MICELO · Forging a link between millennial cycles and enso-like oscillations

Final Activity Report Summary - MICELO (Forging a link between millennial cycles and enso-like oscillations)

This study critically evaluated the causes of millennial-scale cycles by testing the role of the tropical Pacific Ocean as a potential governor of global and sustained climate changes through 'el nino' Southern oscillation (ENSO) like perturbations. We used three sediment cores from the Eastern Tropical North Pacific (ETNP) and the Eastern Equatorial Pacific (EEP) for which we reconstructed diagnostic processes of ENSO such as upwelling strength, productivity, denitrification intensity and nutrient supply at millennial time-scale during the last glacial cycle. ENSO variability has the potential to affect global climate through production of greenhouse gases, either directly via CO2 evasion during upwelling, or indirectly by affecting biogeochemical processes such as denitrification and productivity. Our results demonstrated that upwelling, productivity and denitrification changed at millennial time scale in the ETNP in a manner that was similar to modern ENSO, with increased upwelling (CO2 out gassing), denitrification (N2O production) and productivity (marine C pump) during warm periods, similar to la Nina phases. On the other hand, upwelling, productivity and denitrification were reduced during cold spells, similar to El Nino phases. Therefore, ENSO-like perturbations were in operation in the ETNP during the last glacial period and deglaciation and we showed evidence that these perturbations caused significant and sustained variations in greenhouse gas emissions that could have triggered or modulated global climate change at these time scales. Results from the EEP core also suggested that other processes, non-related to ENSO and operating at longer or similar time scale had potentially an overriding influence on the supply of nutrient in the ETNP and hence on the quantity and quality of marine productivity and the biological carbon pump. In other words, although our study demonstrated that oceanic changes similar to those induced by ENSO were operating at millennial time scale in the ETNP, other mechanisms such as changes in oceanic or atmospheric circulation, global nutrient cycling etc. might also have impacts on global climate which could potentially override or counteract the effects of ENSO-like perturbations at certain times.

Data: CORDIS, © European Union