How do layers form inside Antarctic tabular icebergs?

Antarctic tabular icebergs do not form their layers through a process unique to the iceberg itself; rather, they inherit a layered structure from the parent ice shelf and the continental ice sheet from which they originated.1

These layers are formed by the accumulation of annual snowfall over time. As new snow falls, it covers older layers, which are then compressed by the weight of the overlying material. This process leads to a vertical profile of increasing density:1

• Surface: The uppermost section consists of recently fallen snow, which has a low density.1
• Firn: Below the surface, the material is classified as firn—a transitional state between snow and ice where the density is higher but air spaces still exist between crystal grains.1
• Ice: At depths of approximately 40–60 metres (130–200 feet), the density reaches about 800 kg per cubic metre. At this point, the air channels are sealed off, forming air bubbles and creating true ice.1

Because these annual layers are often clearly visible on the vertical sides of a newly calved iceberg, they serve as a record of the historical accumulation of snow on the Antarctic continent.1