ELEMENT SUPPLY TO SURFACE SEDIMENTS AND INTERRELATIONSHIPS WITH NODULES ALONG THE AITUTAKI-JARVIS TRANSECT, SOUTH-PACIFIC

A suite of surface sediment samples has been studied from sites on the Aitutaki-Jarvis Transect, between the equator and 17-degrees-S at app roximately 160-degrees-W in the Central Pacific Ocean. The sediments w ere analysed by bulk and partition analysis in order to characterize c hanges in sediment geochemistry with water depth and with latitude, wi th particular reference to the effects of variation in supply and diss olution of biogenic material. The surface sediments are heterogeneous, ranging from carbonate or siliceous oozes to pelagic red clays. The e lements in the sediments are variably partitioned into different sedim ent fractions. Examination of the sediments along the Transect has als o provided a profile of the carbonate compensation depth, which shows it to deepen from approximately 4800 m at 16-degrees-S to approximatel y 5300 m at the equator. The relationships between the bulk sediments and the sediment reducible fraction and associated Mn-Fe nodules has b een examined. Variations in the interrelationships between the nodules and the sediment reducible fraction arc ascribed to variations in ele ment supply and early diagenetic reactions. A major decoupling of the relationship between nodules and associated sediment reducible fractio n is observed in the north of the Transect at water depths close to th e position of the CCD. Diagenetic reactions involving the destruction of organic matter which result in the reductive remobilization of Mn a nd the release of trace metals from labile material are thought to be important causes of this decoupling.