Stefan Wastegård

The Mjáuvøtn tephra and other Holocene tephra horizons from the Faroe Islands: a link between the Icelandic source region, the Nordic Seas, and the European continent

Six different tephra horizons were found in peat and lacustrine sediments on the Faroe Islands in the North Atlantic. Their geochemistry showed that they were of Icelandic origin. Three of these can be correlated with previously described tephra horizons from the Faroe Islands: the Saksunarvatn tephra (c. 9000 BP), the Hekla-4 (c. 3800 BP) and Hekla-Selsund (c. 3600 BP). A previously unrecorded basaltic tephra dated to c. 5700-5300 BP was found in two lacustrine successions. This horizon is named the Mjáuvøtn tephra after Mjáuvøtn Lake on the island of Streymoy. Two further tephras were recorded: the basaltic phase of the ‘Landnám’ tephra (VIIa, c. AD 870s), and the rhyolitic Tjørnuvik tephra. These were found in sediments deposited shortly after the first phase of human settlement at Tjørnuvik, which is AMS dated to AD 675-861 (calibrated age). The Faroe Islands are an important link between the volcanic sources on Iceland, and the established tephrochronological frameworks on the British Isles, Scandinavia and Germany. Their position within a sensitive region of the northeastern branch of the North Atlantic Drift make the Faroe Islands ideal for registering climate changes during the Holocene. The establishment of a modern tephrochronology may provide a tool for more precisely dating and correlating regional climate events in and around the Nordic Seas.

Extending the limits of the Borrobol Tephra to Scandinavia and detection of new early Holocene tephras

Analyses of two infilled lakes in Blekinge, southeast Sweden, indicate the presence of at least three tephra horizons of Termination 1 and early Holocene age. Geochemical analyses confirm the presence of the Borrobol Tephra, the Askja Tephra (10,000 14C yr B.P.), and one previously unreported tephra of Icelandic origin. Extending the limits of the Borrobol Tephra to Scandinavia illustrates that this ash is far more widespread than previously realized and is therefore, an important marker horizon for determining the rate and timing of the initial warming at the start of Greenland Interstade 1 (GI-1) within Europe. The relatively unknown Askja Tephra and the newly discovered Hasseldalen Tephra are stratigraphically placed at the Younger Dryas/Preboreal transition. This paper demonstrates the suitability and success associated with the extraction techniques for tracing microtephra horizons in areas distal to volcanic sources.

Extending the known distribution of the Younger Dryas Vedde Ash into northwestern Russia

The known distribution of wind-blown Vedde Ash (ca. 10.3 ka BP) has been extended to the Karelian Isthmus in northwestern Russia. This has been possible as the result of a density separation technique that separates the rhyolitic Vedde Ash shards from the minerogenic host sediment. The Vedde Ash occurs in the middle of a pollen zone with high percentages of, for example, Artemisia and Chenopodiaceae, suggesting that the Younger Dryas (or GS-I in the GRIP ice-core event stratigraphy) was cold and dry throughout its duration. This is in agreement with sites in south Sweden where the Vedde Ash also occurs in the middle of a pollen zone dominated by Artemisia, Chenopodiaceae and Cyperaceae. Copyright

Calendar year ages of three mid-Holocene tephra layers identified in varved lake sediments in west central Sweden

Three intermediate to rhyolitic Icelandic Holocene tephra horizons (Hekla-3, Kebister, and Hekla-4) have been identified in annually laminated (varved) lake sediments in the Province of Varmland, west central Sweden. Calendar year ages were obtained from varve counts and are supported by additional C-14 dating based on terrestrial plant macrofossils. The varve ages of the three tephras are 3295 +/- 95 cal. BP (Hekla-3), 4030 +/- 103 cal. BP (Kebister), and 4390 +/- 107 cal. BP (Hekla-4). The varve age of Hekla-3 refines the former calibrated 14 C age based on studies in the British Isles and Germany. Considering the age-error estimates associated with the varve chronology and calibrated C-14 ages, the ages of Kebister and Hekla-4 are in agreement with former studies. Thus, the age difference between Kebister and Hekla-4 is estimated to be ca 400 +/- 40 varve years (formally estimated to ca 200 C-14 years), between Hekla-3 and Hekla-4 to ca 1135 +/- 55 varve years (formally estimated to ca 1100 calibrated C-14 years) and between Hekla-3 and Kebister, 708 +/- 20 varve years. (Less)

Climate oscillations and tephrochronology in eastern middle Sweden during the last glacial–interglacial transition

ABSTRACT: Two sequences spanning the last glacial–interglacial transition in southern O¨ stergo¨t-land, eastern middle Sweden have been investigated for high-resolution vegetation change andtephrochronology. Organic carbon and pollen analysis indicates that the Younger Dryas–Pre-boreal climatic transition was characterised by at least one well-defined oscillation or possiblytwo shorter climatic oscillations. The Vedde Ash (ca. 12000 GRIP yr BP or ca. 10300 14 CyrBP) has been identified at both sites, significantly increasing the known distribution of thismarker horizon. In addition, a previously unrecorded rhyolitic tephra of Icelandic origin hasbeen identified at ca. 9000 14 C yr BP. The expansion of Corylus into southern O¨ stergo¨tland isestimated to be ca. 9400 14 C yr BP. Copyright 1999 John Wiley & Sons, Ltd. KEYWORDS: Preboreal oscillation; lacustrine records; Vedde Ash; last glacial–interglacial transition; expan-sion of Corylus . Introduction The last glacial–interglacial transition (15–10 k cal. yr BP)was a period characterised by a succession of rapid, extremeclimatic oscillations throughout the North Atlantic. The eventstratigraphy recently proposed by Bjo¨rck

Late warming and early cooling of the sea surface in the Nordic seas during MIS 5e (Eemian Interglacial)

Abstract Geochemical identification of a tephra layer found in two cores from the NE Atlantic Ocean and the SE Norwegian Sea, respectively, and dated to 127 ka BP has enabled us to obtain a precise correlation across the Iceland–Scotland Ridge at the Marine Isotope Stage (MIS) 6/5 transition. The direct distance between the two cores is only about 200 km . South of the Iceland–Scotland Ridge, sea surface temperatures rose abruptly at 130 ka BP at the onset of MIS 5e and at least 2–3000 years earlier than north of the ridge. Maximum sea surface temperatures south of the ridge occurred during this initial phase of MIS 5e, when temperatures in the Nordic Seas were still low. North of the ridge, the sea surface warmed rapidly at 127 ka BP. Correlations between the North Atlantic records and the Eemian of Northwest Europe tentatively indicate that the initial phase of MIS 5e correlates with the early part of the Eemian characterised by a warm, continental type of climate. The period after the warming of the Nordic seas corresponds to the slightly cooler and more oceanic middle Eemian interval in Europe. The sea surface temperatures fell gradually north of the ridge during the later part of MIS 5e and they were low during MIS 5d–5a. South of the ridge the temperatures remained relatively high. The data shows that there was no outflow of deep water from the Norwegian Sea during the later part of MIS 6. Outflow began at the MIS 6/5 transition simultaneous with the sea surface warming south of the ridge.

Different phases of the Yoldia Sea in the north-western Baltic Proper

Four sediment cores from the north-western Baltic Proper, covering the time from the Weichselian deglaciation to the present have been studied. Main interest is focused on the Yoldia stage, and especially the duration of the marine phase of this stage. The lithological compositions of the sediments and results of different analyses (magnetic, carbonate, ostracods and foraminifera) have resulted in a subdivision into five stratigraphical units (A-E, from older to younger). Unit A was deposited in a glaciolacustrine environment, probably during the first non-saline phase of the Yoldia stage. The first ingression of saline water is recorded in unit B. Brackish water ostracods and foraminifera occur exclusively in this unit, which represents the only saline phase of the Yoldia stage. This phase lasted for less than 120 clay varve years. Unit C was deposited in fresh water, probably during the last phase of the Yoldia stage and the Ancylus stage. The uppermost units, D and E are of Holocene age and represent different phases of the Litorina and Post-Litorina stages.

Recommendations for using XRF core scanning as a tool in tephrochronology

X-ray fluorescence (XRF) core scanning is a relatively new arrangement of a classic analytical technique which allows for non-destructive, in situ XRF analysis of sediment cores from submillimetre resolution upwards. In this contribution we explore the use of XRF core scanning for tephrochronology based on the analysis of three gyttja-rich sediment cores from the Faroe Islands. Using a combination of optical and radiographic images, analytical parameters and elemental profiles (Si, K, Ca, Ti, Mn, Fe, Sr and Zr), higher concentration basaltic tephra layers (>1000 shards/cm3) were positively identified. The XRF core scanning did not capture the lower concentration (<850 shards/cm3) rhyolitic layers found in the core. The elemental data generated for the detected tephra layers using XRF core scanning was not comparable to individual shard analysis by electron microprobe. We recommend using XRF core scanning for tephra screening in order to localize depths for high-resolution subsampling and to avoid depths where sediment mixing has caused tailing/mixing of the tephra signal. At the studied site the basaltic Saksunarvatn ash as well as a tephra belonging to the Askja-S/10 ka eruption were identified.

An event stratigraphy for the Last Glacial–Holocene transition in eastern middle Sweden: results from investigations of varved clay and terrestrial sequences

This paper presents an event stratigraphy for the Last Glacial-Holocene transition in eastern middle Sweden. The event stratigraphy for eastern middle Sweden comprises ten events and covers the tim ...

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

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.