Kim, H-J. and A. J. Miller, 2007:

Did the thermocline deepen in the California Current after the 1976-77 climate regime shift?

Journal of Physical Oceanography,37, 1733-1739.

Abstract. The 55-year CalCOFI dataset in the southern California Current reveals a significant surface-intensified warming and stratification (buoyancy frequency) change across the 1976-77 climate regime shift. However, the average depth of the thermocline, defined as the maximum gradient of temperature, did not change significantly across the regime shift. The maximum-gradient criterion for thermocline depth may be more appropriate than following an isotherm because the isotherm necessarily deepens in the presence of surface-intensified warming. As the surface heating changed the strength of stratification, it also changed the slope of the nitrate-temperature relation for the middepth waters (roughly 30m to 200m). Thus, the quality of upwelled water may have been fundamentally altered after the shift.

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