Possible Solar-Linked Climate Controls on Recurring Dispersal of Sediment-Bearing Sea Ice During the Holocene

Records of Holocene IRD (ice rafted debris) in the subpolar North Atlantic have recently been tied to variations in solar output. That finding underscores the importance of understanding how coarse (sand-sized) lithic sediment comprising the IRD is linked to ice in the ocean and to climate. New data from sediment traps in the Greenland and Norwegian Seas suggests that the Holocene IRD is released from melting multiyear sea ice exiting the Arctic through Fram Strait. Analyses of over 50 sediment trap samples demonstrate that large numbers of sand sized grains settle through the water column during all months of the year. Fluxes of those grains are higher by factors of 3 to 4 than those estimated at the sites of the Holocene records, consistent with those locations in warmer waters to the south. In addition, 15 to 20 percent of the sediment trap lithic grains have hematite staining, which is a robust petrologic tracer of the sea ice trajectories associated with the Holocene IRD. New evidence from NCEP-NCAR reanalysis demonstrates that anomalous north to northwesterly winds in the eastern North Atlantic, which are required to explain the record of hematite-stained grains in that region during the Holocene, occurred at rather specific times during the last several decades. Those times correspond to increases in extreme drift ice sightings and to a 1 to 2 degree cooling of the ocean surface. Similar temperature changes during the Holocene IRD events are suggested by Mg/Ca measurements in planktic foraminifera from eastern North Atlantic coring sites. The most persistent north to northwesterly winds occurred during spring and summer and at times when pressure increased in both the Azores and Hawaiian highs. A link therefore appears to exist between the Holocene shifts in North Atlantic drift ice and subtropical atmospheric circulation, which in turn, based on results of recent GCM models, may be influenced by solar variability.