Climate Change and the Oceans
Lead Research Organisation:
University of Southampton
Department Name: Sch of Ocean and Earth Science
Abstract
The research I propose concerns two fundamental feedback processes within the Earth's climate system / the concentration of atmospheric CO2 and the circulation strength of the oceans. Feedback processes amplify any external forcing of the climate caused by, for example, variations in the Earth's orbit around the sun. Both processes play important roles in the modern climate system, yet their roles in the past, and in particular, their predicted roles in future climate change are uncertain. It is the principal aim of this proposal to reduce this uncertainty by reconstructing the behaviour of these two systems at key times in the past. The first part of the proposed research concerns the concentration of carbon dioxide in the atmosphere. CO2 is an important greenhouse gas such that variations in the amount of atmospheric CO2 are thought to have an important control on the Earth's climate. Indeed, over the last 2.5 million years the climate of the Earth has oscillated between periods of extreme cold (called glacial periods) and comparable warmth (interglacial periods like today). Importantly, these swings in climate have been accompanied by changes in the concentration of atmospheric CO2 (pCO2). The overall driving force for the waxing and waning of ice sheets are subtle variations in the orbit of the Earth around the sun, which influence the amount and seasonal distribution of solar radiation received at high latitudes. Variations in the concentrations of CO2 probably globalise and enhance this orbital forcing. The exact mechanisms responsible for altering pCO2 are not known but probably involve the oceans (the largest store of carbon on the planet that can respond with sufficient rapidity). In order to examine this role, I propose to generate a record of past ocean acidity (pH) in a variety of sensitive areas of the ocean using the boron isotopic composition of planktic and benthic foraminifera (calcareous single celled protists that are common throughout the ocean and are preserved in deep sea sediments). Since the acidity of the ocean largely determines pCO2, I will be able, from this record, to identify how CO2 is stored and released from the deep sea during the waxing and waning of the ice sheets and potentially isolate its role in causing the transitions from one climate state to another. The second part of this proposal concerns the circulation of the oceans. The Equator, which receives more heat from the sun, is hotter than the poles, and it is this temperature gradient that drives ocean (and atmospheric) circulation. The Atlantic portion of ocean circulation is a particularly important and sensitive part of the circulation system. Here, the Gulf Stream carries warm, salty water from the low latitudes to the North Atlantic. These waters then cool, lose heat to the atmosphere and become dense (salty cold water is denser than fresh warm water) and, as a result, sink. They then flow southward at depth, forming the return arm of the convection cell. The release of heat by this mode of circulation is not only important in ameliorating the climate of maritime Europe, but it can influence the overall climate of the planet by determining the water temperature in the Artic seas, where sea-ice forms. Sea-ice is highly reflective and more sea-ice results in more of the Sun's energy being reflected back into space, and hence can influence global temperature. The role of this circulation pattern in future climate scenarios is uncertain; one way to reduce this uncertainty is to examine ocean circulation in the geological past. I propose to use a new analytical technique, involving the laser microsampling of ferromanganese crusts (metallic encrustations that precipitate very slowly from seawater at depth) to reconstruct the strengths and patterns of circulation in the past when the climate was significantly colder (during glacial periods) and warmer than today (the Mid-Pliocene).
Organisations
People |
ORCID iD |
Gavin Foster (Principal Investigator) |
Publications
Ni Y
(2010)
The accuracy of d11B measurements of foraminifers
in Chemical Geology
Rae J
(2014)
Deep water formation in the North Pacific and deglacial CO 2 rise N Pacific deep water and deglacial CO2
in Paleoceanography
Rae J
(2011)
Boron isotopes and B/Ca in benthic foraminifera: Proxies for the deep ocean carbonate system
in Earth and Planetary Science Letters
Seki O
(2010)
Alkenone and boron-based Pliocene pCO2 records
in Earth and Planetary Science Letters
Von Der Heydt AS
(2016)
Lessons on Climate Sensitivity From Past Climate Changes.
in Current climate change reports
White L
(2016)
Tracking the provenance of Greenland-sourced, Holocene aged, individual sand-sized ice-rafted debris using the Pb-isotope compositions of feldspars and 40 Ar/ 39 Ar ages of hornblendes
in Earth and Planetary Science Letters
Yu J
(2010)
An evaluation of benthic foraminiferal B/Ca and d11B for deep ocean carbonate ion and pH reconstructions
in Earth and Planetary Science Letters
Yu J
(2019)
More efficient North Atlantic carbon pump during the Last Glacial Maximum.
in Nature communications
Description | A final report has already been submitted for this project Over geological time Earth's climate has oscillated between cold intervals called "icehouses" where ice sheets existed on polar continents to warm periods called "greenhouses" that were ice free. The causes of these grand climate cycles is uncertain. Here we present the first conclusive evidence that changes in the concentration of the greenhouse gas CO2 drove the most recent of these transitions. We were also able to calculate the sensitivity of the climate system to CO2 change which is crucial way to validate the state of the art climate models used to predict our warm future and have shown how cooling impacts oceanic geochemical cycles. |
Exploitation Route | These findings will be very useful for the next stages of the CMIP programme DeepMIP (The deep-time model intercomparison project) that will feed directly into the next IPCC, thereby ensure a wide impact for this research |
Sectors | Environment |
URL | http://www.descentintotheicehouse.com |
Description | This research has contributed to the knowledge base regarding the causes and consequences of climate change. It has also directly fed into the latest IPCC report (of which PI Foster was a contributing author) |
First Year Of Impact | 2011 |
Sector | Environment |
Impact Types | Policy & public services |