Precessional Climate Cyclicity on the Iberian margin: Miocene-recent

IODP Expedition 397 recovered a continuous record of precessionally-paced lithological cycles to the base of the recovered section (~9.55 Ma) at Site U1587. On board ship, three intervals were selected for multi-disciplinary dissection of the cycles in time windows comprising three precessional cycles each ((early Pleistocene 2.284-2.345 Ma, late Pliocene 3.427-3.496 Ma, and late Miocene 5.638-5.5707 Ma). These three intervals are grounded in continuous XRF scanning that allows for a reliable astrochronology based largely on precessional variability. Carbonate cyclicity follows northern hemisphere precession throughout high carbonate content associated with high northern hemisphere summer insolation. The cycles cannot be explained solely by changes in carbonate production or preservation, as the clay-rich phases of the cycles are often expanded relative to the carbonate-rich phases. Sea surface temperature (SST) recorded by alkenone biomarkers shows fluctuations in tandem with the carbonate cycles. For the Pliocene and Pleistocene, higher carbonate correlates to warmer SST and interglacial conditions as inferred from stable isotope measurements. The pattern flips in the Messinian test interval, with high carbonate associated with colder and more glacial climate. Clay mineralogy shows cyclic fluctuations associated with changes in riverine and eolian inputs. High illite (high dust?) corresponds to high carbonate content in the Miocene and Pleistocene test intervals, while the opposite is observed for the Pliocene. An abrupt change in cycle spacing near the terminal Messinian likely records a tectonic event that perhaps influenced transport and deposition of the detrital components.