Contribution of oxygen minimum zone waters to the coastal upwelling off Mauritania

Abstract. Depth profiles of nitrous oxide (N2O) were measured during six cruises to the upwelling area and oxygen minimum zone (OMZ) off Peru in 2009 and 2012/13, covering both the coastal shelf region and the adjacent open ocean. N2O profiles displayed a strong sensitivity towards oxygen concentrations. Open ocean profiles showed a transition from a broad maximum to a double-peak structure towards the centre of the OMZ where the oxygen minimum was more pronounced. Maximum N2O concentrations in the open ocean were about 80 nM. A linear relationship between ΔN2O and apparent oxygen utilization (AOU) could be found for all measurements within the upper oxycline, with a slope similar to studies in other oceanic regions. N2O profiles close to the shelf revealed a much higher variability, with N2O concentrations in the upper oxycline reaching up to several hundred nanomoles per liter at selected stations. Due to the extremely sharp oxygen gradients at the shelf, these maxima occurred in very shallow water depths of less than 50 m. In this area, a linear relationship between ΔN2O and AOU could not be observed. N2O concentrations above 100 nM were observed at oxygen concentrations ranging from close to saturation to suboxic conditions. Our results indicate that the coastal upwelling off Peru at the shelf causes conditions that lead to extreme N2O accumulation.

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Benthic Foraminifera from Middle to Late Pleistocene, coastal upwelling sediments of ODP Hole 686B, Pacific Ocean, off Peru

Journal of Micropalaeontology ◽

10.1144/jm.9.2.153 ◽

1991 ◽

Vol 9 (2) ◽

pp. 153-158 ◽

Cited By ~ 3

Author(s):

Kathryn A. Malmgren ◽

Brian M. Funnell

Keyword(s):

Late Pleistocene ◽

Surface Waters ◽

Benthic Foraminifera ◽

Bottom Water ◽

Coastal Upwelling ◽

Oxygen Minimum Zone ◽

Water Oxygen ◽

Minimum Zone ◽

Water Depths ◽

Oxygen Minimum

Abstract. Benthic Foraminifera from middle to late Pleistocene, (c. 600ka to 0ka), sediments of ODP Hole 686B, off Peru, show highest abundances and diversities during periods of cooler surface waters, (inferred from the Uk37 index), and enhanced upwelling, (inferred from the peridinacean/gonyaulacacean dinoflagellate cyst ratio). During the latest Pleistocene, (c. 160ka to 0ka), these periods are characterised by higher organic carbon contents in the bottom sediments, and occur during the odd-numbered, interglacial_18O stages. The benthic Foraminifera indicate deposition in 120 to 250 metres water depth for the earlier part of the record, (c. 600ka to c. 200ka), within the oxygen-minimum zone, with bottom water oxygen contents of <0.5 to 0.2 ml/l, (inferred from the dominance of Bolivinellina humilis). Deposition in water depths approaching those of the present day, (c. 450 metres), is indicated from c. 160ka onwards, with better oxygenated bottom water conditions, probably corresponding to the lower part of the oxygen-minimum zone.

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Oxygen-minimum zone edge effects: Evidence from the central California coastal upwelling system

Geology ◽

10.1130/0091-7613(1985)13<491:ozeeef>2.0.co;2 ◽

1985 ◽

Vol 13 (7) ◽

pp. 491 ◽

Cited By ~ 118

Author(s):

Henry T. Mullins ◽

Joel B. Thompson ◽

Kristin McDougall ◽

Thomas L. Vercoutere

Keyword(s):

Edge Effects ◽

Coastal Upwelling ◽

Oxygen Minimum Zone ◽

Central California ◽

Upwelling System ◽

Minimum Zone ◽

Zone Edge ◽

Oxygen Minimum

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Sedimentation Across the Central California Oxygen Minimum Zone: An Alternative Coastal Upwelling Sequence

Journal of Sedimentary Research ◽

10.1306/212f8be8-2b24-11d7-8648000102c1865d ◽

1987 ◽

Vol Vol. 57 ◽

Cited By ~ 5

Author(s):

Thomas L. Vercoutere, Henry T. Mull

Keyword(s):

Coastal Upwelling ◽

Oxygen Minimum Zone ◽

Central California ◽

Minimum Zone ◽

Oxygen Minimum

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Extreme N<sub>2</sub>O accumulation in the coastal oxygen minimum zone off Peru

Biogeosciences ◽

10.5194/bg-13-827-2016 ◽

2016 ◽

Vol 13 (3) ◽

pp. 827-840 ◽

Cited By ~ 33

Author(s):

A. Kock ◽

D. L. Arévalo-Martínez ◽

C. R. Löscher ◽

H. W. Bange

Keyword(s):

Linear Relationship ◽

Coastal Upwelling ◽

Nitrogen Loss ◽

Full Range ◽

Oxygen Minimum Zone ◽

Open Ocean ◽

N2o Production ◽

Minimum Zone ◽

Oxygen Minimum ◽

Oxygen Concentrations

Abstract. Depth profiles of nitrous oxide (N2O) were measured during six cruises to the upwelling area and oxygen minimum zone (OMZ) off Peru in 2009 and 2012/2013, covering both the coastal shelf region and the adjacent open ocean. N2O profiles displayed a strong sensitivity towards oxygen concentrations. Open ocean profiles with distances to the shelf break larger than the first baroclinic Rossby radius of deformation showed a transition from a broad maximum close to the Equator to a double-peak structure south of 5° S where the oxygen minimum was more pronounced. Maximum N2O concentrations in the open ocean were about 80 nM. A linear relationship between ΔN2O and apparent oxygen utilization (AOU) could be found for measurements within the upper oxycline, with a slope similar to studies in other oceanic regions. In contrast, N2O profiles close to the shelf revealed a much higher variability, and N2O concentrations higher than 100 nM were often observed. The highest N2O concentration measured at the shelf was ∼  850 nM. Due to the extremely sharp oxygen gradients at the shelf, N2O maxima occurred in very shallow water depths of less than 50 m. In the coastal area, a linear relationship between ΔN2O and AOU could not be observed as extremely high ΔN2O values were scattered over the full range of oxygen concentrations. The data points that showed the strongest deviation from a linear ΔN2O ∕ AOU relationship also showed signals of intense nitrogen loss. These results indicate that the coastal upwelling at the Peruvian coast and the subsequent strong remineralization in the water column causes conditions that lead to extreme N2O accumulation, most likely due to the interplay of intense mixing and high rates of remineralization which lead to a rapid switching of the OMZ waters between anoxic and oxic conditions. This, in turn, could trigger incomplete denitrification or pulses of increased nitrification with extreme N2O production.

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