Solar modulation of North Atlantic central Water formation at multidecadal timescales during the late Holocene

• Published in: Earth and planetary science letters 2011-08, Vol.308 (1), p.161-171
• Main Authors: Morley, Audrey, Schulz, Michael, Rosenthal, Yair, Mulitza, Stefan, Paul, André, Rühlemann, Carsten
• Format: Article
• Language: English
• Subjects: benthic Mg/Ca paleothermometry; Climate; climate signal transfer; Density; Fluxes; Freshwaters; Gyres; Irradiance; Late Holocene; Marine; NAO; North Atlantic central water formation; North Atlantic oscillation; solar minima — LIA; Water circulation
• ISSN: 0012-821X; 1385-013X
• DOI: 10.1016/j.epsl.2011.05.043

Understanding natural climate variability in the North Atlantic region is essential not only to assess the sensitivity of atmosphere–ocean climate signal exchange and propagation, but also to help distinguish between natural and anthropogenic climate change. The North Atlantic Oscillation is one of the controlling modes in recent variability of atmosphere–ocean linkages and ice/freshwater fluxes between the Polar and North Atlantic Ocean. Through these processes the NAO influences water mass formation and the strength of the Atlantic Meridional Overturning circulation and thereby variability in ocean heat transport. However, the impact of the NAO as well as other forcing mechanisms on multidecadal timescales such as total solar irradiance on Eastern North Atlantic Central Water production, central water circulation, and climate signal propagation from high to low latitudes in the eastern subpolar and subtropical basins remains uncertain. Here we use a 1200 yr long benthic foraminiferal Mg/Ca based temperature and oxygen isotope record from a ~ 900 m deep sediment core off northwest Africa to show that atmosphere–ocean interactions in the eastern subpolar gyre are transferred at central water depth into the eastern boundary of the subtropical gyre. Further we link the variability of the NAO (over the past 165 yrs) and solar irradiance (Late Holocene) and their control on subpolar mode water formation to the multidecadal variability observed at mid-depth in the eastern subtropical gyre. Our results show that eastern North Atlantic central waters cooled by up to ~ 0.8 ± 0.7 °C and densities decreased by σ θ = 0.3 ± 0.2 during positive NAO years and during minima in solar irradiance during the Late Holocene. The presented records demonstrate the sensitivity of central water formation to enhanced atmospheric forcing and ice/freshwater fluxes into the eastern subpolar gyre and the importance of central water circulation for cross-gyre climate signal propagation during the Late Holocene. ► 1200 yr. long paired Mg/Ca–δ 18O central water record in the eastern North Atlantic. ► Multidecadal variability of Eastern North Atlantic Central Water. ► Sensitivity of ENACW formation to subpolar gyre sea surface temperatures. ► Cross-gyre climate signal transfer of NAO and solar irradiance into ENACW.