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Soil moisture fluctuations recorded in Saharan dust deposits on Lanzarote (CanaryIslands) over the last 180 ka (2010)

Hans von Suchodoletz Hedi Oberhänsli Ulrich Hambach Ludwig Zöller Markus Fuchs Dominik Faust

Aeolian sediments trapped in volcanically dammed valleys on Lanzarote, Canary Islands, were investigated in order to reveal environmental changes over the last 180 ka. Clay content and frequency dependent magnetic susceptibility were used as proxies for pedogenesis and palaeo-soil moisture. During the last 180 ka, these proxies showed a general pattern of enhanced soil moisture during glacials and stadials and more arid conditions during interglacials and interstadials. Comparisons of these results with proxies from regional palaeoclimate studies identified a positive correlation with proxies of trade wind strength off northwest Africa and inverse correlations with both sea surface temperatures in the northeast Atlantic and the extent of Mediterranean vegetation. Possible causes for the observed pattern include a glacial enhancement of precipitation from westerly cyclones, a change in relative humidity due to fluctuating air temperatures and an occasional influence of the African summer monsoon. Although it is not yet possible to clearly differentiate among these factors, it is clear that the first two factors must have been primarily dominant. These results represent the first quasi-continuous terrestrial data testifying to environmental changes in the northwest African coastal area for the last 180 ka and complement the abundant data derived from marine cores of the region. High latitude dynamics had a major influence in this area and were intermediated by North Atlantic sea surface temperatures. A possible negative correlation can also be observed with the orbital obliquity cycle with a 10 ka time lag, which is similar to the lag recorded from North Atlantic sea surface temperatures.

The evolution of Saharan dust input on Lanzarote (Canary Islands) – influenced by human activity in the Northwest Sahara during the early Holocene? (2009)

Hans von Suchodoletz Hedi Oberhänsli Dominik Faust Markus Fuchs Cécile Blanchet Tobias Goldhammer Ludwig Zöller

An overall Holocene increase of Saharan dust input to the Canary Islands and to the North Canary Basin is accompanied by a strong coarsening of Saharan dust in loess-like sediments deposited on Lanzarote from ~7–8 ka. No similar coarsening events are indicated in investigations of the sedimentological record for the last 180 ka, a period showing several dramatic climate changes. Therefore a mobilisation of Holocene dust by anthropogenic activity in the northwest Sahara east of the Canary Islands is assumed. Although scarce archaeological data from the coastal area of that region does not point to strong anthropogenic activity during the early Holocene, a high density of unexplored archaeological remains is reported from the coastal hinterlands in the Western Sahara. Thus, the hypothesis of early anthropogenic activity cannot be excluded.

Loess-like and palaeosol sediments from Lanzarote (Canary Islands/Spain) —Indicators of palaeoenvironmental change during the Late Quaternary (2009)

Hans von Suchodoletz Peter Kühn Ulrich Hambach Michael Dietze Ludwig Zöller Dominik Faust

On Lanzarote (Canary Islands) Quaternary Saharan dust and weathered local volcanic material were trapped in Miocence to Pliocene valleys dammed by younger volcanic edifices. These sediments show sequences of alternating reddish/clayey and loess-like yellowish/silty material. In order to investigate if reddish/clayey layers contain material derived from local pedogenesis and if so, which pedogenetic processes were active, we performed sedimentological, micromorphological and environmental magnetic analyses. The analyses demonstrate that these layers contain material derived from local soils. These soils were characterised by clay formation, rubefication and the formation of superparamagnetic particles during periods of enhanced soil moisture. Thus, they can serve as natural archives in order to reconstruct the terrestrial palaeoclimatic history of Lanzarote. The distribution of soil material in the profiles shows that cold periods of the Late Quaternary were characterised by more humid conditions than today. Using palaeontological remains and a comparison with recent soils on Tenerife, we can roughly estimate maximal palaeoprecipitation values during more humid periods.

Investigations of the geomorphologic and pedologic system of sedimentary vega deposits from Lanzarote (Canary Islands) supported by luminescence dating – important steps towards their palaeoclimatic interpretation (2007)

Hans von Suchodoletz

On Lanzarote (Canary Islands/Spain), sequences similar to loess-palaeosol-sequences from other regions developed in dammed volcanic valleys during the Middle and Late Pleistocene. Based on former investigations, we assumed that these sequences could serve as palaeoclimate archives for the NW-African region, an area characterised by a lack of investigations from continuous terrestrial palaeoclimate archives. The material deposited in the valleys consists of Saharan dust as well as of local volcanic material. Due to their location in valley positions and adjacent strongly eroded slopes it is obvious that these sequences do not represent classic loess-palaeosol-archives. Instead, they must consist of a mixture of in situ aeolian fallout as well as of sediments derived from colluvial input from the slopes. Consequently, prior to a correct palaeoclimatic interpretation the geomorphologic character of the archives and the properties of their sediments must be analysed. Thus, in this study we intensively investigate the geomorphologic and pedologic system, combining geomorphologic mapping and quantitative GIS-calculations with sedimentological-pedological methods (grain size, XRD, rock magnetic und pedologic analyses as well as investigation of micromorphologic properties). Furthermore, we built up a chronostratigraphy using different luminescence-methods (quartz coarse- and fine grain-OSL, polymineral fine grain-IRSL). Fundamental investigations on the bleaching-behaviour of recent Saharan dust and colluvial sediments on Lanzarote demonstrate, that in spite of partial insufficient bleaching of the luminescence signal a dating of the valley-bottom sediments is possible. These datings were supported by a correlation of local kaolinite-contents with iron and kaolinite contents from nearby marine cores as well as a stratigraphic correlation between different profiles. Thus, we could establish a chronostratigraphy for the last 180 ka. We demonstrate that outcropped sediments were deposited almost continuously from the Middle Pleistocen until the Holocene, wheras the uppermost sections of the profiles consist of anthropogenic colluvia which can not be interpreted in a palaeoclimatic way. The alternation of reddish-clayey and yellowish-silty layers tracks changes of soil humidity on Lanzarote rather than variations of the composition of Saharan dust. Due to the colluvial dynamics of the valleys, reddish-silty layers in the valley bottoms are no palaeosoils sensu strictu but mainly consist of colluvial soil sediments originating from pedogenesis on the slopes. These soils as well as unweathered material were eroded and deposited with high frequency and low amplitude. Thus, their sedimentation age in the valley bottoms is close to the primary time of aeolian deposition on the slopes and the formation of pedogenetic properties. These findings allow a palaeoclimatic interpretation of the sediment sequences. We could demonstrate that glacials and stadials were characterised by higher soil moisture than interglacials and interstadials. When comparing our results with other palaeoclimatic studies from a broader region, we can show that the causes for periods of enhanced humidity were westerly cyclones using a more southern way than at recent, as well as lowered sea and air temperatures in the area of the Canary Islands. During some periods, soil humidity was possibly occasionally amplified by a northward advance of the African summer monsoon up to the latitude of Lanzarote. Although we are not able to directly derive palaeoprecipitation values from soil moisture, we can show that maximal precipitation values must have been in the the range of ca. 560 mm/a. Our results demonstrate that during most of the investigated period of the Late Quaternary the climate of Lanzarote was influenced by northern high latitude processes. Furthermore, during most of the investigated period the recent aridity of the island was somewhat mitigated.

Geomorphological investigations of sediment traps on Lanzarote (Canary Islands) as a key for the interpretation of a palaeoclimate archive off NW Africa (2009)

Hans von Suchodoletz Dominik Faust Ludwig Zöller

On Lanzarote (Canary Islands) Late Quaternary Saharan dust and volcanic material were trapped in Miocence to Pliocene valleys dammed by volcanic lava flows. These trapped sediments are potentially interesting as they can be natural archives useful to reconstruct the terrestrial palaeoclimate history of the NW African margin. Nevertheless, slope wash processes altered the primarily eolian deposits, making climatic interpretation not straightforward. Geomorphological mapping, GIS calculations and sedimentological investigations were used to unravel these processes influencing the temporal resolution of the palaeoclimatic archive, demonstrating that they average the palaeoclimatic signal by some ka. Thus, despite the colluvial geomorphic environment, the valley fillings can be used for palaeoclimatic interpretation of events with a length of at least some ka. The youngest sediments, deposited since at least 2.5 ka, are anthropogenically triggered and thus cannot be used for palaeoclimatic interpretation. The results show that the input of Saharan dust at Lanzarote increased during the last 1.0 Ma and especially during the Early/Middle Holocene.

Geoarchaeological and chronometrical evidence of early human occupation on Lanzarote (Canary Islands) (2003)

Ludwig Zöller Hans von Suchodoletz Nils Küster

Two desert loess–paleosol sequences in sediment traps were investigated using (pedo-) stratigraphy, sedimentology, soil mineralogy and IRSL dating. So far we cannot recognise significant IRSL age-underestimates from the polymineral fine-grain fraction of our samples. We establish a first palaeoclimatic sequence spanning the past ca 200 ka which can be compared to data from other Canary Islands and surrounding areas, including terrestrial and deep sea records. More humid phases on Lanzarote are apparently triggered by Milankovich forcing, but the climate remained semi-arid to arid all over the past 200 ka. The onset of human occupation of the island during a slightly moister period is bracketed between 5 and 10 ka, based on the occurrence of archaeosediments containing bones of ovicaprid. This is the first proof of much earlier occupation than witnessed so far from archaeological records. The early subsidiary economy had a strong impact on soil stability and landscape shaping of the island.

Response to the „Comment on ’Geoarchaeological and chronometrical evidence …’ ” by J.C. Carracedo et al. (2004)

Ludwig Zöller Hans von Suchodoletz Henrik Blanchard Dominik Faust Ulrich Hambach

This paper is a reply to the comments made by Carracedo et al. (Quaternary Science Reviews 23, 2045-2049) to the original paper by Zöller, L., Suchodoletz, H.von & N. Küster (2003): Geoarchaeological and chronometrical evidence of early human occupation on Lanzarote (Canary Islands), Quaternary Science Reviews 22, 1299-1307. The reply copes with comments concerning chronometrical dating, the origin of investigated material and geomorphologic and geoarchaeologic problems.

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