Premium
Factors Regulating Nitrification in the Arctic Ocean: Potential Impact of Sea Ice Reduction and Ocean Acidification
Author(s) -
Shiozaki Takuhei,
Ijichi Minoru,
Fujiwara Amane,
Makabe Akiko,
Nishino Shigeto,
Yoshikawa Chisato,
Harada Naomi
Publication year - 2019
Publication title -
global biogeochemical cycles
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.512
H-Index - 187
eISSN - 1944-9224
pISSN - 0886-6236
DOI - 10.1029/2018gb006068
Subject(s) - nitrification , halocline , ocean acidification , oceanography , environmental science , arctic , ammonium , light intensity , chemistry , nitrogen , seawater , geology , salinity , physics , organic chemistry , optics
Nitrification is susceptible to changes in light and pH and, thus, could be influenced by recent sea ice reductions and acidification in the Arctic Ocean. We investigated the sensitivity of nitrification to light, pH, and substrate availability in a natural nitrifier community of the Arctic Ocean. Nitrification was active near the bottom of the shelf region (<60 m) and in the halocline layer (50–200 m) of the Arctic basin, where ammonium was abundant, but was low in the ammonium‐depleted Atlantic layer (>250 m). In pH control experiments, nitrification rates significantly declined when the pH was manipulated to be 0.22 lower than the controls. However, nitrification was relatively insensitive to changes in pH compared to changes in light. Light control experiments showed that nitrification was inhibited by a light intensity above 0.11 mol photons m −2 day −1 , which was presumably the light threshold. A light intensity greater than the light threshold extended to the shelf bottom and upper halocline layer, limiting nitrification in these waters. Satellite data analyses indicated that the area where light levels inhibit nitrification has increased throughout the Arctic Ocean due to the recent sea ice reduction, which may lead to a declining trend in nitrification. Our results suggest that stronger light levels in the future Arctic Ocean could further suppress nitrification and alter the composition of inorganic nitrogen, with implications for the structure of ecosystems.