Ice ages are usually known as a period of gradual reduction in the temperature of the planetary climate which causes massive expansion of continental ice sheets, polar ice sheets and mountain glaciers. In glaciological terms, an ice age means that ice sheets are present in the northern and southern hemispheres (which means technically we are still in an ice age, given the ice sheets in Greenland and Antarctic (Imbrie and Imbrie, 1986). A study of ice sheets and other sources reveal that the Earths climate is characterized by a cycle between warm periods or interglacial conditions and glacial conditions.
Many theories have emerged to explain the occurrence of these ice ages. One well-known theory was devised by Milutin Milankovitch in 1938. It predicts that the shifts from glacial to interglacial and vice versa are affected by the changes in the tilt of the Earths rotational axis every 41,000 years, differences in the orientation of the planets elliptical orbit around the Sun known as the precession of the equinoxes occurring every 23,000 years and changes in the shape of the orbit happening almost every 100,000 years (Joyce and Keigwin, 2007).
Another theory that explains the origins of the ice ages is the changes in the planetary atmosphere. The rise and fall of greenhouse gases have been linked to the retreat and advance of the ice sheets. It is possible that the changes in the greenhouse gases may have been caused by other factors contributing to the start of the ice age such as continent motion and volcanism. One hypothesis, known as the Snowball Earth hypothesis, claims that the late Proterozoic era saw a severe ice age that began with a reduction of carbon dioxide levels in the atmosphere and ended with an increase of these levels in the atmosphere.
The early anthropocene hypothesis of William Ruddiman claims that during this era where human activities started to cause a significant global impact on the climate and ecosystems more than 8,000 years ago, atmospheric gas levels began to not follow the pattern of the Milankovitch cycles (Macdougall, 2004). Geological events confirm that the position of continents may cause ice ages if they block or decrease the flow of warm water to the poles allowing the formation of ice sheets. These ice sheets will then cause the increase in the Earths reflectivity decreasing the absorption of solar radiation which leads to atmospheric cooling.
This starts a positive feedback loop allowing more ice sheets to form as the temperature cools. Some of these configurations include a continent sitting on top of a pole, a polar sea that is land-locked and a super continent that covers most of the equatorial area (Aber, 2003). Another big factor in the end of an ice age is sudden global warming that could theoretically be caused by the eruption of large undersea volcanoes. These volcanoes and flood basalts could release huge amounts of methane that contribute to a large and rapid increase in the greenhouse effect (Macdougall, 2004).
There are five known periods of glaciation: Huronian (2400 Ma 2100 Ma), Cryogenian (850 Ma 635 Ma), Andean-Saharan (450 Ma 420 Ma), Karoo (360 Ma 260 Ma) and Cenozoic (30 Ma Present). Oceans are very important in maintaining the stability of climate. The balancing of excess heating at the equator and cooling at the poles is accomplished transporting heat via atmospheric and oceanic currents from low to high altitudes. The warm surface waters that arrive at the higher latitudes are cooled and the heat is released to the atmosphere and later on radiated away to space.
This mechanism bridges the gap between equator and pole temperatures. Warm ocean temperatures also cause an excess of evaporation against precipitation in the atmosphere. The water vapor is then transported to the poles through atmospheric currents and there it cools causing an excess of precipitation against evaporation. These two components together with the salinity-dependent mixing of the cold waters returning from the poles with the warm waters at the equator allows the continuity of the great ocean conveyor belt that allows for climate stability (Joyce and Keigwin, 2007).
An ice age will could also begin if the balance is disrupted on this belt. Scientists now speculate that we are heading for another ice age given the current configurations of the continents and other factors. One possible scenario is that as the Earth continues to experience global warming, ice sheets will soon begin to melt. The Arctic sea has 15% less ice compared to levels 40 years ago. Cold fresh water from melted glaciers and ice sheets will flow into the north Atlantic which could weaken the Gulf stream and the great ocean conveyor belt since it would change salinity levels important for mixing and the temperatures of the waters.
This would cause a cold climate change for Europe with temperatures reaching up to 10oC for during the summer. This could also usher in the next ice age since at the height of the last one, the strength of the Gulf stream was only two-thirds that of today. Global warming will slow down the Gulf stream by up to 30% and may cut off Europe completely in the future (McGuire, 2002). Given this possibility of an ice age occurring, it is important to look into the possible effects of an ice age.
The most obvious effect of an ice age on the oceans is the decrease of actual flowing water given that the ice sheets would be formed from waters of both in-land sources and the oceans. Since glaciers are formed from freshwater, this means that the freezing up of oceanic waters could increase the salinity of the remaining flowing water. Scientists at the Lamont Doherty Earth Observatory found that ocean circulation changes did not cause but was rather the effect of climate changes at the start and end of the last ice age. Ice sheet volume and global carbon budget had changed even before the ocean currents were affected.
The possible scenario drawn is that the ice age had been driven by discrepancies with the amount of heat from the sun arriving at the poles. The changes in the carbon cycle were caused by the decline of plant life because of cooler temperatures and glacial advance. This caused an initial change in the great ocean conveyor belt by amplifying the effect of heat at the higher latitudes. Ocean circulation changes that were caused by the beginnings of the ice age further amplified the climate trends that cause the continental ice sheet expansion and also the retreat of the ice sheets later on (LDEO, 2005).
The implication of this research is that this shows a possible effect of an impending ice age on the oceans. It expresses the possibility that once a change in climate is set-off, the great ocean conveyor belt adapts to the new conditions further aggravating the new changes in climate. Thus, a new ice age could bring a change in the current ocean currents prevalent today. Since the oceans are host to an unknown number of species of living organisms, the effects on marine life is also important to consider.
Although terrestrial organisms would rather prefer the current warm climate, evidence shows that aquatic organisms did not share the same preference. A team of scientists from the University of British Columbia in Vancouver, Canada found that ice age oceans some 20,000 years ago had increased concentrations of nitrate, an important nutrient for plankton that producers for the marine food chain. These concentrations could have supported plankton life in waters that are now nutrient deprived. They measured nitrate levels of two nitrogen isotopes N-15 and N-14 in sediments found at the coast of Mazatlan, Mexico.
This is one of three nitrate sinks in the ocean where bacteria cause denitrification. Although the data gathered from two sites coincided with the hypothesis, it is insufficient to definitively conclude that global nitrate levels were as high as those at the sites. However, it is possible and this could mean that more marine life was present given the abundance of plankton. This could also have contributed more to the ice age since more plants could absorb more carbon dioxide reducing even more the greenhouse effect (Monastersky, 1995). All these effects are but glimpses of what truly happens during an ice age.
We can never truly know exactly what all of them are unless we experience it ourselves. But for sure, given the immensity of the worlds oceans and how reliant stable climate is to them, these effects would affect not only the oceans themselves but the entire planet.
Bibliography: Imbrie, J. & Imbrie, K. P. (1986). Ice ages: Solving the Mystery. Cambridge, Massachusetts: Harvard University Press. Joyce, T. & Keigwin, L. (2007). Are we on the brink of a New Little Ice Age? Retrieved 11 May 2007 from http://www. whoi. edu/page. do? pid=12455&tid=282&cid=10046.