New tephra horizons from Oxygen Isotope Stage 5 in the North Atlantic: correlation potential for terrestrial, marine and ice-core archives

doi:10.1016/S0277-3791(01)00055-5

Quaternary Science Reviews

Volume 20, Issue 15, 1 September 2001, Pages 1587-1593

https://doi.org/10.1016/S0277-3791(01)00055-5 Get rights and content

Abstract

Tephra horizons of Oxygen Isotope Stage (OIS) 5 age, from two cores in the North Atlantic have been analysed geochemically. The results show that several discrete tephra horizons are present, which have an Icelandic provenance. Tephras of basaltic geochemistry dominate the sequences. Correlation of the cores is based on the occurrence of a basaltic tephra near the base of OIS 5e. A rhyolitic tephra has been discovered within OIS 5e sediments in a core from the SE Norwegian Sea, which is geochemically identical to the middle Eemian tephra found in several cores from the Nordic Seas. This tephra is probably widespread and thus, the potential exists for its wider detection in terrestrial sequences on mainland Europe and the Greenland ice cores.

Introduction

Tephra horizons provide exceptional tools for correlating between geological records of different origin. For North-western Europe, this correlation has so far been achieved for the Last Glacial-Interglacial transition and the Holocene period (e.g. Haflidason et al., 1995; Birks et al., 1996; Eirı́ksson et al., 2000). Many tephra horizons of Icelandic origin are widespread around the North Atlantic and new methods to extract tephra from both minerogenic and organic deposits have increased the use of tephrochronology as a correlation tool (e.g. Dugmore and Newton, 1992; Rose et al., 1996; Turney, 1998; Caseldine et al., 1999). Time-synchronous tephra horizons make it possible to test hypotheses regarding synchronous or non-synchronous responses to climate fluctuations.

The Last Interglacial, or the Eemian (Oxygen Isotope Stage (OIS) 5e; ca. 127–115 ka BP) has usually been regarded as generally warmer and more stable than the present interglacial, the Holocene (ca. 11.5 ka BP to present). This view was first challenged when data from the GRIP ice-core suggested several high-amplitude climatic fluctuations within OIS 5e (Dansgaard et al., 1993; Johnsen et al., 1995). Cooling events during this period have also been recorded in marine cores mainly from the Nordic Seas (Cortijo et al., 1994; Fronval et al., 1998). Most European continental records, however, suggest a more stable climate during the Eemian, including the re-evaluation of the stratotype locality in the Netherlands (Cleveringa et al., 2000).

The first account of ash zones in the North Atlantic from OIS 5 was made by Sejrup et al. (1989) who described four ash zones from the interglacial OIS 11, 7, 5 and 1 in marine cores from the Iceland Plateau, southern Norwegian Sea (Fig. 1). Geochemical analyses of the ash zone correlated with OIS 5 indicated the presence of two distinct tephra peaks, with a lower peak dominated by light rhyolitic grains and the upper peak dominated by dark basaltic grains (Sjøholm et al., 1991). The ash horizons were thought to be wind-blown in the area and the distinct peaks at 10 cm intervals were interpreted as the products of two different eruptions. This pattern was confirmed by Fronval et al. (1998) who found one ash zone of OIS 5d age and two ash zones of OIS 5e age in cores from the Nordic Seas (the Norwegian and Greenland Seas; Fig. 1). Two of these zones, the early OIS 5e ash zone (ca. 129.5 ka) and the 5d ash zone (ca. 111.5 ka) were dominated by basaltic tephra, while the mid-stage 5e ash zone (ca. 125 ka) consisted of a mixture of rhyolitic and basaltic-intermediate tephra particles. This ash zone coincides with a major cooling event in the cores investigated by Fronval et al. (1998), as reflected by a minimum in reconstructed sea surface temperatures and low benthic δ¹⁸O values.

Ash layers in cores from the North Atlantic were also observed by Rasmussen et al. (1999) who tentatively correlated a rhyolitic ash layer in the middle of the Eemian section with the mid-OIS 5e ash zone of Fronval et al. (1998). However, Rasmussen et al. (1999) did not register any cold event in connection with the ash layer in these cores. A basaltic ash layer near the base of the Eemian section was also observed. Basaltic tephra layers correlated with OIS 5a, 5c and 5d have also been described from marine cores southwest of Iceland by Lacasse et al. (1998) (Fig. 1).

In this paper, we present new records of tephra horizons in marine sediments of OIS 5 age. The study is based on two cores from the Northern Atlantic Ocean, ENAM33 and MD95-2009 (Fig. 1). Only one of the recorded tephra horizons could be correlated with the ash zones described by Sjøholm et al. (1991), Fronval et al. (1998) and Haflidason et al. (2000).

Section snippets

Material and methods

Piston core ENAM33 is from the northeastern Atlantic Ocean south of the Iceland-Scotland Ridge (pos. 61°15.884′N, 11°09.654′W, water depth 1217 m) (Fig. 1). Giant piston core MD95-2009 is from the SE Norwegian Sea north of the Iceland-Scotland Ridge (pos. 62°44.250′N, 03°59.860′W, water depth 1027 m) (Fig. 1). The core sections investigated include the OIS 5 interval. The isotope stratigraphy of ENAM33 was presented by Kuijpers et al. (1998) and the isotope stratigraphy of MD95-2009 was presented

Results

Tephra-rich horizons were observed in both cores during the counting of foraminifera (Fig. 2). Only the basaltic horizon at 1692.5 cm in MD95-2009 was visible when the core was opened. The geochemistry (e.g. the SiO₂/K₂O ratio) suggests that all analysed glass shards have an Icelandic provenance. The tephra horizons found in this study have been given names in accordance with the terminology of Haflidason et al. (2000) (Table 1, Table 2, Table 3).

Discussion and conclusions

These new tephras from OIS 5 offer new possibilities for correlation between records of different origin and between marine cores from the North Atlantic. The different geochemical signatures imply that several volcanic systems were active on Iceland during OIS 5, and produced both rhyolitic and basaltic tephra. Electron microprobe analyses of single shards are therefore necessary to distinguish between different tephra horizons. This investigation also shows that volcanic activity was high

Acknowledgements

Microprobe analyses were performed at the Department of Geology and Geophysics at Edinburgh University with the support of Peter Hill. Tine Rasmussen was funded by the Carlsberg Foundation for the core studies. The microprobe analyses were funded by the Danish Natural Science Research Council under the North Atlantic Programme (Project ‘LINK’). We thank A. Kuijpers, Geological Survey of Denmark and Greenland for the samples from core ENAM33, which formed part of the EU-financed ENAM I and ENAM

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Fossil marine diatom assemblages in a sediment core from the central northern Faroe slope in the Norwegian Sea were used to reconstruct palaeoceanographic changes in the surface water mixed layer from the last ~130,000 years (Marine Isotope Stage (MIS) 6/5 transition to MIS 1 (including the Eemian and Holocene interglacials) and to compare the results with previously published results on planktic foraminifera representing the subsurface conditions of the thermocline. Diatom floras from MIS 5 of the Nordic seas have rarely been studied in detail before and never the entire period from pre-Eemian to present. The composition of diatom species together with maxima in absolute abundance of diatoms, indicate two periods of warmer sea surface temperatures correlating with the Eemian and Holocene interglacials, respectively. The Eemian differs from the Holocene in that the Iceland-Faroe Front never developed, suggesting the cold East Icelandic Current (originating from the East Greenland Current) running north of Iceland was reduced or more mixed with Atlantic water than during the Holocene and that the surface temperature and salinity gradients were weaker. The northern Faroe slope was in the early Weichselian of MIS 5d–5a mainly influenced by weaker inflow of Atlantic water and stronger influence of the East Icelandic Current and by seasonal sea-ice cover. During the later part of the Weichselian (MIS 4–MIS 2) cold conditions prevailed with extensive sea-ice cover except during the warmer interstadials. The diatom floras were more sensitive to climate changes than the planktic foraminifera and indicate longer periods with warm surface conditions, and increased influence of the warm Atlantic surface water from the Faroe Current in MIS 5, suggesting a shallower and much steeper thermocline during the transitional periods compared to today. The diatoms are good indicators for Atlantic water inflow and possible convection in the Nordic seas, not merely reflecting orbital variations in insolation as previously suggested.
Refining the Icelandic tephrachronology of the last glacial period - The deep-sea core PS2644 record from the southern Greenland Sea
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While previously the focus was on marine or terrestrial records (Fig. 1a; e.g., Björck et al., 1992; Haflidason et al., 2000; Kvamme et al., 1989; Lacasse et al., 1996; Lackschewitz and Wallrabe-Adams, 1997; Mangerud et al., 1984; Sjøholm et al., 1991), tephrachronological studies now include the Greenland ice cores (Grönvold et al., 1995; Zielinski et al., 1997; Davies et al., 2008, 2012; Abbott et al., 2012; Bourne et al., 2013), for which the volcanic sulfate records (Zielinski et al., 1996, 1997) always hinted to more frequent eruptions than known from the sediment records. Based on the Greenland ice cores and high-sedimentation rate marine cores more than 100 tephras have now been described for Marine Isotope Stage (MIS) 4 and 5 alone (Wastegard and Rasmussen, 2001; Brendryen et al., 2010; Abbott et al., 2011, 2012). For MIS 3 and 2, the FMAZ I, II, III, and IV have been identified (Rasmussen et al., 2003; Wastegard et al., 2006; Davies et al., 2012; Bourne et al., 2013, 2014; Wastegard and Rasmussen, 2014) as well as several other distinct tephra layers (Haflidason et al., 2000).
The PS2644 deep-sea core sequence, retrieved from the northwestern margin of Iceland and covering the last 86 ka, exhibits high sedimentation rates during the last glacial cycle that allow the clear distinction of Greenland stadial (GS)/interstadial (GI) cycles in the various proxy records. Abundance records of rhyolitic, basaltic and tachylytic tephra grains reveal several maxima. Tephra grains of all types were geochemically analyzed in 44 levels. A total of 92 tephras with a distinctive character have been defined within the glacial sequence of gravity core PS2644-5, whereas the Holocene record is dominated by reworked Vedde Ash grains and not suitable for tephra stratigraphic work. Of the 92 tephras only 19 geochemical populations have been linked with confidence to previously defined tephras such as from the Vedde Ash, Faeroe Marine Ash Zones (FMAZ) II and III and North Atlantic Ash Zone (NAAZ) II. For the glacial period informal names were given to 78 new tephras, most of which are basaltic tephras. Several of these layers have a unique geochemical character and might become new chronostratigraphic markers in the North Atlantic region. Linking the tephra populations to the volcanic system producing them, respectively, revealed that Icelandic eruptions dominate with 83 tephra geochemical populations and Jan Mayen with 9. Around 48% of the informal tephra layers linked to the Icelandic volcanic province are produced from either the Grimsvötn or the Veidivötn-Bardarbunga volcanic systems. The intervals spanning from Greenland Stadial (GS) 3 to Greenland Interstadial (GI) 4 (24.5–29 ka BP), from GI 8 to GS 10 (36.9–40.5 ka BP) and from GI 14 to GI 15.2 (50–56 ka BP) are the periods with the highest number of eruptions, all of which are associated with known tephra zones.
A North Atlantic tephrostratigraphical framework for 130-60kab2k: New tephra discoveries, marine-based correlations, and future challenges
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Firstly, Fronval et al. (1998), Wastegård and Rasmussen (2001), and Brendryen et al. (2010) investigated the tephra content by simply sieving the sediment into different size fractions and counting the number of glass shards within the respective size fraction. Wastegård and Rasmussen (2001) reported all shards >150 μm in size whereas Brendryen et al. (2010) counted the number of shards present within the 63–125 μm (also the component investigated by Fronval et al. (1998)) and 125–150 μm grain-size fractions. This approach has identified several tephras such as the widespread 5e-Eem/RHY-I, 5d-DO25i/RHY-I, 5a-DO21i/BAS-I–III and the 4-DO19i/BAS-I (Fig. 1).
Building chronological frameworks for proxy sequences spanning 130–60 ka b2k is plagued by difficulties and uncertainties. Recent developments in the North Atlantic region, however, affirm the potential offered by tephrochronology and specifically the search for cryptotephra. Here we review the potential offered by tephrostratigraphy for sequences spanning 130–60 ka b2k. We combine newly identified cryptotephra deposits from the NGRIP ice-core and a marine core from the Iceland Basin with previously published data from the ice and marine realms to construct the first tephrostratigraphical framework for this time-interval. Forty-three tephra or cryptotephra deposits are incorporated into this framework; twenty three tephra deposits are found in the Greenland ice-cores, including nine new NGRIP tephras, and twenty separate deposits are preserved in various North Atlantic marine sequences. Major, minor and trace element results are presented for the new NGRIP horizons together with age estimates based on their position within the ice-core record. Basaltic tephras of Icelandic origin dominate the framework with only eight tephras of rhyolitic composition found. New results from marine core MD99-2253 also illustrate some of the complexities and challenges of assessing the depositional integrity of marine cryptotephra deposits. Tephra-based correlations in the marine environment provide independent tie-points for this time-interval and highlight the potential of widening the application of tephrochronology. Further investigations, however, are required, that combine robust geochemical fingerprinting and a rigorous assessment of tephra depositional processes, in order to trace coeval events between the two depositional realms.
Re-evaluation and extension of the Marine Isotope Stage 5 tephrostratigraphy of the Faroe Islands region: The cryptotephra record
2014, Palaeogeography, Palaeoclimatology, Palaeoecology
Citation Excerpt :
This work has considerably increased the number of horizons that could act as isochronous tie-lines between MIS 5 North Atlantic marine sequences and the Greenland ice-core records. Wastegård and Rasmussen (2001) identified a series of coarse-grained tephra horizons across the sub-stages of MIS 5 within two cores from the Faroe Islands region (Table 1). Six basaltic and 3 rhyolitic horizons were identified with a basaltic horizon at the base of MIS 5e traced between the cores.
Previous studies of marine sequences from the Faroe Islands region have identified a series of coarse-grained tephra horizons deposited during Marine Isotope Stage (MIS) 5. Here we reassess the MIS 5 tephrostratigraphy of the Faroe Islands region and focus on the cryptotephra deposits preserved within the fine-grained fraction of marine core LINK 16. We also extend the record to encompass the late MIS 6 and early MIS 4 periods. A density separation technique, commonly used for tephra investigations in lacustrine settings but rarely applied to marine sediments, is utilised to explore the fine-grained material and EPMA and LA-ICP-MS are employed to determine the major and trace element composition of individual tephra shards. In total, 3 basaltic and 3 rhyolitic Icelandic cryptotephra deposits with homogeneous geochemical compositions are identified — all of which have the potential to act as isochronous tie-lines. Geochemical results highlight that the Grímsvötn volcanic system of Iceland is the predominant source of the basaltic horizons and the Öraefajökull or Torfajökull systems are the likely sources of the rhyolitic deposits. Three of the horizons have been previously recognised in Faroe Islands region marine sequences, with two of these deposits traceable into a Norwegian Sea sequence. An early MIS 4 rhyolitic horizon is the most widespread deposit as it can be traced into the Norwegian Sea and to the south into a record from the Rockall Trough. Basaltic and rhyolitic horizons deposited during late MIS 6 have not been recognised in other sequences and represent new additions to the regional tephrostratigraphy.
A detailed framework of Marine Isotope Stages 4 and 5 volcanic events recorded in two Greenland ice-cores
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Sulphate records from Greenland ice-cores indicate that Marine Isotope Stages 4 and 5 were characterised by a higher incidence of large volcanic eruptions than other periods during the last glacial period, however, few investigations have focused on tephra deposits associated with these volcanic eruptions and the nature and origin of the events. Here we present a detailed tephrochronological framework of the products of 15 volcanic events spanning this interval; the majority of which have been preserved as cryptotephra horizons within the Greenland records. The major element compositions of individual glass shards within these horizons indicate that 13 of the eruptions originated from Iceland and 6 of these events can be correlated to the specific volcanic systems of Katla, Grímsvötn, Grímsvötn-Kverkfjöll and either Reykjanes or Veidivötn-Bárdarbunga. For the remaining Icelandic horizons a source from either the rift zone or a flank zone can be suggested based on rock suite affinities. Two horizons have been correlated to a source from the Jan Mayen volcanic system which represents the first discovery of material from this system within any Greenland ice-cores. The robust geochemical characterisations, independent ages for these horizons (derived from the GICC05 ice-core chronology) and stratigraphic positions relative to the Dansgaard-Oeschger climate events recorded in the Greenland ice-cores represent a critical framework that provides new information on the frequency and nature of volcanic events occurring in the North Atlantic region during MIS 4 and 5. This framework can now be utilised in the assessment of the differential timing and rate of response to the millennial-scale climatic events that characterised this period, through the use of the tephra horizons as time-synchronous tie-lines to other palaeoclimatic sequences.
Identification of cryptotephra horizons in a North East Atlantic marine record spanning marine isotope stages 4 and 5a (∼60,000-82,000 a b2k)
2011, Quaternary International
Citation Excerpt :
Although these cryptotephra investigations have largely focused on the Late-glacial and Holocene periods, recent studies have demonstrated the considerable potential that this technique offers for earlier intervals (e.g. Wastegård et al., 2005; Veres et al., 2008; Davies et al., 2010b). In particular, tephrochronological work on North Atlantic marine and Greenland ice-core sequences spanning Marine Isotope Stages (MIS) 4 and 5a has demonstrated that many tephra horizons were deposited over the North Atlantic region throughout this period (e.g. Lacasse et al., 1998; Wastegård and Rasmussen, 2001; Rasmussen et al., 2003; Brendryen et al., 2010; Abbott et al., in press). As this interval falls beyond the limits of radiocarbon dating tephrostratigraphy may represent one of the few methods by which these records can be integrated to assess the nature, rate and timing of climatic changes during the return to glacial conditions following the last interglacial period (Eemian).
Tephrochronology is one of the few techniques that offer considerable, but as yet largely unrealised, potential for the correlation of North Atlantic palaeoclimatic archives spanning the MIS 4 and 5a substage period - a phase of pronounced global cooling during the initiation of the last glacial period. In this investigation, two previously unidentified rhyolitic tephra horizons believed to be sourced from Iceland were isolated within the giant piston core MD04-2822, retrieved from the Rockall Trough, North East Atlantic. One horizon was deposited at the beginning of Greenland Stadial 19 (∼70,150 a b2k) and the other around the cooling transition at the end of Greenland Interstadial 20 (∼75,320 a b2k). Density separation, EPMA and LA-ICP-MS techniques were utilised for the identification of these cryptotephra within the fine-fraction sediment (<80 μm diameter) to aid the discovery of primary deposits and to assess the role of mixing processes. An exploration of the geochemical homogeneity, co-variance of shard concentration with IRD and shard size distribution of the two tephra horizons rules out ice-rafting as a potential transport process and instead suggests deposition from primary airfall or via sea-ice rafting of airfall material. The latter processes would not cause a significant delay in deposition following a volcanic eruption due to more rapid transportation to depositional sites. Therefore, these horizons are potentially valuable chronostratigraphic markers for the GI-19 and GI-20 climatic events, two significant events that occurred around the transition between MIS 5a and 4.

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Rapid communicationNew tephra horizons from Oxygen Isotope Stage 5 in the North Atlantic: correlation potential for terrestrial, marine and ice-core archives

Abstract

Introduction

Section snippets

Material and methods

Results

Discussion and conclusions

Acknowledgements

Quaternary Research

Quaternary Science Reviews

Earth and Planetary Science Letters

Quaternary Research

Marine Geology

Journal of Volcanology and Geothermal Research

A rapid non–destructive scanning method for detecting distal tephra layers in peat

The Holocene

The Eemian stratotype locality at Amersfoort in the central Netherlandsa re-evaluation of old and new data

Geologie en Mijnbouw/Netherlands Journal of Geosciences

Eemian cooling in the Norwegian Sea and North Atlantic Ocean preceding continental ice-sheet growth

Nature

Evidence for general instability of past climate from a 250-kyr ice core record

Nature

Thin tephra layers in peat revealed by X-radiography

Journal of Archaeological Science

Rapid communication
New tephra horizons from Oxygen Isotope Stage 5 in the North Atlantic: correlation potential for terrestrial, marine and ice-core archives