Freshwater Export from the Weddell Gyre: Magnitude, Variability and Impacts

Lead Research Organisation: NERC British Antarctic Survey
Department Name: Science Programmes

Abstract

Freshwater is a key component of the climate system around Antarctica. In general, the fresher seawater is, the less dense it is, and so the injection of freshwater into the ocean controls a range of processes that include deep water formation and ocean circulation. This has implications for global and regional climate, and recent studies have shown that injecting freshwater into regions such as the Weddell Sea (adjacent to Antarctica) can influence climate as far north as the equator and beyond on timescales of just a few years. Climate models indicate that the freshwater budget at high latitudes will change as global warming progresses, but the consequences of these changes are largely unknown. Indeed, due to the difficulties of sampling the Southern Ocean, even detecting such a change here is challenging. We propose to take advantage of an already-scheduled research cruise to make comprehensive measurements of oxygen isotopes around the rim of the Weddell Gyre in the Southern Ocean. Under present climate conditions, the Weddell Gyre is a site of strong deep and bottom water formation, and also a region of strong freshwater export. The measurements of oxygen isotopes will enable us to determine the sources of the freshwater separately, with the contributions of glacial ice melt and precipitation (snow) being distinguished from the contribution of sea ice melt. By combining these measurements with ocean current speed calculations being derived separately, we will provide a benchmark quantification of the freshwater export in different layers of the Weddell Gyre. We will compare our measurements with historical measurements to determine change in any or all of the freshwater components, and interpret these changes in the context of known and expected large-scale climate change, including the changing hydrological cycle. This work is strongly collaborative, and includes workers from Florida State University, Texas A&M University and Woods Hole Oceanographic Institution in the United States. These scientists will provide access to research cruise logistics over and above those provided by UK ships alone, and will also make measurements of noble gases to complement our isotope measurements. This work thus has the potential to make very significant contributions to international science programmes, as well as being strongly relevant to UK science priorities.

Publications

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Brown PJ (2014) Freshwater fluxes in the Weddell Gyre: results from d18O. in Philosophical transactions. Series A, Mathematical, physical, and engineering sciences

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Jullion L (2014) The contribution of the Weddell Gyre to the lower limb of the Global Overturning Circulation in Journal of Geophysical Research: Oceans

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Meredith M (2013) Replenishing the abyss in Nature Geoscience

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Meredith MP (2014) Dense waters of the Weddell and Scotia Seas: recent changes in properties and circulation. in Philosophical transactions. Series A, Mathematical, physical, and engineering sciences

 
Description A freshwater budget of the Weddell Gyre (WG) in the Southern Ocean - a critically important region in the global climate system - has been calculated for the first time using measurements of oxygen isotopes in seawater. It shows that set against regional atmospheric warming and documented changes in the hydrological cycle, the region is currently in approximate balance, although sensitive to changing ocean circulation patterns. It also highlights its importance as a location of substantial net sea-ice production, recently observed to be increasing and a key process associated with the formation of dense, deep waters.
Exploitation Route The dataset and results obtained therefrom represent an unparalleled benchmark for the freshwater budget of this climatically-sensitive region of the Southern Ocean. Future work should address the ongoing changes in the components of this budget using directly comparable techniques, including an assessment of the impact of the reported increase in Antarctic sea ice, and ongoing changes in the mass balance of the Antarctic ice cap.
Sectors Education,Environment

 
Description This Weddell Sea freshwater budget assessment: - has generated a huge quantity of seawater oxygen data in a region noted for its limited spatial and temporal data coverage. This single project has increased such data for the Weddell Gyre in the public domain by ~40%. - has generated a point of reference assessment of the freshwater system in the Weddell Gyre, from which seasonal / inter-annual variability and long-term change can be compared and evaluated in the future. - has provided benchmark budget figures to which the global research community can compare model outputs and measurement-based freshwater assessments. - highlights sensitivity of freshwater system in the Weddell Gyre region to underlying deep water circulation.
First Year Of Impact 2012
Sector Environment
 
Description Prof Mike Meredith: leadership of Polar Regions chapter in IPCC Special Report on Oceans and Cryosphere
Geographic Reach Multiple continents/international 
Policy Influence Type Gave evidence to a government review
URL https://www.ipcc.ch/report/srocc/
 
Description NERC LTSM NC
Amount £8,400,000 (GBP)
Funding ID NE/N018095/1 
Organisation Natural Environment Research Council 
Sector Public
Country United Kingdom
Start 04/2016 
End 03/2021
 
Description Studentship with GW4+ DTP (Gen Hinde)
Amount £100,000 (GBP)
Organisation Natural Environment Research Council 
Sector Public
Country United Kingdom
Start 10/2017 
End 09/2020
 
Description Academic Consultancy to BBC for series "Frozen Planet 2", Mike Meredith 
Form Of Engagement Activity A broadcast e.g. TV/radio/film/podcast (other than news/press)
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Public/other audiences
Results and Impact This series is the successor to BBC's hugely successful Frozen Planet, which reached an audience of 500 million people globally. Prof Mike Meredith has been contracted by the BBC to serve as Academic Consultant for the production of its sequel. This work is underway; the series is due for broadcast in 2021, and will reach an audience similar to its predecessor.
Year(s) Of Engagement Activity 2019