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Geoengineering basis for protection against the AMOC/Gulf Stream collapse.

Briefly on the problem

Greenland dumps approximately 350 cubic km of excess fresh water into the Atlantic every year. This fresh water blocks the thermohaline circulation and the AMOC slows down, gives off heat more slowly, and reduces winter precipitation. In the southern latitudes, heat export is blocked, which leads to powerful typhoons and floods. If nothing is done, the probability of the AMOC/Gulf Stream stopping in the next 10–40 years is already above 50%.

Briefly on the solution

In the 25 largest fjords of Greenland, we install a standard floating curtain, typically 2–3 km long (almost all fjords have such a natural constriction) and 60 meters deep. Each fjord collects fresh water runoff from approximately 15-20 thousand sq km, draining about 10 cubic km of fresh water in the summer.

How it works (for non-physicists)

  • Fresh water from the glacier always flows on top, along the fjord in a layer 20-40 m thick.
  • The curtain blocks its direct exit to the ocean.
  • To escape, the fresh water is forced to accumulate, mix with saline water, and dive under the lower edge of the curtain. We assume salinity there is 30.
  • There it immediately mixes with normal saline Atlantic water at 35 ppt.
  • The less saline water begins to rise, mix, and at the surface, it becomes approximately 34 ppt. It reaches the surface because the freshwater flow is blocked at the top and there is simply no lighter water on the ocean side of the curtain.
  • Since new rising water is pressing on it from below, it has only one path—to exit into the ocean as a current.
  • In the ocean at the mouth of the fjord, it spreads out in a large patch (kilometers and tens of kilometers in diameter) and literally displaces/washes out the accumulated fresh water from there, mixing with it.
  • In winter, this patch cools and sinks, initiating natural convection, which over six months draws hundreds of cubic kilometers of fresh water into the deep ocean and replaces it with normal saline water.
  • Since we accumulated fresh water in the fjord, it exits not in a single discharge in summer, but uniformly, and during autumn, and winter, providing the cold of the polar night and the warm water of the Atlantic with an interlayers of dense saline water.
  • Preliminary figures: 5 cubic km of fresh water mixing with an unlimited volume of ocean water to a salinity of 34 yields 175 cubic km of such water, over the winter season—1 cubic kilometer per day exiting the fjord uniformly. Or a patch 100 meters thick and 10 sq km in area.
  • Salinity parameters are approximate and depend on the season, the fjord, and the curtain settings.

Naturally, all these hypotheses need to be modeled on specialized computers and verified climate models.

Modeling and Experimental Validation

Existing fjord hydrodynamics models (MITgcm, ROMS, FVCOM) accurately reproduce tidal processes, baroclinic pressure, and glacial runoff in an open water column. Installation of a barrier at 50 m depth introduces uncertainty in key parameter estimation. No data exist on the rate of salinization of the freshwater lens beneath the barrier via tidal bottom friction and entrainment from the 100 m horizon. Peak loads on the anchor system from interaction between accumulated hydrostatic head and ebb currents remain undefined. The salinity gradient in the mixing zone beneath the curtain—and consequently, the characteristics of the outflowing oceanic stream (volume, density)—are unknown. Preliminary estimates are hypothetical, while impact calculations at the Labrador Sea scale require quantitative data.

Required Sequence of Actions:

  1. High-resolution modeling of a fjord with barrier.

    A three-dimensional simulation with horizontal resolution ≤ 100 m and vertical resolution ≤ 2 m is required. Includes: multibeam bathymetry; tidal forcing from TPXO data; seasonal glacial runoff; vertical mixing parameterization (k-ε or k-ω) accounting for internal waves; calculation of barrier deformation and tension as a flexible structure. Output: time series of velocity, salinity, and temperature beneath the barrier, plus anchor stress fields.

  2. Pilot project in field conditions.

    Partial or complete closure of a fjord with 1–2 km³ annual runoff. Mobile pontoon structure on 6 anchors, design wave load Hs = 3 m. Measurements: ADCP beneath barrier, CTD profiling, tensiometers, acoustic deformation sensor. Duration: one runoff season (June–November).

  3. Model calibration using field measurement data.

    ADCP provides outflow velocity profiles; CTD supplies salinity gradients; tension sensors yield peak loads. Calibration of entrainment coefficient and source geometry eliminates theoretical inaccuracies.

  4. Regional modeling of impact on Labrador Sea and Atlantic.

    Nested eddy-permitting MITgcm/NEMO domain with 2–4 km resolution. Calibrated forcing from points 1–3 is implemented at the mouths of three fjords.

    Objectives:

    • Water parcel descent to 400–800 m and interaction with deep cold layers;
    • Signal propagation to the 200 m horizon where warm Atlantic water occurs (depths do not everywhere reach 800 m);
    • Changes in NADW export in multi-year integration;
    • Assessment of surface salinity impact area.

Implementation of the fourth stage without preceding data is limited to theoretical assumptions. With them, it becomes a predictable engineered climate intervention.

State

Obviously, the implementation of such a project is impossible without state involvement and permission. However, this does not mean that we consider inaction and waiting for decisions from state unions and international organizations to be the best solution.

We call on individual countries, political forces, and public organizations to formulate their position regarding the elimination of such a huge climate risk as the stopping of AMOC.

This project potentially opens up huge opportunities for building a proactive, active, and strategic position, and we will be happy to provide any necessary clarifications.

Ecology

Several countries have expressed opposition to barrier and enclosure technologies for ecological reasons, arguing that such curtains turn fjords into swamps. This is not the case here. The passage below 50 meters remains open not only to fish but also to marine mammals. Constant upwelling drives a powerful ascent of deep water and, critically, winter ice melt, which maintains extensive polynyas (spanning square kilometers) and prevents mass fish kills from winter hypoxia. Moreover, the gradual consumption of fresh water smoothes salinity fluctuations, reducing stress on the ecosystem. Naturally, a complete inventory of potential effects warrants separate dedicated research.

Additionally, the curtain is almost entirely submerged and does not affect the landscape, cultural perception, or historical interpretation of the environment where it is installed.