Project EARTH-17-HLJ1: Meridional overturning circulation and ocean heat uptake

HLJ1: Meridional overturning circulation and ocean heat uptake

Supervisors: Helen Johnson (Earth Sciences), David Marshall (AOPP) and Mike Bell (Met Office)

NERC Industrial CASE project with guaranteed funding for October 2017 entry

Understanding the ocean’s response to increasing concentrations of greenhouse gases in the Earth’s atmosphere is crucial for predicting regional and global climate on long timescales. The recent hiatus and then surge in global warming has highlighted that improved understanding of what controls variations in ocean heat uptake is a high scientific priority.

The ocean’s meridional overturning circulations (MOCs) can communicate changes in temperature at the surface down into the deep ocean. These circulations therefore influence the rate and location at which heat is taken up by the oceans, how it is re-distributed vertically, and the long-term rise in sea-level due to thermal expansion. They also transport sufficient heat into the North Atlantic to reduce the severity of winters in north-west Europe. A major challenge for climate science is to develop a robust understanding of their dynamics and predict their fluctuations on time-scales of decades to centuries.

This project will develop and employ novel diagnostics that can be used to probe the behaviour of MOCs and ocean heat uptake under future (and past) forcing scenarios in the current generation of Met Office coupled climate models. The student will use existing simple conceptual and numerical models of the global MOC (see selected relevant references below) to better understand what controls variability in ocean stratification, heat content and circulation. For example, they will assess the extent to which wind forcing sets the spatial distribution of heat uptake, determining diagnostic relationships between the temperature field, surface winds and heat fluxes. They will then apply these diagnostics in climate change simulations to provide insight on the attribution of past change in ocean heat uptake along with a robust understanding of predicted future change.

The diagnostic framework developed in this project will contribute directly to the interpretation of Met Office climate forecasts, the assessment of model performance, and the development and design of future predictive systems.

This project would best suit a strongly motivated student with a solid background in maths and physics and a desire to learn about the role that the ocean plays in climate variability and change.  The student will be part of the vibrant Oceans and Climate group at the University of Oxford, which includes ~20 scientists in both the Earth Sciences and Physics departments. They will also be integrated into the Oxford DTP in Environmental Research, which provides an outstanding training environment to a cohort of ~30 students right across the entire NERC remit. This training programme will be supplemented by specialist courses in scientific computing and in running and analyzing coupled climate models at the Met Office. The student will spend a total of up to 6 months at the Met Office in Exeter during the project, and there may also be the opportunity to participate in a research cruise should the student wish.

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Selected relevant references:

  • Marshall, D. P., and L. Zanna (2014) A conceptual model of ocean heat uptake under climate change. Journal of Climate, 27, 8444-8465.
  • Zhai, X., H. L. Johnson and D. P. Marshall (2014) A Simple Model of the Response of the Atlantic to the North Atlantic Oscillation. Journal of Climate, 27, 4052-4069.
  • Bell, M. (2015) Meridional Overturning Circulations Driven by Surface Wind and Buoyancy Forcing. Journal of Physical Oceanography, 45, 2701-2714.