Did the Growth of Indonesia Contribute to the Pleistocene Quaternary Ice Age?

Growth of the Maritime Continent and its Possible Contribution to Recurring Ice Ages

Authors:

Molnar et al

Abstract:

The areal extent of the Maritime Continent (the islands of Indonesia and surrounding region) has grown larger by ~60% since 5 Ma. We argue that this growth might have altered global climate in two ways that would have contributed to making recurring ice ages possible. First, because rainfall over the islands of the Maritime Continent not only is heavier than that over the adjacent ocean, but also correlates with the strength of the Walker Circulation, the growth of the Maritime Continent since 5 Ma may have contributed to the cooling of the eastern tropical Pacific since that time. Scaling relationships between the strength of the Walker Circulation and rainfall over the islands of the Maritime Continent and between sea-surface temperature (SST) of the eastern tropical Pacific and the strength of easterly wind stress suggest that the increase in areal extent of islands would lead to a drop in that SST of 0.75°C. Although only a fraction of the 3-4°C decrease in SSTs between the eastern and western tropical Pacific, the growth of the Maritime Continent may have strengthened the Walker Circulation, increased the east-west temperature gradient across the Pacific, and thereby enabled ice sheets to wax and wane over Canada since 3 Ma. Second, because the weathering of basaltic rock under warm, moist conditions extracts CO2 from the atmosphere more rapidly than weathering of other rock or of basalt under cooler or drier conditions, the increase in weathering due to increasing area of basalt in the Maritime Continent may have drawn down enough CO2 from the atmosphere to affect global temperatures. Simple calculations suggest that increased weathering of basalt might have lowered global temperatures by 0.25°C, possibly important for the overall cooling.