Analysis Of The Great Oxygenation Event

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Prior to the Great Oxygenation Event (GOE) there was little oxygen in the atmosphere. Oxygenation of the atmosphere occurred in two steps, at the beginning and end of the Proterozoic eon (Frei, et al., 2013). In the GOE the surface oceans began to become oxygenated (Holland, 2006). The Second stage of oxygenation is known as the Neoproterozoic Oxygenation Event (NOE) and occurred after the 650-635Ma in the Marinoan glaciation (Sahoo, et al., 2012) (Feulner & Kienert, 2014). The NOE is thought to represent either further oxygenation (Holland, 2009) or deep ocean oxygenation (Canfield, 1998). This event is marked by resurgence in Banded Iron Formation (BIF) deposits which mark this second marine oxidation (Ilyin, 2009) (Frei, et al., 2009). The …show more content…
This occurred due to oxidation of a deep pool of DOC (Rothman, et al., 2003) which could have potentially formed as mentioned above with deep burial of carbon as a marine snow. This hypothesis is supported by decoupling of δ13 C and org13C isotopes (Swanson-Hysell, et al., 2010). If this hypothesis is confirmed the excursion represents injection of oxidants into the deep marine environment (Hayes & Waldbauer, 2006). This is supported by Rothman et al. in 2003 who suggested the negative carbon excursion was caused by the remineralisation of the DOC reservoir. It must be considered what process caused the further oxidation of this deep sea environment. It is well known that colder water increases the solubility of oxygen, thus suggesting this deep sea oxidation was linked to the snowball earth glaciations. Hoffman stated that negative δ13 C excursions are linked to the burial rate of carbon globally but organics are the primary source of 13 C depleted carbonate (Allen & Hoffman, 2005) (Hoffman, et al., 1998). Negative δ13 C excursions began below glacial ice suggesting this negative excursion began before the glaciations as seen in Namibia where the excursion began 600,000 years before the Marinoan glaciation (Halverson, et al., 2002) (Hoffman & Schrag, …show more content…
This is supported as methane production or methane clathrate (ice crystal trapping methane compound within it) could have generated conditions attributed to the end of the glaciations (Kennedy, et al., 2001). Methane (CH4) possesses a very light δ13 C signature however very large releases of methane clathrate for example can impact global δ13 C excursions as seen at Palaeocene-Eocene Thermal Maximum (PETM) where temperature rose by 5oC and the carbon cycle changed vastly (Panchuk, et al., 2008)It has also been suggested that sustained methane release from the ocean caused greenhouse warming which caused draw down of carbon dioxide due to weathering. When this release of methane ended there were low levels of greenhouse gases in the atmosphere triggering the snowball earth glaciation (Halverson, et al., 2002). Alternatively excess methane production could have occurred, though evidence of such is yet to have been seen (Holland, 2003). Methane release to the atmosphere is controlled by oxygen and sulphate cycles and the deep ocean. By the end of the Neoproterozoic oxygen and sulphate levels were higher than in other periods however we do not have an exact timing for this, though it has been argued it happened very late (Kah, et al., 2004). Holland states meanwhile that the deep oceans were locally anoxic in Snowball Earth due to BIF formations. Therefore

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