Characteristics of seafloor morphology and ferromanganese nodule occurrence in the Korea Deep-Sea Environmental Study (KODES) area, NE equatorial Pacific

Seafloor morphology and ferromanganese nodule occurrence were studied using a multibeam side scan sonar (SeaBeam, 2000) and a deep-sea camera system i n the Korea Deep-sea Environmental Study (KODES) area, northeast equatorial Pacific. Seafloor morphology and nodule abundance are highly variable even in this small study area. The NNE-SSW oriented hills are parallel and abou t 100-200 m high. Valleys are very flat-floored, while hilltops are rugged with depressions of tens of meters. Cliffs to about 100 m bound the valleys and the hills. The sturdy area can be classified into three types based bo th on nodule occurrence and seafloor morphology, mostly G- and B-types and some M-type. G-type is characterized by high nodule abundance, ubiquitous b ioturbation, and flat seafloor morphology, while B-type is characterized by irregular-shaped nodules, variable nodule abundance, occurrence of giant n odules and sediment lumps, rugged bottom morphology with depressions, and w hite calcareous surface sediments. Medium nodule abundance and a generally flat seafloor characterize M-type. G-type occurs mostly in the valley regio ns, while B-type is on the hilltop areas. M-type is located between the hil ltop and the valley. Tectonic movement of the Pacific plate resulted in the elongated abyssal hills and cliffs. The rugged morphology on hilltops resu lted from erosion and redistribution of surface siliceous sediments on hill tops by bottom currents, outcropping of underlying calcareous sediments, an d dissolution of the carbonate sediments by corrosive bottom water undersat urated with CaCO3. Sediment eroded from the hills, which is relatively youn g and organic-rich, is deposited in the valleys, and diagenetic metal suppl y to manganese nodules in the valley, area is more active than on the hills . We suggest that tectonic movement ultimately constrains morphology, surfa ce sediment facies, bottom currents and sediment redistribution, bioturbati on, thickness of the sedimentary layer, and other conditions, which are all interrelated and control nodule occurrence. The best potential area for mi ning in the study area is the G-type valley, zones with about 3-4 km width and NNW SSE orientation.