̽��ֱ�� of Cambridge - temperature

Super-slow circulation allowed world’s oceans to store huge amounts of carbon during the last ice age

sc604 — Mon, 27 Jun 2016 09:00:00 +0000

Using the information contained within the shells of tiny animals known as foraminifera, the researchers, led by the ̽��ֱ�� of Cambridge, looked at the characteristics of the seawater in the Atlantic Ocean during the last ice age, including its ability to store carbon. Since atmospheric CO₂ levels during the period were about a third lower than those of the pre-industrial atmosphere, the researchers were attempting to find if the extra carbon not present in the atmosphere was stored in the deep ocean instead.

They found that the deep ocean circulated at a much slower rate at the peak of the last ice age than had previously been suggested, which is one of the reasons why it was able to store much more carbon for much longer periods. That carbon was accumulated as organisms from the surface ocean died and sank into the deep ocean where their bodies dissolved, releasing carbon that was in effect ‘trapped’ there for thousands of years. Their results are reported in two separate papers in Nature Communications.

̽��ֱ��ability to reconstruct past climate change is an important part of understanding why the climate of today behaves the way it does. It also helps to predict how the planet might respond to changes made by humans, such as the continuing emission of large quantities of CO₂ into the atmosphere.

̽��ֱ��world’s oceans work like a giant conveyer belt, transporting heat, nutrients and gases around the globe. In today’s oceans, warmer waters travel northwards along currents such as the Gulf Stream from the equatorial regions towards the pole, becoming saltier, colder and denser as they go, causing them to sink to the bottom. These deep waters flow into the ocean basins, eventually ending up in the Southern Ocean or the North Pacific Ocean. A complete loop can take as long as 1000 years.

“During the period we’re looking at, large amounts of carbon were likely transported from the surface ocean to the deep ocean by organisms as they died, sunk and dissolved,” said Emma Freeman, the lead author of one of the papers. “This process released the carbon the organisms contained into the deep ocean waters, where it was trapped for thousands of years, due to the very slow circulation.”

Freeman and her co-authors used radiocarbon dating, a technique that is more commonly used by archaeologists, in order to determine how old the water was in different parts of the ocean. Using the radiocarbon information from tiny shells of foraminifera, they found that carbon was stored in the slowly-circulating deep ocean.

In a separate study led by Jake Howe, also from Cambridge’s Department of Earth Sciences, researchers studied the neodymium isotopes contained in the foraminifera shells, a method which works like a dye tracer, and came to a similar conclusion about the amount of carbon the ocean was able to store.

“We found that during the peak of the last ice age, the deep Atlantic Ocean was filled not just with southern-sourced waters as previously thought, but with northern-sourced waters as well,” said Howe.

What was previously interpreted to be a layer of southern-sourced water in the deep Atlantic during the last ice age was in fact shown to be a mixture of slowly circulating northern- and southern-sourced waters with a large amount of carbon stored in it.

“Our research looks at a time when the world was much colder than it is now, but it’s still important for understanding the effects of changing ocean circulation,” said Freeman. “We need to understand the dynamics of the ocean in order to know how it can be affected by a changing climate.”

̽��ֱ��research was funded in part by the Natural Environment Research Council (NERC), the Royal Society and the Isaac Newton Trust.

Reference:
Jacob Howe et al. ‘North Atlantic Deep Water Production during the Last Glacial Maximum.’ Nature Communications (2016): DOI: 10.1038/ncomms11765

Emma Freeman et al. ‘Radiocarbon evidence for enhanced respired carbon storage in the Atlantic at the Last Glacial Maximum.’ Nature Communications (2016). DOI: 10.1038/ncomms11998

̽��ֱ��way the ocean transported heat, nutrients and carbon dioxide at the peak of the last ice age, about 20,000 years ago, is significantly different than what has previously been suggested, according to two new studies. ̽��ֱ��findings suggest that the colder ocean circulated at a very slow rate, which enabled it to store much more carbon for much longer than the modern ocean.

We need to understand the dynamics of the ocean in order to know how it can be affected by a changing climate.

Emma Freeman

Psammophile

Foraminifera "Star sand" Hatoma Island - Japan

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Study reveals economic impact of El Niño

fpjl2 — Fri, 11 Jul 2014 13:47:33 +0000

̽��ֱ��Paper, Fair weather or foul: the macroeconomic effects of El Niño, by Dr Kamiar Mohaddes of Cambridge's Faculty of Economics and Paul Cashin and Mehdi Raissi of the International Monetary Fund comes as the Australian Bureau of Meteorology says there is at least a 70% chance of an El Nino weather event developing in 2014.

El Niño is a band of above-average ocean surface temperatures that periodically develops off the Pacific coast of South America, and causes major climatological changes around the world. ̽��ֱ��last one was in 2009/2010.

El Niño can affect commodity prices and the macroeconomy of different countries. It can constrain the supply of rain-driven agricultural commodities; reduce agricultural output, construction, and services activities; create food-price and generalised inflation; and may trigger social unrest in commodity-dependent poor countries that primarily rely on imported food.

̽��ֱ��El Niño effect is found to be most severe in the Asia and Pacific region. For instance, it causes hot and dry summers in southeast Australia; increases the frequency and severity of bush fires; reduces wheat exports, and drives up global wheat prices. Moreover, El Niño conditions usually coincide with a period of weak monsoon and rising temperatures in India, which adversely affects India’s agricultural sector, increases domestic food prices, and adds to inflation and inflation expectations. Furthermore, mining equipment in Indonesia relies heavily on hydropower; with deficient rain and low river currents, less nickel (which is used to strengthen steel) can be produced by the world’s top exporter of nickel. For the United States, on the other hand, El Niño typically brings wet weather to California (benefiting crops such as limes, almonds and avocados), reducing fires in the west and bringing warmer winters in the Northeast, increased rainfall in the South, diminished tornadic activity in the Midwest, and a decrease in the number of hurricanes that hit the East coast.

̽��ֱ��Cambridge paper analyses the international macroeconomic transmission of El Niño weather shocks in a dynamic multi-country framework, taking into account the economic interlinkages and spillovers that exist between different regions.

Overall, the paper shows that while Australia, Chile, Indonesia, India, Japan, New Zealand and South Africa face a short-lived fall in economic activity in response to an El Niño shock, other countries may actually benefit from an El Niño weather shock (either directly or indirectly through positive spillovers from major trading partners), for instance, Argentina, Canada, Mexico and the United States. Furthermore, most countries in the sample experience short-run inflationary pressures following an El Niño shock, while global energy and non-fuel commodity prices increase.

̽��ֱ��researchers argue that, given these implications, macroeconomic policy formulation should take into consideration the likelihood and effects of El Niño episodes. Kamiar Mohaddes says: “Our research shows that the economic consequences of El Niño differs across countries – some lose and some benefit from such a weather shock. This is important for economic planning, particularly as such weather events are happening in cycles and their impact is sometimes very large. Countries with elevated inflation like India could be particularly susceptible to such episodes.”

El Niño has a significant impact on the world and local economies - and not always for the worst - and countries should plan ahead to mitigate its effects, according to a new Working Paper from the ̽��ֱ�� of Cambridge.

Weather effects are becoming more common and their impact is getting stronger and stronger

Kamiar Mohaddes

Jon Sullivan

El Niño waves crash into a pier

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1.5 million years of climate history revealed after scientists solve mystery of the deep

bjb42 — Fri, 10 Aug 2012 02:51:00 +0000

Scientists have announced a major breakthrough in understanding the Earth’s climate machine by reconstructing highly accurate records of changes in ice volume and deep-ocean temperatures over the last 1.5 million years.

̽��ֱ��study, which is reported in the journal Science, offers new insights into a decades-long debate about how the shifts in the Earth’s orbit relative to the sun have taken the Earth into and out of an ice-age climate.

Being able to reconstruct ancient climate change is a critical part of understanding why the climate behaves the way it does. It also helps us to predict how the planet might respond to man-made changes, such as the injection of large quantities of carbon dioxide into the atmosphere, in the future.

Unfortunately, scientists trying to construct an accurate picture of how such changes caused past climatic shifts have been thwarted by the fact that the most readily available marine geological record of ice-ages – changes in the ratio of oxygen isotopes (Oxygen 18 to Oxygen 16) preserved in tiny calcareous deep sea fossils called foraminifera – is compromised.

This is because the isotope record shows the combined effects of both deep sea temperature changes, and changes in the amount of ice volume. Separating these has in the past proven difficult or impossible, so researchers have been unable to tell whether changes in the Earth’s orbit were affecting the temperature of the ocean more than the amount of ice at the Poles, or vice-versa.

̽��ֱ��new study, which was carried out by researchers in the ̽��ֱ�� of Cambridge Department of Earth Sciences, appears to have resolved this problem by introducing a new set of temperature-sensitive data. This allowed them to identify changes in ocean temperatures alone, subtract that from the original isotopic data set, and then build what they describe as an unprecedented picture of climatic change over the last 1.5 million years – a record of changes in both oceanic temperature and global ice volume.

Included in this is a much fuller representation of what happened during the “Mid-Pleistocene Transition” (MPT) - a major change in the Earth’s climate system which took place sometime between 1.25 million and 600 thousand years ago. Before the MPT, the alternation between glacial periods of extreme cold, and warmer interglacials, happened at intervals of approximately 41,000 years. After the MPT, the major cycles became much longer, regularly taking 100,000 years. ̽��ֱ��second pattern of climate cycles is the one we are in now. Interestingly, this change occurred with little or no orbital forcing.

“Previously, we didn’t really know what happened during this transition, or on either side of it,” Professor Harry Elderfield, who led the research team, said. “Before you separate the ice volume and temperature signals, you don’t know whether you’re seeing a climate record in which ice volume changed dramatically, the oceans warmed or cooled substantially, or both.”

“Now, for the first time, we have been able to separate these two components, which means that we stand a much better chance of understanding the mechanisms involved. One of the reasons why that is important, is because we are making changes to the factors that influence the climate now. ̽��ֱ��only way we can work out what the likely effects of that will be in detail is by finding analogues in the geological past, but that depends on having an accurate picture of the past behaviour of the climate system.”

Researchers have developed more than 30 different models for how these features of the climate might have changed in the past, in the course of a debate which has endured for more than 60 years since pioneering work by Nobel Laureate Harold Urey in 1946. ̽��ֱ��new study helps resolve these problems by introducing a new dataset to the picture - the ratio of magnesium (Mg) to calcium (Ca) in foraminifera. Because it is easier for magnesium to be incorporated at higher temperatures, larger quantities of magnesium in the tiny marine fossils imply that the deep sea temperature was higher at that point in geological time.

̽��ֱ��Mg/Ca dataset was taken from the fossil record contained in cores drilled on the Chatham Rise, an area of ocean east of New Zealand. It allowed the Cambridge team to map ocean temperature change over time. Once this had been done, they were able to subtract that information from the oxygen isotopic record. “ ̽��ֱ��calculation tells us the difference between what water temperature was doing and what the ice sheets were doing across a 1.5 million year period,” Professor Elderfield explained.

̽��ֱ��resulting picture shows that ice volume has changed much more dramatically than ocean temperatures in response to changes in orbital geometry. Glacial periods during the 100,000-year cycles have been characterised by a very slow build-up of ice which took thousands of years, the result of ice volume responding to orbital change far more slowly than the ocean temperatures reacted. Ocean temperature change, however, reached a lower limit, probably because the freezing point of sea water put a restriction on how cold the deep ocean could get.

In addition, the record shows that the transition from 41,000-year cycles to 100,000-year cycles, the characteristic changeover of the MPT, was not as gradual as previously thought. In fact, the build-up of larger ice sheets, associated with longer glacials, appears to have begun quite suddenly, around 900,000 years ago. ̽��ֱ��pattern of the Earth’s response to orbital forcing changed dramatically during this “900,000 year event”, as the paper puts it.

̽��ֱ��research team now plan to apply their method to the study of deep-sea temperatures elsewhere to investigate how orbital changes affected the climate in different parts of the world.

“Any uncertainty about the Earth’s climate system fuels the sense that we don’t really know how the climate is behaving, either in response to natural effects or those which are man-made,” Professor Elderfield added. “If we can understand how earlier changes were initiated and what the impacts were, we stand a much better chance of being able to predict and prepare for changes in the future.”

Study successfully reconstructed temperature from the deep sea to reveal how global ice volume has varied over the glacial-interglacial cycles of the past 1.5 million years.

̽��ֱ��only way we can work out what the likely effects of the changes we are making to the climate will be is by finding analogues in the geological past. That depends on having an accurate picture of the past behaviour of the climate system.

Harry Elderfield

Julian Dowdeswell.

Tabular iceberg. ̽��ֱ��production of tabular icebergs is a major mechanism of mass loss from the Antarctic Ice Sheet.

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