What controls the influx and mixing of warm waters onto the polar ocean shelves?

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

Abstract

Two of the main environmental challenges of the coming century will be the response of global sea levels and marine ecosystems to rapid ocean warming, particularly in the polar regions. Recently, large increases in ice melt have been recorded at many locations around Antarctica and Greenland, raising fears that sudden catastrophic ice loss could occur in the coming decades, with significant impacts on global sea level. Despite this, there is still insufficient knowledge about the pathways and mechanisms by which warm offshore ocean waters are delivered to the ice shelves and calving glaciers. One particular region of concern is the West Antarctic Peninsula. Here, much of the increased ice loss appears to have been caused by an enhanced flow of warm offshore water (termed Circumpolar Deep Water or CDW) reaching cavities under the floating ice shelves. Furthermore, the increase in ocean temperature and reducing sea ice in this region are likely to have significant impacts on the operation of the Antarctic ecosystem, particularly for populations of both krill and penguins. Understanding the mechanisms that cause CDW to be mixed both laterally and vertically on the shelves and the role of shelf-edge processes in delivering this water mass is vital to interpreting the regional physical, chemical and biological changes that are occurring.

The key project objectives are thus:

1. To quantify, describe and understand the spatial and time-varying patterns of lateral and vertical mixing on the West Antarctic Peninsula shelf.

2. To resolve the dominant mechanisms driving lateral and vertical heat fluxes, with a specific focus on understanding how and where heat from the deep ocean waters is transferred to the upper ocean.

3. To understand the role of key shelf-edge processes in controlling these phenomena, in particular by understanding and quantifying the importance of these processes in causing intrusions of warm, saline deep-ocean waters onto polar shelves.

The project will use data from both traditional and novel oceanographic platforms, with the aim of describing how warm waters move from the edge of the shelf to the coast, where melting of land-based ice can occur. Ocean gliders, which have been developed extensively over the last 10 years, will provide measurements of temperature, salinity and small-scale velocity, from which the controlling mechanisms can be determined.

The fieldwork will focus on two regions. The first, at the shelf edge, will determine how CDW moves across the shelf break (e.g. through eddies, upwelling or steering by topography). The second region, close to the British Antarctic Survey base at Rothera, will examine the mechanisms by which heat in this layer is mixed both laterally and vertically. As one of the first projects to measure mixing on the West Antarctic Peninsula directly, we will determine whether these processes are driven by wind, tides or processes relating to changing ocean density. To help interpret the glider measurements, moored velocity observations will be made and existing meteorological and hydrographic data from the BAS Rothera Time Series will be incorporated into the analysis. In addition, a through-ice wintertime deployment of an instrument that directly measures turbulence will be carried out to test whether vertical mixing is weakened by the presence of sea ice. In synthesising the data, the project will use a new methodological framework to examine the relative importance of horizontal and lateral processes.

Ultimately, we will use our new mechanistic understanding from objectives 2 and 3 with the quantification of heat flows from objective 1 to devise a conceptual model of how heat moves onto the shelf and either gets into the near-surface layer (and lost to the atmosphere) or moves to the ice shelf edge. Understanding these processes will help to predict future ice sheet stability, regional climate and ecosystem changes in the rapidly warming polar regions.

Planned Impact

In addition to the academic impact outlined elsewhere, the research has a number of wider beneficiaries with which we will engage during the project.

1. NERC and commercial interests

Throughout the course of the project, the Fellow will be in regular contact with the NERC Marine Autonomous Robotic Systems (MARS) technology community to ensure a two-way transfer of knowledge between our group and the rest of the UK community. NERC has recently invested significantly in ocean glider technology, in part because they have the potential to provide routine ocean monitoring of a number of ocean variables at significantly reduced cost when compared with traditional ship-based measurements. The technical successes and challenges of this project (in a relatively remote location) will be shared with the MARS group, which will ultimately benefit both UK science (within 5 years) and, in the longer-term, commercial maritime surveying.

BAS are also involved in a development partnership with Teledyne Webb Research, the manufacturer of the Slocum glider. The expertise gained through the deployments will feed back into the UK science community through a greater availability of novel oceanographic equipment, miniaturization of parts and a reduction in cost of both instruments and spares (2-20 years).

2. Societal beneficiaries

Through an outreach programme planned as part of this fellowship (and outlined in Pathways to Impact), we will engage a number of young scientists at local schools in the glider project. Through the setting up of a website that allows pupils to track gliders, and a programme of school visits by the Fellow, who will explain both the purpose of the project and ocean science more generally, we will engage with pupils of various ages who are considering science as a career. This benefit can be realised within 2-5 years but will benefit UK competitiveness in coming decades, through motivating young people to pursue scientific and technical qualifications.

In addition, as a piece of novel technology, the glider project has the potential to raise the profile of BAS science with the wider public. As outlined in Pathways to Impact, the website will be developed and kept updated to realise this potential.

Publications

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Bown J (2018) Evidences of strong sources of DFe and DMn in Ryder Bay, Western Antarctic Peninsula. in Philosophical transactions. Series A, Mathematical, physical, and engineering sciences

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Brearley J (2017) Controls on turbulent mixing on the West Antarctic Peninsula shelf in Deep Sea Research Part II: Topical Studies in Oceanography

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Sévellec F (2015) Vertical Flow in the Southern Ocean Estimated from Individual Moorings in Journal of Physical Oceanography

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Venables H (2017) Modification of deep waters in Marguerite Bay, western Antarctic Peninsula, caused by topographic overflows in Deep Sea Research Part II: Topical Studies in Oceanography

 
Description We have made significant insights into understanding the mixing processes that control the upward movement of heat in the ocean in the West Antarctic. Through the analysis of two years of mooring data, we have identified that wind is the dominant control on the upward flux of heat between warm deep and cooler surface waters during periods when sea ice is absent. Conversely, during periods when fast ice is present, ocean turbulence and mixing is controlled dominantly by internal tidal processes that generate shear within the water column. Mixing processes associated with double diffusive activity appear, based on our limited data to date, to be relatively weak. Furthermore, it appears that the winter fluxes of heat are significantly smaller than those observed during the summer months, though work is currently underway to establish the statistical significance of this finding. In addition, we have now made further progress in quantifying upper ocean mixing and heat fluxes, in collaboration with Mark Inall at SAMS. Direct microstructure observations from 2016 suggest that wintertime dissipation values in the top 100 m of the water column are reduced by an order of magnitude compared to the ice-free months, with values roughly 2-3 times less between 100 and 300 m.

Analysis of the cross-shelf glider data suggests that small-scale (<5 km) eddies are strongly implicated in the flux of heat up deep glacially-carved troughs of the West Antarctic Peninsula. The relative importance of the instability processes that generate these eddies has yet to be fully assessed (e.g. compared to wind-driven upwelling), but it is clear that realistic model representations of cross-shelf fluxes of heat will require these eddies to be resolved properly. We have also made significant process in understanding the off-shelf fluxes of cold shelf waters. Meanders that form around a sediment drift at the mouth of Marguerite Trough periodically become unstable and flux cold and comparatively dense deep shelf water offshore into the Southern Ocean interior. Through our collaboration with Carlos Moffat (see collaborations), we have established the instability mechanisms that drive these fluxes.
Exploitation Route The findings could be taken forward to develop better parameterizations of ocean mixing within regional and global climate models, which will in turn strongly improve the estimates of heat flux within the polar oceans. This will significantly improve our representations of ocean-cryosphere and ocean-sea surface heat fluxes, with benefits for future climate predictability. As many ice shelves and glaciers of the West Antarctic are melting through warming ocean waters (rather than directly form the atmosphere), improving this term will significantly improve future estimates of ice sheet stability and sea level change.
Sectors Aerospace, Defence and Marine,Environment,Other

 
Description We have worked extensively with Teledyne Webb Research, the manufacturer of the Slocum glider, to develop the ice-coping capability of the glider. This has involved our glider deployments being testbeds for developing new ice coping routines to deal with sea ice and icebergs. A beta version of the Teledyne software is now available for use by Teledyne's glider user community.
First Year Of Impact 2014
Sector Aerospace, Defence and Marine,Environment
Impact Types Economic

 
Description NEXUSS Centre for Doctoral Training
Amount £78,200 (GBP)
Organisation Natural Environment Research Council 
Sector Public
Country United Kingdom
Start 10/2016 
End 06/2019
 
Description Natural Environment Research Council - NCSS
Amount £3,500,000 (GBP)
Organisation Natural Environment Research Council 
Sector Public
Country United Kingdom
Start 04/2018 
End 03/2023
 
Description Woods Hole Exchange Programme
Amount £2,000 (GBP)
Organisation Woods Hole Oceanographic Institution 
Sector Charity/Non Profit
Country United States
Start 06/2018 
End 09/2018
 
Title ADCP Mooring data from Ryder Bay 
Description A year-round time series of current data from the West Antarctic Peninsula 
Type Of Material Database/Collection of data 
Year Produced 2018 
Provided To Others? Yes  
Impact One of the first year-round current datasets from the West Antarctic, submitted to BODC. 
 
Description Moffat 
Organisation University of Delaware
Country United States 
Sector Academic/University 
PI Contribution A new recent collaboration with Carlos Moffat at the University of Delaware has strongly enhanced a paper in preparation concerning export of shelf waters from the West Antarctic. This is through the addition of modelling elements from the ROMS model to our glider-based observations.
Collaborator Contribution Carlos Moffat has analysed model simulations from the ROMS model, and provided information as to the frequency with which cold water eddies are shed from the West Antarctic shelf, and the generation mechanisms of these eddies.
Impact Model runs have been analysed to examine the formation of eddies of shelf water on the continental shelf of the West Antarctic Peninsula. This will form one section of an upcoming paper for submission to Journal of Geophysical Research.
Start Year 2017
 
Description NOCS 
Organisation National Oceanography Centre
Country United Kingdom 
Sector Academic/University 
PI Contribution We are currently in the process of developing a proposal through DSTL to evaulate the current capabilities of, and to propose future requirements for, piloting underwater robotic vehicles under ice. We will provide tehcnical expertise on our operations under ice to date and advise on future needs.
Collaborator Contribution They provide some of the technical expertise to advise what is realistic.
Impact None as yet (only started March 2019).
Start Year 2019
 
Description QUIDDITCH - JHU 
Organisation British Geological Survey
Country United Kingdom 
Sector Public 
PI Contribution We are joint collaborators in a grant proposal to understand the mixing and entrainment mechanisms within and close to Denmark Strait in the North Atlantic. BAS will be providing the observational hydrographic and microstructure data for this experiment.
Collaborator Contribution The University of Exeter will be undertaking a tracer release and subsequent sampling to identify the pathways and mixing of dense waters, whilst the University of Southampton will be contributing to the hydrographic analysis. Johns Hopkins and SAMS will be providing high-resolution modelling capability for the project, allowing us to test how extensive the processes identified in the observational study are likely to be on the East Greenland shelves. URI and the British Geological Survey will be undertaking isotope measurements to identify the dominant sources of freshwater in the East Greenland boundary current.
Impact We have written a NERC large grant, which passed the outline stage and has been called for interview in March 2017.
Start Year 2015
 
Description QUIDDITCH - JHU 
Organisation Johns Hopkins University
Department Infectious Disease Epidemiology
Country United States 
Sector Academic/University 
PI Contribution We are joint collaborators in a grant proposal to understand the mixing and entrainment mechanisms within and close to Denmark Strait in the North Atlantic. BAS will be providing the observational hydrographic and microstructure data for this experiment.
Collaborator Contribution The University of Exeter will be undertaking a tracer release and subsequent sampling to identify the pathways and mixing of dense waters, whilst the University of Southampton will be contributing to the hydrographic analysis. Johns Hopkins and SAMS will be providing high-resolution modelling capability for the project, allowing us to test how extensive the processes identified in the observational study are likely to be on the East Greenland shelves. URI and the British Geological Survey will be undertaking isotope measurements to identify the dominant sources of freshwater in the East Greenland boundary current.
Impact We have written a NERC large grant, which passed the outline stage and has been called for interview in March 2017.
Start Year 2015
 
Description QUIDDITCH - JHU 
Organisation Scottish Association For Marine Science
Country United Kingdom 
Sector Charity/Non Profit 
PI Contribution We are joint collaborators in a grant proposal to understand the mixing and entrainment mechanisms within and close to Denmark Strait in the North Atlantic. BAS will be providing the observational hydrographic and microstructure data for this experiment.
Collaborator Contribution The University of Exeter will be undertaking a tracer release and subsequent sampling to identify the pathways and mixing of dense waters, whilst the University of Southampton will be contributing to the hydrographic analysis. Johns Hopkins and SAMS will be providing high-resolution modelling capability for the project, allowing us to test how extensive the processes identified in the observational study are likely to be on the East Greenland shelves. URI and the British Geological Survey will be undertaking isotope measurements to identify the dominant sources of freshwater in the East Greenland boundary current.
Impact We have written a NERC large grant, which passed the outline stage and has been called for interview in March 2017.
Start Year 2015
 
Description QUIDDITCH - JHU 
Organisation University of Exeter
Department Department of Geography
Country United Kingdom 
Sector Academic/University 
PI Contribution We are joint collaborators in a grant proposal to understand the mixing and entrainment mechanisms within and close to Denmark Strait in the North Atlantic. BAS will be providing the observational hydrographic and microstructure data for this experiment.
Collaborator Contribution The University of Exeter will be undertaking a tracer release and subsequent sampling to identify the pathways and mixing of dense waters, whilst the University of Southampton will be contributing to the hydrographic analysis. Johns Hopkins and SAMS will be providing high-resolution modelling capability for the project, allowing us to test how extensive the processes identified in the observational study are likely to be on the East Greenland shelves. URI and the British Geological Survey will be undertaking isotope measurements to identify the dominant sources of freshwater in the East Greenland boundary current.
Impact We have written a NERC large grant, which passed the outline stage and has been called for interview in March 2017.
Start Year 2015
 
Description QUIDDITCH - JHU 
Organisation University of Rhode Island
Country United States 
Sector Academic/University 
PI Contribution We are joint collaborators in a grant proposal to understand the mixing and entrainment mechanisms within and close to Denmark Strait in the North Atlantic. BAS will be providing the observational hydrographic and microstructure data for this experiment.
Collaborator Contribution The University of Exeter will be undertaking a tracer release and subsequent sampling to identify the pathways and mixing of dense waters, whilst the University of Southampton will be contributing to the hydrographic analysis. Johns Hopkins and SAMS will be providing high-resolution modelling capability for the project, allowing us to test how extensive the processes identified in the observational study are likely to be on the East Greenland shelves. URI and the British Geological Survey will be undertaking isotope measurements to identify the dominant sources of freshwater in the East Greenland boundary current.
Impact We have written a NERC large grant, which passed the outline stage and has been called for interview in March 2017.
Start Year 2015
 
Description QUIDDITCH - JHU 
Organisation University of Southampton
Country United Kingdom 
Sector Academic/University 
PI Contribution We are joint collaborators in a grant proposal to understand the mixing and entrainment mechanisms within and close to Denmark Strait in the North Atlantic. BAS will be providing the observational hydrographic and microstructure data for this experiment.
Collaborator Contribution The University of Exeter will be undertaking a tracer release and subsequent sampling to identify the pathways and mixing of dense waters, whilst the University of Southampton will be contributing to the hydrographic analysis. Johns Hopkins and SAMS will be providing high-resolution modelling capability for the project, allowing us to test how extensive the processes identified in the observational study are likely to be on the East Greenland shelves. URI and the British Geological Survey will be undertaking isotope measurements to identify the dominant sources of freshwater in the East Greenland boundary current.
Impact We have written a NERC large grant, which passed the outline stage and has been called for interview in March 2017.
Start Year 2015
 
Title Ice coping software for Teledyne Webb gliders 
Description The software is a development on previous work done with Teledyne Webb Research to allow more sensible behaviour of underwater gliders in the presence of sea ice and icebergs. In collaboration with Lauren Cooney and Ben Allsup at TWR. 
Type Of Technology Software 
Year Produced 2016 
Impact Reduced vulnerability of the BAS glider fleet to ice-covered conditions. 
 
Description BBC TV Interviews 
Form Of Engagement Activity A press release, press conference or response to a media enquiry/interview
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Media (as a channel to the public)
Results and Impact I was heavily involved in the autonomous underwater vehicles coverage for the RRS Sir David Attenborough, including their use in the Antarctic context as part of this project. I participated in media interviews for BBC News at One, BBC Look East and BBC Radio Solent.
Year(s) Of Engagement Activity 2016
 
Description Distinguished visitor visit (Rothera) 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Policymakers/politicians
Results and Impact One-on-one talks with a range of NERC and government officials (including civil servants) whilst working in Rothera, explaining the importance of the glider work being done there to understanding changes in ocean circulation and climate around the West Antarctic. The visitors asked a number of important questions and were enlightened on their views of Antarctic marine science and the use of underwater robotics.
Year(s) Of Engagement Activity 2015,2016,2017
 
Description Friends of the Earth visit 
Form Of Engagement Activity Participation in an open day or visit at my research institution
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Supporters
Results and Impact 25 senior members of Friends of the Earth visited BAS for an institutional visit. I was involved in showing the visitors various exhibits including ice cores, aquarium and our marine autonomous vehicles. This prompted significant discussion.
Year(s) Of Engagement Activity 2018
 
Description Interview for Dutch TV 
Form Of Engagement Activity A broadcast e.g. TV/radio/film/podcast (other than news/press)
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Public/other audiences
Results and Impact Interviewed for a science programme to be shown in the Netherlands about the underwater glider work funded by this project, onboard RRS James Clark Ross.
Year(s) Of Engagement Activity 2015
 
Description Norwich Science Festival 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach Regional
Primary Audience Public/other audiences
Results and Impact Around 1000 people attended a stand that I was manning showcasing autonomous undrewtare instrumentation at the Norwich science festvial, which spawned fruitful discussion and raised the profile of Southern Ocean science.
Year(s) Of Engagement Activity 2018
URL https://norwichsciencefestival.co.uk