Can Geothermal Abyssal Heating be a Trigger of Abrupt Climate Change?

There are observational data and numerical models suggesting that geothermal heating of ocean bottom waters may play an important role in the large-scale oceanic circulation. However, the role of abyssal geothermal heating in abrupt climate change has not been evaluated. Energy is continuously escaping the interior of Earth at a rate of 47 TW (1012 W), mostly through the ocean floors. Geothermal heat flow density varies from about 40 mWm-2 over the oldest oceanic crust to greater than 200 mWm-2 over the young mid-ocean ridges, with a mean of around 100 mWm-2. In general, this geothermal energy flux is capable of warming a 1000 m thick water layer by 0.0008 °C a year, or around 1.5 °C in two thousand years. Deep ocean waters are layered and rich in minerals and greenhouse gases. When the temperature of a static abyssal water parcel increases, it becomes more buoyant. There must be a buoyancy threshold when deep water starts upwelling due to geothermal heating. Small scale upwelling may not have a significant climate impact. But a basin-wide eruption of upwelling could perhaps interrupt global thermohaline and meridional overturning circulation. Most existing hypotheses on abrupt climate change rely on climate-dependent processes such as albedo feedback, fresh water influx, and wind-driven circulation. However, paleoclimate records indicate that abrupt changes in climate occurred during both glacial and interglacial periods. Geothermal-driven deep ocean water upwelling is a climate-independent hypothesis given that geothermal heat flow is a persistent energy source from below the ocean floor. This conceptual model is consistent with the recent report that the rise in atmospheric CO2 during the last deglaciation was preceded by deep water warming [Stott, et al., 2007, Nature, 466, 1093-1097] and the evidence that the abrupt ending of the last ice age was associated with the release of very old (14C-depleted) CO2 from the deep ocean to the atmosphere on a cross ocean scale [Rose, et al., 2010, Nature, 466, 1093-1097]. We are searching more paleoclimate records to identify abrupt changes that might carry evidence of a geothermal trigger.