Western Iceland Research Articles

Wood and Plant-use in 17th–19th Century Iceland: Archaeobotanical Analysis of Reykholt, Western Iceland

As part of a multidisciplinary investigation of post-medieval Icelandic land and plant use practices, archaeobotanical samples were collected from Reykholt, west Iceland in 1988 and 1989. Analyses included plant macrofossils (seeds and leaves) and wood identification from excavated rooms in a 17th century farm house. In conjunction with earlier palaeoentomological studies, the functions of three different excavated rooms are inferred. Archaeobotanical results suggest that the farm was a prosperous one, with imported foodstuffs and wood implements from continental Europe.

The importance of natal dispersal in a colonial seabird, the Black Guillemot Cepphus grylle

We studied inter-colony natal dispersal in a metapopulation of Black Guillemots Cepphus grylle in the Breidafjordur area in western Iceland 1995-97. About 9000 chicks had beer ringed in a large central colony (Flatey) over the previous 20 years, and by capturing breeding adults in other colonies we collected evidence of emigration from this colony We also included data collected since 1975 on immigration to Flatey from neighbouring colonies. The proportion of Flatey-ringed chicks decreased with distance from the colony, the longest documented dispersal distance was 10.5 km. Over the years, 33 immigrants to Flatey were found, but indirect evidence suggested that about 50% of all breeders on Flatey were immigrants. A Leslie matrix model showed that observed local demographic parameters from the Flatey colony predicted a 7% yearly decline in population size, in contrast to the observed stability. The discrepancy could be resolved by increasing immature survival to account for immigration. Population stability was achieved by assuming 63% of all recruits to be immigrants. Our results support the growing awareness that inter-colony exchanges of immatures are much more important for seabird population dynamics than previously believed.

Adult Survival of the Black Guillemot in Iceland

We studied adult survival of the Black Guillemot (Cepphus grylle) based on a capture-recapture data set collected in 1974-1995 in a colony in western Iceland. A total of 1,483 individuals were observed once or more as breeders; some of these were local or immigrant recruits. There was no evidence that adult survival varied over time; the estimated constant survival was 0.870 (95% confidence limits 0.855-0.884). This was similar to previous estimates for this species, but precision was very high. Because many guillemots drowned in fishing nets near our study site, we attempted to model survival as a function of local fishery effort; we were unable to do this because of excessive variation in capture effort. The final model also included a separate survival estimate for the first year after the first capture as breeder. This apparent first-year survival declined over time from 0.900 to 0.562. Both the lower apparent first-year survival and the negative trend were likely due to the presence of low-capturability individuals in the data set. We suggest that some birds were very difficult to capture because their nests were in shorebird or tern territories. The lower adult survival of Black Guillemots compared to other Atlantic alcids (murres, puffins) is presumably related to their inshore feeding habits, which also allow this species to raise two chicks to fledging.

An attempt to determine the absolute geomagnetic field intensity in Southwestern Iceland during the Gauss–Matuyama reversal

We have measured the variation in the intensity of the geomagnetic field during the Gauss–Matuyama (N4–R3) polarity reversal by application of the Thelliers' method to specimens of lava flows from Hvalfjördur district in Western Iceland (Reynivallahals Mts.). Eleven lava flows all show very similar directions corresponding to an equatorial VGP (Plat=2.9°N, Plong=81.9°E, A 95=4.2, K=119). Twenty-nine specimens from nine of the flows were pre-selected for palaeointensity determination on the basis that specimens from the same drill cores showed a single component of magnetisation upon thermal or AF demagnetisation, and possessed low magnetic viscosity and reversible susceptibility curves upon heating at 600–650°C. Observation that the directional data obtained in the course of the palaeointensity experiments occasionally showed substantial non-linearity indicates that a significant chemical remanent magnetization (CRM) can be acquired in the direction of the laboratory field during heating at T. For each double heating step we calculated the ratio of CRM( T) to the magnitude of the natural remanent magnetization (NRM( T)) in the direction of characteristic remanence (obtained independently from another specimen from the same core). When this ratio exceeded 15%, the paleointensity data was rejected. In addition, specimens for which the quality factor was less than 5 were rejected. Twelve reliable palaeointensity values were obtained from specimens representing five lava flows. The results confirm that the palaeointensity was substantially reduced during the N4–R3 reversal. The range of mean palaeointensity values obtained for the five flows is 8.8 to 20.5 and the overall mean is 14.8±4.6 μT. This corresponds to an equivalent VDM of 3.81±1.19 (10 22 A m 2). A comparison of all Thellier palaeointensity data from the R3 magnetozone in the Rayinivallahals Mts. area reveals a progressive although irregular increase in the palaeointensity between the Gauss–Matuyama and Matuyama–Réunion reversals. This trend is opposite to that expected from the saw tooth model of palaeointensity variations.

Secular variation and reversals in a composite 2.5 km thick lava section in central Western Iceland

The direction and intensity of primary remanence has been measured in oriented specimens from 367 lava flows of Late Miocene age in Western Iceland. The lavas which were sampled in 8 overlapping profiles, were generally good material for paleomagnetic measurements. In a 2500-m composite section, at least 15 reversals of polarity and several excursions are recorded. The mean remanence direction and other overall paleomagnetic parameters for the present collection of lavas are similar to those found elsewhere in Iceland. The average rate of buildup of this lava pile was rather low and possibly episodic. Hence, correlations to the geomagnetic polarity time scale and to polarity patterns in other composite sections mapped in Iceland are not straightforward.

Icelandic Photography 1846–1946

In the summer of 1840, Helgi Sigurosson (1815–88) went as a student to Copenhagen, capital of Denmark, and thus also of Iceland, which was then a Danish colony.1 He can hardly have imagined then that he would become a pioneer of photography in Iceland. Daguerre's invention was already well known in Denmark, and photographers were active in the larger Danish cities, although photography had not yet become established in the Danish colonies. Helgi studied law and medicine at the University of Copenhagen. These studies did not apparently fulfIl Helgi's wishes, as he studied art at the same time at the Royal Academy of Art in Copenhagen in 1942–44,2 Following this, at the end of his studies in Copenhagen, he learned to take daguerreotypes, probably from a Genrman photographer and portrait painter, Gustaf Adolph Schätzig, who worked in Copenhagen.3 This choice of study indicates the link that existed between photography and art in the early days of photography. Helgi returned home to Iceland in 1846 without graduating, and settled on his father's farm in western Iceland. In 1850 he took over the farm, and he subsequently took holy orders. Sources on Helgi's photography are meagre, so little can be said of how much photography he did. His photographic collection was sent to his son in Canada after his death.4

High-resolution Seismic Evidence for Multiple Glaciation across the Southwest Iceland Shelf

Geophysical and lithological data collected from the southwest margin of Iceland provide clear evidence of multiple glaciations across the shelf, many of which reached the shelf-slope break. These paleo-ice sheets delivered much glacial sediment to the slope facing Denmark Strait. A large moraine some 20 to 100 m in height lies at the shelf break due west of Látra Bank. The moraine may mark the Late Weichselian extent of the western Iceland ice, although a single date from a 50-cm gravity core collected from the seaward side of the moraine provided an age of 35,650 ± 560 14C BP. Retreat of this ice sheet appears to have been rapid, except for a minor pause when the ice sheet terminus approached the coastline. A marine reservoir-corrected basal date of 12,705 ± 85 14C BP was obtained from a 17-m giant piston core collected in Jökuldjúp (a shelf trough) which sampled glacial marine sediments close to underlying ice-contact sediment. Because this date is very close to the age of shells near the marine limit in West Iceland, some 100 km to the east-northeast, it suggests that this margin of the Iceland Ice Sheet retreated extremely rapidly during the Bølling/Allerød interstadial (13,000 to 11,000 14C BP).

Philopatry and Dispersal within a Black Guillemot Colony

-We studied patterns of dispersal and philopatry within a Black Guillemot (Cepphus grylle) colony, based on a 22-year capture-recapture study of individually-marked birds. The study colony in western Iceland was divided into 15 subcolonies. Out of 356 local recruits, 122 settled in their natal subcolony, a far higher proportion than expected from a random distribution. The western part of the colony attracted significantly more recruits than did the eastern part. Breeding dispersal among subcolonies only occurred in one percent of all cases in which a bird was captured in two successive years. We suggest that potential recruits select their breeding site based on an assessment of quality as expressed by conspecific breeding success, and also that philopatry occurs because this information acquisition is less than perfect and birds bias their search towards their natal site. Received 18 May 1998, initially accepted 24 November 1998, final acceptance 15 May 1999.

Evidence for a steeper Eemian than Holocene sea surface temperature gradient between Arctic and sub-Arctic regions

Sediment proxy data from the Norwegian, Greenland, and Iceland seas (Nordic seas) are presented to evaluate surface water temperature (SST) differences between Holocene and Eemian times and to deduce from these data the particular mode of surface water circulation. Records from planktic foraminiferal assemblages, CaCO 3 content, oxygen isotopes of foraminifera, and iceberg-rafted debris form the main basis of interpretation. All results indicate for the Eemian comparatively cooler northern Nordic seas than for the Holocene due to a reduction in the northwardly flow of Atlantic surface water towards Fram Strait and the Arctic Ocean. Therefore, the cold polar water flow from the Arctic Ocean was less influencial in the southwestern Nordic seas during this time. As can be further deduced from the Eemian data, slightly higher Eemian SSTs are interpreted for the western Iceland Sea compared to the Norwegian Sea (ca. south of 70°N). This Eemian situation is in contrast to the Holocene when the main mass of warmest Atlantic surface water flows along the Norwegian continental margin northwards and into the Arctic Ocean. Thus, a moderate northwardly decrease in SST is observed in the eastern Nordic seas for this time, causing a meridional transfer in ocean heat. Due to this distribution in SSTs the Holocene is dominated by a meridional circulation pattern. The interpretation of the Eemian data imply a dominantly zonal surface water circulation with a steep meridional gradient in SSTs.

Dynamics of macrofaunal communities of floating seaweed clumps off western Iceland: a study of patches on the surface of the sea

The dynamics of macrofaunal communities of floating clumps of detached intertidal algae were studied by experiments and surveys. The density of some intertidal species tended to decrease slowly with time on experimental fronds of the brown seaweed Ascophyllum nodosum that were put afloat. Many planktonic and benthic species quickly colonized such fronds. Plastic seaweed mimics were also effective in attracting colonizers and it appeared to matter little whether the A. nodosum fronds carried a complement of intertidal animals or had been rinsed of animals before being put afloat. Colonization of experimental fronds was to some extent mediated through transfer from small algal pieces caught by the fronds. Floating algal clumps in coastal areas occur in a large range of sizes. Number of species present on such clumps was closely related to clump size. The density (numbers/100 g algae) of many intertidal species was positively linked with clump size. Distance from nearest shore was a poor predictor of species composition. The clumps form dynamic patches on the surface of the sea that often coalesce or break up. These patches greatly enhance the complexity of the neustonic environment and their species richness is much greater than in the surroundings.

Aeromagnetic results and the presence of an extinct rift zone in western Iceland

Aeromagnetic surveys over western Iceland including Breidafjördur and Faxaflói bays reveal linear features which mostly have a northeasterly trend. However, this trend changes to a northerly direction as the lineations cross the Northwestern peninsula. Over the southern part of the area, the anomaly pattern may be fitted to a simple propagating-rift model. This model is consistent with results from geological mapping in western Iceland in the 1960s and 1970s which yielded evidence for an extinct (> 7 Ma old) rift zone west of the currently active rift zones. The magnetic data provide constraints on the process of rift zone movement and on the age of the bedrock offshore.

Quantification of the effect of plants on weathering: Studies in Iceland

The weathering of calcium and magnesium silicate minerals on the continents has exerted a major control on atmospheric CO 2 over geologic time, and vascular plants may have played an important role in this process. In western Iceland, we have examined the role of plants in weathering by measuring the chemistry of waters draining adjacent areas of basaltic rocks that are either barren (having a partial cover of mosses and lichens) or populated by trees. The study area was chosen to maximize vegetational differences and to minimize differences in microclimate, slope, and lithology, while avoiding hydrothermal waters and anthropogenic acid rain. Results, including data on cation uptake by growing trees, indicate that the rate of weathering release of Ca and Mg to streams and vegetation is two to five times higher in vegetated areas than the release of Ca and Mg to streams in barren areas. This finding suggests a major role for vascular plants in accelerating weathering and thereby lowering atmospheric CO 2 as they invaded upland areas of the continents between 380 and 350 Ma.

Quantification of the Effect of Plants on Weathering: Influence of a Residual Soil Layer on Chemical Fluxes

The weathering of Ca and Mg silicate minerals on the continents has exerted a major control on atmospheric CO2 over geologic time, and vascular plants may have played an important role in this process (e.g. Berner, 1997 and references therein). Before the Devonian, the land may have been populated by algae or lichens (Retallack, 1990) which can affect weathering (Barker et al., 1997), but the very slow metabolism of these plants and the lack of a fine root mass with high surface area argues against their having as strong an effect as vascular plants in accelerating weathering (Cochran and Bemer, 1996). We have examined the role of plants in weathering by measuring the chemistry of waters draining adjacent portions of some basaltic rocks of western Iceland which are either 1) completely bare rock, 2) essentially unvegetated with soil cover, or 3) populated by trees. The study area was chosen to maximize vegetational differences and to minimize differences in microclimate, slope, aspect, and lithology, while avoiding hydrothermal waters and anthropogenic acid rain. In addition, the barren area without soil is compared to one with soil to assess the effect of residual soil cover on chemical fluxes. Results, which are corrected for evapo-transpiration and include data on cation uptake by growing trees, indicate that the rate of weathering release of Ca and Mg is 3 to 8 times higher in vegetated areas than in 'bare' ones. Field Area

Outflow of the Western Boundary Undercurrent vs 230Th-Excesses in the Late Quaternary Sediments of the NW Atlantic Marginal Basins

Late Quaternary sedimentary sequences collected during two campaigns of the CSS Hudson (90-013 and 91-045) in the North Atlantic marginal basins (30-60~ 50-60~ were analysed for their Th and U isotope contents. They include 21 box cores selected along three transects: i) in the Labrador Sea, from Hamilton Inlet on the Labrador coast, to Cape Farewell, south Greenland, ii) in the Irminger and western Iceland basins, along the 60th parallel, and iii) along the northern edge of the Charlie Gibbs Fracture zone. Five long cores spanning at least the Last Glacial Maximum (LGM)-Present, were also used. They were raised respectively, from the Greenland lower slope (PC-012) and upper rise (PC-013), the Orphan Knoll area (PC-094) and the Iceland basin (P-072; TWC-074). Sedimentological, geochemical, and isotopic studies provided independent chronologies. During the Holocene, very low Holocene sedimentological rates (2 to 5 cm/ka) are observed on the lower slope, i.e. along the high velocity core of the Western Boundary Undercurrent (WBUC) as well as in central parts of the major gyres. They contrast with the much higher rates observed below, on the rise (~> 20 cm/ka) (HillaireMarcel et al. , 1994). A reverse situation prevailed during the Last Glacial Maximum (LGM), when a weaker WBUC resulted in higher sedimentation rates

Rift relocation — A geochemical and geochronological investigation of a palaeo-rift in northwest Iceland

A dominant process in the evolution of Iceland is the repeated eastward relocation of the spreading axis in response to westward migration of the plate boundary relative to the plume centre. Two major former rifts can be identified in western Iceland: the Snaefellsnes rift zone, which last erupted tholeiitic lavas at about 7 Ma, and an older spreading system, lava flows from which can be traced some 100 km along a SW-NE strike in the extreme northwest of Iceland. The extinction of the latter is marked by a 14.9 Ma unconformity with a laterite-lignite horizon representing a maximum 200 k.y. hiatus in the lava succession. Lavas below the unconformity dip northwest towards the older axis from which they were erupted, whereas lavas above the unconformity dip southeast towards their source in the younger Snaefellsnes axis. Thus, two nearly complete rift relocation cycles are preserved in western Iceland, each lasting about 8 m.y. as measured between rift extinction events, and for around 12 m.y. from initial propagation to extinction. In this paper we present major- and trace-element analyses, Sr, Nd and Pb isotope data, and 40Ar/ 39Ar dates on basalt samples from above and below the unconformity in northwest Iceland. The Icelandic Tertiary and Quaternary plateau basalts are remarkably homogeneous in composition, in contrast to the much more diverse compositions found in the presently active rift zone. However, basaltic lava flows beneath the unconformity in northwest Iceland show a wider range of incompatible element and radiogenic isotope ratios than do the younger plateau basalts. At least two mantle components, one depleted and the other less depleted with respect to bulk Earth, are required to explain the composition of post-15 Ma Icelandic basalt. The depleted end-member is chemically and isotopically distinct from the N-MORB source. Basalt from the northwest palaeo-rift, however, contains a significant North Atlantic N-MORB component, suggesting that depleted upper mantle can influence the composition of Icelandic basalt in a dying rift that is too far from the plume centre to be dominated by plume mantle. This may account for the periods of low magma productivity represented by troughs between the V-shaped ridges on the Reykjanes Ridge. We suggest that temporal variation in the composition of Icelandic basalt is better explained by crustal accretion and rift relocation processes than by variations in plume composition and temperature.

The dynamic evolution of the Iceland mantle plume: the lead isotope perspective

We report Pb isotope compositions of 42 Tertiary basalts from two widely separated paleo-rift zones from eastern and western Iceland spanning the age range 15.3-2.7 Ma. These samples have previously been well characterized in terms of major and trace element compositions, igneous and zeolite metamorphic petrography, KAr ages, and paleo-magnetostratigraphy. The Pb isotope temporal variation is smooth and cyclic. A maximum in radiogenic Pb is observed around 7–8 Ma, which is coincident in time with maxima in the volcanic production rates on Iceland and along the Reykjanes Ridge. In Pb isotope space the Iceland Tertiary basalts do not fit a binary mixing model between the depleted MORB source and a single radiogenic plume source, as previously suggested by LaSm and 87Sr 86Sr variations. A third EM-I type component, apparently entrained by the 206Pb-rich plume, is suggested. We show that the discrepancy simply reflects that the LaSm, 87Sr 86Sr (and 143Nd 144Nd) of the two enriched plume components proposed are too similar to be resolvable in ternary mixtures containing a significant fraction of the depleted MORB mantle source (i.e. a third component). We also show that the contribution of the radiogenic Pb-rich plume component positively correlates with the lava production rate. The cyclicity in Pb isotope composition is consistent with a pulsating or blob-like plume interacting with the asthenospheric flow related to the Mid-Atlantic ridge spreading plate boundary.

Arctic Ocean deep water masses in the western Iceland Sea

The Icelandic‐Danish contribution to the international Greenland Sea Project was devoted to a study of the distribution and transport of water masses in the Western Iceland Sea. Each year in September from 1987 to 1991, temperature and salinity were observed on a station net in the area off east Greenland from the Denmark Strait in the south to 72°30′N. The data reveal that the deep water column of the western Iceland Sea is occupied by a number of slightly different water masses, which all can be traced back to a formation in the Arctic Ocean. It is especially noticeable that in some years almost undiluted Eurasian Basin Deep Water can be observed as far south as the Denmark Strait.

Molecular characterization of clonal population structure and biogeography of arctic apomictic Daphnia from Greenland and Iceland.

As part of a continuing international project to characterize the population genetic (clonal) structure of arctic members of the Daphnia pulex complex, 34 populations from western Iceland (N = 1373), and 76 populations from western Greenland (N = 2917), were surveyed for allozymic variation at six polymorphic enzyme loci. Mean clonal richness (+/- SE) was 1.91 +/- 0.19 and 1.50 +/- 0.12 for Iceland and Greenland populations, respectively. Mean clonal diversity (+/-1 SE) was 1.20 +/- 0.07 and 1.13 +/- 0.04 for Iceland and Greenland populations, respectively. Four widely distributed clones constituted 92.2% of the total animals surveyed from Iceland, while three locally abundant clones constituted 80.1% of the total animals collected primarily from Disko Island, western Greenland. Selected populations were screened for mitochondrial (mt)DNA variation using PCR-based RFLP analysis of a 2100 bp fragment containing part of the ND4 and ND5 genes. One mtDNA haplotype was very widespread in both western Greenland and western Iceland, although, a number of mutational derivatives were also detected. These data indicate the potential for long-distance dispersal of mtDNA lineages, of the order of hundreds or thousands of kilometers across the arctic. Phylogenetic analysis of the sequence of a 254 base pair (bp) fragment of the control region of the mtDNA molecule revealed two major clades one of which consisted solely of non-melanic lineages, and the other of which consisted almost exclusively of melanic lineages (i.e. one non-melanic lineage also clustered in this clade). Sequence divergence between the two clades averaged 7.3%. Both mitochondrial analyses did not reveal any distinct intraregional clustering of lineages. We discuss our results in reference to previous molecular work done on this arctic Daphnia complex, and we attempt to infer phylogeographic patterning based on geological/glaciological historical events in this region of the arctic.

Geothermal systems in Iceland: Structure and conceptual models—II. Low-temperature areas

A review and assessment of data pertaining to the origin and nature of low-temperature geothermal activity in Iceland are presented. This activity is widely distributed in Quaternary and Tertiary formations on the American plate in western Iceland west of the active belts of volcanism and rifting but it is very sparse on the European plate east of these belts. Low-temperature systems occur in a few places within the active volcanic belts. Temperatures range from just above ambient to a little over 150°C. Generally speaking, resevoir temperatures decrease with increasing distance from the active volcanic belts. The distribution of the low-temperature areas can be correlated to a large extent with active tectonism. In Iceland the European plate is tectonically stable but in the American plate the shear stress field is complicated, leading to complex fracturing and faulting of the crust at present. No single generalized conceptual model describes the basic features of all low-temperature areas in Iceland. Low-temperature geothermal activity is considered to develop by one of the following four processes, or any combination of them: (1) deep flow of groundwater from highland to lowland areas through permeable structures driven by the hydraulic gradient; (2) convection in young fractures formed by tectonic movements in old and relatively impermeable bedrock; (3) drift of high-temperature geothermal systems out of the active volcanic belts in conjunction with their cooling and extinction of the magma heat source; and (4) magma intrusion into Quaternary or Tertiary formations adjacent to the active volcanic belts. Formation of permeable fractures by recent earth movements is probably the most common process responsible for the development of low-temperature activity through convection in these fractures. Convection in low-temperature systems with temperatures above some 60°C is probably mostly driven by pressure differences created by a relatively light hot water column within the system and a denser cold water column outside it. In systems of lower temperature the convection is driven by hydrostatic head in the recharge areas. The source of the low-temperature waters is largely meteoric. However, in some coastal areas a significant seawater-groundwater component is present, up to 10%. Waters not containing a seawater component are low in dissolved solids, or in the range 150–500 ppm. The reason is the low content of anions, particularly Cl, in the basaltic rock forming soluble salts with the major aqueous cations. Geothermal waters from the low-temperature areas in Iceland typically possess lower δD-values (more negative) than the local precipitation. This difference is variable; most often it lies in the range of 10–30% δD, but it may be as large as 70‰. This difference has been considered to indicate that the recharge areas to the low-temperature areas lie inland on higher ground, the distance being as much as 150 km. The interpretation favoured here is that at least some of the low-temperature waters contain a component of “ice-age water”, i.e. water that is older than about 10, 000 years. The “ice-age water” is depleted in deuterium relative to today's precipitation. When “ice-age water” is present in the geothermal water, deuterium cannot be used as a tracer to locate the recharge areas to the geothermal areas and in this way to deduce about regional groundwater flow.

Organochlorine residues in two seal species from Western Iceland

Harbour seals and grey seals from Faxaflói (Western Iceland) were analyzed for contamination with organochlorines (HCB, PCBs, p,p′-DDT, p,p′-DDE, chlordanes and the enantiomers of α-HCH). Although the values strongly varied, both harbour seals and grey seals on average showed comparable levels of PCBs, p,p′-DDT, p,p′-DDE and α-HCH, as well as chlordanes (ΣCD). Differences were measured in the HCB content of the seal species. The HCBα-HCH ratio in harbour seals was <1 and in grey seals >1. The results from seals on Iceland were compared with data derived from seal samples of the Antarctic, the Arctic (Spitzbergen) and the North Sea (Germany) in order to give an insight into the global distribution of pollution with chlorinated organics.