Abstract
Abstract. We analyzed the trace element ratios Cd/Ca and Mn/Ca in three coral colonies (Porites panamensis (1967–1989), Pavona clivosa (1967–1989) and Pavona gigantea (1979–1989)) from Cabo Pulmo reef, Southern Gulf of California, Mexico, to assess the oceanographic changes caused by El Niño – Southern Oscillation (ENSO) events in the Eastern Tropical North Pacific (ETNP). Interannual variations in the coral Cd/Ca and Mn/Ca ratios showed clear evidence that incorporation of Cd and Mn in the coral skeleton was influenced by ENSO conditions, but the response for each metal was controlled by different processes. The Mn/Ca ratios were significantly higher during ENSO years (p<0.05) relative to non-ENSO years for the three species of coral. In contrast, the Cd/Ca was systematically lower during ENSO years, but the difference was significant (p<0.05) only in Pavona gigantea. A decrease in the incorporation of Cd and a marked increase in Mn indicated strongly reduced vertical mixing in the Gulf of California during the mature phase of El Niño. The oceanic warming during El Niño events produces a relaxation of upwelling and a stabilization of the thermocline, which may act as a physical barrier limiting the transport of Cd from deeper waters into the surface layer. In turn, this oceanic condition can increase the residence time of particulate-Mn in surface waters, allowing an increase in the photo-reduction of particulate-Mn and the release of available Mn into the dissolved phase. These results support the use of Mn/Ca and Cd/Ca ratios in biogenic carbonates as tracers of increases in ocean stratification and trade wind weakening and/or collapse in the ETNP during ENSO episodes.
Highlights
The El Nino – Southern Oscillation (ENSO) phenomenon is one of the main sources of global climate variability at interannual time scales
We examine the ratios of Cd/Ca and Mn/Ca in three species of massive corals (Pavona gigantea, Pavona clivosa and Porites panamensis) from Cabo Pulmo reef, Southern Gulf of California, Mexico, to assess oceanographic changes during ENSO events
The Mn/Ca ratio among the different species increased in the same order as observed for the Cd/Ca ratio: the Mn/Ca ratio was lowest in Pavona gigantea (10.45±5.63), moderate in Pavona clivosa (32.3±31.0), and highest in Porites panamensis (41.6±31)
Summary
The El Nino – Southern Oscillation (ENSO) phenomenon is one of the main sources of global climate variability at interannual time scales. The Gulf of California has been studied widely, the regional oceanographic anomalies produced by ENSO have only been derived from synoptic studies; continuous long-term studies of oceanographic variability have been missing. Corals offer significant advantages as paleoceanographic recorders because they contain annual skeletal growth bands that provide a very precise annual chronology. Their widespread presence throughout the tropical seas of the world, and the geochemical signals contained in their skeletons provide a powerful means of reconstructing environmental conditions with a fidelity that is comparable to instrumental records (Gagan et al, 2000). Because the distribution coefficient (D) of Cd/Ca and Mn/Ca ratios in the coral relative to seawater is known (Shen and Sanford, 1990), their variation in the coral skeleton can provide us with detailed oceanographic records on different time scales
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
