Book 2.indb - US Climate Change Science Program

Abrupt Climate Changesmaller in magnitude but opposite in sign to theeruption of a large volcano, such as the MountPinatubo eruption (–2 W/m 2 ), but it would lastlonger (10 years for methane and 2 years for avolcano).It is tantalizing to wonder if there could be anyconnection between the Storegga Landslide andthe 8.2-kyr climate event (Alley and Agustsdottir,2005), which may have been triggeredby freshwater release to the North Atlantic.However, ice cores record a 75-ppb drop inmethane concentration during the 8.2-kyr event(Kobashi et al., 2007), not a rise. A slowdownof convection in the North Atlantic would havecooled the overlying waters. Maslin et al. (2004)suggested that an apparent correlation betweenthe ages of submarine landslides in the NorthAtlantic region and methane variations duringthe deglaciation supported the hypothesis thatclathrate release by this mechanism influencedatmospheric methane. The lack of response forStoregga, by far the largest landslide known,and a relatively weak association of other largeslides with increased methane levels (Fig. 5.11)suggest that it is unlikely that submarinelandslides caused the atmospheric methanevariations during this time period.Much of our knowledge of the StoreggaLandslide is due to research sponsored by theNorwegian oil industry, which is interested intapping the Ormen Lange gas field within theheadlands of the Storegga slide but is concernedabout the geophysical hazard of gas extraction(Bryn et al., 2005). Estimates of potentialmethane emission from the Storegga slide rangefrom 1 to 5 GtC, which is significant but notapocalyptic. As far as can be determined, theStoregga Landslide had no impact on climate.4.2.2 The Paleocene-Eocene ThermalMaximumAbout 55 million years ago, the δ 13 C signatureof carbon in the ocean and on land decreasedby 2.5–5 per mil (‰) on a time scale of lessthan 10 kyr, then recovered in parallel on atime scale of ~120–220 kyr (Kennett and Stott,1991; Zachos et al., 2001). Associated with thisevent, commonly called the Paleocene-EoceneThermal Maximum (PETM), the δ 18 O of CaCO 3from intermediate depths in the ocean decreasedby 2–3‰, indicative of a warming of about 5 °C(Fig. 5.12). The timing of the spikes is to a largeextent synchronous. Planktonic foraminiferaand terrestrial carbon records show a δ 13 C perturbationa bit earlier than benthic foraminiferaFigure 5.11. Timing of submarine landslides in the North Atlantic region and pre-industrial ice coremethane variations. Landslide data from Maslin et al. (2004). Methane data from Brook et al. (2000) andKobashi et al. (2007). Abbreviations: km 3 , cubic kilometers; yr, year; ppb, parts per billion.185