When was Beringia a land connection between Asia and Alaska, and how much ice-free land remained available, and for how long?
During the last glacial period, lower sea level exposed a broad continental shelf now submerged beneath the Bering Sea. To evaluate the possibility that some ancestors of Native Americans lived in this region for thousands of years, it is necessary to examine not only whether a land bridge existed, but also how exposed land, ice cover, ice-free land, coastlines, and connectivity changed through time.
Analysis Scope
The map is centered on Diomede, Alaska (65.76°N, 168.95°W). The 500 km analysis boundary is a 500,000 m buffer constructed in the Beringia True LAEA analysis CRS; it is not generated in the web map. It is transformed to a continuous 0–360° longitude arrangement only for Pacific-centered display across the International Date Line. Provideniya and Anadyr are shown to the west, and Wales and Nome to the east. The boundary explains the analytical mask; it is not a reconstructed paleocoastline.
Use Ctrl + mouse wheel over the map to zoom.
| Center | Diomede, central Bering Strait |
|---|---|
| Spatial extent | Beringia analysis zone within 500 km of the center |
| Map coordinates | Pacific-centered 0–360° longitude display; analysis calculated on a 4 km True LAEA equal-area grid |
| Main period | 22,000–11,000 BP at 100-year intervals |
| Connectivity focus | 12,000–8,000 BP, including the last connected point at 9,900 BP and first disconnected point at 9,800 BP |
| Long-term trend | 500-year centered moving average |
Variables
The variables are read in five groups. Exposed land is all ground above sea level, while ice-free land is the portion not covered by modeled ice. Ice indicators describe its area, share, and thickness. Coastal indicators describe coastline length and the relative share of coastal grid cells. Connectivity and century-scale change show whether an uninterrupted route existed and how rapidly land and ice changed from one 100-year point to the next.
| Variable group | Indicators | Plain-language meaning |
|---|---|---|
| Land extent | Exposed land and ice-free land | Land above sea level and the portion not covered by ice |
| Ice | Covered area, share, mean and maximum thickness | How much ice existed and how thick it was |
| Coast | Coastline length and coastal-cell area share | How prominent the land–sea boundary became |
| Accessibility | Land and effective ice-free connection | Whether an uninterrupted route linked Asia and Alaska |
| Rate of change | Land loss and gain, ice loss, and newly ice-free land | How rapidly the surface was reorganized from one century to the next |
Data: The analysis uses a CHELSA-TraCE21k paleotopographic (orog) foundation on a 4 km True LAEA grid together with corrected ice extent and thickness layers. CHELSA-TraCE21k also supports the climate analyses in the wider project, but the ice, coastline, and connectivity measures shown here are derived spatial statistics rather than CHELSA climate variables.
Time Series and Interpretation by Indicator
Exposed Land Area
What does this indicator measure?
The total area of Beringian land above sea level. It does not yet distinguish whether the land was covered by ice.
How to read the chart
The blue series shows 100-year area values, the dark line shows the 500-year centered average, and the orange series shows land lost since the previous 100-year point.
Observed result
Exposed land declined from about 809.6 thousand km² at 22,000 BP to 459.8 thousand km² at 11,000 BP, a loss of about 349.7 thousand km² or 43.2%.
Environmental meaning
Beringia remained a substantial physical space, but rising sea level greatly reduced it, particularly late in the period.
Limitation
Exposed land is not equivalent to habitable land. Ice, climate, snow, vegetation, water, and productivity must also be considered.
Ice-Free Land Area
What does this indicator measure?
The portion of exposed land not covered by modeled ice. It is an upper limit on potentially usable ground, not a direct measure of habitability.
How to read the chart
The lighter line shows the 100-year values and the dark line shows the 500-year centered average.
Observed result
Ice-free land measured about 796.8 thousand km² at 22,000 BP and 459.8 thousand km² at 11,000 BP. After modeled ice disappears at 15,000 BP, ice-free and exposed land have the same area.
Environmental meaning
Most of the study zone was not buried beneath a continental ice sheet. Later contraction resulted from inundation rather than expanding ice.
Limitation
Ice-free does not mean warm, vegetated, productive, or supplied with adequate food and fuel.
Ice-Covered Land Area
What does this indicator measure?
The area of exposed land classified as ice-covered within the study zone.
How to read the chart
The ice-colored series and dark average show ice-covered area; the orange series shows area lost since the previous century.
Observed result
Ice covered about 12.8 thousand km² at 22,000 BP. After a final major retreat, modeled regional ice cover is zero from 15,000 BP onward.
Environmental meaning
Ice directly constrained only a limited part of the Beringia study zone and ceased to do so as deglaciation proceeded.
Limitation
A 4 km grid may not fully represent small mountain or valley glaciers.
Ice-Covered Share of Exposed Land
What does this indicator measure?
The percentage of exposed land covered by modeled ice.
How to read the chart
This is a share rather than an absolute area. It should be read together with changing exposed-land area.
Observed result
The share was about 1.58% at 22,000 BP, reached only about 1.6% at its maximum, and is zero from 15,000 BP onward.
Environmental meaning
More than roughly 98% of exposed land was ice-free even during the central LGM.
Limitation
A low regional average does not rule out substantial local ice barriers.
Mean Ice Thickness
What does this indicator measure?
The mean thickness calculated only across cells classified as ice-covered; ice-free cells are excluded.
How to read the chart
The 100-year values and 500-year average are plotted together. Thickness becomes zero when no ice-covered cells remain.
Observed result
Mean thickness was about 253 m at 22,000 BP, peaked around 17,500 BP, and falls to zero at 15,000 BP.
Environmental meaning
Although ice occupied little area, ice-covered locations could contain hundreds of meters of ice and create local barriers.
Limitation
This is not average thickness across all Beringian land.
Maximum Ice Thickness
What does this indicator measure?
The thickest modeled ice cell within the study zone at each time point.
How to read the chart
Unlike the mean, this is a local extreme and represents the largest modeled barrier rather than typical conditions.
Observed result
Maximum thickness was about 660 m at 22,000 BP and declines to zero by 15,000 BP.
Environmental meaning
Substantial local barriers could exist even while most of the study zone remained ice-free.
Limitation
A maximum is sensitive to a single cell and should not be treated as representative of all Beringia.
Coastline Length
What does this indicator measure?
The total modeled boundary between land and sea calculated on the 4 km grid.
How to read the chart
The 100-year values and 500-year average show how the boundary changed as the shelf was flooded.
Observed result
Coastline length increased from about 1,031 km at 22,000 BP to about 5,590 km at 11,000 BP.
Environmental meaning
As a broad shelf plain was inundated, islands, bays, and peninsulas created a more complex boundary and made coastal settings relatively more prominent.
Limitation
Coastline length is highly sensitive to grid resolution. A longer coast does not prove greater marine productivity or coastal use.
Asia–Alaska Land Connection
What does this indicator measure?
A binary state showing whether uninterrupted land connected Asia and Alaska within the defined corridor.
How to read the chart
The chart focuses on 12,000–8,000 BP. The state is connected through 9,900 BP and first becomes disconnected at 9,800 BP.
Observed result
Every 100-year point from 22,000 to 11,000 BP is connected. The extended series first becomes disconnected at 9,800 BP.
Environmental meaning
The Bering Land Bridge remained physically continuous throughout the main environmental analysis period.
Limitation
The result depends on the corridor, four-neighbor grid rule, paleotopography, and sea-level model. It does not prove human passage.
Effective Asia–Alaska Ice-Free Connection
What does this indicator measure?
A state requiring both physical land connection and a continuous route after ice-covered cells are excluded.
How to read the chart
The report corrects the original field using: Effective ice-free connection = Land connection AND Ice-free connection. The chart focuses on 12,000–8,000 BP.
Observed result
Effective ice-free connection persists through 9,900 BP and closes with the physical land connection at 9,800 BP.
Environmental meaning
Local ice did not block the entire route between Asia and Alaska during the main analysis period.
Limitation
A grid connection does not describe route width, terrain difficulty, snow cover, food, or actual human movement.
Land Lost and Gained Since the Previous 100 Years
What does this indicator measure?
The areas that became sea and those newly exposed between consecutive 100-year time points, summed separately by location.
How to read the chart
Loss is plotted below zero and gain above zero so both directions remain visible.
Observed result
Long-term loss greatly exceeded gain. Individual late-period losses reached several thousand to more than 10,000 km²; the loss at 11,100 BP was about 10,567 km².
Environmental meaning
Beringia contracted through a series of uneven century-scale losses rather than at one uniform rate.
Limitation
These are spatial loss and gain totals, not simply the difference between two total areas, and they are sensitive to small shoreline shifts.
Ice Retreat and Newly Ice-Free Land
What does this indicator measure?
The decline in ice-covered area and the land that actually changed from ice-covered to ice-free since the previous century.
How to read the chart
When the two series overlap, lost ice area corresponds directly to land newly released from ice.
Observed result
The last major change occurs around 15,000 BP. Both values remain zero afterward.
Environmental meaning
After about 15,000 BP, the dominant change in available land was flooding rather than regional ice retreat.
Limitation
Newly ice-free ground would not necessarily support vegetation or animals immediately; ecological recovery may lag.
Summary by Environmental Phase
| Interval | Terrain and ice state | Plain-language interpretation |
|---|---|---|
| 22,000–20,000 BP | Near-maximum land area, continuous connection, limited regional ice | A broad land bridge was exposed and most of it was not ice-covered. |
| 19,900–15,100 BP | Connection maintained, changing ice area and thickness, gradual coastline growth | The land bridge persisted while its coasts and local ice geometry were reorganized. |
| 15,000 BP | Regional ice cover changes to zero | The final modeled ice disappears from the study zone, although ecological recovery is a separate question. |
| 14,900–11,000 BP | Ice-free connection maintained, accelerating land loss, increasing coastal complexity | The route remained open, but total land area contracted rapidly and coastal settings became more prominent. |
What the Next Analysis Must Establish
Terrain connectivity alone cannot explain the potential for long-term residence. The next stage must analyze temperature, precipitation, snow-cover duration, NPP, LAI, and Biome composition on the same 22,000–11,000 BP timeline to evaluate ecological constraints and relative stability.
Data and Interpretive Limitations
- Terrain and ice values depend on reconstructed data and the 4 km analysis grid.
- Connectivity depends on the Diomede-centered corridor and the four-neighbor grid rule.
- Coastline length and coastal-cell share are sensitive to spatial resolution.
- The 500-year moving average is a trend aid, not a new observation.
- Land or ice-free connectivity does not directly demonstrate human movement or residence.
