Marine Life Survived 8X Current CO2 Levels
Throughout Earth’s history, there is evidence of large carbon dioxide releases, greenhouse conditions, ocean acidification, and major changes in marine life. About 120 million years ago (mya), during the early part of the Cretaceous period, a series of massive volcanic eruptions pumped huge amounts of carbon dioxide into Earth's atmosphere. During the Aptian Oceanic Anoxic Event, atmospheric CO2 content rose to about twice today's level. Eventually, the oceans absorbed much of that CO2, which significantly increased the water's acidity. The change reduced the amount of calcium carbonate (CaCO3) in the water, making it difficult for creatures such as some kinds of plankton to form shells. But the plankton did not die out. In fact, the geological record indicates that ocean biota can adapt to CO2 concentrations as high as 2000 to 3000 ppm—five to eight times current levels.
Proxy evidence indicates that atmospheric CO2 concentrations were higher during long warm intervals in the geologic past, and that these conditions did not prevent the precipitation and accumulation CaCO3 as limestone. The accumulation of alkalinity from rock weathering, brought to the ocean by rivers, kept surface waters supersaturated. But these were gradual changes that lasted for extended periods of time, not perturbations. More rapid additions of CO2 during extreme events in Earth history include the end-permian mass extinction (251 mya), the Aptian Oceanic Anoxic Event 1a (OAE1a, 120 mya), and the paleocene-Eocene Thermal Maximum (PETM, 56 mya).
A team of paleontologists and geochemists have investigated how the high acidity affected the ancient marine ecosystem. Elisabetta Erba, Cinzia Bottini, Helmut J. Weissert, and Christina E. Keller examined fossils from ancient ocean sediments at two drill sites. One site is a now-above-ground formation in northern Italy, while the other lies in deep water in the mid-Pacific Ocean. “The Pacific Ocean was the only big ocean at that time,” Erba says. What they found is contained in a new paper, “Calcareous Nannoplankton Response to Surface-Water Acidification Around Oceanic Anoxic Event 1a,” in the July 23, 2010, issue of Science.
Descendants of ancient calcareous nannoplankton.
In particular, Erba et al. studied the numbers and condition of fossilized specimens of calcareous nannoplankton, the microscopic ancestors of modern plankton. The creatures' shells consist mostly of CaCO3 and therefore could reveal their overall health and the state of the ocean's chemistry. What they found was a bit of a surprise, to say the least:
Reconstructed rates of originations and extinctions at the onset of PETM indicate modest effects of ocean acidification on evolutionary trends. It has also been suggested that a major nannoplankton turnover occurred during OAE1a. However, our data demonstrate that rising pCO2 and surface-ocean acidification during OAE1a triggered false extinctions (a so-called Lazarus effect) among calcareous nannoplankton. Conversely, a major origination episode starts approximately 1 My before global anoxia and persists through OAE1a and associated acidification. Increasing pCO2 triggered coccolith malformation and solicited production of r-strategist taxa, which secreted dwarf coccoliths as a strategy to overcome acidification.
In plainer terms, as ocean acidity increased the skeletons of some species became malformed, other species shrank in size, and others died out altogether. More importantly, most nannoplankton seemed to adapt to acidification. The finding of dwarfism among marine species is also an interesting discovery.
It has long been known from the fossil record that various species of land animals shrank in size during the PETM. For animals this makes thermodynamic sense—the ratio of surface area to volume is higher for small animals than for large ones. This means a small animal can shed excess heat more readily than a large animal. For the marine creatures, the size change is seen as a response to dropping oxygen and carbonate levels.
“Although the negative carbon isotopic event (CIE) at the beginning of global anoxia (~120 Ma) coincides with the drop in carbonate content, there was an increase in relative abundance of Biscutum constans, Zeugrhabdotus erectus, and Discorhabdus rotatorius, represented by dwarfed specimens,” reports the study. Species-specific size variation was observed at both sites, with the most dramtic reduction registered by B. constans, a volume/mass reduction of 50 to 60% for individual coccoliths. Specimins of Z. erectus diminished to a lesser extent, between 30 to 40%, while D. rotatorius displayed the least reduction, only between 5 to 10%. The details are shown in the figure below.
Comparitive average coccolith size.
The authors, at the end of their paper, noted some of the differences between the OAE1a and the PETM. In particular, they comment on the more rapid onset for the PETM. In their words:
A similar, albeit more pronounced, δ13C anomaly occurs ~55.8 Ma at the Paleocene Eocene Thermal Maximum (PETM) and also suggests ocean acidification. However, the initial decrease in δ13C occurred over a few thousand years for the PETM and over ~30 ky for OAE1a. This discrepancy could reflect different causal mechanisms, namely methane hydrate dissociation for PETM and major volcanogenic CO2 injections for OAE1a, or condensation and hiatuses for most PETM sections.
They also note that the recovery phase is also longer for OAE1a, ~160,000 years versus ~30,000 to 80,000 years for the PETM. Consequently, the response of marine life to the PETM is harder to discern.
Of course, in these days of climate change political correctness it is de rigueur to add a disclaimer to any scientific work which might hint that the global warming crisis is not really a crisis at all. So it is with this paper. “The effect of modern surface-water acidification on organisms with CaCO3-based skeletons or tests, such as calcareous nannoplankton, remains elusive,” state the authors, a fairly mild disclaimer. Others, commenting on the paper are not so reserved.
It is a “very important paper [that] provides state-of-the-art understanding of the effects of massive amounts of CO2 in the oceans,” said marine geologist Timothy Bralower of Pennsylvania State University. The difference today is that the rate of CO2 increase “is far faster than anything we see in the ancient geologic record,” he said, in a ScienceNow article online. “The big question is whether modern species will be able to adapt to what I expect will be much more rapid pH reduction in coming centuries.”
Even most land animals got smaller during the PETM.
The charge that the current increase in CO2 is more rapid than historical events is pure conjecture. Trying to nail down precise timing of events 56, 120 or 250 million years in the past is an inexact pursuit at best. Discerning the difference between a few hundred or several thousand years at such a temporal remove is effectively impossible. The passing of time makes the modern-is-faster statement fatuous at best. We do know that these ancient events dwarf humanity's greenhouse gas emissions. Whether human activity can create an event as dramatic as the PETM has been discussed before on this blog (see “Could Human CO2 Emissions Cause Another PETM?”). Such knee-jerk climate alarmist responses can be safely dismissed.
Scientists who study nature, particularly biological organisms, have come to believe that species change. Driven by changing environmental condition, they adapt and they evolve. It should not be surprising that in the past, nature has successfully responded to larger changes in CO2 levels than those created by humans today. Overly sensitive species died out, others had a rough time but most did what successful species always do—they adapted to the new conditions. The lesson here for humans is that continued survival means we must be willing to adapt, because nature is always changing. As the adaptation of simple marine plankton shows, nature has proven predictions of an oceanic apocalypse to be as false as the other climate catastrophes predicted by climate change alarmists.
Be safe, enjoy the interglacial and stay skeptical.