Why do sea ice and icebergs have different origins?

Sea ice and icebergs have fundamentally different origins based on their formation process and location:

• Sea ice forms directly from the freezing of seawater on the ocean surface. This process begins with the formation of small ice crystals (frazil) that aggregate into sheets or pancakes, eventually thickening into floes through congelation or mechanical deformation. Because it forms from ocean water, sea ice contains trapped brine and salt pockets.123
• Icebergs originate on land as part of glaciers or ice sheets. They are formed by the long-term compression of snow into ice. When these massive land-based ice structures flow toward the coast and extend into the ocean as ice shelves or glacier tongues, they eventually fracture and "calve" into the sea. Consequently, icebergs are composed of freshwater ice rather than frozen seawater.1456

In short, sea ice is a product of the ocean's surface freezing, while icebergs are chunks of land-based glaciers that have broken off into the water.1