Formal Subdivision of the Holocene Series/Epoch: A Summary

The Holocene Series/Epoch is the most recent series/epoch in the geological timescale, spanning the interval from 11,700 yr to the present day. Together with the subadjacent Pleistocene, it comprises the Quaternary System/Period. The Holocene record contains diverse geomorphological, biotic, climatological and archaeological evidence, within sequences that are often continuous and extremely well-preserved at decadal, annual and even seasonal resolution. As a consequence, the Holocene is perhaps the most intensively-studied series/epoch within the entire Geological Time Scale. Yet until recently little attention had been paid to a formal subdivision of the Holocene. Here we describe an initiative by the Subcommission on Quaternary Stratigraphy (SQS) of the International Commission on Stratigraphy (ICS) to develop a formal stratigraphical subdivision of the Holocene, with three new stages/ages, two underpinned by Global Boundary Stratotype Sections and Points (GSSPs) in an ice core, and a third in a speleothem. These stages/ages are defined along with their equivalent subseries/subepochs. The new stages/ages are the Greenlandian with its GSSP in the Greenland NGRIP2 ice core and dated at 11,700 yr b2k (before 2000 CE); the NorthGrippian with its GSSP in the Greenland NGRIP1 ice core and dated to 8236 yr b2k; and the Meghalayan, with its GSSP in a speleothem from Mawmluh Cave, northeastern India, with a date of 4250 yr b2k. This subdivision was formally ratified by the Executive Committee of the International Union of Geological Sciences (IUGS) on 14th June 2018.non

A new terrestrial palaeoenvironmental record from the Bering Land Bridge and context for human dispersal

© 2018 The Authors. Palaeoenvironmental records from the now-submerged Bering Land Bridge (BLB) covering the Last Glacial Maximum (LGM) to the present are needed to document changing environments and connections with the dispersal of humans into North America. Moreover, terrestrially based records of environmental changes are needed in close proximity to the re-establishment of circulation between Pacific and Atlantic Oceans following the end of the last glaciation to test palaeo-climate models for the high latitudes. We present the first terrestrial temperature and hydrologic reconstructions from the LGM to the present from the BLB’s south-central margin. We find that the timing of the earliest unequivocal human dispersals into Alaska, based on archaeological evidence, corresponds with a shift to warmer/wetter conditions on the BLB between 14 700 and 13 500 years ago associated with the early Bølling/Allerød interstadial (BA). These environmental changes could have provided the impetus for eastward human dispersal at that time, from Western or central Beringia after a protracted human population standstill. Our data indicate substantial climate-induced environmental changes on the BLB since the LGM, which would potentially have had significant influences on megafaunal and human biogeography in the region

Ancient DNA from lake sediments: Bridging the gap between paleoecology and genetics

<p>Abstract</p> <p>Background</p> <p>Quaternary plant ecology in much of the world has historically relied on morphological identification of macro- and microfossils from sediments of small freshwater lakes. Here, we report new protocols that reliably yield DNA sequence data from Holocene plant macrofossils and bulk lake sediment used to infer ecological change. This will allow changes in census populations, estimated from fossils and associated sediment, to be directly associated with population genetic changes.</p> <p>Results</p> <p>We successfully sequenced DNA from 64 samples (out of 126) comprised of bulk sediment and seeds, leaf fragments, budscales, and samaras extracted from Holocene lake sediments in the western Great Lakes region of North America. Overall, DNA yields were low. However, we were able to reliably amplify samples with as few as 10 copies of a short cpDNA fragment with little detectable PCR inhibition. Our success rate was highest for sediments < 2000 years old, but we were able to successfully amplify DNA from samples up to 4600 years old. DNA sequences matched the taxonomic identity of the macrofossil from which they were extracted 79% of the time. Exceptions suggest that DNA molecules from surrounding nearby sediments may permeate or adhere to macrofossils in sediments.</p> <p>Conclusions</p> <p>An ability to extract ancient DNA from Holocene sediments potentially allows exciting new insights into the genetic consequences of long-term environmental change. The low DNA copy numbers we found in fossil material and the discovery of multiple sequence variants from single macrofossil extractions highlight the need for careful experimental and laboratory protocols. Further application of these protocols should lead to better understanding of the ecological and evolutionary consequences of environmental change.</p

Range Expansion Drives Dispersal Evolution In An Equatorial Three-Species Symbiosis

A-09-14International audienceBackground Recurrent climatic oscillations have produced dramatic changes in species distributions. This process has been proposed to be a major evolutionary force, shaping many life history traits of species, and to govern global patterns of biodiversity at different scales. During range expansions selection may favor the evolution of higher dispersal, and symbiotic interactions may be affected. It has been argued that a weakness of climate fluctuation-driven range dynamics at equatorial latitudes has facilitated the persistence there of more specialized species and interactions. However, how much the biology and ecology of species is changed by range dynamics has seldom been investigated, particularly in equatorial regions. Methodology/Principal Findings We studied a three-species symbiosis endemic to coastal equatorial rainforests in Cameroon, where the impact of range dynamics is supposed to be limited, comprised of two species-specific obligate mutualists –an ant-plant and its protective ant– and a species-specific ant parasite of this mutualism. We combined analyses of within-species genetic diversity and of phenotypic variation in a transect at the southern range limit of this ant-plant system. All three species present congruent genetic signatures of recent gradual southward expansion, a result compatible with available regional paleoclimatic data. As predicted, this expansion has been accompanied by the evolution of more dispersive traits in the two ant species. In contrast, we detected no evidence of change in lifetime reproductive strategy in the tree, nor in its investment in food resources provided to its symbiotic ants. Conclusions/Significance Despite the decreasing investment in protective workers and the increasing investment in dispersing females by both the mutualistic and the parasitic ant species, there was no evidence of destabilization of the symbiosis at the colonization front. To our knowledge, we provide here the first evidence at equatorial latitudes that biological traits associated with dispersal are affected by the range expansion dynamics of a set of interacting species

An event stratigraphy for the last Termination in the North Atlantic region based on the Greenland ice-core record: a proposal by the INTIMATE group

It is suggested that the GRIP Greenland ice-core should constitute the stratotype for the Last Termination. Based on the oxygen isotope signal in that core, a new event stratigraphy spanning the time interval from ca. 22.0 to 11.5 k GRIP yr BP (ca. 19.0-10.0 k C-14 yr BP) is proposed for the North Atlantic region. This covers the period from the Last Glacial Maximum, through Termination 1 of the deep-ocean record, to the Pleistocene-Holocene boundary, and encompasses the Last Glacial Late-glacial of the traditional northwest European stratigraphy. The isotopic record for this period is divided into two stadial episodes, Greenland Stadials 1 (GS-1) and 2 (GS-2), and two interstadial events, Greenland Interstadials 1 (GI-1) and 2 (GI-2). In addition, GI-1 and GS-2 are further subdivided into shorter episodes. The event stratigraphy is equally applicable to ice-core, marine and terrestrial records and is considered to be a more appropriate classificatory scheme than the terrestrially based radiocarbon-dated chronostratigraphy that has been used hitherto. (C) 1998 John Wiley &amp; Sons, Ltd.</p

Holocene treeline history and climate change across northern Eurasia

Radiocarbon-dated macrofossils are used to document Holocene treeline history across northern Russia (including Siberia), Boreal forest development in this region commenced by 10,000 yr B.P, Over most of Russia, forest advanced to or near the current arctic coastline between 9000 and 7000 yr B.P. and retreated to its present position by between 4000 and 3000 yr B.P. Forest establishment and retreat was roughly synchronous across most of northern Russia, Treeline advance on the Kola Peninsula, however, appears to have occurred later than in other regions. During the period of maximum forest extension, the mean July temperatures along the northern coastline of Russia may have been 2.5 degrees to 7.0 degrees C warmer than modern. The development of forest and expansion of treeline likely reflects a number of complimentary environmental conditions, including heightened summer insolation, the demise of Eurasian ice sheets, reduced sea-ice cover, greater continentality with eustatically lower sea level, and extreme Arctic penetration of warm North Atlantic waters. The late Holocene retreat of Eurasian treeline coincides with declining summer insolation, cooling arctic waters, and neoglaciation, (C) 2000 University of Washington