Term Paper on "Heinrich Events"

Term Paper 11 pages (3846 words) Sources: 1+

[EXCERPT] . . . .

This release can be caused from melting, water pressure within the jokulhlaup, or in some cases, simple floodwaters (Sturm and Benson, 1985).

Still another theory, postulated by some of the members of MacAyeal's original team, alters the binge-purge model to include not ice sheets, but ice shelf collapses. According to Hulbe (et al., 2004), the original binge-purge model would not account for the widespread cooling event seen immediately after a Heinrich event. These cool conditions were seen throughout the North Atlantic, and thus, according to Hulbe (et al., 2004), could not have been caused solely by the purging to the Laurentide Ice sheet. Additionally, Hulbe and his colleagues note that thermal processes typical in ice streams tend to slow the motion of that ice stream. This, as a result, would actually prevent the massive iceberg output needed to support the release postulated in a Heinrich event (Hulbe, et al., 2004).

Hulbe (et al., 2004) proposed a theory, based on data retrieved from recent events along the Antarctic Peninsula. The researchers noted that, in this case, the ice shelves were not simply breaking off due to purging, but were instead disintegrating due to climate controlled meltwater filling surface crevices. This disintegration of the ice shelf, due to climate and not internal release mechanisms, would then be the cause of the massive discharge of icebergs seen in a Heinrich event (Hulbe, et al., 2004).

Although the cause of a Heinrich event is still theoretical in nature, the effects of the events are well documents. To understand how Heinrich events affect the global climate, it is imperative to first discuss the Earth cycles in general. First, researchers note that the climate of Europe is not like other countries along the same latitudes, such as North America or Asia. In order for Europe to be as significantly warmer as it is, the cold, dry winds traveling eastward from Canada must be considerably warmer than those in other areas at the same latitude (Calvin, 1998).

As the Gulf Stream merges into the North Atlantic Ocean, it is met by warm water flowing north from the tropical equator. This water flows northward, up the coast of Norway. Additionally, there is a branch of this water that stems westward to Greenland. The effect of this flow is that Europe remains, on average, nine to 10 degrees warmer during the winter seasons than other areas in the same latitude (Calvin, 1998).

However, researchers have noted that when this cycle fails, it is not only Europe that is affected by the change. At the same time, other areas of the world experience a cooling cycle, as well. Tropical swamps have been seen to reduce methane production, and the Gobi desert experiences high winds. These types of changes worldwide show that there is a force switching the climate on a global scale (Calvin, 1998).

According to most scientists, this large force is the North Atlantic Ocean current. The flow of this current is relative to the flow of almost a hundred Amazon Rivers. When this current alters course dramatically, the course of the atmosphere can equally change. This current is a part of a cycle of the Atlantic Ocean that extends through the southern oceans and into the Pacific Ocean (Calvin, 1998).

This north-south ocean current helps to maintain global temperatures by redistributing heat to temperate zones. If this current, assisted by the Gulf winds, reaches too far north, the combined effect is to melt the sea ice. This melting, as mentioned previously, results in less reflective materials responsible for reflecting much of the sunlight received by the northern hemisphere. The result, then, is a state of global warming. This warming allows for ice sheets in other areas to melt, creating a continuous cycle (Calvin, 1998).

It is a well-known fact that surface waters are flushed twice a year in most waters, even those of lakes and streams. The result is that water molecules carrying atmospheric gasses are pulled downward into "sinkholes." As surface water molecule density changes with temperature, the heavier surface water of a lake will sink into the less dense waters below, since those waters are kept warmer than the surface in colder temperatures. This allows for the mixing of these molecules (Calvin, 1998).

However, ocean waters work slightly differently, since those waters also contain high amounts of salt. This salt also plays a role in the flushing of surface water, in that water evaporation leaves behind it the salt content of the water molecules. This results in a higher, heavier salt content in surface waters of the ocean, which causes those waters to sink. These saltier waters are then carried south by the ocean current (Calvin, 1998).

In compensation, the current waters in the Atlantic create a longer circulation path, which brings warmer water north. In 1961, Henry Stommel began to theorize that massive additions of freshwater to this current cycle would severely disrupt the flow of the currents. It is important to note that ocean currents are not well blended in terms of salt at any given time. For example, water flowing from the Mediterranean is approximately 10% saltier than that of the ocean in general, which causes these waters to sink as they flow into the Atlantic. Salty waterfalls in the north as a result of cold northern winds causing evaporation also lead to higher salt content in the northern waters. These heavy waters then sink during the winter months, and are carried southward by the Atlantic current. This current then travels southward, around the tip of Africa through the Indian Ocean and into the Pacific Ocean. This process allows the Atlantic to dump its excess salt into the much less salty Pacific Ocean. From beginning to end, this process is known as the thermohaline circulation cycle (THC) (Stommel, 1961).

Researchers know the Heinrich events occur during the 100,000-year cooling cycle. Theories postulate that the problem begins with the ice sheet growth due to this cooling period. As the ice sheets grow, the winds blowing over them become considerably cooler. These cooler winds, as noted above, cause higher evaporation of the surface waters, and leave behind waters higher in salt content. This alteration in content slows the movement of the Atlantic current, making the north colder than before (Stommel, 1961).

As the saltier water is finally moved through the ocean current, the current is again "switched on" to its fullest potential. However, the warming trend this induces is not sufficient enough to return the north back to its previous temperatures. As precipitation from the increased evaporation occurs, more ice accumulates. With each warming trend, more freshwater is added to the Atlantic, slowing the currents even further. Thus, the cycle begins again (Calvin, 1998).

Once the ice mass reaches its thresh-hold and purges, or once the base becomes melted enough, the ice mass breaks. The result is a massive amount of freshwater ice in the northern Atlantic. This large amount of freshwater completely shuts down the conveyer belt, or Atlantic current. Without the influx of warmer, southern water, the northern hemisphere rapidly drops in temperature (Calvin, 1998).

As a result, researchers theorize that the increased amounts of sea and ice, created as the ice sheets continue to spread, and the meltwater pools over land mass, may be partially responsible for the general cooling of the entire earth climate following a Heinrich event (Calvin, 1998). As these areas increase, more sunlight and heat is reflected back into space, causing a general cooling of the atmosphere. This cooler atmosphere would then result in more ice development, continuing the cycle.

Other researchers have proposed that the cause of the global climate change as a result f a Heinrich event may be related to the relationship between greenhouse gasses and the Atlantic salt conveyer. Walter Broecker, a geochemist, theorized that major greenhouse gasses were disturbed by the failure of the conveyer. This, in turn, would reduce the amount of heat retained by the Earth. As the ocean currents rearranged to accommodate for a lack of flushing, less evaporation would occur in the tropics. This would make the air dryer, and since water molecules are the most powerful greenhouse gas, this decrease in evaporation would reduce global humidity, and thus, would reduce the greenhouse gasses. According to Broecker, a small scale adjustment of just 30% less evaporation would plunge the planet's temperature by as much as nine degrees Fahrenheit (Broecker, 1997).

In a report to the Pentagon by researchers Schwartz and Randall, further speculations on global climate changes resulting from a Heinrich event are outlined, in terms of possible consequences for today's world. According to the researchers, average temperatures in the north could drop as much as six degrees Fahrenheit. As a result, evaporation loss would cause a drought for more than a decade over some of the more critical agricultural regions. Additionally, storms would intensify, increasing wind speeds and further amplifying the effects of the drought damages (Schwartz and Randall,… READ MORE

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