Volcanic iron fertilization of primary productivity at Kerguelen Plateau, Southern Ocean, through the Middle Miocene Climate Transition

摘要

ODP Site 747, central Kerguelen Plateau, contains a nearly complete record of theMiddleMiocene Climate Transition (MMCT). Its unusuallywell preserved and rich foraminiferal assemblages have resulted in theMMCT interval at Site 747 becoming a focus of high-resolution paleoclimatic studies that have established this sequence as a Southern Ocean reference. We combine X-ray fluorescence (XRF) elemental counts of Fe, Ti, and Al and concentration-dependent magnetic parameters to trace volcanic ash input to sediments at ODP Hole 747A.We observe systematic variations in Al/Ti and Fe/Ti ratios that are consistent with increased primary productivity at times of increased terrigenous input and, therefore, increased nutrient supply. A spike in terrigenousmaterial, which we interpret as volcanic ash, coincides with major changes in species abundance and stable oxygen and carbon isotopic shifts within theMMCT interval. This correlation suggests that nutrient flux associated with volcanic iron fertilization played a significant role in controlling phytoplankton communities at Site 747. We demonstrate that rapidly obtained XRF andmagnetic parameters can provide useful proxies for terrigenous input and, therefore, nutrient fluxes in pelagic marine settings that can help to resolve local versus global drivers of paleoenvironmental and paleoceanographic changes.