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Expansion of denitrification and anoxia in the eastern tropical North Pacific from 1972 to 2012
Author(s) -
Horak Rachel E. A.,
Ruef Wendi,
Ward Bess B.,
Devol Allan H.
Publication year - 2016
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1002/2016gl068871
Subject(s) - anoxic waters , denitrification , water column , upwelling , oceanography , oxygen minimum zone , environmental science , hypoxia (environmental) , transect , oxygen , geology , chemistry , nitrogen , organic chemistry
The eastern tropical North Pacific (ETNP) is a large region of anoxic water that hosts widespread water column N loss (denitrification). There is some disagreement about the long‐term trends of denitrification and anoxia and long‐term studies of water column denitrification within the anoxic zone are lacking. In this study, we compared ETNP water column nitrite, N*, and O 2 data along the same transect for four studies ranging from 1972 to 2012. Anoxic water volume increased, and low‐oxygen conditions expanded into shallower isopycnals from 1972 to 2012. A geochemical marker for cumulative N loss indicates that denitrification was highest in 2012 and the upper oxygen‐deficient zone (ODZ) experienced the most change. Oxygen and N loss changes in the world's largest ODZ for 2012 could not be explained by the Pacific Decadal Oscillation, and decreased O 2 in supply currents and increased wind‐driven upwelling are likely mechanisms contributing to increased N loss and anoxia.