Abstract

A suite of surface sediment samples has been studied from sites on the Aitutaki-Jarvis Transect, between the equator and 17°S at approximately 160°W in the Central Pacific Ocean. The sediments were analysed by bulk and partition analysis in order to characterize changes in sediment geochemistry with water depth and with latitude, with particular reference to the effects of variation in supply and dissolution of biogenic material. The surface sediments are heterogeneous, ranging from carbonate or siliceous oozes to pelagic red clays. The elements in the sediments are variably partitioned into different sediment fractions. Examination of the sediments along the Transect has also provided a profile of the carbonate compensation depth, which shows it to deepen from approximately 4800 m at 16°S to approximately 5300 m at the equator.

The relationships between the bulk sediments and the sediment reducible fraction and associated Mn-Fe nodules has been examined. Variations in the interrelationships between the nodules and the sediment reducible fraction are ascribed to variations in element supply and early diagenetic reactions. A major decoupling of the relationship between nodules and associated sediment reducible fraction is observed in the north of the Transect at water depths close to the position of the CCD. Diagenetic reactions involving the destruction of organic matter which result in the reductive remobilization of Mn and the release of trace metals from labile material are thought to be important causes of this decoupling.