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Monday Noon Seminar - Tropical/high latitude connections over the last millennium: Insights from...

Monday, April 20, 2015, 12:00PM - 1:00PM


Samantha Stevenson



ARC room 620

Full title

Tropical/high latitude connections over the last millennium: Insights from coral proxy records


Tropical and extratropical variability are known to be connected through meridional mode dynamics, but how climate change affects these linkages remains unknown. I will present new results showing that a new mode of climate variability, the South Pacific Gyre Oscillation, is responsible for SST, sea surface salinity, and oxygen isotope ratios (∂18O) trends at coral proxy sites in the southwestern tropical Pacific. The SPGO is excited by midlatitude SLP variations near the climatological gyre boundary (40°S), and influences ∂18O by creating midlatitude ascent/subsidence which shifts the South Pacific Convergence Zone (SPCZ). Autoregressive modeling then shows that SPGO trends are in turn due to heating of the western Pacific warm pool, which occurs independently from the El Nino/Southern Oscillation (ENSO). This implies that the previously identified "ENSO residual" trend mode is in fact created by meridional mode dynamics. As the Pacific shifts to a more "SPGO-positive" state under climate change, the Southern Hemisphere meridional mode gains power and SPCZ variability becomes more coherent with the Southern Annular Mode (SAM). Strengthened Southern Hemisphere tropical/midlatitude coupling implies that future tropical variability may lead to more intense oscillations in subtropical gyre strength—and in turn, changes in ocean heat content and global surface temperature.


Free and open to the public.