The ocean is vast, complex, and increasingly threatened by human activities. There is an urgent need to find complementary ways to gather extensive information and promote the comprehensive understanding and management of the ocean. In addition, as coastal populations grow, these regions are becoming more vulnerable to hazardous natural events. The global network of subsea cables provides an opportunity to support a holistic ocean observation system, in particular, to anticipate and provide warning about hazards and to prepare responses to catastrophic events. Large-scale and widespread ocean monitoring may also enable the oversight and tracing of global phenomena that have local impacts.