The presence of ice on both land and sea can be observed to form in colder climates with many similarities between the two. While one forms on the land and the other on the sea, both carry many common properties from fresh water content to surface texture similarities that make it difficult to distinguish between the two if in the appearance of a continuous sheet. So with that knowledge, where does the difference lie?
Located mostly near the poles and sometimes supported in colder winter climates of the Northern Hemisphere, sea ice is the ice that forms on the top layer of the ocean. Due to its salt content, ocean waters require a temperature below 28 F (approximately -2 C) to begin forming a slushy layer in the waves. As this slush lumps together it freezes into either separate plates of ice or one continuous sheet. A continuous sheet will continue to grow in size as snow falls on top of it and more water freezes beneath. During the process of this freeze salt is rejected from the forming ice, increasing the saline content of the water below and lowering the freezing point of the more concentrated solution. It should be noted that sea ice contains as much salt as normal freshwater ice.
Dispersed all over the globe in areas that support year-round snow pack, land ice is formed by the accumulation of great quantities of snow. As more snow mounds on top of itself its weight compresses its ice crystals and forms a layer of ice that starts at the bottom in the greatest density and gradually lessens towards the surface. In mountainous environments, when this snow pack-turned-ice sheet grows too sizable for its current position it begins to creep forward down the slope of the mountain as a mass known as a glacier. Glaciers tend to grow and travel in times of cold and retreat in the spring and summer months. For glaciers near the ocean, they will sometimes have a part of themselves collapse into the water. This water-bound piece of glacier becomes what is known as an iceberg, a separate entity from sea ice.
During the last ice age, much of the Northern Hemisphere was covered in a combination of sea and land ices, a cover that provided an important bridge for the passage of different species between the different continents. Today the ice has since retreated to its current positions, where come winter the northern sea is one of ice, and the Antarctica is a combination of the two. Sea ice is important because of the environment it creates for both hunting and prey animals alike. While land ice can also form a type of habitat, its main benefit is in its spring and summer time contributions to streams and rivers. Many of the world's great rivers near mountains rely on these glaciers as an important source of water until the winter replenishes the supply.
With the continual developments of global warming and the increased understanding of the impact it has, there are many concerns for the future of both types of ice. Though it can only be conjectured at the moment, there are numerous forms of consequence the disappearance can take.