Introduction

The scientific basis for Artificial Upwelling

Carbon fixation through carbon dioxide removal solutions such as plant production in the ocean is driven by vertical mixing of nutrient-enriched deep water into sunlit surface layers –achieving net carbon fixation above baseline and net carbon sequestration (CO2 “offsets”). Ocean gyres, particularly the North Pacific gyre, are areas with relatively low vertical mixing and strong vertical nutrient gradients. Horizontal spatial coherence is very high in these gyres, so measuring the impacts of our carbon dioxide removal machine for pumped upwelling is simplified. The vast gyre areas where conditions are similar suggest scalability of wave-driven pumped upwelling is substantially driven by the number and size of pumps deployed.

The key to producing net carbon sequestration in these low-nutrient, low-chlorophyll (LNLC) ocean gyres is upwelling deep water containing nutrient concentrations greater than the dissolved CO2 concentration on a plant stoichiometry basis, i.e., the Redfield ratio. Thus, making carbon removal projects emerge successfully.

In a 2008 paper, David Karl and Ricardo Letelier calculated the net sequestration potential from pump-driven upwelling using data collected at the long-term monitoring Station ALOHA in the North Pacific gyre near Hawaii. They estimated that upwelling of waters, using a carbon dioxide removal machine, from 200 m or deeper provides excess phosphate, which triggers a sequence of nitrate, and then phosphate uptake triggers blooms of phytoplankton. The secondary phosphate bloom fixes more dissolved CO2 than is upwelled, resulting in net CO2 sequestration. Using the Karl-Letelier calculations, we build our pumps with the intake at 500 m to maximize the carbon fixed per unit area relative to the vertical length of the pump.

Table 1 from Karl and Letelier, 2008.
Table 2. Calculated net CO2 sequestered by one pump, adapted from Karl and Letelier’s 2008 data using volumes pumped from the current pump design (iron upwelling column assumes zero additional tons CO2 sequestered in this table).
Table 3. Annual pumped volume by one pump.

To determine the upwelling flow rate, in 2007, we conducted a sea trial of a 0.75m diameter by 152m deep upwelling pump as a part of our carbon removal solutions, which was similar to our current design except for dimensions and ruggedness. With triaxial accelerometers on the valve flappers recording open/close cycles, and temperature sensors top and bottom, we determined the time for deep cold water to surface. The outlet temperature sensor showed cold water arriving at 08:45:00, about 15 minutes after the first upwelling stroke. Dividing tube volume by elapsed time gives a flow rate of 0.078 m3/s.

Figure 10. Atmocean test data from 2007.
Table 4. Calculated efficiency and flow rate from our upwelling test in 2007.

Oceanographic Locations

Carbon dioxide removal machines are deployed far off-shore and away from coral reefs to circulate in the ocean gyres.

We will deploy our Pumps in low-nutrient, low-chlorophyll ocean regions such as the North Pacific Subtropical Gyre as these regions are best suited for this technology.

Potential gyres for deployment

Monitoring & Tracking

How do we know Pump locations and operating status?

The Artificial Upwelling Pump buoy is equipped with GPS, USCG-approved navigation light, triaxial accelerometer, satellite communications, solar-rechargeable battery, and controller module.

One pair of connecting lines extend to strain gauges on each connector rope between the buoy and pump outlet, measure wave period and steepness, from which we can infer wave amplitude.

The second pair of lines connect to two temperature sensors – one inside the pump outlet measuring the temperature of the upwelled water, and one outside the pump outlet measuring the ambient water temperature at ~5m.

The third pair of lines connect to two electronic paddle-wheel flow meters inside the pump outlet – one with a clutch to record just the upward flow rate (cm/s) and elapsed distance, and the other no-clutch model recording net flow rate (up and down, and elapsed distance).

The triaxial accelerometer records force and vector of the buoy riding up and down passing waves.

This AUP buoy data is uplinked periodically and provides an indication of pump operation:

  • Temperature sensors will verify pumping, as the water inside the outlet registers colder compared to warmer ambient water outside the outlet.
  • Sporadic or missing data from the buoy GPS suggests the buoy is riding low in the water, as waves overtopping the buoy will periodically block the GPS satellite signals. This implies excessive biofouling has offset some buoyancy.
  • If the strain gauge outputs drop to low values, this suggests rope, tube or valve failure.
  • Likewise the flow meter values directly measure rate of upwelled water.

Measurement, Reporting & Verification

Biogeochemical Argo Profiling Floats

Measurement of the carbon from below the pump to the surface is provided by biogeochemical ARGO robotic floats. The sensors incorporated on each BGC ARGO are found at https://www.seabird.com/biogeochemical-floats.

Our patent-pending methodology for determining net carbon sequestration is as follows:

“The BGC floats include a sensor package that measures the bulk properties of the most significant oceanic carbon pools that will be affected by the enhanced vertical exchange of water across the thermocline from the pumping technology.

Temperature, salinity and pressure yield the density field and will be used to generate a mixing model of the pumping effect on the vertical transport of the quasi-conservative heat and salt budgets. This constrains the entire system.

The carbon dynamic response to the vertical exchange is measured by the rest of the sensors. The chlorophyll fluorescence and backscattering sensors measure the particle load of particulate organic carbon (backscattering) and the viable phytoplankton (chlorophyll). The FDOM fluorometer measures the concentration of the fluorescent fraction of the dissolved organic matter pool. The pH sensor measures one component of the pCO2 equilibrium and with the backscattering and FDOM sensors monitors net transfers of carbon between the dissolved and particulate pools through autotrophic and heterotrophic activity. The dissolved oxygen sensor constrains net community production of fixed carbon and the impact of gas exchange kinetics on pCO2, Finally, the nitrate concentration measurement monitors the effectiveness of the exchange of nutrient-rich deep water with nutrient-depleted surface water through the pumping process and therefore the net increase in autotrophic carbon production potential achieved by the pumps.

The floats will be deployed in a near field/far field manner with one float within the pumping volume and the other deployed outside the pumping volume. The float mission profiles (park depth, profile interval, the rate and ratio between deep and shallow profiles) will be adjusted during the initial trial period and subsequently during roll out to optimize modeling of the effect of the pumps.

As the system scales, a network effect of increasing data from the floats relative to the governing scales across time and space will decrease the carbon flux measurement uncertainty between any pair of near and far-field floats, resulting in a measurement system that asymptotically approaches a fixed structural relationship between the pumping and the net sequestration of carbon.”

BGC ARGO data is uplinked near real-time to the ARGO data center in France or the USA where it is quality-controlled, then becomes public according to ARGO procedures.

The pathway of the BGC ARGO can be finetuned by modifying the length of the tether rope extending from the valve/bottom-weight, as seen below (patent pending).

Sketch of BGC ARGO tethering.

A sample of possible pathways assuming pump depth 500m and total tether line 2,000m follows:

Table 6. Geometry of BGC ARGO tethering.

The reference BGC ARGO may be a null pump (complete except no valve thus no upwelling); a free-drifting BGC ARGO we deploy outside the pumping region; or may utilize data from 3rd party BGC ARGO’s in the vicinity (if temporal and spatial variability of the reference data is acceptable and representative of the AUP operating region).

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