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).