Quaternary Science Reviews最新文献

Climatic fingerprint of Heinrich (H) events was characterized by widespread megadroughts over the Asian summer monsoon (ASM) region accompanied by systemic weakening of the ASM. However, recent studies of hydroclimate proxies suggest huge spatial discrepancies in precipitation over the ASM region during some H events, characterized by increased precipitation in the Yangtze River Valley contrasting with the prevalent megadroughts across the whole ASM region. The mechanism responsible for the spatial discrepancies in precipitation and the relationship between local precipitation and the ASM intensity remain elusive. In this study, we investigate the response of the ASM circulation and precipitation to orbital forcing during six H events based on simulations with a coupled atmosphere-ocean general circulation model. The results show that changes in insolation alone can induce spatial discrepancies in precipitation over the ASM region during the H events. During the H1, 3, 4, 5, 6 events, the amplification of the land-sea pressure contrast in response to a positive interhemispheric insolation gradient (30°N-30°S) during boreal summer intensifies moisture transport from the adjacent oceans to the ASM region. The ensuing moisture divergence, combined with anomalous downdrafts, results in decreased precipitation in the South Asian Summer Monsoon (SASM) region, but converse scenario for the East Asian Summer Monsoon (EASM) region. During the H2 event, the increased precipitation across the Yangtze River Valley sharply contrasts the widespread drought over the ASM region, attributing to an anticyclone anomaly over the subtropical Western North Pacific and a cyclone anomaly over Japan and Korea. Moisture budget analysis shows that the dynamic effect, especially the vertical term, rather than the thermodynamic effect, is the dominant control of precipitation changes over the ASM region. Our results also suggest that despite the synchronous variation in the strength of the EASM and SASM in response to orbital forcing, the EASM should not be regarded as an eastward and northward extension of the SASM. Furthermore, our model simulates a weak correlation between the monsoon intensity and precipitation in the SASM region in response to orbital forcing, calling for caution in employing precipitation to reconstruct SASM intensity on orbital time scale.

Understanding the mechanisms behind landscape diversity changes on islands, particularly due to historical human interventions, remains a critical challenge in paleoecology. This study addresses this gap by utilizing over 160 pollen samples combined with multi-proxy data and historical records to reconstruct the late-Holocene ecological and environmental dynamics of Weizhou Island, China, over the last 1400 years. Our analyses reveal the evolution of ecosystem diversity and vegetation succession amid climatic fluctuations and anthropogenic pressures, identifying four distinct phases of transformation: (1) A warm and dry climate from 1400 to 850 cal yr BP fostering a savanna ecosystem; (2) A shift to a North subtropical seasonal rainforest under a more humid climate between 850 and 210 cal yr BP, with increased vegetation diversity; (3) The initiation of agriculture and aquaculture, along with a cooler climate from 210 cal yr BP to 1970 CE, marked by human-induced landscape alterations; and (4) A significant transformation from a once-diverse ecosystem to artificial protective forests from 1970 CE to the present. By correlating environmental indicators with historical accounts across eight Chinese dynasties, our study provides detailed insights into the climatic and human factors shaping the island's history. The findings demonstrate that while climatic shifts are primary drivers of biodiversity changes, anthropogenic disturbances also play a significant role. This research underscores the resilience of ecosystems to both climatic and human pressures and emphasizes the importance of integrating historical context into environmental studies.

Earlier reconstructions of the glacial history of the western Canadian Arctic Archipelago, commonly portrayed Banks Island as an ice-free biological refugium during the Last Glacial Maximum, ostensibly constituting the northeast extremity of Beringia. This has now been contradicted by widespread fieldwork across the northern and western coasts documenting their inundation by the northwest Laurentide Ice Sheet that extended onto the polar continental shelf. Here we report the surficial geology and deglacial sea levels across southern Banks Island completing the island-wide evidence for a pervasive ice cover during the Late Wisconsinan.

Moraines and erratics confirm the passage of an ice stream at least 1.1 km thick through Amundsen Gulf that onlapped the south coast of the island. The inland margin of the ice stream is marked by a prominent 80 km long shear moraine (Sachs moraine) that contacted thin, cold-based Laurentide ice crossing the island's interior. Subsequent thinning and retreat of the Amundsen Gulf Ice Stream from the Sachs moraine occurred in concert with its separation from topographically-confined ice lobes in the interior recorded by prominent ice-marginal meltwater channels. As the ice stream retreated offshore, a prominent kettled outwash plain was deposited along the coast marking marine limit at 20 m asl. From an unknown position offshore, the ice stream readvanced deforming the south shore of the kettled lowland marked by the 40 km long ‘Sand Hills moraine’. Based on updated field mapping, the 'Sand Hills moraine' is now recognized as the westward extension of the more widespread Jesse moraine belt.

Deglacial marine limit rises eastward across the island from 11 to 40 m asl, bordering Prince of Wales Strait. Marine limit and all lower shorelines across the island's south coast (for ∼ 200 km) are barren of marine shells. This is because sea level had regressed from marine limit to a lowstand offshore before Pacific molluscs recolonized the western Canadian Arctic at 13.7 cal ka BP, their entry occasioned by the resubmergence of Bering Strait. This requires that the breakup of the western Amundsen Gulf Ice Stream (including the M'Clure Strait Ice Stream along northern Banks Island) occurred before 14 cal ka BP, documenting that the NW Laurentide Ice Sheet must have contributed to Meltwater-Pulse-1A. Although the retreat from the outermost parts of the Jesse moraine belt also pre-date the arrival of shells, we show that the youngest (central) segment along eastern Amundsen Gulf dates to ∼12.9 cal ka BP, documenting that the Jesse moraine belt is highly time transgressive (spanning >13.7 to 12.9 cal ka BP). Radiocarbon dates on woody plants and bryophytes demonstrate that the island was biologically viable as early as 12.6 cal ka BP and that all coastlines were submergent soon afterwards and remain so today.

The importance of marine resources for the Neolithic hunter-fisher-gathers of the Pitted Ware Culture of Gotland, Sweden, is well documented through zooarchaeological analyses and diet studies of human remains. Terrestrial areas were important for living and supplementing the diet but the extent of the terrestrial territories and regions of land use for different groups is largely unknown. The presence of euryhaline species in recovered zooarchaeological assemblages indicates that freshwater fishing or fishing in the brackish estuaries of the Baltic Sea was part of the subsistence practises. To explore if the inland freshwaters of Gotland were used and, if exploited, where they were located, 18 teeth from euryhaline fish from the Pitted Ware Culture site Ajvide on Gotland were selected. The ⁸⁷Sr/⁸⁶Sr isotope ratios in the fish teeth were analysed using laser ablation-multi collector-inductively coupled plasma-mass spectrometry and correlated with an updated bioavailable baseline of Gotlandic water sources. Through this approach, the habitational origin of the fish was shown to primarily stem from at least six freshwater sources located in the west-central area of Gotland, in close relation to the site, with a few individuals originating from within the Baltic Sea. The study highlights the significance of ichthyoarchaeological analysis in understanding the territorial practice of past foraging societies and recommends further studies on euryhaline species to expand our knowledge of fish habitat, human resource utilization and land use.

On decadal, centennial, and millennial time scales, the South Asian summer monsoon (SASM) precipitation often exhibits distinct east-west or north-south dipole precipitation patterns, presenting large spatial variations in precipitation across the region. However, it remains unclear whether these spatial differences in monsoon precipitation persist over longer orbital timescales. To address this issue, we analyzed a series of equilibrium simulations using the NorESM-L model, spanning the past 425 ka, and investigated the sensitivity of precipitation to potential forcings. Our investigations, in agreement with previous studies, demonstrate that the strength of the SASM is primarily influenced by northern hemisphere summer insolation. The northward shift of the ascending core of the Hadley circulation further modulates the spatial distribution of precipitation in South Asia on the orbital timescale. In general, during periods of strong (weak) SASM associated with high (low) northern hemisphere summer insolation, the simulated precipitation in the northern part of South Asia is higher (lower) compared to the southern region. These findings align to some extent with available geological records, supporting the simulated north-south dipole precipitation pattern in South Asia. This temporal and spatial variability in precipitation within the South Asian monsoon domain highlights the complex hydrological conditions in the monsoon tropic, indicating that higher precipitation is not always accompanied by higher temperatures on the orbital timescale. These findings depart from modern understanding of synchronized precipitation and temperature patterns in the South Asian monsoon region.