Cretaceous (Wealden) climates: a modelling perspective
This paper describes the results from a new palaeoclimate modelling exercise for the Early Cretaceous (Barremian) focussed on the Weald (SE England), using a Limited Area Numerical Climate Model (LAM). The palaeoclimate model uses appropriate Barremian boundary conditions and simulates a climate with seasonal Surface temperatures akin to those occurring in parts of the modern Southern Mediterranean. Cold month mean temperatures are simulated as 4-8 degreesC, whilst warm month mean temperatures may reach 36-40 degreesC. Precipitation rates are high during all seasons with little evidence for prolonged drought. The average precipitation rate simulated for any one month is 4-8 mm/day, whilst during parts of the winter (December, January and February) precipitation rates may exceed 16 mm/day. No present-day analogue is available for the climatological pattern predicted for the Barremian. This result differs from other palaeoclimate interpretations for the Weald based on proxy climate data. These data have been interpreted as showing the existence of a seasonal precipitation pattern with a pronounced dry season. The data/model inconsistency can be resolved by, careful examination of the model-predicted moisture budget as a whole. We argue that many of the palaeoclimate moisture proxies record the net hydrological cycle (i.e., precipitation minus evaporation). Although the climate model simulates precipitation year round, the surface temperatures result in very high evaporation rates. Therefore, moisture availability during the Barremian in the soil and for plants during the summer months (June, July and August) is severely restricted even though precipitation levels are substantial. These results demonstrate the importance of considering the moisture balance as a whole rather than focussing on only precipitation when drawing palaeoenvironmental inferences from proxy data. The work underlines the benefits of using numerical climate models in conjunction with proxy data in understanding past climates and environments.
Authors: Haywood, Alan M., Valdes, Paul J., Markwick, Paul J.