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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]

The Yellow and Bohai Seas (YBS) are shallow marginal seas located at the temperate latitudes of the western North Pacific. The seasonal bottom water temperature variation in the YBS can be greater than 20 °C and therefore generates significant seafloor heat flux, which significantly changes both the sediment temperature profile and heat content of the overlying water column. In this study, we investigated the seafloor heat flux driven by bottom water temperature variation in the YBS using a high-resolution numerical ocean model and a one-dimensional sediment temperature model. The results showed that seafloor heat flux in the area shallower than 50 m was on the order of 10 W/m2. The seafloor heat flux was larger than the lateral heat flux driven by circulation and ranked second only to surface net heat flux accounting for the most important forcing mechanism of ocean heat content variation in the coastal YBS. The accumulated seafloor heat flux during the sediment cooling/warming season could warm/cool the overlying water column by about 1 °C in the coastal YBS where the depth is shallower than 30 m. The depth of sediment affected by seafloor heat flux (seasonal sediment temperature variation >0.1 °C) could be as deep as 10 m. The complex spatial–temporal distribution of seafloor heat flux generated a complex distribution of sediment temperature and sound speed, which may have an important effect on acoustic wave propagation in the YBS. • Bottom water temperature variation generates significant seafloor heat flux. • Seafloor heat flux is on the order of 10 W/m2 in the coastal Yellow and Bohai Seas. • Seafloor heat flux affects ocean heat content significantly. • Seafloor heat flux generates complex sediment sound speed distribution. [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]