Background to the Terrain and Accessibility Analysis
About 22,000 years ago, sea level was far lower than it is today. A broad continental shelf now submerged beneath the Bering Sea and Bering Strait was exposed, creating a continuous landmass between Northeast Asia and Alaska: Beringia.
Beringia is often described as the Bering Land Bridge, a route from Asia into the Americas. Yet it may not have been merely a corridor crossed in a short period. Some ancestors of Native Americans may have lived in Beringia and the surrounding northern regions for thousands of years during the last glacial period. The Beringian Standstill Hypothesis commonly places a major interval of residence and isolation at approximately 23,000–16,000 years ago, a span of about 7,000 years. Its precise beginning and end vary among genetic and archaeological studies, and environmental data alone cannot establish the actual duration of human residence.
The purpose of this project is to reconstruct quantitatively what kind of place Beringia was during the period when these populations may have lived there and how its environment changed through time. The first detailed report begins with the physical foundation of that environment: terrain and accessibility.
See also:
- Beringia’s Exposed Land Area Changes After the LGMBeringia’s Exposed Land Area Changes After the LGM
When Was the LGM?
The Last Glacial Maximum, or LGM, was not an event that occurred in a single year. It generally refers to the interval when global ice-sheet volume was greatest, approximately 26,500–19,000 years ago. The opening date of this analysis, 22,000 BP, therefore lies within the central part of the LGM. The subsequent time series follows the reorganization of Beringia as ice diminished and sea level rose.
The main analytical period is 22,000–11,000 BP. It includes the central and later LGM, deglaciation, and the transition into the Late Glacial. Variables are examined at 100-year intervals. A 500-year centered moving average is used alongside the original values to distinguish short-term changes from longer-term trends.
When Did Beringia Become Submerged?
As climate warmed and continental ice melted, sea level rose. Beringia’s lowlands were progressively flooded, and the land connecting Asia and Alaska contracted in several stages.
Some previous studies place the final flooding of the Bering Land Bridge at around 11,000 years ago. In the paleotopographic, sea-level, and grid-connectivity model used here, however, the land connection persists through 9,900 BP and first becomes disconnected at 9,800 BP. This difference can arise from the sea-level curve, paleotopographic source, spatial resolution, and operational definition of “connection” used in each reconstruction.
Most environmental variables are analyzed from 22,000 to 11,000 BP. The connectivity series is extended to 4,000 BP to identify the final break. In the detailed report, the connectivity charts focus on 12,000–8,000 BP so that the transition is clearly visible.
Analysis Region
The study area is a 500 km radius analysis zone centered on the present-day Bering Strait and Diomede Islands. It includes parts of the Bering continental shelf exposed under lower sea level, together with adjacent land on the Asian and Alaskan sides.
“Beringia” in this report does not mean the largest geographic extent used for Beringia in the scholarly literature. Every area and coastline statistic is calculated only within the Diomede-centered 500 km study zone. These values therefore should not be interpreted as absolute totals for all of Beringia.
The Leaflet map in the detailed report shows the following spatial information:
- Center: Diomede, Alaska, United States
- Center coordinates: approximately 65.76°N, 168.95°W
- Analysis extent: 500 km radius from the center
- Western reference settlements: Provideniya and Anadyr
- Eastern reference settlements: Wales and Nome
- Map display: Pacific-centered longitude arrangement so the study zone is not divided at the International Date Line
- Area calculation: 4 km True LAEA equal-area grid
The circle on the map explains the analytical extent. It does not represent a reconstructed paleocoastline, a human territory, or an actual migration route.
Why Begin with Terrain and Accessibility?
The existence of land does not by itself show that sufficient living space was available. Land above sea level could still have been covered by thick ice, restricting residence and movement. Conversely, a retreating ice sheet could create newly ice-free land even while total exposed land was shrinking.
The analysis therefore separates the following elements:
- Total land exposed above sea level
- Ice-free land within the exposed area
- Area and share covered by ice
- Thickness of local ice barriers
- Coastlines reorganized by rising sea level
- Physical land connection between Asia and Alaska
- Effective connection remaining after ice-covered cells are excluded
- Century-scale land loss and ice retreat
This distinction prevents the “presence of a land bridge” from being treated as equivalent to “space that could actually be used.”
Central Question
When was Beringia a land connection between Asia and Alaska, and how much ice-free land that could potentially be used remained available, and for how long?
The answer provides the physical foundation for interpreting the later analyses of temperature and season length, precipitation and snow cover, vegetation, and productivity.
Scope of the Full Environmental Analysis
The Beringia environmental statistics project examines the following groups of variables in sequence.
Terrain and Accessibility
Exposed land, ice-free land, ice cover, ice thickness, coastline, land connectivity, and 100-year changes are analyzed. This is the subject of the current detailed report.
Temperature and Season Length
The analysis covers annual mean temperature, temperatures during the warmest and coldest seasons, warmest- and coldest-month temperatures, and the number of months suitable for plant growth and outdoor activity.
Precipitation and Snow Cover
Annual and seasonal precipitation, seasonal concentration of precipitation, and snow-cover duration are examined separately. Precipitation is not treated as equivalent to snowfall.
Vegetation and Productivity
NPP, LAI, and the composition and transitions of Biomes and Megabiomes are used to examine vegetation productivity and the food base available to herbivores.
Rate of Change and Stability
Century-scale changes, 500-year trends, abrupt turning points, and long-term variability are distinguished. High productivity and low variability are treated as different environmental properties.
Regional Comparison
After the analysis of Beringia itself, Beringia is compared first with the adjacent northern regions of Chukotka, Alaska, and Yana, and then with all nine study regions and their broader geographic groups.