Elsevier

Global and Planetary Change

Volume 148, January 2017, Pages 258-267
Global and Planetary Change

Discussion
Lakes or wetlands? A comment on ‘The middle Holocene climatic records from Arabia: Reassessing lacustrine environments, shift of ITCZ in Arabian Sea, and impacts of the southwest Indian and African monsoons’ by Enzel et al.

https://doi.org/10.1016/j.gloplacha.2016.11.001Get rights and content

Highlights

  • Sedimentary lake records from Arabia were reinterpreted as wetlands by Enzel et al.

  • Multiple evidence for Early to Mid-Holocene lakes missed by Enzel is compiled.

  • Increased African Summer Monsoon-related rainfalls charged aquifers, fed lakes.

Abstract

Enzel et al. (2015) reassess sedimentary records of Early to Mid-Holocene lake sites in Arabia based on a reinterpretation of published multiproxy data and a qualitative analysis of satellite imagery. The authors conclude that these sites represent palaeo-wetland environments rather than palaeolakes and that the majority of the Arabian Peninsula experienced no or, if at all, only a very minor increase of rainfall at that time mainly due to eastward expansion of the East African Summer Monsoon. We disagree with their reassessment and identify several cases where unequivocal evidence for early Late Pleistocene and Early to Mid-Holocene perennial lake environments in Arabia, lasting for centuries to millennia, was neglected by Enzel et al. (2015). Here we summarize findings which indicate the presence of lakes from the sites of Jubbah, Tayma, Mundafan (all Saudi Arabia), Wahalah, Awafi (both UAE), and the Wahiba Sands (Oman), supported by evidence including occurrence of barnacle colonies in living position, remnant bioclastic shoreline deposits, undisturbed varve formation, shallowing-up lacustrine sequences, various aquatic freshwater, brackish and saline micro- and macrofossils, such as ichnofaunal remains, which are the result of prolonged field-based research. While the precise depth, hydrology and ecology of these water bodies is still not entirely resolved, their perennial nature is indicative of a markedly increased precipitation regime, which, in combination with more abundant groundwater and increased spring outflow in terminal basins fed by charged aquifers, was sufficient to overcome evaporative losses. The palaeolakes' influence on sustaining prehistoric populations is corroborated by the presence of rich archaeological evidence.

Introduction

The magnitude of climatic and environmental changes throughout the Saharo-Arabian belt during the Late Quaternary and their implications for human evolution, dispersal and behavioural change have been a matter of vivid debate and are not yet fully understood (e.g. Holm, 1960, Büdel, 1963, Kuper and Kröpelin, 2006, Parker, 2010). Therefore, the stimulation of the discussion on whether Holocene lacustrine deposits on the Arabian Peninsula (Fig. 1) indicate the presence of perennial lakes or palustrine wetlands by Enzel et al. (2015) is appreciated. For several sites where such deposits were interpreted as lake relicts, Enzel and colleagues conclude a wetland origin based on a reconsideration of sedimentary and fossil evidence and qualitative interpretation of satellite imagery. In synthesising a large body of published information, the authors contribute in clarifying the existence and spatio-temporal pattern of the Early Holocene Humid Period (EHHP) on the Arabian Peninsula. Furthermore, their article stimulates a much-needed discussion on the atmospheric sources of a possible precipitation surplus in the EHHP for different regions. Enzel et al. (2015) correctly recognize the relevance of the East African Summer Monsoon for creating surface runoff and charging aquifers in Arabia and, thereby, support recent evidence from numerical precipitation modelling (Herold and Lohmann, 2009, Jennings et al., 2015, Guagnin et al., 2016) (Fig. 2). However, we feel obliged to comment on specific aspects of their article, particularly on the existence of palaeolakes across the Arabian Peninsula during MIS 5 and in the EHHP.

Section snippets

Wetlands and lakes — a need for definitions

Clear definitions of terms are essential in the discussion of Arabia's aquatic palaeoenvironments. Ramsar (2016, inside cover) provides an extremely broad definition of wetlands including ‘marshes, peatlands, floodplains, rivers and lakes, and coastal areas such as saltmarshes, mangroves, intertidal mudflats and seagrass beds, and also coral reefs and other marine areas no deeper than 6 m at low tide […]’. According to this definition, lakes are a subtype of wetlands. Enzel et al. (2015, p. 70),

Holocene lakes in Arabia — multiple lines of evidence from multiple places

Given these definitions, we disagree with Enzel et al.'s (2015) characterisation of the published evidence for Late Pleistocene and Holocene lakes on the Arabian Peninsula. Enzel et al. (2015) reinterpret and partly disregard evidence for palaeolakes in order to promote the idea that only wetlands were present during the EHHP. In order to demonstrate the existence of palaeolakes, we compile a site-by-site summary of the main lines of argument for the existence of standing water bodies.

Discussion and conclusions

We show that perennial lakes have occurred at several sites in the Arabian Peninsula during the Late Pleistocene as well as during the Early to Mid-Holocene, where a wide range of micro- and macrofossils provide the strongest, in most places unequivocal evidence. The apparent lack of shoreline deposits and landforms cited by Enzel et al. (2015) as sign of prevailing wetlands, is either the result of low preservation potential due to erosion by strong episodic surface discharge, deflation,

Acknowledgments

The authors' research on the Arabian Peninsula was made possible due to kind support by the following institutions: Saudi Commission for Tourism and National Heritage, Saudi Geological Survey, German Archaeological Institute (Orient Department), and Department of Antiquities and Museums, Ras al-Khaimah. Funding of MDP's work is provided by the European Research Council (No. 295719), ME is supported by the Deutsche Forschungsgemeinschaft (EN977/2-1). Two anonymous reviewers gave insightful

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