EXTREME UPWELLING EVENTS IN THE SEAS OF THE ALOR KECIL, ALOR ISLAND, INDONESIA

Upwelling is a process by which deep, colder, higher-nutrient waters are brought to the sea surface. In the tropics, an indicator that an upwelling event has occurred is lowering of sea surface temperatures (SSTs) to 25 degrees-27 degrees C from a mean of similar to 28 degrees C. Based on more than one year of in situ data, we observed an unusual extreme upwelling event (EUE) when the near-surface temperature (NST) dropped by 10 degrees C within one hour during the spring tide in Mulut Kumbang Strait of Alor Kecil. The extreme minimum NST during this EUE was similar to 12 degrees C, and the upward displacement speed of the cold water was similar to 0.012 m s(-1). The increase in salinity from similar to 30%o to 34%o-36 %o during the decrease in NST indicates a deep source for the cold water mass. From bathymetry and CTD data, the source of the cold water mass was a deep basin (>300 m) located at the southern part of Pantar Strait. In this basin, the tem-perature at 270 m depth can be as low as 8 degrees C. We suggest that tidal sloshing (i.e., the back-and-forth movement of water) brings the cold water mass through a channel that connects this deep basin to Mulut Kumbang Strait. Interactions between semi-diurnal (M-2, S-2, and N-2) tidal components strongly modulate the tidal signal with a period of nearly one month. That EUEs only occur from August to November also suggests a strong monsoonal influence. Because tides are predictable, we suggest that future EUEs are predictable.