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Impact of Medieval Fjord Hydrography and Climate on the Western and Eastern Settlements in Norse Greenland
Antoon Kuijpers, Naja Mikkelsen, Sofia Ribeiro, and Marit-Solveig Seidenkrantz

Journal of the North Atlantic, Special Volume 6 (2014): 1–13

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Journal of the North Atlantic A. Kuijpers, N. Mikkelsen, S. Ribeiro, and M.-S. Seidenkrantz 2014 Special Volume 6 1 Introduction With the ongoing debate on climate change, it has become increasingly relevant to understand how past cultures responded to longer, centennial-scale climatic shifts. Based on oxygen isotope analysis applied to Greenland ice-core material, Dansgaard et al. (1975) underlined the significance of climatic change when trying to solve the mystery of the demise of the Norse settlements in Greenland. The Greenland ice cores, however, show quantitative temperature records from high-elevation sites on the Inland Ice that may not be directly representative of the maritime climate setting of the settlement sites. These settlements were founded around AD 985; the largest one, known as the “Eastern Settlement” was located in the far southwest, while the second largest, the “Western Settlement”, was situated near present-day Nuuk. In between these two settlements, the so-called Middle Settlement represents another area inhabited by the Norse presumably until the last quarter of the 14th century (Edwards et al. 2013). In contrast to the Eastern and Western Settlement, there are no specific palaeo-hydrographic records from the Middle Settlement, which will therefore not be discussed in this contribution. Apart from climatic forcing, many other factors have been proposed as causes of the final demise of the Norse settlements. These include economic, political, and ideological structures thought to have been responsible for insufficient adaptation at times of climate deterioration (e.g., Barlow et al. 1997, Dugmore et al. 2012, Pringle 1997). Such conditions may well have forced people to emigrate. Additional factors such as hostilities with immigrating Thule (Inuit) hunters, particularly at the Western Settlement, and soil erosion by grazing livestock leading to a disastrous loss of grassland at the Eastern Settlement have been intensively debated (e.g., Fredskild 1992, Massa et al. 2011). Natural changes in regional storminess may, however, have played a significant role (Kuijpers and Mikkelsen 2009). Within this context, fertile low-lying pastures bordering the fjords have been documented to have been lost due to regional subsidence processes leading to a relative sea-level rise of up to ≈1.5 m during the ≈500-year period of Norse settlements (Mikkelsen et al. 2008). Sea ice must have played a major role in controlling the access to marine food supplies (Ogilvie et al. 2009) and at the same time it was a crucial factor affecting sailing conditions for Norse shipping, which was the means for both communication and transportation of supplies between the local communities in Greenland, Iceland, and Europe. Not only an expanded sea-ice cover, but also Impact of Medieval Fjord Hydrography and Climate on the Western and Eastern Settlements in Norse Greenland Antoon Kuijpers1,*, Naja Mikkelsen1, Sofia Ribeiro1, and Marit-Solveig Seidenkrantz2 Abstract - A comparison of the Medieval fjord hydrography and climate regime of the main Norse settlements in Greenland demonstrates important differences in the timing of sea-ice expansion and storminess when comparing the Western and Eastern Settlement regions. The Western Settlement, as well as the northern hunting grounds around Disko Bugt, had already experienced major climate deterioration in the first decades after AD 1200. This regime shift in West Greenland included an expansion of fjord and sea ice (“West Ice”) in coastal waters as well as a drastic atmospheric cooling and an increase in storminess, mainly in the summer season. In contrast, environmental conditions in the Eastern Settlement deteriorated notably later, i.e., around AD 1400. At that time, ice conditions became much more severe, whereas the previously prevailing strong wind activity decreased, which was coeval with a general decrease in aeolian activity in West Greenland, eastern Canada, and NW Iceland. Summer blockage of the fjord entrance by thick, multi-year sea ice (“Storisen”) is a specific feature of the Eastern Settlement area, whereas in the Western Settlement region, the West Ice would have threatened Norse sailing in late winter. We may thus conclude that by shortly after AD 1200 living conditions in the Western Settlement had already became less attractive due to adverse effects of the early, regional climate deterioration. Since then, the Western Settlement was probably increasingly dependent on supplies from the Eastern Settlement, where milder climate conditions continued to prevail for another century. Increased summer blockage of the Eastern Settlement fjords by the Storisen beginning around AD 1400 would have imposed serious limitations to sailing and pasture productivity in coastal areas and is suggested to have played a crucial role in the final demise of t he Eastern Settlement a few decades later. In The Footsteeps of Vebæk—Vatnahverfi Studies 2005-2011 Journal of the North Atlantic 1Geological Survey of Denmark and Greenland (GEUS), Øster Voldgade 10, DK 1350 Copenhagen K, Denmark. 2Centre for Past Climate Studies and Arctic Research Centre, Department of Geoscience, University of Aarhus, Høegh-Guldbergs Gade 2, DK 8000 Aarhus C, Denmark. *Corresponding author - aku@geus.dk. 2014 Special Volume 6:1–13 Journal of the North Atlantic A. Kuijpers, N. Mikkelsen, S. Ribeiro, and M.-S. Seidenkrantz 2014 Special Volume 6 2 increased storminess would pose a serious threat to the Norse society. Frequent (snow) storms must have had harmful effects not only on shipping but also on agriculture and outdoor livestock. Such conditions and, more generally, adverse climate change continue to have a major impact on societies in modern times (Ogilvie 2010). Hitherto, the climatic, hydrographic, and environmental conditions of the Western and Eastern Settlement have been investigated independently. Based on our previously published geological records of past climatic and hydrographic conditions, we here for the first time compare the timing of major changes in the local hydrography and climate regime, and more specifically sea-ice and wind conditions, in the areas of these two larger Norse settlements in Greenland. This comparison demonstrates important regional differences that may help explain the estimated nearly 100-year time gap between the demise of the two settlements. Present-day Hydrography and Climate Western Settlement The hydrography of the Godthåbsfjord system including Ameralik (Lysefjord), i.e., the fjord from where our environmental records originate (Fig. 1), displays various circulation modes (Mortensen et Figure 1. Overview of Norse settlement remains in the Western Settlement (“Vesterbygden”) and Eastern Settlement (“Østerbygden”).The map (after Arneborg and Grønnow 2006) also shows the location of the analyzed marine sediment cores in Ameralik, Western Settlement, and Igaliku Fjord, Eastern Settlement. References to the respective core studies are referred to in the text (see Data Sources). The small insert map of Greenland shows the geographic setting of the settlements and northern hunting grounds as well as the ocean surfacecurrent pattern and location of the offshore sediment core southwest of Disko Bugt (Ribeiro et al. 2012). Core positions are marked by an asterisk. The darker colored area in the surroundings of Disko outlines the “Northern hunting grounds” (“Nordsetur”). WS = Western Settlement; ES = Eastern Settlement. Journal of the North Atlantic A. Kuijpers, N. Mikkelsen, S. Ribeiro, and M.-S. Seidenkrantz 2014 Special Volume 6 3 al. 2011). Summer seasons are characterized by discharge of cold freshwater from the Inland Ice prevailing at the surface, while basin and deep waters of the fjord, particularly during winter season, are characterized by intermittent dense inflows from the (outer) shelf and upper continental slope (Mortensen et al. 2011). These inflows are sourced in the West Greenland Current (WGC; see Fig. 1, insert map), which entrains a mixture of cold, low-salinity Polar Water derived from the East Greenland Current (EGC) and warmer, saline Atlantic Water originating from the Irminger Current (IC) (e.g., Buch 2000, Cuny et al. 2002). Thus, the WGC is an important agent for northward advection of ocean heat along the West Greenland coast (Zweng and Münchow 2006). Present-day sea ice in the fjords is formed only for brief periods during the coldest winters and under light wind conditions (Bennike 2004). Particularly during high-pressure weather situations in winter, very strong (>10 Bft) katabatic winds may develop, blowing from the Inland Ice towards the sea and causing sudden extreme warming due to the foehn effect. Fast ice in the inner part of the fjord breaks up in May–June, which occurs in a period when winds are observed to change their prevailing direction from out-fjord to in-fjord (Mortensen et al. 2011), preventing a large-scale flushing of the ice to open waters. Offshore, the Davis Strait southern limit of the West Ice (“Vestisen”) normally extends from Disko Bugt in a southwesterly direction towards Canada, i.e., it remains well north of the Nuuk area. However, as demonstrated in the winter of 2011–2012, the sea-ice limit may occasionally reach the latitude of Nuuk, or even further south (Fig. 2). The modern (1961–1990) climate of Nuuk is low Arctic with a mean annual air temperature of -1.4 °C and 752 mm precipitation (Cappelen et al. 2001). During calm summer weather, the funneling effect of the fjord topography may lead to strengthening of the sea breeze. More generally, active cyclone passages may lead to storm winds from a prevailing southwestern direction. Eastern Settlement The hydrography of the fjords in the Eastern Settlement area is characterized by the presence of cold, low-salinity surface-water masses from the EGC (Fig. 1) entering the outer fjord, whereas at depths below ≈200 m, relatively warm (up to 4 °C) and saline Atlantic water derived from the IC is found (Horsted 1956). A seasonal trend reveals the dominance of cold EGC water masses until late summer and an increased influence of Atlantic water prevailing until early winter. In the inner part of Igaliku Fjord, where our palaeo-hydrographic reconstructions were made, freshwater discharge from the Inland Ice is significant, and lower salinities are found over almost the entire water column. The outer fjord has no shallow sill, and the seabed gradually deepens seaward (Herman et al. 1972). Several islands separate the inner parts from the outer Igaliku fjord, limiting water-mass exchange and creating more uniform conditions in the inner part of the fjord. Here, the hydrographic conditions are largely determined by the current pattern of the upper 100 m and by local air temperatures (Horsted 1956). During normal winter conditions, a sea-ice cover is restricted to the innermost part of the fjord and adjacent embayments. In the outer part of Igaliku Fjord, multi-year, polar pack ice (“Storisen”; Fig. 3) entrained by the EGC is present during several months, normally from late winter or early spring until early to mid-summer. In the area around Cape Farewell, the concentration of this drift ice is greatest between February and June (Buch 2000). The climate of the Eastern Settlement is subarctic with a more sub-continental regime prevailing in the inland areas, whereas coastal areas experience more maritime conditions. Weather conditions can change drastically in relation to the respective passage of warm- and cold-front zones of major Atlantic cyclone systems on their easterly track following the oceanic Polar Front zone south of Cape Farewell. The strongest storms normally occur during winter and enter into this area from a southeasterly direction. In addition, particularly in winter and early spring, the area is occasionally exposed to very strong katabatic winds from a predominantly northeasterly direction that influence erosion and aeolian deposition patterns and prevent the formation of more extensive sea ice in the fjord (Jacobsen 1987). Data Sources The palaeo-environmental information used in our study is based on our investigations carried out in the fjords or adjacent coastal waters of both the Western Settlement (Møller et al. 2006, Ribeiro et al. 2012, Seidenkrantz et al. 2007) and Eastern Settlement (Jensen et al. 2004, Lassen et al. 2004, Roncaglia and Kuijpers 2004). For the Eastern Settlement, these previously published results are supported by onshore studies reported by Kuijpers and Mikkelsen (2009) and Mikkelsen et al. (2008) dealing with aeolian activity and relative sea-level rise, respectively. As previously stated, the area around the Middle Settlement has so far not been the target of our fjord investigations and will therefore be excluded from further discussion. Journal of the North Atlantic A. Kuijpers, N. Mikkelsen, S. Ribeiro, and M.-S. Seidenkrantz 2014 Special Volume 6 4 Regional Climate Complexity In contrast to the general global warming trend of the late 20th century, cooling has in fact been observed in coastal southwestern Greenland (Hanna and Cappelen 2003). The authors found that this could only partly be explained by the large-scale atmospheric circulation pattern associated with a positive North Atlantic Oscillation (NAO; Hurrell 1995) mode. Moreover, a cooling trend had already started in the 1940s in eastern Canada (Kaspar and Allard 2001), which clearly predated the transition to a positive NAO regime later in the 20th century. Thus, Figure 2. Extent of the “West Ice” (“Vestisen”) in Baffin Bay and the northern Labrador Sea reaching far south into coastal waters south of Nuuk, early March 2012 (Ice Service, Danish Meteorological Institute). Various sea-ice classes and types (e.g., thickness, coverage, etc.) are indicated by the standard sea ice “egg” symbols of the World Meteorological O rg a n i s a t i o n (see also Fig. 3). Journal of the North Atlantic A. Kuijpers, N. Mikkelsen, S. Ribeiro, and M.-S. Seidenkrantz 2014 Special Volume 6 5 apparently a complex relation exists between the Labrador Sea region in the west and the North Atlantic region further to the east. An air-temperature “seesaw” during winter between West Greenland and northern Europe was first reported in AD 1765 (van Loon and Rogers 1978). This early observation of the effect of the now well-known phenomenon of the NAO was reported in a diary of Hans Egede Saabye, who was a missionary in Greenland during the late 18th century. He wrote: “In Greenland, all winters are severe yet they are not all alike. The Danes have noticed that when the winter in Denmark was severe, as we perceive it, the winter in Greenland in its manner was mild, and conversely.” Such North Atlantic regional climate complexity is also underlined by the study of Dawson et al. (2003), who report the absence of a low-temperature extreme in the Greenland GISP2 ice-core record between AD 1650 and 1710, the period when the “Little Ice Age” (LIA) cooling was at its maximum in Europe. Also, on longer time scales, accumulating evidence points to more persistent, centennial-scale regional contrasts in marine climate conditions when comparing the Labrador Sea and Davis Strait region with the Northeast Atlantic region (Krawczyk et al. 2010; Ribeiro et al. 2012; Seidenkrantz et al. 2007, 2008). Such a regionally complex pattern thus seems also to have existed for the Medieval (warm) Climate Anomaly (MCA) and its intervening cooling episodes. The timing of the transition to the generally colder LIA regime likewise appears not to have been synchronous across the North Atlantic (e.g., Dawson et al. 2003). Within the above context, it is important to note the location of the Western and Eastern Settlements with regard to dominant patterns of cyclone activity. The Western Settlement is mainly affected by the behavior of the low-pressure “Baffin Bay Trough” (Williams and Bradley 1985), whereas the Eastern Settlement is strongly exposed to the frontal passages associated with major North Atlantic cyclone systems on their (north-) easterly tracks south of Cape Farewell. Thus, with this background information, the question arises as to how much the Medieval hydrographic and climatic conditions of the Western Settlement may have differed from those which prevailed in the Eastern Settlement, a possibly important factor when trying to explain the different timing for the demise of the two settlements (e.g., Barlow et al. 1997, McGovern 1991). Figure 3. Areal distribution of multi-year pack ice (“Storisen”) entrained by the East Greenland Current that blocked the fjord entrances of the Eastern Settlement area, 11–12 May 2012 (Ice Service, Danish Meteorological Institute). With the gradual retreat of the West Ice, coastal waters offshore West Greenland had meanwhile become ice-free all the way up to Disko. Journal of the North Atlantic A. Kuijpers, N. Mikkelsen, S. Ribeiro, and M.-S. Seidenkrantz 2014 Special Volume 6 6 Widespread sea-ice cover in the fjord after ca. AD 1200 is also suggested by an increasing sand size fraction. Gravel-sized and coarser material typically produced by ice rafting processes, including glacial ice in the form of drifting icebergs, is, however, lacking in the marine sediment cores (Møller et al. 2006). The timing of this environmental change is part of a major re-organization of the entire North Atlantic circulation regime, and presumably linked to a centennial-scale climate shift at inter-hemispheric scale (Kuijpers et al. 2009). Offshore West Greenland, evidence has been found for increased primary productivity prevailing from around AD 1250 until shortly after AD 1500 (Ribeiro et al. 2012), which is the time of more extreme LIA cooling referred to above. This enhanced productivity can be explained by upwelling processes along the Baffin sea-ice edge moving southward at that time. Within this context, it should be noted that the core site referred to in Ribeiro et al. (2012) is located on the open shelf well outside the normal reach of the annually forming local sea-ice cover within Disko Bugt. Alternatively, the increased productivity signal may be interpreted to reflect stronger wind-induced surface-water mixing during the plankton-blooming season in (early) summer. An increase in aeolian activity between AD 1280 and 1410 is supported by studies of aeolian deposits related to West Greenland valley-sandurs (Willemse et al. 2003). This period appears to represent the transitional stage from the MCA into the LIA in West Greenland. Thus, it appears that environmental conditions in the Western Settlement area had already deteriorated around or shortly after AD 1200. This change thus included a drastic expansion of sea ice in the fjords, implying a cold winter climate with a low storm frequency. In contrast, combined evidence from aeolian deposits (Willemse et al. 2003) and offshore environmental records (Ribeiro et al. 2012) demonstrates increased storminess, which consequently must have been concentrated in the warmer season. This scenario may also imply a higher spring–autumn snowstorm frequency and repeated thawing and freezing, which must have been devastating for livestock and crops as these are entirely dependent on growing and grazing conditions during the warmer part of the year. Eastern Settlement The fjord hydrography of the Eastern Settlement was characterized between AD 885 and ca. AD 1250 by intensive mixing of the water column and associated increased productivity (Lassen et al. 2004, Medieval Hydrography and Climate Western Settlement Palaeo-oceanographic investigations have shown that at the time of arrival of the first Norse settlers (ca. AD 1000), hydrographic conditions in the fjords of the Western Settlement were characterized by reduced bottom-water ventilation due to limited inflow of saline water masses (subsurface) sourced in the WGC, presumably as a consequence of significant melt-water outflow and reduced contribution of IC water to the WGC (Seidenkrantz et al. 2007). Enhanced freshwater discharge from the West Greenland Inland Ice margin at that time is also indicated by a retreat of the Jacobshavn Isbræ in Disko Bugt (Lloyd 2005), i.e., the main northern hunting ground for the Norse (for location, see Disko in Fig. 1 insert map). Under calm winter weather, low salinity of the surface waters in the fjords must have favored the occasional growth of a fjord sea-ice cover as reported by Seidenkrantz et al. (2007). The WGC over the shelf further offshore, however, appears to display generally warmer conditions between the time of Norse arrival and ca. AD 1250 (Ribeiro et al. 2012), which is followed here by increasing cooling towards the onset of the LIA. This conclusion is supported by alkenone-based palaeo-temperature estimates of West Greenland lake records (D’Andrea et al. 2011) showing an abrupt temperature decline beginning near AD 1200 with a temperature decrease of 4 °C within about 80 years. At approximately the same time, the fjord environment of the Western Settlement drastically changed. Sea-ice formation became widespread along with increased water-column stratification. This change can be ascribed to an enhanced influx of saline, WGC-derived subsurface water concurrent with a surface melt-water outflow (Seidenkrantz et al. 2007, 2009). In addition, another important factor required for the formation of widespread ice in the fjords is calm weather and the absence of strong katabatic winds that otherwise would drive the ice seaward out of the fjords. A decrease in melt-water discharge is also indicated by the lower counts of the chemical elements potassium (K) and titanium (Ti) (Seidenkrantz et al. 2007), both representing detrital minerals of continental origin. Lake records from the area (D’Andrea et al. 2011, Olsen et al. 2012) indicate persisting lower temperatures until approx. AD 1380. This scenario is confirmed by the K and Ti data referred to above showing a marked K and Ti peak at ca. AD 1400 suggesting a short-term return to warmer climate at that time. A renewed and significant decrease in K and Ti counts reflects a transition into the following, more extreme LIA cooling. Journal of the North Atlantic A. Kuijpers, N. Mikkelsen, S. Ribeiro, and M.-S. Seidenkrantz 2014 Special Volume 6 7 happened concurrent with an increased influx of Atlantic- derived subsurface water (Lassen et al. 2004), somewhat resembling the hydrographic scenario previously described for the Western Settlement fjords (e.g., Seidenkrantz et al. 2007). It is assumed that this change also represents a major increase in the duration of the blockage of the fjord entrance by annual multi-year sea (Figs. 3, 4). This change coincided with a general decrease in wind activity in the area, an aeolian pattern also recognized in South Greenland lake deposits (Andresen et al. 2004) and in records of storm activity from northwest Iceland (Andresen et al. 2005). During the preceding time span, i.e., between ca. AD 850 and AD 1370, eastern Canada was also affected by strong cyclone activity (Kaspar and Allard 2001). In contrast, the ice-core deuterium record from central Greenland shows that here storm frequencies did increase after AD 1400, presumably as a consequence of a major re-organization in atmospheric circulation dated at about AD 1420 (Mayewski et al.1993, Meeker and Mayewski 2002). As the main North Atlantic extra-tropical cyclone tracks tend to follow the ocean polar front zone, it thus seems that the Eastern Settlement experienced pronounced changes in ice and wind conditions associated with the latter large-scale shift in atmosphere-ocean interaction patterns, which occurred about two centuries after the West Greenland regime shift. Discussion and Conclusion The specific climatic and hydrographic responses to the transitional period between the MCA and LIA are notably different for the Western and Eastern Settlements (Table 1). This fundamental difference in the climatic and environmental history of the two settlements is proposed to have played a crucial role for the timing of the demise of the respective settlements. Here it must be underlined that this does not imply that factors of societal and economic relevance could not also have played a further, important role (e.g., Dugmore et al. 2012). As previously mentioned, the presence of sea ice during longer periods can be assumed to have had a serious impact on the Norse. Apart from imposing hazards to regional and transatlantic sailing, fishing and hunting of marine mammals would also be affected. In addition, the production potential of low- Roncaglia and Kuijpers 2004). Significant bottomwater ventilation is characteristic for most of this period, i.e., AD 960–1285, with a peak oxygenation event dated at ca. AD 1125 (Roncaglia and Kuijpers 2004). The latter authors further documented an increased influx of terrestrial leaf tissue, suggesting an important material input by wind transport or freshwater run-off processes. A reduction in local pollen fluxes (Jessen et al. 2011) suggests a change in wind pattern or run-off conditions close to AD 1200, i.e., at the time of the marked regime shift in West Greenland coastal areas (Nørgaard-Pedersen and Mikkelsen 2009). Onshore studies of aeolian deposits confirm that MCA wind activity was strongest after AD 1000, reaching a maximum close to AD 1300 (Kuijpers and Mikkelsen 2009), after which the atmospheric circulation intensity in this area decreased. The marine evidence of strong, atmospherically induced surface-water mixing suggests that erosion around the Eastern Settlement during the Norse period may thus have been primarily related to increased wind strength instead of being attributable to farming activities (e.g., Jacobsen 1991). Lake records document decreasing agro-pastoral activities during the Norse era (Massa et al. 2011), which supports a shift in diet toward other, increasingly marine resources (Arneborg et al. 1999). Enhanced wind-induced water-mass mixing favoring marine primary production during the latter part of the Norse era can be assumed to have had positive effects on the fish and marine mammals standing stock in the fjords, making fishing and hunting here more profitable. More generally, the hydrographic reconstruction in Igaliku Fjord reveals two major climate regimes: i.e., the MCA between ca. AD 800 and AD 1250 and the LIA between ca. AD 1580 and AD 1850, separated by a variable transitional period (Jensen et al. 2004). Cold, ice-loaded EGC water masses did not significantly affect the area prior to about AD 1400. This scenario based on diatom data is confirmed by the foraminiferal studies of Lassen et al. (2004), who document a first cooling step culminating at AD 1405. Jensen et al. (2004) report that since the arrival of the Norse, sea-ice formation in the fjords had been very limited. A marked change occurred around AD 1435 as the Igaliku Fjord was flooded by cold, EGC-derived surface-water masses and fjord ice expanded (Jensen et al. 2004). This shift Table 1. Timing of Medieval ice- and wind-regime shift in the Greenland Norse settlements. Western Settlement Eastern Settlement Widespread fjord ice formation starting ca. AD 1200 ca. AD 1400 Enhanced aeolian activity/storminess ca. AD 1250–1410 (1500) spring-summer-autumn ca. AD 900–1370 (1420) all-season? Journal of the North Atlantic A. Kuijpers, N. Mikkelsen, S. Ribeiro, and M.-S. Seidenkrantz 2014 Special Volume 6 8 Figure 4. Aerial photographs illustrating belts of dense, multi-year pack-ice (“Storisen”) blocking South Greenland fjord entrances in the Eastern Settlement area (Ice Service, Danish Meteorological Institute). Photograph A provides an overview of long stretches of Storisen extending along the coast, whereas photograph B illustrates in more detail the potential hazards for small vessels when attempting to navigate in this type of dense drift ice. Journal of the North Atlantic A. Kuijpers, N. Mikkelsen, S. Ribeiro, and M.-S. Seidenkrantz 2014 Special Volume 6 9 land pastures adjacent to (summertime) ice-filled fjords is known to be significantly reduced due to the ice-cooling effect on the near-field air temperature regime, which during calm weather often leads to the formation of fog. In the present day, a marked difference in sea-ice formation and pack-ice drift can be noted for the areas of the Western and Eastern Settlements. Due to the warming effect of the WGC, and particularly the occurrence of strong katabatic winds during winter, the region of Nuuk is today normally characterized by the absence of locally formed, coastal sea ice of any significance. The seldom occurrence of more extensive sea ice along the coast (see Fig. 2) is the result of advection of the West Ice in late winter, a process strongly controlled by the prevailing wind pattern, which depends on the actual position of the “Baffin Bay Trough” and large-scale NAO regime. These conditions are in marked contrast to those prevailing in the Eastern Settlement area, where from late winter to midsummer large amounts of thick, multi-year drift ice (“Storisen”) entrained by the East Greenland Current can block the entrance of the fjord systems (Fig. 4). This blockage occurred, for instance, in 1995, as drift ice appeared as early as January and reached as far as 250 km south of Cape Farewell. In 1970, the fjord entrance did not become ice-free until August (Centre for Ocean and Ice, Danish Meteorological Institute). Previous observations, i.e., in the mid-19th century, have documented this Storisen blockage persisting all through the summer and on into late autumn (Fig. 5), a situation which may have been not uncommon during the preceding Little Ice Age. Deterioration of the ice situation in Igaliku fjord around AD 1400 may be linked to a significant increase of drift ice entrained by the East Greenland Current, as is supported by historical observations made on Iceland (Ogilvie 1984). Before AD 1400, intense wind-induced surface-water mixing of both Greenland coastal waters and inner fjord waters (Kuijpers and Mikkelsen 2009, Lassen et al. 2004) suggest a largely ice-free fjord system during most of the year. This situation is in marked contrast to the ice conditions in the fjords of the Western Settlement prior to AD 1400. Here, a major shift in the hydrography of the fjords with the formation of a more extensive sea-ice cover in the fjords (Seidenkrantz et al. 2007) and an abrupt atmospheric cooling (D’Andrea et al. 2011) had already occurred shortly after AD 1200. Offshore sailing and hunting conditions in the northern hunting ground area (see Fig. 1) presumably also deteriorated, as suggested by southward expansion of the Baffin Bay sea ice after ca. AD 1250 and increased storminess during the warmer season based on combined onshore and offshore evidence (Ribeiro et al. 2012, Willemse et al. 2003). In contrast, expanding sea ice in the fjords implies a lower frequency of katabatic wind episodes during winter, i.e., an altered atmospheric pressure regime. Adverse ice and weather conditions during spring and summer, respectively, affecting the northern hunting grounds around Disko Bugt may have led to losses not only in terms of food supply, but also in terms of the economy. Resources (e.g., walrus ivory) from this area had been an important export to Europe, but the increasingly harsh weather conditions made this hunting and trade less profitable at a time when prices in Europe for walrus ivory were also decreasing (Guérin 2010). This early expansion of Baffin Bay sea ice was notably coeval with a general increase of the Arctic Ocean sea-ice cover during the period AD 1200 to AD 1450 (Kinnard et al. 2011). As a consequence, after AD 1200, sea-ice export from the Arctic via the East Greenland Current and Canadian archipelago may also have increased, as observed on Iceland (Ogilvie 1984). The regime shift recorded in West Greenland around AD 1200 appears to have been part of an Atlantic-wide, large-scale re-organization of ocean and atmosphere circulation (Kuijpers et al. 2009). The hydrographic and climatic implications of this early shift were, however, initially less pronounced in southernmost Greenland. Apart from a slight increase in the advection of EGC waters into Igaliku Fjord (Jensen et al. 2004) and an apparently Figure 5. Scan of a table (Fritz 1881) reporting observed variations in the duration of dense, multi-year pack-ice (“Storisen”) blockage of southwest Greenland fjords during the period 1867–1879. Note the extreme long period of blockage in 1868 lasting until November, a situation which may have been not uncommon during the preceding “Little Ice Age”, i.e., the period after ca. AD 1400. Journal of the North Atlantic A. Kuijpers, N. Mikkelsen, S. Ribeiro, and M.-S. Seidenkrantz 2014 Special Volume 6 10 in atmospheric circulation (wind pattern) over the Davis Strait and Baffin Bay, which must have had an important effect on both sea-ice formation in the fjords of the Western Settlement and particularly, on the drift pattern of “West Ice” (Vestisen) offshore West Greenland. This shift seems to have occurred at an early stage concurrent with the expansion of Arctic sea ice (Kinnard et al. 2011). The transatlantic cyclone belt from eastern Canada towards Iceland thus moved gradually south, and even at this initial stage, the shift from strongly zonal (NAO+) to a more frequent meridional atmospheric circulation (NAO-) regime must have had an immediate impact on Baffin Bay atmospheric circulation and the position of the Baffin Bay trough. With a major decrease in storminess over southernmost Greenland coinciding with a significant expansion of ice-loaded Polar water masses around AD 1400, the Eastern Settlement would also have been affected by a major, long-term environmental change. This change would include widespread ice formation in the fjords and presumably a markedly increased summer blockage of the fjord entrance by multi-year Polar drift ice. The latter is suggested by a significantly enhanced influx of EGC polar surface-water masses reaching also the inner parts of Igaliku Fjord (Jensen et al. 2004). The demise of the Eastern Settlement in the mid-fifteenth century (Arneborg et al. 1999) thus occurred relatively fast, i.e., only a few decades after the summer ice-blockage situation had severely deteriorated. In contrast, the population in the Western Settlement had survived for roughly a century after they had been confronted with a marked deterioration of the winter ice conditions and cooling in combination with a more stormy summer weather climate towards the end of their settling history. One possible explanation for this much shorter period until the final demise of the Eastern Settlement may be that during a large part of the summer season the fjord entrance to the Eastern Settlement was blocked by Storisen, which made small-vessel shipping in and out of the Eastern Settlement extremely risky or impossible (Fig. 4). Moreover, with the summer pack ice and calmer weather, the probability of days with coastal fog due to cooling of warmer air masses advected over the pack ice zone may also have increased, another factor adding to navigational risks. A similar physical threat by pack ice to maritime transport during summer most likely did not exist at the Western Settlement, but after AD 1200, the living conditions here had already become more and more unattractive due to the adverse effects of the early climate deterioration in this region. During minor change in prevailing wind direction or precipitation regime suggested by a marine pollen record (Jessen et al. 2011), no drastic change in the general ice situation or climate regime can be noted here at that time. More generally, the regional complexity of reconstructing large-scale changes of ocean and atmospheric circulation has been clearly illustrated by Dawson et al. (2003), who found that LIA storminess as recorded at the central Greenland GISP2 icecore site was not coincident with the stormiest winters of the last millennium known from Iceland and Western Europe. This pattern is also evident from marine sediment records obtained from the fjord entrance to the Eastern Settlement (Nørgaard-Pedersen and Mikkelsen 2009) and thus also applies to the low-elevation areas of our study where periods of aeolian activity were not completely synchronous. Storminess in southernmost Greenland was notably coincident with storminess in eastern Canada (Kaspar and Alard 2001) and NW Iceland (Andresen et al. 2005). Maximum aeolian activity in the Eastern Settlement close to AD 1300 (Kuijpers and Mikkelsen 2009) was, however, concurrent with the West Greenland storminess peak (AD 1280–1410) recorded by Willemse et al. (2003) and may result from a combination of frequent outbreaks of cold, polar air masses and relatively warm sea-surface conditions promoting strong atmospheric instability and cyclone genesis. A positive ocean surface-temperature anomaly that developed after AD 1200 has been found to characterize waters around southern Greenland and large parts of the sub-polar gyre including the Irminger Sea and the northeastern Labrador Sea (Andresen et al. 2012, Krawczyk et al. 2013, Miettinen et al. 2012, Seidenkrantz et al. 2007). In addition, Gulf Stream temperatures off the northeastern US were anomalously high (Van der Schrier and Weber 2010). Miettinen et al. (2011) could demonstrate for the later, coldest part of the LIA, a systematic negative correlation between reconstructed positive SST anomalies recorded in the central North Atlantic south of Iceland and negative NAO conditions. This correlation is confirmed by other evidence (Van der Schrier and Barkmeijer 2005) showing that during periods of anomalously LIA cold in Western Europe, for example during the so-called “Dalton (solar) Minimum” (AD 1790–1820), the North Atlantic extra-tropical cyclone belt was displaced to the south, a typical feature of a negative NAO circulation regime. A trend towards more negative NAO patterns after AD 1200 (Kuijpers et al. 2009, Trouet et al. (2009) implies an important change Journal of the North Atlantic A. Kuijpers, N. Mikkelsen, S. Ribeiro, and M.-S. Seidenkrantz 2014 Special Volume 6 11 summer and early autumn, sufficient supplementary supplies for daily subsistence could probably still be provided through shipping support from the Eastern Settlement. This supplementation may have included food, (winter) fodder for domestic animals and fuel for heating. Such a scenario would simultaneously contribute to the interpretation of preliminary results from lead isotope studies (Frei 2012), which show that the Western Settlement Norse have a lead isotope composition representative of the Eastern Settlement geological background. Within this context, it may not be a coincidence that the final demise of the Western Settlement is dated in the years around AD 1350 (Barlow et al. 1997, Pringle 1997), which in the northern North Atlantic represents an episode characterized by a series of extremely severe winters and very cold summers (Stuiver et al. 1995). Such a climatic regime suggests that in the Eastern Settlement area, which is more directly influenced by North Atlantic climate, grass harvesting during these years would have been at a minimum, leading to a local shortage with no excess supplies of fodder and fuel available for any further support of the Western Settlement. Acknowledgments This is a contribution to the TROPOLINK and OCEANHEAT projects funded by the Danish Council for Independent Research/Natural Science (FNU Grants 09-069833 and 12-126709, AKU and MSS), the EU FP7 project “Past4Future” (Project No. 243908, MSS), and former projects funded by FNU/SNF (Grants 9701901 and 9802945, AKU et al.) as well as the Nordic Arctic Research Programme (NM). The German Research Council (“DFG”) is gratefully acknowledged for having funded the research cruises of RV Poseidon (1998), Alexander von Humboldt (2002), and Maria S. Merian (2007), during which the respective cores discussed in this study were collected. Furthermore, the Commission for Scientific Research in Greenland, the Royal Greenland Foundation, and the Bikuben Foundation are thanked for financial support of the Greenland leg (2006) of the Danish Galathea3 Expedition. Special thanks are due to Dr. Gerd Hoffmann-Wieck (IfMGeomar Kiel) and Prof. Jan Harff (IOW Warnemünde) for their crucial role in German ship-time application procedures and organizational efforts related to respective (1998–2002, 2007) cruises. We thank the Ice Service, Centre for Ocean and Ice at the Danish Meteorological Institute, for the aerial photographs used in this contribution. Literature Cited Andresen, C.S., S. Björck, and G. Bond. 2004. Holocene climate changes in southern Greenland: Evidence from lake sediments. Journal of Quaternary Science 19:783–795. Andresen, C.S., G. Bond, A. Kuijpers, P.C. Knutz, and S. Björck. 2005. Holocene climate variability and multidecadal time-scales detected by sedimentological indicators in a shelf core NW off Iceland. Marine Geology 214:323–338. Andresen, C.S., M. Hansen, M.-S. Seidenkrantz, A.E. Jennings, M.F. Knudsen, N. Nørgaard- Pedersen, N. Larsen, A. Kuijpers, and C. Pearce. 2012. Late Holocene oceanographic variability on the Southeast Greenland shelf. The Holocene doi: 10.1177/0959683612460789. Arneborg, J., and B. Grønnow (Eds.). 2006. Dynamics of Northern Societies. National Museum, Copenhagen, Denmark. 415 pp. Arneborg, J., J.Heinemeier, N. Lynnerup, L.H. Nielsen, N, Rud, and A.E. Sveinbjørnsdottir.1999. Change of diet of the Greenland Vikings determined from stable carbon isotope analysis and 14C dating of bones. Radiocarbon 41:157–168. Barlow, L.K., J.P. Sadler, A.E.J. Ogilvie, P.C. Buckland, T. Amorosi, J.H. Ingimundarson, P. Skidmore, A.J. Dugmore, and T.H. McGovern. 1997. Interdisciplinary investigations of the end of the Norse Western Settlement in Greenland. The Holocene 7:489–499. Bennike, O. 2004. Holocene sea-ice variations in Greenland: Onshore evidence. The Holocene 14:607–613. Buch, E. 2000. A monograph on the physical oceanography of the Greenland waters. Danish Meteorological Institute, Copenhagen, Denmark. Scientific Report 00-12. 405 pp. Cappelen, J., B.V. Jørgensen, E.V. Laursen, L.S. Stannius, and R.S.Thomsen. 2001. The observed climate of Greenland, 1958–1999 with climatological standard normals, 1961–1990. Danish Meteorological Institute, Copenhagen, Denmark. Report 00-18. 115 pp. Cuny, J., P.B. Rhines, P.P. Niiler, and S. Bacon. 2002. Labrador Sea boundary currents and the fate of the Irminger Sea Water. Journal of Physical Oceanography 32:627–647. D’Andrea, W.J., Y. Huang, S.C. Fritz, and N.J. Anderson. 2011. Abrupt Holocene climate change as an important factor for human migration in West Greenland. PNAS 108 (24):9765–9769. Dansgaard, W., S.J. Johnsen, N. Reeh, N. Gundestrup, H.B. Clausen, and C. Hammer. 1975. Climatic changes, Norsemen, and modern man. Nature 255:24–28. Dawson, A.G., L. Elliott, P. Mayewski, P. Lockett, S. Noone, K. Hickey, T. Holt, P. Wadhams, and I. Foster. 2003. Late Holocene North Atlantic climate seesaws, storminess changes, and Greenland ice sheet (GISP2) palaeoclimates. The Holocene 13:381–392. Dugmore, A.J., T.H. McGovern, O. Vésteinsson, J. Arneborg, R. Streeter, and C. Keller. 2012. Cultural adaption, compounding vulnerabilities, and conjunctures in Norse Greenland. PNAS 109(10):3658–3663. Edwards, K.J., G.T. Cook, G. Nyegaard, and J.E. Schofield. 2013. Towards a first chronology for the Middle Settlement of Norse Greenland: 14C and related studies of animal bone and environmental material. Radiocarbon 55(1):13–29. Fredskild, B. 1992. Erosion and vegetational changes in South Greenland caused by agriculture. Geografisk Tidskrift 92:14–21. Journal of the North Atlantic A. Kuijpers, N. Mikkelsen, S. Ribeiro, and M.-S. Seidenkrantz 2014 Special Volume 6 12 Frei, D. 2012. Lead isotopes and the Viking Colonization of the North Atlantic. Paper presented at the Vatnahverfi Workshop, National Museum, Copenhagen, Denmark. 21–22 March 2012. Fritz, S. 1881. Nogle Iagttagelser om Isforholdene paa Grønlands Sydvestkyst. Geografisk Tidsskrift 5:78–81. Guérin, S.M. 2010. Avorio d’ogni ragione: The supply of elephant ivory to northern Europe in the Gothic era. Journal of Medieval History 36(2):156–174. Hanna, E., and J.Cappelen. 2003. Recent cooling in coastal southern Greenland and relation with the North Atlantic Oscillation. Geophysical Research Letter 30(3), DOI:10.1029/2002GL015797. Herman, Y., J. O’Neil, and C.L. Drake. 1972. Micropaleontology and paleotemperature of postglacial SW Greenland fjord cores. Pp 357–407, In Y. Vasari, H. Hyvärinen, S. Hicks (Eds.). Climatic Changes in Arctic Areas During the Last Ten Thousand Years, University of Oulu, Geological Series A (1, 3), 469 pp. Horsted, S.A. 1956. Hydrographic-biological investigations of the southwest Greenland prawn grounds. Meddelelser fra Danmarks Fiskeri- og Havundersøgelser, Ny Serie 1:61–116. Hurrell, J.W. 1995. Decadal trends in the North Atlantic Oscillation and relationships to regional temperature and precipitation. Science 269:676–679. Jacobsen, N.K. 1987. Studies on soils and potential for soil erosion in the sheep farming area of South Greenland. Arctic and Alpine Research 19(4):498–507. Jacobsen, B.H. 1991. Soil resources and soil erosion in the Norse settlement area of Østerbygden in Southern Greenland. Acta Borealia 1:56–68. Jensen, K.G., A. Kuijpers, N. Koc, and J. Heinemeier. 2004. Diatom evidence of hydrographic changes and ice conditions in Igaliku Fjord, South Greenland, during the past 1500 years. The Holocene 14 (2):152–164. Jessen, C.A., S. Solignac, N. Nørgaard-Pedersen, N. Mikkelsen, A. Kuijpers, and M.-S. Seidenkrantz. 2011. Exotic pollen as an indicator of variable atmospheric circulation over the Labrador Sea during the mid- to late Holocene. Journal of Quaternary Science 26(3):286–296. Kaspar, J.N., and M. Allard. 2001. Late Holocene climatic changes as detected by the growth and decay of ice wedges on the southern shore of Hudson Strait, northern Québec, Canada. The Holocene 11(5):563–577. Kinnard, C., C.M. Zdanowicz, D.A. Fisher, E. Isaksson, A. de Vernal, and L.G. Thompson. 2011. Reconstructed changes in Arctic sea-ice cover over the past 1450 years. Nature 479:509–512. Krawczyk, D., A. Witkowski, M. Moros, J.M. Lloyd, A. Kuijpers, and A. Kierzek. 2010. Late-Holocene interaction between climate and hydrology of the West Greenland Current from Disko Bugt, central West Greenland. The Holocene doi:10.1177/0959683610371993. Krawczyk, D., A. Witkowski, J.M. Lloyd, M.Moros, J. Harff, and A. Kuijpers. 2013. Late-Holocene diatomderived seasonal variability in hydrological conditions off Disko Bay, West Greenland. Quaternary Science Reviews 67:93–104. Kuijpers, A., and N. Mikkelsen. 2009. Geological records of changes in wind regime over South Greenland since the Medieval Warm Period: a tentative reconstruction. Polar Record 45(232):1–8. Kuijpers, A., B.A. Malmgren, and M.-S. Seidenkrantz. 2009. Termination of the Medieval Warm Period: Linking subpolar and tropical N-Atlantic circulation changes to ENSO. PAGES News 17(2):76–77. Lassen, S.J., A. Kuijpers, H. Kunzendorf, G. Hoffmann- Wieck, N. Mikkelsen, and P. Konradi. 2004. Late Holocene Atlantic bottom water variability in Igaliku Fjord, South Greenland, reconstructed from foraminiferal faunas. The Holocene 14(2):165–171. Lloyd, J.M. 2005 Late Holocene environmental change in Disko Bugt, West Greenland: Interaction between climate, ocean circulation and Jakobshavn Isbræ. Boreas 35:35–49. Massa, C., V. Bichet, É. Gauthier, B.B. Perren, O. Mathieu, C. Petit, F. Monna, J. Giraudeau, R. Losno, and H. Richard. 2011. A 2500-year record of natural and anthropogenic soil erosion in South Greenland. Quaternary Science Reviews doi:10.1016/j.quascirev. 2011.11.014. Mayewski, P.A., L.D. Meeker, M.C. Morrison, M.S. Twickler, S. Whitlow, K.K. Ferland, D.A. Meese, M.R. Legrand, and J.P.Steffensen.1993. Greenland ice-core signal characteristics: An expanded view of climate change. Journal of Geophysical Research 98(D7):12839–12847. McGovern, T.H. 1991. Climate, correlation, and causation in Norse Greenland. Arctic Anthropology 28:77–100. Meeker, L.D., and P.A.Mayewski. 2002. A 1400-year high-resolution record of atmospheric circulation over the North Atlantic and Asia. The Holocene 12:257–266. Miettinen, A., N. Koc, I.R. Hall, F. Godtliebsen, and D. Divine. 2011. North Atlantic sea-surface temperatures and their relation to the North Atlantic Oscillation during the last 230 years. Climate Dynamics 36:533–543. Miettinen, A., D. Divine, N. Koc, F. Godtliebsen, and I.R. Hall. 2012. Multicentennial variability of the Sea Surface Temperature gradient across the subpolar North Atlantic over the last 2.8 kyr. Journal of Climate 25:4205–4219. Mikkelsen, N., A. Kuijpers, and J. Arneborg, J. 2008. The Norse in Greenland and late Holocene sea-level change. Polar Record 44(228):45–50. Mortensen, J., K. Lennert, J. Bendtsen, and S. Rysgaard. 2011. Heat sources for glacial melt in a sub-arctic fjord (Godthåbsfjord) in contact with the Greenland Ice Sheet. Journal of Geophysical Research 116 (C1) doi:10.1029/2010JC006528. Møller, H.S., K.G. Jensen, A. Kuijpers, S. Aagaard- Sørensen, M.-S. Seidenkrantz, M. Prins, R. Endler, and N. Mikkelsen. 2006. Late Holocene environment and climatic changes in Ameralik Fjord, southwest Greenland. Evidence from the sedimentary record. The Holocene 16(5):685–695. Nørgaard-Pedersen, N., and N. Mikkelsen. 2009. A 8000-years marine record of climate variability and fjord dynamics from Southern Greenland. Marine Geology 264:177–189 Journal of the North Atlantic A. Kuijpers, N. Mikkelsen, S. Ribeiro, and M.-S. Seidenkrantz 2014 Special Volume 6 13 Research 59:322–344. Williams, L.D., and R.S. Bradley. 1985. Paleoclimatology of the Baffin Bay region. Pp. 741–772, In J.T. Andrews (Ed.). Quaternary Environments of the Eastern Canadian Arctic, Baffin Bay and Western Greenland. Allen and Unwin, New York, NY, USA. 798 pp. Zweng, M.M., and A. Münchow. 2006. Warming and freshening of Baffin Bay, 1916–2003. Journal of Geophysical Research 111 (C7) doi:10.1029/2005JC003093. Ogilvie, A.E.J. 1984. The past climate and sea-ice record from Iceland, Part I: Data to AD 1780. Climatic Change 6:131–152. Ogilvie, A.E.J. 2010. Historical climatology, climatic change, and implications for climate science in the 21st century. Climatic Change 100:33–47. Ogilvie, A.E.J., J.M. Woollett, K. Smiarowski, J. Arneborg, S. Troelstra, A. Kuijpers, A.Pálsdóttir, and T.H. McGovern. 2009. Seals and sea ice in medieval Greenland. Journal of the North Atlantic 2:60–80. Olsen, J., N.J. Anderson, and M.F. Knudsen. 2012. Variability of the North Atlantic Oscillation over the past 5200 years. Nature Geoscience 5:808–812. Pringle, H.1997. Death in Norse Greenland. Science 275:924–926. Ribeiro, S., M. Moros, M. Ellegaard, and A. Kuijpers. 2012. Climate variability in West Greenland during the past 1500 years: Evidence from a high-resolution marine palynological record from Disko Bay. Boreas 41:68–83. Roncaglia, L., and A. Kuijpers. 2004. Palynofacies analysis and organic-walled dinoflagellate cysts in late Holocene sediments from Igaliku Fjord, South Greenland. The Holocene 14(2):172–184. Seidenkrantz, M.-S., S. Aagaard-Sørensen, H. Sulsbrück, A. Kuijpers, K.G. Jensen, and H. Kunzendorf. 2007. Hydrography and climate of the last 4400 years in a SW Greenland fjord: Implications for Labrador Sea palaeoceanography. The Holocene 17(3):387–401. Seidenkrantz, M.-S., L. Roncaglia, A. Fischel, C. Heilmann- Clausen, A.Kuijpers, and M. Moros. 2008. Variable North Atlantic climate seesaw patterns documented by a Late Holocene marine record from Disko Bugt, West Greenland. Marine Micropaleontology 68:66–83. Seidenkrantz, M.-S., A. Kuijpers, and T. Schmith. 2009. Comparing past and present climate: A tool to distinguish between natural and human-induced climate change. IOP Conference Series, Earth and Environmental Sciences 8 doi:10.1088/1755-1315/8/1/012012. Stuiver, M., P.M. Grootes, and T.F. Braziunas. 1995. The GISP2 δ18 O climate record of the past 16,500 years and the role of the sun, ocean, and volcanoes. Quaternary Research 44:341–354. Trouet, V., J. Esper, N.E. Graham, A. Baker, J.D. Scourse, and D.C. Frank. 2009. Persistent positive North Atlantic Oscillation mode dominated the medieval climate anomaly. Science 324:78–80. van Loon, H., and J.C. Rodgers. 1978. The seesaw in winter temperatures between Greenland and northern Europe, Part I: General description. Monthly Weather Review 106:295. Van der Schrier, G., and J. Barkmeijer. 2005. Bjerknes’ hypothesis on the coldness during AD 1790–1820 revisited. Climate Dynamics 24:537–553. Van der Schrier, G., and S.L. Weber. 2010. The Gulf Stream and Atlantic sea-surface temperatures in AD 1790–1825. International Journal of Climatology 30:1747–1763. Willemse, N.W., E.A. Koster, B. Hoogakker, and F.G.M. van Tatenhove. 2003. A continuous record of Holocene eolian activity in west Greenland. Quaternary