The Sensitivity of Modelled Ocean Upwelling and Terrestrial Runoff to Changing Boundary Conditions: Implications for Predictions of Source, Reservoir and Seal Facies

Paul J. Valdes¹ and Paul J. Markwick^2
1 Bristol University, Bristol, United Kingdom
² GETECH, Leeds, United Kingdom

The use of climate models in frontier exploration, in particular for predicting the past distribution of high productivity marine systems (ocean upwelling), dates back to the early 1980s. However, the logistics and costs of such models, especially the current suite of coupled ocean-atmosphere models, has largely precluded an examination of the sensitivity of such predictions to changing boundary conditions, which are a major contributor to the inherent uncertainties associated with all modelling. Such an assessment is essential if derived conclusions of exploration risk are to be of actual value.

Over the last five years we have conducted a series of coupled ocean-atmosphere experiments for the Maastrichtian (Late Cretaceous, 70 Ma) using the HadCM3 GCM, in order to quantitatively investigate these uncertainties. Here we present results for two suites of sensitivity tests: 1. the effect of changing concentrations of atmospheric CO₂ (with experiments for 2x, 3x and 4x pre-Industrial values); 2. changing how the geography is represented in the model (whether based on averages derived from compiled polygons representing highs and lows, or explicitly on a grid cell by grid cell basis using a palaeo-DEM). In both cases we concentrate on how these affect exploration pertinent output: oceanic upwelling (the principle production system linked with marine source facies), and runoff (which dictates fluvial sediment and nutrient fluxes that have direct and indirect affects on terrestrial and marine reservoir and source facies).

The results show that for these two sources of uncertainty, ocean upwelling is less sensitive to changes in these boundary conditions than runoff; this would suggest that for any frontier area explorationists may need to place a greater emphasis on understanding clastic reservoir facies.