Ullah Ezat

Assessing the actual size distribution of atmospheric aerosols collected with a cascade impactor

Abstract A set of elemental mass-particle size distributions is obtained from a low volume cascade impactor whose characteristics are discussed. The data processing used [Puttocks data inversion fitting technique; Puttock, J. S. (1981) Atmos. Envir. 15, 1709], shows that bounce-off can severely affect the interpretation of data when the ambient aerosol presents a coarse mode of dust particles ( D > 2 μ m). This study proposes an improvement of the fitting method, for correcting experimental mass-particle size distributions for these particle bouncing effects when usual preventive procedures cannot be applied. The bounce-off contribution to the final filter of the impactor could be estimated by a microscopic examination and compared to the one predicted by the method developed in this work.

Geomagnetic-assisted stratigraphy and sea surface temperature changes in core MD94-103 (Southern Indian Ocean): possible implications for North–South climatic relationships around H4

Abstract New records of past sea surface temperatures (SSTs) were derived in the 30–50 kyr B.P. time interval from a core located at 45°S in the Southern Indian Ocean, MD94-103. To investigate the climatic phasing between the Southern Indian Ocean, the Greenland and the Antarctic ice, the magnetic signal of core MD94-103 was synchronized at better than millennial accuracy in the vicinity of the Laschamp geomagnetic to a reference record, NAPIS-75, already placed on the GISP2 age model. Coccolithophorid and diatom species abundances both point to a cooling of surface waters during H4. Specific diatoms also indicate lower salinity waters during the same time interval. These observations do not support the idea that the South hemisphere warmed 1.5–2 kyr before the North hemisphere (Nature 394 (1998) 739). Rather, alkenone-derived SSTs suggest that cold conditions have characterized the surface waters in the south latitudes during H4 and H5, and that temperature at evaporation sites contributed to the isotopic events A1 and A2 visible in the isotopic records of central Antarctica (Earth Planet. Sci. Lett. 177 (2000) 219). SSTs obtained from foraminifera assemblages depict somewhat different temperature patterns, possibly indicative of water stratification.

A 27 kyr terrestrial biomarker record in the southern Indian Ocean

Terrestrial inputs were reconstructed using high molecular weight n-alkane concentrations recorded in the sub-Antarctic Indian Ocean core MD94-103 (45°35′S, 86°31′E, 3560 m) to examine regional changes in the atmospheric circulation over the last 27 kyr. This record was compared to the dust content of EPICA-Dome C ice and continental data from South Africa (e.g., pollen sequences and isotope records in speleothems) to get a comprehensive understanding of atmospheric links between low and midlatitudes of the Indian Ocean. Terrestrial n-alkanes indicate higher glacial than Holocene inputs and marked glacial oscillations. Minimum values during the Last Glacial Maximum (LGM) are consistent with colder and drier climate and presumably caused by the persistence of subtropical anticyclones over southern Africa limiting the amount of rainfall and vegetation growth. The otherwise higher glacial n-alkanes suggest a stronger influence of the tropical rainfall in southern Africa, likely associated with a contraction of the polar vortex with respect to its LGM position. During northern Heinrich events, moderate decline of n-alkanes suggests reduced rainfall over southern Africa possibly caused by weaker tropical easterly winds when, according to Stott et al. (2002), the Pacific Ocean would have experienced Super-ENSO conditions.