Climate stage· The columns of time

MIS 7

243 ka → 191 ka

Marine isotope stage 7, from 243,000 to 191,000 years ago, counts as an interglacial but is made of several temperate intervals separated by cold episodes.

Marine isotope stage 7, classed as an interglacial but composed of several temperate intervals separated by cold episodes. It illustrates the smoothing imposed by representing a stage as a single band.

What the evidence shows

The underlying isotopic curve presents for this stage several distinct maxima separated by cold minima; these subdivisions are called substages and designated by letters, from 7a to 7e. The lettering convention follows that of the numbers: it runs from the most recent to the oldest and alternates, letters a, c and e designating the temperate intervals and b and d the cold episodes interposed. MIS 7e is therefore the oldest warm maximum of the stage and MIS 7d the cold episode succeeding it. The timeline represents the stage and not its subdivisions, which at this scale would occupy only a few pixels.

Bounds and conventions

The representation masks the internal structure of the stage. A band of uniform colour presupposes underlying oscillations: the LR04 curve is continuous, and each limit drawn results from a decision on the point at which a gradual variation is treated as a threshold.

Interglacial, interrupted by cool episodes (7b, 7d).