29 July 2019

Ocean Barrier Layers in E3SM

E3SM results show how rainfall and wind affect ocean salinity stratification and influence mixing between surface and cold deep water.

Science

In some regions of Earth's oceans, warm, relatively fresh surface waters are separated from cold deep water by a layer of warm but relatively salty water - termed a barrier layer. This work, focussing on E3SM, is the first global assessment of barrier layers in Earth system models. Causes and effects of model biases are investigated.

 

Impact

It is demonstrated that barrier layers affect the mixing of cold water up to the surface in the tropics, but not so much at midlatitudes. It is also shown that modeling barrier layers can be made more difficult by interactions between the ocean model and other Earth system model components, for example through rainfall, wind, and river runoff model errors. 

Summary

Most regions of the Earth's oceans exhibit a thermocline, separating relatively warm surface water from colder water below. In some regions, salinity varies sharply within the warm layer, displaying a fresh layer at the surface, and a salty warm layer, termed a barrier layer, between the surface layer and the thermocline. Here we assess barrier layers in three Earth system models, focusing on the Energy Exascale Earth System Model. We show that: Earth system models can capture barrier layers, albeit with errors in thickness; barrier layers affect exchange of water and heat between the surface and the thermocline in the tropics, but not at midlatitudes; and barrier layer model errors are not purely due to the ocean model component, but are caused by several model components (ocean, atmosphere, land and river runoff) and interactions between them. 

Contact
Jack Reeves Eyre
University of Arizona
Publications
Reeves Eyre, J, L Van Roekel, X Zeng, MA Brunke, and J Golaz.  2019.  "Ocean Barrier Layers in the Energy Exascale Earth System Model."  Geophysical Research Letters.  https://doi.org/10.1029/2019gl083591.