The Atlantic meridional overturning circulation (AMOC) transports warm salty surface waters to high latitudes, where they cool, sink and return southwards at depth. Through its attendant meridional heat transport, the AMOC helps maintain a warm northwestern European climate, and acts as a control on the global climate. Past climate fluctuations during the Holocene epoch (∼11,700 years ago to the present) have been linked with changes in North Atlantic Ocean circulation1,2. The behaviour of the surface flowing salty water that helped drive overturning during past climatic changes is, however, not well known. Here we investigate the temperature and salinity changes of a substantial surface inflow to a region of deep-water formation throughout the Holocene. We find that the inflow has undergone millennial-scale variations in temperature and salinity (∼3.5 °C and ∼1.5 practical salinity units, respectively) most probably controlled by subpolar gyre dynamics. The temperature and salinity variations correlate with previously reported periods of rapid climate change3. The inflow becomes more saline during enhanced freshwater flux to the subpolar North Atlantic. Model studies predict a weakening of AMOC in response to enhanced Arctic freshwater fluxes4, although the inflow can compensate on decadal timescales by becoming more saline5. Our data suggest that such a negative feedback mechanism may have operated during past intervals of climate change.
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We thank the crew of RV Charles Darwin 159; M. Greaves, A. Huckle and L. Booth for laboratory assistance; J. Rolfe and M. Hall for stable isotope analyses; J. Hillier for the Atlantic base map; and S. Crowhurst, T. Dokken, M. Schulz and L. Skinner for discussions. Radiocarbon dates were run by the UK Natural Environment Research Council (NERC) radiocarbon laboratory. Labrador Sea data was provided by A. de Vernal. Funding was provided by the NERC Rapid Climate Change programme.
Author Contributions H.E. and I.N.M. were responsible for initiating the study, and D.J.R.T. collected data, performed analyses and interpreted data. The manuscript was written by D.J.R.T. H.E. and I.N.M. contributed equally to the study. All authors contributed to the work at sea on RV Charles Darwin 159, discussed the results and commented on the manuscript.
This file contains Supplementary Methods, Supplementary Figures 1-3 with Legends, Supplementary Table 1, a Supplementary Discussion, Supplementary Notes and Supplementary References