@article{fdi:010075523,
  title = {{F}irst evidence of anoxia and nitrogen loss in the {S}outhern {C}anary {U}pwelling {S}ystem},
  author = {{M}achu, {E}ric and {C}apet, {X}. and {E}strade, {P}. {A}. and {N}doye, {S}. and {B}rajard, {J}. and {B}aurand, {F}ran{\c{c}}ois and {A}uger, {P}. {A}. and {L}azar, {A}. and {B}rehmer, {P}atrice},
  editor = {},
  language = {{ENG}},
  abstract = {{T}he northeastern {A}tlantic hosts the most ventilated subsurface waters of any eastern boundary upwelling system, while coastal upwelling source waters are slightly above hypoxic levels. {A}noxic conditions have previously been found offshore inside mesoscale eddies whose core waters undergo oxygen consumption for many months. {B}ased on circumstantial in situ observations, this study demonstrates that the {S}enegalese coastal ocean is subjected to episodic occurrence of zero dissolved oxygen concentration at depth along with elevated nitrite concentration (11mmol/m(3)) and nitrate/nitrite deficit to phosphate, thereby indicating severe anoxia and intense nitrogen loss. {T}he anoxic event was associated with a prolonged upwelling relaxation episode in {M}arch 2012 and a nearshore diatom bloom that underwent degradation while being advected offshore in stratified waters. {T}his is consistent with scenarios observed in other upwelling systems ({B}enguela and {C}alifornia), and such conditions are presumably frequent in the southern part of the {C}anary system. {P}lain language summary {O}xygen is a key requirement for respiration by marine living organisms. {W}arming of the atmosphere and the ocean surface reduces the oxygenation of offshore waters. {S}imilarly, the extra load of nutrients from agriculture or waste waters modifies algal production, particularly in coastal regions, often resulting in oxygen-depleted waters. {S}pecific reactions affecting the ionic forms of nitrogen also occur within oxygen-depleted waters, which also impact the nitrogen cycle by generating nitrite, which is poisonous for marine organisms, and nitrous oxide, a powerful greenhouse gas. {W}e took measurements at sea to show that a poorly studied coastal sector of the {N}orth {A}tlantic {O}cean, the {S}enegalese continental shelf, can be episodically subjected to complete depletion of subsurface oxygen (anoxia) as well as high nitrite concentrations, constituting the first report of anoxia for this oceanic region. {W}e also show that this anoxia is likely the consequence of the decay of a bloom of diatoms, a group of microalgae common in this type of ecosystem that initially developed in shallow waters and transported offshore by anomalous currents associated with low-wind conditions.},
  keywords = {oxygen ; canary upwelling system ; anoxia ; denitrification ; shallow ; continental shelf ; {ATLANTIQUE} ; {SENEGAL} ; {ZONE} {TROPICALE}},
  booktitle = {},
  journal = {{G}eophysical {R}esearch {L}etters},
  volume = {46},
  numero = {5},
  pages = {2619--2627},
  ISSN = {0094-8276},
  year = {2019},
  DOI = {10.1029/2018gl079622},
  URL = {https://www.documentation.ird.fr/hor/fdi:010075523},
}