Wish me Fair Winds and Following Seas: investigating the Southern Ocean Part 1…by Melanie Leng

 

 

In less than a week I will be heading off to the Southern Ocean to help with “fieldwork” (seawork is more appropriate!) collecting seawater samples for ORCHESTRA. ORCHESTRA (Ocean Regulation of Climate by Heat and Carbon Sequestration and Transports) is a programme funded by NERC and includes partners at the British Antarctic Survey (lead), the National Oceanography Centre, Plymouth Marine Laboratory, and many more including BGS.

Why are we collecting seawater samples from the World’s oceans?

Since the industrial revolution, the global ocean has absorbed around 30% of anthropogenic (human-produced) CO₂ emissions. In addition, 93% of the total extra heat in the Earth system since the onset of global warming has been absorbed by the global ocean. This is equivalent to around 170 terawatts — the power that would be required for each of the seven billion people on Earth to continuously operate sixteen 1500 watt hairdryers! Improving climate prediction requires us to learn more about how the global ocean works, and how it interacts with the atmosphere to control the split of heat and carbon between them, especially given the extra heat and carbon we are currently producing.

The Southern Ocean is key

The overturning circulation in the Southern Ocean.
The circulation around the Antarctic enables deep waters rise
to the surface, allowing new water masses to form and sink
back into the ocean interior taking heat and carbon with it.

A key region in this context is the Southern Ocean, the vast sea that encircles Antarctica. The Southern Ocean occupies around 20% of the total ocean area, but absorbs about three-quarters of the heat that is taken into the ocean, and approximately half of the CO₂. This is because of its unique pattern of ocean circulation: it is the main region where deep waters rise to the surface, allowing new water masses to form and sink back into the ocean interior. This exposure of “old” waters to the atmosphere, and the production of new waters at the surface, is fundamental to the exchanges of heat and carbon with the atmosphere.

Despite knowing the key role that the Southern Ocean plays in global climate, there are many important unknowns. These include how exactly heat and carbon are taken up by the oceans and how fast this occurs (especially important because of the Anthropocene period we are living in), and how much heat and carbon is currently stored in the oceans. These questions are being addressed using various chemical and physical measurements of the ocean, including the stable isotope composition of the seawater (which we are responsible for at the BGS). Oxygen isotopes will tell us about how much freshwater to seawater there is at particular locations (which will help us understand melting of the Antarctic ice mass and therefore heat) and carbon isotopes will tell us where the carbon is formed and how the ocean uses the carbon.   

Progress

The James Clarke Ross.

ORCHESTRA is in the second year of a five year collection programme around the World’s oceans. I will be collecting samples from the RRS James Clark Ross. Next week I will fly to the Falklands Islands and then cruise south across the Drake Passage to Antarctica, collecting samples and making measurements along the way. Finally we will return to Port Stanley before flying home. I hope for Fair Winds and Following Seas!  

I will be tweeting @MelJLeng and @ORCHESTRAPROJ and Facebooking (Orchestra project) along the way, as well as updating the BGS Geoblogy and drakepassageblog.wordpress.com when I have time.

Melanie Leng is the Science Director for Geochemistry at the BGS and the BGS lead scientist for ORCHESTRA.