ALBERT

Description: We investigated the size distribution, scattering and absorption properties of Amazonian aerosols and the optical thickness of the aerosol layer under the pristine background conditions typical of the wet season, as well as during the biomass-burning-influenced dry season. The measurements were made during two campaigns in 1999 as part of the European contribution to the Large-Scale Biosphere-Atmosphere Experiment in Amazonia (LBA-EUSTACH). In moving from the wet to the dry season, median particle numbers were observed to increase from values comparable to those of the remote marine boundary layer (~400 cm-3) to values more commonly associated with urban smog (~4000 cm-3), due to a massive injection of submicron smoke particles. Aerosol optical depths at 500 nm increased from 0.05 to 0.8 on average, reaching a value of 2 during the dry season. Scattering and absorption coefficients, measured at 550 nm, showed a concomitant increase from average values of 6.8 and 0.4 Mm-1 to values of 91 and 10 Mm-1, respectively, corresponding to an estimated decrease in single-scattering albedo from ca. 0.97 to 0.91. The roughly tenfold increase in many of the measured parameters attests to the dramatic effect that extensive seasonal biomass burning (deforestation, pasture cleaning) is having on the composition and properties of aerosols over Amazonia. The potential exists for these changes to impact on regional and global climate through changes to the extinction of solar radiation as well as the alteration of cloud properties.

Description: We present the results of airborne measurements of carbon monoxide (CO) and aerosol particle number concentration (CN) made during the Balanço Atmosférico Regional de Carbono na Amazônia (BARCA) program. The primary goal of BARCA is to address the question of basin-scale sources and sinks of CO2 and other atmospheric carbon species, a central issue of the Large-scale Biosphere-Atmosphere (LBA) program. The experiment consisted of two aircraft campaigns during November–December 2008 (BARCA-A) and May–June 2009 (BARCA-B), which covered the altitude range from the surface up to about 4500 m, and spanned most of the Amazon Basin. Based on meteorological analysis and measurements of the tracer, SF6, we found that airmasses over the Amazon Basin during the late dry season (BARCA-A, November 2008) originated predominantly from the Southern Hemisphere, while during the late wet season (BARCA-B, May 2009) low-level airmasses were dominated by northern-hemispheric inflow and mid-tropospheric airmasses were of mixed origin. In BARCA-A we found strong influence of biomass burning emissions on the composition of the atmosphere over much of the Amazon Basin, with CO enhancements up to 300 ppb and CN concentrations approaching 10 000 cm−3; the highest values were in the southern part of the Basin at altitudes of 1–3 km. The ΔCN/ΔCO ratios were diagnostic for biomass burning emissions, and were lower in aged than in fresh smoke. Fresh emissions indicated CO/CO2 and CN/CO emission ratios in good agreement with previous work, but our results also highlight the need to consider the residual smoldering combustion that takes place after the active flaming phase of deforestation fires. During the late wet season, in contrast, there was little evidence for a significant presence of biomass smoke. Low CN concentrations (300–500 cm−3) prevailed basinwide, and CO mixing ratios were enhanced by only ~10 ppb above the mixing line between Northern and Southern Hemisphere air. There was no detectable trend in CO with distance from the coast, but there was a small enhancement of CO in the boundary layer suggesting diffuse biogenic sources from photochemical degradation of biogenic volatile organic compounds or direct biological emission. Simulations of CO distributions during BARCA-A using a range of models yielded general agreement in spatial distribution and confirm the important contribution from biomass burning emissions, but the models evidence some systematic quantitative differences compared to observed CO concentrations. These mismatches appear to be related to problems with the accuracy of the global background fields, the role of vertical transport and biomass smoke injection height, the choice of model resolution, and reliability and temporal resolution of the emissions data base.

Description: We present simulations of atmospheric CO2 concentrations provided by two modeling systems, run at high spatial resolution: the Eulerian-based Weather Research Forecasting (WRF) model and the Lagrangian-based Stochastic Time-Inverted Lagrangian Transport (STILT) model, both of which are coupled to a diagnostic biospheric model, the Vegetation Photosynthesis and Respiration Model (VPRM). The consistency of the simulations is assessed with special attention paid to the details of horizontal as well as vertical transport and mixing of CO2 concentrations in the atmosphere. The dependence of model mismatch (Eulerian vs. Lagrangian) on models' spatial resolution is further investigated. A case study using airborne measurements during which two models showed large deviations from each other is analyzed in detail as an extreme case. Using aircraft observations and pulse release simulations, we identified differences in the representation of details in the interaction between turbulent mixing and advection through wind shear as the main cause of discrepancies between WRF and STILT transport at a spatial resolution such as 2 and 6 km. Based on observations and inter-model comparisons of atmospheric CO2 concentrations, we show that a refinement of the parameterization of turbulent velocity variance and Lagrangian time-scale in STILT is needed to achieve a better match between the Eulerian and the Lagrangian transport at such a high spatial resolution (e.g. 2 and 6 km). Nevertheless, the inter-model differences in simulated CO2 time series for a tall tower observatory at Ochsenkopf in Germany are about a factor of two smaller than the model-data mismatch and about a factor of three smaller than the mismatch between the current global model simulations and the data.

Description: The Amazon region, being a large source of methane (CH4), contributes significantly to the global annual CH4 budget. For the first time, a forward and inverse modelling framework on regional scale for the purpose of assessing the CH4 budget of the Amazon region is implemented. Here, we present forward simulations of CH4 as part of the forward and inverse modelling framework based on a modified version of the Weather Research and Forecasting model with chemistry that allows for passive tracer transport of CH4, carbon monoxide, and carbon dioxide (WRF-GHG), in combination with two different process-based bottom-up models of CH4 emissions from anaerobic microbial production in wetlands and additional datasets prescribing CH4 emissions from other sources such as biomass burning, termites, or other anthropogenic emissions. We compare WRF-GHG simulations on 10 km horizontal resolution to flask and continuous CH4 observations obtained during two airborne measurement campaigns within the Balanço Atmosférico Regional de Carbono na Amazônia (BARCA) project in November 2008 and May 2009. In addition, three different wetland inundation maps, prescribing the fraction of inundated area per grid cell, are evaluated. Our results indicate that the wetland inundation maps based on remote-sensing data represent the observations best except for the northern part of the Amazon basin and the Manaus area. WRF-GHG was able to represent the observed CH4 mixing ratios best at days with less convective activity. After adjusting wetland emissions to match the averaged observed mixing ratios of flights with little convective activity, the monthly CH4 budget for the Amazon basin obtained from four different simulations ranges from 1.5 to 4.8 Tg for November 2008 and from 1.3 to 5.5 Tg for May 2009. This corresponds to an average CH4 flux of 9–31 mg m−2 d−1 for November 2008 and 8–36 mg m−2 d−1 for May 2009.

Description: This paper describes the background, instrumentation, goals, and the regional influences on the HUMPPA-COPEC intensive field measurement campaign, conducted at the Boreal forest research station SMEAR II (Station for Measuring Ecosystem-Atmosphere Relation) in Hyytiälä, Finland from 12 July–12 August 2010. The prevailing meteorological conditions during the campaign are examined and contrasted with those of the past six years. Back trajectory analyses show that meteorological conditions at the site in 2010 were characterized by a higher proportion of southerly flow than in the other years studied. As a result the summer of 2010 was anomalously warm and high in ozone making the campaign relevant for the analysis of possible future climates. A comprehensive land use analysis, provided on both 5 and 50 km scales, shows that the main vegetation types surrounding the site on both the regional and local scales are: coniferous forest (Scots pine and/or Norway spruce); mixed forest (Birch and conifers); and woodland scrub (e.g. Willows, Aspen); indicating that the campaign results can be taken as representative of the Boreal forest ecosystem. In addition to the influence of biogenic emissions, the measurement site was occasionally impacted by sources other than vegetation. Specific tracers have been used here to identify the time periods when such sources have impacted the site namely: biomass burning (acetonitrile and CO), urban anthropogenic pollution (pentane and SO2) and the nearby Korkeakoski sawmill (enantiomeric ratio of chiral monoterpenes). None of these sources dominated the study period, allowing the Boreal forest summertime emissions to be assessed and contrasted with various other source signatures.

Description: This paper describes the background, instrumentation, goals, and the regional influences on the HUMPPA-COPEC intensive field measurement campaign, conducted at the Boreal forest research station SMEAR II (Station for Measuring Ecosystem-Atmosphere Relation) in Hyytiälä, Finland from 12 July–12 August 2010. The prevailing meteorological conditions during the campaign are examined and contrasted with those of the past six years. Back trajectory analyses show that meteorological conditions at the site were characterized by a higher proportion of southerly flow. As a result the summer of 2010 was anomalously warm and high in ozone making the campaign relevant for the analysis of possible future climates. A comprehensive land use analysis, provided on both 5 and 50 km scales, shows that the main vegetation types surrounding the site on both the regional and local scales are: coniferous forest (Scots pine and/or Norway spruce); mixed forest (Birch and conifers); and woodland scrub (e.g. Willows, Aspen); indicating that the campaign results can be taken as representative of the Boreal forest ecosystem. In addition to the influence of biogenic emissions, the measurement site was occasionally impacted by sources other than vegetation. Specific tracers have been used here to identify the time periods when such sources have impacted the site namely: biomass burning (acetonitrile and CO), urban anthropogenic pollution (pentane and SO2) and the nearby Korkeakoski sawmill (enantiomeric ratio of chiral monoterpenes). None of these sources dominated the study period, allowing the Boreal forest summertime emissions to be assessed and contrasted with various other source signatures.

Description: To date, North Sea tidal flat sediments have been intensively studied down to a depth of 5 m below sea floor (mbsf). However, little is known about the biogeochemistry, microbial abundance, and activity of sulfate reducers as well of methanogens in deeper layers. For this study, we hypothesized that the imprint of the paleo-environment is reflected in current microbiogeochemical processes. Therefore, 20 m-long cores were retrieved from the tidal-flat area of Spiekeroog Island, NW Germany. Two drill sites were selected with a close distance of only 900 meters, but where sedimentation occurred under different environmental conditions: first, a paleo-channel filled with Holocene sediments and second, a mainly Pleistocene sedimentary succession. In general, the numbers of bacterial 16S rRNA genes are one to two orders of magnitude higher than those of Archaea. The abundances of key genes for sulfate reduction and methanogenesis (dsrA and mcrA) correspond to the sulfate and methane profiles. A co-variance of these key genes at sulfate-methane interfaces and enhanced potential AOM rates suggest that anaerobic oxidation of methane may occur in these layers. Microbial and biogeochemical profiles are vertically stretched relative to 5 m-deep cores from shallower sediments in the same study area. Compared to the deep marine environment, the profiles are transitional between the shallow subsurface and the marine deep biosphere. Our interdisciplinary analysis shows that the microbial abundances and metabolic rates are elevated in the Holocene compared to Pleistocene sediments. However, this is mainly due to present environmental conditions such as pore water flow and organic matter availability. The paleo-environmental imprint is still visible but superimposed by these processes.

Description: During the GWADASEIS cruise (Lesser Antilles volcanic arc, February–March 2009) a very high resolution (VHR) seismic-reflection survey was performed in order to constrain Late Quaternary to Present faulting. The profiles we obtained evidence frequent "ponding" of reworked sediments in the deepest areas, similar to the deposition of Mediterranean "homogenites". These bodies are acoustically transparent (few ms t.w.t. thick) and are often deposited on the hanging walls of dominantly normal faults, at the base of scarps. Their thickness appears sufficient to compensate (i.e. bury) co-seismic scarps between successive earthquakes, resulting in a flat and horizontal sea floor through time. In a selected area (offshore Montserrat and Nevis islands), piston coring (4 to 7 m long) was dedicated to a sedimentological analysis of the most recent of these particular layers. It corresponds to non-stratified homogenous calcareous silty sand (reworked calcareous plankton and minor volcanoclastics). This layer can be up to 2 m thick, and overlies fine-grained hemipelagites. The upper centimeters of the latter represent the normal RedOx water/sediment interface. 210Pb and 137Cs activities lack in the massive sands, while a normal profile of unsupported 210Pb decrease is observed in the hemipelagite below, together with a 137Cs peak corresponding to the Atmospheric Nuclear Experiments (1962). The RedOx level was thus capped by a recent instantaneous major sedimentary event considered as post-1970 AD; candidate seismic events to explain this sedimentary deposits are either the 16 March 1985 earthquake or the 8 October 1974 one (Mw = 6.3 and Mw = 7.4, respectively). This leads to consider that the syntectonic sedimentation in this area is not continuous but results from accumulation of thick homogenites deposited after the earthquakes (as observed in the following weeks after Haiti January 2010 event, McHugh et al., 2011). The existence of such deposits suggests that, in the area of study, vertical throw likely results from cumulated effects of separated earthquakes rather than from aseismic creep. Examination of VHR profiles shows that all major co-seismic offsets are recorded in the fault growth sequence and that co-seismic offsets can be precisely estimated. By using a sedimentation rate deduced from 210Pb decrease curve (0.5 mm yr−1) and taking into account minor reworking events detected in cores, we show that the Redonda system may have been responsible for five 〉M6 events during the last 34 000 yr. The approach presented in this work differs from fault activity analyses using displaced sets of isochronous surfaces and postulating co-seismic offsets. Combining VHR seismic imagery and coring we can decipher co-seismic vs. slow continuous displacement, and thus actually estimate the amplitude and the time distribution of major co-seismic offsets.

Description: In the deep part of the Sea of Marmara (Turkey), the sedimentation developing upon the North Anatolian Fault is strongly influenced by the associated seismic activity. Specific layers (homogenites-turbidites), representing individual sedimentary events, have been characterized along three giant piston cores retrieved from Çinarcik and Central (or Orta) basins. Analyzed sediments represent the last 12 to 17 kyr BP. For a 2 kyr-lasting interval, 11 events could be precisely correlated on both sides of the Central Basin's southern scarp. For each of them, based on the specific depositional process, the thickness difference between the two sites was considered as a direct estimation of the vertical component of a coeval co-seismic offset. The homogenite (upper) term accounts for the major part of the thickness difference. The 6 most significant values range from 36 cm to 144 cm and are likely representing dominantly normal throws, with estimated paleomagnitudes (Mw) ranging from 5.9 to 6.6.

Description: The main source of information on future climate conditions are global circulation models (GCMs). While the various GCMs agree on an increase of surface temperature, the predictions for precipitation exhibit high spread among the models, especially in shorter-than-daily temporal resolution. This paper presents a method to predict regional distributions of the hourly rainfall depth based on daily mean sea level pressure and temperature data. It is an indirect downscaling method avoiding uncertain precipitation data from the GCM. It is based on a fuzzy logic classification of atmospheric circulation patterns (CPs) that is further subdivided by means of the average daily temperature. The observed empirical distributions at 30 rain gauges to each CP-temperature class are assumed as constant and used for projections of the hourly precipitation sums in the future. The method was applied to the CP-temperature sequence derived from the 20th-century run and the scenario A1B run of ECHAM5. For the study region in southwestern Germany ECHAM5 predicts that the summers will become progressively drier. Nevertheless, the frequency of the highest hourly precipitation sums will increase. According to the predictions, estival water stress and the risk of extreme hourly precipitation will both increase simultaneously during the next decades. However, the results are yet to be confirmed by further mbox{investigation} based on other GCMs.