Climate change and ecosystems dynamics over the last 6000 years in the Middle Atlas, Morocco

Nourelbait, Majda; Rhoujjati, Ali; Benkaddour, Abdelfattah; Carré, Matthieu; Eynaud, Frédérique; Martinez, Philippe; Cheddadi, Rachid

doi:10.5194/cp-12-1029-2016

Cited by 19 publications

(18 citation statements)

References 89 publications

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“…2b). High-resolution speleothem data from southern Iberia show Mediterranean climate conditions in southern Iberia between 4800 and 3000 cal BP (Walczak et al, 2015) for the Alboran Sea during the late Holocene is consistent with a climate reconstruction available from the Middle Atlas (Morocco), which show a trend over the last years towards arid conditions as well as higher precipitation seasonality between 4000 and 2000 cal yrs BP (Nourelbait et al, 2016). There is also good evidence from many records to support late Holocene aridification in southern Iberia.…”

Section: Late Holocene (4000 To 2000 Cal Yrs Bp)supporting

confidence: 78%

“…Very few large-scale climate reconstruction of precipitation exist for the whole Holocene (Bartlein et al, 2011;Mauri et al, 2014;Guiot andKaniewski, 2015, Tarroso et al, 2016) and, even at local scales, pollen-inferred reconstructions of seasonal precipitation are very rare (Wu et al, 2007;Peyron et al, 2011Peyron et al, , 2013Combourieu-Nebout et al, 2013, Nourelbait et al, 2016.…”

Section: A North-south Precipitation Pattern?mentioning

confidence: 99%

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The climate of the Mediterranean basin during the Holocene from terrestrial and marine pollen records: A model/data comparison

Peyron¹,

Combourieu-Nebout²,

Brayshaw³

et al. 2016

Preprint

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Abstract. Climate evolution of the Mediterranean region during the Holocene exhibits strong spatial and temporal variability. The spatial differentiation and temporal variability, as evident from different climate proxy datasets, has remained notoriously difficult for models to reproduce. In light of this complexity, we examine the previously described evidence for (i) opposing northern and southern precipitation regimes during the Holocene across the Mediterranean basin, and (ii) an east-to-west precipitation gradient or dipole during the early Holocene, from a wet eastern Mediterranean to dry western Mediterranean. Using quantitative climate information from marine and terrestrial pollen archives, we focus on two key time intervals, the early to mid-Holocene (8000 to 6000 cal yrs BP) and the late Holocene (4000 to 2000 yrs BP), in order to test the above mentioned hypotheses on a Mediterranean-wide scale. Palynologically derived climate information is compared with the output of regional-scale climate-model simulations for the same time intervals. Quantitative pollen-based precipitation estimates were generated along a longitudinal gradient from the Alboran (West) to the Aegean Sea (East); they are derived from terrestrial pollen records from Greece, Italy and Malta as well as from pollen records obtained from marine cores. Because seasonality represents a key parameter in Mediterranean climates, special attention was given to the reconstruction of season-specific climate information, notably summer and winter precipitation. The reconstructed climatic trends corroborate a previously described north-south partition of precipitation regimes during the Holocene. During the early Holocene, relatively wet conditions occurred in the south-central and eastern Mediterranean region, while drier conditions prevailed from 45° N northwards. These patterns reversed during the late Holocene, with a wetter northern Mediterranean region and drier conditions in the east and south. More sites from the northern part of the Mediterranean basin are needed to further substantiate these observations. With regard to the existence of a west-east precipitation dipole during the Holocene, our pollen-based climate data show that the strength of this dipole is strongly linked to the seasonal parameter reconstructed: Early Holocene summers show a clear east-to-west gradient, with summer precipitation having been highest in the central and eastern Mediterranean and lowest over the western Mediterranean. In contrast, winter precipitation signals are less spatially coherent. A general drying trend occurred from the early to the late Holocene; particularly in the central and eastern Mediterranean. However, summer precipitation in the east remained above modern values, even during the late Holocene interval. Pollen-inferred precipitation estimates were compared to regional-scale climate modelling simulations based on the HadAM3 GCM coupled to the dynamic HadSM3 and the high-resolution regional HadRM3 models. Climate model outputs and pollen-inferred precipitation estimates show remarkably good overall correspondence, although many simulated patterns are of marginal statistical significance. Nevertheless, models weakly support an east to west division in summer precipitation and there are suggestions that the eastern Mediterranean experienced wetter summer and winter conditions during the early Holocene and wetter summer conditions during the late Holocene. The extent to which summer monsoonal precipitation may have existed in the southern and eastern Mediterranean during the mid-Holocene remains an outstanding question; our model, consistent with other global models, does not suggest an extension of the African monsoon into the Mediterranean. Given the difficulty in modelling future climate change in Southern Europe, more simulations based on high resolution global models and very high resolution regional downscaling, perhaps even including transient simulations, are required to fully understand the patterns of change in winter and summer circulation patterns over the Mediterranean region

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Section: Late Holocene (4000 To 2000 Cal Yrs Bp)supporting

confidence: 78%

Section: A North-south Precipitation Pattern?mentioning

confidence: 99%

The climate of the Mediterranean basin during the Holocene from terrestrial and marine pollen records: A model/data comparison

Peyron¹,

Combourieu-Nebout²,

Brayshaw³

et al. 2016

Preprint

View full text Add to dashboard Cite

show abstract

“…This pattern was reversed at around 4500 cal yr BP (Magny et al, 2013). Quantitative pollenbased precipitation reconstructions from sites in northern Italy indicate humid winters and dry summers during the early to mid-Holocene, whereas southern Italy was characterized by humid winters and summers; the N-S pattern reverses in the late Holocene, with drier conditions at southern sites and wet conditions at northern sites (Peyron et al, 2011(Peyron et al, , 2013. These findings support a north-south partition for the central Mediterranean with regards to precipitation, and they also confirm that precipitation seasonality is a key parameter in the evolution of Mediterranean climates.…”

Section: Introductionmentioning

confidence: 93%

Precipitation changes in the Mediterranean basin during the Holocene from terrestrial and marine pollen records: a model–data comparison

Peyron

Nebout²,

Brayshaw

et al. 2017

Clim. Past

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Abstract. Climate evolution of the Mediterranean region during the Holocene exhibits strong spatial and temporal variability, which is notoriously difficult for models to reproduce. We propose here a new proxy-based climate synthesis synthesis and its comparison – at a regional (∼ 100 km) level – with a regional climate model to examine (i) opposing northern and southern precipitation regimes and (ii) an east-to-west precipitation dipole during the Holocene across the Mediterranean basin. Using precipitation estimates inferred from marine and terrestrial pollen archives, we focus on the early to mid-Holocene (8000 to 6000 cal yr BP) and the late Holocene (4000 to 2000 cal yr BP), to test these hypotheses on a Mediterranean-wide scale. Special attention was given to the reconstruction of season-specific climate information, notably summer and winter precipitation. The reconstructed climatic trends corroborate the north–south partition of precipitation regimes during the Holocene. During the early Holocene, relatively wet conditions occurred in the south–central and eastern Mediterranean regions, while drier conditions prevailed from 45° N northwards. These patterns then reverse during the late Holocene. With regard to the existence of a west–east precipitation dipole during the Holocene, our results show that the strength of this dipole is strongly linked to the reconstructed seasonal parameter; early-Holocene summers show a clear east–west division, with summer precipitation having been highest in Greece and the eastern Mediterranean and lowest over Italy and the western Mediterranean. Summer precipitation in the east remained above modern values, even during the late-Holocene interval. In contrast, winter precipitation signals are less spatially coherent during the early Holocene but low precipitation is evidenced during the late Holocene. A general drying trend occurred from the early to late Holocene, particularly in the central and eastern Mediterranean. For the same time intervals, pollen-inferred precipitation estimates were compared with model outputs, based on a regional-scale downscaling (HadRM3) of a set of global climate-model simulations (HadAM3). The high-resolution detail achieved through the downscaling is intended to enable a better comparison between site-based paleo-reconstructions and gridded model data in the complex terrain of the Mediterranean; the model outputs and pollen-inferred precipitation estimates show some overall correspondence, though modeled changes are small and at the absolute margins of statistical significance. There are suggestions that the eastern Mediterranean experienced wetter summer conditions than present during the early and late Holocene; the drying trend in winter from the early to the late Holocene also appears to be simulated. The use of this high-resolution regional climate model highlights how the inherently patchy nature of climate signals and paleo-records in the Mediterranean basin may lead to local signals that are much stronger than the large-scale pattern would suggest. Nevertheless, the east-to-west division in summer precipitation seems more marked in the pollen reconstruction than in the model outputs. The footprint of the anomalies (like today, or dry winters and wet summers) has some similarities to modern analogue atmospheric circulation patterns associated with a strong westerly circulation in winter (positive Arctic Oscillation–North Atlantic Oscillation (AO–NAO)) and a weak westerly circulation in summer associated with anticyclonic blocking; however, there also remain important differences between the paleo-simulations and these analogues. The regional climate model, consistent with other global models, does not suggest an extension of the African summer monsoon into the Mediterranean. Therefore, the extent to which summer monsoonal precipitation may have existed in the southern and eastern Mediterranean during the mid-Holocene remains an outstanding question.

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“…Recent studies have contributed further knowledge regarding patterns and processes of Holocene vegetation change in the northwestern Middle Atlas at Ras el Ma and Dayat Hachlaf (Nourelbait et al, 2014(Nourelbait et al, , 2016Tabel et al, 2016), and forthcoming data for the Holocene are indicated for Lake Tifounassine (Cheddadi et al, 2015). At Dayat Hachlaf, forested conditions with Quercus (undifferentiated) and Pinus are recorded throughout the record from 6,000 cal yr BP, and include a shift in forest composition around 3,500 cal yr BP, with the expansion of Cedrus (Nourelbait et al, 2016). In contrast, the nearby record of Ras el Ma documents a late development of forest with Quercus and Cedrus only after 5,000 cal yr BP (Nourelbait et al, 2014).…”

Section: Background and Rationalementioning

confidence: 99%

“…The biological and bioclimatic diversity of the region, particularly as contained within the Atlas mountain ranges (Ozenda, 1975;Medail and Quezel, 1997), furthermore provides a valuable "test-bed" for understanding the wider response of FIGURE 1 | The study region and location of pollen records, showing: (a) the location of the Middle Atlas (MA), High Atlas (HA) and Rif mountain ranges in Morocco; (b) the western Middle Atlas and the location of the study site and other Holocene pollen studies cited in the text; and (c) length and chronological control of dated pollen records for the Middle Atlas. Key to sites: AFO-Dayat Afourgagh (Lamb et al, 1991); ALI-Lake Sidi Ali (1-Sidi Ali sub-basin, Lamb et al, 1999; 2-Sidi Ali deep lake, this study); CDZ-Col du Zad (Reille, 1976); HAC-Dayet Hachlaff (Nourelbait et al, 2016); HAR-Taguelmam N'Harcha (Lamb et al, 1991); ICH-Ait Ichou (Tabel et al, 2016); IFF-Dayat Iffir (Lamb et al, 1991); IFR-Dayat Ifrah (Rhoujjati et al, 2010;Reddad et al, 2013); RAS-Ras el Ma (Nourelbait et al, 2014); TIF-Tifounassine (Cheddadi et al, 2015); TIG-Tigalmamine (Lamb et al, 1989Lamb and van der Kaars, 1995;Cheddadi et al, 1998).…”

Section: Background and Rationalementioning

confidence: 99%

Environmental Drivers of Holocene Forest Development in the Middle Atlas, Morocco

et al. 2017

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Climate change and ecosystems dynamics over the last 6000 years in the Middle Atlas, Morocco

Cited by 19 publications

References 89 publications

The climate of the Mediterranean basin during the Holocene from terrestrial and marine pollen records: A model/data comparison

The climate of the Mediterranean basin during the Holocene from terrestrial and marine pollen records: A model/data comparison

Precipitation changes in the Mediterranean basin during the Holocene from terrestrial and marine pollen records: a model–data comparison

Environmental Drivers of Holocene Forest Development in the Middle Atlas, Morocco

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