42 research outputs found
Field measurements of methylglyoxal using proton transfer reaction time-of-flight mass spectrometry and comparison to the DNPHâHPLCâUV method
Methylglyoxal (MGLY) is an important atmospheric
α-dicarbonyl species for which photolysis acts as a significant source of
peroxy radicals, contributing to the oxidizing capacity of the atmosphere
and, as such, the formation of secondary pollutants such as organic aerosols
and ozone. However, despite its importance, only a few techniques exhibit
time resolutions and detection limits that are suitable for atmospheric
measurements.This study presents the first field measurements of MGLY by proton transfer reaction time-of-flight mass spectrometry (PTR-ToF-MS) performed during the
ChArMEx SOP2 field campaign. This campaign took place at a Mediterranean
site characterized by intense biogenic emissions and low levels of
anthropogenic trace gases. Concomitant measurements of MGLY were performed
using the 2,4-dinitrophenylhydrazine (DNPH) derivatization technique and
high performance liquid chromatography (HPLC) with UV detection. PTR-ToF-MS
and DNPHâHPLC measurements were compared to determine whether these
techniques can perform reliable measurements of MGLY.Ambient time series revealed levels of MGLY ranging from 28 to 365 pptv, with a
clear diurnal cycle due to elevated concentrations of primary biogenic
species during the daytime, and its oxidation led to large production rates of
MGLY. A scatter plot of the PTR-ToF-MS and DNPHâHPLC measurements indicates a
reasonable correlation (R2â=â0.48) but a slope significantly lower than
unity (0.58±0.05) and a significant intercept of 88.3±8.0 pptv. A careful investigation of the differences between the two
techniques suggests that this disagreement is not due to spectrometric
interferences from H3O+(H2O)3 or methyl ethyl ketone (or butanal) detected
at mâz 73.050 and mâz 73.065, respectively, which are close to the MGLY mâz of 73.029. The differences are more likely due to uncorrected sampling
artifacts such as overestimated collection efficiency or loss of MGLY into
the sampling line for the DNPHâHPLC technique or unknown isobaric
interfering compounds such as acrylic acid and propanediol for the
PTR-ToF-MS.Calculations of MGLY loss rates with respect to OH oxidation and direct
photolysis indicate similar contributions for these two loss pathways.</p
A "critical" climatic evaluation of last interglacial (MIS 5e) records from the Norwegian Sea
Sediment cores from the Norwegian Sea were studied to evaluate interglacial climate conditions of the marine isotope stage 5e (MIS 5e). Using planktic forminiferal assemblages as the core method, a detailed picture of the evolution of surface water conditions was derived. According to our age model, a step-like deglaciation of the Saalian ice sheets is noted between ca. 135 and 124.5 Kya, but the deglaciation shows little response with regard to surface ocean warming. From then on, the rapidly increasing abundance of subpolar forminifers, concomitant with decreasing iceberg indicators, provides evidence for the development of interglacial conditions sensu stricto (5e-ss), a period that lasted for about 9 Ky. As interpreted from the foraminiferal records, and supported by the other proxies, this interval of 5e-ss was in two parts: showing an early warm phase, but with a fresher, i.e., lower salinity, water mass, and a subsequent cooling phase that lasted until ca. 118.5 Kya. After this time, the climatic optimum with the most intense advection of Atlantic surface water masses occurred until ca. 116 Kya. A rapid transition with two notable climatic perturbations is observed subsequently during the glacial inception. Overall, the peak warmth of the last interglacial period occurred relatively late after deglaciation, and at no time did it reach the high warmth level of the early Holocene. This finding must be considered when using the last interglacial situation as an analogue model for enhanced meridional transfer of ocean heat to the Arctic, with the prospect of a future warmer climate
Sea level and climate changes during OIS 5e in the Western Mediterranean
Palaeontological, geomorphological and sedimentological data supported by isotopic dating on Oxygen
Isotopic Stage (OIS) 5e deposits from the Spanish Mediterranean coast, are interpreted with the aim of
reconstructing climatic instability in the Northern Hemisphere. Data point to marked climatic instability
during the Last Interglacial (OIS 5e), with a change in meteorological conditions and, consequently, in the
sedimentary environment. The oolitic facies generated during the first part of OIS 5e (ca. 135 kyr) shift into
reddish conglomeratic facies during the second part (ca. 117 kyr). Sea surface Temperature (SST) and salinity
are interpreted mainly on the basis of warm Senegalese fauna, which show chronological and spatial
differential distribution throughout the Western Mediterranean. Present hydrological and meteorological
conditions are used also as modern analogues to reconstruct climatic variability throughout the Last
Interglacial, and this variability is interpreted within the wider framework of the North Atlantic record. All
the available data indicate an increase in storminess induced by an increase in the influence of northwesterlies,
a slight drop of SST in the northern Western Mediterranean, and an important change in
meteorological conditions at the end of OIS 5e (117 kyr). These changes correlate well with the decrease in
summer insolation and with the climatic instability recorded in North Atlantic high latitudes
Magnetic stratigraphy at Sites 907 and 985 in the Norwegian-Greenland Sea and a revision of the Site 907 composite section
International audienc
Ice rafted debris in the Nordic Seas
A continuous 3.5 Myr IRD record was produced from Ocean Drilling Program (ODP) Site 907. A timescale based on magnetic polarity chrons, oxygen isotope stratigraphy (for the last 1Myr) and orbital tuning was developed. The record documents a stepwise inception of large-scale glacial cycles in the Nordic Seas region, the first being a marked expansion of the Greenland ice sheet at 3.3 Ma. A second step occurred at 2.74 Ma by an expansion of large scale ice sheets in the Northern Hemisphere. Ice sheet variability around the Nordic Seas was tightly coupled to global ice volume over the past 3.3 Myr. Between 3 and 1 Ma, most of the variance of the IRD signal is in the 41 kyr band, whereas the last 1 Myr is characterized by stronger 100 kyr variance. The Gamma Ray Porosity Evaluator (GRAPE) density record is closely linked with IRD variations and documents sub orbital variability resembling the late Quaternary Heinrich/Bond cycles
Revised depth scale, splice tie points and chron boundaries of ODP Hole 151-907A and Site 162-907
The magnetic polarity stratigraphy at Site 907 obtained from the shipboard pass-through magnetometer and from discrete samples is readily interpretable back to the onset of the Gilbert Chron (5.89 Ma). From this level to the base of the section at ~14 Ma, the interpretation is corroborated by silicoflagellate datums with predictable correlation to polarity chrons. The resulting magnetostratigraphic interpretation differs from those proposed in the Leg 151 (Hole 907A) and 162 (Holes 907B and 907C) Initial Reports volumes. An important hiatus in the 7-10 Ma interval at Site 907 caused sedimentation to slow or cease for ~2.7 m.y. We have revised the shipboard correlation among the three holes at Site 907, resulting in a new composite section splice and recalculation of composite depths.
For Site 985, magnetostratigraphic interpretation is possible down to ~150 meters below seafloor (mbsf) (C3An/C3Ar) at ~6 Ma. There are no useful biostratigraphic datums from Site 985 to support this interpretation; however, the interpretation is supported by the correlation of Sites 985 and 907 using natural gamma data from the shipboard multisensor track. Below ~150 mbsf at Site 985, drilling-related deformation at the onset of extended core barrel drilling precluded magnetostratigraphic interpretation