On the effects of ENSO on ocean biogeochemistry in the Northern Humboldt Current System (NHCS): A modeling study

Mogollón, Rodrigo; Calil, Paulo H. R.

doi:10.1016/j.jmarsys.2017.03.011

Cited by 30 publications

(46 citation statements)

References 52 publications

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“…The increase of water column oxygen concentrations during El Niño events leads to a reduction of the SW volume as shown in previous modelling studies (Mogollón and Calil, 2017;Yang et al, 2017;Espinoza-Morriberón et al, 2019). The reduction of SW volume, which occurs not only in the onshore (Figure 5-a) but also in the offshore (Figure 5-b) regions of the ETSP OMZ, reflects the reduction of the most oxygen-poor waters (with concentrations below 5 µmol/l, Figure 5-c,d).…”

Section: Added On Page 5 Lines 3-8supporting

confidence: 69%

“…Added in Material and methods section of the manuscript, Page 5 lines 25-34 and page 6 lines 1-11 2.3 Model output analysis 2.3.1 Calculation of oxygen transport across the SW marginsIn the present study, we analyse the dynamics of oxygen-poor waters in terms of suboxic waters (SW), defined here as waters with oxygen concentrations below 20 µmol/l. As shown in previous studies on the OMZ of the ETSP (Llanillo et al, 2013;Mogollón and Calil, 2017;Yang et al, 2017;Espinoza-Morriberón et al, 2019), the upper position of oxygen poor waters varies with time and due to ENSO fluctuations. Changes may also occur in the lateral margins of the OMZ.…”

Section: Interactive Commentmentioning

confidence: 51%

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Response to reviewer 1 comments

José¹

2019

Preprint

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Dear anonymous Reviewer I We would like to thank referee 1 for the constructive comments, which have allowed a considerable improvement of the manuscript. The most substantial point the referee stated concerned the common volume used in the calculation of oxygen transport. In revised version of the manuscript, we have used a more extensive volume, which also includes the onshore region. The respective analysis has been added to the revised C1

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Section: Added On Page 5 Lines 3-8supporting

confidence: 69%

Section: Interactive Commentmentioning

confidence: 51%

Response to reviewer 1 comments

José¹

2019

Preprint

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“…/ 16 O at oxygen position of the N 2 O molecule. The value of δX is expressed as per mill (‰) deviation relative to a set of reference materials: atmospheric N 2 for δ 15 N bulk , δ 15 N α , and δ 15 N β(Mohn et al, 2014), and Vienna standard mean ocean water (VSMOW) for δ 18 O.…”

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confidence: 99%

Investigating the effect of El Niño on nitrous oxide distribution in the eastern tropical South Pacific

Altabet

Bange

et al. 2019

Biogeosciences

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Abstract. The open ocean is a major source of nitrous oxide (N2O), an atmospheric trace gas attributable to global warming and ozone depletion. Intense sea-to-air N2O fluxes occur in major oceanic upwelling regions such as the eastern tropical South Pacific (ETSP). The ETSP is influenced by the El Niño–Southern Oscillation that leads to inter-annual variations in physical, chemical, and biological properties in the water column. In October 2015, a strong El Niño event was developing in the ETSP; we conduct field observations to investigate (1) the N2O production pathways and associated biogeochemical properties and (2) the effects of El Niño on water column N2O distributions and fluxes using data from previous non-El Niño years. Analysis of N2O natural abundance isotopomers suggested that nitrification and partial denitrification (nitrate and nitrite reduction to N2O) were occurring in the near-surface waters; indicating that both pathways contributed to N2O effluxes. Higher-than-normal sea surface temperatures were associated with a deepening of the oxycline and the oxygen minimum layer. Within the shelf region, surface N2O supersaturation was nearly an order of magnitude lower than that of non-El Niño years. Therefore, a significant reduction of N2O efflux (75 %–95 %) in the ETSP occurred during the 2015 El Niño. At both offshore and coastal stations, the N2O concentration profiles during El Niño showed moderate N2O concentration gradients, and the peak N2O concentrations occurred at deeper depths during El Niño years; this was likely the result of suppressed upwelling retaining N2O in subsurface waters. At multiple stations, water-column inventories of N2O within the top 1000 m were up to 160 % higher than those measured in non-El Niño years, indicating that subsurface N2O during El Niño could be a reservoir for intense N2O effluxes when normal upwelling is resumed after El Niño.

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“…The mechanism consists in a leaking of the coastal nutrient inventory by horizontal advection of nutrients into the oligotrophic ocean, eventually leading to a reduction of biological production in the coastal zone. Mogollón and Calil () demonstrated that the cold ENSO phase, La Niña, induces an increase in EKE in the southern NHCS, which leads to substantial offshore nitrogen advection (in the form of nitrate) at a rate of 0.5 kg N m −2 day −1 at the surface.…”

Section: Resultsmentioning

confidence: 99%

“…The Humboldt Current System (HCS) sustains high levels of biological productivity due to yearlong upwelling‐favorable southeast trade winds, which induce the vertical advection of cold, nutrient‐rich and oxygen‐poor waters from relatively shallow depths (Strub, Combes, Shillington, & Pizarro, ; Strub & Mesías, ). The low‐latitude of the HCS allows a strong upwelling circulation due to larger offshore Ekman transport but also makes it very sensitive to equatorial oceanic perturbations, such as El Niño Southern Oscillation (ENSO) (Colas, Capet, McWilliams, & Shchepetkin, ; Mogollón & Calil, ; Montes, Schneider, Colas, Blanke, & Echevin, ; Sanchez, Calienes, & Zuta, ). This intrinsic variability makes the HCS resilient to natural climate variability (Bakun et al., ).…”

Section: Introductionmentioning

confidence: 99%

Counterintuitive effects of global warming‐induced wind patterns on primary production in the Northern Humboldt Current System

Mogollón

Calil

2018

Global Change Biology

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It has been hypothesized that global warming will strengthen upwelling-favorable winds in the Northern Humboldt Current System (NHCS) as a consequence of the increase of the land-sea thermal gradient along the Peruvian coast. The effect of strengthened winds in this region is assessed with the use of a coupled physical-biogeochemical model forced with projected and climatological winds. Strengthened winds induce an increase in primary production of 2% per latitudinal degree from 9.5°S to 5°S. In some important coastal upwelling sites primary production is reduced. This is due to a complex balance between nutrient availability, nutrient use efficiency, as well as eddy- and wind-driven factors. Mesoscale activity induces a net offshore transport of inorganic nutrients, thus reducing primary production in the coastal upwelling region. Wind mixing, in general disadvantageous for primary producers, leads to shorter residence times in the southern and central coastal zones. Overall, instead of a proportional enhancement in primary production due to increased winds, the NHCS becomes only 5% more productive (+5 mol C m year ), 10% less limited by nutrients and 15% less efficient due to eddy-driven effects. It is found that regions with a initial strong nutrient limitation are more efficient in terms of nutrient assimilation which makes them more resilient in face of the acceleration of the upwelling circulation.

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On the effects of ENSO on ocean biogeochemistry in the Northern Humboldt Current System (NHCS): A modeling study

Cited by 30 publications

References 52 publications

Response to reviewer 1 comments

Response to reviewer 1 comments

Investigating the effect of El Niño on nitrous oxide distribution in the eastern tropical South Pacific

Counterintuitive effects of global warming‐induced wind patterns on primary production in the Northern Humboldt Current System

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