[A-OS19] Physical Oceanography (General)

[AOS19-P02] Temporal variation of heat content within surface mixed layer in the western Arctic from Iridium-based autonomous thermistor strings

*EunYae Son¹, Yusuke Kawaguchi¹ (1.University of Tokyo)

Keywords:Western Arctic, Sea ice onset, Upper heat variation

In recent years, the delayed sea ice onset has been detected from satellite observations. The suspended sea ice onset can generate the longer sea surface exposure, which can enhance the kinetic energy input to the ocean from atmosphere. The increased kinetic energy can be a direct source to deepen the bottom of surface mixed layer (SML). We deployed two drifting buoys, with 17 thermistors and 3 pressure sensors on a 60 m long wire to investigate the heat and SML variation in the upper part of the Canada Basin, Arctic. The buoy collects the temperature, pressure, and GPS data with an hour interval and send it via the Iridium satellite. The deployment was done during the Mirai Arctic cruises of 2019 and 2020. Each buoy was deployed in the outer edge of pack ice in mid-October when the sea ice started to freeze up. The buoy deployed in 2019 survived only for three weeks and continued to report the cold surface water near -1.5 °C at 2.5 m depth. The surface temperature at the depth in the same season of 2020 showed warmer water near -1.2°C than that collected in 2019. Another noticeable point is that the signal of the near-surface temperature maximum (NSTM), a thin warm water layer near 20 m, is more well-defined with the temperature of -0.5°C in 2020 than in 2019. The upper water temperature showed that the signal of NSTM was weakened by a strong wind event. The difference between temperatures from the two buoys can also be found in the Pacific Summer Water layer (PSW) that forms the upper pycnocline. The PSW was located about 50 m depth in October 2020 where it was about 10 m deeper in October 2019. We found the several cases of upwelling and downwelling, which were recognized from the isothermal fluctuation, and which were driven by gale winds. In the data collected in 2020, periodic motion of sea ice showed variation according to ice formation. In melting phase when sea surface temperature is higher than the local freezing point, inertial motion is dominant in sea ice drift. When the surface temperature becomes colder than the point, the inertial motion disappeared. The detailed interpretation on the surface heat budget and SML thickness variation will be given in presentation.