Two seminars by Kevin Oliver from Southampton University

 link to Kevin Oliver's page 


"Solving the glacial-interglacial CO2 problem. A silver bullet or many interacting processes?"

Thursday May 16 at 10.15
DeGeer Salen, level 2, Geovetenskapens hus
 link to IGV's house plan

Atmospheric carbon dioxide concentrations varied by about 90 ppm over the ~100,000 year glacial cycles, comparable in magnitude to the anthropogenic increase over the last 150 years. Three decades of research have led to the view that the principal cause of lower atmospheric CO2 during glacial periods was marine in origin, and that changes in the Southern Ocean circulation played a key role, but more specific assertions cannot be justified. A series of mechanisms have been proposed as a "silver bullet" that will solve the glacial-interglacial CO2 problem, only to be rejected on the grounds of (a) inconsistency with the proxy record; and/or (b) lacking potential in models to produce sufficiently large variations in CO2.

It is likely that many carbon cycle components interacted to produce CO2 cycles, and this requires us to reconsider how we address the problem. Simulations with the carbon-isotope-enabled Earth System Model GENIE are used to demonstrate that the response of the carbon cycle to changes in physical processes is strongly non-linear. As a consequence of this, it is impossible to estimate with confidence the potential of an individual mechanism to contribute to glacial CO2 cycles based on the traditional experiment design of Perturbation Experiment versus Control Experiment. Instead, ensemble experiments in which different processes are varied simultaneously, and then statistically emulated to isolate the role of individual processes, are required. I will present examples of the use of ensembles, and use these to narrow uncertainty in the causes of glacial CO2 cycles.

"Understanding ocean circulation through gravitational potential energy"

Thursday May 16 at 15.30
at MISU, room R609

The transport of the global meridional overturning circulation (MOC) is recognised to be limited by the supply of mechanical energy, but much debate surrounds how ocean energetics and dynamics are linked. I will present a theoretical framework that demonstrates the direct effect of gravitational potential energy (GPE) sources and sinks on baroclinic pressure gradients, and summarise how this supports three distinct lines of investigation into controls on the MOC:

(1) MOC theory, rooted in seminal studies by Gnanadesikan (1999) and Nilsson & Walin (2001), is extended to account for co-existing and competing Atlantic and Antarctic overturning cells;

(2) The role of diapyncal mixing in ocean dynamics is shown to depend strongly on local thermohaline structure, due to the non-linear equation of state;
(3) An energy budget for a global climate model is presented, illustrating the complementary roles of surface buoyancy forcing and diapycnal mixing in the MOC.

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