Grain Size on the Saipan Coast Across Varying Slopes and Distances from Shore

Abstract

Submarine topography affects sediment transport, deposition, and benthic habitats by influencing erosion and current flow. This study investigated a correlation between sediment grain size and submarine slope, and correlation between grain size and offshore distance. The hypothesis was that average grain size would be larger at locations closer to shore and with steeper slopes. Sediment samples were collected over an 11-day research cruise at five Western Saipan stations with various bathymetric slopes and offshore distances. Seafloor topography was mapped using ship-mounted multibeam acoustic sensors, and sediment samples were dried, sieved into seven grain-size categories, and analyzed by percent weight distribution. Average grain size (microns) at each station was compared to both seafloor slope and distance from shore. After weight distributions were calculated, a linear regression test determined statistical significance. Overall trends suggested areas with steeper slopes contained larger grains, with the steepest slopes of 9% and 12.5% containing the largest sediment, averaging 940 and 760 microns, respectively. Locations farther from shore also contained finer grains, with the farthest site at 15.63 km averaging 225 micron grains. Although the graph showed correlation, the hypothesis could not be confirmed because the results lacked statistical significance, with a p-value of 0.27 for grain size and slope, and 0.26 for grain size and distance from shore. Although the study was unable to confirm that slope or distance from shore affects sediment grain size along western Saipan, it provides initial observations of deposition patterns in a region where few previous studies have been conducted.