Frontiers | Ocean Artificial Upwelling – Ecological Responses and Biogeochemical Impacts

ORIGINAL RESEARCH

25 November 2022

Nutrient composition (Si:N) as driver of plankton communities during artificial upwelling

Silvan Urs Goldenberg, 7 more and Ulf Riebesell

6,718 views

29 citations

ORIGINAL RESEARCH

8 November 2022

The importance of the dissolved organic matter pool for the carbon sequestration potential of artificial upwelling

Markel Gómez-Letona, 6 more and Javier Arístegui

6,456 views

11 citations

ORIGINAL RESEARCH

5 July 2023

Counteracting effects of nutrient composition (Si:N) on export flux under artificial upwelling

Moritz Baumann, 5 more and Ulf Riebesell

4,612 views

6 citations

ORIGINAL RESEARCH

22 November 2023

Microzooplankton communities and their grazing of phytoplankton under artificial upwelling in the oligotrophic ocean

Kristian Spilling, 6 more and Ulf Riebesell

4,051 views

7 citations

ORIGINAL RESEARCH

14 October 2022

Response of plankton community respiration under variable simulated upwelling events

Isabel Baños, 7 more and Ulf Riebesell

2,644 views

5 citations

Expected Limits on the Potential for Carbon Dioxide Removal From Artificial Upwelling

ORIGINAL RESEARCH

29 June 2022

Expected Limits on the Potential for Carbon Dioxide Removal From Artificial Upwelling

David A Koweek

Artificial upwelling, the engineered upward pumping of deep ocean water, has long been proposed as a technique to fertilize the ocean and, more recently, remove atmospheric carbon dioxide. This study investigated the potential of artificial upwelling to contribute to carbon dioxide removal using a simple model with high-resolution (1deg x 1deg) gridded monthly climatologies of upper ocean and deep ocean physical and chemical properties. The potential for carbon dioxide removal was explored across a range of observationally-informed carbon-to-nitrogen-to-phosphorus ratios for microalgae and macroalgae communities, providing information on the sensitivity of the estimates to any assumed carbon-to-nutrient ratios. Simulated carbon dioxide removal across the tropical-to-subpolar ocean did not exceed 0.66 tons per square kilometer per year for microalgae, and did not exceed 0.85 tons per square kilometer per year for macroalgae. Using current technology, the estimated global aggregate potential for carbon dioxide removal using microalgae was less than 50 megatons (0.05 gigatons) of carbon dioxide annually and the estimated global aggregate potential for carbon dioxide removal using macroalgae was approximately 100 megatons (0.1 gigatons) of carbon dioxide annually. While controlled field trials are needed to validate or invalidate the findings of this study, this study suggests that artificial upwelling is unlikely to support annual carbon dioxide removal at, or close to, the rate of one gigaton of carbon dioxide annually.

9,804 views

23 citations

ORIGINAL RESEARCH

20 June 2022

Oligotrophic Phytoplankton Community Effectively Adjusts to Artificial Upwelling Regardless of Intensity, but Differently Among Upwelling Modes

Joaquin Ortiz, 3 more and Ulf Riebesell

Artificial upwelling has been proposed as a means of enhancing oceanic CO2 sequestration and/or raising fishery yields through an increase in primary production in unproductive parts of the ocean. However, evidence of its efficacy, applicability and side effects is scarce. Here we present part of the results of a 37-day mesocosm study conducted in oligotrophic waters off the coast of Gran Canaria. The goal was to assess in situ the effects of artificial upwelling on the pelagic community. Upwelling was simulated via two modes: i) a singular deep-water pulse and ii) a recurring supply every 4 days; each mode at four different intensities defined by the total amount of nitrate added: approx. 1.5, 3, 5.7, and 11 µmol L-1. In this study we focus on the phytoplankton response through size-fractionated 14C primary production rates (PP), Chlorophyll a and biomass. We observed increases in PP, accumulated PP, Chlorophyll a and biomass that scaled linearly with upwelling intensity. Upwelling primarily benefitted larger phytoplankton size fractions, causing a shift from pico- and nano- to nano- and microphytoplankton. Recurring deep-water addition produced more biomass under higher upwelling intensities than a single pulse addition. It also reached significantly higher time-integrated PP per unit of added nutrients and showed a stronger reduction in percentage extracellular release with increasing upwelling intensity. These results demonstrate that oligotrophic phytoplankton communities can effectively adjust to artificial upwelling regardless of upwelling intensity, but differently depending on the upwelling mode. Recurring supply of upwelled waters generated higher efficiencies in primary production and biomass build-up than a single pulse of the same volume and nutrient load.

5,137 views

17 citations

Artificial Upwelling in Singular and Recurring Mode: Consequences for Net Community Production and Metabolic Balance

ORIGINAL RESEARCH

12 January 2022

Artificial Upwelling in Singular and Recurring Mode: Consequences for Net Community Production and Metabolic Balance

Joaquin Ortiz, 2 more and Ulf Riebesell

Artificial upwelling of nutrient-rich waters and the corresponding boost in primary productivity harbor the potential to enhance marine fishery yields and strengthen the biological pump for sequestration of atmospheric CO2. There is increasing urgency to understand this technology as a “ocean-based solution” for counteracting two major challenges of the 21st century – climate change and overfishing. Yet, little is known about the actual efficacy and/or possible side effects of artificial upwelling. We conducted a large-scale off-shore mesocosm study (~44 m3) in the oligotrophic waters of the Canary Islands to identify the community-level effects of artificial upwelling on a natural oligotrophic plankton community. Four upwelling intensities were simulated (approx. 1.5/3/5.7/10 µmol L-1 of nitrate plus phosphate and silicate) via two different upwelling modes (a singular deep-water pulse versus recurring supply every 4 days) for 37 days. Here we present results on the response of net community production (NCP), metabolic balance and phytoplankton community composition (<250 µm). Higher upwelling intensities yielded higher cumulative NCP. Following upwelling onset, the phytoplankton community became dominated by diatoms in all treatments, but other taxa such as Coccolithophores increased later in the experiment. The magnitude of effects on the metabolic balance scaled with the amount of added deep water, leading to (i) a balanced to net-heterotrophic system in the singular and (ii) a net-autotrophic system in the recurring upwelling treatments. Accordingly, the mode in which nutrients are supplied to an oligotrophic system plays a crucial role ecosystem response, with recurring upwelling leading to higher long-term NCP than singular upwelling. These results highlight the importance of empirically measured local responses to upwelling such as community structure and metabolism, with major implications not only for upwelling system model simulations, but specifically for the potential employment of artificial upwelling as an ocean-based solution to generate (primary) production.

5,483 views

21 citations

ORIGINAL RESEARCH

3 January 2022

Numerical Flow Modeling of Artificial Ocean Upwelling

Jost Kemper, 1 more and Kai Graf

5,274 views

7 citations

ORIGINAL RESEARCH

27 October 2021

Effect of Intensity and Mode of Artificial Upwelling on Particle Flux and Carbon Export

Moritz Baumann, 10 more and Ulf Riebesell

Reduction of anthropogenic CO2 emissions alone will not sufficiently restrict global warming and enable the 1.5 °C goal of the Paris agreement to be met. To effectively counteract climate change, measures to actively remove carbon dioxide from the atmosphere are required. Artificial upwelling has been proposed as one such carbon dioxide removal technique. By fueling primary productivity in the surface ocean with nutrient-rich deep water, it could potentially enhance downward fluxes of particulate organic carbon (POC) and carbon sequestration. In this study we investigated the effect of different intensities of artificial upwelling combined with two upwelling modes (recurring additions versus one singular addition) on POC export, sinking matter stoichiometry and remineralization depth. We carried out a 39 day-long mesocosm experiment in the subtropical North Atlantic, where we fertilized oligotrophic surface waters with different amounts of deep water. The total nutrient inputs ranged from 1.6 to 11.0 µmol NO3- L-1. We found that on the one hand POC export under artificial upwelling more than doubled, and the molar C:N ratios of sinking organic matter increased from values around Redfield (6.6) to ~8-13, which is beneficial for potential carbon dioxide removal. On the other hand, sinking matter was remineralized at faster rates and showed lower sinking velocities, which led to shallower remineralization depths. Particle properties were more favorable for deep carbon export in the recurring upwelling mode, while in the singular mode the C:N increase of sinking matter was more pronounced. In both upwelling modes roughly half of the produced organic carbon was retained in the water column until the end of the experiment. This suggests that the plankton communities were still in the process of adjustment, possibly due to the different response times of producers and consumers. There is thus a need for studies with longer experimental durations to quantify the responses of fully adjusted communities. Finally, our results revealed that artificial upwelling affects a variety of sinking particle properties, and that the intensity and mode with which it is applied control the strength of the effects.

9,430 views

36 citations