Article History

Received: 2 September 2015

Accepted: 9 March 2016

First Online: 18 April 2016

Change Date: 6 May 2016

Change Type: Corrigendum

Change Date: 8 August 2016

Change Type: Update

Change Details: In the version of the Letter originally published, in the first sentence of the Fig. 4 caption, 'δ18C' should have been 'δ18O'. This has been corrected in the online versions of the Letter.

Change Details: In the version of this Letter originally published the data availability statement was not included and it should have read: All seawater data are publicly and freely available at; δ18O-data plotted in Fig. 4 are from ref. 60 and are available at the Britishweb site.

Competing interests

: The authors declare no competing financial interests.