The Times Australia
The Times World News

.
The Times Real Estate

.

Oceans absorb 30% of our emissions, driven by a huge carbon pump. Tiny marine animals are key to working out its climate impacts

  • Written by Tyler Rohr, Lecturer in Southern Ocean Biogeochemical Modelling, IMAS, University of Tasmania
Oceans absorb 30% of our emissions, driven by a huge carbon pump. Tiny marine animals are key to working out its climate impacts

The ocean holds 60 times more carbon than the atmosphere and absorbs almost 30% of carbon dioxide (CO₂) emissions from human activities. This means the ocean is key to understanding the global carbon cycle and thus our future climate.

The Intergovernmental Panel on Climate Change (IPCC) uses earth system models to project climate change. These projections inform critical political, social and technological decisions. However, if we can’t accurately model the marine carbon cycle then we cannot truly understand how Earth’s climate will respond to different emission scenarios.

In research published today[1], we show that zooplankton, tiny animals near the base of the ocean food chain, are likely to be the biggest source of uncertainty in how we model the marine carbon cycle. Getting their impact on the cycle right could add an extra 2 billion tonnes to current models’ assumptions about annual carbon uptake by the ocean. That’s more carbon than the entire global transportation sector emits.

Graph showing global carbon budget with emissions and sinks
The ocean (dark green) is a major carbon sink that partly offsets emissions in the global carbon budget. Global Carbon Budget 2022, Friedlingstein et al, CC BY[2][3]

Read more: Oceans are better at storing carbon than trees. In a warmer future, ocean carbon sinks could help stabilise our planet[4]

Marine carbon cycling is a $3 trillion thermostat

Roughly 10 billion tonnes[5] of carbon are being released into the atmosphere each year. But the ocean quickly absorbs about 3 billion tonnes of these emissions, leaving our climate cooler and more hospitable. If we price carbon[6] at the rate the IPCC believes is needed to limit warming to 1.5℃, this adds up to over A$3 trillion worth of emission reductions accomplished naturally by the ocean every year.

However, we know the size of the ocean carbon sink has changed in the past, and even small changes can lead to big changes in the atmosphere’s temperature. Thus, we understand the ocean acts as a thermostat for our climate. But what controls the dial?

Extensive geological evidence[7] suggests microscopic marine life could be in control. Phytoplankton photosynthesise and consume as much CO₂ as all land plants[8].

When phytoplankton die, they sink and trap much of their carbon deep in the ocean. It can remain there for centuries to millennia, locked away safely out of contact with the atmosphere.

Any changes to the strength of this biological carbon pump will be felt in the atmosphere and will change our climate[9]. Some have even proposed enhancing this biological pump by artificially fertilising the ocean with iron to stimulate phytoplankton. It’s possible this could sequester as much as an extra 20% of our annual CO₂ emissions.

The marine biological carbon pump A diagram of the natural biological carbon pump and how iron fertilisation could artificially enhance it. Rohr et al (2019), Author provided[10]

Read more: Smoke from the Black Summer fires created an algal bloom bigger than Australia in the Southern Ocean[11]

Right for the wrong reasons

Despite its importance for the global climate[12] and food production, there are large gaps in our understanding of how the marine carbon cycle is expected to change. Most earth system models differ in how the cycle’s major components will respond to a changing climate. Models simply can’t agree on what will happen to:

  • net primary production – the carbon consumed by phytoplankton resulting in growth of marine plants at the base of the food web

  • secondary production – zooplankton growth, which is an indicator for fisheries, since fish eat zooplankton

  • export production – the biological pump of carbon transferred to the deep sea.

To diagnose what might be going wrong, we compared the marine carbon cycle in 11 IPCC earth system models. We found the largest source of uncertainty is how fast zooplankton consume their phytoplankton prey, known as grazing pressure.

Models differ hugely in their assumptions about this grazing pressure. Even if zooplankton were exposed to the exact same amount of phytoplankton, the highest assumed grazing rate would be almost 100 times as fast as the slowest rate.

This is because some models effectively assume the ocean is filled entirely with slow-grazing shrimp. Others assume it is teeming exclusively with microscopic, but rapidly grazing ciliates[13]. In reality, neither is true.

Differences in prominent models’ estimates of the amount of zooplankton at different latitudes. Adapted from Rohr et al (2023), Author provided[14]

Read more: Tiny plankton drive processes in the ocean that capture twice as much carbon as scientists thought[15]

Models must make up for such large differences in zooplankton grazing by making additional assumptions about how fast phytoplankton grow and how quickly zooplankton die. Together, these differences can be balanced in a way that allows most models to simulate the present-day amount of carbon consumed by phytoplankton and transferred to the deep sea.

However, that is only because we can observe what those values should be. We can then tune models until we ensure they get the right answer.

Yet, even though our best models can admirably recreate the present-day ocean, they do so for different reasons and with dramatically different assumptions about the role of zooplankton. This means these models are built with fundamentally different machinery. When used to test future emissions scenarios, they will project fundamentally different outcomes.

We cannot know which projections are correct unless we know the true role of zooplankton.

Read more: Climate: modelling micro-algae to better understand the workings of the ocean[16]

Tiny plankton with a big impact

We ran a sensitivity experiment to show how small changes in zooplankton grazing can dramatically alter marine carbon cycling. We considered two sets of experiments, one control and one in which we increased both zooplankton grazing rates and phytoplankton growth rates, such that both were tuned to the exact same total carbon consumption by phytoplankton.

This increase in how fast zooplankton can graze was only a fraction of the difference between assumed grazing rates seen across IPCC models. Despite this, we found even this small increase led to a huge difference in the percentage of carbon consumed by phytoplankton that was eventually exported to depth and transferred up the food chain.

Ocean carbon storage increased by 2 billion tonnes per year. Zooplankton carbon consumption increased by 5 billion tonnes.

From a climate perspective, that is double the maximum theoretical potential of iron fertilisation. From a fisheries perspective, that leads to a 50% increase in the size of the global zooplankton population on which many fish feed. This matters for global food supply as the ocean feeds 10% of the global population.

This work shows we must improve both our understanding and modelling of zooplankton. With limited resources and an immense ocean, we will never have enough observations to build perfect models. However, new technologies for measuring zooplankton are making it easier to make autonomous, high-resolution measurements of many important variables.

We must make a concerted effort to leverage these new technologies to better understand the role of zooplankton in the marine carbon cycle. We will then be able to reduce uncertainties about future climate states, advance our ability to assess marine-based CO₂ removal, and improve global fisheries projections.

References

  1. ^ research published today (www.nature.com)
  2. ^ Global Carbon Budget 2022, Friedlingstein et al (essd.copernicus.org)
  3. ^ CC BY (creativecommons.org)
  4. ^ Oceans are better at storing carbon than trees. In a warmer future, ocean carbon sinks could help stabilise our planet (theconversation.com)
  5. ^ 10 billion tonnes (essd.copernicus.org)
  6. ^ price carbon (www.ipcc.ch)
  7. ^ geological evidence (www.nature.com)
  8. ^ as much CO₂ as all land plants (www.nature.com)
  9. ^ will change our climate (scitechdaily.com)
  10. ^ Rohr et al (2019) (www.nature.com)
  11. ^ Smoke from the Black Summer fires created an algal bloom bigger than Australia in the Southern Ocean (theconversation.com)
  12. ^ importance for the global climate (scitechdaily.com)
  13. ^ ciliates (www.britannica.com)
  14. ^ Adapted from Rohr et al (2023) (www.nature.com)
  15. ^ Tiny plankton drive processes in the ocean that capture twice as much carbon as scientists thought (theconversation.com)
  16. ^ Climate: modelling micro-algae to better understand the workings of the ocean (theconversation.com)

Read more https://theconversation.com/oceans-absorb-30-of-our-emissions-driven-by-a-huge-carbon-pump-tiny-marine-animals-are-key-to-working-out-its-climate-impacts-207219

The Times Features

Itinerary to Maximize Your Two-Week Adventure in Vietnam and Cambodia

Two weeks may not seem like much, but it’s just the right time for travelers to explore the best of Vietnam and Cambodia. From the bustling streets of Hanoi to the magnificent te...

How to Protect Your Garden Trees from Wind Damage in Australia

In Australia's expansive landscape, garden trees hold noteworthy significance. They not only enhance the aesthetic appeal of our homes but also play an integral role in the local...

Brisbane Homeowners Warned: Non-Compliant Flexible Hoses Pose High Flood Risk

As a homeowner in Brisbane, when you think of the potential for flood damage to your home, you probably think of weather events. But you should know that there may be a tickin...

Argan Oil-Infused Moroccanoil Shampoo: Nourish and Revitalize Your Hair

Are you ready to transform your hair from dull and lifeless to vibrant and full of life? Look no further than the luxurious embrace of Argan Oil-Infused Moroccanoil Shampoo! In a...

Building A Strong Foundation For Any Structure

Building a home or commercial building can be very exciting. The possibilities are endless and the future is interesting. You can always change aspects of the building to meet the ...

The Role of a Family Dentist: Why Every Household Needs One

source A family dentist isn’t like your regular dentist who may specialise in a particular age group and whom you visit only when something goes wrong. A family dentist takes proa...

Times Magazine

"Eternal Nurture" by Cara Barilla: A Timeless Collection of Wisdom and Healing

Renowned Sydney-born author and educator Cara Barilla has released her latest book, Eternal Nurture, a profound collection of inspirational quotes designed to support mindfulness, emotional healing, and personal growth. With a deep commitment to ...

How AI-Driven SEO Enhancements Can Improve Headless CMS Content Visibility

Whereas SEO (search engine optimization) is critical in the digital landscape for making connections to content, much of it is still done manually keyword research, metatags, final tweaks at publication requiring a human element that takes extensiv...

Crypto Expert John Fenga Reveals How Blockchain is Revolutionising Charity

One of the most persistent challenges in the charity sector is trust. Donors often wonder whether their contributions are being used effectively or if overhead costs consume a significant portion. Traditional fundraising methods can be opaque, with...

Navigating Parenting Arrangements in Australia: A Legal Guide for Parents

Understanding Parenting Arrangements in Australia. Child custody disputes are often one of the most emotionally charged aspects of separation or divorce. Parents naturally want what is best for their children, but the legal process of determining ...

Blocky Adventures: A Minecraft Movie Celebration for Your Wrist

The Minecraft movie is almost here—and it’s time to get excited! With the film set to hit theaters on April 4, 2025, fans have a brand-new reason to celebrate. To honor the upcoming blockbuster, watchfaces.co has released a special Minecraft-inspir...

The Ultimate Guide to Apple Watch Faces & Trending Wallpapers

In today’s digital world, personalization is everything. Your smartwatch isn’t just a timepiece—it’s an extension of your style. Thanks to innovative third-party developers, customizing your Apple Watch has reached new heights with stunning designs...

LayBy Shopping