GeoX Raster Lab · Project 01 · Engineering Case Study

PalaeoCoast — Historical Coastline Explorer

An experimental geospatial modelling and visualisation sandbox investigating European prehistoric coastlines from 22 000 BP through present day. The project explores how bathymetric baselines can be coupled with relative sea-level curves, topological ocean connectivity, and geomorphological displacement. Powered by the computational engine SeaLevelRize.

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Interactive Scenario Viewer

Explore coastal horizons, toggle topological ocean connectivity, and inspect simulated terrain scenarios.

PalaeoCoast Console · Europe · Aegean · Doggerland Fullscreen Window ↗
Computational Physics & Methodology

How Coastline Reconstruction & Land Uplift are Calculated

From modern DEM and bathymetry baselines to prehistoric topography via GIA anomalies, isostasy, and topological ocean fill.

Panel A · Pedagogical Control

Sea Level Only (Simplified Control)

Modern topography is used without modification. Only the selected sea level is varied. This serves as a simplified baseline and is not a complete historical reconstruction of the landscape.

Modern Sea Level (0 m datum) Past Sea Level S (e.g. -120 m) Coastline (DEM slice) Modern Elevation (Z_now) unchanged
Panel B · Geophysical Modelling

GIA / RSL-Informed Reconstruction

A spatially and temporally varying relative height anomaly shifts cell elevations relative to the contemporaneous sea before land and ocean are classified.

Modern Datum (0 m) Contemporaneous Sea Level A_rel (GIA) Reconstructed Coastline Land relative to past sea
Modern DEM Reconstructed Elevation (Z_past) Modern 0m Datum Contemporaneous Sea Level

* Simplified principle sketch — not actual model values and not to scale. Panel A illustrates a pedagogical control where only sea level drops. Panel B illustrates the model's combined elevation adjustment relative to contemporaneous sea. The ICE-6G_C field combines solid-Earth, geoid/sea-surface and ocean volume dynamics (not solely vertical land movement).

General Terrain Elevation Calculation

For each raster grid cell, reconstructed elevation Z_past and vertical elevation margin M relative to the contemporaneous sea surface are calculated as:

Z_past = Z_now + A_rel − U + E − D M = Z_past − S

For scenarios with constant process rates, cumulative displacement is computed as:

cumulative displacement [m] = rate [mm/yr] × age [yr] / 1000

Physical Explanation of Signs:

  • − U (Subsequent Land Uplift): If land has risen after the historical epoch (e.g. postglacial crustal rebound in Scandinavia), the ancient ground surface lay lower relative to the geoid than today. A negative U value denotes land subsidence (which adds height, as the ancient surface stood higher).
  • + E (Subsequent Erosion): If surface material was eroded away in subsequent millennia, the original ancient land surface stood higher than modern bathymetric soundings.
  • − D (Subsequent Deposition): If sediment deltas accumulated later, the ancient land surface lay lower than modern soundings.
  • All processes are defined retroactively from the selected historical age to the reference baseline 1950 (0 BP).

Inside the interactive cell inspector: Modern Elevation − subsequent uplift + subsequent erosion − subsequent deposition = reconstructed past elevation.

Three Reference Modes & Double-Counting Guard ▼

To prevent geological processes from being accidentally compounded, the computation engine enforces three mutually exclusive reference modes:

Mode Description Double-Counting Protection
relative Sea level is already expressed as a local relative sea-level (RSL) curve. Separate land uplift must not be added. The engine rejects this combination automatically.
separate Sea surface is expressed in the modern DEM datum. Intended crustal displacement is supplied separately. Cannot be combined with an RSL curve.
relative_anomaly A complete spatial relative elevation anomaly relative to contemporaneous sea is supplied (ICE-6G_C). Separate sea-level and land uplift terms must be zero. This is the mode for ICE-6G_C scenarios.
Key Geological Principle: Glacial Isostatic Adjustment affects the coastline only when a validated relative height grid is part of the cell calculation. A visual ice sheet layer or tectonic vector map in the viewer is not in itself a coastal correction.
ICE-6G_C (VM5a) Formulation & Geophysical Limitations ▼

Preprocessing for the scientific GIA engine employs ICE-6G_C (VM5a) and calculates the net relative anomaly:

H_rel(t) = Topo(t) − stgit(t) A_rel(t) = H_rel(t) − H_rel(0) = [Topo(t) − stgit(t)] − [Topo(0) − stgit(0)] Z_past = Z_now + A_rel(t) M = Z_past

In this mode, the contemporaneous sea level is mathematically inherent to the relative anomaly, setting independent sea-level terms to zero.

Confirmed Scientific Limitations:

  • Grid Resolution: ICE-6G_C has a native resolution of ~1° (~100 km). Bilinear resampling to 5 km, 600 m or 450 m creates smoother raster display but adds no new geophysical ground truth.
  • Combined Quantity: The anomaly is a composite field (solid Earth displacement + geoid/sea-surface shift), not pure vertical crustal motion.
  • Datum Harmonization: For Doggerland, vertical datum alignment between terrestrial DEMs and EMODnet bathymetry is provisional.
  • Tectonics: The Aegean sandbox does not yet include a complete regional tectonic reconstruction.
Topological Ocean Fill: Land, Connected Sea, and Enclosed Basins ▼

Once the vertical margin M is calculated, cells are categorized:

M > 0 → Land M ≤ 0 → Candidate for Water

Sub-sea-level cells are not automatically flooded. The engine executes a breadth-first 4-neighbour connectivity flood fill initiated exclusively from verified open-ocean seeds:

  • Connected Ocean: Subaqueous cells possessing an unbroken hydraulic conduit to the open marine boundary.
  • Enclosed Basins: Depressions below contemporaneous sea level protected by a subaerial topography sill. These remain dry. An enclosed basin is not automatically a lake — hydrology, precipitation and drainage are not yet modelled.
  • Coastline Vectors: Generated strictly along shared raster edges between Land and Connected Ocean, never along dataset borders. Nodata never bridges marine connectivity.
Data Register: Calculation Inputs vs. Display Layers ▼

To avoid misinterpreting map overlays as physical model parameters, layers are strictly segregated:

Layer / Dataset Application Function Affects Coastline Calculation?
Modern DEM / Bathymetry (GEBCO / EMODnet) Primary topographic datum (Z_now) Yes · Baseline
Selected Sea Level or ICE-6G_C Anomaly Relative height displacement & water line Yes · Determines Margin
Configured Uplift / Erosion / Deposition Geometric displacement (U, E, D) Yes · Alters Terrain
Ocean Seeds & Sensitivity Tolerance Hydraulic connectivity & uncertainty bands Yes · Controls Topology
DATED-1 Eurasian Ice Sheet (22–10 ka) Empirical visual reference margin No · Display Layer
BRITICE-CHRONO British-Irish Ice (22 & 16 ka) Empirical visual reference margin No · Display Layer
EMODnet Geology Palaeochannels Ancient river channel features No · Display Layer
Hillshade & Shaded Relief Visual depth rendering No · Display Layer

* Toggling display layers does not trigger coastline recalculation or alter physical cell attributes.

Data Architecture

Datasets & Reference Baselines

The model synthesizes high-resolution bathymetric soundings with peer-reviewed eustatic sea-level curves.

Bathymetry

GEBCO 2020 Grid

Global terrain and ocean bathymetry at 15 arc-second resolution (~450m European equivalent), providing the foundational elevation datum.

Coastal Bathymetry

EMODnet DTM 2024

High-density European marine data providing shallow-water acoustic soundings across the North Sea, Baltic, and Mediterranean basins.

Eustasy

Sea Level Curves

Global eustatic sea-level curves (Lambeck et al. 2014, Peltier et al.) calibrating global ocean volume drops (~125m at LGM).

Projection

EPSG:3035 (ETRS89-LAEA)

Lambert Azimuthal Equal-Area projection preserving true geographic area measurements across all European continental shelf scenarios.

Geodynamics

ICE-6G_C & NKG2016LU

Viscoelastic mantle rheology grids and Nordic geodetic uplift measurements incorporated into the active GIA development module.

Resolution

600m Model Raster Cells

Optimized balance between regional continental shelf scale, computational topological flood fill speed, and client-side rendering.