Located at the southern boundary of the Alpine chain in Morocco, the deformation front of the Southern Rif Mountains is a region of moderate tectonic activity, which makes it a good natural laboratory to understand whether, and how, low compressional strains are located on specific structures. Along the ≈80 km‐long left‐lateral, transpressive and reverse fault zone that runs at the toe of the Pre‐Rif Ridges, an analysis of high‐resolution digital topography provides new geomorphic lines of evidence supporting Quaternary activity along, 20 km‐long fault segments. The fault zone can be divided into the Meknès and the Fès segments, which are constrained at depth by reactivated, NE‐trending basement faults, delimitating paleo‐grabens associated with the Late Triassic‐Jurassic opening of the Atlantic Ocean. For selected sites, we used in situ‐produced 36Cl, 10Be and 26Al and high‐resolution topography to infer the timing of abandonment of fluvial markers, which suggest incision rates on the order of 0.6‐2 mm/yr. Given their lengths, scaling laws suggest that the identified fault segments should root at about 7‐12 km‐depth, possibly reactivating former basement normal faults and making them potential seismogenic sources capable of generating Mw6+ earthquakes, with return times of the order of several hundreds of years. Our new morphochronological dataset confirms that the Southern Rif deformation front is a key structure that may have accommodated most of the lateral extrusion of the Rif between the Nubia and Iberia tectonic plates

Lire le billet

Reconstructing the spatial and temporal response of mountain glaciers to rapid climate change in the past provides access to the effects of current climate change. Yet, the spatial and temporal variability of past glacier fluctuations is not fully understood. In this study, we focus on the timing of glacier fluctuations in the European Alps during the Younger Dryas/Early Holocene (YD/EH) transition. In an effort to elucidate whether glacier fluctuations were synchronous during this period, we present a new chronology of the Alpine Talèfre glacier, based on 14 new 10Be ages of moraines and roches moutonnées. The retreat of Talèfre glacier was initiated during the mid‐YD (~12.4 ka), then it experienced a gradual retreat punctuated by at least three oscillations until ∼11 ka before shrinking substantially within its Little Ice Age limits (13th−19th centuries). Comparison of our findings with published glacier chronologies in the Alpine region highlights broadly synchronous behaviour of glaciers across the Alps between 12 and 10 ka. The coeval glacier fluctuations at a regional scale suggest that common regional climate conditions had a major impact on Alpine glacier variations during the YD/EH transition. The similarity of glacier behaviour and independent temperature records in both the Alpine region and the northern high latitudes suggests a teleconnection between these regions, but differences in the amplitude of the mean annual temperature signals relative to summer temperature indicate pronounced changes in seasonality between the YD and the EH.

Lire le billet

The atmospheric fluxes of Fe and Al were determined from bulk (wet + dry) plus wet only deposition and aerosol samples collected at Bermuda from 1999 to 2001. During the sampling period, dry deposition accounted for majority (>70%) of total Fe deposition estimated by both modeled and measured means. This contrasts the North Pacific, where generally wet dominates dry deposition. This may be caused by the size and proximity of continental dust sources and seasonal patterns of precipitation to the North Atlantic. Comparing time series measurement of wet soluble Fe deposition indicates that the North Atlantic Oscillation (NAO) may impact the deposition mode of Fe in these areas. The dry deposition velocities of Fe-bearing aerosols (DDV Fe) were estimated from paired averages of measured dry deposition (bulk-wet fluxes) divided by corresponding aerosol concentrations, and a seasonal trend was observed. During the summer months of 1999, the DDV Fe ranged from 0.1 to 0.3 cm s À1 ; yet, during the fall and winter months, the DDV Fe ranged from 2.0 to 6.0 cm s À1. It is hypothesized that with increased humidity and wind speeds at Bermuda during fall and winter, mineral aerosol particles could be internally mixed with sea salt and gaseous S and N pollutants to increase effective particle sizes. Such marine particle aggregation is reported elsewhere and could seasonally increase the apparent dry deposition velocity of mineral aerosols.

Lire le billet

[...]

Lire le billet