Big data refers to huge amount of data that we can't handle using our traditional programming concerns. Wireless Sensor
Networks is one of the main contributors of big data. Data dissemination and data gathering are two important operations in wireless sensor networks. Mobile sink approach is an efficient way to gather data in wireless sensor networks. Earlier works [1][6] have considered the mobile sink approach for energy efficient data gathering. In that works, Mobile sinks gather data from centroid of each cluster in the wireless sensor networks. However this approach considered distance as the parameter for clustering and centroid calculation which is not possible for a dynamic wireless sensor networks. Hence a new approach is needed for the clustering and cluster head selection in dynamic wireless sensor networks which in turn helps for the big data gathering. Modified clustering algorithm with mobile sink based data gathering is proposed in this paper for clustering and big data gathering in dynamic wireless sensor networks. The proposed algorithm can gather data from dynamic wireless sensor networks in an energy efficient manner.