DOES THE SOUTHERN HEMISPHERE COOL THE NORTH PACIFIC OCEAN?

Coincidence of Pacific region glacial chronologies suggests a causal linkage between native Southern Hemisphere cooling and climate fluctuations in NW North America. Specifically, glacial chronologies in New Zealand, the southern Andes, and the coastal NW United States reveal glacial advances coincident with SH insolation minima.

That SH glacial advances should occur during SH insolation minima is not surprising. SH cooling should overwhelm relative NH warmth and drive SH glacial systems to maximum or near-maximum positions. However, glaciers in the Olympic Peninsula in the northwestern USA advanced to maximum Late Pleistocene positions 30-35 ka BP and ca. 55-65 ka BP, coincident with ice advances in New Zealand and Chile, and with SH insolation minima. Throughout most of western North America, glaciers reached maximum positions around the Last Glacial Maximum, and ice advances in the 30-35 ka and 60-65 ka periods are not apparent. However, local alluvial fan and fluvial aggradation events do appear to have occurred during those time periods.

We hypothesize that ocean currents transmit SH-sourced cooling to NW North America via ocean currents. This transmission most likely occurs via augmentation of bottom water formation in the Antarctic region during SH insolation minima, and northward advection of the cold water via the Pacific deep western boundary current. Upwelling of cold water would cool air masses over the North Pacific Ocean, and the cold air would be advected into NW North America in the westerly wind belts. The cold air advection may be augmented by westerly wind enhancement during the NH insolation maxima. Glaciation in the Olympic Mountains has been shown to be most pronounced during cool, moist periods, and cool, moist air advected into the inland NW would likely exert strong influences on alluvial processes. Thus some, but not all, NW USA geomorphic records appear to display this SH climatic signal.