AH

Polar Regions - Biol 3711 Lecture Notes

Polar Regions

Overview of Polar Regions

  • Similarities between Antarctic and Arctic regions:

    • Dominance by ice and snow

    • Year-round cold temperatures

    • Drastic changes in photoperiod affecting primary production

  • Differences:

    • Fundamental physical and biological variances.

Physical Conditions - Arctic Ocean

  • Geographical Features:

    • Isolated sea surrounded by landmasses.

    • 2 main outlets to other oceans:

    • Bering Strait: 70 m sill depth (Pacific)

    • Fram Strait: 400 m sill depth (Atlantic)

    • Shallow shelves and sills restrict deep water circulation.

Ocean Currents

  • Major Currents:

    • Beaufort Gyre (anticyclonic)

    • Transpolar Drift

  • Important for nutrient distribution and ice cover dynamics.

Sediment and Nutrient Dynamics

  • Large rivers discharge sediment into the Arctic Ocean, creating a

    • Low salinity surface layer.

  • Provides an important source of nutrients for primary production.

Ice Cover in Arctic Ocean

  • Pack ice:

    • Persists longer (several years) and is thicker than Antarctic ice.

    • Central Arctic Ocean often permanently covered by ice.

Physical Conditions - Southern Ocean

  • Circumpolar Characteristics:

    • Encloses Antarctica and connects with Atlantic, Pacific, and Indian Oceans.

    • Antarctic continental shelf is narrow and drops sharply.

  • Boundary Features:

    • Antarctic Convergence: Persistent winds create a front.

    • Cold water sinks, forming bottom water in deep oceans.

Ice Dynamics in Southern Ocean

  • Seasonal pack ice (typically younger than one year).

  • Minimal sediment input with no stratified surface layer.

Seasonal and Nutritional Variations

  • Greater temperature variability in the Arctic compared to Antarctica.

  • Nutrient availability:

    • Euphotic zone nutrient depletion in Arctic summer.

    • Consistently high nutrient levels in Antarctic waters year-round.

Shallow Water Communities

  • Communities mainly under ice, facing minimal wave disturbance.

  • Ice Scour:

    • Ice coming into contact with the ocean floor leads to destruction of fauna.

    • No permanent shallow depth communities; seasonal transients appear when the ice melts.

Ice Scour Effects on Fauna

  • Sediments affected by ice scour:

    • Dominated by disturbance-associated fauna.

    • Outside scour: large bivalves, urchins, sea cucumbers, and algae.

    • Inside recent scour: annelids, amphipods, diatoms.

Adaptations to Cold Temperatures

  • Water temperatures range from 1.5 ext{°C} to -1.8 ext{°C}.

  • Invertebrate adaptations: High solute concentration helps lower body fluid freezing points.

  • Marine fish:

    • Hypoosmotic with freeze points at around -0.8 ext{°C} and produce antifreeze glycoproteins.

Notothenioid Fish

  • Endemic to polar regions, making up 90% of fish biomass in Antarctica.

  • Notable example: Crocodile icefish - vertebrates lacking red blood cells, resulting in more fluid blood.

Sea Ice Communities

  • Unique habitats supporting various organisms, heavily dominated by diatoms (200 species in Arctic, 100 species in Antarctic).

  • Active bacteria and archaea, especially during winter.

Sea Ice Food Web

  • Sea ice acts as a temporary habitat for certain planktonic species.

  • Diatoms at ice edges serve as food sources grazed by various metazoans (important for the ecosystem).

Zooplankton Comparisons

  • Antarctic Dominance: Krill (Euphausia superba) as major herbivores south of the Antarctic Convergence Zone.

  • No equivalent dominant species in the Arctic Ocean.

  • Role of Krill:

    • Essential for Antarctic food webs, competing with salps for phytoplankton.

    • Target of major fisheries.

Marine Birds and Mammals

  • Dependent on sea ice for habitat, breeding, and hunting.

  • Important for rearing young and as a platform for moulting.

Human Impacts on Polar Environments

  • Arctic sea ice thickness declining 11% per decade since 1979.

  • Projected ice-free summers in the Arctic Ocean within a few decades.

  • Vulnerable species include polar bears, walrus, bearded seals, and ringed seals.

Outside scour refers to sediment areas affected by ice that has not recently moved, typically supporting larger fauna such as bivalves, sea urchins, sea cucumbers, and algae. In contrast, inside scour refers to areas that have been recently disturbed by moving ice, which tends to dominate with smaller organisms like annelids, amphipods, and diatoms.