Nitrogen cycling in shallow low oxygen coastal waters off Peru from nitrite and nitrate nitrogen and oxygen isotopes

Hu, H., Bourbonnais, A., Larkum, J., Bange, Hermann W. and Altabet, M. A. (2016) Nitrogen cycling in shallow low oxygen coastal waters off Peru from nitrite and nitrate nitrogen and oxygen isotopes Biogeosciences (BG), 13 (5). pp. 1453-1468. DOI 10.5194/bg-13-1453-2016.

[img]
Preview
Text
bg-13-1453-2016.pdf - Published Version
Available under License ["licenses_description_cc_by_3.0" not defined].

Download (2746Kb) | Preview

Supplementary data:

Abstract

O2 minimum zones (OMZ) of the world's oceans are important locations for microbial dissimilatory NO3- reduction and subsequent loss of combined nitrogen (N) to biogenic N2 gas. This is particularly so when the OMZ is coupled to a region of high productivity leading to high rates of N-loss as found in the coastal upwelling region off Peru. Stable N isotope ratios (and O in the case of NO3- and NO2-) can be used as natural tracers of OMZ N-cycling because of distinct kinetic isotope effects associated with microbially-mediated N-cycle transformations. Here we present NO2- and NO3- stable isotope data from the nearshore upwelling region off Callao, Peru. Subsurface O2 was generally depleted below about 30 m depth with O2 less than 10 μM, while NO2- concentrations were high, ranging from 6 to 10 μM and NO3- was in places strongly depleted to near 0 μM. We observed for the first time, a positive linear relationship between NO2- δ15N and δ18O at our coastal stations, analogous to that of NO3- N and O isotopes during assimilatory and dissimilatory reduction. This relationship is likely the result of rapid NO2- turnover due to higher organic matter flux in these coastal upwelling waters. No such relationship was observed at offshore stations where slower turnover of NO2- facilitates dominance of isotope exchange with water. We also evaluate the overall isotope fractionation effect for N-loss in this system using several approaches that vary in their underlying assumptions. While there are differences in apparent fractionation factor (ε) for N-loss as calculated from the δ15N of [NO3-], DIN, or biogenic N2, values for ε are generally much lower than previously reported, reaching as low as 6.5‰. A possible explanation is the influence of sedimentary N-loss at our inshore stations which incurs highly suppressed isotope fractionation.

Document Type: Article
Additional Information: WOS:000372082500006
Keywords: ANAEROBIC AMMONIUM OXIDATION; TROPICAL NORTH PACIFIC; MINIMUM ZONE; SOUTH-PACIFIC; ARABIAN SEA; FRESH-WATER; INORGANIC NITROGEN; DENITRIFIER METHOD; ANAMMOX BACTERIA; DEFICIENT WATERS; RV Meteor; M91
Research affiliation: OceanRep > SFB 754 > B4
OceanRep > SFB 754
OceanRep > GEOMAR > FB2 Marine Biogeochemistry > FB2-CH Chemical Oceanography
Refereed: Yes
DOI etc.: 10.5194/bg-13-1453-2016
ISSN: 1726-4170
Related URLs:
Projects: SOPRAN, SFB754
Expeditions/Models:
Date Deposited: 22 Dec 2015 13:04
Last Modified: 19 Dec 2017 12:48
URI: http://eprints.uni-kiel.de/id/eprint/30742

Actions (login required)

View Item View Item

Document Downloads

More statistics for this item...