Sediment core ER11-16 from Køge Bugt in Southeast Greenland is used to assess early Holocene palaeoceanographic changes and sediment rafting from icebergs calved from the large outlet glaciers in the ...area. Diatom analysis reconstructs variability in surface water temperature, salinity and sea-ice concentrations, and benthic foraminiferal assemblages is used to reconstruct subsurface ocean conditions. We report Holocene Thermal Maximum in Southeast Greenland during the early Holocene (at least since onset of the record 9100 cal yr BP) until around 4500 cal yr BP, which contrasts with a delay until the mid-Holocene of the Holocene Thermal Maximum in South and Southwest Greenland. The early Holocene warming in Southeast Greenland was caused by a combination of high solar insolation and a weakened subpolar gyre, both of which served to warm the Irminger Current waters subducting onto the shelf. At the same time, the surface temperature was relatively high and sea-ice cover in the polar surface waters of the East Greenland Current was relatively low. High levels of iceberg rafting occurred in Køge Bugt during the early Holocene, synchronously with these warm oceanic temperatures. This is attributed to an increase in iceberg production from the extensive, but retreating, Greenland Ice Sheet. The warm surface conditions were interrupted by a marked and short-lived increase in sea ice around 8200 years ago, providing the first evidence of this global cold episode in Southeast Greenland. After 4500 cal. yr BP, sea-ice cover increased with an expansion of the East Greenland Current, suppressing the inflow of warmer subsurface Irminger Current water to the Southeast Greenland shelf. We relate this oceanic shift to the decreased Northern Hemisphere summer solar insolation. Multi-centennial variability is observed in the grain size spectrum of iceberg rafted debris; a finding we interpret in the context of palaeoceanographic changes.
The microstructure evolutions during 1000 °C-1000 h long-term aging and relevant 800 ~ 840 °C/220 ~ 300 MPa creep behaviors of a novelly designed multiphase Ni3Al-based intermetallic alloy were ...investigated. Results showed this alloy presented excellent intermediate temperature creep properties even after 1000 °C-1000 h long-term aging. A kind of bimodal R-type γ′ rafting structures were observed in the 800 °C/220 MPa creep process of the long-term aged alloy, and the creep resistance levels of three kinds of γ′ rafting structures were evaluated to be in the order of bimodal R-type γ′ rafting structures > R-type γ′ rafting structure > N-type γ′ rafting structure. The 1000 °C-1000 h long-term aging can promote the inhomogeneous precipitation of Cr4.6MoNi2.1 phase at the edge γ′+γ dendrite area, which can play the role of pinning dislocations and inhibiting the further rafting and coarsening of the R-type γ′ rafts during creep. Differed from Ni-based alloys and other Ni3Al-based alloys, this long-term aged alloy exhibited abnormal four-stage creep characteristics, which consisted of atypical short steady-state creep stage with step fluctuant feature and atypical long accelerated creep stage with creep rate increasing at a constant rate.
Rare, long‐distance dispersal events are a key process in generating and maintaining patterns in biological diversity and species distributions across space and time. The 9.0 magnitude earthquake ...that struck the eastern coast of Japan in 2011, and the subsequent 38 m high tsunami washed large amounts of shoreline debris into the Pacific Ocean that led to a large‐scale biological rafting event carrying nearly 300 marine species to the western shores of North America. Whether oceanic, trans‐Pacific dispersal via rafting generates long distance dispersal events for small, flightless, terrestrial species is unknown. By sampling beach debris associated with known hot‐spots of tsunami debris along the north and east shores of Graham Island, Haida Gwaii, Canada, I document significantly dissimilar invertebrate communities associated with tide‐line beach debris and the occurrence of several putative Japanese species of soil‐dwelling mites (Acari: Oribatida). Previous explanations of Haida Gwaii's unique flora and fauna have been attributed to a proximity to the Beringian land bridge and the accumulated evidence of near‐offshore glacial refugia during the last glacial period. However, my research also suggests that stochastic, trans‐Pacific rafting events contribute to the biodiversity and biogeography of soil communities on the west coast of North America.
According to the Out-of-Africa theory, humans originated in Africa and from there expanded into Eurasia. Besides entering Eurasia via a terrestrial route, humans may have used sea straits. These ...routes would have shaped the subsequent expansions in Eurasia. Sea straits, in particular, are an additional option for entering Eurasia. However, the chances of sea crossings into Eurasia have not yet been quantified.
Here, we apply an agent-based model for human water crossing to quantify the crossing success for the Gibraltar Strait, the Sicily Strait, and the Bab-al-Mandab Strait during the Late Pleistocene. The environment of the model consists of geographic explicit reconstructions of the sea straits, including water temperature, current speed and direction, along with terrestrial data of resource distribution and topography. We tested five behavioral scenarios of water movement skills of Late Pleistocene modern humans in a cold phase, represented by the Last Glacial Maximum, and a warm phase, represented by the Last Interglacial.
We quantified the impact of water movement skills and climate on the crossing success by the crossing success rate (CSR). Our results show that Africa could be left via the Bab-al-Mandab Strait without specific rafting technology. At low sea level, even passive drifting was sufficient to cross the strait. In contrast, the Gibraltar- and Sicily Strait were barriers to humans without rafting technology.
Severe microplastic pollution from anthropogenic activities in coastal zones presents an imminent risk to marine ecosystems. In this study, abundant microplastics (15–12,852 items kg−1) with sizes ...ranging between 0.16 and 5.0 mm were extracted from 17 sediment samples collected in sandy beaches and mangrove wetlands of the Qinzhou Bay, Guangxi Province, Southwest China. Three types of microplastics (i.e. polystyrene, polypropylene, and polyethylene) were identified with Fourier transform infrared (FTIR) spectroscopy analysis. These detected microplastics were characterized by different colors (white, transparent, yellow, green, red, and blue) and shapes (fragment, fiber, and sphere). Microplastics were concentrated on supratidal beaches and wetlands outside of mangrove, and less abundant on intertidal beaches and inside of mangrove wetlands. Meanwhile, high microplastic concentrations were observed near mollusk farms. The spatial distribution and chemical speciation indicated that microplastics were derived from disintegration of large plastic debris (e.g., Styrofoam buoys used to support mollusk rafts) abandoned by aquaculture industry. Further, coastal vegetation (e.g. mangrove) could trap microplastic particles.
•Abundance of microplastics (15 to 12,852 items kg−1) varied in sandy beaches and mangrove wetlands.•Most microplastics (>98%) were white polystyrene in fragment shape.•Microplastics were mainly from fragmentation of styrofoam in mollusk farming.•Coastal vegetation (e.g. mangrove and trailing plant) served as traps of plastic particles.
The morphological evolution of the γ′ precipitates has been studied in a second generation nickel-based single crystal superalloy during isothermal creep straining at 1093°C under multiaxial stress ...state. For this purpose, a specific V-shaped specimen has been designed to induce an evolving multiaxial stress state along its thickness. These stress conditions are quantified by the stress triaxiality obtained using viscoplastic finite element simulations. γ channel width and γ′ rafting orientation have been analyzed along the thickness for several triaxiality values, using Rose diagrams and specifically developed image processing tools. The γ′ rafting process is shown to be highly sensitive to the sign and magnitude of the stress triaxiality. Finally, it is shown that the γ/γ′ topological inversion development is faster under compression.
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•Directional coarsening of γ′ precipitates in creep in a Ni-based SX superalloy•Impact of the stress triaxiality on the γ′ rafting morphology•Impact of the stress triaxiality on γ′ kinetics•Impact of the stress triaxiality on the γ/γ′ topological inversion kinetics.
Several late Quaternary studies have recorded cold and disturbed climates centred during the mid-first millennium AD and discussed these conditions under the term ‘Dark Ages Cold Period’ (DACP). A ...review of 114 palaeoclimate papers indicated that cold climates were common in the Northern Hemisphere between AD 400 and 765. There are also suggestions that some regions may have been relatively wet during the DACP, while those around the Mediterranean and the China/Tibetan Plateau indicate coinciding droughts. A set of environmental responses, however, indicate a delayed DACP interval (AD 509–865) postdating the actual climate signal. Previously, the DACP has been linked with the North Atlantic ice-rafting event at about 1400 years ago, while some evidence suggests an involvement of the North Atlantic Oscillation and/or El Niño–Southern Oscillation. More recently, another proposed phase of widespread cooling, the ‘Late Antique Little Ice Age’ (LALIA), overlaps with the DACP and has been tentatively linked with volcanic aerosol and solar irradiance variations reinforcing the climatic downturn since AD 536. Importantly, a higher number of proxy records extending over the first millennium AD is required for more rigorous assessments of climate variability and the forcing during these centuries and to disentangle the DACP and LALIA fingerprints in the proxy data, particularly to determine whether the DACP and the LALIA are distinct features. Also a richer network of both climate and environmental proxies is needed to evaluate the human–environment interactions, during the historical Migration Period, and thus through the DACP.
One hundred mega-boulders were tagged to survey their movements (RFID) for five winters (2012–2017) in Sainte-Luce, St. Lawrence Maritime Estuary, where the foreshore is frozen for two to four months ...per year. In addition, four boulders were fitted with accelerometers to determine the exact periods of motion. It was found that 81% of the boulders moved during at least one of the winters studied. The maximum transport recorded in one winter was 151.87 m for a 3.1 t boulder, but most boulders moved shorter distances (2012–2017 average transport: 9.74 m, standard deviation 23.71). The relationships between length/direction of boulder movements and fast-ice activity as well as weather and oceanic conditions were analyzed. 61% of mobility events took place at the end of the ice period during ice-foot break-up by storm waves or melting, but 37% took place at the beginning of the fast-ice phase during storms and/or high tide, which was unexpected. The length and direction of transport was found to depend on conditions during ice break-up (wind, waves, currents, ice thickness), which have large interannual variabilities. However, a greater proportion of boulders moved landward between 2012 and 2017. Two transport modes occurred: short pushing by ice floes and ice-rafting over longer distances. The first is much more common (70 to 90%) while the second seems to be more frequent during cold winters, when ice is thicker. Moreover, we demonstrated that the geomorphological setting exerts a strong control on boulder transport distance. The longest movements took place near mean sea level, where the ice foot is thicker and the rock platform smooth while cobble and boulder pavements inhibit movements.
•Ice pushing and ice rafting are effective at moving boulders on cold coasts.•Roughness of the shore platform (pavement, isolated boulders) can inhibit movements.•Transport occurs during short periods of winter thaw or at the end of the ice period.•Waves, tide and winds during fast-ice break-up can explain interannual variability.•Winter harshness would control the length of transport via ice thickness.
The end of the Last Glacial Maximum (LGM) dramatically reshaped temperate ecosystems, with many species moving poleward as temperatures rose and ice receded. Whereas reinvading terrestrial taxa ...tracked melting glaciers, marine biota recolonized ocean habitats freed by retreating sea ice. The extent of sea ice in the Southern Hemisphere during the LGM has, however, yet to be fully resolved, with most palaeogeographic studies suggesting only minimal or patchy ice cover in subantarctic waters. Here, through population genetic analyses of the widespread Southern Bull Kelp (Durvillaea antarctica), we present evidence for persistent ice scour affecting subantarctic islands during the LGM. Using mitochondrial and chloroplast genetic markers (COI; rbcL) to genetically characterize some 300 kelp samples from 45 Southern Ocean localities, we reveal a remarkable pattern of recent recolonization in the subantarctic. Specifically, in contrast to the marked phylogeographic structure observed across coastal New Zealand and Chile (10- to 100-km scales), subantarctic samples show striking genetic homogeneity over vast distances (10,000-km scales), with a single widespread haplotype observed for each marker. From these results, we suggest that sea ice expanded further and ice scour during the LGM impacted shallow-water subantarctic marine ecosystems more extensively than previously suggested.
Discoveries of persistent coastal species in the open ocean shift our understanding of biogeographic barriers. Floating plastic debris from pollution now supports a novel sea surface community ...composed of coastal and oceanic species at sea that might portend significant ecological shifts in the marine environment.
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