| 1. |
- Bentley, Michael J., et al.
(författare)
-
A community-based geological reconstruction of Antarctic Ice Sheet deglaciation since the Last Glacial Maximum
- 2014
-
Ingår i: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791 .- 1873-457X. ; 100, s. 1-9
-
Tidskriftsartikel (refereegranskat)abstract
- A robust understanding of Antarctic Ice Sheet deglacial history since the Last Glacial Maximum is important in order to constrain ice sheet and glacial-isostatic adjustment models, and to explore the forcing mechanisms responsible for ice sheet retreat. Such understanding can be derived from a broad range of geological and glaciological datasets and recent decades have seen an upsurge in such data gathering around the continent and Sub-Antarctic islands. Here, we report a new synthesis of those datasets, based on an accompanying series of reviews of the geological data, organised by sector. We present a series of timeslice maps for 20 ka, 15 ka, 10 ka and 5 ka, including grounding line position and ice sheet thickness changes, along with a clear assessment of levels of confidence. The reconstruction shows that the Antarctic Ice sheet did not everywhere reach the continental shelf edge at its maximum, that initial retreat was asynchronous, and that the spatial pattern of deglaciation was highly variable, particularly on the inner shelf. The deglacial reconstruction is consistent with a moderate overall excess ice volume and with a relatively small Antarctic contribution to meltwater pulse la. We discuss key areas of uncertainty both around the continent and by time interval, and we highlight potential priorities for future work. The synthesis is intended to be a resource for the modelling and glacial geological community.
|
|
| 2. |
- Li, Chuxian, et al.
(författare)
-
Recent 210Pb, 137Cs and 241Am accumulation in an ombrotrophic peatland from Amsterdam Island (Southern Indian Ocean)
- 2017
-
Ingår i: Journal of Environmental Radioactivity. - : Elsevier BV. - 0265-931X. ; 175-176, s. 164-169
-
Tidskriftsartikel (refereegranskat)abstract
- Over the past 50 years, 210Pb, 137Cs and 241Am have been abundantly used in reconstructing recent sediment and peat chronologies. The study of global aerosol-climate interaction is also partially depending on our understanding of 222Rn-210Pb cycling, as radionuclides are useful aerosol tracers. However, in comparison with the Northern Hemisphere, few data are available for these radionuclides in the Southern Hemisphere, especially in the South Indian Ocean. A peat core was collected in an ombrotrophic peatland from the remote Amsterdam Island (AMS) and was analyzed for 210Pb, 137Cs and 241Am radionuclides using an underground ultra-low background gamma spectrometer. The 210Pb Constant Rate of Supply (CRS) model of peat accumulations is validated by peaks of artificial radionuclides (137Cs and 241Am) that are related to nuclear weapon tests. We compared the AMS 210Pb data with an updated 210Pb deposition database. The 210Pb flux of 98 ± 6 Bq·m−2·y−1 derived from the AMS core agrees with data from Madagascar and South Africa. The elevated flux observed at such a remote location may result from the enhanced 222Rn activity and frequent rainfall in AMS. This enhanced 222Rn activity itself may be explained by continental air masses passing over southern Africa and/or Madagascar. The 210Pb flux at AMS is higher than those derived from cores collected in coastal areas in Argentina and Chile, which are areas dominated by marine westerly winds with low 222Rn activities. We report a 137Cs inventory at AMS of 144 ± 13 Bq·m−2 (corrected to 1969). Our data thus contribute to the under-represented data coverage in the mid-latitudes of the Southern Hemisphere.
|
|
| 3. |
- Van der Putten, Nathalie, et al.
(författare)
-
Postglacial sedimentary and geomorphological evolution of a small sub-Antarctic fjord landscape, Stromness Bay, South Georgia
- 2013
-
Ingår i: Antarctic Science. - 1365-2079. ; 25:3, s. 409-419
-
Tidskriftsartikel (refereegranskat)abstract
- A detailed stratigraphical, palaeoecological and geomorphological reconstruction of a fjord head on South Georgia (Husvik, Stromness Bay) is presented. Six sites were chosen to reconstruct the lithostratigraphy of the area by means of coring. A maximum depth of 11m was attained and the sediments encountered vary from coarse gravel over sands to fine silts with, in some cases, intercalated peat layers. Diatom analysis allowed determination of whether the sedimentological units were deposited in a marine or freshwater environment. Six radiocarbon dates constrain the chronology. Deglaciation of the area was completed in the early Holocene and the postglacial geomorphological evolution of Husdal (unofficial name) was controlled by fluvio-deltaic deposition and sea level changes. Relative sea level rise was faster than, or kept pace with the isostatic rebound of the land. Our results challenge the presence of Late Glacial and Holocene raised beach deposits in the area as reported in earlier geomorphological studies.
|
|
| 4. |
- Björck, Svante, et al.
(författare)
-
A South Atlantic island record uncovers shifts in westerlies and hydroclimate during the last glacial
- 2019
-
Ingår i: Climate of the Past. - : Copernicus GmbH. - 1814-9324 .- 1814-9332. ; 15:6, s. 1939-1958
-
Tidskriftsartikel (refereegranskat)abstract
- Changes in the latitudinal position and strength of the Southern Hemisphere westerlies (SHW) are thought to be tightly coupled to important climate processes, such as cross-equatorial heat fluxes, Atlantic Meridional Overturning Circulation (AMOC), the bipolar seesaw, Southern Ocean ventilation and atmospheric CO2 levels. However, many uncertainties regarding magnitude, direction, and causes and effects of past SHW shifts still exist due to lack of suitable sites and scarcity of information on SHW dynamics, especially from the last glacial. Here we present a detailed hydroclimate multiproxy record from a 36.4-18.6 kyr old lake sediment sequence on Nightingale Island (NI). It is strategically located at 37ĝF S in the central South Atlantic (SA) within the SHW belt and situated just north of the marine Subtropical Front (SF). This has enabled us to assess hydroclimate changes and their link to the regional climate development as well as to large-scale climate events in polar ice cores. The NI record exhibits a continuous impact of the SHW, recording shifts in both position and strength, and between 36 and 31 ka the westerlies show high latitudinal and strength-wise variability possibly linked to the bipolar seesaw. This was followed by 4 kyr of slightly falling temperatures, decreasing humidity and fairly southerly westerlies. After 27 ka temperatures decreased 3-4 ĝC, marking the largest hydroclimate change with drier conditions and a variable SHW position. We note that periods with more intense and southerly-positioned SHW seem to be related to periods of increased CO2 outgassing from the ocean, while changes in the cross-equatorial gradient during large northern temperature changes appear as the driving mechanism for the SHW shifts. Together with coeval shifts of the South Pacific westerlies, our results show that most of the Southern Hemisphere experienced simultaneous atmospheric circulation changes during the latter part of the last glacial. Finally we can conclude that multiproxy lake records from oceanic islands have the potential to record atmospheric variability coupled to large-scale climate shifts over vast oceanic areas..
|
|
| 5. |
- Clymans, Wim, et al.
(författare)
-
The contribution of tephra constituents during biogenic silica determination : implications for soil and palaeoecological studies
- 2015
-
Ingår i: Biogeosciences. - : Copernicus GmbH. - 1726-4170 .- 1726-4189. ; 12:12, s. 3789-3804
-
Tidskriftsartikel (refereegranskat)abstract
- Biogenic silica (BSi) is used as a proxy by soil scientists to identify biological effects on the Si cycle and by palaeoecologists to study environmental changes. Alkaline extractions are typically used to measure BSi in both terrestrial and aquatic environments. The dissolution properties of volcanic glass in tephra deposits and their nanocrystalline weathering products are hypothesized to overlap those of BSi; however, data to support this behaviour are lacking. The potential that Si-bearing fractions dissolve in alkaline media (Si-Alk) that do not necessarily correspond to BSi brings the applicability of BSi as a proxy into question. Here, analysis of 15 samples reported as tephra-containing allows us to reject the hypothesis that tephra constituents produce an identical dissolution signal to that of BSi during alkaline extraction. We found that dissolution of volcanic glass shards is incomplete during alkaline dissolution. Simultaneous measurement of Al and Si used here during alkaline dissolution provides an important parameter to enable us to separate glass shard dissolution from dissolution of BSi and other Si-bearing fractions. The contribution from volcanic glass shards (between 0.2 and 4 wt % SiO2), the main constituent of distal tephra, during alkaline dissolution can be substantial depending on the total Si-Alk. Hence, soils and lake sediments with low BSi concentrations are highly sensitive to the additional dissolution from tephra constituents and its weathering products. We advise evaluation of the potential for volcanic or other non-biogenic contributions for all types of studies using BSi as an environmental proxy.
|
|
| 6. |
- Edvardsson, Johannes, et al.
(författare)
-
Late-Holocene expansion of a south Swedish peatland and its impact on marginal ecosystems: Evidence from dendrochronology, peat stratigraphy and palaeobotanical data
- 2014
-
Ingår i: The Holocene. - : SAGE Publications. - 0959-6836 .- 1477-0911. ; 24:4, s. 466-476
-
Tidskriftsartikel (refereegranskat)abstract
- In this study, a reconstruction of the long-term development and lateral expansion of a south Swedish peat bog was performed using a multi-proxy approach, including dendrochronology, peat stratigraphy and macrofossil and pollen analyses. By combining mapping of cross-dated subfossil trees with radiocarbon-dated peat sequences, an improved approach to reconstruction of lateral peat expansion was applied. Apart from providing approximate ages of tree burial episodes, the ring-width records offer information on hydrological variations prior to the bog expansion. New bog oak, pine and alder chronologies are presented and their potential as a dating tool for peatland expansion as well as for local to regional environmental interpretations is examined. Our tree-replication records show that increased amounts of bog trees in the central parts can be linked to drier bog-surface conditions, whereas an increase in wood remains in the marginal zone is related to enhanced preservation due to lateral bog expansion. Our reconstructions of the development of the peat deposit and associated changes in the distribution of vegetation communities provide new insight into peatland responses to climate change at the end of the 'Holocene Thermal Maximum' (5000-4000 cal. yr BP).
|
|
| 7. |
- Fernandez, Marilen, et al.
(författare)
-
Diatom assemblage changes in lacustrine sediments from Isla de los Estados, southernmost South America, in response to shifts in the southwesterly wind belt during the last deglaciation
- 2013
-
Ingår i: Journal of Paleolimnology. - : Springer Science and Business Media LLC. - 0921-2728 .- 1573-0417. ; 50:4, s. 433-446
-
Tidskriftsartikel (refereegranskat)abstract
- Isla de los Estados (54A degrees 45'S, 63A degrees 10'aEuro64A degrees 46'W) lies east of the main island of Tierra del Fuego and is the southeastern-most point in Argentina. Because of its geographic position near the latitudes of the Southern Hemisphere Westerlies and the strong influence of the Antarctic Circumpolar Current (ACC), the area is suitable for paleoecological and paleoclimate research. The island is not far north of the Subantarctic Front, which limits the northern boundary of the ACC. Paleoenvironmental study in this geographic location can shed light on past changes in atmospheric and marine circulation patterns. Diatom analysis of the lower part of a sediment sequence from Laguna Cascada (54A degrees 45' 51.3''S, 64A degrees 20' 20.07''W) enabled inference of changing lake conditions between 16 and 11.1 cal ka BP. Between 16 and 14.4 cal ka BP fragilarioid diatom species, often a pioneer group, dominated the record. Their presence shows seasonally open-water conditions from the onset of sedimentation. In zone II (14.4-12.8 cal ka BP), the dominance of planktonic/tychoplanktonic Aulacoseira spp. might represent longer ice-free periods and windier conditions, which would have kept this heavy species suspended in the water column. This period corresponds to the Antarctic Cold Reversal, when the Southern Hemisphere Westerlies were possibly centered on the latitudes of Tierra del Fuego, resulting in windy and wet conditions. Zone III (12.8-11.1 cal ka BP) is dominated by benthic diatom taxa that are mainly associated with peat and wetland vegetation. This suggests that climate conditions had become milder and less windy, favoring aquatic productivity and terrestrial vegetation development. This change in environmental conditions may have been a consequence of the southward movement of the Southern Hemisphere Westerlies at the start of the Antarctic Holocene thermal optimum.
|
|
| 8. |
- Hodgson, Dominic A., et al.
(författare)
-
Terrestrial and submarine evidence for the extent and timing of the Last Glacial Maximum and the onset of deglaciation on the maritime-Antarctic and sub-Antarctic islands
- 2014
-
Ingår i: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791. ; 100, s. 137-158
-
Tidskriftsartikel (refereegranskat)abstract
- This paper is the maritime and sub Antarctic contribution to the Scientific Committee for Antarctic Research (SCAR) Past Antarctic Ice Sheet Dynamics (PAIS) community Antarctic Ice Sheet reconstruction. The overarching aim for all sectors of Antarctica was to reconstruct the Last Glacial Maximum (LGM) ice sheet extent and thickness, and map the subsequent deglaciation in a series of 5000 year time slices. However, our review of the literature found surprisingly few high quality chronological constraints on changing glacier extents on these timescales in the maritime and sub Antarctic sector. Therefore, in this paper we focus on an assessment of the terrestrial and offshore evidence for the LGM ice extent, establishing minimum ages for the onset of deglaciation, and separating evidence of deglaciation from LGM limits from those associated with later Holocene glacier fluctuations. Evidence included geomorphological descriptions of glacial landscapes, radiocarbon dated basal peat and lake sediment deposits, cosmogenic isotope ages of glacial features and molecular biological data. We propose a classification of the glacial history of the maritime and sub Antarctic islands based on this assembled evidence. These include: (Type I) islands which accumulated little or no LGM ice; (Type II) islands with a limited LGM ice extent but evidence of extensive earlier continental shelf glaciations; (Type III) seamounts and volcanoes unlikely to have accumulated significant LGM ice cover; (Type IV) islands on shallow shelves with both terrestrial and submarine evidence of LGM (and/or earlier) ice expansion; (Type V) Islands north of the Antarctic Polar Front with terrestrial evidence of LGM ice expansion; and (Type VI) islands with no data. Finally, we review the climatological and geomorphological settings that separate the glaciological history of the islands within this classification scheme. (C) 2014 The Authors. Published by Elsevier Ltd. All rights reserved.
|
|
| 9. |
- Lindvall, Hanna, et al.
(författare)
-
A Holocene peat record in the central South Atlantic: an archive of precipitation changes
- 2011
-
Ingår i: GFF. - : Informa UK Limited. - 2000-0863 .- 1103-5897. ; 133:3-4, s. 195-206
-
Tidskriftsartikel (refereegranskat)abstract
- Peat deposits from the littoral part of the wetland 2nd Pond on Nightingale Island in the central South Atlantic have been analysed to investigate the Holocene climate development on the island and to test a hypothesis about regionally persistent humidity variations. A variety of proxies were analysed - total carbon and nitrogen, biogenic silica, diatoms, amount of organic matter, macrofossils and magnetic susceptibility - and together with the lithology they are interpreted as a record reflecting changes in humidity/precipitation. Early Holocene (10,000-8500 cal. BP) was possibly significantly drier than today, probably caused by a southerly displacement of the Southern Hemisphere Westerlies (SHW) during the Antarctic climate optimum. From 8500 cal. BP and onwards, the climate became generally more humid and surface run-off increased due to higher precipitation, possibly as an effect of increased influence from the SHW as it moved north. During this generally humid period, our data disclose a distinct pattern of recurrent centennial- to millennial-long events of increased precipitation and the results corroborate the only other study in the region with a similar humidity record. The events might represent large-scale climate oscillations in the Southern Hemisphere, such as latitudinal shifts of the SHW, but may also be related to changes in sea surface temperatures.
|
|
| 10. |
- Ljung, Karl, et al.
(författare)
-
The last termination in the central South Atlantic
- 2015
-
Ingår i: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791 .- 1873-457X. ; 123, s. 193-214
-
Tidskriftsartikel (refereegranskat)abstract
- Lake sediments and peat deposits from two basins on Nightingale Island (37 degrees S), in the Tristan da Cunha archipelago, South Atlantic, have been analyzed. The studies were focused on the time period 16.2-10.0 cal ka BP, determined by 36 C-14 dates from the two sequences. A wide variety of proxies were used, including pollen and diatom analyzes, biogenic silica content, C and N analyzes, stable isotopes (C-13 and N-15), elemental concentrations and magnetic susceptibility measurements, to detect environmental changes that can be related to shifts of the circulation belts of the Southern Ocean. In addition, climate model simulations were carried out. We find that the sediments are underlain by a >2 cal ka BP long hiatus, possibly representing a dried-out lake bed. The climate simulations corroborate that the area might have been exposed to arid conditions as a consequence of the Heinrich I event in the north and a southward displacement of the ITCZ. The development on the island after 16.2 cal ka BP is determined by the position of the Subtropical Front (STF) and the Southern Hemisphere Westerlies (SHW). The period 16.2-14.75 cal ka BP was characterized by varying influence from SHW and with STF situated south of Tristan da Cunha, ending with a humidity peak and cooler conditions. The stable conditions 14.7-14.1 cal ka BP with cool and fairly arid conditions imply that STF and SHW were both north of the islands during the first part of the Antarctic Cold Reversal. The most unstable period, 14.1-12.7 cal ka BP, indicates incessant latitudinal shifts of the zonal circulation, perhaps related to climate variability in the Northern Hemisphere and bipolar seesaw mechanisms as the strength of the Atlantic Meridional Overturning Circulation (AMOC) varied. At 12.7 cal ka BP the Holocene warming began with a gradually drier and warmer climate as a result of a dampened AMOC during the Younger Dryas cooling in the north with ITCZ, STF and SHW being displaced southwards. Peak warming seems to have occurred in the earliest part of the Holocene, but this period was also characterized by humidity shifts, possibly an effect of retraction and expansion phases of SHW during AMOC variations in the north. (C) 2015 Elsevier Ltd. All rights reserved.
|
|
| 11. |
- Mellström, Anette, et al.
(författare)
-
A shift towards wetter and windier conditions in southern Sweden around the prominent solar minimum 2750 cal a BP
- 2015
-
Ingår i: Journal of Quaternary Science. - : Wiley. - 1099-1417 .- 0267-8179. ; 30:3, s. 235-244
-
Tidskriftsartikel (refereegranskat)abstract
- A variety of palaeoclimatic records show a shift towards cooler, wetter and windier conditions in Europe around 2800 cal a BP. The shift broadly coincides with an increase of the atmospheric C-14 concentration, suggesting a connection between solar activity variations and climate change. Here we investigate a peat record from Undarsmosse in southern Sweden. In a previous study, based on a low-resolution chronology, this record showed increased aeolian sand influx and Sphagnum spore content around 2800 cal a BP, indicating high storm activity and wetter conditions. We applied the C-14 wiggle-match dating technique on the same record to construct a robust chronology to evaluate the temporal relationship to solar forcing. In addition, we performed plant macrofossil analysis to determine local vegetation changes. Based on the new chronology, a shift to a Sphagnum-dominated bog, representing wetter conditions, and the onset of a period with increased storminess occurred around 2700 cal a BP. These changes are, within age model uncertainties, synchronous with climatic changes inferred from other sites in Europe, suggesting a shift in the larger scale atmospheric circulation, possibly triggered by decreased solar activity.
|
|
| 12. |
- Ponel, Philippe, et al.
(författare)
-
Novel insights from coleopteran and pollen evidence into the Lateglacial/Holocene transition in Aubrac, French Massif Central
- 2016
-
Ingår i: Palaeogeography, Palaeoclimatology, Palaeoecology. - : Elsevier BV. - 0031-0182. ; 463, s. 83-102
-
Tidskriftsartikel (refereegranskat)abstract
- The aim of this study is to describe the environmental and climate changes that occurred in the mountains of Aubrac at the transition between the Lateglacial and the Holocene, from a comparative analysis of fossil Coleoptera and pollen, and a series of 23 14C dates. The changes affecting the ecological categories of Coleoptera lead to a division of the sequence into 5 beetle assemblage zones (BAZ): the lowermost BAZ A is characterized by extremely poor assemblages (periglacial environment); BAZ B (Oldest Dryas and Lateglacial Interstadial) is marked by regular occurrences of taxa associated with open environments, aquatic taxa associated with running and highly oxygenated water, and cold adapted taxa with relatively low numbers; BAZ C (Younger Dryas) corresponds to two important events: a particular abundance of cold adapted taxa and a marked decrease of running water taxa, beetles associated with herbaceous vegetation and open environments are also well represented; BAZ D (Early Holocene) corresponds to the total disappearance of cold adapted taxa; the transition BAZ C/BAZ D is marked also by a dramatic peak of running water taxa; the uppermost BAZ E (Early/Mid Holocene) is marked by a total absence of running water taxa which are replaced by standing water or taxa tolerant of a range of water conditions, a particular abundance of wetland taxa, and taxa associated with herbaceous vegetation and open environments. Beetle and pollen data suggest that the harsh climatic conditions prevailing in the Aubrac mountains did not allow warm dependent fauna and trees to establish during the Lateglacial Interstadial, at least in the Roustières region, and that wide open landscapes occupied the plateau at that time. The Older Dryas, a cold spell previously recorded at La Taphanel (Cantal), is not visible in the Roustières record, probably because of the higher altitude at Roustières, whereas the Younger Dryas is strongly expressed. During the Holocene, concordant beetles and pollen data enable to reconstruct the rapid recolonization of the plateau by mesophilous trees (Ulmus, Quercus), suggesting the possible presence of refugia to the southern slopes of the Aubrac plateau. Insect/pollen comparisons provide evidence for hydrological changes in the former lake of Roustières and suggest that lacustrine water level changes often used as indicator of precipitation regime changes should be taken with caution.
|
|
| 13. |
- Van der Putten, Nathalie, et al.
(författare)
-
Is palynology a credible climate proxy in the Subantarctic?
- 2012
-
Ingår i: The Holocene. - : SAGE Publications. - 0959-6836 .- 1477-0911. ; 22:10, s. 1113-1121
-
Tidskriftsartikel (refereegranskat)abstract
- Pollen and spore analysis is the most successfully used palaeobotanical discipline for reconstructing Holocene vegetation and climate history throughout the world. Subantarctic islands are very specific areas. They are located in the circum-Antarctic Southern Ocean in latitudes that are under strong influence of the southern westerly winds, and are characterised by a treeless, phanerogam-poor flora. Palynological research on many of these islands has resulted in diverging conclusions about how to infer climate history from pollen data. In this study we compare pollen data with macrofossil data on the one hand, and the palaeoenvironmental history based on a multiproxy record on the other hand, of two peat sequences from two different subantarctic islands, South Georgia and Île de la Possession (Îles Crozet). We conclude that palynology must be used with caution as a proxy for climate change on these islands, especially when no other proxy data are available. The upland–lowland principle, as it has been applied in pollen studies in the South Indian Ocean islands, results in erroneous conclusions about climate change on Île de la Possession. More palaeoclimatic multiproxy and pollen studies, in combination with pollen–vegetation relationship studies, can, however, contribute to a more reliable model of how to interpret pollen data in the Subantarctic. We want to stress that our conclusions are only based on Holocene records. Consequently, the question remains if palynology can be used as a palaeoclimatic proxy when climatic changes were more pronounced such as during the last glacial–interglacial transition.
|
|
| 14. |
- Van der Putten, Nathalie, et al.
(författare)
-
Subantarctic peatlands and their potential as palaeoenvironmental and palaeoclimatic archives
- 2012
-
Ingår i: Quaternary International. - : Elsevier BV. - 1873-4553 .- 1040-6182. ; 268, s. 65-76
-
Tidskriftsartikel (refereegranskat)abstract
- Subantarctic islands are located within the Antarctic Circumpolar Current and the southern westerly wind belt, the latter called Southern Westerlies, making them unique terrestrial archives to investigate past changes in oceanic and atmospheric circulation patterns in the southern mid-latitudes. The islands are characterised by a treeless, phanerogam-poor flora in which bryophytes are of major importance. Several peat-based Holocene palaeoenvironmental and palaeoclimatic studies have recently been published for South Georgia and Ile de la Possession (Iles Crozet). A range of techniques have been used in these studies, mainly plant macrofossil analysis, but also analyses of diatoms, pollen and non-pollen microfossils, geochemical and geomagnetic measurements. The records are chronologically constrained by radiocarbon dating. This paper brings together these data in order to give an overview of the Subantarctic peat-based palaeoclimatic records. A new plant macrofossil record for the island of South Georgia is added. Evidence for millennial scale Holocene climate variability was found for both islands of which the most striking one occurred in the late Holocene. However, within the uncertainty of the age/ depth models, the timing for this climate shift to wetter and/or colder conditions on South Georgia and windier/wetter conditions on Ile de la Possession is different for both islands. Ile de la Possession (Iles Crozet) seems to follow the Northern Hemisphere climate evolution as the event was dated to w2800 cal BP, a well-known climate event present in many peat-based records in north-western Europe. In contrast, the South Georgian late Holocene climate records reveal a shift around w2200e2000 cal BP
|
|
| 15. |
- Van der Putten, Nathalie, et al.
(författare)
-
The Last Termination in the South Indian Ocean: A unique terrestrial record from Kerguelen Islands (49 degrees S) situated within the Southern Hemisphere westerly belt
- 2015
-
Ingår i: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791. ; 122, s. 142-157
-
Tidskriftsartikel (refereegranskat)abstract
- The awareness of the significance of the Southern Ocean in the Earth's climate system has become increasingly obvious. The deglacial atmospheric CO2 rise during warming periods in Antarctica has been attributed to CO2 ventilation from the deep ocean caused by enhanced upwelling around the Antarctic Divergence. It has been hypothesized that, more intense Southern Hemisphere westerly winds aligned with the Antarctic Circumpolar Current due to a southward shift of the wind belt from its Last Glacial Maximum equator-ward position, are the main drivers. Reconstructions of past changes in atmospheric circulation in the Southern Hemisphere are still scarce and the overall picture is patchy with sometimes contradictory results. For obvious reasons, most terrestrial records originate from southern South America and New Zealand. Here we present a terrestrial record from the Indian sector of the Southern Ocean, from Kerguelen Islands located at 49 degrees S. A peat record is investigated using a multi-proxy approach (pollen and plant macrofossils, magnetic susceptibility, XRF analyses, biogenic silica content, Rock-Eval6 analysis and humification degree). Peat accumulation starts at about 16,000 cal yr BP with relatively warm and dry conditions. The most prominent change in our proxy data occurs at 13,600 cal yr BP, when peat ponds were established on the peat surface, resulting in lacustrine-type deposits, as a result of very high humidity, and with proxies implying very windy conditions. Within chronological uncertainties, this onset coincides with the onset of the so-called Oceanic Cold Reversal, based on the deuterium excess data in the EPICA Dome C ice core record. Kerguelen Islands are located in the moisture source area of Dome C and a change in atmospheric circulation at that time could explain both records. Around 12,900 cal yr BP, at the end of the Antarctic Cold Reversal, pond/lake sediments give way to more peaty deposits, with proxies suggesting slightly drier, less windy and probably warmer conditions. Kerguelen Islands became less influenced by the Southern Hemisphere westerly winds and these conditions were amplified during the early Holocene climate optimum as found in Antarctic ice core records. (C) 2015 Elsevier Ltd. All rights reserved.
|
|
