| 1. |
- Li, Dongling, et al.
(författare)
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A diatom record of mid- to late Holocene palaeoenvironmental changes in the southern Okinawa Trough
- 2015
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Ingår i: Journal of Quaternary Science. - : Wiley. - 1099-1417 .- 0267-8179. ; 30:1, s. 32-43
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Tidskriftsartikel (refereegranskat)abstract
- Palaeoceanographic changes over the last 6800 years are documented in a diatom record from core MD05-2908 from the southern Okinawa Trough. Changes in diatom components are used to reflect variations in the strength of the Kuroshio Current and the influence of coastal waters, and these changes are compared with records of the East Asian summer monsoon, which exerts an important influence on regional climate and oceanography. A decreasing trend in the contribution of coastal diatoms during the last 6800 years is related to the weakening of the East Asian summer monsoon during the Holocene in response to diminishing insolation and a southward shift in the intertropical convergence zone. Relatively high abundances of the Kuroshio Current indicator species during the intervals 2600-2200 and 4800-3600 cal a BP, and lower abundances during the intervals 3200-2800 and 2200-1300 cal a BP, imply that there is no consistent weakening of the Kuroshio Current during the interval 4500-3000 cal a BP-the Pulleniatina Minimum Event, which is a widespread feature in the East China Sea and the South China Sea. A major reduction in coastal diatoms at 3200cal a BP and a slight decrease in the Kuroshio Current indicator species during the interval 3200-2800 cal a BP indicate that a palaeoceanographic shift occurred in the southern Okinawa Trough, which coincided with a Northern Hemisphere climatic cooling, denoted the Neoglaciation in Europe. In addition, changes in the freshwater species component of the record are suggested mainly to result from variations in flood frequency in north-eastern Taiwan caused by typhoons. A dramatic increase in the frequency of flood events during the last millennium may have been caused by relatively strong El Nino-Southern Oscillation activity, compared with the more stable period between 6800 and 1000 cal a BP, which experienced a low frequency of flood events.
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| 2. |
- Li, Dongling, et al.
(författare)
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East Asian Winter Monsoon Variations and Their Links to Arctic Sea Ice During the Last Millennium, Inferred From Sea Surface Temperatures in the Okinawa Trough
- 2018
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Ingår i: Paleoceanography and Paleoclimatology. - 2572-4517. ; 33:1, s. 61-75
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Tidskriftsartikel (refereegranskat)abstract
- The East Asian winter monsoon (EAWM) significantly impacts living conditions in a large part of Asia, and therefore, it is important to understand its major driving mechanisms. Winter sea surface temperature (SSTW) and circulation in the southern Okinawa Trough are today both primarily controlled by the EAWM. Here we present a new SSTW reconstruction for the last millennium based on a diatom record from sediment core MD05-2908, from the continental slope of the southern Okinawa Trough off northeastern Taiwan. Our reconstruction indicates that SSTW varied between 14.1 and 19.6°C over the past 1,000 years. Changes in SSTW in the southern Okinawa Trough correspond closely to the index of warm winters based on historical documents from the East Asian monsoon domain. This implies that our SSTW record can be used to reconstruct EAWM variability during the last millennium. Comparisons with the reconstructed winter Arctic Oscillation (AO, developed from historical snow anomaly events in Eastern Asia) and Arctic sea ice cover reveal a significant positive correlation between the EAWM and AO during the time interval from 1000–1400 Common Era (C.E.), coinciding with reduced sea ice cover. However, there is no significant correlation with increased sea ice cover during the interval from 1400 to 1700 C.E. This suggests that the reduction in Arctic sea ice may periodically have played a role in strengthening the relationship between the EAWM and the AO during the last millennium and that the current and future reduction in Arctic sea ice may have significant consequences for the EAWM.
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| 3. |
- Björck, Svante, et al.
(författare)
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Relative sea level changes and glacio-isostatic modelling in the Beagle Channel, Tierra del Fuego, Chile : glacial and tectonic implications
- 2021
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Ingår i: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791. ; 251
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Tidskriftsartikel (refereegranskat)abstract
- The Beagle Channel crosses the southernmost tip of South America (Tierra del Fuego), connecting the South Atlantic with the Southeastern Pacific. Raised beaches occur up to 10 m above mean sea level (m a.m.s.l.), especially along the northern (Argentinian) shore, and have been dated using marine shells. The southern (Chilean) shore is well-known for its abundance of shell middens at different levels above the present shore, particularly along the island of Isla Navarino, but the relative sea level history in this glacially impacted landscape has not previously been investigated. In this study we present postglacial relative sea level changes on Isla Navarino, based on sediment cores from six lagoons, bogs or lakes, and stratigraphic investigations of three open sections, of which one is of MIS 5e age. In addition, one core from a lagoon in the south-western Beagle Channel has been analysed and a system of terraces was mapped in the north-western Beagle Channel. The analyses of the core sites have resulted in two tentative relative sea level curves, displaying a rapid sea level rise at 8500−6500 cal yr BP, amounting to ∼10 and 14 m in eastern and western Isla Navarino, respectively, and reaching levels of ∼8 and > 10 m, respectively, followed by a slow relative sea level fall. Our sea level observations have been compared with a range of modelling results of glacial-isostatic adjustments (GIA) for estimating timing of deglaciation and ice sheet thicknesses. Based mainly on the GIA modelling of the altitude of the MIS 5e beach sediments, situated at 13 m, we can conclude that no other uplift than GIA is needed to explain their altitude. Regarding the modelling of postglacial sea levels we can conclude that no model has been found that satisfies all of the observational evidence, but that deglaciation most likely preceded Northern Hemisphere main deglaciation by at least 3 kyr, which agrees with the deglaciation age of Isla Navarino (>16 000 cal yr BP). In addition, our model runs imply that the Patagonian and Tierra del Fuego ice sheet thicknesses were in the order of ∼1500 m.
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| 4. |
- Sha, Longbin, et al.
(författare)
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Diatom-reconstructed summer sea-surface temperatures and climatic events off North Iceland during the last deglaciation and Holocene
- 2022
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Ingår i: Palaeogeography, Palaeoclimatology, Palaeoecology. - : Elsevier BV. - 0031-0182. ; 602
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Tidskriftsartikel (refereegranskat)abstract
- Lateglacial and Holocene summer sea-surface temperature (SST) variability in the northern North Atlantic was reconstructed based on diatom records from two sediment cores from the North Icelandic shelf. The temperature changes are discussed in relation to palaeoceanographic circulation patterns and past climatic changes. Modern diatom data from surface sediments from around Iceland and Southeast and West Greenland, with known modern environmental variables, were used as the basis for the quantitative reconstruction of summer SST. The results show that summer SSTs varied during both the Lateglacial and the Holocene, but the amplitude of SST variations during the Lateglacial was greater than that during the Holocene. No pronounced warm or cool events were recorded on the North Icelandic shelf during the GI-1e to GI-1a events (Bølling-Allerød) and the GS-1 event (Younger Dryas). The changes in SST were possibly caused by major changes in the ocean circulation pattern around Iceland, and by minor variations in the interaction between the cold and warm currents in the region. Comparison of the reconstructed summer SSTs with other marine records from the North Atlantic suggests an antiphase relationship between the oceanic climatic responses off North Iceland and in the eastern North Atlantic during the Lateglacial and the earliest part of the Holocene (the Preboreal).
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