“Clark finds that with returning daylight the diatoms are again appearing. His nets and line are stained a pale yellow, and much of the newly formed ice has also a faint brown or yellow tinge. The diatoms cannot multiply without light, and the ice formed since February can be distinguished in the pressure-ridges by its clear blue colour. The older masses of ice are of a dark earthy brown, dull yellow, or reddish brown.”

— Ernest Shackleton, South