Multibeam Synthesis of the Northwestern Hawaiian Islands Supports Diverse Research in the Papahānaumokuākea Marine National Monument

The Papahānaumokuākea Marine National Monument (PMNM) in the Northwestern Hawaiian Islands (NWHI) was established in 2006 and is both the single largest conservation area under U.S. jurisdiction (366,631 km2), and one of the largest marine protected areas in the world. The NWHI stretches over 2200 km to the northwest of the 775 km-long Main or Southeastern Hawaiian Islands and contains 47 individual islands, seamounts, atolls, ridges, and submerged banks. The PMNM boundary is 100 nm (185 km) wide centered on the emergent landforms and thus nearly the entire monument (98%) is in deepwater (>100 m) beyond the range of technical wet diving. Because of its remote location, dedicated multibeam mapping of the PMNM region began only ten years ago, although research in the NWHI has taken place for decades. In an effort to consolidate the more recent systematic surveys with older transit data swaths for this region, a synthesis of all existing multibeam data was undertaken between 2009 and 2010. This dataset was then merged with the much lower resolution global bathymetry dataset to generate a more complete picture and allow users to visualize the remainder of the as yet unmapped features within and adjacent to the PMNM boundaries. One of the primary benefits of the synthesis has been to provide researchers with base maps for study site selection including submersible and ROV dive locations. In addition, fusion with the global dataset permits calculation of statistics using geospatial software and may serve as input for physical oceanographic models. With a number of different entities carrying out mapping activities in the PMNM in recent years, this data compilation also provides a road map showing where existing multibeam data are located so as to avoid duplication of effort. The synthesis was prepared with a grid cell interval of 120 m in order to accommodate the large area and water depths to >5000 m, although some of the individual surveys are of much higher resolution, especially in shallow water. Nearly all of the data included are currently available from the National Geophysical Data Center. Mapping products showing the synthesis will be presented along with an example of how it is being used in a deepwater biological survey project in the PMNM studying ancient volcanic ridges, seamounts, and isolated pinnacles where extensive deep-sea coral and sponge communities were discovered. The synthesis also reveals many other complex deepwater features in the monument where important biological resources will likely be revealed.