Quaternary, Volume 2, Issue 2 (June 2019) – 8 articles

Easter Island (Rapa Nui) deforestation has traditionally been viewed as a single event, synchronous in time and space across the island and caused by Polynesian settlers. However, recent studies have challenged this idea, introducing the concept of spatiotemporal heterogeneity and suggesting a role for climate change. This paper presents a continuous paleovegetation record of the last millennium (~960 to ~1710 CE), based on palynological analysis of a core from Lake Kao. During this time interval, deforestation was gradual, with three main pulses at ~1070 CE, ~1410 CE, and ~1600 CE, likely driven by drought, anthropogenic practices (mostly fire), or the coupling of both. Some forest regeneration trends have been documented after the first and the second deforestation pulses. Forests were totally removed by 1600 CE, coinciding with the full permanent human settlement of the Kao area. Comparison with other continuous palynological records available for the last millennium (Aroi marsh and Lake Raraku) confirms that forest clearing was heterogeneous in time and space, rather than synchronous island-wide. Full article

The western Makran coast displays evidence of surface uplift since at least the Late Pleistocene, but it remains uncertain whether this displacement is accommodated by creep on the subduction interface, or in a series of large earthquakes. Here, we address this problem by looking at the short-term (Holocene) history of continental vertical displacements recorded in the geomorphology and sedimentary succession of the Makran beaches. In the region of Chabahar (Southern Iran), we study two bay-beaches through the description, measurement and dating of 13 sedimentary sections with a combination of radiocarbon and Optically Stimulated Luminescence (OSL) dating. Our results show that lagoonal settings dominate the early Holocene of both studied beach sections. A flooding surface associated with the Holocene maximum transgression is followed by a prograding sequence of tidal and beach deposits. Coastal progradation is evidenced in Pozm Bay, where we observe a rapid buildup of the beach ridge succession (3.5 m/years lateral propagation over the last 1950 years). Dating of Beris Beach revealed high rates of uplift, comparable to the rates obtained from the nearby Late Pleistocene marine terraces. A 3150-year-old flooding surface within the sedimentary succession of Chabahar Bay was possibly caused by rapid subsidence during an earthquake. If true, this might indicate that the Western Makran does produce large earthquakes, similar to those that have occurred further east in the Pakistani Makran. Full article

We investigated 34 sediment cores to reconstruct spatiotemporal variations in hypolimnetic hypoxia for the past 200 years in Lehmilampi, a small lake in Eastern Finland. As hypoxia is essential for varve preservation, spatiotemporal changes in varve distribution were used as an indicator for hypolimnetic hypoxia oscillations. The hypoxic water volume was used as a variable reflecting hypolimnetic hypoxia and determined for each year by estimating the water volume beneath the water depth where shallowest varves were preserved. As a result, seven hypoxia periods, highlighting the variations in hypolimnetic hypoxia, are established. These periods may be influenced by bioturbation, lake infill, and lake level changes. Furthermore, we evaluated the relationship between hypolimnetic hypoxia oscillations and climatic factors. Diatom assemblage changes were also analyzed to estimate whether the hypoxia periods could be related to anthropogenic eutrophication. The diatom analyses suggest relatively stable nutrient conditions for the past 200 years in Lake Lehmilampi. Climate, on the other hand, seems to be an important driver of hypoxia oscillations based on correlation analysis. The role of individual forcing factors and their interaction with hypolimnetic hypoxia would benefit from further investigations. Understanding climatic and anthropogenic forcing behind hypolimnetic hypoxia oscillations is essential when assessing the fate of boreal lakes in a multi-stressor world. Full article

The debates about naming the unfolding times of anthropogenic global change the ‘Anthropocene’ are ultimately debates about the ‘human condition’. The proposal to amend the geological time scale by adding an ‘Anthropocene’ epoch (that is, the ‘Anthropocene proposal’ in its strict sense) is both an intra-geoscience debate about scientific sense-making and a debate about the societal context of the geosciences. This essay juxtaposes these debates, starting from three postulates: first, that the scientific methods of geological chronostratigraphy are applied rigorously; second, that anthropogenic global change is happening; and third, that the ‘Anthropocene proposal’ may be rejected if it does not meet the conditions required for its approval based on the rigorous application of the scientific methods of geological chronostratigraphy. These postulates are analysed through the lenses of the Cape Town Statement on Geoethics and the normative statements of the ‘geoethical promise’. It is found that an ethical quandary would arise if the ‘Anthropocene proposal’ were to be rejected. Consequently, and given the societal contexts of the geosciences, it is explored whether distinguishing between the geological past (as demarcated according to current chronostratigraphic methodology) and contemporary geological–historical times (characterised somewhat differently) could offer a work-around to tackle the quandary. Full article

The purpose of this study was to identify relationships between meteorological and hydrological observations and sediment flux rate changes, in order to better understand catchment dynamics. The meteorological and hydrological observations included local air temperature, wind speed, water temperature, and ice cover, while the sediment flux rate was observed in the lake basin using a modified sediment trap technique. This study demonstrates the advantages of a new online methodology applied in conventional sediment trapping to obtain flux rate information with daily resolution. A prototype of a high-resolution online sediment trap was tested in Savilahti Bay, Lake Kallavesi, eastern Finland, during the period from 22 October 2017 to 6 October 2018. The daily resolutions of meteorological, hydrological, and sediment flux rate data were analyzed using statistical methods. The results indicate relationships between temperature, precipitation, wind speed, and sediment flux rate, but the urban site also showed erosional changes due to anthropogenic land use. Sediment flux ceased during winter season and spring floods were recorded as pronounced peaks in sediment flux, while the growing season showed generally higher sediment accumulation rates. This research also provides valuable information on the catchment response to short-term weather events. The influence of a storm led to larger sediment flux for several days. The importance of wind speed and frost formation on sedimentation, which has been difficult to address due to trap deployment times of typically several months, is now supported. Used together with varved sediment archives, online sediment trapping will facilitate the interpretation of paleoclimatic proxy records and modeling of detailed weather and erosion conditions that are related to climate change. Full article

Non-glaciated mountain headwater catchments feature high-resolution geomorphic archives, which provide important insight into erosive processes and sediment dynamics in mountain ranges. As such the Valle de la Fueva catchments in the southern Pyrenees present high-lying talus remnants, extensive denudation surfaces (pediments), deeply incised tributary ravines, and low-lying fluvial-cut terraces. Based on geomorphic analyses and absolute dating using terrestrial cosmogenic nuclides and optically stimulated luminescence, a (late stage) catchment erosion model for the Valle de la Fueva was elaborated and indicates successive development stages of (i) lasting pedimentation under cold-climate conditions during Marine Isotope Stages 4–2, (ii) rapid fluvial dissection, sediment remobilization and downcutting of ravines in response to the last major climate transition and establishing interglacial conditions, and (iii) late stage fluvial incision after 3–4 ka due to regionally increased flood magnitudes, and/or intensification of agriculture and forest management. Valle de la Fueva headwater catchment analysis indicated that the styles and magnitudes of basin surface processes were directly correlated with the amplitude and nature of paleoclimatic changes, modified by the interplay of environmental parameters. In contrast to large-scale fluvial systems, mountain headwater catchments seemed to be less afflicted with temporal and spatial averaging biases. They are thus useful targets for investigating direct climate change effects, surface process coupling, and non-linear response mechanisms in Quaternary fluvial systems. Full article

The Middle East (ME) spans the transition between a temperate Mediterranean climate in the Levant to hyper-arid sub-tropical deserts in the southern part of the Arabian Peninsula (AP), with the complex alpine topography in the northeast feeding the Euphrates and Tigris rivers which support life in the Southeastern Fertile Crescent (FC). Climate projections predict severe drying in several parts of the ME in response to global warming, making it important to understand the controls of hydro-climate perturbations in the region. Here we discuss 23 ME speleothem stable oxygen isotope (δ¹⁸Occ) records from 16 sites from the SISAL_v1 database (Speleothem Isotope Synthesis and Analysis database), which provide a record of past hydro-climatic variability. Sub-millennial changes in ME δ¹⁸Occ values primarily indicate changes in past precipitation amounts the result of the main synoptic pattern in the region, specifically Mediterranean cyclones. This pattern is superimposed on change in vapor source δ¹⁸O composition. The coherency (or lack thereof) between regional records is reviewed from Pleistocene to present, covering the Last Glacial Maximum (~22 ka), prominent events during deglaciation, and the transition into the Holocene. The available δ¹⁸Occ time-series are investigated by binning and normalizing at 25-year and 200-year time windows over the Holocene. Important climatic oscillations in the Holocene are discussed, such as the 8.2 ka, 4.2 ka and 0.7 ka (the Little Ice Age) Before Present events. Common trends in the normalized anomalies are tested against different climate archives. Finally, recommendations for future speleothem-based research in the region are given along with comments on the utility and completeness of the SISAL database. Full article

The discovery and settlement of the tiny and remote Easter Island (Rapa Nui) has been a classical controversy for decades. Present-day aboriginal people and their culture are undoubtedly of Polynesian origin, but it has been debated whether Native Americans discovered the island before the Polynesian settlement. Until recently, the paradigm was that Easter Island was discovered and settled just once by Polynesians in their millennial-scale eastward migration across the Pacific. However, the evidence for cultivation and consumption of an American plant—the sweet potato (Ipomoea batatas)—on the island before the European contact (1722 CE), even prior to the Europe-America contact (1492 CE), revived controversy. This paper reviews the classical archaeological, ethnological and paleoecological literature on the subject and summarizes the information into four main hypotheses to explain the sweet potato enigma: the long-distance dispersal hypothesis, the back-and-forth hypothesis, the Heyerdahl hypothesis, and the newcomers hypothesis. These hypotheses are evaluated in light of the more recent evidence (last decade), including molecular DNA phylogeny and phylogeography of humans and associated plants and animals, physical anthropology (craniometry and dietary analysis), and new paleoecological findings. It is concluded that, with the available evidence, none of the former hypotheses may be rejected and, therefore, all possibilities remain open. For future work, it is recommended to use the multiple working hypotheses framework and the strong inference method of hypothesis testing, rather than the ruling theory approach, very common in Easter Island research. Full article