Could this be proof of earlier minor climate shifts?

Either that, or it's some chimera that has resulted from the unholy union of an iceberg and a zebra...

Layering of that nature is usually down to environmental changes, so I would subscribe to your theory. Hell, ice cores have been analysed to ascertain their gaseous contents... this has to be historically significant. :-)

Green stripes from when there were more algae in the water. Blue–green algal blooms usually develop during the warmer months of the year. The effect is similar to the formation of growth rings in trees.

Tree Ring Widths Vary from Year to Year

Tree rings—also known as annual growth rings—vary in size each year depending upon the environmental conditions that the tree experiences. For most locations, tree rings will be wider during years of abundant rainfall and narrower during times of drought.

There have been numerous climate changes in the past, ice ages and tropical eras. Were dinosaurs responsible for global warming?