Hard to say. It is an optical network. Good answers would by both. It carries circuit switch and packet switch type of traffic. As far I know, a submarine cable packs many fiber optics. Over each fiber are carrying optical communications. Each fiber carries many optical signals multiplexed in colors. If you stop here, you can said that it is a circuit kind of network, because one color can be assimilated as one circuit, but over each color can be carried a packet type of signal or a circuit type like SDH. But over one of this kind of signal (circuits type for example) can be transported many packets type of networks and, simultaneosly, many circuit type of networks. So, talking about circuit or packet type of network is (in my opinion) an oversimplification. Can be useful in some circumstances, but not in this case.