Climate Variability The Equatorial Pacific

My main interest is in the relationship between equatorial Pacific dynamics and the background mean climate state on different time scales, the mechanisms behind these changes and their implications for regional and global climate. Initially, we have focused on the dynamics of climate variability of the WPWP on orbital scales (Dannenmann, et al., 2003; de Garidel-Thoron et al., 2007; Oppo, et al., 2003; Rosenthal, et al., 2003). Our results support the proposed ~3°C glacial cooling of WEP SSTs, while showing close links to the North Atlantic climate variability especially in hydroclimatic changes. We have suggested that past changes in WPWP hydrography cannot be explained by simple analogies with modern interannual ENSO variability (de Garidel-Thoron et al., 2007; Rosenthal and Broccoli, 2004). To further investigate these processes, I have developed an extensive research program to understand the importance of the tropical Pacific Ocean to global climate on centennial to millennial and orbital time scales. The programs included two cruises to the WPWP (R/V Baruna Jaya VIII-2003 and R/V Sonne – 2005) to collect high-resolution records for documenting Holocene climate variability in this region and the effect on Pacific-Indian Ocean heat transport through the Indonesia Throughflow (Oppo and Rosenthal, 2010). A cruise to the eastern Pacific (R/V Knorr – 2009) has provided a window into Holocene climate variability in the eastern equatorial Pacific.

The program has provided significant insights into climate variability in this region. Our studies suggest that early Holocene SST in the WPWP was ~0.5°C warmer than at present, which we attribute to expansion of the warm pool at this time (Linsely et al., 2010) possibly in response to changes in higher latitudes (Rosenthal et al., 2013). A close link to the Northern Hemisphere climate is evident in the late Holocene, as WPWP SST follows the pattern seen in the Northern Hemisphere during the Common Era (Oppo et al., 2009). This work provides a strong validation for the mostly terrestrial-based reconstruction of Common Era temperature by Michael Mann. These studies also suggest that the regional hydroclimate, which seasonally is dominated by the East Asian monsoon (EAM) system, is mostly sensitive to shifts in the position of the ITCZ in response to changes in the meridional temperature gradient rather than changes in ENSO activity and regional SST (Oppo et al., 2009; Tierney et al., 2010, 2012; Gibbons et al., 2014; Dubois et al., 2014). Our studies suggest that during the Common Era centennial variability in the ITF is controlled to a large extent by buoyancy fluxes from the South China Sea, likely related to EAM activity (Kalansky et al., submitted). On G-IG time scales, however, sea level changes are the main control on the ITF (Linsley et al., 2010). While ENSO variability exert significant effect on modern ITF variability, its importance on decadal and millennial time scale seems far less significant (Kalansky et al., submitted).

In 2013, we carried out a site survey cruise (R/V Revelle 1313) in preparation for an IODP expedition in the Western Pacific Warm Pool:

Subsequently in 2016 I was the co-chief of IODP Expedition 363 to the western equatorial Pacific onboard the D/V Joides Resolution (JR), which sought to document the regional expression and driving mechanisms of climate variability (e.g., temperature, precipitation, and productivity) in the Western Pacific Warm Pool (WPWP) as it relates to the evolution of Neogene climate on millennial, orbital, and geological timescales. Nine sites were cored during Expedition 363, recovering a total of 6956 m of sediment in 875–3421 m water depth with an average recovery of 101.3% during 39.6 days of on-site operations. The wide spatial distribution of the cores, variable accumulation rates, exceptional biostratigraphic and paleomagnetic age constraints, and mostly excellent foraminifer preservation allow us to trace the evolution of the WPWP through the Neogene at different temporal resolutions. High sedimentation–rate cores off PNG will allow us to better constrain mechanisms influencing millennial-scale variability in the WPWP, their links to high-latitude climate variability, and implications for temperature and precipitation variations in this region under variable climate conditions. These high accumulation rates offer the opportunity to study climate variability during previous warm periods at a resolution similar to existing studies of the Holocene. With excellent recovery, Expedition 363 sites are suitable for detailed paleoceanographic reconstructions at orbital and suborbital resolution from the middle Miocene to Pleistocene, and thus will be used to refine the astronomical tuning, magneto-, isotope, and biostratigraphy of hitherto poorly constrained intervals within the Neogene timescale (e.g., the late Miocene) and to reconstruct the history of the East Asian and Australian monsoon and the Indonesian Throughflow on orbital and tectonic timescales. Results from high-resolution interstitial water sampling at selected sites will be used to reconstruct density profiles of the western equatorial Pacific deep water during the Last Glacial Maximum. Additional geochemical analyses of interstitial water samples in this tectonically active region will be used to investigate volcanogenic mineral and carbonate weathering and their possible implications for the evolution of Neogene climate.

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To better constrain these linkages we have developed and new expedition (JR100) to drill cores on the Chilean Margins (scheduled for July 2019).