Holocene paleomagnetic records from the St. Lawrence Estuary, eastern Canada: centennial- to millennial-scale geomagnetic modulation of cosmogenic isotopes

Two long Holocene piston cores (MD99-2220 and MD99-2221) were raised from the St. Lawrence Estuary, eastern Canada because of the expanded Holocene sediment sequence this location provides. A u-channel-based paleomagnetic study, supported by an accelerator mass spectrometry (AMS) 14C chronology, rock-magnetic and sedimentological data, indicates that these sediments provide a paleomagnetic directional secular variation (PSV) and relative paleointensity (RPI) proxy records for the last ∼8500 cal BP. Sedimentation rates vary from ∼1.2 to 4.2 m/kyr. Comparison of inclination and declination features with other North American Holocene PSV records are generally consistent and temporal offsets are within chronological uncertainties. The normalized natural remanent magnetization intensity record, a RPI proxy, from the postglacial sediments of core 2220 compares favorably with North American and European Holocene RPI records at millennial and even some centennial timescales. Comparisons between core 2220 RPI proxy and the 10Be flux record from the Greenland Summit (GISP2) ice core [Finkel and Nishiizumi, J. Geophys. Res. 102 (1997) 26699–26706] and a 14C production rate record [Bond et al., Science 294 (2001) 2130–2136] suggest that geomagnetic modulation may control the millennial- and even some centennial-scale variability within cosmogenic isotope records. This implies that the core 2220 RPI record reflects changes in global-scale geomagnetic field at these timescales.