Paleoceanography of the Eastern Equatorial Pacific over the last eight million years

Abstract: Many studies have investigated the evolution of the Eastern Equatorial Pacific (EEP) Ocean paleoceanography since the late Neogene because of its role in regulating the Earth’s climate and because global climate has undergone major changes during this time period. However, current understanding of the EEP paleoceanography encounters two basic problems. First, this region is characterized by steep east-west and meridional gradients in Sea Surface Temperatures (SSTs) and biological productivity, which can vary from one year to another. Second, the seafloor lies below the lysocline in most of the area, leading to poor preservation of biogenic carbonate. As a result, sediments from the EEP exhibit major changes in their physical and compositional properties over short time, and hence sediment depth, increments. Therefore, the study of bulk sediment properties is crucial to further understand the paleoceanography of EEP during the past 8 Myr. Bulk sediment properties are highly appropriate proxies for achieving highly resolved and time comparable SST and biological productivity data because changes in such properties can be traced across the EEP over large distances.This thesis presents two manuscripts. In Paper 1 we examine the positive second-order relationship between wet bulk density (WBD) and carbonate content of sediments from the EEP. This relationship is important because it can be used to determine high-resolution carbonate content records. In Paper 2 we examine bulk sediment stable isotopes records from the EEP to understand what these records actually represent and whether these records are robust across the EEP. The main conclusions of these studies are (1) a single two-component equation cannot be used to determine carbonate content from the WBD. Instead, the WBD-carbonate relationship can only be described by an infinite series of curves representing the mixing of different components; (2) bulk sediment stable isotope records are robust across the EEP and changes in grain-size are not the primary cause of variations of these records.