Today, cabled seafloor observatories are installed at many sites around the globe, gathering different types of sensors in the marine environment where a Global Positioning System (GPS) signal is not accessible. Accurate time marking of ocean sensor data is highly important in many marine applications. This paper presents a smart GPS emulator based on the IEEE–1588 Precision Time Protocol (PTP). The device was designed and implemented to be able to provide accurate timing data (trigger + time code) to any ocean sensor as a broadband seismometer. In this case, accurate location and magnitude of a detected earthquake are dependent on the accuracy of the data time marks. The performance of time synchronization is tested, using a commercial broadband seismometer, and the results are presented. These tests are based on a comparison of the synchronization trigger between master and slave clocks as well as the analysis of the data acquired by the seismometer. The work presented here leads to an improved performance of the ocean-bottom seismometers as well as tsunami warning systems.