The "Indonesian Throughflow" or the origin of the indonesian marine biodiversity
In the Pacific Ocean, at the north-east of the indonesian archipelago, the sea level is 150 mm above the average, however we find the Indian Ocean at the south and there, the sea level is 150 mm under the average.
This difference of 30 cm is caused by the association of tradewinds and oceanic current which are running in opposite directions in the Northern and the Southern hemisphere. This is the biggest water movement on Earth which is crossing the Indonesian archipelago from Pacific to Indian Ocean.
We estimate that the total quantity of water movement of the indonesian throughflow is between 20 and 22 Sverdrups*. This massive flow of water makes its way around the southern chain of islands of the Indonesian archipelago, called the Sunda islands (from Bali to Timor at the east).
The vital quality of this huge quantity of water is to carry eggs and larvas of the indo-pacific marine life. This zone of incredible diversity contains over 4000 identified species, compared to approximately 1000 in Red Sea and 400 in the Caribbean.
This is why we can find this unique biodiversity of wonderful reefs and dive sites in Bali. Another factor which makes this abundance is the seasonal deep and cold water upwelling around Bali.
*The Sverdrup is a measurement unit of volume transport. Named in honor of Harald Sverdrup, a norwegian oceanographer. It’s used to calculate the flow of oceanic currents. It’s equal to 0,001 km³/s.