Martin K. Vollmer

Shrubland fluxes of methyl bromide and methyl chloride

Flux measurements in coastal sage scrub, chamise chaparral, and creosote bush scrub environments show that methyl bromide (CH3Br) and methyl chloride (CH3Cl), compounds that are involved in stratospheric ozone depletion, are both produced and consumed by southern California shrubland ecosystems. CH3Br and CH3Cl are produced in association with a variety of plants and are consumed by the soils, although there is a large variability in the fluxes, depending on predominant vegetation and environmental conditions. At sites with a net uptake of both compounds the fluxes of CH3Cl and CH3Br show a strong correlation, with a molar ratio of roughly 40:1, pointing to a similar mechanism of consumption. In contrast, the net production rates of these compounds show no apparent correlation with each other. The average observed net CH3Br uptake rates are an order of magnitude smaller than the previously reported average soil consumption rates assigned to shrublands. Extrapolations from our field measurements suggest that shrublands globally have a maximum net consumption of <1 Gg yr−1 for CH3Br and <20 Gg yr−1 for CH3Cl and may, in fact, be net sources for these compounds. Consequently, the measured net fluxes from shrubland ecosystems can account for part of the present imbalance in the CH3Br budget by adding a new source term and potentially reducing the soil sink term. These results also suggest that while shrubland soil consumption of CH3Cl may be small, soils in general may be a globally significant sink for CH3Cl.

Stratospheric CO2 isotopic anomalies and SF6 and CFC Tracer Concentrations in the Arctic Polar Vortex

Isotopic measurements (δ17O and δ18O) of CO2 along with concentration measurements of SF6, CCl3F (CFC-11), CCl2F2 (CFC-12) and CCl2FCClF2 (CFC-113) in stratospheric samples collected within the Arctic polar vortex are reported. These are the first simultaneous measurements of the concentration of fluorinated compounds and the complete oxygen isotopic composition of CO2 in the middle atmosphere. A mass-independent anomaly in the oxygen isotopic composition of CO2 is observed that arises from isotopic exchange with stratospheric O(¹D) derived from O3 photolysis. The data exhibit a strong anti-correlation between the Δ17O (the degree of the mass-independent anomaly) and molecular tracer concentrations. The potential ability of this isotopic proxy to trace mesospheric and stratospheric transport is discussed.

Deep-water renewal in Lake Issyk-Kul

[1] The deep-water renewal rates of Lake Issyk-Kul are studied using the time-dependent anthropogenically produced tracers sulfur hexafluoride (SF 6 ), chlorofluorocarbons (CFCs) and tritium-helium-3. SF 6 and the CFCs are used to calibrate a mixing model from which the vertical age distribution is calculated and found to be comparable to the SF 6 apparent ages. Based on this model, the mean age of the water below 100 m depth is 6.1 yrs. The mean oxygen consumption rate for the same depth range is 6.4 μmol kg -1 yr -1 and the mean remineralization rates for nitrate, phosphate and silicate are 0.53, 0.003 and 0.67 μmol kg -1 yr -1 , respectively.