Natural marine bromoform emissions in the fully coupled ocean-atmosphere-model NorESM2
Oceanic bromoform (CHBr 3 ) is an important precursor of atmospheric bromine. Although highly relevant for the future halogen burden and ozone layer in the stratosphere, the global CHBr 3 production in the ocean and its emissions are still poorly constrained in observations and are mostly neglected...
| Main Authors: | , , , , |
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| Format: | Text |
| Language: | English |
| Published: |
2024
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| Subjects: | |
| Online Access: | https://doi.org/10.5194/esd-2024-3 https://esd.copernicus.org/preprints/esd-2024-3/ |
| Summary: | Oceanic bromoform (CHBr 3 ) is an important precursor of atmospheric bromine. Although highly relevant for the future halogen burden and ozone layer in the stratosphere, the global CHBr 3 production in the ocean and its emissions are still poorly constrained in observations and are mostly neglected in climate models. Here, we newly implement marine CHBr 3 in the state-of-the-art Norwegian Earth System Model (NorESM2) with fully coupled ocean-sea-ice-atmosphere biogeochemistry interactions. Our results are validated with oceanic and atmospheric observations from the HalOcAt (Halocarbons in the Ocean and Atmosphere) data base. The simulated mean oceanic concentrations (6.61±3.43pmolL -1 ) are in good agreement with observations in open ocean regions (5.02±4.50pmolL -1 ), while the mean atmospheric mixing ratios (0.76±0.39 ppt) are lower than observed but within the range of uncertainty (1.45±1.11 ppt). The NorESM2 ocean emissions of CHBr 3 (214 Gg yr -1 ) are in the range of or higher than previously published estimates from bottom-up approaches but lower than estimates from top-down approaches. Annual mean emissions are mostly positive (sea-to-air), driven by oceanic concentrations, sea surface temperature and wind speed, dependent on season and location. During low-productivity winter seasons, model results imply some oceanic regions in high latitudes as sinks of atmospheric CHBr 3 , because of its elevated atmospheric mixing ratios. We further demonstrate that key drivers for the oceanic and atmospheric CHBr 3 variability are spatially heterogeneous. In the tropical West Pacific, which is a hot spot for oceanic bromine delivery to the stratosphere, wind speed is the main driver for CHBr 3 emissions on annual basis. In the North Atlantic as well as in the Southern Ocean region the atmospheric and oceanic CHBr 3 variabilities are interacting during most of the seasons except for the winter months where sea surface temperature is the main driver. Our study provides improved process understanding of the ... |
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