ALBERT

Description: Halocarbons, halogenated short-chained hydrocarbons, are produced naturally in the oceans by biological and chemical processes. They are emitted from surface seawater into the atmosphere, where they take part in numerous chemical processes such as ozone destruction and the oxidation of mercury and dimethyl sulfide. Here we present oceanic and atmospheric halocarbon data for the Peruvian upwelling obtained during the M91 cruise onboard the research vessel Meteor in December 2012. Surface waters during the cruise were characterized by moderate concentrations of bromoform (CHBr3) and dibromomethane (CH2Br2) correlating with diatom biomass derived from marker pigment concentrations, which suggests this phytoplankton group as likely source. Concentrations measured for the iodinated compounds methyl iodide (CH3I) of up to 35.4 pmol L-1, chloroiodomethane (CH2ClI) of up to 58.1 pmol L-1 and diiodomethane (CH2I2) of up to 32.4 pmol L-1 in water samples were much higher than previously reported for the tropical Atlantic upwelling systems. Iodocarbons also correlated with the diatom biomass and even more significantly with dissolved organic matter (DOM) components measured in the surface water. Our results suggest a biological source of these compounds as significant driving factor for the observed large iodocarbon concentrations. Elevated atmospheric mixing ratios of CH3I (up to 3.2 ppt), CH2ClI (up to 2.5 ppt) and CH2I2 (3.3 ppt) above the upwelling were correlated with seawater concentrations and high sea-to-air fluxes. The enhanced iodocarbon production in the Peruvian upwelling contributed significantly to tropospheric iodine levels.

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 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 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. 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 for CHBr3, 10 ± 12 pmol/m**3/h for CH2Br2, 21 ± 24 pmol/m**3/h for CH3I and 384 ± 318 pmol/m**3/h for CH2I2 determined from 13 depth profiles.

Description: Absorption coefficients (abs) and optical density (OD) by total particles, phytoplankton and non-algal particles (NAP) were measured with standard deviation (sd) estimated on water samples collected from underway AC-S flow-through system outflow and CTD. Measurements were performed using QFT-ICAM (Röttgers et al., 2016) as described in Liu et al. (2018) and Liu et al. (2019). 1. About sampling: a) underway samples were collected from unfiltered AC-S outflow (depth: 11m); CTD samples with 5-6 depths were collected on upcast. b) vacuum pressure for filtration: maximum 200 hPa c) samples were measured fresh (not preserved). d) blank filters were collected by soaking them in 0.2um filtered seawater. e) replicates were not collected. 2. About measurements: a) Instrument: light source: UV-VIS lamp (CF-1000- HC lamp, Illumination Technology, USA); absorption meter: Quantitative Filter Technique - Integrating Cavity Absorption Meter (QFT-ICAM) (Röttgers et al., 2016) with 80 mm- diameter integrating sphere; detector: photodiode array spectrometer (AVASPEC-ULS2048-RS-USB2, Avantes, the Netherlands). b) wavelength range of scan and resolution: 313.5-875.7 nm, 0.3 nm. c) slit band width: 2 nm. d) sample filters were bleached with 10% sodium hypochlorite (NaClO) solution for the OD measurement of NAP. e) samples were measured for four times and bleached samples were measured twice. f) dark current and blank filters were measured and subtracted. 3. About data analysis: a) interpolated wavelength range and resolution: 320-844 nm, 2nm. b) wavelength range for fluorescence correction: 670:800 nm. c) diameter of sample patch on GF/F filter: 2.133 cm. d) pathlength amplification factor (beta correction factor): 4.06 (Röttgers et al., 2016). e) no scattering correction for total particle absorption is applied; NAP absorption was adjusted with an offset in the range of 710-750 nm so that the median value of NAP absorption equals the median value of in total particle absorption in this spectral range. This adjustment is based on the assumption that phytoplankton pigments do not absorb in near-infrared (Neeley et al., 2018). This adjustment was not applied to NAP OD data. f) NAP absorption data from underway samples collected during 2016-06-17T21:20, 2016-06-18T00:26, 2016-06-18T03:19, 2016-06-18T06:38, 2016-06-15T12:12, and 2016-06-15T15:09 were missing. To calculate the corresponding phytoplankton absorption, the missing NAP data were taken the same as the ones from 2016-06-17T18:13, 2016-06-18T18:09, 2016-06-18T18:09, 2016-06-18T18:09, 2016-06-15T09:15, and 2016-06-15T09:15, respectively. However, this was not applied to NAP OD data.

Description: Absorption coefficients (abs) and optical density (OD) by total particles, phytoplankton and non-algal particles (NAP) were measured with standard deviation (sd) estimated on water samples collected from underway AC-S flow-through system outflow and CTD. Measurements were performed using QFT-ICAM (Röttgers et al., 2016) as described in Liu et al. (2018) and Liu et al. (2019). 1. About sampling: a) underway samples were collected from unfiltered AC-S outflow (depth: 11m); CTD samples with 5-6 depths were collected on upcast. b) vacuum pressure for filtration: maximum 200 hPa c) samples were measured fresh (not preserved). d) blank filters were collected by soaking them in 0.2um filtered seawater. e) replicates were not collected. 2. About measurements: a) Instrument: light source: UV-VIS lamp (CF-1000- HC lamp, Illumination Technology, USA); absorption meter: Quantitative Filter Technique - Integrating Cavity Absorption Meter (QFT-ICAM) (Röttgers et al., 2016) with 80 mm- diameter integrating sphere; detector: photodiode array spectrometer (AVASPEC-ULS2048-RS-USB2, Avantes, the Netherlands). b) wavelength range of scan and resolution: 313.5-875.7 nm, 0.3 nm. c) slit band width: 2 nm. d) sample filters were bleached with 10% sodium hypochlorite (NaClO) solution for the OD measurement of NAP. e) samples were measured for four times and bleached samples were measured twice. f) dark current and blank filters were measured and subtracted. 3. About data analysis: a) interpolated wavelength range and resolution: 320-844 nm, 2nm. b) wavelength range for fluorescence correction: 670:800 nm. c) diameter of sample patch on GF/F filter: 2.133 cm. d) pathlength amplification factor (beta correction factor): 4.06 (Röttgers et al., 2016). e) no scattering correction for total particle absorption is applied; NAP absorption was adjusted with an offset in the range of 710-750 nm so that the median value of NAP absorption equals the median value of in total particle absorption in this spectral range. This adjustment is based on the assumption that phytoplankton pigments do not absorb in near-infrared (Neeley et al., 2018). This adjustment was not applied to NAP OD data. f) NAP absorption data from underway samples collected during 2016-06-17T21:20, 2016-06-18T00:26, 2016-06-18T03:19, 2016-06-18T06:38, 2016-06-15T12:12, and 2016-06-15T15:09 were missing. To calculate the corresponding phytoplankton absorption, the missing NAP data were taken the same as the ones from 2016-06-17T18:13, 2016-06-18T18:09, 2016-06-18T18:09, 2016-06-18T18:09, 2016-06-15T09:15, and 2016-06-15T09:15, respectively. However, this was not applied to NAP OD data.