean Atlas (WOA13), the hydraulic theory is revisited and applied to the Luzon Strait, providing a fresh look at the deepwater overflow there. The result reveals that: (1) the persistent density difference between two sides of the Luzon Strait sustains an all year round deepwater overflow from the western Pacific to the South China Sea (SCS); (2) the seasonal variability of the deepwater overflow is influenced not only by changes in the density difference between two sides of the Luzon Strait, but also by changes in its upstream layer thickness; (3) the deepwater overflow in the Luzon Strait shows a weak semiannual variability; (4) the seasonal mean circulation pattern in the SCS deep basin does not synchronously respond to the seasonality of the deepwater overflow in the Luzon Strait. Moreover, the deepwater overflow reaches its seasonal maximum in December (based on GDEM-V3.0) or in fall (October–December, based on the WOA13), accompanied by the lowest temperature of the year on the Pacific side of the Luzon Strait. The seasonal variability of the deepwater overflow is consistent with the existing longest (3.5 a) continuous observation along the major deepwater passage of the Luzon Strait.

Mesoscale eddies (MEs) in the South China Sea (SCS) simulated by a quasi-global eddy-resolving ocean general circulation model are evaluated against satellite data during 1993–2007. The modeled ocean data show more activity than shown by the satellite data and reproduces more eddies in the SCS. A total of 345 (428) cyclonic eddies (CEs) and 330 (371) anti-cyclonic eddies (AEs) generated for satellite (model) data are identified during the study period, showing increase of ~24% and ~12% for the model data, respectively. Compared with eddies in satellite, the simulated eddies tend to have smaller radii, larger amplitudes, a slightly longer lifetime, faster movement and rotation speed, a slightly larger nonlinear properties (U/c) in the model. However, the spatial distribution of generated eddies appears to be inhomogeneous, with more CEs in the northern part of SCS and fewer AEs in the southern part. This is attributed to the exaggerated Kuroshio intrusion in the model because the small islands in the Luzon Strait are still not well resolved although the horizontal resolution reaches (1/10)°. The seasonal variability in the number and the amplitude of eddies generated is also investigated.

The spatial and temporal variations of turbulent diapycnal mixing along 18°N in the South China Sea (SCS) are estimated by a fine-scale parameterization method based on strain, which is obtained from CTD measurements in yearly September from 2004 to 2010. The section mean diffusivity can reach ~10^–4 m²/s, which is an order of magnitude larger than the value in the open ocean. Both internal tides and wind-generated near-inertial internal waves play an important role in furnishing the diapycnal mixing here. The former dominates the diapycnal mixing in the deep ocean and makes nonnegligible contribution in the upper ocean, leading to enhanced diapycnal mixing throughout the water column over rough topography. In contrast, the influence of the wind-induced near-inertial internal wave is mainly confined to the upper ocean. Over both flat and rough bathymetries, the diapycnal diffusivity has a growth trend from 2005 to 2010 in the upper 700 m, which results from the increase of wind work on the near-inertial motions.

New satellite-derived latent and sensible heat fluxes are performed by using WindSat wind speed, WindSat sea surface temperature, the European Centre for Medium-range Weather Forecasting (ECMWF) air humidity, and ECMWF air temperature from 2004 to 2014. The 55 moored buoys are used to validate them by using the 30 min and 25 km collocation window. Furthermore, the objectively analyzed air-sea heat fluxes (OAFlux) products and the National Centers for Environmental Prediction-National Center for Atmospheric Research reanalysis 2 (NCEP2) products are also used for global comparisons. The mean biases of sensible and latent heat fluxes between WindSat flux results and buoy flux data are –0.39 and –8.09 W/m², respectively. In addition, the root-mean-square (RMS) errors of the sensible and latent heat fluxes between them are 5.53 and 24.69 W/m², respectively. The RMS errors of sensible and latent heat fluxes are observed to gradually increase with an increasing buoy wind speed. The difference shows different characteristics with an increasing sea surface temperature, air humidity, and air temperature. The zonal average latent fluxes have some high regions which are mainly located in the trade wind zones where strong winds carry dry air in January, and the maximum value centers are found in the eastern waters of Japan and on the US east coast. Overall, the seasonal variability is pronounced in the Indian Ocean, the Pacific Ocean, and the Atlantic Ocean. The three sensible and latent heat fluxes have similar latitudinal dependencies; however, some differences are found in some local regions.

This work aims to contribute to the characterization and understanding of infragravity waves on two beaches with erosion problems. For this reason, we have used an array of ADCP and a pressure sensor to measure wave parameters and pressure inside and outside of the surf zone during the dry and rainy period in the beaches of Galerazamba and Manzanillo del Mar (both dissipative and eroded beaches) located in the Colombian Caribbean coast. Based on these measurements, we have carried out a spectral analysis in order to identify the frequency components that characterize the wave and its energy; thus, we identified the characteristic frequencies of infragravity waves to finally filter the infragravity signal on each beach in different seasonal periods. Among the results of the Welch spectrum applied to surface elevation time series, we found that, the frequencies’ energy of the sea-swell band decreases due to bottom friction and wave breaking as the wave approaches the shore, while the frequencies’ energy of the infragravity band increases significantly. In addition, for the wavelet analysis, we could observe how the energy of the infragravity band, especially the lowest frequencies gain energy as the waves approaches the coast. Furthermore, based on the infragravity wave obtained from the extreme wave event registered during the field campaign we can conclude that the contribution of this signal is important in the erosion problems presented in the beaches of Galerazamba and Manzanillo del Mar. Finally, these results show the need to realize other studies that allow us to understand deeply, the role of infragravity waves on the morphological changes that occurs in these beaches.

As rain drops change the radiation and scattering characteristic of the oceans and the atmosphere, the wind speed measuring by spaceborne remote sensors under rainy conditions remains challenging for years. On the basis of a microwave radiometer (RM) loaded on HY-2 satellite, the sensitivity of some brightness temperature (TB) channels to a rain rate and the wind speed are analyzed. Consequently, two TB combinations which show minor sensitivity to rain are obtained. Meanwhile, the sensitivity of the TB combination to the wind speed is even better to the original TB channel. On the basis of these TB combinations, a wind speed retrieval algorithm is developed and compared with WindSat all-weather wind speed product, HY-2 RM original wind speed product and buoy in situ data. The wind speed retrieval accuracy is better than 2 m/s for rainy conditions, which is evidently superior to HY-2 RM original product. The applicability of this new algorithm is testified for the wind speed measuring in rainy weather with HY-2 RM.

Vertically exploring the characteristics of the typhoon boundary layer (TBL) plays an important role in recognizing typhoon structure. The boundary layer radial direction and tangential wind characteristics of Typhoon Usagi based on the observational data of three boundary layer wind profiler stations along the route of Typhoon Usagi (No. 1319) and by combining with sounding data. The results show that: (1) maximum tangential wind appears in the vicinity of the eye area of Usagi, and it basically maintains a height of around 1 800 m when Usagi keeps a strong typhoon level, with the rapidly decreasing strength of Usagi after it lands, the speed of the maximum tangential wind and its vertical range both decrease; (2) the height of the maximum tangential wind is close to that of the inflow layer top of the typhoon, and is greater than that of the boundary layer estimated on the basis of Richardson number or potential temperature gradient, while the height of mixed layer judged on the basis of the signal-to-noise ratio (SNR) or its gradient is usually low; (3) the the boundary layer height can reach higher than 2 100 m before Usagi lands. When the typhoon level or above is achieved, the boundary layer height observed by various stations does not change much, basically staying at between 1 200 and 1 600 m. With the decreasing strength of Usagi after its landfall, the boundary layer height rapidly drops.

On the basis of the European Centre for Medium-range Weather Forecasts (ECMWF) 20 a wind field reanalysis data, the wave field of the north area of the South China Sea is calculated with the combination of the HIRHAM wind field model and the SWAN wave model. Then a significant wave height compared with the El Niño index to study the relationships between these variables. The following conclusions are drawn: (1) the wave height of the South China Sea has a strong seasonal variation, the wave height is much larger in winter than in summer; (2) in the South China Sea, the monthly average wave height of the north area has a negative correlation with the Niño3.4 index, most area of the South China Sea has a moderate correlation and the area between Taiwan Province of China and Philippines is highly correlated; and (3) in the strong El Niño years, the significant wave height in the north area of the South China Sea is significantly smaller than in other years; if the El Niño index variability is greater, the wave height decreases. In contrast, the significant wave height in the north area of the South China Sea is larger in the strong La Niña years.

As a case study, refined iron (Fe) speciation and quantitative characterization of the reductive reactivity of Fe (III) oxides are combined to investigate Fe diagenetic processes in a core sediment from the eutrophic Jiaozhou Bay. The results show that a combination of the two methods can trace Fe transformation in more detail and offer nuanced information on Fe diagenesis from multiple perspectives. This methodology may be used to enhance our understanding of the complex biogeochemical cycling of Fe and sulfur in other studies. Microbial iron reduction (MIR) plays an important role in Fe(III) reduction over the upper sediments, while a chemical reduction by reaction with dissolved sulfide is the main process at a deeper (> 12 cm) layer. The most bioavailable amorphous Fe(III) oxides [Fe(III)_am] are the main source of the MIR, followed by poorly crystalline Fe(III) oxides [Fe(III)_pc)] and magnetite. Well crystalline Fe(III) oxides [Fe (III)_wc] have barely participated in Fe diagenesis. The importance of the MIR over the upper layer may be a combined result of the high availability of highly reactive Fe oxides and low availability of labile organic matter, and the latter is also the ultimate factor limiting sulfate reduction and sulfide accumulation in the sediments. Microbially reducible Fe(III) [MR-Fe(III)], which is quantified by kinetics of Fe(II)-oxide reduction, mainly consists of the most reactive Fe(III)_am and less reactive Fe(III)_pc. The bulk reactivity of the MR-Fe(III) pool is equivalent to aged ferrihydrite, and shows down-core decrease due to preferential reduction of highly reactive phases of Fe oxides.