Bidecadal variability in ocean related to the 18.6-year modulation of tide-induced vertical mixing

Abstract

The 18.6-year modulation of the short-period tides related to the precession of the moonʼs ascending node probably modulates vertical mixing in the ocean through microscale dissipation processes of internal waves. It is hypothesized that the modulation of mixing contributes to the bidecadal variability in physical and biogeochemical variables in the North Pacific and its marginal seas. Previous studies support this hypothesis. However, the quantitative importance of this modulation remains far from clear. Even qualitatively, we do not understand well the mechanism linking the modulation of mixing and the bidecadal variability in the ocean. To verify the hypothesis, it is necessary to evaluate the quantitative importance of ocean variability as a result of the direct ocean response to the modulation of mixing, which requires us to quantitatively discuss the response to both atmospheric forcing variations and mixing modulation. One promising way to do this is via numerical experiments using a reliable ocean model that can reproduce both the mean states and temporal variations through realistic processes. It is also important to obtain more information about bidecadal variability based on observations.