The Onset of the Northern Hemisphere Glaciation
By Christina Ohrazda
Student at Stockholm University
The Northern Hemisphere Glaciation (NHG) is believed to have initiated into large scale, permanent ice sheets ~2.5 Ma, which is almost 31.5 Ma after the initiation of the Antarctica ice sheets. There are many possible causes for the onset of this climate event, some of which we will be reviewing in this essay. In this essay we will look at the cores from IODP and ODP sites 302, Arctic Ocean; 913, Greenland basin; and 907, north of Iceland, in order to identify the characteristics and possible causes of the northern hemisphere glaciations. First we will look at the evidence for the onset of this event and the proxies…show more content… John et al. 2012). These clasts, embedded in the fine-grained pelagic sediment at site 913, are confirmed to be glacial deposits due to the evidence of glacial abrasion on the surfaces of the clasts (Eldrett et al. 2007). Additionally, the lack of sedimentary structures that would suggest gravity flow-initiated deposition of these glacially deposited clasts, results in a dropstone classification. A summary of the lithological units of site 913 can be seen in table 2. Note. From ‘Proceedings of the Ocean Drilling Program, Initial Reports’ (Myhre et al.…show more content… However, proxies show that the initiation of IRD ~46.25 Ma at site 306, correspond to a >1000 ppm decrease in CO2 gases in the atmosphere (See Figure 5. Note. From ‘Cenozoic ice-rafting history of the central Arctic Ocean: Terrigenous sands on the Lomonosov Ridge’ (St. John 2007)). This correlation between IRD and pCO2 is critical since it leads us to the hypothesis that a decline of pCO2 could have driven the climate in the polar regions over a temperature threshold, which enabled the onset of continental glaciers and ice sheets on the surface of the Arctic Sea (St. John 2008). This is only one of many possible reasons of the NHG onset, where other potential causes suggested for the initiation of the NHG are: events of mountain building; plateau uplift in southern Asia and the American West; Volcanic triggering, resulting in aerosols in the atmosphere; and the closure of Panama Seaway, which would have changed the whole ocean circulation and distribution of cold vs. warm ocean water (St. John et al.