• MJO;
  • upper ocean;
  • Indian Ocean

[1] A moored buoy was recently deployed at 8°S, 67°E in the shallow thermocline region of the Indian Ocean known as “Seychelles-Chagos Thermocline Ridge” (SCTR), where the Madden Julian Oscillation (MJO) is associated with strong sea surface temperature (SST) variability. We use observations from this mooring to describe the oceanic signature of two MJOs between November 2007 and February 2008. The four-month average upper ocean heat balance was largely between heating by atmospheric forcing (2.0 ± 0.3°C/month) and a significant cooling by subsurface processes (−2.2 ± 0.8°C/month), consistent with climatological Ekman pumping in the region. The two MJO events resulted in strong intraseasonal SST variations (1.5 to 2°C in ∼20 days) in the SCTR. At the mooring site, atmospheric fluxes dominated the upper ocean heat balance at the MJO timescale, with the net surface heat flux into the ocean decreasing from an average 105 W m−2 during suppressed phases to 15 W m−2 during active phases of the MJO. It is difficult to establish if MJO-induced variations of subsurface processes also contributed to the cooling because of large uncertainty in this term. Lateral advection had no systematic fluctuations on MJO timescales, but cannot be neglected at the mooring site.