Research on the Variation of Ice Condition in the Key Areas of the Arctic Northwest Passage

Research on the Variation of Ice Condition in the Key Areas of the Arctic Northwest Passage

The Arctic Northwest Passage (NWP) is a potential shipping route that connects the Atlantic and Pacific Oceans through the Canadian Arctic Archipelago. The NWP has attracted increasing attention in recent years due to the rapid decline of sea ice in the Arctic region, which may offer new opportunities for maritime transportation, resource exploration, and tourism. However, the NWP also poses significant challenges for navigation, such as ice hazards, extreme weather, environmental protection, and sovereignty issues. Therefore, it is important to understand the variation of ice condition in the key areas of the NWP and its influencing factors.

This blog post aims to provide an overview of the current research on the variation of ice condition in the key areas of the NWP, based on the latest data and literature. The key areas include the Baffin Bay, Lancaster Sound, Parry Channel, McClure Strait, and Beaufort Sea. The main aspects of ice condition are sea ice extent, concentration, thickness, age, and movement. The influencing factors are atmospheric and oceanic circulation, temperature, precipitation, wind, and human activities.

Sea Ice Extent

Sea ice extent is the total area covered by sea ice within a region. It is usually measured by satellite remote sensing or aerial surveys. Sea ice extent in the NWP shows a clear seasonal cycle, with a maximum in March and a minimum in September. The annual average sea ice extent in the NWP has decreased by about 8% per decade since 1979, according to the National Snow and Ice Data Center (NSIDC). The September sea ice extent has declined more rapidly, by about 12% per decade. The lowest September sea ice extent in the NWP was recorded in 2012, when almost all of the NWP was ice-free. The highest September sea ice extent was recorded in 2014, when only a small portion of the NWP was navigable.

Sea Ice Concentration

Sea ice concentration is the fraction of sea surface area covered by sea ice within a grid cell. It is usually derived from passive microwave sensors on satellites or from visual observations on ships or aircraft. Sea ice concentration in the NWP also varies seasonally, with higher values in winter and lower values in summer. The threshold for navigability is often set at 30% or 10% sea ice concentration, depending on the type and size of vessels. According to NSIDC data, the average summer (June-August) sea ice concentration in the NWP has decreased by about 9% per decade since 1979. The lowest summer sea ice concentration in the NWP was observed in 2016, when most of the NWP had less than 10% sea ice concentration. The highest summer sea ice concentration was observed in 2014, when most of the NWP had more than 30% sea ice concentration.

Sea Ice Thickness

Sea ice thickness is the vertical distance between the upper and lower surfaces of sea ice. It is usually measured by upward-looking sonars on submarines or moorings, laser altimeters on satellites or aircraft, or electromagnetic induction devices on helicopters or sleds. Sea ice thickness in the NWP is influenced by both thermodynamic and dynamic processes, such as freezing and melting, ridging and rafting, and deformation and advection. Sea ice thickness in the NWP varies spatially and temporally, with thicker ice in the western and northern parts and thinner ice in the eastern and southern parts. The average winter (December-February) sea ice thickness in the NWP has decreased by about 1.5 m since 1980, according to submarine data from Rothrock et al. (2008). The thinnest winter sea ice was found in 2007, with an average thickness of about 1.8 m. The thickest winter sea ice was found in 1986, with an average thickness of about 3.6 m.

Sea Ice Age

Sea ice age is a proxy for sea ice thickness and stability. It is usually classified into first-year ice (FYI) and multi-year ice (MYI), based on whether it has survived at least one summer melt season. FYI is generally thinner and more saline than MYI, and more susceptible to melting and breaking. MYI is generally thicker and less saline than FYI, and more resistant to melting and breaking. Sea ice age in the NWP is determined by both local growth and decay and remote advection from other regions. Sea ice age in the NWP has changed significantly over the past decades, with a decrease of MYI and an increase of FYI. According to NSIDC data, the average winter MYI fraction in the NWP has decreased by about 15% per decade since 1984. The lowest winter MYI fraction in the NWP was observed in 2016, when only about 5% of the NWP was covered by MYI. The highest winter MYI fraction in the NWP was observed in 1988, when about 45% of the NWP was covered by MYI.

Sea Ice Movement

Sea ice movement is the horizontal displacement of sea ice due to wind, ocean currents, and Coriolis force. It is usually calculated from satellite tracking or drifting buoys. Sea ice movement in the NWP is affected by both large-scale and regional-scale circulation patterns, such as the Arctic Oscillation (AO), the Beaufort Gyre (BG), and the Transpolar Drift (TPD). Sea ice movement in the NWP has implications for sea ice export and import, sea ice deformation and ridging, and sea ice navigation and safety. According to NSIDC data, the average winter sea ice speed in the NWP has increased by about 0.5 cm/s per decade since 1979. The fastest winter sea ice speed in the NWP was observed in 2017, with an average speed of about 9.5 cm/s. The slowest winter sea ice speed in the NWP was observed in 1981, with an average speed of about 6.5 cm/s.

Influencing Factors

The variation of ice condition in the key areas of the NWP is influenced by a combination of natural and anthropogenic factors, which interact with each other in complex ways. The main natural factors are atmospheric and oceanic circulation, temperature, precipitation, and wind. The main anthropogenic factors are greenhouse gas emissions, aerosol emissions, and human activities.

Atmospheric and oceanic circulation play a dominant role in determining the large-scale variability and trends of sea ice in the NWP. The AO is a mode of atmospheric variability that reflects the strength and location of the polar vortex. A positive AO phase is associated with a stronger and more centered polar vortex, which tends to confine cold air over the Arctic and reduce sea ice export from the Arctic Ocean. A negative AO phase is associated with a weaker and more displaced polar vortex, which tends to allow cold air to spill over the mid-latitudes and increase sea ice export from the Arctic Ocean. The BG is a clockwise circulation of surface water and sea ice in the Beaufort Sea, driven by wind stress and Coriolis force. A stronger BG tends to accumulate more sea ice in the western part of the NWP and reduce sea ice inflow from other regions. A weaker BG tends to release more sea ice from the western part of the NWP and increase sea ice inflow from other regions. The TPD is a counterclockwise circulation of surface water and sea ice from the Siberian coast to the Fram Strait, driven by wind stress and Coriolis force. A stronger TPD tends to transport more sea ice from the eastern part of the NWP to the North Atlantic and reduce sea ice inflow from other regions. A weaker TPD tends to transport less sea ice from the eastern part of the NWP to the North Atlantic and increase sea ice inflow from other regions.

Temperature is a key factor that controls the thermodynamic processes of sea ice growth and decay. Higher temperature leads to more melting in summer and less freezing in winter, resulting in thinner and less extensive sea ice. Lower temperature leads to less melting in summer and more freezing in winter, resulting in thicker and more extensive sea ice. Temperature is influenced by both natural variability and anthropogenic forcing. Natural variability includes solar radiation, volcanic eruptions, El Niño-Southern Oscillation (ENSO), Pacific Decadal Oscillation (PDO), etc. Anthropogenic forcing includes greenhouse gas emissions, aerosol emissions, land use change, etc. According to NSIDC data, the average annual surface air temperature over the NWP has increased by about 0.4°C per decade since 1979. The highest annual surface air temperature over
the NWP was observed in 2016, with an average temperature of about -10°C. The lowest annual surface air temperature over
the NWP was observed in 1984, with an average temperature of about -13°C.

Precipitation is another factor that affects the thermodynamic processes of sea ice growth and decay. Precipitation can be either solid (snow) or liquid (rain). Snowfall on sea ice can act as an insulator that reduces heat loss from sea ice to the atmosphere, leading to slower freezing in winter and faster melting in summer. Rainfall on sea ice can act as a catalyst that enhances heat transfer from sea ice to the atmosphere, leading to faster freezing in winter and slower melting in summer. Precipitation is influenced by both natural variability and anthropogenic forcing. Natural variability includes moisture transport, storm tracks, cloud cover, etc. Anthropogenic forcing includes greenhouse gas emissions, aerosol emissions, land use change, etc. According to NSIDC data, the average