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The large difference in carbon and oxygen isotope data from the marine record between marine oxygen isotope stage 12 (MIS 12) and MIS 11, spanning the interval between about 480 and 380 kyr ago, has been interpreted as a transition between an extremely cold glacial period and an unusually warm interglacial period, with consequences for global ice volume, sea level and the global carbon cycle1,2,3,4. The extent of the change is intriguing, because orbital forcing is predicted to have been relatively weak at that time5. Here we analyse a continuous sediment record from Lake Baikal, Siberia, which reveals a virtually continuous interglacial diatom assemblage, a stable littoral benthic diatom assemblage and lithogenic sediments with ‘interglacial’ characteristics for the period from MIS 15a to MIS 11 (from about 580 to 380 kyr ago). From these data, we infer significantly weaker climate contrasts between MIS 12 and 11 than during more recent glacial–interglacial transitions in the late Pleistocene epoch (about 130 to 10 kyr ago). For the period from MIS 15a to MIS 11, we also infer an apparent lack of extensive mountain glaciation.

The new BDP-98 drill core of the Baikal Drilling Project is a key palaeoclimate record in continental Asia because globally sensitive sedimentary records of such length and continuity are very rare1,2,3. Kashiwaya et al.4 have attempted signal processing of the BDP-98 average grain-size record, but in constructing their age model they excised a 100-metre interval from the 600-metre section, stating that it is “erroneous”4. On the basis of our lithological studies, we consider that this excision is unjustified.