Description: Mud is the sediment-size fraction finer than 63 µm, with abundance expressed as percentage by weight. Computing separate maps for silt (coarse mud) and clay (mud finer than 2 µm) contents is not possible because their routine measurement is unreliable. Nevertheless, clay content is a strong determinant of how cohesive (sticky) the bottom is.
Copyright Text: Institute of Arctic and Alpine Research (INSTAAR), University of Colorado at Boulder
Description: Gravel is the sediment-size fraction coarser than 2 mm. At the coarser end gravel includes cobbles and boulders. In this database, objects larger than 256 mm are regarded as rock, beyond gravel. The gravel percentages are by weight.
Copyright Text: Institute of Arctic and Alpine Research (INSTAAR), University of Colorado at Boulder
Description: Rock occurs as crusts and pavements, pinnacles, and bedrock outcrops. Areas of hard biological framework, such as coral-algal reef fronts, can also be classified as rock. Rock is difficult to map by direct sampling or even visual observations, so results from geophysical techniques, such as sidescan sonar, sonar acoustic classification, and seismic wave analysis, were included in the mapping. Rock percent is in terms of estimated areal exposure, thus allowing for sediment veneers that may be present.
Copyright Text: Institute of Arctic and Alpine Research (INSTAAR), University of Colorado at Boulder