Biogeochemical timescales of climate change onset and recovery in the North Atlantic interior under rapid atmospheric CO2 forcing

Abstract

Ocean biogeochemistry is expected to change because of future climate change, with apparent consequences for marine ecosystem services that are essential for human well-being (IPCC, 2019). These changes are a result of direct and indirect impacts on the climate system and involve not only warming due to increasing greenhouse gases but also subsequent changes in the large-scale circulation of the global ocean. Many studies investigating future climate change projections have highlighted that it is not just the surface and subsurface layers of the oceans which are subject to significant change because of anthropogenic forcing. The ocean interior is also

Irreversible loss in marine ecosystem habitability after a temperature overshoot

“…With increasing depth, some decoupling of DO from temperature occurs, as it becomes evident with a slight delay in the minimum of DO with respect to peak temperature in epipelagic waters (one year after temperature peaks), and an earlier minimum of DO in mesopelagic waters (~48 years before temperature peaks). Furthermore, DO presents slightly positive hysteresis (~1.0% higher than at the beginning of the experiment) at this depth layer consistent with the increase of oxygen found in deep waters of the North Atlantic by Bertini and Tjiputra 23 . After looking at the evolution of temperature and DO, we look at φ (green lines in Fig.…”

“…According to recent studies (for example ref. 60,64 ), several processes linked with ocean warming and deoxygenation are largely reversible (within centuries) at the sea surface, while they will take centuries to millennia to recover at depth 23,[65][66][67][68] . To discern whether this is the case in our study, we also estimate the same deviation-slope pairs arising from internal climate variability.…”

“…Using these simulations, the hysteresis of relevant Earth system parameters has been investigated as the difference between their ramp-up and ramp-down paths (for example ref. [19][20][21][22][23][24]. Hysteresis refers here to the dependence of the Earth system to its past state and not only on its current state.…”

Reviews and syntheses: Abrupt ocean biogeochemical change under human-made climatic forcing – warming, acidification, and deoxygenation

“…In the interior ocean, this time lag is considerably longer due to the delayed propagation of the warming/cooling signal from the surface to the deep ocean, which primarily follows the large-scale overturning circulation pattern. In the interior Atlantic, the delay in peak warming varies from decades in the well ventilated subpolar region to multicenturies in the less-well ventilated tropical region (Bertini and Tjiputra, 2022). Warming in the interior North Atlantic is projected to be reversible at millennia or longer timescales.…”

“…Under an idealized peak-and-decline scenario, the evolution of surface pH in the North Atlantic corresponds strongly to the 1555 atmospheric CO2 concentration trajectory, such that when the CO2 concentration is returned to the preindustrial level, the ocean gradually turns from a carbon sink to a carbon source and the surface pH level returns to its initial state (Bertini and Tjiputra, 2022). pH change in the interior is more sophisticated, however, as low-pH water masses are transported to depth by the overturning circulation at a much slower rate than the atmospheric CO2 evolution.…”