A chironomid-based reconstruction of summer temperatures in NW Iceland since AD 1650

Few studies currently exist that aim to validate a proxy chironomid-temperature reconstruction with instrumental temperature measurements. We used a reconstruction from a chironomid percentage abundance data set to produce quantitative summer temperature estimates since AD 1650 for NW Iceland through a transfer function approach, and validated the record against instrumental temperature measurements from Stykkishólmur in western Iceland. The core was dated through Pb-210, Cs-137 and tephra analyses (Hekla 1693) which produced a well-constrained dating model across the whole study period. Little catchment disturbance, as shown through geochemical (Itrax) and loss-on-ignition data, throughout the period further reinforce the premise that the chironomids were responding to temperature and not other catchment or within-lake variables. Particularly cold phases were identified between AD 1683–1710, AD 1765–1780 and AD 1890–1917, with relative drops in summer temperatures in the order of 1.5–2°C. The timing of these cold phases agree well with other evidence of cooler temperatures, notably increased extent of Little Ice Age (LIA) glaciers. Our evidence suggests that the magnitude of summer temperature cooling (1.5–2°C) was enough to force LIA Icelandic glaciers into their maximum Holocene extent, which is in accordance with previous modelling experiments for an Icelandic ice cap (Langjökull)

Faroe Marine Ash Zone IV: a new MIS 3 ash zone on the Faroe Islands margin

A basaltic tephra layer from MIS 3 has been discovered by analysis of cores from the Faroe Islands margin. The tephra layer appears up to 20 cm thick in some records. After the first main fall-out event the tephra is believed to be mainly deposited and redistributed by bottom currents. Geochemical analyses suggest that the tephra is relatively undisturbed by allochtonous tephra grains and unmixed. The peak occurrences are in the lower part of GIS (Greenland Interstadial) 12 and we suggest naming this new tephra Faroe Marine Ash Zone IV (FMAZ IV), following the nomenclature adopted for previous ash zones found on the Faroe Islands margin. Geochemical analyses of the tephra show affinities with the Grímsvötn volcanic system in the Eastern Volcanic Zone in south Iceland. The average age of FMAZ IV from four independent age models is 46 800±1000 years BP. We suggest that the V5 ash zone, found on the Reykjanes Ridge is a correlative to the FMAZ IV

Data for: Towards a Holocene tephrochronology for the Faroe Islands

Major element geochemistry of tephras from seven sites on the Faroe Islands, previously not published in full: A1: Hovsdalur, Suduroy; A2: Tjørnuvík, Streymoy; A3: Eidi bog, Eysturoy; A4: Mjáuvøtn, Streymoy; A5: Starvatn, Eysturoy; A6: Gróthusvatn, Sandoy; A7: Havnardalsmyren, Streymo

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

Composition and origin of ash zones from Marine Isotope Stages 3 and 2 in the North Atlantic.

The composition and distribution of four North Atlantic ash zones from the Faroe Islands margin is presented, including the widespread North Atlantic Ash Zone II (NAAZ II; 52–53 ka BP) and three mainly basaltic ash zones here referred to as the Faroe Marine Ash Zones (FMAZ) I (ca 15.4 14C ka BP), II (ca 23 14C ka BP, also referred to as the Fugloyarbanki Tephra) and III (ca 33 14C ka BP). One core from the south-east Labrador Sea was also analysed. NAAZ II was found in all investigated cores, indicating very large eruption events in the early Marine Isotope Stage (MIS) 3. Detailed investigations of NAAZ II in high-resolution cores show that two separate layers can be distinguished; a lower mixed alkalic basalt and rhyolitic layer and an upper predominantly tholeiitic basalt tephra. The main component of the basaltic FMAZ II was found in all cores from the Faroe Island margin and the Labrador Sea indicating that this tephra is the most widespread tephra from MIS 2 in the North Atlantic discovered so far. We discuss the possibility to use these tephra layers for exact correlations between marine records and land sections such as the Greenland ice-cores and terrestrial records on the European mainland

A tephra-based correlation between the Faroe Islands and the Norwegian Sea raises questions about chronological relationships during the last interglacial

Marine ash zones from the last interglacial period have been described from cores from the North Atlantic and an ash zone from the middle part of the interglacial has been observed in connection with a major cooling event. Here we present evidence for a coeval ash zone in a terrestrial site on the Faroe Islands. The investigated sediments are correlated with the upper part of oxygen isotope stage 5e and the beginning of stage 5d. The Eemian climatic optimum is represented in the lower part of the sequence close to the first occurrence of the ash zone. A tephra-based correlation suggests that the climatic optimum was synchronous with the marine record from the Norwegian Sea, but several thousand years later than in Eemian sections of west central Europe. However, many questions on the chronological relationship between the Eemian and oxygen isotope stage 5e still remain to be answered

Holocene tephra horizons at Klocka Bog, west-central Sweden: aspects of reproducibility in subarctic peat deposits

This paper presents one of the most extensive Holocene tephra records found to date in Scandinavia. Microtephra horizons originating from Icelandic eruptions were recorded in two ca. 2 m thick peat profiles at Klocka Bog in west-central Sweden. Five of the microtephra horizons were geochemically correlated to the Askja-1875, Hekla-3, Kebister, Hekla-4 and Lairg A tephras respectively. Radiocarbon-based dating of these tephras broadly agree with previously published ages from Iceland, Sweden, Germany and the British Isles. The identification of the Lairg A tephra demonstrates a more widespread distribution than previously thought, extending the usefulness of Icelandic Holocene tephrochronology further north into west-central Scandinavia. Long-lasting snow cover and seasonal wind distribution in the lower stratosphere are suggested as factors that may be responsible for fragmentary tephra deposition patterns in peat deposits of subarctic Scandinavia

Environmental changes in northern New Zealand since the Middle Holocene inferred from stable isotope records (d15N, d13C) of Lake Pupuke

Maar lakes in the Auckland Volcanic Field are important high-resolution archives of Holocene environmental change in the Southern Hemisphere mid-latitudes. Stable carbon and nitrogen isotope analyses were applied on bulk organic matter and the green alga Botryococcus from a sediment core from Lake Pupuke (Auckland, North Island, New Zealand) spanning the period since 7,165 cal. year BP. The origin of organic matter was established using total-organic-carbon-to-nitrogen ratios (TOC/TN) as well as organic carbon (delta C-13(OM)) and nitrogen (delta N-15) isotope composition of potential modern sources. This approach demonstrated that the contribution of allochthonous organic matter to the lake sediment was negligible for most of the record. The sedimentary TOC/TN ratios that are higher than Redfield ratio (i.e. > 7) are attributed to N-limiting conditions throughout the record. Variations of nitrogen and carbon isotopes during the last 7,165 years are interpreted as changes in the dominant processes in the lake. While epilimnetic primary productivity controlled isotope composition before 6,600 cal. year BP, microbial processes, especially denitrification and methane oxidation, caused overall shifts of the delta N-15 and delta C-13 values since the Mid-Holocene. Comparisons with climate reconstructions from the Northern Island suggest that changes in the wind-induced lake overturn and a shift to more pronounced seasonality were the most likely causes for lake-internal changes since 6,600 cal. year BP

Climate change and human settlement as drivers of late-Holocene vegetational change in the Faroe Islands

Changes in Faroese land surfaces during the late Holocene reflect intimate interactions between cultural and environmental development. Analyses of fossil wood, pollen and plant macrofossils indicate that the present open landscape replaced shrubby vegetation that was present from c. 6000 BC Up to c. AD 660. Conditions altered during the late Holocene, with loss of woody vegetation and increasing erosion: trends that were initiated prior to human settlement. AMS dating of sub-fossil Betula, Salix and Juniperus found buried in peat profiles from the islands of Suouroy, Sandoy, Eysturoy, Vagar and Streymoy, revealed that the islands had at least partial woody vegetation cover up to the time of continuous settlement. The settlement horizon, identified in a lacustrine sequence on the island of Eysturoy, dated to c. AD 570. It comprised pollen evidence for the cultivation of Hordeum, cultural macrofossil assemblages, charcoal fragments, diatom assemblage changes indicating lake nutrient enrichment and physical measurements showing increased sedimentation rates. The pollen record showed that heathland development was initiated prior to anthropogenic impact. The ecosystem impacts of settlement were therefore superimposed on landscape changes that began around AD 250. The earlier changes were most likely forced by increased storminess and declining atmospheric temperatures