Sr isotope evidence for sources of terrigenous sediment in the southeast Atlantic Ocean: Is there increased available Fe for enhanced glacial productivity?

Sr isotope ratios of the terrigenous sediments from the Cape Basin (southeast Atlantic Ocean) exhibit a systematic pattern of climate‐related variability from the Holocene through the last glacial period. Values are high during warm climate intervals (marine isotope stages (MISs) 1 and 3) and lower during full glacial periods (MISs 2 and 4). The variability is large ( 87 Sr/ 86 Sr = 0.717–0.723), and the rapid changes correspond temporally to abrupt climate change during the MIS 5a/4 and 2/1 transitions and through MIS 3. The Sr isotope variability corresponds to changes in δ 13 C of benthic foraminifera at orbital frequencies and within periods of rapid variability. Prior studies have suggested that benthic δ 13 C records from the Cape Basin follow Greenland ice core variability and thus global overturning circulation. Other studies suggest that these benthic δ 13 C records contain a strong overprint from isotopically light carbon, possibly associated with high fluxes of organic matter to the seabed. We explore the scenario that the relationship between lower terrigenous 87 Sr/ 86 Sr and lighter benthic δ 13 C may reflect high productivity during cold climatic intervals as a result of iron fertilization of the southern Atlantic Ocean. Increased supply of iron during cold periods may be associated with greater terrigenous sediment fluxes from South America, characterized by a less‐radiogenic Sr isotopic signature.