Browsing articles from "May, 2013"

Coccoliths thrive despite ocean acidification

May 21, 2013   //   by Athena   //   Blog  //  Comments Off on Coccoliths thrive despite ocean acidification

21 May 2013, by Harriet Jarlett – Planet Earth Online

Ocean acidification is damaging some marine species while others thrive, say scientists.

An international team studied the effect of ocean acidification on plankton in the North Sea over the past forty years, to see what impact future changes may have.

The study, published in PLoS One found that different species react in different ways to changes in their environment. As carbon dioxide emissions dissolve in seawater they lower the pH of the oceans making them more acidic and more corrosive to shells.

Limacina helicina. Credit: Planet Earth

Foraminifera and coccoliths, which are small shelled plankton and algae, appear to be surviving remarkably well in the more acidic conditions. But numbers of pteropods and bivalves – such as mussels, clams and oysters – are falling.

‘Ecologically, some species are soaring, whilst others are crashing out of the system,’ says Professor Jason Hall-Spencer, of Plymouth University, who co-authored the paper.

The scientists are unsure whether this drop in certain species is because of changing pH levels, or whether it is due to a combination of stress factors like warming, overfishing and eutrophication -which results from a build up of excess nutrients in water.

‘We found no statistical connection between the abundance of calcifying plankton and the changes in pH. If pH is affecting calcifying plankton in the area then its effect is being masked by other climatic effects. What we do know is that laboratory experiments have shown pH changes affect pteropods adversely,’ he says.

Scientists had previously thought the reason species react so differently to ocean acidification was due to variations in the mineral composition of the shells.

‘The aragonite skeleton of pteropods dissolves more easily in corrosive waters than the low-magnesium calcite that typifies many clams and other molluscs,’ explains Hall-Spencer. ‘But now we think that it’s not as simple as that. It depends partly on how stressed organisms are by other factors, such as lack of food. It also depends on their shape and their ability to protect their skeletons.’

It is possible that the rising levels of CO2 are boosting coccolith numbers by causing them to photosynthesise more and produce more energy.

The scientists used a database collected by the Sir Alaistair Hardy Foundation for Ocean Science, which has been continuously recording levels of plankton in the North Sea since 1931. But, despite being the best database available, it fails to monitor chemical changes, like acid levels, alongside ecological ones, like shifts in pteropod numbers.

Plankton sits at the bottom of the food chains, where it underpins all of our marine food sources. So if numbers drop significantly it could lead to food shortages, particularly in countries where people eat lots of seafood and fish.

Read more >>

When was CO2 last at 400 ppm? And what was the climate like?

May 13, 2013   //   by Athena   //   Blog, Earth System  //  Comments Off on When was CO2 last at 400 ppm? And what was the climate like?
Paul N. Pearson, School of Earth and Ocean Sciences, Cardiff University CF10 3AT, UK.
Email: [email protected]
 
Summary Atmospheric CO2 is approaching the 400 ppm mark for the first time in human history which begs the question: when was it last that high? A recent high profile suggestion is that CO2 was that high in the Pliocene epoch (approximately 2.6-5.3 million years ago) and this is now being repeated in the press and around the internet. Here I point out that this claim is based on a few extreme estimates, mostly from sites that systematically overestimate more recent CO2 levels, while the majority of published Pliocene CO2 values are in the 250-400 ppm range. The last time we have consistent evidence for pCO2 over 400 ppm is in the Early Oligocene epoch more than 26 million years ago. This post presents the key graphs and comments on some of the methods used to calculate past pCO2.
 
Read the article
Download the article (pdf)

 
Images and graphs are subject to copyright.

Bristol University: Oligocene discussion day

May 7, 2013   //   by Athena   //   Blog, Earth System  //  Comments Off on Bristol University: Oligocene discussion day
 For many years the Oligocene has received little attention from the Cenozoic palaeoclimate community. This event hopes to promote awareness of the Oligocene (34-23 million years ago)and encourage future research within this field.
On the 16th of May, Bristol University will be hosting a full day event dedicated to the discussion of the Oligocene

Programme

10.30 -10.45: Welcome

10.45 -11.15: Ellen Thomas (Yale/Bristol)

11.15 -11.45: Diederik Liebrand (NOC)

11.45 -12.00: Gordon Inglis (Bristol)

12.00-13.00: Lunch

13.00-14.00: Bridget Wade (Leeds) Oligocene

14.00-15.00: Discussion for Phds and PDRAs

15.00-16.00: Optional seminar in Earth Science by Kirsty Edgar concerning the middle Eocene (G25)

16.00 – onwards: Drinks/dinner

All events, except for Bridget’s departmental seminar, will be held in Seminar Room 2, Geographical Sciences.

Bridget’s talk will be held in the Peel lecture theatre in Geographical Sciences.

For more information, contact Gordon Inglis ([email protected]) or check the event page
 This event is only open to University of Bristol staff and students.