Evolution of upwelling in the Atlantic Ocean basin

• Main Authors: Handoh, IC, Bigg, GR, Jones, EJ
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: Elsevier 2003
• Subjects: Atlantic; upwelling; palaeogeography; palaeo-productivity; numerical modelling; Pacific; North Atlantic
• Online Access: http://discovery.ucl.ac.uk/8807/

Understanding the evolution of the surface circulation and the patterns of upwelling in the Atlantic is important not only because of the ocean’s crucial role in the present-day thermohaline circulation, in supplying heat to high latitudes, but also because of the significant petroleum reservoirs found around the basin. In this paper we examine the upper ocean circulation during four time-slices – the Kimmeridgian (c. 155 Ma), the Cenomanian (c. 100 Ma), the Maastrichtian (c. 70 Ma) and the Early Eocene (c. 50 Ma) – using a 1.5-layer, reduced-gravity, ocean model. For each time-slice the upwelling fields predicted from simulations of wind-driven upper layer circulation are compared with the deep-sea and continental margin sedimentary records. The boundary configurations at each time-slice are the subject of sensitivity tests, where matching of both deep-sea and coastal sedimentary records with the model-predicted upwelling fields is used to suggest best fits between model and geological data. Our model runs are consistent with there being a deep-water connection to the Pacific at each time period after the Kimmeridgian, with such a link being most important to the geological–ocean-model match in the Maastrichtian. No period after the Kimmeridgian produced a stable ocean simulation with a deep-water connection to Tethys. Our simulations c. 100 Ma suggest that a deep-water connection between the North and South Atlanctic was not established until after the Cenomanian. All time-slices show a clear western boundary current in the North Atlantic, although generally only a third to half the strength of today’s. A similar difference is found between tropical palaeo-productivity at each run, and today’s more productive Atlantic Ocean. We conclude that upwelling and anoxia are not necessarily independent means of producing organic-rich marine sediments. Most such sedimentary deposits laid down during the four time-slices can be linked to the presence of upwelling zones. Thus, where anoxia is well-established we suggest that upwelling may help supply organic material to the de-oxygenated bottom waters.