Antarctic Circumpolar Current: Processes, Separation From Australia And South America, And Impact On Global Ocean Circulation And Climate

The processes driving Antarctic Circumpolar Current today

There are various currents flowing in Oceans that determine the direction of the flow of water. There are various forces that act in determining the direction and speed of the ocean currents one of which is wind. Other factors that produce similar results are breaking waves, temperature of water and cabbeling among others. The only current that flows around the globe is the Antarctic Circumpolar Current and this is also the most important current that flows in the Southern Ocean. This particular current which is known as Antarctic Circumpolar Current completes a full circle around the continent of Antarctica and the path that they take is eastern side of Atlantic, Indian, and Pacific Oceans. In this assignment the focus is going to be upon the process that drives the current in today’s time, the separation of Antarctica from Australia and South America and details regarding the Antarctic Circumpolar Current.

The current is regarded by many scholars as the strongest in the oceans and it also transports and moves more water than other currents. The current has a slower eastward flow which is less than 20 cm s^-1(Kim &Orsi 2014, p.2060). The depth of the Antarctic Circumpolar Current starts from 2000 m and may extend till 4000 m, the width can be 1000 to 2000 km. The large area of cross section is what helps in the transport of the large volume of water in the Ocean. The primary driving force of the eastward flow of the Ocean is the strong westerly winds. These winds generally flow between the latitudes of 40^oS to 60^oS. The Antarctic Circumpolar Current is strongest between the latitudes of 45^oS to 55^oS. The Northern edge of the Antarctic Circumpolar Current is Subtropical Convergence or Subtropical Front. This is the area where the temperature of the Sea also known as the Sea Surface Temperature varies between 12°C to 7 to 8°C. The trail of the ACC is bounded by the Drake Passage, the Cape Horn and the Antarctic Peninsula (Hill et al. 2013, p.5200).

Gondwana land was the single undivided landmass that existed in the Neoproterozoic age and existed till the Carboniferous age. The time when this land existed was 550 million years ago to 320 million years ago (Scher et al. 2015). The large land mass of Gondwana started to break in the Jurassic age. The present geological features of the various continents can be termed as features of the division of Gondwana into various parts. It is said that during the formation of the Gondwana land the continent of Australia collided with the continent of Antarctica. Australia was mainly placed on the outer edge of the Super Continent called the Gondwana. It has been found presently that the stretching of the crust of the continent happened before the start of the actual rifting that caused the complete separation of land masses. The stretching of the continental crust started about 160 million years ago. “The first upwelling of sea floor crust, basalt, is estimated to have occurred when the rift valley was about 600 km wide and the inner 360 km of crust had stretched and thinned. Because of the thinning of the crust it becomes lighter and isostatic adjustment caused the thinned crust to rise, allowing the underlying hot lithosphere to rise closer to the surface” (Assmyet al. 2013, p.20670). There was a time when the crust started getting reduced in thickness ranging from around 40 km to 10 km, the change in pressure on the upper Lithosphere which caused the inner magma and lava to come out through the thinnest areas of the stretch.  The split happened with South America and Africa, this happened 170 and 180 million years ago. About 140 million years ago the South Atlantic Ocean. The eastern half of the Gondwana, India and Madagascar broke away and both of these had moved apart from Antarctica and Australia. This is how the separation of the Antarctica from Australia and South America Occurred (Sommers, Donohue &Rosburg 2014).

Separation of Antarctica from Australia and South America

The Antarctic Circumpolar Current originates at the Antarctic region and completes a full circle around the continent of Antarctica and the path that they take is eastern side of Atlantic, Indian, and Pacific Oceans. The Ocean currents have their origin driven by various factors like wind, early tectonic movement, temperature of water and similar other factors.

The Antarctic Circumpolar Current was first discovered by the British Astronomer called Edmond Halley. The discovery happened when the astronomer was surveying the region between 1699 and 1700 in the HMS Paramore Expedition. Various sailors in expeditions kept records of the Antarctic Circumpolar Current, these people include James Cook in 1772-1775, Thaddeus Bellingshausen (Russia) in 1819-1821, and James Clark Ross in 1839-1843. The first person to use the term Antarctic Circumpolar Current is James Cook. Various other people who made expeditions to make significant developments about the ACC are Sir Drake, Abel Tasman, and James Weddell (Donohue et al. 2016).

Extremely strong westerly winds which are nearly zonal force a great northward pressure gradient. Stronger gradients of wind result in stronger flow of current along the Oceans. There are a section of meridional ridges in the lower part of the topography which creates a balance for the ACC (Atlantic Circumpolar Current), this happens due to the generation of friction from the lower drag. There might be variations in the ACC transport, this variability is because of the tides, mesoscale eddies, near-inertial motion, and those forced by variations in the large-scale wind pressure.

Therefore the commencement of the Antarctic Circumpolar Current are mainly natural forces that carry the water in a particular direction.

According to Katz et al (2011, p.1080) “benthic foraminiferal stable isotope comparisons show that a large δ¹³C offset developed between mid-depth (~600 meters) and deep (>1000 meters) western North Atlantic waters in the early Oligocene, indicating the development of intermediate-depth δ¹³C and O₂ minima closely linked in the modern ocean to northward incursion of Antarctic Intermediate Water. At the same time, the ocean’s coldest waters became restricted to south of the ACC, probably forming a bottom-ocean layer, as in the modern ocean.” The researcher has stated that the four layer Ocean structures of the modern day divided into layers such as surface water, intermediate water, deep water and bottom water, had developed in the early Oligocene because of the Antarctic Circumpolar Current.

Commencement of Antarctic Circumpolar Current

The Antarctic Circumpolar Current is effective in the movement of the water in the region where this particular current exists, the adjoining regions also experiences changes in temperature because of the existence and activities of the current (Thompson &NaveiraGarabato2014, p.1820). The Antarctic Circumpolar Current being the strongest Ocean current in the region heavily affects the movement of the clouds and hence affect the rainfall and climate of the regions in the Antarctic.

Conclusion: 

Thus it can be concluded from the above discussion that the oceans themselves are very important and crucial in the heating of the earth and for climatic balance. In the regions which are situated outside of the earth’s equatorial region the ocean currents play an important role in maintenance of weather balance. In the northern hemisphere the weather currents flow clockwise and the opposite in southern hemisphere. These currents act as conveyer belts that that carry the precipitation and warm water from the equator to the poles and just the opposite happens with the cold water which is brought from the poles to the tropics. The Antarctic Circumpolar Current helps in maintaining the global climate and balances the uneven distribution of the solar radiation on the earth surface. Without the presence of the ocean currents in general the equatorial and polar climate would be more extreme.

Reference:

Assmy, P., Smetacek, V., Montresor, M., Klaas, C., Henjes, J., Strass, V.H., Arrieta, J.M., Bathmann, U., Berg, G.M., Breitbarth, E. &Cisewski, B., 2013. Thick-shelled, grazer-protected diatoms decouple ocean carbon and silicon cycles in the iron-limited Antarctic Circumpolar Current. Proceedings of the National Academy of Sciences, 110(51), pp.20633-20638.

Donohue, K.A., Tracey, K.L., Watts, D.R., Chidichimo, M.P. &Chereskin, T.K., 2016. Mean antarctic circumpolar current transport measured in drake passage. Geophysical Research Letters, 43(22).

Hill, D.J., Haywood, A.M., Valdes, P.J., Francis, J.E., Lunt, D.J., Wade, B.S. & Bowman, V.C., 2013. Paleogeographic controls on the onset of the Antarctic circumpolar current. Geophysical Research Letters, 40(19), pp.5199-5204.

Katz, M.E., Cramer, B.S., Toggweiler, J.R., Esmay, G., Liu, C., Miller, K.G., Rosenthal, Y., Wade, B.S. & Wright, J.D., 2011. Impact of Antarctic Circumpolar Current development on late Paleogene ocean structure. Science, 332(6033), pp.1076-1079.

Kim, Y.S. &Orsi, A.H., 2014. On the variability of Antarctic Circumpolar Current fronts inferred from 1992–2011 altimetry. Journal of Physical Oceanography, 44(12), pp.3054-3071.

Scher, H.D., Whittaker, J.M., Williams, S.E., Latimer, J.C., Kordesch, W.E. & Delaney, M.L., 2015. Onset of Antarctic Circumpolar Current 30 million years ago as Tasmanian Gateway aligned with westerlies. Nature, 523(7562), p.580.

Sommers, L.A., Donohue, K.A. &Rosburg, K., 2014, December. Revisiting Antarctic Circumpolar Current Transport Estimates. In AGU Fall Meeting Abstracts.

Thompson, A.F. &NaveiraGarabato, A.C., 2014. Equilibration of the Antarctic Circumpolar Current by standing meanders. Journal of Physical Oceanography, 44(7), pp.1811-1828.