Twentieth century Atlantic meridional overturning circulation as an indicator of global ocean multidecadal variability: influences on sea level anomalies and small pelagic fishery synchronies

The Atlantic dipole phosphate utilization (ADPU) index, derived through statistical conversion of 20th century Atlantic basin subpolar sea surface temperatures, is used as a fingerprint of Atlantic meridional overturning circulation (AMOC) variability and as an indicator of global Meridional Overturing Circulation (MOC) variability. ADPU index correlations with differences in sea level anomalies (SLAs) between Canada and the UK and across the Isthmus of Panama demonstrate intrabasin and interbasin associations with MOC variability. Cross-correlation analyses of ADPU index, SLAs, and sardine (S) and anchovy (A) catch differences [S A] (normalized sardine catch minus normalized anchovy catch) confirm strong correlations between ADPU and [S A] off Japan, California, Peru and Southwest Africa (Benguela). Statistically significant cross correlations also exist between the ADPU index and SLAs for Japan, California, Peru and Benguela, and for SLAs and [S A] for Japan, California and Peru, but the short time-series lengths compared with the length of the multidecadal cycle limit the interpretation of the observed lead-lags. Though correlation is not causality, the correlation analyses developed here are useful in support of hypothesis generation. The proposed hypothesis to explain the observed small pelagic fishery synchronies asserts: (i) ocean bathymetry and continental distributions interact with multidecadal variations in MOC strength that occur along the conceptual global conveyor belt to generate changes in global oceanic planetary waves and mesoscale eddies that propagate through the world ocean; (ii) each small pelagic fishery region has a unique spatial relationship with pertinent oceanic planetary wave and mesoscale eddy source regions that affect the timing and strength of the waves and eddies that influence the nearby boundary current; (iii) synchronous changes or phasing among global fisheries depend on how and when MOC variability mediated by oceanic planetary waves and mesoscale eddies reaches each fishery region; (iv) oceanic planetary waves and/or mesoscale eddies influence the strength or meandering of the boundary current adjacent to a small pelagic fishery region to change local SLAs and environmental conditions to favour sardine or anchovy populations at different times.