Alternatively, an increase in regional precipitation could have caused elevated terrestrial runoff (C/N ratios, kaolinite) and lower surface water salinity above 2618 m before the CIE onset (Fig. 9). The North Sea Basin surrounding landmasses were within the northern rain belt (the southern boundary today is 40°N), which would have experienced elevated precipitation if the global hydrologic cycle became enhanced (Pagani et al., 2006b; Schmitz et al., 2001). This scenario would be consistent with a gradual increase in the global hydrologic cycle before the CIE, perhaps from gradual warming, which was hypothesised to have triggered ocean circulation changes, methane hydrate destabilisation, and global carbon release at the CIE (Bice and Marotzke, 2002). We note however that there is currently no evidence for an enhanced hydrologic cycle well before the CIE in other regions.
CIE onset
above 2618 m
m
northern rain belt
southern boundary
40°N
°N