Global oceanic emission of ammonia: Constraints from seawater and atmospheric observations

Abstract

Current global inventories of ammonia emissions identify the ocean as the largest natural source. This source depends on seawater pH, temperature, and the concentration of total seawater ammonia (NH x (sw)), which reflects a balance between remineralization of organic matter, uptake by plankton, and nitrification. Here we compare [NH x (sw)] from two global ocean biogeochemical models (BEC and COBALT) against extensive ocean observations. Simulated [NH x (sw)] are generally biased high. Improved simulation can be achieved in COBALT by increasing the plankton affinity for NH x within observed ranges. The resulting global ocean emissions is 2.5 TgN a −1 , much lower than current literature values (7-23 TgN a −1 ), including the widely used Global Emissions InitiAtive (GEIA) inventory (8 TgN a −1 ). Such a weak ocean source implies that continental sources contribute more than half of atmospheric NH x over most of the ocean in the Northern Hemisphere. Ammonia emitted from oceanic sources is insufficient to neutralize sulfate aerosol acidity, consistent with observations. There is evidence over the Equatorial Pacific for a missing source of atmospheric ammonia that could be due to photolysis of marine organic nitrogen at the ocean surface or in the atmosphere. Accommodating this possible missing source yields a global ocean emission of ammonia in the range 2-5 TgN a −1 , comparable in magnitude to other natural sources from open fires and soils.

Constraints on global oceanic emissions of N<sub>2</sub>O from observations and models

“…The number of data points reported for each database are after gridding to 1 • × 1 • × 12 months × 33 depths (World Ocean Atlas 2009). The databases used are (1) NH + cific nitrification rate (d −1 , raw data n = 425, gridded data n = 296) as described in Yool et al (2007); (2) surface NH + 4 concentration distribution (µmol L −1 , raw data n = 33 079, gridded data n = 2343) that combines the dataset used in Paulot et al (2015) with data held by the British Oceanographic Data Centre (Martin Johnson, personal communication, 2015, http://www.bodc.ac.uk, last access: January 2014); (3) depth-resolved N 2 O concentration from the MEMENTO project (nmol L −1 , https://memento.geomar. de/; Bange et al, 2009; downloaded 4 June 2014, raw data n = 14 342, gridded data n = 8047); and (4) surface partial pressure of N 2 O (pN 2 O) also from MEMENTO (ppb, downloaded 16 September 2015, raw data n = 227 463, gridded data n = 6136).…”

Spatial variations in snowpack chemistry, isotopic composition of NO<sub>3</sub><sup>−</sup> and nitrogen deposition from the ice sheet margin to the coast of western Greenland

“…Unlike largerscale studies of Arctic precipitation showing sulfur to be the main acidifying substance (Hole et al, 2009) (Table 5). At the coast, NO is comparable (17 mol ha −1 a −1 ), possibly suggesting an influence of ammonium sulfate aerosols (Fisher et al, 2011;Paulot et al, 2015). Local urban, marine or shipping emis-sions could also account for higher deposition fluxes of all these ions in coastal snowpack, especially given the proximity of the town and port at Sisimiut, but since NO Modelled wet deposition of nss-SO 2− 4 for western Greenland in a global analysis was found to be in the region of 0.2 kg ha −1 a −1 S (Vet et al, 2014), which falls in the middle of the spatial range suggested by our study (0.08-0.35 kg ha −1 a −1 ).…”

First detection of ammonia (NH<sub>3</sub>) in the Asian summer monsoon upper troposphere

“…With a share of around 70-80 %, the bulk of ammonia emissions is due to anthropogenic activity, namely the use of synthetic fertilizers and livestock manure management (Bouwman et al, 1997;Paulot et al, 2015). Major source regions of NH 3 are located in southeast China and northern India (Paulot et al, 2014;Van Damme et al, 2015).…”