NW Iceland Research Articles

Cooling and freshening at 8.2 ka on the NW Iceland Shelf recorded in paired δ18O and Mg/Ca measurements of the benthic foraminifer Cibicides lobatulus

A shallow marine sediment core from NW Iceland provides evidence for a brief cooling and freshening at ~8200calyr BP, consistent with the hypothesis that the catastrophic outburst flood of the proglacial lakes Oijbway and Agassiz caused the 8.2ka event. This is the first high-resolution record reconstructing near-surface temperatures and δ18Osw by paired measurements of Mg/Ca and δ18Ocalcite of a benthic foraminifer. We developed a new Mg/Ca temperature calibration for Cibicides lobatulus. Our down-core Mg/Ca derived temperature reconstruction dates the 8.2ka cooling event between ~8300calyr BP and ~8100calyr BP, which is similar to the timing and 160-yr duration recorded in the Greenland ice cores. The near-surface temperature drop of ~3 to 5°C during the 8.2ka event was accompanied by lighter δ18Osw values. Synchronously to the changes in the geochemical proxies, the percentages of two Arctic benthic foraminifers increased and the percent calcium carbonate decreased. Our record, combined with several others from the region, suggests that the freshwater outburst spread far from the source into the high-latitude North Atlantic. This freshwater input could have directly caused substantial high-latitude cooling, with reduced North Atlantic Deep Water formation amplifying the climatic impact.

Litorilinea aerophila gen. nov., sp. nov., an aerobic member of the class Caldilineae , phylum Chloroflexi , isolated from an intertidal hot spring

A thermophilic, aerobic, Gram-stain-negative, filamentous bacterium, strain PRI-4131(T), was isolated from an intertidal hot spring in Isafjardardjup, NW Iceland. The strain grew chemo-organotrophically on various carbohydrates. The temperature range for growth was 40-65 °C (optimum 55 °C), the pH range was pH 6.5-9.0 (optimum pH 7.0) and the NaCl range was 0-3 % (w/v) (optimum 0.5 %). Phylogenetic analysis based on 16S rRNA gene sequences revealed that strain PRI-4131(T) represented a distinct lineage within the class Caldilineae of the phylum http://dx.doi.org/10.1601/nm.550Chloroflexi. The highest levels of sequence similarity, about 91 %, were with Caldilinea aerophila STL-6-O1(T) and Caldilinea tarbellica D1-25-10-4(T). Fermentative growth was not observed for strain PRI-4131(T), which, in addition to other characteristics, distinguished it from the two Caldilinea species. Owing to both phylogenetic and phenotypic differences from the described members of the class Caldilineae, we propose to accommodate strain PRI-4131(T) in a novel species in a new genus, Litorilinea aerophila gen. nov., sp. nov. The type strain of Litorilinea aerophila is PRI-4131(T) ( = DSM 25763(T) = ATCC BAA-2444(T)).

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).

Pseudobranchial X-cell pseudotumors in young wild and farmed Atlantic cod Gadus morhua in Iceland

This study investigated the prevalence of pseudobranchial X-cell pseudotumors in 2 year classes of wild juvenile cod and to a lesser extent in older cod in NW Iceland. The disease was also monitored in farmed wild-caught juvenile cod. The youngest wild cod detected that had X-cell infections were 6.5 to 13.0 cm in length, with prevalence reaching a maximum level of 7%. The highest prevalence (23%) was recorded in 18.5 to 27.0 cm fish. The mean prevalence in older cod (25.0 to 76.0 cm in length) was 7% but decreased with increasing age. The mean prevalence of X-cell pseudotumors in farmed juvenile cod was < or =1% during winter rearing in land-based tanks. Higher prevalence (2 to 15%) was noted in dead and moribund fish. Diseased farmed fish were usually emaciated, and mortality due to the disease was noticeable.

The Historic Landscape of the Saga of the People of Vatnsdalur: Exploring the Saga Writer's Use of the Landscape and Archaeological Remains to Serve Political Interests

The saga of the People of Vatnsdalur (Vatnsdaelasaga) provides a case study for a new approach to the Sagas of Icelanders (Íslendingasögur). This treats the saga as a cultural product of the 13th century that can give insights into its creator's ideas and worldviews. Fieldwork at five sites in the Vatnsdalur valley in NW Iceland seeks to establish what these places were like in the 13th century. This knowledge, alongside the saga and place-name evidence, illustrates how the saga writer, presumed to come from a powerful 13th-century family, systematically used the landscape and archaeological remains in the valley to serve his political interests when describing 10th-century events.

Sea ice and marine climate variability for NW Iceland/Denmark Strait over the last 2000 cal. yr BP

MD99-2263 is a 46 cm box core collected from Djupall, a trough that cuts across the NW Iceland Shelf and ends above Denmark Strait. We provide a multiproxy record that documents changes in the regional marine climate over the last ~1700 yr. The depth/age model is based on seven calibrated radiocarbon dates on mollusk shells and on 210Pb and 137Cs. Sediment accumulation rates were variable (0.2—0.8 mm/yr) but increased dramatically ~AD 1500. Grain-size, magnetic properties, quantitative mineral composition of the &lt;2 mm sediment fraction, benthic foraminiferal composition, benthic and planktic Δ18O ratios, and abundances/fluxes of the sea ice biomarker IP25 were determined. To better compare the various proxies, 12 of the critical climate proxies were co-ordinated into 100-yr/sample time series, which were examined by Principal Component Analysis. The 1st axis explained 49% of the variance and the 2nd axis explained an additional 17%. The variables most strongly associated with the 1st axis were sediment properties (phi mean, clay%) and the sea ice biomarker. Mineralogical indicators of drift ice rafting, such as the presence of quartz and potassium- and sodium-feldspars, coincide with the IP25 biomarker data and show an increase after AD 1200, but high values of quartz and some feldspars also occurred between c. AD 300 and 900 with pronounced minima between AD 900 and 1100. Overall, our data suggest a simple two-fold division in climate conditions over the last 1700 yr, with the major change occurring c. AD 1200. In the last few decades, conditions have reverted towards those experienced prior to AD 1200.

Combined Sr isotope and trace element analysis of melt inclusions at sub-ng levels using micro-milling, TIMS and ICPMS

This paper describes a technique, which allows precise and accurate Sr isotope measurement combined with trace element analysis of individual melt inclusions, of sample sizes ≪1 ng of Sr. The technique involves sampling by micro-milling, chemical dissolution, micro Sr column chemistry, TIMS, and ICPMS analyses. A 10% aliquot of each sample solution is used for trace element analysis by double focusing magnetic sector field ICPMS, while Sr is chemically separated from the remaining 90% and used for 87Sr/86Sr determinations by TIMS.During the development of the technique outlined above, we documented in detail the potential sources of blank contributions and their magnitude. The average size and Sr isotope composition of our laboratory total procedural blank during this study was 5.4 pg±0.3 pg Sr (n=21) with an 87Sr/86Sr of 0.7111±0.0002 (2SE, n=3). The total procedural Rb blank was 1.9±0.7 pg (n=21). The total procedural blank was found to have minimal effect (<150 ppm shift) on the 87Sr/86Sr of sample material containing down to ∼250 pg Sr. Applying a blank correction allows ‘in house’ standards of this size to be corrected back to within 175 ppm of their accepted values. By applying blank corrections we can confidently measure the Sr isotope composition on sample sizes down to ∼25 pg Sr to an accuracy better than 400 ppm.The utility of the technique is illustrated by application to a suite of melt inclusions from NW Iceland and their host olivines. It is shown that the effect of a small amount of entrainment of the host olivine during sampling of 50 μm melt inclusions has a negligible effect on the measured Sr isotope and trace element composition. Furthermore, where melt inclusions are <50 μm it is possible to obtain Sr isotope and trace element data on multiple melt inclusions hosted in a single olivine. This provides similar information to that of the single melt inclusions.

Environmental controls on modern chironomid faunas from NW Iceland and implications for reconstructing climate change

Reconstructing climate change quantitatively over millennial timescales is crucial for understanding the processes that affect the climate system. One of the best methods for producing high resolution, low error, quantitative summer air temperature reconstructions is through chironomid analyses. We analysed over 50 lakes from NW and W Iceland covering a range of environmental gradients in order to test whether the distribution of the Icelandic chironomid fauna was driven by summer temperature, or whether other environmental factors were more dominant. A range of analyses showed the main environmental controls on chironomid communities to be substrate (identified through loss-on-ignition and carbon content) and mean July air temperature, although other factors such as lake depth and lake area were also important. The nature of the Icelandic landscape, with numerous volcanic centres (many of which are covered by ice caps) that produce large quantities of ash, means that relative lake carbon content and summer air temperature do not co-vary, as they often do in other chironomid datasets within the Arctic as well as more temperate environments. As the chironomid–environment relationships are thus different in Iceland compared to other chironomid training sets, we suggest that using an Icelandic model is most appropriate for reconstructing past environmental change from fossil Icelandic datasets. Analogue matching of Icelandic fossil chironomid datasets with the Icelandic training set and another European chironomid training set support this assertion. Analyses of a range of chironomid-inferred temperature transfer functions suggest the best to be a two component WA-PLS model with r2jack = 0.66 and RMSEP = 1.095°C. Using this model, chironomid-inferred temperature reconstructions of early Holocene Icelandic sequences show the magnitude of temperature change compared to contemporary temperatures to be similar to other NW European chironomid sequences, suggesting that the predictive power of the model is good.

Late Quaternary glacial and deglacial history of eastern Vestfirdir, Iceland using cosmogenic isotope (36Cl) exposure ages and marine cores

AbstractThe late glacial and deglacial history of Vestfirdir, NW Iceland is interpreted from terrestrial field‐based evidence and compared with marine cores and seismic studies. Understanding the timing of deglaciation is complicated by a lack of dateable organic material on land, uncertainties associated with interpretation of diamictons, and ambiguities in radiocarbon dating. New 36Cl exposure ages of boulders and bedrock surfaces suggest that at least part of the coastal uplands were ice‐free by approximately 20 ka. Deglaciation of the valleys followed. Boulders from the crest of an end‐moraine in the Selá river valley have a mean 36Cl age of 14.6 ka ± 0.8 ka (n = 4), and the outermost moraine in the valley adjacent to Kaldalónjökull has a mean 36Cl age of 11.7 ka ± 0.9 ka (n = 2). Tephrochronology provides a link between the terrestrial and marine sequences around Vestfirdir. The Vedde Ash (ca. 12 k cal. yr BP) is present in some offshore cores, but it is absent from terrestrial sites, suggesting that its distribution provides a constraint on ice extent during the Younger Dryas. The Saksunarvatn Ash (10.2 ± 0.6 k cal. yr BP), confirmed by geochemical analyses and radiocarbon dating, is present in at least three terrestrial locations on eastern Vestfirdir and in many cores from the fjords and shelf, which constrains early Holocene ice extent. Copyright © 2006 John Wiley &amp; Sons, Ltd.

Late Quaternary lithofacies, provenance, and depositional environments (∼12–30 cal ka), north and south of the Denmark Strait

This paper describes the lithofacies and chronology of cores from north and south of the Denmark Strait for a period when ice sheets flanked both sides of the strait. A wide range of sediments have been recovered indicating a complex of depositional processes. JM96-1229GGC1 (1047 m water depth) is from the base of the NW Iceland slope at the southern edge of the Blosseville Basin, whereas JM96-1226GGC4 retrieved sediments south of the sill in 1519 m of water. Additional information is based on JM96-1220GGC2 and 1221GGC2 which were recovered from the upper W. Iceland slope at ∼500 m water depth below the Latra Moraine, of possible Last Glacial Maximum age, and upslope of JM96-1226. AMS 14C dates indicate that JM96-1226 and -1229 span the last 10 to 27–32 ka BP whereas JM96-1220 and -1221 recovered sediments dated between ca. 8 and 18 ka BP. Closely-spaced radiocarbon dates on JM96-1229 indicate an erosional hiatus of ∼7 ky between 12 and 19 cal ka. Lithofacies descriptions are based on visual descriptions and X-radiographs. JM96-1229 consists of fine-grained sediments, sometimes graded, with scattered ice-rafted debris, whereas JM96-1226 consists largely of beds of matrix supported diamicton. Provenance indicators (mass magnetic susceptibility and geochemistry) for JM96-1229 support the delivery of sediments from NW Iceland, but there is a substantial difference in these properties between sediments from the W. Iceland upper slope and the sediments in JM96-1226 south of the Denmark Strait. This indicates that the diamictons on the floor of the strait did not derive entirely from the Iceland Ice Sheet and adjacent upper slope. The general absence of sediments <12 cal ka on the slopes and floor of the Denmark Strait indicates that Denmark Strait Overflow Waters inhibited sediment accumulation during the Holocene. Between ca. 12 and 30 cal ka, however, a combination of more proximal sediment sources (ice sheets) and reduced thermohaline activity resulted in the accumulation of sediments on the slopes and basin floors.

Efstadalsvatn – a multi-proxy study of a Holocene lacustrine sequence from NW Iceland

Multi-proxy data, both lithostratigraphic and biostratigraphic, are presented from Efstadalsvatn, a lake in NW Iceland. The sequence covers the period 10,000 to 3500 14C yr B.P. The biostratgraphic data include the first Icelandic chironomid-based reconstruction of Holocene mean July air temperatures, using a Norwegian training set in the absence of modern Icelandic data. The results show that deglaciation and ecosystem development probably began before 10,000 14C yr B.P. and that July temperatures were around 4°C at ca. 9500 14C yr B.P. Temperatures then rose to ca. 8°C at the time of the deposition of the Saksunarvatn tephra (9100 14C yr B.P.), reaching ca. 10°C by 8500 14C yr B.P., high enough for the growth of tree birch, although successful birch colonisation did not take place until 6750 14C yr B.P. There is some evidence for cooling immediately preceding 9100 14C yr B.P. There is little firm biostratigraphic evidence for the 8200 cal. B.P. event, although this may be due to a relatively low resolution pollen sampling interval, but there are changes at this time in the total carbon (TC) and mass susceptibility (MS) data. Optimal temperatures and relative vegetation stability may have occurred between 8000–6100 14C yr B.P. but the chironomid assemblages indicate higher temperatures after 5000 14C yr B.P. This latter interpretation may, however, reflect delayed colonisation of thermophilous taxa and requires further investigation. There is evidence in the lithostratigraphy for greater local terrestrial instability after 6100 14C yr B.P. but it seems unlikely that this led to the redevelopment of ice in the catchment. The biostratigraphic records appear to show a degree of resistence to climate forcing throughout the early and middle Holocene. The new chironomid-based temperature reconstruction needs to be refined by further studies in Iceland, particularly the development of an Icelandic training set, but has already demonstrated the problems of paleoclimatic interpretations based on pollen and/or macrofossil evidence alone.

Spatial distribution of otter trawl effort in Icelandic waters: comparison of measures of effort and implications for benthic community effects of trawling activities

AbstractWe examined the spatial distribution of trawling effort from logbook data from all Icelandic vessels fishing for demersal fish between 1991 and 1997 with a spatial resolution of 1 degree of latitude and 1 degree of longitude. The trawling effort was widely distributed but was intensive only in small and localised areas. Three measures of effort were compared; tow frequency, tow duration and separate estimates of swept area for otter boards and trawls. In each year, the area swept with otter trawl was 1.7 times greater than the total area in which fishing occurred over the 7 year period. In contrast, the area swept with otter boards was 4% of the total fishing area. Most of the fishing effort was confined to depths shallower than 400 m. With increasing depth, the size of trawls became larger and accordingly, also the area swept per haul. Calculations assuming no variation in the size of the trawl in relation to depth, produced inaccurate swept area estimates. Furthermore, swept area estimates based on depth corrected door spreads were greater than estimates where no such correction was made. Swept area was considered to be a more appropriate measure of effort than tow frequency and tow duration as long as variation in the size of the gear (e.g. in relation to depth) was taken into account. Effort within Icelandic waters was compared in five depth strata within seven zones. Effort was highest off the south and NW coasts and lowest off the north and east coasts. Effort was most intensive at the 100–500 m depth in all zones but in some areas (such as off NW Iceland), effort extended to deeper waters. Knowledge of the distribution of fishing effort is important for predicting larger scale effects of fishing gears on benthic communities.

Polymorphic segregation in Arctic charr Salvelinus alpinus (L.) from Vatnshlídarvatn, a shallow Icelandic lake

We studied the salmonid fish Arctic charr, Salvelinus alpinus , in a small and shallow landlocked lake in NW Iceland. The lake is productive but the only fish present is Arctic charr. Despite the apparent absence of discrete benthic and limnetic habitats for fish, two forms of Arctic charr are found in the lake. They show subtle differences in morphology related to swimming performance and manoeuvrability, but differences in life history such as growth, and age and size at sexual maturation are more pronounced. Both forms have benthic feeding habits with one form consuming greater number of species than the other. We suggest that the segregation of these forms is based on the evolution of a specialist from a local generalist and that this has been made possible by the absence of a common fish competitor in similar lakes, the threespined stickleback Gasterosteous aculeatus .

Polymorphic segregation in Arctic charr Salvelinus alpinus (L.) from Vatnshlı́darvatn, a shallow Icelandic lake

We studied the salmonid fish Arctic charr, Salvelinus alpinus, in a small and shallow landlocked lake in NW Iceland. The lake is productive but the only fish present is Arctic charr. Despite the apparent absence of discrete benthic and limnetic habitats for fish, two forms of Arctic charr are found in the lake. They show subtle differences in morphology related to swimming performance and manoeuvrability, but differences in life history such as growth, and age and size at sexual maturation are more pronounced. Both forms have benthic feeding habits with one form consuming greater number of species than the other. We suggest that the segregation of these forms is based on the evolution of a specialist from a local generalist and that this has been made possible by the absence of a common fish competitor in similar lakes, the threespined sticklebackGasterosteous aculeatus .

Petrogenesis of Silicic Rocks from the Kr ksfj rdur Central Volcano, NW Iceland

Petrogenesis of Silicic Rocks from the Kr ksfj rdur Central Volcano, NW Iceland

Resources for Long Distance Migration: Intertidal Exploitation of Littorina and Mytilus by Knots Calidris Canutus in Iceland

We investigated the resource basis and energy budget of migrating knots Calidris canutus on spring stopover in NW Iceland, where large concentrations of birds deposit extensive fuel reserves for long distance flights to high arctic breeding grounds. Prey composition was determined on the basis of crushed shell and other fragments in faecal droppings. The daily foraging time, and dropping frequency, in two main intertidal habitats - seaweed beds on rocky shores and mudflats - was monitored in relation to the tidal cycle. Main food sources were 4-15 mm periwinkles Littorina spp. (providing 147 kJ of daily gross energy intake) taken from seaweed, and 8-23 mm common mussels Mytilus edulis (134 kJ), taken from both seaweed and mud. Additional contributions obtained from mud include chironomid larvae (9 kJ), small gastropods (3 kJ) and probably also unidentified softbodied prey (about 73 kJ). Food resources at the stopover site are probably not limiting for the population of migrating knots. Estimated seasonal prey depletion rates were low, only 1-4% for Littorina, 0.5-1.7% for Mytilus and 11% for chironomid larvae. The knots' estimated daily energy intake was below the predicted limit for maximum metabolisable energy intake. Although this indicates that the knots' rate of fuel deposition probably was constrained by food availability and foraging time rather than the metabolic capacity, it could not be ruled out that the knots at least on some days reach their metabolic ceiling for energy accumulation. A combination of factors may explain why the study region offers highly favourable stopover conditions for transient knots, and why the surplus of resources are not exploited instead for breeding or winter survival by resident shorebirds: (a) macrotidal variation; (b) pronounced seasonality; (c) combined exploitation of different intertidal habitats (seaweed and mud) during different tidal phases; (d) exuberant food availability. The shore crab and limpet are absent from the study region, which may explain the unusually high Littorina densities as a result of significant release from predation and competition, respectively.

A cummingtonite-porphyritic dacite with amphibole-rich xenoliths from the tertiary central volcano at Króksfjördur, NW Iceland

An instrusive dacite and a salic pumice, emplaced late in the evolution of the Miocene (c. 10 m.y.) Króksfjördur volcano, NW Iceland, contain a varied assemblage of xenolithic metaigneous rocks. Mineral and rock chemistry shows that the dacite is very similar to calc-alkaline salic rocks from the SW Pacific. It contains phenocrystic plagioclase, quartz, pyroxene, cummingtonite, hornblende, biotite, two oxides, apatite and zircon in a rhyolitic glass. The rock equilibrated at 700 to 750°C. P ∼ 1.6 Kbar and P H 2O ∼ 1 Kbar. The xenoliths are layered gabbros, granophyres and various fine-grained hornfelses and show that the dacite magma was residing within a gabbro intrusion capped by granophyre prior to the eruption. The hornfelses are amphibole-plagioclase, amphibole-pyroxene-plagioclase and pyroxene-plagioclase rocks formed during high-temperature metamorphism of basic dykes cutting the gabbro intrusion. The gabbros and hornfelses mostly record higher metamorphic temperatures (850–940°C) than the dacite, and indicate that they were equilibrated during the ascent of a magma body into a hydrous high-level region within the volcano. During a following thermal decline, the hydrated magma cooled to form the first cummingtonite-bearing low-T magma to be recorded from the ocean ridge systems.