Final answer:
In summer, pack ice is mainly first-year ice that is thin and prone to melting. In winter, pack ice is older ice that is thicker and more stable. The Antarctic ice sheet has been accumulating for over 420,000 years and can reach depths of over 3,000 meters, while the thickness of the Arctic ice sheet varies depending on the region.
Step-by-step explanation:
In summer, pack ice refers to the ice that forms on the Arctic and Antarctic seas during the warmer months. It consists mainly of first-year ice, which is relatively thin and has a high salt content. This pack ice is less stable and more prone to melting.
In winter, pack ice refers to the ice that forms on the Arctic and Antarctic seas during the colder months. It consists of older ice that has survived multiple summers, making it thicker and more stable. This pack ice can extend over larger areas and is less prone to melting.
As for the age and thickness of the Arctic and Antarctic ice sheets, the ice cores from the Vostok station in East Antarctica have provided valuable data. These ice cores show that the Antarctic ice sheet has been accumulating for over 420,000 years and can reach depths of over 3,000 meters. The age and thickness of the Arctic ice sheet vary depending on the region, with the thickest ice found in the central Arctic Basin.