Description: Halocarbons from oceanic sources contribute to halogens in the troposphere, and can be transported into the stratosphere where they take part in ozone depletion. This paper presents distribution and sources in the equatorial Atlantic from June and July 2011 of the four compounds bromoform (CHBr3), dibromomethane (CH2Br2), methyl iodide (CH3I) and diiodomethane (CH2I2). Enhanced biological production during the Atlantic Cold Tongue (ACT) season, indicated by phytoplankton pigment concentrations, led to elevated concentrations of CHBr3 of up to 44.7 and up to 9.2 pmol L−1 for CH2Br2 in surface water, which is comparable to other tropical upwelling systems. While both compounds correlated very well with each other in the surface water, CH2Br2 was often more elevated in greater depth than CHBr3, which showed maxima in the vicinity of the deep chlorophyll maximum. The deeper maximum of CH2Br2 indicates an additional source in comparison to CHBr3 or a slower degradation of CH2Br2. Concentrations of CH3I of up to 12.8 pmol L−1 in the surface water were measured. In contrary to expectations of a predominantly photochemical source in the tropical ocean, its distribution was mostly in agreement with biological parameters, indicating a biological source. CH2I2 was very low in the near surface water with maximum concentrations of only 3.7 pmol L−1. CH2I2 showed distinct maxima in deeper waters similar to CH2Br2. For the first time, diapycnal fluxes of the four halocarbons from the upper thermocline into and out of the mixed layer were determined. These fluxes were low in comparison to the halocarbon sea-to-air fluxes. This indicates that despite the observed maximum concentrations at depth, production in the surface mixed layer is the main oceanic source for all four compounds and one of the main driving factors of their emissions into the atmosphere in the ACT-region. The calculated production rates of the compounds in the mixed layer are 34 ± 65 pmol m−3 h−1 for CHBr3, 10 ± 12 pmol m−3 h−1 for CH2Br2, 21 ± 24 pmol m−3 h−1 for CH3I and 384 ± 318 pmol m−3 h−1 for CH2I2 determined from 13 depth profiles.

Description: Halogens are highly efficient at destroying ozone in the stratosphere, and rising concentrations from human activities has led to depletion of global stratospheric ozone over the last three decades, and formation of the Antarctic “ozone hole”. It is also known that ozone depleting substances (ODSs) enter the stratosphere principally in the tropics, where ascending warm air carries them aloft. The EU-project SHIVA (Stratospheric Ozone: Halogen Impacts in a Varying Atmosphere) aims to reduce uncertainties in the amount of halogen-containing ODSs reaching the stratosphere, and the resulting ozone depletion, in a climate that is changing now, and which will change in the future. During the SHIVA field campaign on board RV Sonne in the South China Sea and Sulu Sea in November 2011, we investigated the potential of phytoplankton being a source for halocarbons emissions in detail by comparing collocated field samples. Phytoplankton parameters such as pigment concentration, functional group type, and PSII efficiency were undergoing a detailed analysis to investigate the relationship between phytoplankton and different halocarbon species. Significant (p 〈 0.05) relationships were observed between the cyanobacterial marker pigment zeaxanthin, the group of cyanobacteria without Prochlorococcus and methyl iodide (CH3I). In the vertical profiles, high concentration of bromoform was found to correspond to maximum chl a concentration (indicator of total phytoplankton biomass) and maximum 19-hexanoyl-fucoxanthin (the marker pigments for haptophytes) layers observed in depth between 20 to 60 m. These findings are based on statistical analysis based on Kendall’s rank correlations which examine the relationship between halocarbons, phytoplankton groups’ marker pigments and total chl a concentration. Also the relationship of phytoplankton groups and pigments to water temperature, salinity and surface winds only showed for salinity an inverse correlation to total chl-a and especially to cyanobacteria, but a bit weaker also to the other phytoplankton groups.