Brown University2014-11-10 1:20 PM

Isotopic evidence for a marine ammonium source in rainwater at Bermuda

Abstract

Emissions of anthropogenic nitrogen (N) to the atmosphere have increased tenfold since preindustrial times, resulting in increased N deposition to terrestrial and coastal ecosystems. 


The sources of N deposition to the ocean, however, are poorly understood. Two years of event-based rainwater samples were collected on the island of Bermuda in the western North Atlantic, which experiences both continent- and ocean-influenced air masses. The rainwater ammonium concentration ranged from 0.36 to 24.6 μM, and the ammonium δ15N from −12.5 to 0.7‰; and neither has a strong relationship with air mass history (6.0 ± 4.2 μM, −4.1 ± 2.6‰ in marine air masses and 5.9 ± 3.2 μM, −5.8 ± 2.5‰ in continental air masses; numerical average ± standard deviation). 


A simple box model suggests that the ocean can account for the concentration and isotopic composition of ammonium in marine rainwater, consistent with the lack of correlation between ammonium δ15N and air mass history. If so, ammonium deposition reflects the cycling of N between the ocean and the atmosphere, rather than representing a net input to the ocean. The δ15N data appear to require that most of the ammonium/a flux to the ocean is by dissolution in surface waters rather than atmospheric deposition. This suggests that the atmosphere and surface ocean are near equilibrium with respect to air/sea gas exchange, implying that anthropogenic ammonia will equilibrate near the coast and not reach the open marine atmosphere. Whereas ~90% of the ammonium deposition to the global ocean has previously been attributed to anthropogenic sources, the evidence at Bermuda suggests that the anthropogenic contribution could be much smaller.


Keywords:ammonium;marine rain;Bermuda;isotopes


Full Article:

http://onlinelibrary.wiley.com/doi/10.1002/2014GB004809/abstract

KEYWORDS

SHARE & LIKE

COMMENTS

ABOUT THE AUTHOR

Brown University

0 Following 0 Fans 0 Projects 15 Articles

SIMILAR ARTICLES

Abstract To overcome the current impasse in global climate negotiations we propose a compromise for sharing the remaining carbon budget, based on four

Read More

ABSTRACTCarnivorous mammals use their forelimbs in different ways to capture their prey. Most terrestrial carnivores have some cursorial (running) adap

Read More

AbstractAchieving trainee diversity in science, technology, engineering, and mathematics is rapidly becoming a challenge faced by many nations. Success

Read More

AbstractThis letter uses satellite remote sensing to examine patterns of cropland expansion, cropland abandonment, and changing cropping frequency in M

Read More

AbstractFirst released in 2011, the Costs of War report has been compiled and updated by more than 30 economists, anthropologists, lawyers, humanitaria

Read More

Highlights•Hypervelocity impact experiments reveal time-resolved damage evolution in spherical targets.•Models of small-scale experiments and large-sca

Read More

ABSTRACTThe Procellarum region is a broad area on the nearside of the Moon that is characterized by low elevations1, thin crust2, and high surface conc

Read More

AbstractIn many lower-income countries, there is a paucity of assessment services for autism spectrum disorders (ASD)., Guidelines will be provided for

Read More

AbstractAimA major implication of natural selection is that species from different parts of the world will vary in their efficiency in converting resou

Read More

AbstractBackground Living near major roadways has been linked with increased risk of cardiovascular events and worse prognosis. Residential proximity t

Read More