Age and duration of Laschamp and Iceland Basin geomagnetic excursions in the South Atlantic Ocean

•Rare recording of Laschamp and Iceland Basin excursions in the South Atlantic.•Age model links excursions to Antarctic ice core and cosmogenic nuclide flux.•South Atlantic ages consistent with North Atlantic ages for the excursions.•No evidence of global diachroneity of magnetic excursions.•Estimated mid-point ages (durations) are 40.9 ka (1 kyr) and 188 kyr (3.5 kyr).

Age models for new records of the Laschamp and Iceland Basin excursions from the eastern flank of the South Atlantic mid-ocean ridge (44.15°S, 14.22°W) are derived from radiocarbon dates, and from matching sea-surface temperature records to Antarctic (EPICA) air-temperature records from ice cores. The onset of the Laschamp excursion occurred during Antarctic Isotopic Maximum (AIM) 10, consistent with its occurrence during Greenland Interstadial 10. The end of the Laschamp excursion occurred prior to AIM 9 in Greenland Stadial 10. The age model is supported by synchroneity of directional and relative paleointensity manifestations of the Laschamp excursion in the marine core with peaks in EPICA10Be and nitrate flux. The Iceland Basin excursion is synchronous with the final phase of the transition from marine isotope stage (MIS) 7a to MIS 6e as recorded in the EPICA δD record. The onset of the Laschamp and Iceland Basin excursions, defined here by component inclinations >−40°, occurred at 41.4 ka and 190.0 ka, and durations are ∼1 kyr and ∼3.5 kyr, respectively, although these estimates depend on the criteria used to define the directional excursions. By comparison with Laschamp and Iceland Basin excursion records from the North Atlantic Ocean, the two excursions are synchronous at centennial timescales between the two hemispheres, based on synchronization of the GICC05 and AICC2012 age models for Greenland and Antarctic ice cores.