Canterbury drifts at ocean drilling program site 1119, New Zealand: climatic modulation of southwest Pacific intermediate water flows since 3.9 Ma

Abstract

We provide a record of variations in southwest Pacific Ocean intermediate water flow that shows a strong correlation between periods of vigorous flow and warm climate phases. Ocean Drilling Program Site 1119, located at 395 m water depth on the upper continental slope east of New Zealand, penetrated 514 m of silts and silty clays (glacial deposits) punctuated by muds and episodic 0.02–1.2-m-thick terrigenous sands (interglacial deposits). The natural gamma-ray record reflects the waxing and waning of the South Island ice cap since 3.91 Ma. Below 86.19 m composite depth, the succession comprises drift sediments deposited from north-flowing intermediate Subantarctic Mode Water (SAMW, ~250–800 m depth) and Antarctic Intermediate Water (~800–1100 m depth). A change from the deposition of large, low-energy drifts on the middle slope to smaller, higher-energy drifts on the upper slope coincided with global climatic deterioration that occurred after ca. 3.25 Ma. This change marks an upward expansion of intermediate cold waters, perhaps caused by the inception of the Subantarctic Front and the consequent commencement of Southland Current–driven SAMW flow.