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Previous in situ observations have suggested that bottom water temperature variations in shelf seas can drive significant ocean bottom heat flux (BHF) by heat conduction. The BHF-driven bottom water temperature variations, however, have been overlooked in ocean general circulation models. In this study, we established a sea-sediment fully coupled model through incorporating the BHF. The coupled model included a sediment temperature module/model, and the BHF was calculated based on the sediment heat content variations. Meanwhile, we applied temporally varying BHF in the calculation of the bottom water temperature, which further determined the sediment temperature. The two-way coupled BHF process presents a more complete and physically reasonable heat budget in the ocean model and a synchronously varying sediment temperature profile. The coupled model was validated using a one-dimensional test case, and then it was applied in a domain covering the Bohai and Yellow Seas. The results suggest that when a strong thermocline exists, the BHF can change the bottom water temperature by more than 1°C because the effects of the BHF are limited to within a shallow bottom layer. However, when the water column is well mixed, the BHF changes the temperature of the entire water column, and the heat transported across the bottom boundary is ventilated to the atmosphere. Thus, the BHF has less effect on water temperature and may directly affect air–sea heat flux. The sea-sediment interactions dampen the amplitude of the bottom water temperature variations, which we propose calling the seabed dampening ocean heat content variation mechanism (SDH). [ABSTRACT FROM AUTHOR]

In this study, we for the first time observed two subsurface cyclonic eddies (SCEs) in the southeastern Tropical Indian Ocean. One SCE (SCE‐C) was observed along 8°S transect during the cruise conducted in July 2016. Another SCE (SCE‐A) was also observed near 8°S but by an Argo float in November 2005. The SCE‐C had a maximum thickness of about 500 m (300–800 m) and a radius of ~90 km, while the SCE‐A has a vertical extent of 700 m (200–900 m) and a radius larger than 110 km. The water trapped by SCE shows a three‐compartment structure. Both the two SCEs are characterized by stratified water with negative lens structure and cause prominent temperature/salinity/spiciness anomalies in a wide density range. As the water carried by SCEs is stratified, we can trace the SCE origin by finding an area sharing the same water property with the SCE on different density surfaces. The result suggests that the two SCEs originate from the southwest coast of the Sumatra Island. Considering the topography and hydrologic characteristics of the SCE origin, we speculate that the SCEs are generated due to topography‐induced South Java Undercurrent instability. Plain Language Summary: Subsurface eddies usually have long lifespans and can carry fluid parcels and transport them far away from the eddy origin. However, compared with surface eddies, subsurface eddies are poorly observed because they usually have small or no surface signatures. In this study, we for the first time observed two subsurface cyclonic eddies (SCEs) in the southeastern tropical Indian Ocean. The SCEs were characterized by stratified water with negative lens structure. Further analysis suggested that the SCEs should be generated off southwest coast of the Sumatra Island due to topography‐induced South Java Undercurrent instability and move southwestward. These results provide new insight into the SCEs in the southeastern tropical Indian Ocean. Key Points: Two subsurface cyclonic eddies are observed in the southeastern Tropical Indian OceanThe subsurface cyclonic eddies are characterized by stratified water and cause prominent water property anomalies in a wide density rangeThe subsurface cyclonic eddies should be generated off southwest coast of the Sumatra due to topography‐induced undercurrent instability [ABSTRACT FROM AUTHOR]

Typhoon Damrey 2012 has been the strongest typhoon to strike the area north of the Yangtze River since 1949. Two cruise observations to examine the shallow water response to typhoon were carried out just before and after the passage of Damrey in the shallow water near the Jiaozhou Bay on 1 and 5 August 2012. The observation results indicate that, after the passage of Damrey, the thermocline was deepened and weakened significantly. The water temperature below the surface increased by about 4–10 °C. A significant temperature gradient was generated at the bottom of the water column. The salinity decreased throughout the water column. The surface heat flux and precipitation data indicate that the temperature increase and salinity decrease of the bottom water were mainly caused by the intrusion of warm, low-salinity water from the surface (depth < 7 m). The model results suggest that the mechanism that drive the variations as follows: the warm low-salinity surface water was driven by wind and flowed onshore, accumulated and sank as it encountered the coast, which forced the cold bottom water of the Yellow Sea Cold Water Mass (YSCWM) to flow offshore. [ABSTRACT FROM AUTHOR]

In this study, to investigate the synoptic time-scale variability of sediment temperature profile and sound speed in shallow seas, one-month-long in situ observations were conducted in Jiaozhou Bay using a newly designed sediment measurement system. A typhoon passage and a heavy rainfall process were captured during the observation. The sediment temperature increased immediately after the significant bottom water temperature increase induced by typhoon passage. A significant increase in the sediment warming rate could be identified at a depth as deep as 0.8 m below seafloor (mbs), and a significant increase in downward sediment heat flux at 0.5 mbs lasted until five days after the typhoon passed. The sediment sound speed was also observed to decrease or increase as soon as the bottom water salinity significantly decreased or the bottom water temperature significantly increased. Moreover, the pore water salinity—which can affect the sediment sound speed—cannot be conducted like heat but can be changed only by diffusion or convection processes, and the static diffusion of salt was too slow for the observed sediment sound speed variation; we therefore conclude that in addition to heat conduction, the pore water convection may play an important role in the synoptic time-scale variations of the sediment temperature and sound speed, which is also consistent with the simulation results. • Synoptic time-scale variability of sediment is derived from in situ observations. • Sediment temperature profile and sound speed respond quickly to weather process. • Both heat conduct and pore water convection contribute to synoptic sediment variation. [ABSTRACT FROM AUTHOR]