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

Yücel, Mustafa; Beaton, Alexander D.; Dengler, Marcus; Mowlem, Matthew C.; Sohl, Frank; 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. https://doi.org/10.1371/journal.pone.0132785

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Official URL: http://dx.doi.org/10.1371/journal.pone.0132785

Abstract/Summary

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 (ΣNOx) 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 ΣNOx concentration, with 15.2 to 23.4 μM (median=18.3 μM); while at the 100 site ΣNOx varied between 21.0 and 30.1 μM over 40 hours (median = 25.1μM). The 170 m site had the highest median ΣNOx level (25.8 μM) with less variability (22.8 to 27.7 μM). At the 50 m site, nitrite concentration decreased fivefold from 1 to 0.2 μM 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.

Item Type:	Publication - Article
Digital Object Identifier (DOI):	https://doi.org/10.1371/journal.pone.0132785
ISSN:	1932-6203
NORA Subject Terms:	Marine Sciences
Date made live:	21 Jul 2015 12:50 +0 (UTC)
URI:	https://nora.nerc.ac.uk/id/eprint/511343

Item Type:

Publication - Article

Digital Object Identifier (DOI):

https://doi.org/10.1371/journal.pone.0132785

ISSN:

1932-6203

NORA Subject Terms:

Marine Sciences

Date made live:

21 Jul 2015 12:50 +0 (UTC)

URI:

https://nora.nerc.ac.uk/id/eprint/511343