Modelling the Late Devonian Climate: Implications for evolution and extinction

Thesis

The Devonian period (419.2 - 358.9 Ma) was characterised by a warm greenhouse climate which transitioned towards glaciation throughout the Late Devonian. This period in Earth’s history was punctuated by repeated environmental and biotic crises. A common feature accompanying these events was widespread ocean anoxia, typically recorded in the geological record by periodic organic-rich laminated shales. However, the relationship between climate, evolution and extinction in the Late Devonian remains unclear.

In the first part of this thesis, Late Devonian (375 Ma) boundary conditions are applied to an Ocean General Circulation Model (OGCM) forced by monthly atmospheric surface forcing to determine ocean circulation and likely regions of ocean anoxia. The model simulation oscillates between two quasi-stable states: (1) an unventilated phase where the ocean circulation is dominated by shallow tropical/sub-tropical cells; (2) a ventilated phase with globally strong deep ocean overturning. In the second part of this thesis, Late Devonian boundary conditions are applied to a Coupled Atmosphere-Ocean-Ice General Circulation Model (CGCM) and an Atmospheric Slab Ocean General Circulation Model (ASGCM). Comparisons of the atmospheric results highlight the importance of a dynamic ocean in transporting heat polewards. The CGCM ocean also exhibits two ocean states, although the ‘unventilated’ equivalent is termed the partly-ventilated state since there is a weak, deep overturning circulation restricted to the Northern Hemisphere.

Authors: Mack, CLJ

• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: University of Oxford
• Language: English
• Keywords: Paleoclimate Modelling; Physical Oceanography; Devonian
• Subjects: Physics; Physical oceanography; Geology; Climate