Dust Deposition and Migration of the ITCZ through the Last Glacial Cycle in the Central Equatorial Pacific (Line Islands).

Abstract:

Atmospheric dust can be used to record climate change in addition to itself playing a role in several key climate processes, such as affecting Earth’s albedo, fomenting rain coalescence, encouraging biological productivity, and enhancing carbon export though particle sinks. Using deep sea sediments, it is possible to quantify and locate the sources and sinks of atmospheric dust. A key area of research is the shift in the inter-tropical converge zone (ITCZ), a thermally influenced area that shifts according to the northern and southern hemisphere temperature gradient. This ongoing project focuses on the changes of the ITCZ over the Central Equatorial Pacific (CEP) over the past ~25000 years. The research focuses on two cores taken from the Line Islands Ridge at 0° 29' N (ML1208-18GC), and 4° 41' N (ML1208-31BB). The main aim is to quantify the magnitude and provenance of windblown dust deposited in the CEP, and to address questions regarding the nature of the variations of dust through ice-age climate transitions.

Radiogenic isotopes (Sr, Nd, Pb) have been successfully used to distinguish between different potential dust sources in the aluminosilicates fractions of Pacific Sediments. Our preliminary Pb isotope ratios suggest that, for modern deposition, the northern core’s (31BB) detrital sediment fraction is likely sourced from Asian Loess (average ratios are ²⁰⁶Pb/²⁰⁴Pb = 18.88, ²⁰⁷Pb/²⁰⁴Pb = 15.69, ²⁰⁸Pb/²⁰⁴Pb = 39.06). The equatorial core’s (18GC) detrital fraction has a less radiogenic Pb signature, which is consistent with South American dust sourcing (²⁰⁶Pb/²⁰⁴Pb = 18.62, ²⁰⁷Pb/²⁰⁴Pb = 15.63, ²⁰⁸Pb/²⁰⁴Pb = 38.62). This is indicative of a strong modern ITCZ that acts as an effective barrier for inter-hemispheric dust transport. Prior to Holocene time, the changes in Pb isotope ratios in both cores appear to be in anti-phase; the northern core becomes less radiogenic up to the LGM, while the southern core becomes more radiogenic. This is potentially due to a weakening of the ITCZ during glacial times. Future work on Nd isotope will shed additional light on subtle differences in dust isotopic composition within the source regions of interest, including the different volcanic zones of South America.