The deep ocean floor between the Clarion and Clipperton fracture zones (NE<br/>equatorial Pacific) has the highest known manganese nodule abundance in the world oceans. A detailed analysis of MR1 (Mapping Researcher 1, 11–12 kHz) sonar images and free-fall grab data in the Korean manganese nodule field areas reveals a<br/>close relationship between side-scan sonar characteristics of the seafloor and manganese nodule abundance. Eight sonar facies are identified based on back-scattering intensity and distribution patterns. These sonar facies can be interpreted as (1) volcanic seamounts (facies I-1), (2) bounding faults of abyssal hills (facies I-2 and II-1), (3) lava flows or volcanoclastic mass-flow deposits around the volcanic<br/>seamounts (facies I-3 and II-2), (4) crests of abyssal hills (facies II-1), (5) abyssal<br/>troughs between abyssal hills (facies III-1), (6) relatively flat areas (facies II-3 and<br/>III-2). In the areas where facies II-1 (abyssal hill crests with thin sediment cover)<br/>and II-3 (relatively flat areas draped by thin sediments) are dominant, manganese<br/>nodules occur abundantly. In contrast, zones comprising facies III-1 (abyssal<br/>troughs with thick sediment cover) and III-2 (relatively flat areas covered by thick<br/>sediments) are characterized by low abundance of manganese nodules. This relationship between distribution of sonar facies and manganese nodule abundance<br/>implies that (1) the qualitative difference in acoustic reflectivity of long-range sidescan sonar with some ground truth data is useful for regional assessment of manganese nodule occurrence over wide areas in a reasonable time, and (2) seafloor topography and sediment thickness are important controlling factors for regional occurrences of manganese nodules
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