[1] Surface seawater and atmospheric concentrations of methyl iodide, chloroiodomethane, bromoform, dichlorobromomethane, and chlorodibromethane were measured during three open ocean cruises in the Atlantic and Southern oceans. The measurements spanned a longitudinal range of 115°, between 50°N and 65°S. The saturation anomalies and the instantaneous air-sea fluxes of the gases during one of these cruises (ANT XVIII/1) are presented and discussed. Methyl iodide and chloroiodomethane were highly supersaturated (>1000%) throughout the temperate and tropical regions, with calculated mean fluxes of 15 and 5.5 nmol m À2 d À1 , respectively. The oceanic emissions of the brominated compounds were less substantial, and a significant area of the temperate Atlantic Ocean was found to be a sink for bromoform. Correlation analyses have been used to investigate possible controls on the concentrations of these gases. In particular, the relationship of CH 3 I with sea surface temperature and light is discussed, with the tentative conclusion that this compound may be formed abiotically.
Alkyl nitrates are a significant component of the "odd nitrogen" reservoir and play an important role in regulating tropospheric ozone levels in remote marine regions. Measurements of methyl and ethyl nitrate in seawater and air samples along two Atlantic Ocean transects provide the first direct evidence for an oceanic source of these compounds. Equatorial surface waters were highly supersaturated (up to 800%) in both species, with the waters in the temperate regions generally being closer to equilibrium. A simple box model calculation suggests that the equatorial source could be a major component of the local atmospheric alkyl nitrate budget.
[1] Sea-to-air emissions of bromocarbon gases are known to play an important role in atmospheric ozone depletion. In this study, seawater concentrations of bromoform (CHBr 3 ) and dibromomethane (CH 2 Br 2 ) were measured regularly between
A recent study of coupled atmospheric carbon dioxide and the biosphere (Cox et al., 2000, Nature,408, 184–187) found alarming sensitivity of next‐century atmospheric pCO2 (and hence planetary temperature) to uncertainties in terrestrial processes. Here we investigate whether there is similar sensitivity associated with uncertainties in the behaviour of the ocean carbon cycle. We investigate this important question using three models of the ocean carbon cycle of varying complexity: (1) a new three‐box oceanic carbon cycle model; (2) the HILDA multibox model with high vertical resolution at low latitudes; (3) the Hadley Centre ocean general circulation model (HadOCC). These models were used in combination to assess the quantitative significance (to year 2100 pCO2) of potential changes to the ocean stimulated by global warming and other anthropogenic activities over the period 2000–2100. It was found that an increase in sea surface temperature and a decrease in the mixing rate due to stratification give rise to the greatest relative changes in pCO2, both being positive feedbacks. We failed to find any comparable large sensitivity due to the ocean.
study of coupled atmospheric carbon dioxide and the biosphere (Cox et al., 2000, Nature, 408, 184-187) found alarming sensitivity of next-century atmospheric pCO 2 (and hence planetary temperature) to uncertainties in terrestrial processes. Here we investigate whether there is similar sensitivity associated with uncertainties in the behaviour of the ocean carbon cycle. We investigate this important question using three models of the ocean carbon cycle of varying complexity: (1) a new three-box oceanic carbon cycle model; (2) the HILDA multibox model with high vertical resolution at low latitudes; (3) the Hadley Centre ocean general circulation model (HadOCC). These models were used in combination to assess the quantitative significance (to year 2100 pCO 2 ) of potential changes to the ocean stimulated by global warming and other anthropogenic activities over the period 2000-2100. It was found that an increase in sea surface temperature and a decrease in the mixing rate due to stratification give rise to the greatest relative changes in pCO 2 , both being positive feedbacks. We failed to find any comparable large sensitivity due to the ocean.
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