GER­ALD HAUG: "Ice Ages, In­ter­gla­cials and a 450ppm CO2 world"

Gerald H. Haug (Max Planck Institute for Chemistry and ETH Zürich), Anja Studer (MaxPlanck Institute for Chemistry), Samuel L. Jaccard (Bern University), Alfredo Martinez-Garcia (Max Planck Institute for Chemistry), Ralf Tiedemann (Alfred Wegener Institute), and Daniel M. Sigman (Princeton University)

We ar­gue for a per­vas­ive link between cold cli­mates and po­lar ocean strat­i­fic­a­tion. In boththe Sub­arc­tic North Pa­cific and the Ant­arc­ticZone of the South­ern Ocean, ice ages were­marked by low pro­ductiv­ity. The ac­cu­mu­lated evid­ence from sed­i­ment cores points to anin­crease in dens­ity strat­i­fic­a­tion that re­ducedthe sup­ply of nu­tri­ents from the ocean in­teri­or­into the sun­lit sur­face in both of these re­gions. The last ice age was as­so­ci­ated with­strat­i­fic­a­tion of the Ant­arc­tic and the sub­arc­tic North Pa­cific and it can be ar­gued that thewell-known gla­cial de­crease in North At­lantic Deep Wa­ter in­dic­ates a sim­ilar strat­i­fic­a­tionof the North At­lantic. This link also ap­plies to longer times­cales, in­clud­ing the on­set ofex­tens­ive north­ern hemi­sphere gla­ci­ation 2.7 mil­lion years ago, which was con­cur­rent with­strat­i­fic­a­tion of the Sub­arc­tic North Pa­cific and the South­ern Ocean. The gen­er­al­ity of the­cool­ing/​strat­i­fic­a­tion con­nec­tion calls for agen­eral mech­an­ism.

Such a mech­an­ism is­provided by the non-lin­e­arrela­tion­ship between the tem­per­at­ure of sea­wa­t­er­and its dens­ity:cool­ing of the ocean will de­crease the role that­tem­per­at­ure plays in the dens­ity struc­ture of­the po­lar wa­ter column, al­low­ing the fresh­wa­ter capthat is al­ways present in po­lar re­gions to­cause greater dens­ity strat­i­fic­a­tion, al­low­ing the fresh­wa­ter cap toin­tensify fur­ther. Nu­tri­ent-rich po­lar ocean re­gions such as the Ant­arc­tic­and the Sub­arc­tic Pa­cific rep­res­ent a “leak” inthe bio­lo­gical pump, al­low­ing deeply se­questered car­bon di­ox­ide to es­cape back into theat­mo­sphere, and strat­i­fic­a­tion of these re­gionslargely stops that leak. Thus, the link between­cli­mate cool­ing and the strat­i­fic­a­tion of nu­tri­ent-rich po­lar re­gions rep­res­ents a pos­it­ive­feed­back in the cli­mate sys­tem, rais­ing at­mo­spheric car­bon di­ox­ide dur­ing warm peri­ods an­dre­du­cing it dur­ing cold peri­ods.