ALBERT

Description: Emissions of air pollutants and their precursors determine regional air quality and can alter climate. Climate change can perturb the long-range transport, chemical processing, and local meteorology that influence air pollution. We review the implications of projected changes in methane (CH4), ozone precursors (O3), and aerosols for climate (expressed in terms of the radiative forcing metric or changes in global surface temperature) and hemispheric-to-continental scale air quality. Reducing the O3 precursor CH4 would slow near-term warming by decreasing both CH4 and tropospheric O3. Uncertainty remains as to the net climate forcing from anthropogenic nitrogen oxide (NOx) emissions, which increase tropospheric O3 (warming) but also increase aerosols and decrease CH4 (both cooling). Anthropogenic emissions of carbon monoxide (CO) and non-CH4 volatile organic compounds (NMVOC) warm by increasing both O3 and CH4. Radiative impacts from secondary organic aerosols (SOA) are poorly understood. Black carbon emission controls, by reducing the absorption of sunlight in the atmosphere and on snow and ice, have the potential to slow near-term warming, but uncertainties in coincident emissions of reflective (cooling) aerosols and poorly constrained cloud indirect effects confound robust estimates of net climate impacts. Reducing sulfate and nitrate aerosols would improve air quality and lessen interference with the hydrologic cycle, but lead to warming. A holistic and balanced view is thus needed to assess how air pollution controls influence climate; a first step towards this goal involves estimating net climate impacts from individual emission sectors. Modeling and observational analyses suggest a warming climate degrades air quality (increasing surface O3 and particulate matter) in many populated regions, including during pollution episodes. Prior Intergovernmental Panel on Climate Change (IPCC) scenarios (SRES) allowed unconstrained growth, whereas the Representative Concentration Pathway (RCP) scenarios assume uniformly an aggressive reduction, of air pollutant emissions. New estimates from the current generation of chemistry-climate models with RCP emissions thus project improved air quality over the next century relative to those using the IPCC SRES scenarios. These two sets of projections likely bracket possible futures. We find that uncertainty in emission-driven changes in air quality is generally greater than uncertainty in climate-driven changes. Confidence in air quality projections is limited by the reliability of anthropogenic emission trajectories and the uncertainties in regional climate responses, feedbacks with the terrestrial biosphere, and oxidation pathways affecting O3 and SOA.

Description: The northwest trending walls of the Pito Deep Rift (PDR), a tectonic window in the southeast Pacific, expose in situ oceanic crust generated ?3 Ma at the superfast spreading southern East Pacific Rise (SEPR). Whole rock analyses were performed on over 200 samples of dikes and lavas recovered from two ~8 km**2 study areas. Most of the PDR samples are incompatible-element-depleted normal mid-ocean ridge basalts (NMORB; (La/Sm)N 〈 1.0) that show typical tholeiitic fractionation trends. Correlated variations in Pb isotope ratios, rare earth element patterns, and ratios of incompatible elements (e.g., (Ce/Yb)N) are best explained by mixing curves between two enriched and one depleted mantle sources. Pb isotope compositions of most PDR NMORB are offset from SEPR data toward higher values of 207Pb/204Pb, suggesting that an enriched component of the mantle was present in this region in the past ?3 Ma but is not evident today. Overall, the PDR crust is highly variable in composition over long and short spatial scales, demonstrating that chemically distinct lavas and dikes can be emplaced within the same segment over short timescales. However, the limited spatial distribution of high 206Pb/204Pb samples and the occurrence of relatively homogeneous MgO compositions (ranging 〈2.5 wt %) within a few of the individual dive transects (over distances of ~1 km) suggests that the mantle source composition evolved and magmatic temperatures persisted over timescales of tens of thousands of years. The high degree of chemical variability between pairs of adjacent dikes is interpreted as evidence for along-axis transport of magma from chemically distinct portions of the melt lens. Our findings suggest that lateral dike propagation occurs to a significant degree at superfast spreading centers.

Description: Records of long-term sediment deposition in the Caribbean Sea were recovered during Ocean Drilling Program Leg 165. Samples from the Cayman Rise (Site 998), the Colombian Basin (Site 999), and the Hess Escarpment (Site 1001) were analyzed for calcium carbonate (CaCO3) by coulometry and for selected major and trace elements by X-ray fluorescence and inductively coupled plasma-emission spectrometry. These data were used to quantify in the bulk sediment the absolute concentrations of CaCO3, terrigenous matter, and dispersed ash (as opposed to discrete ash layers). The weight percent of terrigenous matter was computed using a Cr-based normative calculation, and dispersed ash content was calculated by difference; the assumption of a three component system (CaCO3, ash, and terrigenous matter) is justified by and consistent with petrographic analysis. Sites 998 and 999 broadly exhibit the same pattern of terrigenous accumulation. Both show a general decrease in terrigenous accumulation rates during the Oligocene and early Miocene, except for a sharp increase at Site 998 during the early Oligocene (30-40 Ma) and significant increases in the late Miocene and late Pliocene/early Pleistocene. The same pattern in terrigenous accumulation is recorded at Sites 925 and 929 in the Ceara Rise (Atlantic Ocean), which receives input from an Amazon River source, demonstrating that Sites 925, 929, 998, and 999 collectively provide a circum-Andean record of tectonic uplift, with the Leg 165 sites responding to inputs from the Magdelena River system. Both Sites 998 and 999 appear to be responding to South and Central American inputs, particularly after the middle Miocene; however, the variation in the terrigenous, carbonate, and dispersed ash at Site 998 point to an erosional event during the Oligocene that is apparently unique to this site's location. Dispersed ash commonly accounts for 15-20 wt% of the bulk sediment, and in some cases up to 45 wt%. The accumulation of dispersed ash typically leads the accumulation of discrete layers by 2-10 m.y. These changes in sediment composition could signify (1) the distance from the source of volcanism, (2) periods of small volume volcanic activity preceding the large eruptions, or (3) the transportation to the deep sea of terrestrially deposited ash preceding the large eruptions.

Description: This dataset of radio-echo sounding internal reflecting horizons (IRH) which were traced across the radar surveys conducted in the 2019/20 Antarctic summer season at Little Come C, in the Dome C region of the East Antarctic Plateau. The data set is associated to publication: Chung, A., et al. (2023). The data were collected during a radar survey conducted in the Antarctic field seasons of 2019-20 using the Little Dome C - Very High Frequency (LDC-VHF) multichannel coherent radar depth sounder developed through a collaboration of The University of Alabama (UA), the University of Copenhagen (CPH) and the Alfred Wegener Institute (AWI). The survey covered Patches A and B of Little Dome C (Lilien et al., 2021), in order to select the exact drill site for the Beyond EPICA Oldest Ice drilling project. The datasets consists of 12 transects systematically covering Patches A and B with parallel lines, over an area of approximately 5×8 km^2. The dataset contains 19 IRHs, the basal unit horizon and the ice-bed interface which were manually traced by Ailsa Chung, using the seismic environment of the Echos software from Paradigm Geophysical. A single file for each IRH is provided in a text file, tab separated format with both depth and two-way travel time. The conversion to depth done using c = 0.1685 m/μs and firn correction of 10 m. The IRHs are provided at approximately 3.5 m spacial resolution.

Description: This dataset of radio-echo sounding internal reflecting horizons (IRH) which were traced across the radar surveys conducted in the 2019/20 Antarctic summer season at Little Come C, in the Dome C region of the East Antarctic Plateau. The data set is associated to publication: Chung, A., et al. (2023). The data were collected during a radar survey conducted in the Antarctic field seasons of 2019-20 using the Little Dome C - Very High Frequency (LDC-VHF) multichannel coherent radar depth sounder developed through a collaboration of The University of Alabama (UA), the University of Copenhagen (CPH) and the Alfred Wegener Institute (AWI). The survey covered Patches A and B of Little Dome C (Lilien et al., 2021), in order to select the exact drill site for the Beyond EPICA Oldest Ice drilling project. The datasets consists of 12 transects systematically covering Patches A and B with parallel lines, over an area of approximately 5×8 km^2. The dataset contains 19 IRHs, the basal unit horizon and the ice-bed interface which were manually traced by Ailsa Chung, using the seismic environment of the Echos software from Paradigm Geophysical. A single file for each IRH is provided in a text file, tab separated format with both depth and two-way travel time. The conversion to depth done using c = 0.1685 m/μs and firn correction of 10 m. The IRHs are provided at approximately 3.5 m spacial resolution.