EGU2020-3350
https://doi.org/10.5194/egusphere-egu2020-3350
EGU General Assembly 2020
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Resolution-dependent variations of sinking particle trajectories in general circulation models: Implications for data-model comparison in past climate

Peter Nooteboom1,2, Philippe Delandmeter1, Peter Bijl3, Erik van Sebille1,2, Henk Dijkstra1,2, and Anna von der Heydt1,2
Peter Nooteboom et al.
  • 1Utrecht University, IMAU, Department of Physics, Utrecht, Netherlands
  • 2Centre for Complex Systems Studies, Utrecht University, Utrecht, Netherlands
  • 3Laboratory of Paleobotany and Palynology, Department of Earth Sciences, Utrecht University, Utrecht, Netherlands

Any type of non-buoyant material in the ocean is transported by currents during its sinking journey. This transport can be far from negligible for typical (plankton) particles with a low sinking velocity. To estimate the lateral transport, the material can be modelled as a set of Lagrangian particles advected by currents that are obtained from Ocean General Circulation Models (OGCMs). State-of-the-art OGCMs are often strongly eddying, providing flow fields with a horizontal resolution of  10km on a daily basis. However, many long term climate modelling studies (e.g. in palaeoclimate) rely on low resolution models that cannot capture mesoscale features. The lower model resolution could influence data-model comparisons using Lagrangian techniques, but this is not properly evaluated yet through a direct comparison.

In this study, we simulate the transport of sinking Lagrangian particles using low (1°; non-eddying)  and high (0.1°; eddying) horizontal resolution OGCMs of the present-day ocean, and evaluate the effect of the two resolutions on particle transport. We find major differences between the transport in the non-eddying versus the eddying OGCM (in terms of the divergence of particle trajectories and their mean trajectory). Addition of stochastic noise to the particle trajectory parameterizes the effect of eddies well in some regions (e.g. in the North Pacific gyre).

We recommend to apply sinking Lagrangian particles only in velocity fields with eddying OGCMs, which basically excludes all paleo-simulations. We are currently simulating the equilibrium Eocene (38Ma) climate using an eddying OGCM, to be able to apply these Lagrangian techniques in an eddying ocean of the past. We expect this to lead towards a better agreement between the OGCM and sedimentary fossil microplankton.

How to cite: Nooteboom, P., Delandmeter, P., Bijl, P., van Sebille, E., Dijkstra, H., and von der Heydt, A.: Resolution-dependent variations of sinking particle trajectories in general circulation models: Implications for data-model comparison in past climate, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3350, https://doi.org/10.5194/egusphere-egu2020-3350, 2020

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Presentation version 1 – uploaded on 17 Apr 2020
  • CC1: Comment on EGU2020-3350, Bas de Boer, 04 May 2020

    Hi Peter, nice work. Any other resolutions of the (paleo) model you've used? Would it make a difference if you go to even lower resolutions (with parameterisations). More specific, does it make sense to use this in a transient ocean model? Just curious :).

    • AC1: Reply to CC1, Peter Nooteboom, 04 May 2020

      Hi Bas, thank you! We did not test for other model resolutions, altough we think that it will not make a large difference. The key difference between the model resolutions that we tested (0.1 and 1 degree horizontally) is that the flow is eddying in the first and laminar in the second. Technically you could apply the same analysis in transient ocean models of other resolutions, the question is for what purpose you like to use it and which question you would like to answer.