The importance of the terrestrial weathering feedback for multimillennial coral reef habitat recovery

Abstract

[1] Modern-day coral reefs have well defined environmental envelopes for light, sea surface temperature (SST) and seawater aragonite saturation state (W arag ). We examine the changes in global coral reef habitat on multimillennial timescales with regard to SST and W arag using a climate model including a three-dimensional ocean general circulation model, a fully coupled carbon cycle, and six different parameterizations for continental weathering (the UVic Earth System Climate Model). The model is forced with emission scenarios ranging from 1,000 Pg C to 5,000 Pg C total emissions. We find that the long-term climate change response is independent of the rate at which CO 2 is emitted over the next few centuries. On millennial timescales, the weathering feedback introduces a significant uncertainty even for low emission scenarios. Weathering parameterizations based on atmospheric CO 2 only display a different transient response than weathering parameterizations that are dependent on temperature. Although environmental conditions for SST and W arag stay globally hostile for coral reefs for millennia for our high emission scenarios, some weathering parameterizations induce a near-complete recovery of coral reef habitat to current conditions after 10,000 years, while others result in a collapse of coral reef habitat throughout our simulations. We find that the multimillennial response in sea surface temperature (SST) substantially lags the aragonite saturation recovery in all configurations. This implies that if corals can naturally adapt over millennia by selecting thermally tolerant species to match warmer ocean temperatures, prospects for long-term recovery of coral reefs are better since W arag recovers more quickly than SST.

Time-dependent climate sensitivity and the legacy of anthropogenic greenhouse gas emissions

“…My results suggest a longer lifetime of human-induced future warming than previous studies (15,(38)(39)(40)(41) (Fig. 2B).…”

Primary production sensitivity to phytoplankton light attenuation parameter increases with transient forcing

“…Solar insolation at the top of the atmosphere, wind stress, and wind fields varied seasonally (Kalnay et al, 1996), and the wind fields were geostrophically adjusted to air temperature anomalies (Weaver et al, 2001). The sediment and weathering models (Meissner et al, 2012) were not used. Model equilibration was achieved by integrating over 10 000 years prior to application of climate forcing.…”

Carbon cycle implications of terrestrial weathering changes since the last glacial maximum

“…This effectively suppresses the long-term negative feedback mechanism by preventing the weathering rate from adapting to changes in environmental factors such as temperature and atmospheric CO 2 concentration. Meissner et al (2012) replaced the standard parameterization of weathering in the UVic ESCM with a number of adaptations from previous carbon-cycle box-models (see "Methods" section) to introduce and investigate the weathering negative feedback mechanism in the context of future climate change scenarios. They found that the long-term climate response to various emission scenarios depends almost exclusively on the total amount of CO 2 released, regardless of the rate at which it is being emitted, and that carbon uptake through an increase in terrestrial weathering has a significant effect on the climate system.…”

“…Using a similar approach as Meissner et al (2012), we introduced a set of box-model parameterizations of terrestrial weathering to examine potential impacts on the carbon cycle as weathering rates adjust to the increase in temperature and atmospheric CO 2 levels during the latest deglacial period. These weathering schemes were adapted from Berner (1994), Lenton and Britton (2006), and Uchikawa and Zeebe (2008), and a full description of their implementation into the UVic ESCM is given by Meissner et al (2012).…”

“…These weathering schemes were adapted from Berner (1994), Lenton and Britton (2006), and Uchikawa and Zeebe (2008), and a full description of their implementation into the UVic ESCM is given by Meissner et al (2012).…”