Fusulines and Climate Change: Insights from Ancient Oceans

Introduction

Earth’s oceans serve as extensive archives of climate change, with some of the most detailed records preserved in fusulines—microscopic shells smaller than a grain of sand. A recent study led by Professor Shuzhong Shen of Nanjing University reveals that these tiny organisms thrived during periods of global cooling but nearly vanished twice during episodes of volcanic-induced global warming.

Fusulines as Indicators of Carbon Cycle Changes

Fusulines belong to the order Fusulinida, a group of foraminifera—single-celled protists that produce carbonate shells. These organisms dominated the seafloor from 344 million to 252 million years ago, acting as “carbonate rock factories” by forming extensive reefs.

1. Two major diversification events were identified:
   • During the late Carboniferous cooling period, small and simple shells proliferated.
   • At the onset of the Permian period, larger fusulines with honeycomb-like walls emerged, likely hosting photosynthetic partners.

Impact of Climate Fluctuations on Fusuline Populations

Cooling Periods and Habitat Expansion

During global cooling phases, glaciers trapped water, causing sea levels to drop and creating new shallow marine habitats. This environmental shift led to a threefold increase in fusuline species diversity over a 40-million-year period, paralleling similar patterns observed in later planktonic species during the Cenozoic era.

Warming Events and Population Declines

1. The Kasimovian warming (~304 million years ago) resulted in a rapid extinction of approximately 45% of fusuline species within less than one million years.
2. Subsequent temperature rises between 294 and 284 million years ago caused another significant decline.
3. The end-Permian supervolcanic eruptions led to the disappearance of 59.5% of remaining species in a geologically brief interval.

Volcanic Carbon Emissions as Drivers of Extinction

The extinction events align closely with massive basaltic eruptions from volcanic provinces such as Emeishan and Siberia. These eruptions released large amounts of carbon dioxide, causing:

• Surface ocean temperature increases of 5 to 10°F.
• Seawater acidification.
• Oxygen depletion in marine environments.

This combination severely impacted benthic organisms, including fusulines. Carbon-isotope data further confirm ocean acidification linked to volcanic rock weathering, while oxygen levels dropped below thresholds necessary to sustain diverse seafloor life.

Role of Orbital Cycles in Biodiversity Patterns

While Milankovitch orbital cycles—Earth’s long-term orbital variations—were detected as minor influences on fusuline diversity, they accounted for no more than 10% of observed fluctuations. These cycles may have facilitated glacier growth and nutrient runoff during their minima, modestly promoting speciation. However, the dominant drivers of diversity changes were rapid volcanic events and associated climate severity.

Contemporary Implications and Sustainable Development Goals (SDGs)

Professor Shen emphasizes the urgency of mitigating climate change and protecting ecosystems, aligning with several United Nations Sustainable Development Goals:

• SDG 13: Climate Action – The study highlights the rapid pace of current human-driven warming, which is at least ten times faster than past events that caused fusuline extinctions.
• SDG 14: Life Below Water – Modern reef-building organisms are already exhibiting stress due to warmer, more acidic oceans, mirroring ancient patterns.
• SDG 15: Life on Land – The fossil record warns that rapid environmental changes can disrupt dominant species, underscoring the need for sustainable ecosystem management.

If greenhouse gas emissions continue unabated, today’s marine carbonate shell builders—including corals, coccolithophores, and large benthic foraminifera—face risks similar to those that led to fusuline extinction.

Methodology: High-Resolution Fossil Analysis

The research utilized a constrained-optimization algorithm called CONOP to achieve sub-45,000-year resolution in fossil appearance and disappearance data. Millions of stratigraphic sequences were analyzed to construct a precise timeline of fusuline diversity.

• Sampling bias was minimized through rarefaction tests with multiple resample sizes.
• Long-term trends exceeding ten million years were filtered out to isolate shorter cycles related to orbital influences.

Environmental Drivers of Fusuline Diversity

Multivariate regression analyses incorporating seven environmental proxies—including carbon dioxide levels, seawater strontium ratios, oxygen availability, and carbon isotopes—explained 81% of the variance in fusuline diversity. This robust model confirms that physical climate factors predominantly governed the rise and fall of fusulines.

Conclusions and Future Outlook

• Fusulines demonstrate that rapid warming events can decimate even resilient marine lineages.
• Cooling periods can foster biodiversity and evolutionary innovation.
• Current anthropogenic climate change parallels ancient volcanic warming events but occurs at a much faster rate, posing significant threats to marine ecosystems.

The fossil record offers a cautionary tale, emphasizing the need for urgent climate action to preserve marine biodiversity and ecosystem health in line with the Sustainable Development Goals.

Publication and Further Information

This study is published in the journal Science Advances.

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1. Sustainable Development Goals (SDGs) Addressed or Connected

1. SDG 13: Climate Action
   • The article discusses historical climate changes, volcanic CO2 emissions, ocean acidification, and warming, highlighting the urgent need to mitigate climate change.
2. SDG 14: Life Below Water
   • The focus on marine ecosystems, ocean acidification, oxygen depletion, and impacts on marine organisms like fusulines and reef-building calcifiers directly relates to conserving and sustainably using oceans.
3. SDG 15: Life on Land
   • Although less direct, the article’s emphasis on biodiversity loss and extinction events links to protecting terrestrial ecosystems and biodiversity.

2. Specific Targets Under Those SDGs Identified

1. SDG 13: Climate Action
   • Target 13.1: Strengthen resilience and adaptive capacity to climate-related hazards and natural disasters.
   • Target 13.2: Integrate climate change measures into national policies, strategies, and planning.
   • Target 13.3: Improve education, awareness-raising, and human and institutional capacity on climate change mitigation, adaptation, impact reduction, and early warning.
2. SDG 14: Life Below Water
   • Target 14.2: Sustainably manage and protect marine and coastal ecosystems to avoid significant adverse impacts.
   • Target 14.3: Minimize and address the impacts of ocean acidification.
   • Target 14.5: Conserve at least 10% of coastal and marine areas.
3. SDG 15: Life on Land
   • Target 15.5: Take urgent and significant action to reduce the degradation of natural habitats and halt biodiversity loss.

3. Indicators Mentioned or Implied to Measure Progress

1. Indicators Related to SDG 13 (Climate Action)
   • Atmospheric CO2 concentration levels (implied through volcanic CO2 emissions and modern greenhouse gas emissions).
   • Global surface temperature changes (warming spikes and cooling trends described).
   • Frequency and intensity of climate-related hazards (volcanic events as analogs to current emissions).
2. Indicators Related to SDG 14 (Life Below Water)
   • Diversity and abundance of marine species (fusuline species counts and extinction rates).
   • Ocean acidification levels (carbon isotope data, 87Sr/86Sr ratio as proxy for acidification).
   • Oxygen concentration in seawater (oxygen availability thresholds for benthic organisms).
   • Health and stress indicators of reef-building calcifiers and carbonate shell builders.
3. Indicators Related to SDG 15 (Life on Land)
   • Biodiversity loss rates and extinction events (percentage of species lost during warming spikes).

4. Table of SDGs, Targets, and Indicators

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