Significance

Vikings occupied Greenland from 985 CE to the mid-15th century. Hypotheses regarding their disappearance include combinations of environmental change, social unrest, and economic disruption. Occupation coincided with a transition from the Medieval Warm Period to the Little Ice Age and Southern Greenland Ice Sheet advance. We demonstrate using geophysical modeling that this advance would have (counterintuitively) driven local sea-level rise of ~3 m (when combined with a long-term regional trend) and inundation of 204 km2. This largely overlooked process led to the abandonment of some sites and pervasive flooding. Progressive sea-level rise impacted the entire settlement and may have acted in tandem with social and environmental factors to drive Viking abandonment of Greenland.

Abstract

The first records of Greenland Vikings date to 985 CE. Archaeological evidence yields insight into how Vikings lived, yet drivers of their disappearance in the 15th century remain enigmatic. Research suggests a combination of environmental and socioeconomic factors, and the climatic shift from the Medieval Warm Period (~900 to 1250 CE) to the Little Ice Age (~1250 to 1900 CE) may have forced them to abandon Greenland. Glacial geomorphology and paleoclimate research suggest that the Southern Greenland Ice Sheet readvanced during Viking occupation, peaking in the Little Ice Age. Counterintuitively, the readvance caused sea-level rise near the ice margin due to increased gravitational attraction toward the ice sheet and crustal subsidence. We estimate ice growth in Southwestern Greenland using geomorphological indicators and lake core data from previous literature. We calculate the effect of ice growth on regional sea level by applying our ice history to a geophysical model of sea level with a resolution of ~1 km across Southwestern Greenland and compare the results to archaeological evidence. The results indicate that sea level rose up to ~3.3 m outside the glaciation zone during Viking settlement, producing shoreline retreat of hundreds of meters. Sea-level rise was progressive and encompassed the entire Eastern Settlement. Moreover, pervasive flooding would have forced abandonment of many coastal sites. These processes likely contributed to the suite of vulnerabilities that led to Viking abandonment of Greenland. Sea-level change thus represents an integral, missing element of the Viking story.
Southwestern Greenland was settled by Norse immigrants in ~985 CE when Erik the Red was exiled from Iceland for manslaughter (c. 982 CE) and relocated West. Erik’s family and other colonizers established the Eastern Settlement (Fig. 1A) and the Western Settlement, which remained until the disappearance of Vikings in the 14th century [Western Settlement; (1)] and in the mid-15th century [Eastern Settlement; (2)]. The first records of the Norse in Greenland come from both the Book of Icelanders (3) and the Saga of Erik the Red (4). Life in the settlements was inherently tied to the land, religious practices, and social standing, closely mirroring the Icelandic Norse colonies (5, 6). Archaeological evidence for Viking occupation includes ruins, middens (trash heaps), as well as human and animal bones (7). The last written evidence of Norse habitation in Greenland is a record of a wedding ceremony at Hvalsey Church in the Eastern Settlement in the early 15th century (8), and radiocarbon dates indicate a further half century of occupation (9).
Fig. 1.
Regional setting and ice history. (A) The Eastern Settlement of Southern Greenland. The inset shows the entirety of Greenland; dark gray depicts grounded ice cover at present, light gray is land, and white is ocean. Eight black stars show locations of the Viking sites considered herein and also Nanortalik, where Late Holocene relative sea-level data have been collected (11). B is Brattahlid, D is Dyrnaes, G is Gardar, H is Hvalsey, N is Narsaq, N2 is Nanortalik, S1 is Site 1, S2 is Site 2, and uS is Undir Solarfjollum. (B) The tetrahedral grid across Southern Greenland used in the sea-level simulation (top 72 km of Earth’s interior is shown in light gray; surface shading reflects grid resolution and is discussed in Material and Methods Section 3B) with ice mask (blue to white gradient) overlain. The ice mask is estimated from ref. 12. The yellow box shows an area encompassing the Eastern Settlement and the area of ice growth (the same area is shown in Fig. 3A). The green box shows an area with several important Viking settlements, where coastal flooding is assessed (also seen in Fig. 4A). For more details, Section 3A. (C) Time-varying growth for our ice history, normalized to a maximum value of 1.0, and adapted from refs. 1315.
The cause of the Viking abandonment of Greenland and the deteriorating conditions leading up to it remain controversial, and it is likely that a combination of factors and vulnerabilities (Below) led to the end of Norse settlement in Greenland (7). We explore the hypothesis that regional sea-level rise and pervasive flooding contributed to the abandonment of farms and shielings that were close to the shoreline during Viking occupation and potentially played a role in the abandonment of Greenland. Gulløv (10) provides motivation for this hypothesis (translated into English):
Sea level rise was another problem the Greenlanders were confronted with ... In Tunulliarfik Fjord and Igaliku Fjord in the Eastern Region, “drowned” land has been found. Calculations estimate that the sea level rose by around one meter during the almost 500 y that Østerbygden was inhabited. This may seem small, but according to the calculations, the Brattahlid farm alone lost around 50 ha of home land during the settlement, while another 200 ha of land disappeared at the bottom of Tunulliar got.
As we demonstrate, a readvance of the Greenland Ice Sheet (GrIS), which peaked during the Little Ice Age [LIA; 1250-1900 CE; (1518)], would have driven a contemporaneous sea-level rise near the ice margin due to crustal subsidence and load self-gravitation, the latter referring to the increased gravitational attraction of the ocean toward the growing ice sheet (19). This component of rise, which encompassed the entire Eastern Settlement and which has not been previously considered, would have had a peak amplitude nearly three orders of magnitude greater than the global mean sea-level fall associated with the ice volume increase (19) and can be larger than the regional sea-level rise associated with ongoing effects of the Pleistocene ice age (20).

A. Regional Setting.

In this study, we focus on the Eastern Settlement (Fig. 1A). This settlement was established ~985 CE and was likely abandoned in the mid-15th century (8, 9), ~100 y later than the abandonment of the Western Settlement farther North at ~1350 CE (1). The Eastern Settlement encompassed the region between 59.75°to 61.5°N and 47.75°to 53.55°W and extended from present-day Cape Farewell headland to Sermesoq municipality. The Settlement included ~500 Norse sites and an average population of ~2000 inhabitants (2123).
The topography of the Eastern Settlement is characterized by glacially carved fjords (24) with Viking sites concentrated along the associated shorelines (5), while some were closer to the GrIS margin. Upon arrival in ~985 CE, the climate was warmer than the average late Holocene temperature, but by the 12th century, it began to deteriorate abruptly (25), as we discuss below.

B. Deteriorating Conditions in Southern Greenland.

It is likely that a combination of climate and environmental change (1, 2528), a shifting resource landscape (22, 29), the flux of supply and demand of exclusive products for the foreign market (7), and interactions with Inuit in the North (30) contributed to deteriorating conditions for the Vikings and their ultimate abandonment of Southern Greenland. The abandonment is commonly attributed to the beginning of the LIA creating unfavorable climatic conditions for the region, especially in contrast to fair conditions during the Medieval Warm Period (MWP; 900 to 1250 CE) (1, 25, 26, 31). We note that it has been argued that the effects of the MWP may not have been uniform or extended to the entirety of Greenland, and in this case, the LIA climate of this region would have varied only slightly from the original settlement climate (26, 28, 32). Furthermore, Vikings arrived in Greenland during a period of high demand for ivory in Europe, which allowed them to act as suppliers of the luxury good until the closure of trade between the Settlements and Europe in the early 1400s (6). Additionally, there are various accounts of negative interactions between the Norse and Inuit in Southern Greenland (33).
There is ample evidence for sea-level rise during and after the period of Viking occupation, and the close proximity of the settlements to the margin of the GrIS would have made them vulnerable to gradual flooding and loss of habitable land (34). In the vicinity of the Eastern Settlement, this evidence includes drowned ruins and sediment core analysis (35), a largely submerged warehouse close to Igaliku Church (36), and a drowned beach observed by side-scan sonar (26). Wilken et al. (36) and Mikkelsen et al. (35) used a combination of archaeological and geophysical evidence to estimate that sea level rose at least 1 m during the period when the Eastern Settlement was occupied and another meter subsequent to the abandonment of the settlement. Farther north, in Southern Disko Bugt, partially drowned Inuit ruins provide evidence for approximately 3 m of sea-level rise over the past millennium (2). Additionally, analyses of human remains from church yards and animal remains from middens show that beginning in the early 12th century, Vikings may have gradually transitioned their diet from majority land-based (i.e., livestock) to marine-based (i.e., seal) (22). This behavioral change would be consistent with an ongoing attempt to adapt to a loss of arable land due to rising sea level across the period of occupation (29, 35, 37). In this study, we quantify the sea-level change and resulting land loss to better understand the role of this process as a possible contributor to the Viking abandonment of sites within the Eastern Settlement and, ultimately, out of Greenland.

C. Sea-Level Changes.

Past studies of human–landscape interaction have commonly employed a “bathtub” (also called eustatic) model of sea-level change, wherein the change is assumed to be globally uniform (e.g., refs. 3840). This method does not accurately simulate the past environment as it neglects the effects of glacial isostatic adjustment (GIA). GIA encompasses the deformational, gravitational, and rotational Earth perturbations that arise from surface (ice and ocean) mass loading throughout glacial cycles. These effects can cause regional sea level (and therefore topography relative to sea surface height) to depart significantly from “bathtub” predictions of global mean sea level (GMSL) and have consequences for human migration research (34, 41).
During the time of Viking habitation, the Eastern Settlement would have been subject to two components of sea-level change. First, the settlement was located on the periphery of both the massive Laurentide Ice Sheet (located over Canada, the Northeastern United States, and the Arctic), and the GrIS. It was thus subject to ongoing crustal subsidence and sea-level rise that began during the Holocene and continued to the present day (20, 34). Second, as noted above, ice advance in Southern Greenland contemporaneous with Viking habitation would have led to a sea-level rise associated with crustal deformation and gravitational effects (19). The first process, peripheral subsidence, has been discussed in the context of the field evidence for sea-level rise across the period of Viking occupation of the Eastern Settlement and subsequent to it (17, 26, 35, 36). The second process, sea-level rise local to ice advance during the Viking habitation, has not been considered in discussions of the Eastern Settlement, and as we demonstrate below, it was likely the main contributor to the sea-level rise experienced in these settlements.

1. Results

A. Prediction of Regional Sea-Level Change.

Our calculations are based on a high-resolution, finite-volume simulation of sea-level change on a viscoelastic Earth model (Fig. 1B and Material and Methods Section 3A). The areal extent of the ice advance during Viking occupation is based on a review of ice cover in the region since the LGM (42) and focused on three zones that are thought to have experienced significant ice growth leading into the LIA (12, 14, 42) (Fig. 1B and Material and Methods 4B). Following Adhikari et al. (14) and the work of Larsen et al. (13) and Kjaer et al. (15), we adopted a time history of ice growth characterized by a period of decelerating ice advance extending from 1000 to 1840 CE, followed by a retreat back to the original (1000 CE) ice cover by 2000 CE (Fig. 1C).
The net ice volume change associated with the advance is a free parameter of the modeling. To constrain this parameter, we considered sea-level records from Nanortalik (Figs. 1A and 2), which include lake core data spanning the last 14,000 y (20) and salt marsh records from 1400 to 1800 CE (11). Using a subset of the data spanning 5000 to 1000 y ago from the former, we determined a linear (pre-LIA) relative sea-level (RSL) trend of 1.92 ± 0.72 mm/y that we adopted as a background signal on which to superimpose the RSL signal due to MWP-LIA ice-loading changes (Fig. 1C). We varied the volume of the latter to obtain a best fit to the salt marsh data (Fig. 2). This exercise yields a preferred ice volume increase, culminating at 1840 CE, equivalent to 7-mm GMSL fall. Fig. 3A shows a simulation of geographically variable sea-level change from 1000 CE to 1450 CE across the area of the Eastern Settlement in response to this scenario of ice advance and the background trend. The modeled sea-level rise peaks at just over 4 m (3.3 m outside the zone of glaciation), ~3 orders of magnitude greater than the modeled GMSL fall associated with LIA ice sheet advance in Southern Greenland. The peak is located at the site of the ice advance, and the signal decreases with distance from this location.
Fig. 2.
Modeled relative sea level compared to Nanortalik observations. Modeled RSL curve at Nanortalik for a scenario in which local ice sheet advance (Fig. 1) is sufficient to lower GMSL by 7 mm, augmented by the addition of a background sea-level trend due to ongoing ice age effects (Section 1A). Our estimate of the 1-σ uncertainty in the modeled curve is shown in gray shading. Nine orange data points show RSL data of LIA age reconstructed from salt marsh sediments at Nanortalik, with 2-σ age and elevation uncertainty (11).
Fig. 3.
Modeled sea-level change from 1000 to 1450 CE in the Eastern Settlement. (A) Map of modeled sea-level change from 1000 to 1450 CE. Black is the present-day Greenland coastline. Eight colored stars show sites of archaeological interest. (B) Prediction of sea-level change during the settlement period at eight archaeological sites from panel A (line colors correspond to site location symbol colors).
Fig. 3B shows the predicted sea-level change during Viking occupation (1000 to 1450 CE) for a series of archaeologically significant sites, including Brattahlid, Undir Solarfjollum, Dyrnaes, Narsaq, Gardar, and Hvalsey (26, 43). The predictions include both the site-specific signal from the ice advance during the settlement period and the ongoing regional sea-level rise associated with ice mass changes following the LGM (20); 0.864 m; 1.92 mm/y × 450 y]. The net sea-level rise across these sites ranges from roughly 1 m to 3 m, indicating that the ice advance acts to amplify the ongoing ice age signal by up to a factor of ~4. In the next section, we assess how this relative sea-level change manifested as coastal flooding.

B. Coastal Settlement Inundation.

As demonstrated in Fig. 3, Viking territory was more vulnerable to sea-level rise than previously appreciated due to ice sheet advance in the region, and land within the Eastern Settlement would have experienced progressive sea-level rise and inundation during the entire period of occupation. The sea-level model (Material and Methods Section 4A) tracks the migration of the shoreline as a function of time. It is an iterative process over initially unknown topography at the start of the simulation. We deem the process convergent when the modeled present-day coastline matches the observed location. Fig. 4AD shows coastal inundation in the Eastern Settlement in Southern Greenland, and portions of this area that were highly populated and near the ice margin. The beige-shaded region is land cover in Southwestern Greenland at 1450 CE upon Viking abandonment, and the light blue represents coastal inundation from 1000 to 1450 CE (i.e., the land that was flooded during occupation) on a triangular grid with a spatial resolution of 15 m. In the region shown in panel A, we predict 204 km2 of coastal inundation from 1000 to 1450 CE with shoreline migration reaching hundreds of meters as a result of relative sea-level rise (as shown in Fig. 3A). Approximately two-thirds of the observed coastal flooding in the Eastern settlement was caused by GrIS advance near the settlements, and the remaining was caused by the ongoing sea-level response to earlier glacial change.
Fig. 4.
Coastal inundation of the Eastern Settlement from 1000 to 1450 CE, roughly the period of Viking occupation. Beige shading depicts land above sea level by 1450 CE, dark blue is the ocean area at 1000 CE, and light blue is the flooded coastline between 1000 and 1450 CE. Stars on the map denote areas of archaeological interest, as in Fig. 3A. The white star denotes Nanortalik. The grid lines in all panels are spaced ~1 km apart. (A) Coastal flooding of the whole Eastern Settlement region. (BD) Coastal flooding in the northwest, northern-central, and southern regions of the Eastern Settlement. (E) Location of 461 Viking sites tabulated by ref. 23 in white. Zones 1-3, defined in Section 2C as being located 0 to 20 km, 20 to 40 km, and beyond 40 km from the Atlantic coastline, are specified in green contours. The number of sites within each zone is 112, 152, and 197, respectively. (F) Histogram showing the distance of 461 Viking sites to the closest zone of predicted flooding.

2. Discussion & Conclusions

A. Previous Assessments of Sea-Level Change.

Several aforementioned studies have estimated sea-level change in the Eastern Settlement ranging from 1 to 4 m depending on the site. Wilken et al. (36) and Mikkelsen et al. (35) found 1 m of sea-level rise at Gardar and the Igaliku Fjord region, respectively. In addition, in the Igaliku Fjord, Kuijpers et al. (26) estimated 3 m sea-level rise over the last 1,000 y, or greater than 1 m rise likely during the period of Viking occupation. These estimates generally agree with our range of 1- to 3-m sea-level rise across the settlement. Previous research also supports our hypothesis of increased ice growth leading to sea-level rise near the ice margin. From Disko Bugt farther North, research by Rasch (17) also determined that relative sea level reached present-day levels in areas close to the ice margin sooner than in areas farther away, consistent with the pattern we show in Fig. 3A.

B. Sensitivity Tests.

We performed an analysis to consider how much ice growth from peripheral Greenland glaciers outside the settlement would be required to raise sea level by ~1 m at the Eastern Settlement and found that an ice mass increase equivalent to a GMSL fall of 0.25 m would be required. This is an order of magnitude more ice growth than is estimated by Adhikari et al. (14) for 1000 to 1400 CE. Similar calculations were also performed for glaciers in Svalbard, Iceland, and Arctic Canada; this analysis demonstrated that the impact on the Eastern Settlement from realistic growth of these glacier systems would be negligible. We performed two additional sensitivity tests. First, we used modeling results from ref. 20 to assess the accuracy of our assumption that the long-term trend we inferred using RSL data from Nanortalik was appropriate for sites in the Eastern settlement. We found that the trends at the eight sites in Fig. 3A were all within 8% of the Nanortalik value. Second, we considered whether the calculation of total flood area was sensitive to the spatial resolution of the adopted DEM by considering two topography grids (Material and Methods Section 3A) of distinct resolution and found that the computed flood area varied by ~1%.

C. Impact on Viking Sites and Settlements.

The pattern of sea-level rise and flooding predicted by our model yields insight into key issues of abandonment during Viking occupation in the Eastern Settlement. For example, Viking sites within our computed flood zone, whether farms, shielings, or otherwise, would have certainly been abandoned. As noted earlier, we predict that a total of 204 km2 of land within the Eastern Settlement would have flooded during the period of occupation. Exploring this number in more detail provides additional insight into the relative impact that flooding may have had on the settlers. For example, we separated the Eastern Settlement into three geographic zones distinguished on the basis of distance from the Atlantic coastline: 0 to 20 km, 20 to 40 km, and beyond 40 km, which roughly coincide with the outer, middle, and inner sections of the fjords that run-through the settlement (Fig. 4E). During the occupation period, 70 to 75%, 17 to 22%, and ~9% of the flooding took place in these zones, respectively. These relative values (and the number of Viking sites in each zone: Fig. 4E) are consistent with the results of ref. 44 (see also figure 5 of ref. 45), which suggest an abandonment of settlements in the outer fjords in favor of areas within the middle and inner fjords during the period of occupation.
The full geographic extent of the predicted 204 km2 of flooding within the Eastern Settlement is difficult to discern from Fig. 4. To investigate this issue, we computed the minimum distance of each of the 461 sites in the Nunniffiit database (23) to any area of flooding. The result (Fig. 4F) indicates that ~60% and ~75% of the sites are located within 500 m and 1,000 m, respectively, of a location experiencing flooding. As a point of comparison, the mean distance between farms within the Eastern Settlement was ~4 km (43). We conclude that even if a site was not directly flooded by regional sea-level rise, areas of significant flooding would have been pervasive from the perspective of the settlers.
It is difficult to assess the relative impact that sea-level rise had on the abandonment of the Eastern Settlement and the end of Viking habitation in Greenland in the mid 15th century compared to the other factors that have been identified in the literature (e.g., social unrest, relations with Inuit, resource depletion, climate and other environmental changes, and economic strain). However, our reconstruction of sea-level change indicates that the entire Eastern Settlement experienced progressively rising sea level throughout the period of occupation and ubiquitous flooding. The predicted sea-level rise at sites tabulated in ref. 23 ranged from ~1.2 to 3.3 m (Fig. 4F) over 450 y or 2 to 6 times the rate of 20th century rate of GMSL change (46). This rise may have been accompanied by many of the physical (e.g., increased vulnerability to storms, coastal erosion, disrupted drainage) and social (e.g., a changed connection to the environment) impacts discussed in the modern context of sea-level change (47). Several of these factors may have impacted the resources that defined the Norse Vikings’ diet, which evolved to rely on marine over terrestrial resources over time (9, 22). Any loss of fertile lowland would have been compounded by a contemporaneous long-term drying trend in the Eastern Settlement (28) as well as ongoing soil erosion (48). The pervasiveness of the sea-level change, whether it flooded occupied Viking sites or not, added to the “compounding vulnerabilities” (7) felt by the Viking settlers as climatic conditions deteriorated into the Little Ice Age.

3. Materials and Methods

A. Sea-Level Model.

Our sea-level model utilizes the finite-volume software of ref. 49, as revised by ref. 50 to allow lateral grid refinement and composite (nested) Earth models. We account for viscoelastic deformation of the Earth, and the associated perturbations to the gravitational field and rotational axis. Sea level is defined here as the difference between the sea surface and the solid surface; therefore, changes in sea level may result from perturbations to either bounding surface. Shoreline migration is an integral part of the formulation when assigning surface loads and can be extracted and visualized via changes in the ocean-land topography mask in postprocessing. Fig. 1B shows the three-dimensional tetrahedral grid our sea-level model utilizes. Grid lines are shown in shades of gray to blue (higher density reflects higher spatial resolution). Outside the region shown in panel B, the grid resolution varies from 12 km on the Earth’s surface to 50 km at the core–mantle boundary (CMB). In the region shown in the panel, we add two refinement levels from the surface to the CMB, plus two additional nested near-surface refinements. The latter successively improves resolution from 3 to 4 km (gray) to 1.5 to 2 km (gray-blue) and 0.75 to 1 km (blue).
The sea level model requires inputs of a spatiotemporal history of ice (described in the next section) and the viscoelastic structure of the solid Earth. We construct a 3-D Earth model in two steps. First, we adopt a one-dimensional viscoelastic Earth model with an average viscosity of ~2.5 × 10 21 Pa s in the lower mantle as in VM5 (51), 0.3 × 10 21 Pa s in the upper mantle, and a lithospheric thickness of 72.5 km (52). The simulations are relatively insensitive to the adopted viscosity model since the rapid advance of the ice sheet yields a largely elastic Earth response. For the elastic structure of the Earth, we adopt the seismically inferred model PREM (53). Second, we patch into this model the 3-D EUNAseis crustal model (54), which is characterized by a strong north–south thickness gradient, from continent to ocean, in the vicinity of the Eastern Settlement. We run our model simulation from 1000 CE to the present day with uniform 20-y time steps. We estimate initial (1000 CE) topography by adding the difference between predicted present-day and 1000-CE sea level to observed present-day topography. For the purposes of generating sea-level output, which is a relatively smooth function, a 1 km topography resolution limit after mapping onto the computational grid is adequate. However, a much finer grid is required to extract the flooded area. We construct a near-equilateral triangular grid with an internodal spacing of 15 m, which traces the shoreline between 1000 and 1450 CE (plus a small lateral margin) and interpolate the sea-level output and high-resolution topography (55) onto that grid. The flooded area is extracted as an ocean-land mask difference between 1450 and 1000 CE. To compute the total flooded area, we sum up the areas of the remaining triangular elements after cutting out the rest of the grid. We compared the results of our calculated total flooded area to an analogous calculation based on the GMRT topography grid (56) in order to test the sensitivity of the result to the resolution of the DEM (Main text).

B. Ice Model.

We estimate the areal extent of local ice growth from the Larsen et al. overview of ice extents from the Last Glacial Maximum (LGM) to the present day (42). Our ice mask (shown in Fig. 1B) is based on the difference between the ice extent at the Holocene minimum at 4 ka and present day, as this represents a reasonable estimate for the actual time frame. Weidick and colleagues (57) summarized geologic and paleoclimate data indicating that upon Viking arrival to Southern Greenland, the ice extent was likely slightly greater than that of the Holocene minimum. Larsen (12) assessed ice margin sediment cores that suggest that the extent of ice upon Viking departure in the LIA was likely just beyond that of the present day. We approximate the area of ice that was growing during Viking occupation as the patches of ice in Fig. 1B. The three specific regions of the Southern GrIS we advance were chosen because they are consistently ice-covered areas that experienced high growth during this time (12, 14). We shift the ice margins between Viking arrival and departure southwards relative to their present-day and Holocene minimum locations in order to reconcile our ice geometry with the locations of ice-covered threshold lakes during the period presented in Larsen et al. (42) and therefore more realistically capture the ice sheet terminus throughout the occupation period. Note that the ice mask is tapered to generate more ice growth toward the ice sheet margins. To test the sensitivity of regional sea-level change to various ice loads, we scale our ice mask for ice growth scenarios equivalent to 1, 3, 5, 7, and 10 mm GMSL fall from 1000 to 1840 CE. Fig. 1C inset shows the time-varying ice growth scenario based on Larsen et al. (13), Adhikari et al. (14), and Kjær et al. (15). Small changes to the ice history which encompass uncertainty in the timing of ice growth and retreat evident from the literature (1315) result in minor changes to the flooding area.
In addition to sea-level change due to local ice growth during this time, the region was also undergoing sea-level change due to ongoing isostatic adjustment associated with pre-1000 CE ice-loading changes, with impacts that lasted through Viking occupation and extending to present day. A study by Lecavalier and colleagues (20) provides lake core data from an isolation basin in Nanortalik (Fig. 1A) in Southern Greenland, which demonstrate the background trend of sea-level change over a 5,000-y period. We perform a Deming linear regression on these data (58) and determine that the background trend of sea-level change from pre-1000 CE ice loading is 1.92 ± 0.72 mm/y. Two phases of Neoglacial readvance have been inferred between 2,500 and 950 y B.P. (15). Because the net (cumulative) ice loading changes during these earlier advance and retreat phases are zero (to within uncertainty), the remnant sea-level response to these phases associated with nonelastic Earth deformation during Viking occupation would be of low amplitude and therefore is not considered in our analysis.
Relative sea-level data from a salt marsh study dated postoccupation in Nanortalik (11) capture both the background signal from ongoing GIA and sea-level changes associated with LIA ice growth in our region of interest. When combining our 1- to 10-mm ice growth scenarios with the estimated background trend from the Lecavalier et al. data (20), we find that the 7-mm GMSL equivalent ice growth scenario provides the best fit to the salt marsh sea-level data, as shown in Fig. 2.

Data, Materials, and Software Availability

The following data sets, computer codes and associated scripts necessary to reproduce results in the article are provided in the public repository https://zenodo.org/record/7126141 (59): 1) the surface computational grid; 2) model Greenland Ice Sheet history in time steps of 20 y from 1000 CE to present-day; 3) code to compute the relative sea-level change at any user specified set of sites across the same time steps; 4) code to map (2) and (3) on to conventional grids (e.g., latitude-longitude; Gauss-Legendre, etc.) based on a non-linear interpolation of data on a triangular grid via a second-order scheme; 5) code to convert sea level changes into time series of past topography from which flooding geometry (i.e., shoreline migration) can be tracked; and 6) code to integrate the flood geometries in (5) to compute time series of total flood area.

Acknowledgments

Support for this work was provided by the Heising-Simons Foundation 2018-0769 (R.B.A.), a Los Alamos National Laboratory Director’s Postdoctoral Fellowship (S.C.), NASA grant 80NSSC21K1790 (E.M.P.), Harvard University (M.B., E.M.P., J.X.M.), and the John D. and Catherine T. MacArthur Foundation (J.X.M.).

Author contributions

M.B., J.X.M., and R.B.A. designed research; M.B., K.L., S.C., E.M.P., J.X.M., and G.A.M. performed research; M.B., K.L., S.C., J.X.M., and G.A.M. analyzed data; K.L., S.C., E.M.P., G.A.M., R.B.A., and J.X.M. edited the manuscript; and M.B. wrote the paper.

Competing interests

The authors declare no competing interest.

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Information

Published in

Go to Proceedings of the National Academy of Sciences
Go to Proceedings of the National Academy of Sciences
Proceedings of the National Academy of Sciences
Vol. 120 | No. 17
April 25, 2023
PubMed: 37068242

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Data, Materials, and Software Availability

The following data sets, computer codes and associated scripts necessary to reproduce results in the article are provided in the public repository https://zenodo.org/record/7126141 (59): 1) the surface computational grid; 2) model Greenland Ice Sheet history in time steps of 20 y from 1000 CE to present-day; 3) code to compute the relative sea-level change at any user specified set of sites across the same time steps; 4) code to map (2) and (3) on to conventional grids (e.g., latitude-longitude; Gauss-Legendre, etc.) based on a non-linear interpolation of data on a triangular grid via a second-order scheme; 5) code to convert sea level changes into time series of past topography from which flooding geometry (i.e., shoreline migration) can be tracked; and 6) code to integrate the flood geometries in (5) to compute time series of total flood area.

Submission history

Received: June 10, 2022
Accepted: February 28, 2023
Published online: April 17, 2023
Published in issue: April 25, 2023

Keywords

  1. sea-level change
  2. Norse
  3. glacial isostatic adjustment
  4. archaeology

Acknowledgments

Support for this work was provided by the Heising-Simons Foundation 2018-0769 (R.B.A.), a Los Alamos National Laboratory Director’s Postdoctoral Fellowship (S.C.), NASA grant 80NSSC21K1790 (E.M.P.), Harvard University (M.B., E.M.P., J.X.M.), and the John D. and Catherine T. MacArthur Foundation (J.X.M.).
Author Contributions
M.B., J.X.M., and R.B.A. designed research; M.B., K.L., S.C., E.M.P., J.X.M., and G.A.M. performed research; M.B., K.L., S.C., J.X.M., and G.A.M. analyzed data; K.L., S.C., E.M.P., G.A.M., R.B.A., and J.X.M. edited the manuscript; and M.B. wrote the paper.
Competing Interests
The authors declare no competing interest.

Notes

This article is a PNAS Direct Submission. S.W. is a guest editor invited by the Editorial Board.

Authors

Affiliations

Department of Earth and Planetary Sciences, Harvard University, Cambridge, MA 02138
Department of Earth and Planetary Sciences, Harvard University, Cambridge, MA 02138
Department of Earth and Planetary Sciences, Harvard University, Cambridge, MA 02138
Fluid Dynamics and Solid Mechanics Group, Los Alamos National Laboratory, Los Alamos, NM 87545
Department of Earth and Planetary Sciences, Harvard University, Cambridge, MA 02138
Lamont-Doherty Earth Observatory, Columbia University, Palisades, NY 10964
Jerry X. Mitrovica
Department of Earth and Planetary Sciences, Harvard University, Cambridge, MA 02138
Department of Earth and Environmental Sciences, University of Ottawa, Ottawa, ON K1N 6N5, Canada
Department of Geosciences, and Earth and Environmental Systems Institute, Pennsylvania State University, University Park, PA 16802

Notes

1
To whom correspondence may be addressed. Email: [email protected].

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Sea-level rise in Southwest Greenland as a contributor to Viking abandonment
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