Nitrogen cycling driven by organic matter export in the South Pacific oxygen minimum zone
"Oxygen minimum zones are expanding globally, and at present account for around 20–40% of oceanic nitrogen loss. Heterotrophic denitrification and anammox—anaerobic ammonium oxidation with nitrite—are responsible for most nitrogen loss in these low-oxygen waters. Anammox is particularly significant in the eastern tropical South Pacific, one of the largest oxygen minimum zones globally. "
Source: Nature Geoscience (2013)
Authors: Tim Kalvelage et al.
Hydroxylamine as a Potential Indicator of Nitrification in the Open Ocean
"Hydroxylamine (NH2OH), a short‐lived intermediate in the nitrogen cycle, is a potential precursor of nitrous oxide (N2O) in the ocean. However, measurements of NH2OH in the ocean are sparse. Here we present a data set of depth profiles of NH2OH from the equatorial Atlantic Ocean and the eastern tropical South Pacific and compare it to N2O, nitrate, and nitrite profiles under varying oxygen conditions. The presence of NH2OH in surface waters points toward surface nitrification in the upper 100 m. [...]"
Source: Geophysical Research Letters
Authors: Frederike Korth et al.
Pacific Decadal Oscillation and recent oxygen decline in the eastern tropical Pacific Ocean
"The impact of the positive and negative phases of the Pacific Decadal Oscillation (PDO) on the extension of the poorly oxygenated regions of the eastern Pacific Ocean was assessed using a coupled ocean circulation–biogeochemical model. We show that during a “typical” PDO-positive phase the volume of the suboxic regions expands by 7 % over 50 years due to a slowdown of the large-scale circulation related to the decrease in the intensity of the trade winds. Changes in oxygen levels are mostly controlled by advective processes between 10∘ N and 10∘ S, whereas diffusive processes are dominant poleward of 10∘: in a “typical” PDO-positive phase the sluggish equatorial current system provides less oxygen to the eastern equatorial part of the basin while the oxygen transport by diffusive processes significantly decreases south of 10∘ S. [...]"
Authors: Olaf Duteil, Andreas Oschlies, and Claus W. Böning
Forcings and Evolution of the 2017 Coastal El Niño Off Northern Peru and Ecuador
"El Niño events, in particular the eastern Pacific type, have a tremendous impact on the marine ecosystem and climate conditions in the eastern South Pacific. During such events, the accumulation of anomalously warm waters along the coast favors intense rainfall. The upwelling of nutrient-replete waters is stopped and the marine ecosystem is strongly impacted. These events are generally associated with positive surface temperature anomalies in the central and eastern equatorial Pacific. [...]"
Source: Frontiers in Marine Science
Authors: Vincent Echevin et al.
Transport, properties, and life cycles of mesoscale eddies in the eastern tropical South Pacific
"The influence of mesoscale eddies on the flow field and the water masses, especially the oxygen distribution of the eastern tropical South Pacific, is investigated from a mooring, float, and satellite data set. Two anticyclonic (ACE1/2), one mode-water (MWE), and one cyclonic eddy (CE) are identified and followed in detail with satellite data on their westward transition with velocities of 3.2 to 6.0cms−1 from their generation region, the shelf of the Peruvian and Chilean upwelling regime, across the Stratus Ocean Reference Station (ORS; ∼ 20°S, 85°W) to their decaying region far west in the oligotrophic open ocean. [...]"
Source: Ocean Science
Authors: Rena Czeschel et al.
Diapycnal dissolved organic matter supply into the upper Peruvian oxycline
"The Eastern Tropical South Pacific (ETSP) hosts the Peruvian upwelling system, which represents one of the most productive areas in the world ocean. High primary production followed by rapid heterotrophic utilization of organic matter supports the formation of one of the most intense oxygen minimum zones (OMZ) in the world ocean where dissolved oxygen (O2) concentrations reach well below 1 µmol kg−1. The high productivity leads to an accumulation of dissolved organic matter (DOM) in the surface layers that may serve as a substrate for heterotrophic respiration. [...]"
Authors: lexandra N. Loginova et al.
Oxygen Pathways and Budget for the Eastern South Pacific Oxygen Minimum Zone
"Ventilation of the eastern South Pacific Oxygen Minimum Zone (ESP‐OMZ) is quantified using climatological Argo and dissolved oxygen data, combined with reanalysis wind stress data. We (1) estimate all oxygen fluxes (advection and turbulent diffusion) ventilating this OMZ, (2) quantify for the first time the oxygen contribution from the subtropical versus the traditionally studied tropical‐equatorial pathway, and (3) derive a refined annual‐mean oxygen budget for the ESP‐OMZ. In the upper OMZ layer, net oxygen supply is dominated by tropical‐equatorial advection, with more than one‐third of this supply upwelling into the Ekman layer through previously unevaluated vertical advection, within the overturning component of the regional Subtropical Cell (STC). [...]"
Authors: P. J. Llanillo et al.
Impact of mesoscale eddies on water mass and oxygen distribution in the eastern tropical South Pacific
"The influence of mesoscale eddies on the flow field and the water masses, especially the oxygen distribution of the eastern tropical South Pacific is investigated from a mooring, float and satellite data set. Two anticyclonic (ACE1/2), one mode water (MWE) and one cyclonic eddy (CE) are identified and followed in detail with satellite data on their westward transition with velocities of 3.2 to 6.0 cm/s from their generation region, the shelf of the Peruvian and Chilean upwelling regime, across the Stratus Ocean Reference Station (ORS) (~ 20° S, 85° W) to their decaying region far west in the oligotrophic open ocean. [...]"
Source: Ocean Science (under review)
Authors: Rena Czeschel et al.
Community composition of nitrous oxide consuming bacteria in the oxygen minimum zone of the Eastern Tropical South Pacific
"The ozone-depleting and greenhouse gas, nitrous oxide (N2O), is mainly consumed by the microbially mediated anaerobic process, denitrification. N2O consumption is the last step in canonical denitrification, and is also the least O2 tolerant step. Community composition of total and active N2O consuming bacteria was analyzed based on total (DNA) and transcriptionally active (RNA) nitrous oxide reductase (nosZ) genes using a functional gene microarray. The total and active nosZ communities were dominated by a limited number of nosZ archetypes, affiliated with bacteria from marine, soil and marsh environments. [...]"
Source: Frontiers in Microbiology
Authors: Xin Sun, Amal Jayakumar and Bess B. Ward