Hydrographic and fish larvae distribution during the “Godzilla El Niño 2015–2016” in the northern end of the shallow oxygen minimum zone of the Eastern Tropical Pacific Ocean

Abstract

Based on hydrographic data and vertical distributions of tropical species of fish larvae (Diogenichthys laternatus, Vinciguerria lucetia, Bregmaceros bathymaster, and Auxis spp.), effects of “Godzilla El Niño 2015–2016” in the shallow oxygen minimum zone off Mexico were analyzed. Zooplankton samples were collected during four cruises, before (February 2010 and April 2012) and during (June 2015 and March 2016) the warm event. Temporal series of sea surface temperature revealed that June 2015 was the warmest June of the last years. Conservative temperature was >2°C higher than normal in the surface mixed layer, and the suboxic layer (4.4 µmol/kg) reached as shallow as 100 m depth. Unexpected results were that larval abundances were relatively high during the warm event, unlike zooplankton volumes, which declined. Before the warm event, V. lucetia and Auxis spp. were more abundant in the surface mixed layer, while B. bathymaster and D. laternatus dominated in the thermocline and shallow hypoxic layer (44 µmol/kg). However, during the event in June 2015, all species were most abundant in the surface mixed layer, which implied that the species adapted to hypoxia had inverted their normal pattern of distribution, possibly as consequence of the rise of the suboxic layer; however, further observations are required to confirm this generality. Results showed no dramatic change in the total larval abundance during the warm event. Nevertheless, a differential response in their vertical distribution was evident in association with changes in the depth of the shallow hypoxic and suboxic layers. This might indicate adaptability of tropical species to prolonged periods of warming in the oceans.

Ventilation of the Upper Oxygen Minimum Zone in the Coastal Region Off Mexico: Implications of El Niño 2015–2016

“…The exit of GCW was observed on the peninsular side as a front with high salinity (Castro et al, 2006;Collins et al, 2015) as was the entrance of TW over the continental platform in front of the coasts of Sonora, in accordance with the typical circulation scheme for this zone (Lavín et al, 2009). The depth of the oxycline was shallow in comparison to the region of Cabo Corrientes, but the intensity of the oxycline was amongst the lowest recorded (Sánchez-Velasco et al, 2017). This is due to the GCW being more oxygenated and dominating depths below 150 m (Figures 3, 5), causing the oxycline to become the thickest in this region.…”

“…In southern latitudes, below 22 • N for coastal stations and 20.5 • N for oceanic stations, the surface layer was dominated by the incursion of TSW. Its anomalous presence was related to the seasonally expected pattern, associated with a developing ENSO event (Sánchez-Velasco et al, 2017). In this region, the greatest stratification in our study period was registered, from 1000 to 1400 J•m −3 along an ocean-coast gradient ( Figure 9A).…”

Warm Events Induce Loss of Resilience in Organic Carbon Production in the Northeast Pacific Ocean

“…The warm anomalies impacted the Bering Sea from 2014 until 2016 by shifting phytoplankton blooms to early spring (Stabeno et al, 2017), similar to the early increase in phytoplankton abundance observed in the Gulf of Alaska in 2014 (Peña et al, 2019) and early NCP from this work (Figure 4c). Still, in 2015, there was a decline in zooplankton stocks off the coast of Mexico and a shift in the vertical distribution of fish larvae in response (Sánchez-Velasco et al, 2017). Still, in 2015, there was a decline in zooplankton stocks off the coast of Mexico and a shift in the vertical distribution of fish larvae in response (Sánchez-Velasco et al, 2017).…”

“…The development of the Arc pattern along the west coast of United States between 2014 and 2015 altered the local phytoplankton community structure (Du & Peterson, 2018), with elevated SSTs stimulating harmful algae blooms in the northern California Current (McKibben et al, 2017;Zhu et al, 2017). Still, in 2015, there was a decline in zooplankton stocks off the coast of Mexico and a shift in the vertical distribution of fish larvae in response (Sánchez-Velasco et al, 2017). For the first time on record, the northeast Pacific Ocean was a pCO 2 source (Sutton et al, 2017) at the same time that net organic carbon production declined in 2015 (Figure 5a).…”

“…The period between 2013 and 2016 was remarkable for the northeast Pacific as it involved consecutive warm events, starting with "the Warm Blob" that developed in the central Gulf of Alaska and concluding with a strong El Niño (Bond et al, 2015;Hu & Fedorov, 2016). These events severely reduced the vertical mixing for two consecutive winters (Bond et al, 2015), impacting ecosystem functions ranging from primary to fisheries productivity (Du & Peterson, 2018;McKibben et al, 2017;Peterson et al, 2017;Sánchez-Velasco et al, 2017). From a biogeochemical perspective, the thinning and increased buoyancy of the mixed layer over consecutive winters should have been fundamental in regulating primary production and, consequently, net organic carbon production (i.e., NCP) and its potential for export.…”