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

Best Deals on Home Furniture Online

Key Highlights Discover the best deals on high-quality outdoor furniture online. Transform your outdoor space into a stylish and comfortable oasis. Explore a wide range of d...

Discover the Best Women's Jumpers for Every Season

Key Highlights Explore lightweight jumpers for spring and summer, ensuring breathability and ease. Wrap up warm with cozy wool jumpers for the chilly autumn and winter season...

Uncover the Elegance of Gorgeous Diamond Tennis Necklaces

Key Highlights Diamond tennis necklaces are a timeless piece of jewelry that exudes elegance and sophistication. They feature a continuous line of brilliant-cut diamonds, cre...

Dental Implants vs. Dentures: Which Is Better for You?

When it comes to replacing missing teeth, two of the most common options are dental implants and dentures. Both have their advantages and disadvantages, so choosing between them ...

What Neck Pain Really Means (And Why It’s More Than Just Poor Posture)

Neck pain is often brushed off as something temporary — a tight spot after a long day at the desk or a poor night’s sleep. But when the discomfort keeps returning, it could be a ...

The Work of Gosha Rubchinskiy: Fashion, Culture, and Youth

From Designer to Cultural Architect Gosha Rubchinskiy is not just a fashion designer—he's a cultural force. Born in Moscow in 1984, Rubchinskiy began his career in fashion in t...

Times Magazine

The Essential Guide to Transforming Office Spaces for Maximum Efficiency

Why Office Fitouts MatterA well-designed office can make all the difference in productivity, employee satisfaction, and client impressions. Businesses of all sizes are investing in updated office spaces to create environments that foster collaborat...

The A/B Testing Revolution: How AI Optimized Landing Pages Without Human Input

A/B testing was always integral to the web-based marketing world. Was there a button that converted better? Marketing could pit one against the other and see which option worked better. This was always through human observation, and over time, as d...

Using Countdown Timers in Email: Do They Really Increase Conversions?

In a world that's always on, where marketers are attempting to entice a subscriber and get them to convert on the same screen with one email, the power of urgency is sometimes the essential element needed. One of the most popular ways to create urg...

Types of Software Consultants

In today's technology-driven world, businesses often seek the expertise of software consultants to navigate complex software needs. There are several types of software consultants, including solution architects, project managers, and user experienc...

CWU Assistive Tech Hub is Changing Lives: Win a Free Rollator Walker This Easter!

🌟 Mobility. Independence. Community. All in One. This Easter, the CWU Assistive Tech Hub is pleased to support the Banyule community by giving away a rollator walker. The giveaway will take place during the Macleod Village Easter Egg Hunt & Ma...

"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 ...

LayBy Shopping