Hi everyone, Shalom Aleichem!
Good afternoon GanSist everyone! 
Welcome back to the Nusantara Series, a series that invites us to get to know Indonesia from various sides, starting from culture, history, local wisdom, tourist attractions, to the unique landscape and sea of the archipelago. After in the previous series we discussed Minahasa Batik, this time we will explore one of the seas that is very important in Indonesian history, namely the Java Sea.
If you look at the map, the Java Sea looks like ordinary waters. This sea is between the islands of Java, Kalimantan, Sumatra and Sulawesi. However, geologists, oceanographers, archaeologists and biologists actually consider the Java Sea to be one of the most interesting areas in Southeast Asia.
Why is that? The answer is because the Java Sea is not just a sea. The base holds traces of world climate change, traces of ancient land, human and animal migration routes, enormous fishing resources, as well as the history of Indonesian trade for thousands of years.
Here are 5 unique facts about the Java Sea that will make us see this sea from a different perspective.
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1. The Java Sea is a shallow sea that stands on the Sunda Shelf
One of the most distinctive characteristics of the Java Sea is its relatively shallow depth. The average depth of the Java Sea is only around 40 to 50 meters. Compared to the Indian Ocean which is thousands of meters deep, the Java Sea is much shallower. This is because the bottom of the Java Sea is actually part of the Sunda Shelf (Sunda Shelf), which is an extension of the Asian continent which is now covered by sea water.
The Sunda Shelf is one of the largest continental shelves in the world. At a time when sea levels were lower due to the ice age, the area that is now the Java Sea was still a vast land area connecting the islands of Java, Sumatra, Kalimantan, and even the Malay Peninsula.
This means that if we could go back in time to around 20,000 years ago, we could most likely walk from Java to Kalimantan without having to cross the sea.
This fact shows that the shape of Indonesia that we know today is actually the result of sea level changes that have occurred over thousands of years.
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2. The Java Sea has been an important trade route for centuries
The Java Sea has a very strategic position. Since the time of the archipelago kingdoms such as Sriwijaya, Majapahit, Demak, to Islamic Mataram, the Java Sea has been the main shipping route connecting various ports in the archipelago.
Trade ships brought rice, spices, wood, cloth, metal and ceramics from various regions. This route also connected Indonesia with traders from India, China, the Middle East and then Europe.
Due to very busy trading activities, port cities such as Tuban, Gresik, Jepara, Cirebon and Banten developed into influential economic centers.
In other words, the Java Sea does not only separate large islands, but is actually a “highway” that unites the archipelago.
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3. At the bottom there is an ancient river of the former Sundanese mainland
This is the most astonishing fact. When the last ice age reached its peak, world sea levels fell by more than 100 meters. As a result, the Sunda Shelf turned into a very large landmass.
It was during this time that a network of ancient rivers was formed that flowed across the area that is now the bottom of the Java Sea. These rivers connect flows from Sumatra, Kalimantan and Java to the open sea.
Through seismic surveys, bathymetric mapping and sediment analysis, experts have succeeded in identifying ancient river valleys that are now buried beneath marine sediments. The former river channel can still be recognized today as paleovalleyor ancient river valleys.
This discovery is very important because it helps scientists understand climate change, sea level rise after the ice age, and the possible migration routes of ancient humans and various Asian animals to the area that is now the Indonesian archipelago.
It is difficult to imagine that beneath the ships sailing in the Java Sea today, large rivers once flowed over vast land.
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4. The Java Sea is one of the most important fishing areas in Indonesia
Apart from having historical and geological value, the Java Sea also has a big role in people’s lives. These waters are one of the most productive fishing areas in Indonesia. Various types of small pelagic fish, demersal fish, squid, shrimp and other marine products are caught by fishermen from Java, Kalimantan and Madura.
This productivity is influenced by shallow waters, the influx of nutrients from large rivers on the islands of Java and Kalimantan, as well as the process of mixing water masses which supports the growth of plankton as the basis of the food chain.
It is not surprising that the Java Sea has long been a source of livelihood for millions of coastal communities.
However, high fishing activity also poses a challenge in itself. Therefore, sustainable management of marine resources is very important so that these riches can still be enjoyed by future generations.
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5. The Java Sea holds many historical shipwrecks
The final fact relates to Indonesian maritime history. For centuries, the Java Sea has been a very busy international shipping lane. As a result, quite a few merchant ships and warships sank in this area.
Some of the shipwrecks date from the Asian trade period, others from the Second World War. These findings are an important source of information for underwater archaeologists to understand the history of trade, shipping technology, and military conflicts in the Southeast Asian region.
Unfortunately, a number of shipwrecks have also experienced looting, resulting in many valuable artifacts being lost before they could be scientifically examined.
Therefore, protecting underwater cultural heritage is an important part of efforts to preserve Indonesia’s maritime history.
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CLOSURE
The Java Sea may appear calm when viewed from the surface. However, behind the expanse of water there is an extraordinarily long story. This sea was once a vast landmass in prehistoric times, traversed by large rivers, became a trade link between islands, supported the lives of millions of fishermen, and preserved traces of the history of world shipping.
Through these 5 facts, we can see that the Java Sea is not just an ordinary water area. It is a natural archive that records changes in the earth over tens of thousands of years and is also a witness to the long journey of Indonesian civilization.
Through the Nusantara Series, we learn again that Indonesia is not only rich in culture and tradition, but also has a natural landscape that holds extraordinary scientific value. The more we understand Indonesia’s natural history, the greater our sense of responsibility to protect the sea, coast and all the riches of the archipelago so that it remains sustainable.
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SOURCE
Hanebuth, T., Stattegger, K., & Grootes, P. M. (2004). Depositional sequences on a Late Pleistocene-Holocene tropical siliciclastic shelf (Sunda Shelf, Southeast Asia). Journal of Asian Earth Sciences, 23(1)113-126.
Alqahtani, F., Johnson, H. D., Jackson, C. A.-L., & Somoza, L. (2015). Nature, origin and evolution of a Late Pleistocene incised valley-fill, Sunda Shelf, Southeast Asia. Sedimentology, 62(4)1198-1229.
Susilohadi, S., Jones, B. G., Widodo, J., Sianipar, A. H., & Subarsyah. (2026). Sea-level fluctuations and tectonics controlled post-Middle Pleistocene sedimentary architecture on the southeastern Sunda Shelf. Journal of Asian Earth Sciences.
Ministry of Maritime Affairs and Fisheries of the Republic of Indonesia. (2023). Indonesian Capture Fisheries Statistics. Jakarta: KKP.
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