What were the effects of rapid ocean acidification events in
the Earth’s past?
Global warming is not the only consequence of rising levels of
carbon dioxide in the atmosphere. As CO2 is an
acidic gas, and a high proportion of the human emissions eventually
get mixed into the ocean, the oceans are becoming more acidic. As
humanity aims to limit emissions it is vital to predict what effect
such acidification will have on marine life and chemical processes
in the ocean. Experimental work suggests that plankton that
construct their shells out of calcium carbonate ('calcify') may be
particularly affected.
One way to predict the future is to study similar events in the
geological past. The geological record contains a number of abrupt
events where acidification increased rapidly in response to natural
emissions (the largest being the Paleocene / Eocene thermal maximum
event, 55 million years ago). So far the acidification during these
events has not been measured adequately and details of the way
marine life was affected have not been fully investigated.
The project will investigate a variety of geological records
from the deep sea and the margins of the oceans. Unique among these
is a newly recovered borehole through marine sediments in Tanzania.
Preliminary work revealed the presence of a highly expanded (thick)
record of the onset of the Paleocene / Eocene thermal maximum
(PETM) event with very well-preserved planktonic microfossils that
is suitable for new geochemical and biological studies.
Specific aims are:
- To produce new estimates of seawater
acidity and atmospheric carbon dioxide levels for the period 65-40
million years ago
- To study the response of the carbon cycle
during the rapid onset of the PETM using new data from Tanzania and
elsewhere and new computer models
- To compare the PETM with other known
smaller ocean acidification events in the Earth’s past
- To quantify the biotic response to ocean
acidification events both directly (speciation, extinction,
migration, malformation , etc.) and indirectly (ecosystem function,
biogeochemical cycles)
The outputs of this programme will:
- Feed into the cross-government Climate
Change Adaptation programme
- Make a significant contribution to the
Living With Environmental Change programme
- Provide evidence to the IPCC 5th
Assessment Report on Climate Change
- Provide information to marine bioresource
managers, policy makers negotiating CO2 emissions
reduction and other stakeholders
This project will produce new data in the form of:
- Geochemical records (boron isotopes,
oxygen isotopes, carbon isotopes, trace elements) through a variety
of drill cores constraining the rate and amount of ocean
acidification, temperature increase, and evolving atmospheric
CO2 levels
- High resolution quantitative biotic
records of calcifying plankton and benthos during abrupt ocean
acidification events (groups such as foraminifera,
coccolithophorids and echinoderms)
- Carbon cycle models focusing on the
functioning of the Earth System during past ocean acidification
events of various magnitudes, constrained by the new
data
- Identification of thresholds for observed
biological responses and, as part of the broader thematic
programme, comparison with experimental work on calcifying
organisms and observations from the modern ocean