Arctic ice pack in the context of "Last Glacial Period"

The Arctic Ocean is the smallest and shallowest of the world's five oceanic divisions. It spans an area of approximately 14,060,000 km (5,430,000 sq mi) and is the coldest of the world's oceans. The International Hydrographic Organization (IHO) recognizes it as an ocean, although some oceanographers call it the Arctic Mediterranean Sea or North Polar Sea. It has also been described as an estuary of the Atlantic Ocean. It is also seen as the northernmost part of the all-encompassing world ocean.

The Arctic Ocean includes the North Pole region in the middle of the Northern Hemisphere and extends south to about 60°N. The Arctic Ocean is surrounded by Eurasia and North America, and the borders follow topographic features: the Bering Strait on the Pacific side and the Greenland Scotland Ridge on the Atlantic side. It is mostly covered by sea ice throughout the year and almost completely in winter. The Arctic Ocean's surface temperature and salinity vary seasonally as the ice cover melts and freezes; its salinity is the lowest on average of the five major oceans, due to low evaporation, heavy fresh water inflow from rivers and streams, and limited connection and outflow to surrounding oceanic waters with higher salinities. The summer shrinking of the ice has been quoted at 50%. The US National Snow and Ice Data Center (NSIDC) uses satellite data to provide a daily record of Arctic sea ice cover and the rate of melting compared to an average period and specific past years, showing a continuous decline in sea ice extent. In September 2012, the Arctic ice extent reached a new record minimum. Compared to the average extent (1979–2000), the sea ice had diminished by 49%.

The Last Glacial Period (LGP), also known as the last glacial cycle, occurred from the end of the Last Interglacial to the beginning of the Holocene, c. 115,000 – c. 11,700 years ago, and thus corresponds to most of the timespan of the Late Pleistocene. It thus formed the most recent period of what is colloquially known as the "Ice Age".

The LGP is part of a larger sequence of glacial and interglacial periods known as the Quaternary glaciation which started around 2,588,000 years ago and is ongoing. The glaciation and the current Quaternary Period both began with the formation of the Arctic ice cap. The Antarctic ice sheet began to form earlier, at about 34 Mya (million years ago), in the mid-Cenozoic (Eocene–Oligocene extinction event), and the term Late Cenozoic Ice Age is used to include this early phase with the current glaciation. The previous ice age within the Quaternary is the Penultimate Glacial Period, which ended about 128,000 years ago, was more severe than the Last Glacial Period in some areas such as Britain, but less severe in others.

The polar regions, also called the frigid zones or polar zones, of Earth are Earth's polar ice caps, the regions of the planet that surround its geographical poles (the North Pole and the South Pole), lying within the polar circles. These high latitudes are dominated by floating sea ice covering much of the Arctic Ocean in the north, and by the Antarctic ice sheet on the continent of Antarctica and the Southern Ocean in the south.

Sea ice forms as seawater freezes. Because ice is less dense than water, it floats on the ocean's surface (just like fresh water ice). Sea ice covers about 7% of the Earth's surface and about 12% of the world's oceans. Much of the world's sea ice is enclosed within the polar ice packs in the Earth's polar regions: the Arctic ice pack of the Arctic Ocean and the Antarctic ice pack of the Southern Ocean. Polar packs naturally undergo significant yearly cycling, reaching their greatest surface extent in winter and retreating in summer.

Within the ice, salty brine channels provide habitat for microorganisms that form the base of unique food webs. The presence or absence of sea ice also shapes navigation routes, regional weather, and global ocean circulation. Sea ice plays a key role in Earth's climate. Its white surface reflects the Sun's energy back into space, helping to keep the planet cool in a process known as the albedo effect. Sea ice also insulates the ocean below, limiting the transfer of heat, water vapor, and gases such as carbon dioxide between the sea and the atmosphere.

Global or barystatic sea level has fluctuated significantly over Earth's history. Over geologic time scales, the primary factors affecting sea level are the volume of available water due to growth or melting of ice caps, and the storage volume of the ocean basins due to plate tectonics. The secondary and tertiary influences on water volume are sedimentation, oceanic plume volcanism, the temperature of the seawater, which affects density, and the amounts of water retained in other reservoirs like aquifers, glaciers, lakes, and rivers. In addition to these global changes, local changes in sea level are caused by Earth's crust uplift, known as dynamic topography, and subsidence.

Over geologic timescales sea level has fluctuated by more than 100's of metres. In Archean times, most of the earth was covered by water, and early oceanic crust was relatively shallow. With time oceanic crustal composition changed, plate tectonics commenced at some point in the Proterozoic, and oceanic crust became older and deeper, creating oceans like we have currently. During the Phanerozoic, for which more geological information is available, i.e. marine fossils, sea level fluctuated by several 100's of meters, with the highest peaks generally reconstructed during the middle Paleozoic, and Cretaceous.