OCEANIC RESPONSE TO HIGH-LATITUDE CLIMATE VARIABILITY AT ODP SITE 1123 DURING THE PLIO-PLEISTOCENE

The distribution of heat, salts, gasses, and nutrients relies on water circulation originating in high latitudes. At these high latitudes, water circulates in the deepest portions of the ocean, aided by deep western boundary currents (DWBC) which transport the waters to the equator. At present, the majority of deep-water masses form both in the North Atlantic and around Antarctica, named North Atlantic Deep Water (NADW) and Antarctic Bottom Water (AABW), respectively, while current research suggests that the overturning processes that create NADW is now in a weakened state compared to the last 2000 years. Alternatively, over past glacial-interglacial periods, the rate of NADW production is thought to have been enhanced during interglacial periods, notably during the mid-Pliocene warm period when global mean temperatures were 2°C warmer than pre-industrial values. Further, AABW production is understood to have been greater during periods of Southern Hemisphere cooling, such as during the late Pliocene.

Here, we focus on ODP Site 1123, situated off the east coast of New Zealand in the South Pacific Ocean, where the Antarctic Circumpolar Current is deflected by the Chatham Rise. In this study, the downstream response of high-latitude climate variability on oceanic overturning along the SW Pacific DWBC during the mid-Pliocene to early Pleistocene is highlighted. We present an integrated record of oxygen (δ18O) and carbon (δ13C) isotopes, inorganic geochemical measurements derived from X-Ray fluorescence (XRF) core scanning data, a mass accumulation rate record of terrigenous vs. carbonate sedimentation, and a sortable silt record composed of particle size data from the 10–63μm grain size range of sediment samples. In this data, a previously unidentified threshold is seen, where a warming of >2°C, similar to that which our current climate is approaching, results in an overall more sluggish deep ocean circulation regime along the SW Pacific DWBC than we see currently.