Centennial‐scale Holocene North Atlantic surface temperatures from Mg/Ca ratios in Globigerina bulloides

Abstract

A high‐resolution record of Mg/Ca ratios from the planktonic foraminifer Globigerina bulloides has been produced for IMAGES core MD99–2251 from the subpolar North Atlantic. The record extends from the Younger Dryas‐Preboreal transition through the Holocene at ∼70 year resolution, with a more detailed section at ∼20 year resolution through the interval encompassing the major cooling episode 8200 years ago. Mg/Ca derived temperatures show significant variations through the Holocene, with surface temperatures ranging from ∼8 to 13°C. The onset of the Holocene is marked by an abrupt warming, with a further increase in early Holocene temperatures occurring prior to 9.5 ka. This is followed by a mid‐Holocene period of cooler and more stable conditions before temperatures show a stepped increase at ∼3.5 ka. The late Holocene period has the highest temperatures of the entire interglacial but also exhibits coolings of 2–3°C approximately every 500 years. Variations of this magnitude typify the high‐frequency component of temperature variability and do not seem to be restricted to the 8.2 ka event or the early Holocene, when stronger freshwater forcing associated with the decay of the ice sheets might be anticipated. However, episodes of enhanced drift ice input to North Atlantic are coincident with many of the Mg/Ca temperature minima over the last 6 ka. The long‐term warming trend and stepped increase in temperature at ∼3.5 ka are consistent with other planktonic foraminiferal records and appear to reflect regional‐scale changes in the atmospheric forcing of the North Atlantic Current during periods of rapid climate change. Alternatively, changes in ecology may contribute to the Holocene Mg/Ca record, either by species changing their depth habitat or by a shift in seasonal production patterns.