Simulation of Holocene cooling events in a coupled climate model

• Published in: Quaternary Science Reviews
• Main Authors: Renssen, Hans, Goosse, Hugues, Fichefet, Thierry
• Other Authors: UCL - SST/ELI/ELIC - Earth & Climate
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2007
• Subjects: 1443; Labrador Sea; Nordic Seas; North Atlantic; Sea ice
• Online Access: http://hdl.handle.net/2078.1/71472; https://doi.org/10.1016/j.quascirev.2007.07.011

Three potential mechanisms behind centennial-scale Holocene cooling events are studied in simulations performed with the coupled climate model ECBilt–CLIO: (1) internal variability, (2) solar forcing, and (3) freshwater forcing. In experiments with constant preindustrial forcings, three centennial-scale cooling events occur spontaneously in 15,000 years. These rare events represent an unstable internal mode of variability that is characterised by a weaker thermohaline circulation, a more southward location of the main site of deep-water formation, expanded sea-ice cover and cooling of 10 °C over the Nordic Seas. This mode is visited more frequently when the climate is cooled by abruptly reducing the solar constant by 5 or 3 Wm?2. Prescribing a solar forcing of the same magnitude, but following a sinusoidal function with a period of 100 or 1000 years, does not result in any centennial-scale cooling events. The latter forcing does however result in more frequent individual cold years in the North Atlantic region that are related to local weakening of the deep convection and sea-ice expansion. Adding realistic freshwater pulses to the Labrador Sea is also able to trigger centennial-scale cooling events with temperature anomalies resembling proxy evidence for the cooling event at 8.2 kyr BP, suggesting that freshwater forcing is a valid explanation for early Holocene cooling events.