Eastern Equatorial Pacific Ocean Sedimentation: Investigating Constant Flux Proxies

Age-model derived sediment mass accumulation rates (MARs) are consistently higher than 230Th-normalized MARs in the Equatorial Pacific Ocean during the past 25 ka. The offset, being highest in the Panama Basin, suggests sediment redistribution in this region is prominent. I test the hypothesis that downslope transport of sediments from topographically highs that surround the Panama Basin is the cause of higher-than-expected xs230Th inventories in the deeper parts of the basin. There is little difference in xs230Th inventories between the highest and lowest reaches of the basin suggesting that the topographic highs did not serve as a source of xs230Th. A spatial analysis suggests that there may be an enhanced scavenging of xs230Th closest to the equator in productive waters.

To examine whether lateral mixing of productive equatorial waters with adjacent waters delivers xs230Th to the Panama Basin, I measured dissolved 230Th in eight deep-water casts within the Guatemala, Panama, and Peru Basins along a meridional transect at ~86?W. Below 1000 m, the Panama Basin shows the highest deficit (~50%) of 230Th in deep waters assuming a reversible exchange of 230Th between dissolved and sinking particulate matter. Peru Basin waters have a larger range of dissolved 230Th concentrations (7.9-16.5 fg/kg) than that within Panama Basin waters (5.7-7.1 fg/kg). There is a progressive decrease, suggesting advection, in average dissolved deep-water (>1000 m) 230Th concentrations from the southernmost sites in the Peru Basin toward the Panama Basin. My calculations suggest that advected 230Th is between 15-30% of the total 230Th being produced within waters of the Panama Basin itself.

In the Panama Basin, the averaged biogenic barium and opal MARs suggest that productivity was greater during the Holocene (0-13000 years) than that during the last glacial (13000-25000 years) suggesting higher productivity during the Holocene. Uauth, however, is higher in sediments deposited during the last glacial than in those deposited during the Holocene, suggesting that low bottom water oxygen contents rather than respiration of organic matter drives Uauth enrichment. This oxygen depletion during the last glacial suggests that bottom waters were enriched in respired carbon, which, in turn, could be a driver of lower glacial atmosphere pCO2 values.