| 1. |
- Stokes, Chris R., et al.
(författare)
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On the reconstruction of palaeo-ice sheets : Recent advances and future challenges
- 2015
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Ingår i: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791 .- 1873-457X. ; 125, s. 15-49
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Forskningsöversikt (refereegranskat)abstract
- Reconstructing the growth and decay of palaeo-ice sheets is critical to understanding mechanisms of global climate change and associated sea-level fluctuations in the past, present and future. The significance of palaeo-ice sheets is further underlined by the broad range of disciplines concerned with reconstructing their behaviour, many of which have undergone a rapid expansion since the 1980s. In particular, there has been a major increase in the size and qualitative diversity of empirical data used to reconstruct and date ice sheets, and major improvements in our ability to simulate their dynamics in numerical ice sheet models. These developments have made it increasingly necessary to forge interdisciplinary links between sub-disciplines and to link numerical modelling with observations and dating of proxy records. The aim of this paper is to evaluate recent developments in the methods used to reconstruct ice sheets and outline some key challenges that remain, with an emphasis on how future work might integrate terrestrial and marine evidence together with numerical modelling. Our focus is on pan-ice sheet reconstructions of the last deglaciation, but regional case studies are used to illustrate methodological achievements, challenges and opportunities. Whilst various disciplines have made important progress in our understanding of ice-sheet dynamics, it is clear that data-model integration remains under-used, and that uncertainties remain poorly quantified in both empirically-based and numerical ice-Sheet reconstructions. The representation of past climate will continue to be the largest source of uncertainty for numerical modelling. As such, palaeo-observations are critical to constrain and validate modelling. State-of-the-art numerical models will continue to improve both in model resolution and in the breadth of inclusion of relevant processes, thereby enabling more accurate and more direct comparison with the increasing range of palaeo-observations. Thus, the capability is developing to use all relevant palaeo-records to more strongly constrain deglacial (and to a lesser extent pre-LGM) ice sheet evolution. In working towards that goal, the accurate representation of uncertainties is required for both constraint data and model outputs. Close cooperation between modelling and data-gathering communities is essential to ensure this capability is realised and continues to progress.
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| 2. |
- Jakobsson, Martin, et al.
(författare)
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Geological record of ice shelf break-up and grounding line retreat, Pine Island Bay, West Antarctica
- 2011
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Ingår i: Geology. - 0091-7613 .- 1943-2682. ; 39:7, s. 691-694
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Tidskriftsartikel (refereegranskat)abstract
- The catastrophic break-ups of the floating Larsen A and B ice shelves (Antarctica) in 1995 and 2002 and associated acceleration of glaciers that flowed into these ice shelves were among the most dramatic glaciological events observed in historical time. This raises a question about the larger West Antarctic ice shelves. Do these shelves, with their much greater glacial discharge, have a history of collapse? Here we describe features from the seafloor in Pine Island Bay, West Antarctica, which we interpret as having been formed during a massive ice shelf break-up and associated grounding line retreat. This evidence exists in the form of seafloor landforms that we argue were produced daily as a consequence of tidally influenced motion of mega-icebergs maintained upright in an iceberg armada produced from the disintegrating ice shelf and retreating grounding line. The break-up occurred prior to ca. 12 ka and was likely a response to rapid sea-level rise or ocean warming at that time.
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| 3. |
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| 4. |
- Kylander, Malin E., et al.
(författare)
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It's in your glass : a history of sea level and storminess from the Laphroaig bog, Islay (southwestern Scotland)
- 2020
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Ingår i: Boreas. - : Wiley. - 0300-9483 .- 1502-3885. ; 49:1, s. 152-167
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Tidskriftsartikel (refereegranskat)abstract
- Severe winter windstorms have become an increasingly common occurrence over recent decades in northwestern Europe. Although there exists considerable uncertainty, storminess is projected to increase in the future. On centennial to millennial time scales in particular, the mechanisms forcing storminess remain unsettled. We contribute to available palaeostorm records by reconstructing changes over the last 6670 years using a coastal peat sequence retrieved from the ombrotrophic Laphroaig bog on Islay, southwestern Scotland. We use a combination of ash content, grain size and elemental chemistry to identify periods of greater storminess, which are dated to 6605, 6290-6225, 5315-5085, 4505, 3900-3635, 3310-3130, 2920-2380, 2275-2190, 2005-1860, 1305-1090, 805-435 and 275 cal. a BP. Storm signals in the first half of the record up to similar to 3000 cal. a BP are mainly apparent in the grain-size changes. Samples from this time period also have a different elemental signature than those later in the record. We speculate that this is due to receding sea levels and the consequent establishment of a new sand source in the form of dunes, which are still present today. The most significant events and strongest winds are found during the Iron Ages Cold Epoch (2645 cal. a BP), the transition into, and in the middle of, the Roman Ages Warm Period (2235 and 1965 cal. a BP) and early in the Little Ice Age (545 cal. a BP). The Laphroaig record generally agrees with regionally relevant peat palaeostorm records from Wales and the Outer Hebrides, although the relative importance of the different storm periods is not the same. In general, stormier periods are coeval with cold periods in the region as evidenced by parallels with increased ice-rafted debris in the North Atlantic, highlighting that sea-ice conditions could impact future storminess and storm track position.
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| 5. |
- Kylander, Malin E., 1977-, et al.
(författare)
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Storm chasing : Tracking Holocene storminess in southern Sweden using mineral proxies from inland and coastal peat bogs
- 2023
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Ingår i: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791 .- 1873-457X. ; 299, s. 107854-
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Tidskriftsartikel (refereegranskat)abstract
- Severe extratropical winter storms are a recurrent feature of the European climate and cause widespread socioeconomic losses. Due to insufficient long-term data, it remains unclear whether storminess has shown a notable response to changes in external forcing over the past millennia, which impacts our ability to project future storminess in a changing climate. Reconstructing past storm variability is essential to improving our understanding of storms on these longer, missing timescales. Peat sequences from coastal ombrotrophic bogs are increasingly used for this purpose, where greater quantities of coarser grained beach sand are deposited by strong winds during storm events. Moving inland however, storm intensity decreases, as does sand availability, muting potential paleostorm signals in bogs. We circumvent these issues by taking the innovative approach of using mid-infrared (MIR) spectral data, supported by elemental information, from the inorganic fraction of Store Mosse Dune South (SMDS), a 5000-year-old sequence from a large peatland located in southern Sweden. We infer past changes in mineral composition and thereby, the grain size of the deposited material. The record is dominated by quartz, whose coarse nature was confirmed through analyses of potential local source sediments. This was supported by further mineralogical and elemental proxies of atmospheric input. Comparison of SMDS with within-bog and regionally relevant records showed that there is a difference in proxy and site response to what should be similar timing in shifts in storminess over the-100 km transect considered. We suggest the construction of regional storm stacks, built here by applying changepoint modelling to four transect sites jointly. This modelling approach has the effect of reinforcing signals in common while reducing the influence of random noise. The resulting Southern Sweden-Storm Stack dates stormier periods to 4495-4290, 3880-3790, 2885-2855, 2300-2005, 1175-1065 and 715-425 cal yr BP. By comparing with a newly constructed Western Scotland-Storm Stack and proximal dune records, we argue that regional storm stacks allow us to better compare past storminess over wider areas, gauge storm track movements and by extension, increase our understanding of the drivers of storminess on centennial to millennial timescales.
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| 6. |
- Andersson, Thommy
(författare)
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Geology of Lagoa das Furnas, a crater lake on São Miguel, Azores archipelago
- 2015
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In this thesis, the results from a geophysical mapping and coring campaign of Lagoa das Furnas are presented. Specific focus is placed on the origin of a subaqueous volcanic cone mapped in the southern part of the lake. Lagoa das Furnas is a crater lake within the Furnas volcanic centre which is located on the island of São Miguel in the Azores archipelago. The Furnas volcanic centre has a long history of earthquakes and volcanic activity. The area is relatively well-studied, except for the lake floor. Therefore, a high resolution geophysical and geological mapping survey was conducted at Lagoa das Furnas. Sidescan sonar was used to map the surface of the lake floor and single beam sonar was used to acquire sub-bottom profiles. In addition to the geophysical mapping, sediment surface sampling and core drilling were carried out followed by geochemical analyses of the retrieved material. The mapped data permitted a characterisation of the floor of Lagoa das Furnas and revealed several volcanic features including fumarole activity and a volcanic cone in the southern part of the lake. In order to unravel the origin of this cone several methods were applied, including analyses of tephra and minerals collected from the cone itself and from nearby deposits of two known eruptions Furnas I and Furnas 1630. Sedimentological, petrological, geochemical and geochronological studies of pyroclastic deposits from the cone suggest a subaqueous eruption linked to the Furnas 1630 eruption. The chemistry of glass and crystal fragments sampled from the cone suggests that it is composed of more evolved magma than that of the main Furnas 1630 implying that the lake cone is likely a product of the last eruptional phase. Historical documents reveal three lakes in Furnas valley before the 1630 eruption. Two of these lakes were lost due the eruption and the remaining lake is most likely Lagoa das Furnas and consequently did exist before the 1630 eruption.
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| 7. |
- Briner, Jason P., et al.
(författare)
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Configuration of the Scandinavian Ice Sheet in southwestern Norway during the Younger Dryas
- 2023
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Ingår i: Norwegian Journal of Geology. - 2387-5844. ; 103
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Tidskriftsartikel (refereegranskat)abstract
- The extent of the Scandinavian Ice Sheet in southwestern Norway is precisely located during the well-characterized Younger Dryas re-advance. However, the thickness of the ice sheet is less well constrained inland from the terminal position. Some exceptions include lateral moraines traced inland and up to 1000 m a.s.l. along Hardangerfjorden. Here, we apply 10Be dating in two areas: (1) bedrock and boulders in the high-relief landscapes near the Younger Dryas margin around the Bergen urban area, and (2) boulders from an upland 1600 m a.s.l. much farther (120 km) inland. We find that coastal summits ranging from ~400 to ~680 m a.s.l. and located only ~10–15 km up-flow from the ice margin, were covered by the Scandinavian Ice Sheet during the Younger Dryas. The scatter in the 10Be age population of 22 boulder samples is best explained by isotopic inheritance owing to inefficient subglacial erosion during the foregoing glaciation. Most of the 11 bedrock samples also exhibit inheritance, pointing to the source of inheritance in boulders and implying inefficient subglacial erosion during the last glaciation even in valley-bottoms near Bergen. Regional glacial striae compilations suggest that ice flow during maximum Younger Dryas ice-sheet configurations was for the most part cross-valley, with potentially low basal slip rates. Five new 10Be ages from the inland site help to constrain ice height far inland. We combine these new results with prior information to generate a cross profile of the Younger Dryas ice sheet in southern Norway.
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| 8. |
- Chabangborn, Akkaneewut, 1977-
(författare)
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The Asian monsoon - 50-7 ka BP
- 2012
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The Asian monsoon is one of the largest climatic systems on Earth. It covers an area from the Arabian Sea to the South China Sea and from northern Australia to northern China with the world’s highest population density. Moreover, the Asian monsoon transports heat energy and humidity to higher latitudes. In order to better understand the behaviour of the Asian monsoon and its environmental impact, its variability between 50 and 7 ka BP is analysed using paleo-data compilation, data-model comparisons, and lake sediment analysis. The main results presented here are from the compilation of the Asian monsoon variability during the last glacial maximum (LGM) (23 - 19 ka BP) which is presumed to be under persistence cool and dry climatic conditions. The pattern of reconstructed and simulated precipitation agrees well in most of the region. However, the data-model discrepancies show in some areas, which may come from low resolution of the model or the local topographic effect. The reconstructed SSTs are well correlation with simulated SSTs, except in the Arabian Sea. The LGM Asian monsoon changes around 20 – 19 ka BP. The simulated ITCZ varies between 5°N and 15°N in the west and the east of the Asian monsoon region. However, the reconstructed ITCZ is ~5°N in the Arabian Sea, shifts northward in the Bay of Bengal, reaches ~30°N over central of China and migrates southward in the South China Sea. The ITCZ is likely shift northward after 20 ka BP. The climatic change might have been triggered by several factors, e.g., an increased land-sea thermal contrast and a variation of Pacific water inflow.
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| 9. |
- Chiu, Pin-Yao, et al.
(författare)
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New constraints on Arctic Ocean Mn stratigraphy from radiocarbon dating on planktonic foraminifera
- 2017
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Ingår i: Quaternary International. - : Elsevier BV. - 1040-6182 .- 1873-4553. ; 447, s. 13-26
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Tidskriftsartikel (refereegranskat)abstract
- Variations in the abundance of manganese (Mn) in Arctic Ocean sediments are used as a tool to identify glacial and interglacial periods. This study aims to provide new insight into the applicability of Mn as a stratigraphic tool in the topmost sediment and to investigate the occurrence of Mn peaks in sediments within the range of radiocarbon dating. In combination with variations in ice-rafted debris (IRD), radiocarbon dating is used to better constrain the stratigraphic occurrence of Mn peaks, and the synchroneity between multiple records, especially during the late glacial and the Holocene. We find that a hiatus spanning MIS 2 is widely observed in most of our cores, resulting in a merging of Mn peaks of Holocene age and the later part of MIS 3. The Holocene Mn peak is usually high amplitude but short, while the MIS 3 Mn peak has a lower amplitude and is protracted. Where preserved, MIS 2 sediments form a 2-3 cm thick layer characterized by a light color, low Mn content, sparse IRD and low foraminiferal abundance. IRD variations provide a powerful tool to identify the boundary of the Holocene and late MIS 3 in cores with a MIS 2 hiatus. Because the IRD content displays a general increment from the start of MIS 3, and both the Holocene and MIS 2 show small IRD variations, the end of MIS 3 can be pinpointed to the point of decrease in IRD. The hiatus of MIS 2 is widely observed in our cores, suggesting extensive persistent sea ice coverage during the peak of the last glacial cycle, with sharply reduced sedimentation throughout the Arctic Ocean. Identifying similar events during previous glacial periods may be an important step towards constructing longer and more accurate chronologies for Arctic Ocean sediments.
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| 10. |
- Erbs-Hansen, Dorthe Reng, et al.
(författare)
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Holocene climatic development in Skagerrak, eastern North Atlantic : Foraminiferal and stable isotopic evidence
- 2012
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Ingår i: The Holocene. - : SAGE Publications. - 0959-6836 .- 1477-0911. ; 22:3, s. 301-312
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Tidskriftsartikel (refereegranskat)abstract
- A high-resolution multiproxy study of core MD99-2286 reveals a highly variable hydrographic environment in the Skagerrak from 9300 cal. yr BP to the present. The study includes foraminiferal faunas, stable isotopes and sedimentary parameters, as well as temperature and salinity reconstructions of a c. 29 m long radiocarbon-dated core record. The multivariate technique fuzzy c-means was applied to the foraminiferal counts, and it was extremely valuable in defining subtle heterogeneities in the foraminiferal faunal data corresponding to hydrographic changes. The major early-/mid-Holocene (Littorina) transgression led to flooding of large former land areas in the North Sea, the opening of the English Channel and Danish straits, and initiation of the modern circulation system. This is reflected by fluctuating C/N values and an explosive bloom of Hyalinea balthica. A slight indication of ameliorated conditions between 8000 and 5750 cal. yr BP is related to the Holocene Thermal Maximum. A subsequent increase in freshwater/Baltic water influence between 5750 and 4350 cal. yr BP is reflected by dominance of Bulimina marginata and depleted delta O-18 values. The Neoglacial cooling (after 4350 cal. yr BP) is seen in the Skagerrak as enhanced turbidity, increasing TOC values and short-term changes in an overall Cassidulina laevigata-dominated fauna suggesting a prevailing influence of Atlantic waters. This is in agreement with increased strength of westerly winds, as recorded for this period. The last 2000 years were also dominated by Atlantic Water conditions with generally abundant nutrient supply. However, during warm periods, particularly the 'Medieval Warm Period'and the modern warming, the area was subject to a restriction in the supply of nutrients and/or the nutrient supply had a more refractory character.
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