Abstract: Combined measurements of δ18O, δ17O, and δD in ice cores, leading to d excess and 17O excess, are expected to provide new constraints on the water cycle and past climates. We explore different processes, both in the source regions and during the poleward transport, that could explain the 17O excess increase by 20 per meg observed from the Last Glacial Maximum (LGM) to Early Holocene (EH) at the Vostok station. Using a single-column model over tropical and subtropical oceans, we show that the relative humidity at the surface is the main factor controlling 17O excess in source regions. Then, using a Rayleigh-type model, we show that the 17O excess signal from the source region is preserved in the polar snowfall, contrary to d excess. Evaporative recharge over mid and high latitudes and δ18O seasonality in polar regions can also affect the Vostok 17O excess but cannot account for most of the 20 per meg deglacial increase from LGM to EH. On the other hand, a decrease of the relative humidity at the surface (rhs) by 8 to 22% would explain the observed change in 17O excess. Such a change would not necessarily be incompatible with a nearly unchanged boundary layer relative humidity, if the surface thermodynamic disequilibrium decreased by 4C. Such a change in rhs would affect source and polar temperatures reconstructions from δ18O and d excess measurements, strengthening the interest of 17O excess measurements to better constrain such changes.

Abstract: Bolometric Interferometry (BI) is one of the most promising techniques for precise measurements of the Cosmic Microwave Background polarization. In this paper, we present the results of DIBO (Demonstrateur d'Interferometrie Bolometrique), a single-baseline demonstrator operating at 90 GHz, built to proof the validity of the BI concept applied to a millimeter-wave interferometer. This instrument has been characterized in the laboratory with a detector at room temperature and with a 4 K bolometer. This allowed us to measure interference patterns in a clean way, both (1) rotating the source and (2) varying with time the phase shift among the two interferometer's arms. Detailed modelisation has also been performed and validated with measurements.