A Global Ocean Conveyor Belt
The Lombok Strait is a critical chokepoint in the planet's circulatory system. It is one of the primary passages for a large ocean current system called the Indonesian Throughflow (ITF). This current transports enormous volumes of water from the Pacific to the Indian Ocean, acting as the only low-latitude connection between major oceans. The total flow of the ITF is estimated to average around 15 Sverdrups (Sv), a unit of measure equal to one million cubic meters per second. For comparison, all the world's rivers combined discharge only about one Sverdrup into the oceans.
The strait itself is a geological feature. It is approximately 60 km long and varies in width from about 20 km at its narrow southern opening to 40 km in the north. While other straits in the region are relatively shallow, the Lombok Strait has an average depth of 250 meters and contains channels that plunge to over 1,000 meters. This depth is what allows it to be a significant conduit. Data from the International Nusantara Stratification and Transport (INSTANT) program, a multi-national study from 2004 to 2006, measured the Lombok Strait's contribution to the total ITF at about 2.6 Sv. The flow is controlled by a submarine ridge, or sill, between the islands of Nusa Penida and Lombok that has a depth of about 250-350 meters. This sill dictates which water masses can pass, effectively straining the deep ocean layers.