Multiproxy analyses of Lake Allos reveal synchronicity and divergence in geosystem dynamics during the Lateglacial/Holocene in the Alps

Abstract

Palaeoenvironmental reconstructions of ecosystem responses to external forcing are generally limited by the difficulty of understanding the geosystem as a whole, because of the complex interactions between ecological compartments. Therefore, identifying which geosystem compartments or proxies co-vary is a prerequisite in unravelling the propagation of disturbances (e.g. climatic or anthropogenic) from one compartment to another. A multiproxy study of a continuous 13,500-year sedimentary profile cored in Lake Allos (European Alps, 2200 m a.s.l) was carried out on the basis of high-resolution sedimentological, geochemical, and botanical analyses, as well as determination of aquatic biotic proxies (diatoms, ostracods). These multiproxy datasets are rare at these high altitudes. Major changes occurred in the course of the palaeoenvironmental history of this alpine watershed at 12,000, 8600, 7200 and 3000 cal. BP. During the Holocene, two main transitions were recorded in all the ecological compartments (8600 and 3000 cal. BP), but the period 4500-3000 cal. BP stands out because of major changes that concerned only the lacustrine ecosystem. The frequent switches in lake level might correspond to the 4.2 ka climatic event. Proximity of this alpine lake to climatically-sensitive thresholds (ice-cover, thermal stratification, hydrological balance) may have amplified climatic signals in the lake ecosystem. This study illustrates the difficulties inherent to the use of common intra-Holocene stratigraphical limits, given that ecological compartments are likely to have different responses to forcing factors depending on the characteristics of the watershed and its capacity to accommodate disturbances.

Paleohydrological history of Lake Allos (2200 m a.s.l) since 13 500 cal a bp in the Mediterranean Alps inferred from an ostracod δ18O record

“…Ostracod valves are absent in the sediments from 5800 to 2800 cal a BP during a period with high diatom concentrations (data published in Cartier et al, 2018; Figure 5). Mean C. lacustris abundance in core sediment slices 5 cm long is 3.1 valves from the bottom to 5800 cal a BP and 2.8 valves from 2800 cal a BP to the top of the record (Cartier et al, 2018). Concentrations in valves cm -3 are presented in Fig.…”

“…In the Southern French Alps, long‐term paleoclimate records remain scarce and/or do not cover the entire Lateglacial/Holocene periods (Harrison et al , 1993; Digerfeldt et al , 1997; Drysdale et al , 2006; Wilhelm et al , 2012; Wirth et al , 2013; Cartier et al , 2019; Regattieri et al , 2019). Climate, environmental changes and vegetation succession that have occurred since the last glaciation are not entirely documented and understood (Brisset et al , 2015; Cartier et al , 2018). In the Mercantour Massif, deglaciation of cirque‐glacier catchments occurred between 14 000 and 13 500 cal a bp , i.e.…”

“…This relationship with lacustrine conditions has led to successful reconstructions of past δ 18 O lake water (δ 18 O lw ) for Mediterranean lakes (Develle et al , 2010; Roberts et al , 2010). δ 18 O lw provides a regional paleoclimate proxy, not influenced by local human activities, allowing a comparison with environmental and geomorphological studies (glacier advances, Holzhauser et al , 2005; Rea et al , 2020; torrential activity, Brisset et al , 2017; pollen assemblages, Cartier et al , 2018) and large‐scale climate oscillations in Europe (e.g. Younger Dryas, Medieval Climate Anomaly (MCA), LIA).…”

Socio-Ecological Contingencies with Climate Changes over the Prehistory in the Mediterranean Iberia

“…In the course of this period, the~4.2 kyr cal. BP climate event [79] was likely expressed by drier hydrological conditions in the Western Mediterranean [94][95][96][97], in the context of high river alluviation [98] and more frequent summer rainfall [99]. Regarding the variety of the proxies, this climate event was likely a centennial-scale exacerbation of the Mediterranean climate, meaning a stronger seasonality of temperatures and precipitations [97].…”

Introductory Chapter: An Introduction to the Stratigraphic Setting of Paleozoic to Miocene Deposits Based on Paleoecology, Facies Analysis, Chemostratigraphy, and Chronostratigraphy - Concepts and Meanings

“…The high resolution chronostratigraphy of the paleo-lakes is a main research topic, which has been deeply studied by several authors [17][18][19][20][21][22][23][24][25][26][27]. In particular, the Ibate paleolake has shown a distal lacustrine environment with low-oxygen conditions in its bottom waters [17].…”