What Formed the Ice Ages? Key Evidence With Tiny Ocean Fossils Was Found.
Past atmospheric carbon dioxide changes by the ocean come into view.
The last years of Earth’s set of histories have been described by frequent “glacial-interglacial cycles,” enormous swings in a climate that are connected to the developing and contracting of shrinking, continent-spanning ice sheets. These cycles are set off by subtle oscillations in Earth’s rotation and orbit, yet the orbital oscillations are too subtle to even think about explaining the enormous changes in the climate.
“The cause of the ice ages is one of the great unsolved problems in the geosciences,” said Daniel Sigman, the Dusenbury Professor of Geological and Geophysical Sciences. “Explaining this dominant climate phenomenon will improve our ability to predict future climate change.”
During the 1970s, researchers found that the concentration of the atmosphere’s greenhouse gas carbon dioxide (CO2) was about 30% lower during the ice ages. That provoked speculations that the diminishing in atmospheric CO2 levels is a critical ingredient in the cycle of glacial formation; however, the reasons for the CO2 change stayed unknown. Some information proposed that, during the ice ages, CO2 was caught in the deep ocean, but the reason for this was debated.
Presently, an international collaboration effort drove by researchers and scientists from Princeton University and the Max Planck Institute for Chemistry (MPIC) has discovered proof showing that during ice ages, changes in the surface waters of the Antarctic Ocean attempted to store more CO2 in the deep ocean. Using sediment cores from the Antarctic Ocean, the scientists produced detailed records of the chemical composition of organic matter caught in the fossils of diatoms — floating algae growth that filled in the surface waters then died and sank to the ocean floor. Their estimated measurements gave proof to methodical reductions in wind-driven upwelling in the Antarctic Ocean during the ice ages. The current research shows up in the current issue of the journal Science.
For quite a long time, scientists realized that the development and sinking of marine algae pump CO2 deep into the sea, a cycle frequently referred to as the “biological pump.” The biological pump is driven generally by the tropical, subtropical, and temperate oceans and is negatively closer to the poles, where CO2 is vented back to the environment by the rapid exposure of profound waters to the surface. The worst culprit is the Antarctic Ocean: the strong eastward winds surrounding the Antarctic continent pull CO2-rich deep water up to the surface, “leaking” CO2 to the atmosphere.
The potential for a decrease in wind-driven upwelling to keep more CO2 in the ocean waters, and to explain and clarify the ice age atmospheric CO2 drawdown, has additionally been perceived for quite a long time. Until now, in any case, researchers have come up short on an approach to unambiguously test for such a change.
The Princeton-MPIC collaboration has grown such an approach, with the use of little diatoms. Diatoms are floating algae that abundantly grow in Antarctic surface waters, and their silica shells amass deep-sea sediments. The nitrogen isotopes in diatoms’ shells vary with the measure of unused nitrogen in the surface water. The Princeton-MPIC group estimated the nitrogen isotope proportions of the trace organic matter caught in the mineral walls of these fossils, which uncovered the advancement of nitrogen concentrations in Antarctic surface waters in the course of 150,00 years, covering two ice ages and two warm interglacial periods.
“Analysis of the nitrogen isotopes trapped in fossils like diatoms reveals the surface nitrogen concentration in the past,” said Ellen Ai, first author of the study and a Princeton graduate student working with Sigman, along with Alfredo Martínez-García and Gerald Haug at MPIC. “Deepwater has high concentrations of the nitrogen that algae rely on. The more upwelling that occurs in the Antarctic, the higher the nitrogen concentration in the surface water. So our results also allowed us to reconstruct Antarctic upwelling changes.”
The information was made all the more powerful by another approach for dating the Antarctic sediments. The surface water temperature change was reconstructed in the sediment cores and is contrasted to the Antarctic ice core records of air temperature.
“This allowed us to connect many features in the diatom nitrogen record to coincident climate and ocean changes from across the globe,” said Martínez-García. “In particular, we are now able to pin down the timing of upwelling decline, when the climate starts to cool, as well as to connect upwelling changes in the Antarctic with the fast climate oscillations during ice ages.”
This more exact timing allowed these scientists to home in on the winds as the vital driver of the upwelling changes.
The new findings additionally permitted and gave way for the researchers to unravel how the adjustments in Antarctic upwelling and atmospheric CO2 are connected to the glacial cycles, bringing researchers a bit closer to a complete theory for the true origin of the ice ages.
“Our findings show that upwelling-driven atmospheric CO2 change was central to the cycles, but not always in the way that many of us had assumed,” said Sigman. “For example, rather than accelerating the descent into the ice ages, Antarctic upwelling caused CO2 changes that prolonged the warmest climates.”
Their discoveries additionally have implications for anticipating how the sea will react to global warming. Computer models have yielded ambiguous outcomes on the sensitivity of polar winds to climate change. The scientists’ perception of significant intensification in wind-driven upwelling in the Antarctic Ocean during warm periods of the past proposes that upwelling will also be fortified under global warming. Stronger Antarctic upwelling is probably going to accelerate the ocean’s heat absorption from progressing global warming while also affecting the biological states of the Antarctic Ocean and the ice on Antarctica.
“The new findings suggest that the atmosphere and ocean around Antarctica will change greatly in the coming century,” said Ai. “However, because the CO2 from fossil fuel burning is unique to the current times, more work is needed to understand how Antarctic Ocean changes will affect the rate at which the ocean absorbs this CO2.”
