scholarly journals How could the Viking Sun compass be used with sunstones before and after sunset? Twilight board as a new interpretation of the Uunartoq artefact fragment

2014 ◽  
Vol 470 (2166) ◽  
pp. 20130787 ◽  
Author(s):  
Balázs Bernáth ◽  
Alexandra Farkas ◽  
Dénes Száz ◽  
Miklós Blahó ◽  
Ádám Egri ◽  
...  
Keyword(s):  
North Atlantic ◽  
Eleventh Century ◽  
Field Tests ◽  
Baffin Island ◽  
Sun Compass ◽  
The North ◽  
Skylight Polarization ◽  
Before And After ◽  
Birefringent Crystals ◽  
New Interpretation

Vikings routinely crossed the North Atlantic without a magnetic compass and left their mark on lands as far away as Greenland, Newfoundland and Baffin Island. Based on an eleventh-century dial fragment artefact, found at Uunartoq in Greenland, it is widely accepted that they sailed along chosen latitudes using primitive Sun compasses. Such instruments were tested on sea and proved to be efficient hand-held navigation tools, but the dimensions and incisions of the Uunartoq find are far from optimal in this role. On the basis of the sagas mentioning sunstones, incompatible hypotheses were formed for Viking solar navigation procedures and primitive skylight polarimetry with dichroic or birefringent crystals. We describe here a previously unconceived method of navigation based on the Uunartoq artefact functioning as a ‘twilight board’, which is a combination of a horizon board and a Sun compass optimized for use when the Sun is close to the horizon. We deduced an appropriate solar navigation procedure using a twilight board, a shadow-stick and birefringent crystals, which bring together earlier suggested methods in harmony and provide a true skylight compass function. This could have allowed Vikings to navigate around the clock, to use the artefact dial as a Sun compass during long parts of the day and to use skylight polarization patterns in the twilight period. In field tests, we found that true north could be appointed with such a medieval skylight compass with an error of about ±4° when the artificially occluded Sun had elevation angles between +10° and −8° relative to the horizon. Our interpretation allows us to assign exact dates to the gnomonic lines on the artefact and outlines the schedule of the merchant ships that sustained the Viking colony in Greenland a millennium ago.

scholarly journals On the trail of Vikings with polarized skylight: experimental study of the atmospheric optical prerequisites allowing polarimetric navigation by Viking seafarers

2011 ◽  
Vol 366 (1565) ◽  
pp. 772-782 ◽  
Author(s):  
Gábor Horváth ◽  
András Barta ◽  
István Pomozi ◽  
Bence Suhai ◽  
Ramón Hegedüs ◽  
...  
Keyword(s):  
North Atlantic ◽  
Laboratory Experiments ◽  
High Arctic ◽  
Exact Nature ◽  
The Sun ◽  
Birefringent Crystal ◽  
The North ◽  
Open Sea ◽  
Skylight Polarization ◽  
The North Atlantic

Between AD 900 and AD 1200 Vikings, being able to navigate skillfully across the open sea, were the dominant seafarers of the North Atlantic. When the Sun was shining, geographical north could be determined with a special sundial. However, how the Vikings could have navigated in cloudy or foggy situations, when the Sun's disc was unusable, is still not fully known. A hypothesis was formulated in 1967, which suggested that under foggy or cloudy conditions, Vikings might have been able to determine the azimuth direction of the Sun with the help of skylight polarization, just like some insects. This hypothesis has been widely accepted and is regularly cited by researchers, even though an experimental basis, so far, has not been forthcoming. According to this theory, the Vikings could have determined the direction of the skylight polarization with the help of an enigmatic birefringent crystal, functioning as a linearly polarizing filter. Such a crystal is referred to as ‘sunstone’ in one of the Viking's sagas, but its exact nature is unknown. Although accepted by many, the hypothesis of polarimetric navigation by Vikings also has numerous sceptics. In this paper, we summarize the results of our own celestial polarization measurements and psychophysical laboratory experiments, in which we studied the atmospheric optical prerequisites of possible sky-polarimetric navigation in Tunisia, Finland, Hungary and the high Arctic.

scholarly journals Predictable Climate Impacts of the Decadal Changes in the Ocean in the 1990s

2013 ◽  
Vol 26 (17) ◽  
pp. 6329-6339 ◽  
Author(s):  
Jon Robson ◽  
Rowan Sutton ◽  
Doug Smith
Keyword(s):  
North America ◽  
North Atlantic ◽  
Major Change ◽  
Climate Impacts ◽  
First Year ◽  
Prediction System ◽  
The North ◽  
Surface Climate ◽  
Before And After ◽  
Dry Conditions

Abstract During the 1990s there was a major change in the state of the world's oceans. In particular, the North Atlantic underwent a rapid warming, with sea surface temperatures (SSTs) in the subpolar gyre region increasing by 1°C in just a few years. Associated with the changes in SST patterns were changes in the surface climate, in particular, a tendency for warm and dry conditions over areas of North America in all seasons, and warm springs and wet summers over areas of Europe. Here, the extent to which a climate prediction system initialized using observations of the ocean state is able to capture the observed changes in seasonal mean surface climate is investigated. Rather than examining predictions of the mid-1990s North Atlantic warming event itself, this study compares hindcasts started before and after the warming, relative to hindcasts that do not assimilate information. It is demonstrated that the hindcasts capture many aspects of the observed changes in seasonal mean surface climate, especially in North, South, and Central America and in Europe. Furthermore, the prediction system retains skill beyond the first year. Finally, it is shown that, in addition to memory of Atlantic SSTs, successfully predicting Pacific SSTs was likely important for the hindcasts to predict surface climate over North America.

scholarly journals Relationship between Holocene climate variations over southern Greenland and eastern Baffin Island and synoptic circulation pattern

2009 ◽  
Vol 5 (2) ◽  
pp. 879-910 ◽  
Author(s):  
B. Fréchette ◽  
A. de Vernal
Keyword(s):  
North Atlantic ◽  
Circulation Pattern ◽  
Baffin Island ◽  
North Atlantic Current ◽  
Climate Trends ◽  
Sea Temperature ◽  
The North ◽  
Labrador Current ◽  
Temperature Records ◽  
Southwest Greenland

Abstract. Lake pollen records from southwest Greenland and eastern Baffin Island show strong regionalism in climate trends of the last 7000 years. Air temperature reconstructions from pollen indicate larger amplitude cooling in southwest Greenland (>3.0°C) than in eastern Baffin Island (<1.0°C). Such west-east gradient in climate change is consistent with paleoceanographical data that indicate decreasing temperature and/or strength of the North Atlantic Current to the east during the Holocene while the eastern Canadian margins under the Labrador Current influence display slight warming. Complementary to air and sea temperature records, the lake pollen data led to reconstruct increased cloudiness in southern Greenland, which points to increasing cyclonic activity since 7000 years west of Greenland. Together, the terrestrial and marine records of the northwest North Atlantic therefore suggest a shift from a dominant NAO+ during the early-mid Holocene to dominant NAO- in the late Holocene.

scholarly journals Weakening and warming of the European Slope Current since the late 1990s attributed to basin-scale density changes

2021 ◽  
Author(s):  
Matthew Clark ◽  
Robert Marsh ◽  
James Harle
Keyword(s):  
Continental Slope ◽  
North Atlantic ◽  
Deep Ocean ◽  
Ocean Model ◽  
Latitude Range ◽  
The North ◽  
Basin Scale ◽  
Before And After ◽  
Shelf Seas ◽  
Northern North Sea

Abstract. Oceanic influences on shelf seas are mediated by flow along and across continental slopes, with consequences for regional hydrography and ecosystems. Here we present evidence for the variable North Atlantic influence on European shelf seas over the last four decades, using ocean analysis and reanalysis products, and an eddy-resolving ocean model hindcast. To first order, flows oriented along isobaths at the continental slope are related to the poleward increase of density in the adjacent deep ocean that supports a geostrophic inflow towards the slope. In the North Atlantic, this density gradient and associated inflow has undergone substantial, sometimes abrupt, changes in recent decades. Inflow in the range 10–15 Sv is identified with eastward transport in temperature classes at 30° W, in the latitude range 45–60° N. Associated with major subpolar warming around 1997, a cool and fresh branch of the Atlantic inflow was substantially reduced, while a warm and more saline inflow branch strengthened, with respective changes of the order 5 Sv. Total inflow fell from ~ 15 Sv pre-1997 to ~ 10 Sv post-1997. In the model hindcast, particle tracking is used to trace the origins of poleward flows along the continental slope to the west of Ireland and Scotland, before and after 1997. Backtracking particles up to 4 years, a range of subtropical and subpolar pathways is identified from a statistical perspective. In broad terms, cold, fresh waters of subpolar provenance were replaced by warm, saline waters, of subtropical provenance. These changes have major implications for the downstream shelf regions that are strongly influenced by Atlantic inflow, the northern North Sea in particular, where “subtropicalization” of ecosystems has already been observed since the late 1990s.

scholarly journals North Atlantic Subpolar Gyre Surface Variability (1895–2009)

2010 ◽  
Vol 23 (17) ◽  
pp. 4571-4584 ◽  
Author(s):  
G. Reverdin
Keyword(s):  
North Atlantic ◽  
Heat Fluxes ◽  
Subpolar Gyre ◽  
Multidecadal Variability ◽  
The North ◽  
Nao Index ◽  
Before And After ◽  
Different Seasons ◽  
North Atlantic Subpolar Gyre ◽  
Surface Variability

Abstract Surface temperature, salinity, and density are examined in the northeastern part of the North Atlantic subpolar gyre over the last 115 years of measurements. This region presents coherent variability in space but also between different seasons, with relatively small trends and large multidecadal variability. The most significant trend is a lowering in surface density. Multidecadal variability in T and S is large and is usually similar, with the largest difference between the two in the 1920s and a tendency of T to lead S. Multidecadal T and S are correlated with the winter North Atlantic Oscillation (NAO) index at 0 or 1-yr lag for T and 0 to 3-yr lag for S. This suggests a strong contribution of advection. The lag between T and S is also suggestive of a contribution of air–sea fluxes of heat or freshwater, but probably more so at high frequencies than at the multidecadal time scales. Salinity higher frequency is correlated with NAO at a 2–3-yr lag, whereas T higher frequency variability presents no correlation with NAO at any lag. This suggests different relations between seasonal NAO indices and air–sea heat fluxes patterns in this region before and after 1960; also the advective signal is more clearly identified in salinity in this region.

A high-resolution late-glacial and early Holocene diatom record from Baffin Island, eastern Canadian Arctic

1996 ◽  
Vol 33 (6) ◽  
pp. 928-937 ◽  
Author(s):  
Alexander P. Wolfe
Keyword(s):  
North Atlantic ◽  
North Atlantic Ocean ◽  
Sediment Accumulation ◽  
Late Glacial ◽  
Early Holocene ◽  
Baffin Island ◽  
Diatom Analysis ◽  
The North ◽  
Holocene Climatic Optimum ◽  
Water Ph

An interval of late-glacial to early Holocene sedimentation, spanning the period 12.9–8.4 ka BP (14C dated by accelerator mass spectrometry), is contained within 15 cm of gyttja in a core from a small lake on southwestern Cumberland Peninsula, Baffin Island. This sediment was subsampled in continuous 2.5 mm increments for diatom analysis. Extremely low sediment accumulation rates (~1.8 cm ka−1) are characteristic of the initial phase of organic sedimentation, but they increase rapidly (to 14.2 cm ka−1) after 9 ka BP. The first 0.5 cm of gyttja contained an acidophilous diatom flora resembling that of underlying mineral sediments. Thereafter, and throughout the late glacial and earliest Holocene, diatom floras were dominated by alkaliphilous and circumneutral species of Fragilaria. Around 9 ka BP, shifts to acidophilous floras dominated by Brachysira brebissonii, and, later, Eunotia rhomboidea and Frustulia rhomboides vars. saxonica and crassinervia, suggest a period of natural lake acidification. High diatom production accompanied the lowered lake-water pH, which reflects, respectively, the paleolimnological response to an early Holocene climatic optimum, and progressive depletion of lake alkalinity sources. There is no evidence of diatom or sediment responses attributable to the Younger Dryas oscillation, implying that deglacial reorganizations of the North Atlantic Ocean did not necessarily affect paleoclimatic conditions in the southern Cumberland Sound region.

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