Plankton as a climate driver instead of the sun?

May 22, 2019

The climate history of the earth is marked by periodic changes that are usually ascribed to the solar radiation reaching the surface of the earth. This insolation is not constant over geological time but modulated by cyclic changes in the earth's orbital parameters. One of the key parameters affecting insolation is the tilt of the earth's rotation axis (obliquity) that changes periodically over time with a cycle length of about 40 000 years. Chemical and isotopic signatures of sediments that were deposited during the Cretaceous and other periods of earth's history document regular changes in temperature and carbon cycling on this time scale. The 40 kyr cycles observed in the geological climate archives are believed to be the result of obliquity-triggered insolation changes affecting the surface temperature, the circulation of ocean and atmosphere, the hydrological cycle, the biosphere, and ultimately the carbon cycle. One of the problems with this standard theory is that changes in global insolation are very small and have to be amplified by poorly understood positive feedback mechanisms to affect global climate.

A group of scientists from Kiel, Germany propose a very different perspective that emerges from a new numerical model of the marine biosphere. It simulates the turnover of plankton biomass in the ocean and resolves the associated microbial oxidation and reduction reactions controlling the standing stocks of dissolved oxygen, sulfide, nutrients and plankton in the ocean. In their model experiments the scientists found surprisingly a self-sustained 40 kyr climate cycle using the biogeochemical model integrated in a circulation model of the Cretaceous Ocean without applying obliquity forcing.

"In our model, the carbon cycle is largely controlled by plankton living in the surface ocean", explains Prof. Dr. Klaus Wallmann from GEOMAR, lead author of the study which was recently published in Nature Geoscience. Plankton consumes atmospheric CO2 via photosynthesis and by microorganisms that degraded plankton biomass and release CO2 back into the atmosphere. Since CO2 is a potent greenhouse gas, the biological CO2 turnover affects surface temperatures and global climate. The growth of plankton is controlled by nutrients that take part in a range of microbial oxidation and reduction reactions.

"We have integrated this new biogeochemical model in a circulation model of the Cretaceous Ocean, and it creates a self-sustained 40 kyr climate cycle without applying obliquity forcing", says Dr. Sascha Flögel, co-author from GEOMAR. "From our perspective, the cycle is induced by a web of positive and negative feedbacks that are rooted in the oxygen-dependent turnover of nitrogen, phosphorus, iron and sulfur in the ocean. Chemical and isotopic data recorded in sediments deposited in the Cretaceous Ocean show periodic changes that are consistent with the model results", Flögel continues

In this new view on climate change, the relationship between causes and effects is radically different from the standard orbital theory. The marine biosphere rather than insolation is setting the pace and amplitude by controlling the partial pressure of CO2 in the atmosphere. "Our new theory is supported by observations and consistent with our understanding of biogeochemical cycles in the ocean", according to Prof. Wallmann.

"However obliquity and other orbital parameters may also affect global climate change when their delicate effects on insolation are amplified by positive feedback mechanisms. Therefore, the periodic climate change documented in the geological record may reflect both the breath of the biosphere and the response of the earth system to external orbital and insolation forcing", summarizes Prof. Dr. Wolfgang Kuhnt from Kiel University who participated in this study.
-end-


Helmholtz Centre for Ocean Research Kiel (GEOMAR)

Related Climate Change Articles from Brightsurf:

Are climate scientists being too cautious when linking extreme weather to climate change?
Climate science has focused on avoiding false alarms when linking extreme events to climate change.

Mysterious climate change
New research findings underline the crucial role that sea ice throughout the Southern Ocean played for atmospheric CO2 in times of rapid climate change in the past.

Mapping the path of climate change
Predicting a major transition, such as climate change, is extremely difficult, but the probabilistic framework developed by the authors is the first step in identifying the path between a shift in two environmental states.

Small change for climate change: Time to increase research funding to save the world
A new study shows that there is a huge disproportion in the level of funding for social science research into the greatest challenge in combating global warming -- how to get individuals and societies to overcome ingrained human habits to make the changes necessary to mitigate climate change.

Sub-national 'climate clubs' could offer key to combating climate change
'Climate clubs' offering membership for sub-national states, in addition to just countries, could speed up progress towards a globally harmonized climate change policy, which in turn offers a way to achieve stronger climate policies in all countries.

Review of Chinese atmospheric science research over the past 70 years: Climate and climate change
Over the past 70 years since the foundation of the People's Republic of China, Chinese scientists have made great contributions to various fields in the research of atmospheric sciences, which attracted worldwide attention.

A CERN for climate change
In a Perspective article appearing in this week's Proceedings of the National Academy of Sciences, Tim Palmer (Oxford University), and Bjorn Stevens (Max Planck Society), critically reflect on the present state of Earth system modelling.

Fairy-wrens change breeding habits to cope with climate change
Warmer temperatures linked to climate change are having a big impact on the breeding habits of one of Australia's most recognisable bird species, according to researchers at The Australian National University (ANU).

Believing in climate change doesn't mean you are preparing for climate change, study finds
Notre Dame researchers found that although coastal homeowners may perceive a worsening of climate change-related hazards, these attitudes are largely unrelated to a homeowner's expectations of actual home damage.

Older forests resist change -- climate change, that is
Older forests in eastern North America are less vulnerable to climate change than younger forests, particularly for carbon storage, timber production, and biodiversity, new research finds.

Read More: Climate Change News and Climate Change Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.