Lake Baikal amphipods under climate change: Thermal constraints and ecological consequences, links to supplementary material

Lake Baikal, the world's most voluminous freshwater lake, has experienced unprecedented warming during the last decades. A uniquely diverse amphipod fauna inhabits the littoral zone and can serve as a model system to identify the role of thermal tolerance under climate change. This study aimed to identify sublethal thermal constraints in two of the most abundant endemic Baikal amphipods, Eulimnogammarus verrucosus and Eulimnogammarus cyaneus, and Gammarus lacustris, a ubiquitous gammarid of the Holarctic. As the latter is only found in some shallow isolated bays of the lake, we further addressed the question whether rising temperatures could promote the widespread invasion of this non-endemic species into the littoral zone. Animals were exposed to gradual temperature increases (4 week, 0.8 °C/d; 24 h, 1 °C/h) starting from the reported annual mean temperature of the Baikal littoral (6 °C). Within the framework of oxygen- and capacity-limited thermal tolerance (OCLTT), we used a nonlinear regression approach to determine the points at which the changing temperature-dependence of relevant physiological processes indicates the onset of limitation. Limitations in ventilation representing the first limits of thermal tolerance (pejus (= "getting worse") temperatures (Tp)) were recorded at 10.6 (95% confidence interval; 9.5, 11.7), 19.1 (17.9, 20.2), and 21.1 (19.8, 22.4) °C in E. verrucosus, E. cyaneus, and G. lacustris, respectively. Field observations revealed that E. verrucosus retreated from the upper littoral to deeper and cooler waters once its Tp was surpassed, identifying Tp as the ecological thermal boundary. Constraints in oxygen consumption at higher than critical temperatures (Tc) led to an exponential increase in mortality in all species. Exposure to short-term warming resulted in higher threshold values, consistent with a time dependence of thermal tolerance. In conclusion, species-specific limits to oxygen supply capacity are likely key in the onset of constraining (beyond pejus) and then life-threatening (beyond critical) conditions. Ecological consequences of these limits are mediated through behavioral plasticity in E. verrucosus. However, similar upper thermal limits in E. cyaneus (endemic, Baikal) and G. lacustris (ubiquitous, Holarctic) indicate that the potential invader G. lacustris would not necessarily benefit from rising temperatures. Secondary effects of increasing temperatures remain to be investigated.

Tab. 1: Age of biogene material from the ice margin, Kofoed-Hansen Bræ and Storstrømmen

Early Holocene recession of the ice cover over Germania Land in North-East Greenland 7.5 ka B.P. brought the Inland Ice margin back to a position close to the present. Continued recession after that time lead to the formation of a "Storstrømmen Sound" which separated Germania Land from mainland Greenland in the period from about 6 to 1 ka B.P. The present filling of the approximately 100 km long sound by the glaciers of Storstrømmen and Kofoed-Hansen Bræ must therefore have taken place during the Little lce Age. In an archaeological sense this implies deterioration of the living conditions of Neo-Eskimos compared to those of Palaeo-Eskimos. The neoglacial re-formation and present existence of the glaciers as a Little Ice Age relict may imply a present-day instability in their dynamics, as demonstrated by the pulsations (surge-like behaviour) in the last part of the 20th century. An earlier Little Ice Age advance might possibly have had the same amplitude as that documented from the 20th century but its exact age and character is not known. The glacio-isostatic response of the earth's crust to the variations in the Holocene glacier load implies a relatively slow and slight emergence and subsequent submergence. The shift from emergence to submergence must have taken place between about 2 and 1 ka B.P.

Grain-size distribution and frictional behaviour of sediment cores from the Nice Slope

The upper shelf of the landslide-prone Ligurian Margin (Western Mediterranean Sea) off Nice well-known for the 1979 Airport Landslide is a natural laboratory to study preconditioning factors and trigger mechanisms for submarine landslides. For this study low-stress ring shear experiments have been carried out on a variety of sediments from >50 gravity cores to characterise the velocity-dependent frictional behaviour. Mean values of the peak coefficient of friction vary from 0.46 for clay-dominated samples (53 % clay, 46 % silt, 1 %) sand up to 0.76 for coarse-grained sediments (26 % clay, 57 % silt, 17 % sand). The majority of the sediments tested show velocity strengthening regardless of the grain size distribution. For clayey sediments the peak and residual cohesive strength increases with increasing normal stress, with values from 1.3 to 10.6 kPa and up to 25 % of all strength supported by cohesive forces in the shallowmost samples. A pseudo-static slope stability analysis reveals that the different lithologies (even clay-rich material with clay content >=50 %) tested are stable up to slope angles <26° under quasi-drained conditions.