Sediment focusing in the panama basin, eastern equatorial pacific ocean

摘要

Age-model derived sediment mass accumulation rates (MARs) are consistently higher than ~(230)Th-normalized MARs in the Equatorial Pacific Ocean during the past 25ka. The offset, being highest in the Panama Basin, suggests a significant role for deep-sea sediment redistribution (i.e., sediment focusing) in this region. Here, we test the hypothesis that downslope transport of sediments from topographically high regions that surround the Panama Basin is the cause of higher-than-expected xs~(230)Th inventories over the past 25ka in the deeper parts of the basin. We find little difference in xs~(230)Th inventories between the highest and lowest reaches of the basin. Furthermore, there is no correlation between xs~(230)Th-derived sediment focusing factors and water depth which suggests that the topographic highs do not serve as a source of xs~(230)Th. A spatial analysis suggests that there may be an enhanced scavenging effect on xs~(230)Th concentrations in sediment closest to the equator where productivity is the highest, although further data is necessary to corroborate this. At the equator xs~(230)Th-derived focusing factors are high and range from about 1 to 5 during the Holocene and about 1 to 11 during the last glacial. In contrast, non-equatorial cores show a smaller range in variability from about 0.7 to 2.8 during the Holocene and from 0.7 to 3.6 during the last glacial. Based on ~(232)Th flux measurements, we hypothesize that the location at which eolian detrital fluxes surpass the riverine detrital fluxes is approximately 300km from the margin. While riverine fluxes from coastal margins were higher during the Holocene, eolian fluxes were higher during the last glacial.