Atlas, E.

Bange, Hermann W.

Hepach, Helmke

Körtzinger, Arne

Quack, Birgit

Raimund, Stefan

Wittke, Franziska

English

OceanRep

Halocarbons in and above the tropical AtlanticH. Hepach1, B. Quack1, E. Atlas2, F. Wittke1, S. Raimund1 , H. Bange1, and A. Körtzinger1AbstractShort lived halogenated substances (halocarbons) occur naturally in the oceans. They contribute either direct or indirect to the overall halogen budget inthe atmosphere, thus also taking part in ozone depletion in both the stratosphere and troposphere. Tropical convection leads to enhanced verticaltransport of halocarbons in this area. Oceanic high productivity areas such as coasts and upwelling regions have been identified to be of highsignificance to the budget of brominated halocarbons. Bromoform (CHBr3) and dibromomethane (CH2Br2) generally represent the largest fractions ofnaturally occuring very short-lived gases that contribute to the atmospheric bromine content.Here, results of two cruises in the tropical Atlantic are presented. The first campaign from May and June 2010 investigated diurnal and regional variabilityof halogen emissions in the Mauretanian upwelling which is also exposed to strong coastal influences. The second cruise took place in June and July2011 with the equatorial upwelling as the main research area.1 Leibniz Institute of Marine Sciences (IFM-GEOMAR), Deparment of Marine Biogeochemistry, Kiel, Germany, e-mail: hhepach@ifm-geomar.de2 Rosenstiel School of Marine and Atmospheric Science, University of Miami, USADRIVE – Diurnal and RegIonal Variability of halogen EmissionsMSM18/3 – Halocarbon concentrations in the equatorial upwellingFigure 1: Cruise track and Sea SurfaceTemperatures during DRIVE, J. SchafstallFigure 2: CHBr3 and CH2Br2 concentrations in water and air duringDRIVE•Increasing regional gradient of CHBr3 and CH2Br2towards the coast with maxima and most diurnalvariabilities at station 5 (figure 2)•Station 5: closest to the coast, but not associated withthe lowest temperatures (figure 1) that often indicatestronger upwelling with possibly higher primaryproductionFigure 3: Air-sea fluxes of CHBr3 and CH2Br2 during DRIVE• This flux is not sufficient to explain the observedrapid elevations in atmospheric mixing ratios•To achieve an increase of 2 ppt in 1 h, a flux of200,000 pmol/(m²*h) would be neededFigure 4: Location of Banc d‘Arguin in relation tostation 5SOLAS Summer School 2011Figure 6: Preliminary data of CHBr3 concentrations in sea water during MSM18/3•The RV Maria S. Merian followed a cruisetrack from Cape Verde to the equator•Rather low temperatures were observedaround the equator (figure 5), possibilyassociated to oceanic upwelling•Sea water concentrations of CHBr3 of up to41 pmol/l could be observed (figure 6), but, inagreement to DRIVE, these do not necessarilycoincide with the lowest temperatures.Is the air-sea gas exchange the only source forhalocarbons in the air in this region?The ocean is generally a net source for bothcompounds with a maximum flux of 6800pmol/(m²*h) for CHBr3 at station 5 (figure 3)There must be an additional source forhalocarbons in the air in this region.Where could the possible source be?•Northern source region indicated by air mass backtrajectories Banc d‘Arguin? (figure 4)•Rich in seagrasses which have been identified ashalocarbon source•The RV Poseidon started at the Tropical Eastern North Atlantic Time-Series Observatory (TENATSO) and followed a cruise track to the coast offMauretania where coastal upwelling could be observed (figure 1).•Parallel sampling of air and sea surface water on a nearly hourly basis at six 24-hour stations (indicated by red dots) in different distances to the coastgave the unique opportunity to investigate diurnal variations in concentrations and air-sea fluxes of halocarbons.Figure 5: Projection of SSTs for July 8th 2011 for theequatorial Atlantic (provided by Mercator)Flux calculations and comparisons tobiological parameters will help further identifyhalocarbon sources there.

Halocarbons in and above the tropical Atlantic

Halocarbons in and above the tropical Atlantic

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