Shoshiro Minobe, Hokkaido University, Japan
Causality linkages in atmosphere, ocean and marine ecosystem over the North Pacific: Modes, processes and prediction
Climate variability and change influence marine ecosystems, including small pelagic fish .The major cause and effect relationship is such that the atmosphere forces the ocean, which in turn influences the marine ecosystems. In order to find such linkages especially between the ocean and marine ecosystems, climate indices such as Pacific Decadal Oscillation (PDO) index are very useful, as they provide a big picture for coherent marine ecosystem responses to physical forcings. In order to understand better, however, it is necessary to know what physical and biological processes are operating for the relations. In particular, the PDO is a sea surface temperature (SST) pattern forced by variability in the pressure of the Aleutian low system, with several different physical processes shaping the PDO pattern.
What causes Aleutian low variability?
An apparent phenomenon that drives Aleutian Low variability is the El Niño/Southern Oscillation (ENSO), which influences the Northern Hemisphere via Pacific/North American (PNA) pattern. PNA impacts are strong on the eastern side of the North Pacific basin, but not on the western one. Therefore, marine ecosystem forecasting utilizing ENSO prediction information will be quite useful, for example for the US and Canada regions, but not so much in the western North Pacific. In this case, marine ecosystem forecasting in the western North Pacific should employ a different approach from ENSO-based predictions.
In the western North Pacific, mechanisms other than ENSO – including oceanic Rossby wave propagation, migration of ocean mesoscale eddies, and atmospheric bridge from the tropical Indian and western Pacific oceans – can provide some predictability. It is likely, however, that none of these phenomena on their own can provide high enough predictability for marine ecosystem forecasting. Rather, higher predictability can be expected as the combined effects of these and other processes. A more interesting approach is to use direct outputs of prediction data (such as SST or mixed layer depth) of air-sea coupled models. The predicted data of physical variables can be used to forecast marine ecosystem conditions based on a statistical relationship.
There are two requirements for achieving success with this approach: Firstly, the important physical conditions for a marine ecosystem should be identified, and secondly, meaningful predictability for these conditions must be confirmed based on climate models. Feasibility studies that examine these requirements for marine ecosystem indices, and which examine a wide range of indices, should therefore be encouraged. If these studies confirm that this prediction approach is promising, PICES, ICES, and IMBER will be encouraged to work with physical climate projects such as those at CLIVAR and WCRP for the realization of marine ecosystem prediction using direct outputs of air-sea coupled models.