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Nitrate and nitrite variability at the seafloor of an oxygen minimum zone revealed by a novel microfluidic in-situ chemical sensor

Nitrate and nitrite variability at the seafloor of an oxygen minimum zone revealed by a novel microfluidic in-situ chemical sensor
Nitrate and nitrite variability at the seafloor of an oxygen minimum zone revealed by a novel microfluidic in-situ chemical sensor
Microfluidics, or lab-on-a-chip (LOC) is a promising technology that allows the development of miniaturized chemical sensors. In contrast to the surging interest in biomedical sciences, the utilization of LOC sensors in aquatic sciences is still in infancy but a wider use of such sensors could mitigate the undersampling problem of ocean biogeochemical processes. Here we describe the first underwater test of a novel LOC sensor to obtain in situ calibrated time-series (up to 40 h) of nitrate+nitrite (?NOx) and nitrite on the seafloor of the Mauritanian oxygen minimum zone, offshore Western Africa. Initial tests showed that the sensor successfully reproduced water column (160 m) nutrient profiles. Lander deployments at 50, 100 and 170 m depth indicated that the biogeochemical variability was high over the Mauritanian shelf: The 50 m site had the lowest ?NOx concentration, with 15.2 to 23.4 ?M (median=18.3 ?M); while at the 100 site ?NOx varied between 21.0 and 30.1 ?M over 40 hours (median = 25.1?M). The 170 m site had the highest median ?NOx level (25.8 ?M) with less variability (22.8 to 27.7 ?M). At the 50 m site, nitrite concentration decreased fivefold from 1 to 0.2 ?M in just 30 hours accompanied by decreasing oxygen and increasing nitrate concentrations. Taken together with the time series of oxygen, temperature, pressure and current velocities, we propose that the episodic intrusion of deeper waters via cross-shelf transport leads to intrusion of nitrate-rich, but oxygen-poor waters to shallower locations, with consequences for benthic nitrogen cycling. This first validation of an LOC sensor at elevated water depths revealed that when deployed for longer periods and as a part of a sensor network, LOC technology has the potential to contribute to the understanding of the benthic biogeochemical dynamics.
1932-6203
e0132785
Yücel, Mustafa
0a2613c8-38ed-4863-baf9-eb0a5eea046f
Beaton, Alexander D.
b33c89f0-5c08-4cbb-9718-51c5c5179ff0
Dengler, Marcus
aade11b7-f20e-466a-8402-c0c66d506d5c
Mowlem, Matthew C.
6f633ca2-298f-48ee-a025-ce52dd62124f
Sohl, Frank
0963ed1b-8c55-4010-9410-09b351b919c1
Sommer, Stefan
bc68ea8f-c71c-471e-8a90-3a0ce74774a0
Yücel, Mustafa
0a2613c8-38ed-4863-baf9-eb0a5eea046f
Beaton, Alexander D.
b33c89f0-5c08-4cbb-9718-51c5c5179ff0
Dengler, Marcus
aade11b7-f20e-466a-8402-c0c66d506d5c
Mowlem, Matthew C.
6f633ca2-298f-48ee-a025-ce52dd62124f
Sohl, Frank
0963ed1b-8c55-4010-9410-09b351b919c1
Sommer, Stefan
bc68ea8f-c71c-471e-8a90-3a0ce74774a0

Yücel, Mustafa, Beaton, Alexander D., Dengler, Marcus, Mowlem, Matthew C., Sohl, Frank and Sommer, Stefan (2015) Nitrate and nitrite variability at the seafloor of an oxygen minimum zone revealed by a novel microfluidic in-situ chemical sensor. PLoS ONE, 10 (7), e0132785. (doi:10.1371/journal.pone.0132785).

Record type: Article

Abstract

Microfluidics, or lab-on-a-chip (LOC) is a promising technology that allows the development of miniaturized chemical sensors. In contrast to the surging interest in biomedical sciences, the utilization of LOC sensors in aquatic sciences is still in infancy but a wider use of such sensors could mitigate the undersampling problem of ocean biogeochemical processes. Here we describe the first underwater test of a novel LOC sensor to obtain in situ calibrated time-series (up to 40 h) of nitrate+nitrite (?NOx) and nitrite on the seafloor of the Mauritanian oxygen minimum zone, offshore Western Africa. Initial tests showed that the sensor successfully reproduced water column (160 m) nutrient profiles. Lander deployments at 50, 100 and 170 m depth indicated that the biogeochemical variability was high over the Mauritanian shelf: The 50 m site had the lowest ?NOx concentration, with 15.2 to 23.4 ?M (median=18.3 ?M); while at the 100 site ?NOx varied between 21.0 and 30.1 ?M over 40 hours (median = 25.1?M). The 170 m site had the highest median ?NOx level (25.8 ?M) with less variability (22.8 to 27.7 ?M). At the 50 m site, nitrite concentration decreased fivefold from 1 to 0.2 ?M in just 30 hours accompanied by decreasing oxygen and increasing nitrate concentrations. Taken together with the time series of oxygen, temperature, pressure and current velocities, we propose that the episodic intrusion of deeper waters via cross-shelf transport leads to intrusion of nitrate-rich, but oxygen-poor waters to shallower locations, with consequences for benthic nitrogen cycling. This first validation of an LOC sensor at elevated water depths revealed that when deployed for longer periods and as a part of a sensor network, LOC technology has the potential to contribute to the understanding of the benthic biogeochemical dynamics.

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Published date: 10 July 2015
Organisations: Ocean Technology and Engineering

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Local EPrints ID: 379468
URI: https://eprints.soton.ac.uk/id/eprint/379468
ISSN: 1932-6203
PURE UUID: 2a619a1c-a876-492e-9b79-35ec4ee6dcfb

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Date deposited: 21 Jul 2015 12:46
Last modified: 17 Jul 2017 20:43

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Contributors

Author: Mustafa Yücel
Author: Alexander D. Beaton
Author: Marcus Dengler
Author: Frank Sohl
Author: Stefan Sommer

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