Temporal variability of vertical heat flux in the Makarov Basin during the ice camp observation in summer 2010

Based on hydrographic data obtained at an ice camp deployed in the Makarov Basin by the 4th Chinese Arctic Research Expedition in August of 2010, temporal variability of vertical heat flux in the upper ocean of the Makarov Basin is investigated together with its impacts on sea ice melt and evolution of heat content in the remnant of winter mixed layer (rWML). The upper ocean of the Makarov Basin under sea ice is vertically stratified. Oceanic heat flux from mixed layer (ML) to ice evolves in three stages as a response to air temperature changes, fluctuating from 12.4 W/m² to the maximum 43.6 W/m². The heat transferred upward from ML can support (0.7±0.3) cm/d ice melt rate on average, and daily variability of melt rate agrees well with the observed results. Downward heat flux from ML across the base of ML is much less, only 0.87 W/m², due to enhanced stratification in the seasonal halocline under ML caused by sea ice melt, indicating that increasing solar heat entering summer ML is mainly used to melt sea ice, with a small proportion transferred downward and stored in the rWML. Heat flux from ML into rWML changes in two phases caused by abrupt air cooling with a day lag. Meanwhile, upward heat flux from Atlantic water (AW) across the base of rWML, even though obstructed by the cold halocline layer (CHL), reaches 0.18 W/m² on average with no obvious changing pattern and is also trapped by the rWML. Upward heat flux from deep AW is higher than generally supposed value near 0, as the existence of rWML enlarges the temperature gradient between surface water and CHL. Acting as a reservoir of heat transferred from both ML and AW, the increasing heat content of rWML can delay the onset of sea ice freezing.