Geological perspectives on the Monte Verde archeological site in Chile and pre-Clovis coastal migration in the Americas

2011 ◽  
Vol 76 (2) ◽  
pp. 201-210 ◽  
Author(s):  
William R. Dickinson
Keyword(s):  
Continental Shelf ◽  
Sea Level ◽  
New World ◽  
Human Movement ◽  
Migration Route ◽  
Projectile Points ◽  
The Pacific ◽  
First Americans ◽  
Monte Verde ◽  
Archeological Site

AbstractDiscovery of the Monte Verde archeological site in Chile overturned the previous consensus that the first Americans into the New World from Asia were the makers of Clovis projectile points, and rejuvenated the hypothesis that migration through the Americas occurred largely on portions of the Pacific continental shelf exposed by Pleistocene drawdown in eustatic sea level. The postulate of travel along a paleoshoreline now hidden underwater is an attractive means to posit pre-Clovis human movement southward from Beringia to Chile without leaving traces of migration onshore. Geologic analyses of the Pleistocene paleoenvironment at Monte Verde and of the morphology of the potential migration route along the continental shelf raise questions that have not been fully addressed. The periglacial setting of Monte Verde may call its antiquity into question and the narrowness of the Pacific continental shelf of the Americas makes it unlikely that people could travel the length of the Americas without impacting ground still onshore and no farther inland than Monte Verde itself. Geological perspectives on Monte Verde and coastal migration jointly suggest that the Clovis-first hypothesis for peopling the New World may have been abandoned prematurely.

scholarly journals Setting the Stage: The Late Pleistocene Colonization of North America

Quaternary ◽  
2018 ◽  
Vol 2 (1) ◽  
pp. 1 ◽  
Author(s):  
Michael O’Brien
Keyword(s):  
North America ◽  
Late Pleistocene ◽  
New World ◽  
Pacific Coast ◽  
Ice Sheets ◽  
Land Bridge ◽  
Projectile Points ◽  
Bering Land Bridge ◽  
The Pacific ◽  
Northern Half

The timing of human entrance into North America has been a topic of debate that dates back to the late 19th century. Central to the modern discussion is not whether late Pleistocene-age populations were present on the continent, but the timing of their arrival. Key to the debate is the age of tools—bone rods, large prismatic stone blades, and bifacially chipped and fluted stone weapon tips—often found associated with the remains of late Pleistocene fauna. For decades, it was assumed that this techno-complex—termed “Clovis”—was left by the first humans in North America, who, by 11,000–12,000 years ago, made their way eastward across the Bering Land Bridge, or Beringia, and then turned south through a corridor that ran between the Cordilleran and Laurentide ice sheets, which blanketed the northern half of the continent. That scenario has been challenged by more-recent archaeological and archaeogenetic data that suggest populations entered North America as much as 15,300–14,300 years ago and moved south along the Pacific Coast and/or through the ice-free corridor, which apparently was open several thousand years earlier than initially thought. Evidence indicates that Clovis might date as early as 13,400 years ago, which means that it was not the first technology in North America. Given the lack of fluted projectile points in the Old World, it appears certain that the Clovis techno-complex, or at least major components of it, emerged in the New World.

scholarly journals Amphi-Pacific tropical disjunctions in the bryophyte floras of Asia and the New World

2018 ◽  
Vol 12 (1) ◽  
Keyword(s):  
New World ◽  
Flowering Plants ◽  
Migration Route ◽  
Tropical Asia ◽  
The Pacific ◽  
Tropical America ◽  
The Pacific Ocean ◽  
Northern Atlantic ◽  
Human Introduction ◽  
Northern Atlantic Ocean

Disjunctions between tropical America and tropical Asia, commonly called amphi-Pacific tropical disjunctions, have frequently been discussed among flowering plants but have received very little attention in bryology. A screening of the literature revealed nine species and sixteen genera or infrageneric taxa of bryophytes with amphi-Pacific tropical (or subtropical) ranges. They include Austinia tenuinervis, Diphyscium chiapense, D. longiflorum, Elmerobryum, Fissidens sect. Sarawakia, Ganguleea angulosa, Hydrogonium arcuatum, Hymenostyliella, Hymenostylium aurantiacum, Luisierella barbula, Mniomalia, Rozea, Sphaerotheciella and Sorapilla among the mosses and Ceratolejeunea grandiloba, Drepanolejeunea subg. Rhaphidolejeunea, Lejeunea sect. Echinocolea, Lobatiriccardia, Myriocoleopsis sect. Myriocoleopsis, Phycolepidozia, Pictolejeunea, Rectolejeunea, Southbya organensis and Vitalianthus among liverworts. All of them occur in tropical or subtropical Asia and the Neotropics but are not known from Africa. The causes of the amphi-Pacific tropical disjunctions in bryophytes are still unclear. In flowering plants, molecular analyses indicate that amphi-Pacific tropical ranges frequently resulted from past migration across Eurasia and the northern Atlantic Ocean, followed by local extinction. This scenario may also have operated in amphi-Pacific bryophytes but some might have reached South America via the southern Pacific migration route. The possibility of direct long-range dispersal across the Pacific Ocean cannot be ruled out and this scenario seems likely for Southbya organensis, which occurs on Hawaii and freely produces spores and small gemmae. The possibility that the disjunctive ranges reflect insufficient collecting and that some taxa also occur in Africa should also be taken into account. There is no strong evidence for human introduction of amphi-Pacific tropical bryophytes. The new combinations Lejeunea sect. Echinocolea (R.M.Schust.) Gradst. comb. nov. and Myriocoleopsis sect. Protocolea (R.M.Schust.) Gradst. comb. nov. are proposed.

Projected sea-level changes in the marginal seas near China based on dynamical downscaling

2021 ◽  
pp. 1-52
Author(s):  
Yi Jin ◽  
Xuebin Zhang ◽  
John A. Church ◽  
Xianwen Bao
Keyword(s):  
Climate Change ◽  
Sea Level ◽  
Climate Models ◽  
Dynamical Downscaling ◽  
Global Climate Models ◽  
Open Boundary ◽  
Open Boundary Conditions ◽  
Sea Level Changes ◽  
Marginal Seas ◽  
The Pacific

AbstractProjections of future sea-level changes are usually based on global climate models (GCMs). However, the changes in shallow coastal regions, like the marginal seas near China, cannot be fully resolved in GCMs. To improve regional sea-level simulations, a high-resolution (~8 km) regional ocean model is set up for the marginal seas near China for both the historical (1994-2015) and future (2079-2100) periods under representative concentration pathways (RCPs) 4.5 and 8.5. The historical ocean simulations are evaluated at different spatiotemporal scales, and the model is then integrated for the future period, driven by projected monthly climatological climate change signals from 8 GCMs individually via both surface and open boundary conditions. The downscaled ocean changes derived by comparing historical and future experiments reveal greater spatial details than those from GCMs, e.g., a low dynamic sea level (DSL) centre of -0.15 m in the middle of the South China Sea (SCS). As a novel test, the downscaled results driven by the ensemble mean forcings are almost identical with the ensemble average results from individually downscaled cases. Forcing of the DSL change and increased cyclonic circulation in the SCS are dominated by the climate change signals from the Pacific, while the DSL change in the East China marginal seas is caused by both local atmosphere forcing and signals from the Pacific. The method of downscaling developed in this study is a useful modelling protocol for adaptation and mitigation planning for future oceanic climate changes.

scholarly journals A model of the methane cycle, permafrost, and hydrology of the Siberian continental margin

2015 ◽  
Vol 12 (10) ◽  
pp. 2953-2974 ◽  
Author(s):  
D. Archer
Keyword(s):  
Continental Shelf ◽  
Sea Level ◽  
Methane Hydrate ◽  
Fossil Fuel ◽  
Methane Flux ◽  
Pore Fluid ◽  
Permafrost Zone ◽  
Sediment Surface ◽  
Sediment Column ◽  
Atmospheric Flux

Abstract. A two-dimensional model of a sediment column, with Darcy fluid flow, biological and thermal methane production, and permafrost and methane hydrate formation, is subjected to glacial–interglacial cycles in sea level, alternately exposing the continental shelf to the cold atmosphere during glacial times and immersing it in the ocean in interglacial times. The glacial cycles are followed by a "long-tail" 100 kyr warming due to fossil fuel combustion. The salinity of the sediment column in the interior of the shelf can be decreased by hydrological forcing to depths well below sea level when the sediment is exposed to the atmosphere. There is no analogous advective seawater-injecting mechanism upon resubmergence, only slower diffusive mechanisms. This hydrological ratchet is consistent with the existence of freshwater beneath the sea floor on continental shelves around the world, left over from the last glacial period. The salt content of the sediment column affects the relative proportions of the solid and fluid H2O-containing phases, but in the permafrost zone the salinity in the pore fluid brine is a function of temperature only, controlled by equilibrium with ice. Ice can tolerate a higher salinity in the pore fluid than methane hydrate can at low pressure and temperature, excluding methane hydrate from thermodynamic stability in the permafrost zone. The implication is that any methane hydrate existing today will be insulated from anthropogenic climate change by hundreds of meters of sediment, resulting in a response time of thousands of years. The strongest impact of the glacial–interglacial cycles on the atmospheric methane flux is due to bubbles dissolving in the ocean when sea level is high. When sea level is low and the sediment surface is exposed to the atmosphere, the atmospheric flux is sensitive to whether permafrost inhibits bubble migration in the model. If it does, the atmospheric flux is highest during the glaciating, sea level regression (soil-freezing) part of the cycle rather than during deglacial transgression (warming and thawing). The atmospheric flux response to a warming climate is small, relative to the rest of the methane sources to the atmosphere in the global budget, because of the ongoing flooding of the continental shelf. The increased methane flux due to ocean warming could be completely counteracted by a sea level rise of tens of meters on millennial timescales due to the loss of ice sheets, decreasing the efficiency of bubble transit through the water column. The model results give no indication of a mechanism by which methane emissions from the Siberian continental shelf could have a significant impact on the near-term evolution of Earth's climate, but on millennial timescales the release of carbon from hydrate and permafrost could contribute significantly to the fossil fuel carbon burden in the atmosphere–ocean–terrestrial carbon cycle.

scholarly journals Flowing into the unknown: inferred paleodrainages for studying the ichthyofauna of Brazilian coastal rivers

2018 ◽  
Vol 16 (3) ◽  
Author(s):  
Andréa T. Thomaz ◽  
L. Lacey Knowles
Keyword(s):  
Information System ◽  
Continental Shelf ◽  
Sea Level ◽  
Brazilian Coast ◽  
Strongly Correlated ◽  
Bathymetric Data ◽  
Biological Studies ◽  
Coastal Rivers ◽  
Coastal Basins ◽  
Geologic Data

ABSTRACT The eastern coastal basins of Brazil are a series of small and isolated rivers that drain directly into the Atlantic Ocean. During the Pleistocene, sea-level retreat caused by glaciations exposed the continental shelf, resulting in enlarged paleodrainages that connected rivers that are isolated today. Using Geographic Information System (GIS), we infer the distribution of these paleodrainages, and their properties for the east Brazilian coast. Specifically, using elevation/bathymetric data for the largest sea-level retreats during the Pleistocene, the paleodrainages, their area and the number of contemporary basins connected by each palaeodrainage, was inferred. For the 145 inferred paleodrainages, total paleodrainage area is strongly correlated with the contemporary area encompassed by each paleodrainage, as well as with the number of contemporary basins encompassed by a paleodrainage. Differences in the continental shelf exposure along the coast affected the degree of past connectivity among contemporary rivers. With our results freely available, we discuss how paleodrainages have tremendous utility in biological studies, especially in regions with limited geologic data. With respect to the diverse ichthyofauna of the Brazilian coast, and its high endemism, we highlight how the inferred paleodrainages provide a backdrop to test hypotheses about the effect of past riverine connectivity on diversity patterns.

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