Chemical oceanography. Increasing anthropogenic nitrogen in the North Pacific Ocean

Area of Science:

• Oceanography
• Environmental Science
• Marine Chemistry

Background:

• Anthropogenic reactive nitrogen emissions from northeastern Asia are increasing.
• Enhanced nitrogen deposition is observed across the North Pacific Ocean (NPO).
• The NPO is historically a nitrogen-limited marine ecosystem.

Purpose of the Study:

• To quantify the increase in upper ocean nitrate (N) concentration in the NPO.
• To assess the spatial distribution of this N increase relative to phosphate (P).
• To understand the implications of changing nutrient ratios for primary production.

Main Methods:

• Analysis of oceanic nutrient concentrations (nitrate and phosphate).
• Assessment of nitrogen deposition patterns from atmospheric sources.
• Modeling the impact of nutrient changes on marine ecosystems.

Main Results:

• A detectable increase in upper ocean nitrate concentration was observed in the NPO.
• The rate of increase in excess nitrogen relative to phosphate was highest near Asia (~0.24 µmol/kg/year) and decreased eastward.
• Results align with the distribution of atmospheric nitrogen deposition.

Conclusions:

• Anthropogenic nitrogen emissions are altering the nutrient balance in the NPO.
• Increased nitrogen availability may enhance primary production in this previously N-limited region.
• A potential long-term shift from nitrogen-limitation to phosphate-limitation in the NPO is indicated.