1.5 - Geography Notes 30

Elaborate Notes

Siberian Type (Cool Temperate Continental) Climate

Nomenclature and Location: This climatic type is also known as the Taiga Climate or the Boreal Climate. It is named after the vast coniferous forest region of Siberia. A key characteristic, as noted by climatologists like A.N. Strahler, is its exclusive presence in the Northern Hemisphere, spanning from approximately 50° to 70° North latitude. This is due to the absence of large, contiguous landmasses at these latitudes in the Southern Hemisphere. Major regions include the majority of Siberia, northern European Russia, Scandinavia (excluding the western coast), large parts of Canada, and Alaska.
Climatic Characteristics:
- Temperature: It is defined by extreme temperature variations, a hallmark of its continentality. Summers are brief and warm, with temperatures potentially reaching 20-25°C. However, winters are exceedingly long and severe. Regions within this belt, such as Verkhoyansk and Oymyakon in Siberia, have recorded some of the lowest temperatures on Earth (below -60°C), earning them the title of the ‘cold pole of the Northern Hemisphere’. The annual temperature range is the largest of any climate type.
- Pressure and Precipitation: During the harsh winter, the intense cooling of the landmass leads to the development of a strong high-pressure system, known as the Siberian High. This results in stable, anti-cyclonic conditions with outward-flowing cold, dry winds, leading to very little winter precipitation. The modest annual precipitation (around 380-630 mm) is concentrated in the summer months, primarily through convectional rainfall when the continental landmass heats up. In winter, what little precipitation occurs falls as light, dry snow.
Vegetation (The Taiga):
- Dominance of Conifers: The vegetation is overwhelmingly coniferous forest, known as the Taiga. This biome represents the single largest continuous stretch of forest on Earth.
- Adaptations: Coniferous trees like pine, fir, spruce, and larch are adapted to the harsh conditions. Their needle-like leaves minimize water loss through transpiration, a crucial adaptation for a region with frozen ground (permafrost) for much of the year. Their conical shape helps shed heavy snow, preventing branch damage.
- Biodiversity and Economic Value: While the biodiversity is low due to the uniform vegetation and harsh climate, its economic value is immense. These forests are the world’s primary source of softwood, used for lumber, paper pulp, and cellulose production, forming the basis of major industries in Canada, Russia, and Scandinavian countries.

British Type (Cool Temperate Western Margin) Climate

Nomenclature and Location: Also termed the Marine West Coast Climate. It is found on the western margins of continents in the mid-latitudes, typically between 40° and 60° North and South. It is best developed in the United Kingdom, but also characterises Western Europe (e.g., France, Belgium, Netherlands), the Pacific Northwest of North America (Western Canada, Washington, Oregon), Southern Chile, Tasmania, and the South Island of New Zealand.
Climatic Characteristics:
- Influence of Westerlies: The defining feature is its year-round exposure to the on-shore Westerlies. These winds, blowing from over the ocean, bring abundant moisture, resulting in moderate and reliable precipitation throughout the year. The rainfall is often orographic on windward slopes and cyclonic in nature.
- Oceanic Influence: The climate is heavily moderated by the influence of warm ocean currents. The North Atlantic Drift (an extension of the Gulf Stream) keeps the ports of Western Europe, including Murmansk in Russia, ice-free in winter. Similarly, the Alaskan Current warms the coast of Western Canada. This oceanic influence results in a small annual temperature range, with famously mild winters (rarely dropping far below freezing) and cool summers. The weather is often described as variable and cloudy.
Vegetation:
- The original vegetation was temperate broad-leaf deciduous forest. Trees like oak, elm, ash, and birch shed their leaves in the autumn to conserve water and survive the cooler winter—a process known as abscission.
- In many regions, these native forests have been extensively cleared for agriculture and settlement due to the favourable climate and fertile soils. In higher altitude or poorer soil areas, coniferous trees may be present, leading to a mixed forest type.

Polar Type (Tundra) Climate

Nomenclature and Location: The Polar Climate is found beyond the Arctic and Antarctic circles, primarily along the coastal fringes of the Arctic Ocean. It is classified as ET in the Wladimir Köppen classification system (first published in 1884), where ‘E’ denotes a polar climate and ‘T’ signifies Tundra.
Climatic Characteristics:
- Temperature: It is characterized by extremely long, cold winters and very short, cool summers. The warmest month has an average temperature above 0°C but below 10°C. For most of the year, temperatures are below freezing.
- Permafrost: A critical feature is permafrost, or permanently frozen subsoil. During the brief summer, only the top layer of soil (the active layer) thaws, creating waterlogged and marshy conditions because the meltwater cannot drain through the frozen ground below.
Vegetation:
- The severe climate and permafrost prevent the growth of trees. The vegetation is stunted and low-lying.
- It primarily consists of mosses, lichens (e.g., reindeer moss), sedges, and grasses, along with some dwarf shrubs like willows and birches. This vegetation bursts into life during the short summer growing season.

Oceanography

Oceanography as a modern science has its roots in expeditions like that of the HMS Challenger (1872-1876), which systematically collected data on ocean depths, chemistry, and life, laying the foundation for our understanding of the marine environment.

Ocean Bottom Topography

The study of the ocean floor, or bathymetry, revealed that it is not a flat, featureless plain but possesses a varied topography shaped by tectonic, volcanic, and depositional processes.

Continental Shelf: This is the geologically submerged extension of a continent. Its shallow depth (average 150-200m) allows sunlight to penetrate, a region known as the photic zone. This, combined with nutrient runoff from land, supports a high concentration of phytoplankton and zooplankton, which form the base of the marine food web. Consequently, over 90% of the world’s fishing grounds, such as the Grand Banks off Newfoundland and the Dogger Bank in the North Sea, are located on continental shelves. The width is variable: the Siberian Shelf in the Arctic Ocean is one of the widest (over 1,500 km), while the shelf off the mountainous coast of Chile is extremely narrow.
Continental Slope: This marks the true edge of the continental crust, where the seafloor descends steeply from the shelf edge to the deep ocean floor. The gradient is significantly steeper than the shelf, typically ranging from 2° to 5°.
Continental Rise: Located at the base of the continental slope, it is a gentler incline formed by the accumulation of sediments transported down the slope, often by turbidity currents. This feature is more developed along passive continental margins (e.g., the Atlantic coast of North America) and less so along active margins with trenches.
Submarine Canyons: These are steep-sided valleys incised into the continental shelf and slope, resembling river canyons on land. The Hudson Canyon off New York and the Monterey Canyon off California are notable examples. While some may have been formed by river erosion during periods of lower sea level (e.g., the Pleistocene ice ages), the dominant theory, proposed by Reginald Daly (1936), attributes their formation and maintenance to powerful turbidity currents—dense, sediment-laden underwater flows.
Abyssal Plain: These are vast, exceptionally flat areas of the deep ocean floor, typically found at depths of 3,000 to 6,000 meters. Their flatness is a result of a thick blanket of fine-grained pelagic sediments (clays and oozes from dead microorganisms) that has buried the original rugged volcanic terrain over millions of years. They cover more than 50% of the Earth’s surface.
Seamounts and Guyots: Seamounts are isolated submarine mountains of volcanic origin. When they emerge above the sea surface, they become volcanic islands. The Hawaiian-Emperor seamount chain is a classic example of seamounts formed over a tectonic hotspot. Guyots are flat-topped seamounts. Geologist Harry Hess (1946) proposed that they are ancient volcanic islands that were eroded to sea level by wave action and subsequently subsided below the surface as the oceanic crust moved and cooled.
Mid-Oceanic Ridges (MORs): These are extensive submarine mountain ranges formed at divergent plate boundaries where magma upwells to create new oceanic crust. The Mid-Atlantic Ridge is the most famous example. The discovery of MORs was central to the development of the theory of seafloor spreading by Harry Hess and Robert Dietz in the early 1960s.
Trenches: These are the deepest parts of the ocean, long, narrow, and steep-sided depressions formed at convergent plate boundaries where one tectonic plate subducts beneath another. The Mariana Trench in the Pacific Ocean contains the deepest known point on Earth, the Challenger Deep (approx. 11,000 meters).

Ocean Temperature

Differences concerning the Atmosphere:
- Specific Heat Capacity: Water has a much higher specific heat capacity than land. It heats up and cools down much more slowly, giving it a powerful moderating effect on coastal climates.
- Penetration of Light: Solar radiation penetrates the water, distributing heat over a larger volume, unlike on land where it is concentrated at the surface. This penetration is limited to the upper 200m (the photic zone).
- Albedo: The ocean’s albedo (reflectivity) is low (around 6-10%), meaning it absorbs a high percentage of incoming solar radiation.
- Mixing: Unlike the static land surface, ocean water is constantly in motion (currents, waves, convection), which allows for the distribution of heat to greater depths.
Factors Influencing Temperature Distribution:
- Latitude: Insolation is highest in the tropics and decreases towards the poles, making it the primary determinant of sea surface temperature.
- Winds: Winds drive ocean currents and cause mixing. Offshore winds can lead to upwelling, bringing cold, nutrient-rich deep water to the surface (e.g., off the coast of Peru).
- Ocean Currents: These act as a global heat conveyor belt. Warm currents like the Gulf Stream transport heat from the tropics to higher latitudes, while cold currents like the Canary Current bring cold water towards the equator.
- Enclosed Seas: Seas in low latitudes surrounded by land (e.g., the Red Sea, Persian Gulf) tend to have higher surface temperatures and salinities than the open ocean due to intense solar heating and limited circulation.
Vertical Distribution of Temperature: The ocean is typically stratified into three layers, most distinct in the tropics:
1. Epilimnion (Surface Layer): Extends to about 200m. This is the mixed layer, where temperature is relatively uniform due to wind and wave action. It is the warmest layer and corresponds to the photic zone.
2. Thermocline (Metalimnion): From 200m to about 1000m. This is a transition zone characterized by a rapid decrease in temperature with increasing depth. It acts as a barrier separating the warm surface water from the cold deep water.
3. Hypolimnion (Deep Layer): Extends from 1000m to the ocean floor. In this zone, the water is uniformly very cold, with temperatures hovering just above freezing (around 4°C). Seawater reaches its maximum density at approximately this temperature, causing it to sink and fill the deep ocean basins. This three-layer structure is absent in polar regions, where the entire water column is uniformly cold.

Salinity

Definition and Measurement: Salinity is the total amount of dissolved solid material (salts) in grams per kilogram (1000g) of seawater. It is expressed in parts per thousand (ppt or ‰). The average salinity of the world’s oceans is approximately 35 ppt.
Sources and Balance: The salinity of the oceans has remained relatively stable over geologic time, suggesting a state of equilibrium.
- Addition of Salts: The primary source is the weathering and erosion of continental rocks, with dissolved minerals carried to the sea by rivers. Submarine volcanism and hydrothermal vents also release minerals directly into the ocean water.
- Concentration of Salts: Evaporation removes freshwater from the ocean surface, leaving the salts behind and increasing salinity.
- Reduction of Salinity: The addition of freshwater through precipitation (rain and snow), river discharge, and the melting of icebergs and sea ice decreases salinity.
- Removal of Salts: Salts are removed from the water through biological processes (e.g., shell formation by marine organisms) and chemical precipitation, eventually becoming part of the seafloor sediments.
Composition of Sea Salt: The relative proportions of the major dissolved ions in seawater are remarkably constant worldwide, a concept known as the Principle of Constant Proportions or Dittmar’s Law, established by chemist William Dittmar in 1884. The major constituents in decreasing order of abundance are:
1. Chloride (Cl⁻)
2. Sodium (Na⁺)
3. Sulfate (SO₄²⁻)
4. Magnesium (Mg²⁺)
5. Calcium (Ca²⁺)
6. Potassium (K⁺)

Prelims Pointers

Siberian Climate: Also known as Taiga or Boreal climate.
The Siberian climate is found only in the Northern Hemisphere.
It is characterised by extreme annual range of temperature.
Winter condition: Anti-cyclonic, dominated by the Siberian High pressure cell.
Vegetation: Coniferous forests (Taiga), a source of softwood.
British Climate: Also known as Cool Temperate Western Margin or Marine West Coast climate.
It is under the year-round influence of onshore Westerlies.
Warm ocean currents like the North Atlantic Drift cause mild winters and ice-free ports.
Vegetation: Originally temperate deciduous forests (oak, elm, birch).
Polar Climate: Also known as Tundra Climate (Koeppen: ET).
Key feature: Permafrost (permanently frozen subsoil).
Vegetation: Treeless; consists of mosses, lichens, sedges, and dwarf shrubs.
Ocean Bottom Features:
1. Continental Shelf: Shallow, submerged part of the continent; depth 150-200m.
2. Continental Slope: Steep boundary between continental and oceanic crust.
3. Abyssal Plain: Deep (3000-6000m), flat regions of the ocean floor.
4. Seamounts: Submerged volcanic mountains.
5. Guyots: Flat-topped seamounts.
6. Mid-Oceanic Ridges: Formed at divergent plate boundaries.
7. Trenches: Deepest parts of the ocean; formed at convergent (subduction) boundaries.
Ocean Temperature Layers (Vertical):
1. Epilimnion: Top layer (0-200m), warm, mixed, uniform temperature.
2. Thermocline: Zone of rapid temperature decrease with depth (200-1000m).
3. Hypolimnion: Bottom layer (>1000m), uniformly cold (approx. 4°C).
Salinity:
- Average ocean salinity is 35 parts per thousand (ppt or ‰).
- Factors increasing salinity: Evaporation, formation of sea ice.
- Factors decreasing salinity: Precipitation, river inflow, melting of ice.
Order of Dissolved Salts in Seawater (decreasing): Chloride > Sodium > Sulfate > Magnesium > Calcium > Potassium.

Mains Insights

GS Paper I (Geography)

Climate-Vegetation-Economy Linkage: The Siberian climate provides a clear example of how physical geography shapes economic activity. The vast Taiga forests, a direct result of the climatic conditions, support large-scale lumbering, pulp, and paper industries, which are cornerstones of the economies of Canada and Russia. This illustrates the concept of environmental determinism, though modern geography prefers a possibilistic approach.
Significance of Ocean Currents: The British Type climate is a testament to the profound impact of ocean currents on regional climates. The North Atlantic Drift makes Western Europe significantly warmer than other regions at similar latitudes (e.g., Labrador in Canada). This has had immense historical consequences, facilitating the development of maritime cultures, year-round trade, and dense human settlement in Europe.
Ocean Floor Topography and Plate Tectonics: The study of ocean floor features like Mid-Oceanic Ridges and Trenches provided the crucial evidence for the theory of Plate Tectonics. An answer on plate tectonics would be incomplete without mentioning how bathymetric mapping revolutionized our understanding of Earth’s dynamic crustal processes, moving from continental drift to a more comprehensive model.
Geopolitical Significance of Continental Shelves: The economic richness of continental shelves (fisheries, oil, and gas) makes them zones of immense geopolitical importance. This has led to international disputes over their demarcation, which are adjudicated under the framework of the United Nations Convention on the Law of the Sea (UNCLOS). Understanding the geography of shelves is crucial to understanding maritime boundary disputes (e.g., in the South China Sea).

GS Paper III (Environment & Economy)

Climate Change and Tipping Points: The Polar and Siberian climates are at the forefront of climate change. The melting of permafrost is a critical concern as it can release vast quantities of trapped greenhouse gases (methane and CO₂), potentially creating a positive feedback loop that accelerates global warming. This is a potential climatic ‘tipping point’.
Ocean as a Climate Regulator: The ocean’s role in absorbing heat (over 90% of excess heat from global warming) and CO₂ is a vital buffer against climate change. The vertical temperature structure (thermocline) plays a key role in this. However, ocean warming can lead to stronger stratification, which can inhibit the mixing of nutrients and oxygen, impacting marine productivity and creating ‘dead zones’.
Resource Management and Sustainability: The economic value of the Taiga forests must be balanced against the need for sustainable forestry practices to prevent deforestation and loss of a critical carbon sink. Similarly, the rich fishing grounds on continental shelves are vulnerable to overfishing, highlighting the need for robust international agreements and regulations for the sustainable management of marine resources. The concept of Exclusive Economic Zones (EEZ) under UNCLOS is directly linked to the resource potential of continental shelves.

GS Notes