South Iceland Research Articles

Long-term changes in abundance of Calanus finmarchicus south and north of Iceland in relation to environmental conditions and regional diversity in spring 1990–2013

Abstract A 24-year time series of the abundance of Calanus finmarchicus from two standard sections differing in hydrographical conditions (Atlantic Water south of Iceland, Subarctic Water north of Iceland) was examined in relation to hydrography, phytoplankton dynamics, and large-scale climatic forcing (North Atlantic Oscillation, NAO). In the sea area around Iceland, C. finmarchicus is the most abundant mesozooplankter. The long-term variations were evaluated using multivariate statistics, principal component analyses, redundancy analyses (RDA), and principal response curves. Both south and north of Iceland, significant (RDA, p < 0.05, Monte-Carlo permutation tests) fluctuations in abundance and stages structure of C. finmarchicus between years were observed. The variations were, however, not in tune in south and north, indicating that the C. finmarchicus abundance may be influenced by different forcing factors in the two regions. South of Iceland, the analyses failed to find an effect of any of the environmental variables tested, whereas in the north the year-to-year variability was related to freshwater thickness west of Iceland and temperature north of the island (RDA, p < 0.05, Monte-Carlo permutation tests), indicating that advection of animals with currents from the south is important. In neither of the two regions was it possible to detect a unidirectional temporal trend in abundance of C. finmarchicus (RDA, p < 0.05, Monte-Carlo permutation tests). Based on a comparison with time series from nearby areas and the lack of a relationship with NAO, it is hypothesized that the growth and development of C. finmarchicus in Icelandic waters is more affected by local conditions than large-scale climatic forcing.

Effects of yoga practice on stress-related symptoms in the aftermath of an earthquake: A community-based controlled trial

To evaluate the effect of an integrated hatha yoga practice on perceived stress and stress-related symptoms in the aftermath of an earthquake. Inhabitants, aged 20-67 years, from highly exposed earthquake areas of two villages in South Iceland were offered to participate in a yoga program subsequent to an earthquake. Sixty-six individuals were self-selected into the study and divided by residential convenience into an experimental group (n=31) and a waiting list control group (n=35). The yoga program was conducted twice a week for six weeks, in normal situations among the inhabitants in the community. Several validated questionnaires assessing stress and stress-related symptoms, posttraumatic symptoms, depression, anxiety and health related quality of life were administered at pre- and post-intervention. Multivariate analysis of variance (MANOVA) revealed differences between the experimental group and waiting list control group on sleep quality (p=.03) and social relations (p=.04). These differences did not prevail at Bonferroni correction for multiple testing (at alpha level of .005). Participants in both groups showed significant improvements in stress and some stress-related symptoms such as sleep, concentration, well-being, quality of life, depression and anxiety from pre- to post-intervention. The data from this small study show no statistically significant improvement of an integrated hatha yoga program above and beyond waiting list control, following exposure to an earthquake. However, the observed trend toward improved sleep quality and social relations deserve further exploration in larger effectiveness studies on the impact of Hatha yoga on recovery after natural disaster.

Late-Holocene land surface change in a coupled social–ecological system, southern Iceland: a cross-scale tephrochronology approach

The chronological challenge of cross-scale analysis within coupled socio-ecological systems can be met with tephrochronology based on numerous well-dated tephra layers. We illustrate this with an enhanced chronology from Skaftártunga, south Iceland that is based on 200 stratigraphic profiles and 2635 individual tephra deposits from 23 different eruptions within the last 1140 years. We present new sediment-accumulation rate based dating of tephra layers from Grímsvötn in AD 1432 ± 5 and AD 1457 ± 5. These and other tephras underpin an analysis of land surface stability across multiple scales. The aggregate regional sediment accumulation records suggest a relatively slow rate of land surface change which can be explained by climate and land use change over the period of human occupation of the island (after AD ∼870), but the spatial patterning of change shows that it is more complex, with landscape scale hysteresis and path dependency making the relationship between climate and land surface instability contingent. An alternative steady state of much higher rates of sediment accumulation is seen in areas below 300 m asl after AD ∼870 despite large variations in climate, with two phases of increased erosion, one related to vegetation change (AD 870–1206) and another related to climate (AD 1597–1918). In areas above 300 m asl there is a short lived increase in erosion and related deposition after settlement (AD ∼870–935) and then relatively little additional change to present. Spatial correlation between rates of sediment accumulation at different profiles decreases rapidly after AD ∼935 from ∼4 km to less than 250 m as the landscape becomes more heterogeneous. These new insights are only possible using high-resolution tephrochronology applied spatially across a landscape, an approach that can be applied to the large areas of the Earth's surface affected by the repeated fallout of cm-scale tephra layers.

A saga of the 1896 South Iceland earthquake sequence: magnitudes, macroseismic effects and damage

This paper describes Professor Ambraseys’s work on the quantification of magnitudes of the main events in the 1896 South Iceland earthquake sequence, using original teleseismic data recorded by primitive seismological instruments located in Russia and Italy. This includes an example of his original worksheets showing surface-wave magnitude re-appraisal along with the initial part of the parametric earthquake catalogue of Iceland. A brief description of the macroseismic effects of the earthquake sequence is presented. Earthquake damage to buildings in the most affected area is quantified as fractions of collapsed farmhouses. Spatial distribution of the quantified damage shows good correspondence to the estimated epicentres of the earthquakes of the sequence. The macroseismic effects of the earthquake sequence are described and compared to those of the South Iceland earthquakes in June 2000 and May 2008. It is argued that the magnitude estimate of the largest event of the sequence as obtained by Professor Ambraseys, based entirely on teleseismic measurements, is likely to be more accurate than other estimates based on the extent of the damaged area. This argument is supported by a discussion based on a comparison between the felt area, damaged area, and seismic moment estimates of the June 2000 earthquakes with the documented effects of the 1896 main shock. The observations and discussions presented here highlight the importance of Professor Ambraseys in the study of historic earthquakes.

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

Abstract 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. Supplementary material: Single-grain analyses of tephra from FMAZ IV in cores from the northern Faroe margin and the central Faroe-Shetland Channel are available at http://www.geolsoc.org.uk/SUP18714

Magma–ice–sediment interactions and the origin of lava/hyaloclastite sequences in the Síða formation, South Iceland

Products of subglacial volcanism can illuminate reconstructions of paleo-environmental conditions on both local and regional scales. Competing interpretations of Pleistocene conditions in south Iceland have been proposed based on an extensive sequence of repeating lava-and-hyaloclastite deposits in the Siða district. We propose here a new eruptive model and refine the glacial environment during eruption based on field research and analytical data for the Siða district lava/hyaloclastite units. Field observations from this and previous studies reveal a repeating sequence of cogenetic lava and hyaloclastite deposits extending many kilometers from their presumed eruptive source. Glasses from lava selvages and unaltered hyaloclastites have very low H2O, S, and CO2 concentrations, indicating significant degassing at or close to atmospheric pressure prior to quenching. We also present a scenario that demonstrates virtual co-emplacement of the two eruptive products. Our data and model results suggest repeated eruptions under thin ice or partially subaerial conditions, rather than eruption under a thick ice sheet or subglacial conditions as previously proposed.

Modeling Wet Snow Accretion on Power Lines: Improvements to Previous Methods Using 50 Years of Observations

AbstractMethods to model wet snow accretion on structures are developed and improved, based on unique records of wet snow icing events as well as large datasets of observed and simulated weather. Hundreds of observed wet snow icing events are logged in detail in an icing database, most of which include an estimate of the mean and maximum diameter of observed icing on overhead power conductors. Observations of weather are furthermore available from a dense network of weather stations. The existing models for wet snow accretion on a standard cylinder are updated with realistic values for the terminal fall speed of wet snowflakes together with a snowflake liquid fraction–based criterion to identify wet snow. The widely used parameterization of the sticking efficiency is found to strongly underestimate the accretion rate. A calibrated parameterization of the sticking efficiency is suggested on the basis of long-term statistics of observed and modeled wet snow loads. Application of the improved method is demonstrated in a high-resolution simulation for a case of observed widespread and intensive wet snow icing in south Iceland. The results form a basis for mapping the climatology of wet snow icing in the complex terrain of Iceland as well as for preparing operational forecasts of wet snow icing and severe weather for overhead power transmission lines in complex terrain.

Fault ruptures and geothermal effects of the second earthquake, 29 May 2008, South Iceland Seismic Zone

The Reykjafjall N–S source fault ruptured during the Mw 6.3 earthquake doublet on May 29, 2008, in the South Iceland Seismic Zone (SISZ). The northern part of the fault intersects the easternmost high-temperature geothermal field of Hengill in an extinct volcano that began shifting away from the Western Rift Zone 120,000 years ago. Geophysical data indicate that the N–S fault ruptured over 20km length at depth. Our detailed field mapping along the fault length shows that the southern part of the fault did not rupture the surface mostly due to the greater depth of seismicity (down to 9km) there. The surface ruptures were dominantly found along the northern half of the fault in the highland within the high-temperature field where aftershocks were shallower than 5km. There, the surface ruptured on portions of six parallel N–S fault segments and not on a single fault plane. Hot springs are aligned on the two westernmost fault segments within the area of increased geothermal activity after the earthquake. Other Riedel shears (ENE, E–W, WNW and NNW) hosting geothermal activity also ruptured. On the N–S faults, surface ruptures and hot springs are organised in left-stepping arrays indicating dextral motion with offsets between 0.5 and 2m. On other Riedel shear sets ruptures have a right-stepping arrangement indicating sinistral motion with a maximum horizontal offset of a metre. All fresh ruptures had centimetre-scale normal-slip and openings <1m but up to 1.5m along atypical N–S structures.Our results fit with the lineations in the aftershocks and with fault plane solutions. They also show that the 2008 source fault ruptured within a 2-km wide deformation zone where previous earthquakes and changes to geothermal activity have occurred at least since 1706. This implies that major earthquakes in this area may have a common source fault at depth and a wider deformation zone at the surface. Our study demonstrates how transform faulting at the junction of a rift segment causes recurring medium–large earthquakes that control fault behavior and permeability in fractured geothermal fields.

Symptoms following exposure to the Eyjafjallajökull volcanic eruption – at the eruption's end and six months later

Background The 2010 Eyjafjallajokull eruption in Iceland spring dispersed fine grained ash over South Iceland. It also posed an opportunity to study health effects of a volcanic eruption in a moder...

A remarkable anniversary: Surtsey becomes 50 years

Announcements ISSN 1948‐6596 A remarkable anniversary: Surtsey becomes 50 years old Every year there is a lot of round anniversaries to celebrate, and 2013 is no exception. Opera fans celebrate Wagner and Verdi, and we biogeogra‐ phers highlight Wallace and the MacArthur– Wilson plot. There is a round anniversary of another kind in 2013. It is 50 years since Surtsey emerged from the sea, in the Vestmanna Archipelago south of Iceland. I still remember the excitement in the press and the extraordinary pictures on black‐and‐ white television. But after a certain time the inter‐ est seemed to dwindle a bit, and in the interna‐ tional press (journalistic as well as scientific) re‐ ports from Surtsey became rather rare. This is strange for at least two reasons. One is that Surtsey was born right in the middle of the debate on two of the most important paradigms in the twentieth century: that of plate tectonics and that on island biogeography. And for both fields the processes on Surtsey yield unique evi‐ dence for the theories. The other reason is that Surtsey was not left alone. Our Icelandic col‐ leagues within geology, geomorphology, oceanog‐ raphy and biology have carefully and meticulously followed the island, and, through repeated and systematic surveys, they have built up a wealth of data on the infancy of an island. They have care‐ fully reported their observations (for example there is a long series of ‘Surtsey Reports’ and a home page where almost everything can be found). But Surtsey does not appear so often in textbooks or reviews as, for example, Galapagos, Krakatau or Hawai’i. Some of the findings are quite extraordi‐ nary. To mention a few: it has been shown that the geochemical transition of volcanic ash to tufa is a question of decades and not of centuries— and erosion of basaltic rocks occurs within the same time scale (Surtsey has lost half of its area already). Furthermore, the build‐up of a plant cover has proved to be rapid: so far roughly 100 species of higher plants have been reported and many of them have disappeared again. This is far more than in the rest of the Vestmanna Archipel‐ ago and around 20% of the entire flora of Iceland. The colonization of birds has also been docu‐ mented and the influence of seabird colonies on vegetation succession has been recorded from scratch. Our Icelandic colleagues have decided to seize the 50 th anniversary as an opportunity both to synthesize the existing knowledge and to com‐ municate it to the international scientific commu‐ nity. They will host an international conference in Reykjavik in August 2013 (12 th –15 th ), focusing on the geological and biological processes on Surtsey. The first and second circulars have been distrib‐ uted, and more information and details can be found on http://www.surtsey.is. The organizers have tried to urge Surt (the equivalent in Nordic mythology to Vulcan/ Hephaistos) to let Surtsey have a younger brother be born just south of El Hierro in the Canary Is‐ lands. He is on the way; let us see whether he makes it in 2013. Henning Adsersen Centre of Macroecology, Evolution, and Climate, Department of Biology, University of Copenhagen, Den‐ mark. adser@bio.ku.dk To post jobs, advertisements, or other announcements please contact the Frontiers of Biogeography editoral office (frontiersofbiogeography@googlemail.com). Advertisements are $50 per quarter page for professional or institutional positions. Announcements are free to members for vacancies in their lab. All advertisements and announcements also appear at no additional cost on the IBS facebook pa‐ ge (in abbreviated form) and on the IBS Blog (in long, or longer form). frontiers of biogeography 5.1, 2013 — © 2013 the authors; journal compilation © 2013 The International Biogeography Society

Pre-eruptive volatile content, degassing paths and depressurisation explaining the transition in style at the subglacial rhyolitic eruption of Dalakvísl, South Iceland

Many volcanoes express a variety of contrasting eruptive styles with behavioural transitions between explosive and effusive activities. Understanding eruptive mechanisms is of key importance but we currently have little insight into the behavioural controls for rhyolitic eruptions beneath ice. This paper addresses a subglacial rhyolitic eruption at Dalakvísl in South Iceland that involved both explosive and effusive activities. We present measurements of pre- and post-eruptive magmatic volatile contents that we use to track magma degassing from the chamber to the surface and reconstruct pressure conditions during the eruption. Explosive and effusive phases involve significant differences in: (1) pre-eruptive volatile contents; (2) the ‘openness’ of magma degassing; and (3) inferred confining pressure. This final factor is potentially associated with a jökulhlaup-induced decompression. Due to the combination of these factors Dalakvísl experienced a change from effusive to explosive behaviour, although we cannot currently resolve cause from effect. Our work points towards complex interactions between the dynamics of magma ascent and the response of overlying ice and meltwater during rhyolitic eruptions beneath ice.

From surface fault traces to a fault growth model: The Vogar Fissure Swarm of the Reykjanes Peninsula, Southwest Iceland

The Vogar Fissure Swarm is one of four en-echelon fracture swarms that connect the Reykjanes Ridge to the South Iceland Seismic Zone and the Western Volcanic Zone. Occurring in an area of flat topography, this fissure swarm is clearly visible at the surface, where it can be seen to affect recent postglacial lavas. Using remote sensing methods to identify and measure all the faults and fractures in the swarm, combined with additional field observations and measurements, we measured 478 individual fractures, 33% of them being faults and 67% being fissures. The fracture lengths show roughly log-normal distributions. Most of the individual fractures belong to 68 main composite fractures, seven of which are longer than 2500 m and correspond to the main fault scarps of the fissure swarm. We showed that these main faults are distributed along five, equally spaced zones, ∼500 m apart and a few kilometers long. We drawn 71 across-strike profiles to characterize the shape of the fault scarps, and 5 along-strike profiles to characterize the evolution of vertical throw along the main faults. Each fault consists of a coalescence of individual segments of approximately equal length. Fault throws are never larger than 10 m and are smallest at the junctions between individual segments. Analyses of along-strike throw profiles allowed us to determine the early stages of growth after coalescence. The earliest stage is characterized by an increase in the throw of the central parts of segments. This is followed by a second stage during which the throw increases at the junctions between segments, progressively erasing these small-throw zones.

Nutrient conditions in the subpolar North Atlantic during the last glacial period reconstructed from foraminifera‐bound nitrogen isotopes

Surface nitrate concentration is a potentially useful diagnostic in reconstructing the past circulation of high‐latitude North Atlantic waters. Moreover, nutrient consumption in the North Atlantic surface impacts the atmospheric concentration of carbon dioxide. To reconstruct nutrient conditions in the subpolar North Atlantic region during the last ice age, a record of foraminifera‐bound δ15N was measured in Neogloboquadrina pachyderma (sin.) from core V28‐73 south of Iceland (57.2°N, 20.9°W). Foraminifera‐bound δ15N is up to 2‰ lower during the last ice age than during the Holocene, suggesting as much as ~25% less complete nitrate consumption during the former. This is consistent with stronger light limitation associated with a deeper summer surface mixed layer, perhaps related to the formation of Glacial North Atlantic Intermediate Water previously suggested to have occurred near the core site. However, three single‐point maxima in δ15N in the glacial section and the sharp deglacial δ15N rise coincide with Heinrich event layers. This suggests that increased water column stratification during Heinrich events, presumably due to surface freshening, reduced the nutrient supply from below and led to nearly complete nitrate consumption in the summertime mixed layer. The Heinrich layers in V28‐73 are not accompanied by δ18O minima in either N. pachyderma (sin.) or Globigerinoides bulloides, which we tentatively attribute to extreme mixed‐layer shoaling. The reconstructed subpolar North Atlantic upper water column changes—both glacial/interglacial and millennial—are inverse to those inferred for the Antarctic.

Late Holocene and modern glacier changes in the marginal zone of Sólheimajökull, South Iceland

The forefield of the Sólheimajökull outlet glacier, South Iceland, has a variety of glacial landforms and sediments that are products of late Holocene and modern glacier oscillations. Several sets of moraine ridges reflect past ice front positions and river-cut sedimentary sections provide information about past environments. Here, we describe sediments and landforms deposited during the late Holocene. Chronology is obtained by $^{14}$C dating and cosmogenic exposure dating. The age determinations suggest that Sólheimajökull had major advances in the late Holocene prior to the Little Ice Age, and more restricted advances during the Little Ice Age, after AD 1539. Oscillations of the Sólheimajökull ice margin between 1938 and 2010 are documented by aerial photographs. Digital elevation models were produced from selected years in order to quantify ice thickness changes at the glacier margin over the last 50 years. The glacier margin thickened 70–100 m from 1960 to 1996 and then thinned 120–150 m between 1996 and 2010. In 2010, the glacier snout was 20–40 m thinner than in 1960. Additionally, the DEM time-series detect areas of erosion and deposition in the forefield.

Volcano deformation at active plate boundaries: Deep magma accumulation at Hekla volcano and plate boundary deformation in south Iceland

Most magmatic systems on Earth are located at actively deforming plate boundaries. In these systems, the magmatic and plate boundary deformation signals are intertwined and must be deconvolved to properly estimate magma flux and source characteristics of the magma plumbing system. We investigate the inter‐rifting and inter‐seismic deformation signals at the Eastern Volcanic Zone (EVZ) – South Iceland Seismic Zone (SISZ) ridge ‐ transform intersection and estimate the location, depth, and volume rate for magmatic sources at Hekla and Torfajökull volcanoes, which are located at the intersection. We solve simultaneously for the source parameters of the tectonic and volcanic deformation signals using a new ten‐year velocity field derived from a dense network of episodic and continuous GPS stations in south Iceland. We find the intersection of the axes of the EVZ and the SISZ is located within the Torfajökull caldera, which itself is subsiding. Deformation at Hekla is statistically best described in terms of a horizontal ellipsoidal magma chamber at 24−2+4 km depth aligned with the volcanic system and increasing in volume by 0.017−0.002+0.007 km3 per year. A spherical magma chamber centered at 24−2+5 km depth with a volume rate of 0.019−0.002+0.011 km3per year, or a vertical pipe‐shaped magma chamber between 10−1+3 km and 21−4+7 km with a volume rate of 0.008−0.001+0.003 km3 per year are also plausible models explaining the deformation at Hekla. All three models indicate magma accumulation in the lower crust or near the Moho under Hekla.

Probabilistic Earthquake Damage Curves for Low-Rise Buildings Based on Field Data

All buildings in Iceland are registered in an official database that contains detailed information about them, and insurance against natural disasters is obligatory. When a destructive earthquake occurs, all damage is reported, and the repair and replacement cost for every affected building is evaluated. In May 2008, a shallow earthquake of magnitude Mw = 6.3 struck in South Iceland. A great deal of damage occurred, but fortunately, there was no loss of life. The recorded maximum PGA was 0.88 g. Detailed and complete information of all real estate property and the damage incurred, along with recorded strong-motion data and an area-specific attenuation model, have provided an opportunity to create probabilistic damage curves for the building stock in the affected area. The damage model obtained from the 2008 earthquake was tested and verified by using it to back-calculate the damage that occurred in the two South Iceland earthquakes of June 2000 ( Mw = 6.5).

Identification of stock components using morphological markers

This study investigated the development of a quantitative method for distinguishing stock components of Icelandic cod Gadus morhua based on visual examination of morphology. The stock is known to be structured into genetically distinct geographic components (north and south of Iceland) and behavioural types that spawn sympatrically. Differences in morphology were tested between locations, genotypes (a proxy for behaviour) and sexes. Results show morphological markers on the head, fins and body of G. morhua that are correlated with the sex, genotype of the fish at the pantophysin (pan-I) locus and the location at which the fish were caught. Females were found to have relatively deep bodies, and the pan-I(BB) genotype (associated with deep-water feeding behaviour) have greater gaps between their fins. Overall, morphology is more useful for distinguishing sympatric genotypes but less powerful at identifying genetically distinct geographic sub-populations, perhaps because counter-gradient evolution reduces phenotypic differences even with an underlying genetic cause.

Catastrophic soil erosion in Iceland: Impact of long-term climate change, compounded natural disturbances and human driven land-use changes

This study examines the interplay between long-term climate changes, compounded natural disturbances and human driven land-use changes on catastrophic soil erosion of the heathland ecosystem of Haukadalsheiði, south Iceland. Soil erosion was catastrophic for three centuries (~ 1660–1960 AD) and was characterized by almost total loss of vegetation and underlying soil. Soil erosion resulted in a desertified, barren landscape that had no resemblance to the original heathland ecosystem. Soil erosion was spatially reconstructed in a chronological order using information on the average progress of eroding fronts, anecdotal and historical evidence along with tephrochronological information. The progress of the fastest eroding front was rapid (29.7 m yr− 1). Human driven land‐use changes played a role in the heathland degradation: relentless free-range grazing by livestock resulted in decreased resistance of heathland communities to soil erosion. Adverse climate-change during Little Ice Age (LIA: 1550–1850 AD) intensified the effect of grazing. The catastrophic soil erosion was triggered by a massive sand encroachment ~ 1660 AD from three outwash sand-plains along the glacial River Far. The sand drift was sustained by dry northern glacial (katabatic) winds that drove the soil erosion. Long-term climate change resulted in glacier fluctuation that caused changes in water discharge in the River Far; sand drift was intense during periods of no water discharge (~ 1660–1708 AD and ~ 1800–1929 AD) and following glacial river floods (1708, 1884, 1902, 1929 and 1939 AD).Also, sand drift was intense due to unusually frequent volcanic tephra fallouts (1693, 1721 and 1766 AD). Information on factors that increase the risk of soil erosion and trigger and drive soil erosion is critical in understanding catastrophic soil erosion.

Early Holocene hybridisation between Betula pubescens and B. nana in relation to birch vegetation in Southwest Iceland

The aims of the present research were to gain better insight into the early Holocene vegetation history of Betula in South Iceland and to investigate whether hybridisation between downy tree-birch (Betula pubescens) and dwarf birch (Betula nana) could be discovered in this region, similar to that previously found in North Iceland. A peat monolith spanning the period from about 10.3 to 7.6calkaBP from Eyvík, Southwest Iceland, provided 44 samples for pollen analysis. The samples were dated by known tephra layers, Saksunarvatn and Seydishólar tephras, and two 14C datings. The macrofossil and spore/pollen results showed several progressive phases of vegetation development in the area until birch woodland became established around 9.5calkaBP. The timing of birch colonisation is in good agreement with results from other sites in Iceland. From these Eyvík samples, all morphologically normal Betula pollen grains were size-measured and abnormal pollen grains recorded. Species proportions within samples were estimated statistically on the basis of pollen size. As birch woodland in this area became established rather late, statistical analysis of Betula pollen size was only possible in the uppermost 18 samples, approximately spanning the period between 7.6 and 9.5calkaBP. The frequency distribution of pollen size indicated populations of B. nana predating those of B. pubescens. The proportion of B. pubescens pollen was oscillating but increased with time. In two samples at the top of the peat monolith, more than half of the measured Betula pollen grains belonged to B. pubescens. Evidence of hybridisation based on high frequencies of non-triporate Betula pollen was found in two samples dated at about 8.8 and 7.7calkaBP. Conditions appeared to be comparable to the corresponding hybridisation events previously reported for North Iceland, i.e. in warm periods when downy birch was expanding near dwarf birch habitats.

High‐resolution sea surface reconstructions off Cape Hatteras over the last 10 ka

This study presents high‐resolution foraminiferal‐based sea surface temperature, sea surface salinity and upper water column stratification reconstructions off Cape Hatteras, a region sensitive to atmospheric and thermohaline circulation changes associated with the Gulf Stream. We focus on the last 10,000 years (10 ka) to study the surface hydrology changes under our current climate conditions and discuss the centennial to millennial time scale variability. We observed opposite evolutions between the conditions off Cape Hatteras and those south of Iceland, known today for the North Atlantic Oscillation pattern. We interpret the temperature and salinity changes in both regions as co‐variation of activities of the subtropical and subpolar gyres. Around 8.3 ka and 5.2–3.5 ka, positive salinity anomalies are reconstructed off Cape Hatteras. We demonstrate, for the 5.2–3.5 ka period, that the salinity increase was caused by the cessation of the low salinity surface flow coming from the north. A northward displacement of the Gulf Stream, blocking the southbound low‐salinity flow, concomitant to a reduced Meridional Overturning Circulation is the most likely scenario. Finally, wavelet transform analysis revealed a 1000‐year period pacing the δ18O signal over the early Holocene. This 1000‐year frequency band is significantly coherent with the 1000‐year frequency band of Total Solar Irradiance (TSI) between 9.5 ka and 7 ka and both signals are in phase over the rest of the studied period.