Understanding the Arctic continental shelf mixing regimes and their impact on shelf sea-circulation and upper ocean stratification

Lead Research Organisation: Bangor University
Department Name: Sch of Ocean Sciences

Abstract

Rapid climate change is indisputable in the Arctic, where the record minimum sea-ice extent of September 2007 has been followed by the fastest recorded rate of sea-ice loss in August 2008 leading to near-minimum record levels again this year. A serious concern is that global climate models consistently underpredict the observed rate of Arctic climate change. A key environment in the Arctic are the continental shelf seas that account for 53% of the area covered by the Arctic Ocean and are the critical link between terrestrial and oceanic components of the earth system. There is much we still do not understand about how the energy from tides, wind, winter cooling and summertime heating can interact to mix fresh light river water with saltier sea water on the Arctic continental shelves. This gap in understanding has led to poorly parameterised shelf-sea physics in the global numerical computer models used to predict future climate. What happens in the Arctic shelf seas is tremendously important to the Arctic Ocean environment as lighter fresher shelf waters spread out into the layers of the interior basins, while denser shelf waters cascade down the continental slopes, penetrating to deeper levels where they encounter dense, warm, salty water from the Atlantic that has come from Fram Strait. The lighter cold, fresh shelf waters are thought to replenish the Arctic halocline layer that acts as critical barrier to heat fluxes from the deep warm Atlantic waters that may undermine Arctic sea-ice cover. The denser shelf waters mix with the Atlantic water at depth as it circumnavigates the Arctic Ocean, before exiting as a denser cooler fresher overflow current through the Nordic Seas. This dense Nordic Sea overflow is critical component of the global oceanic 'conveyor belt' of heat and freshwater know as the global overturning circulation that helps regulate global climate. Therefore, the Arctic shelf water production mechanisms are not just important for regional climate but also global climate. In the research proposed here, I aim to characterize mixing processes on Arctic continental shelfs, taking the important first step towards a comprehensive understanding of the Arctic earth-ocean system and improving predictions of future change and the consequences for global climate. I am interested in specific questions about how tidal energy can be used to mix water masses either by generating turbulence or by straining a vertically well-mixed but laterally differentiated water column and causing convection. Another key question I will address is how energy from the wind can be used to generate inertial oscillations that may also interact with the tide and cause mixing. These processes have been shown to be important in temperate shelf seas, but have yet to be investigated in an environment subjected to the extreme seasonal fluctuations, large riverine freshwater discharges and ice-formation-melt-cycle experienced on the Arctic continental shelves. My strategy is to use all the available data to gain an understanding of the shelf sea state and its seasonal heating and cooling cycles and then map out the different mixing regimes on the shelves, so that we can determine how, where and what kind of shelf water is being produced. These ideas will then be incorporated into a shelf-sea numerical computer model to test the sensitivity of the shelf seas system to scenarios of increasing river discharge and sea-ice loss which are resulting from climate change. This will enable us to diagnose feedbacks in the continental shelf -ocean circulation and climate system and help us improve the representation of the important shelf processes in global climate models, and ultimately, the predictions of our future climate.

Publications

10 25 50

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Brannigan L (2013) Shear at the Base of the Oceanic Mixed Layer Generated by Wind Shear Alignment in Journal of Physical Oceanography

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Dmitrenko I (2012) Tide-induced vertical mixing in the Laptev Sea coastal polynya TIDE-INDUCED VERTICAL MIXING in Journal of Geophysical Research: Oceans

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Polton J (2013) Can Drake Passage Observations Match Ekman's Classic Theory? in Journal of Physical Oceanography

 
Description This grant was focused on understudying the various mixing regimes on the Arctic continental shelf seas that helps to disperse the fresh river outputs over the tidally-driven shelves and into the central Arctic Basins. I have identified new mechanisms that act to mix the shelf waters even under 100% ice cover and am in the process of shelf-wide analyses of how different mechanism act in different areas on the Eurasian Arctic shelf. But my research has also expanded to encompass the surface mixed layer processes and the Antarctic continental slope region through the supervision of student projects.
Exploitation Route My work has so far focussed on identifying and understanding the mixing mechanisms that are responsible for polar water mass transformations that drive overturning. Knowledge in this area is still a critical deficiency in our ability to predict ocean circulation and climate. My work is many steps away from being able to represent these processes in the climate models we reply on in determining environmental policy. I and others will be working to take present and future results further toward adequate parameterisations that can be utilised by the climate modellers and be of use to policy makers and the public.
Sectors Environment

URL http://www.bangor.ac.uk/oceansciences/research/php/publications.php?person=0143
 
Description Scientific research has been presented in international conferences and has contributed to the motivation for current successfully funded projects (NERC OSMOSIS consortium, NERC TEA-COSI consortium) as well as upcoming proposals (MAMMOth, NERC January 2015 round).
First Year Of Impact 2010
Sector Environment
 
Description NRN-LCEE Research Development Fund
Amount £5,000 (GBP)
Organisation National Research Network for Low Carbon Energy and Environment 
Start 09/2016 
End 12/2018
 
Description AWI 
Organisation Alfred-Wegener Institute for Polar and Marine Research
Country Germany 
Sector Public 
PI Contribution We have shared data that we collected and analysed and collaborated on published scientific articles.
Collaborator Contribution They have shared data that they collected, and collaborated on published scientific articles.
Impact At present there are two scientific publications in the Journal of Physical Oceanography (Lenn et al, 2011 and Janout & Lenn, 2014), with two more manuscripts in preparation. We have also collaborated on ongoing observations and expect these to also culminate in more research that will be published in the future on topics that pertain to freshwater dispersion within the Arctic and its impact on climate.
Start Year 2009
 
Description NOC-students 
Organisation National Oceanography Centre
Country United Kingdom 
Sector Academic/University 
PI Contribution I participated on two separate NOC-led cruises to Drake Passage and the Antarctic Peninsula, in order to assist with the collection of hydrographic data and lead turbulence data collection. Data from these two cruises has since become the focus of an MSc project I supervised and a current PhD project that I co-supervise with NOC colleagues. I mentored both these students through to the publication of of their results in the peer-reviewed Journal of Physical Oceanography and Geophysical Research Letters.
Collaborator Contribution My NOC partners were the grant holders and/or responsible for the national capability projects that funded my participation in those cruises. Additionally NOC provided the Phd studentship currently held by three-year Phd student Jess Mead Silvester who is registered at Bangor University. Jess is co-supervised by Miguel Angel Morales Maqueda and Jeff Polton at NOC, and together we have mentored her through to her first publication that is in press at GRL.
Impact Three peer-reviewed articles have so far been published: Mead Silvester, Jess; Lenn, Yueng-Djern; Polton, Jeff A; Rippeth, Tom. P; Morales Maqueda, Miguel Observations of a diapycnal shortcut to adiabatic upwelling of Antarctic Circumpolar Deep Water, Geophys. Res. Lett. in press Brannigan, Liam; Lenn, Yueng-Djern; Rippeth, Tom P.; Elaine McDonagh, TK Chereskin and Janet Spintall (2013) Shear at the Base of the Oceanic Mixed Layer Generated by Wind Shear Alignment Journal of Physical Oceanography Volume: 43 Issue: 8 Pages: 1798-1810 DOI: 10.1175/JPO-D-12-0104.1 (id:2299) Polton, Jeff A., Lenn, Yueng-Djern, Elipot, Shane, et al (2013) Can Drake Passage Observations Match Ekman's Classic Theory? Journal of Physical Oceanography, 43(8), 1733-1740. (id:2420)
Start Year 2009
 
Description TEA-COSI 
Organisation National Oceanography Centre
Country United Kingdom 
Sector Academic/University 
PI Contribution I have been collaborating with Bangor colleagues and NOC colleagues on collecting and analysing data from the Arctic. Together we have worked to produce several publications led by me and others on mixing with the Arctic Ocean.
Collaborator Contribution Some of the data was collected under the previous NERC UK International Polar Year Consortium : Arctic Synoptic Basin-wide Observations (ASBO), and the remainder was collected with funding from the current NERC consortia : The Environment of the Arctic: Climate, Ocean and Sea Ice (TEA-COSI). The analysis was funded through both the ASBO and TEA-COSI consortia, as well as through my NERC Fellowship
Impact The ASBO and TEA-COSI projects were and are multi-disciplinary and multi-institutional in that it encompasses both oceanography and all manner of sea-ice research, from observations all the way to climate modelling. As far publications so, ASBO produced at least 17 peer-revied articles of which I authored two and contributed to several more. TEA-COSI analyses that I have been involved in has been prepared for Nature Geosciences and a revised manuscript is currently under review at that journal. In addition, the TEA-COSI Princicple Investigator (Sheldon Bacon) is a member of the International Arctic Science Committee that defines research objectives for the whole community. Other investigators (Including me) have been invited to present research at IASC workshops and meetings.
Start Year 2012
 
Description US-Arctic 
Organisation Earth and Space Research (ESR)
Country United States 
Sector Charity/Non Profit 
PI Contribution Collaborators at the University of Alaska, Fairbanks have and continue to lead long-term monitoring observations along the margins of the Eurasian Arctic. On two separate occasions, Bangor colleagues and I have participated in these cruises to make turbulence measurements to complement the repeat hydrography. Together the data have been used in several joint publications in respected peer-reviewed journals and the collaboration continues through the sharing of data between partners in ongoing efforts to study the effects of shear on double diffusion that has been funded by the US. National Science Foundation. We have also hosted a collaborative visit of our ESR partner Dr Laurie Padman.
Collaborator Contribution They organise the long-term monitoring and carried a large part of the financial burden of the cruise costs (USD $75000 per day on a Russian Icebreaker). My partners have shared cruise and historical data with us and continue to collaborate on Arctic mixing studies.
Impact joint publications include: Dmitrenko, Igor A., Kirillov, Sergey A., Bloshkina, Ekaterina, Lenn, Yueng-Djern (2012). Tide-induced vertical mixing in the Laptev Sea coastal polynya. J. Geophys. Res., 117, C00G14 (id:2044) Igor V. Polyakov, Andrey V. Pnyushkov, Robert Rember, Vladimir V. Ivanov, Y.-D. Lenn, Laurie Padman, Eddy C. Carmack Mooring-Based Observations of Double-Diffusive Staircases over the Laptev Sea Slope. Journal of Physical Oceanography 42 95-109. PDF or website (id:2007) Polyakov, Igor V. , Vladimir A. Alexeev, Igor M. Ashik, Sheldon Bacon, Agnieszka Beszczynska-Möller, Eddy C. Carmack, Igor A. Dmitrenko, Louis Fortier, Jean-Claude Gascard, Edmond Hansen, Jens Hölemann, Vladimir V. Ivanov, Takashi Kikuchi, Sergey Kirillov, Yueng-Djern Lenn, Fiona A. McLaughlin, Jan Piechura, Irina Repina, Leonid A. Timokhov, Waldemar Walczowski, Rebecca Woodgate (2011). Fate of Early 2000s Arctic Warm Water Pulse. Bulletin of the American Meterological Society, 92(5), 561-566. (id:1914) Yueng-Djern Lenn, Tom P. Rippeth, Chris P. Old, Sheldon Bacon, Igor Polyakov, Vladimir Ivanov, Jens Hölemann (2011). Intermittent Intense Turbulent Mixing under Ice in the Laptev Sea Continental Shelf. Journal of Physical Oceanography, 41(3), 531-547 (id:1924) Yueng-Djern Lenn, Wiles, P. J., Torres-Valdes, S., Abrahamsen, E. P., Rippeth, T. P., Simpson, J. H., Bacon, S., Laxon, S. W., Polyakov, I., Ivanov, V., Kirillov, S. (2009) Vertical mixing at intermediate depths in the Arctic boundary current. Geophysical Research Letters, 36 (5). 5, pp. doi:10.1029/2008GL036792 (id:1724)
Start Year 2007
 
Description US-Arctic 
Organisation University of Alaska
Country United States 
Sector Academic/University 
PI Contribution Collaborators at the University of Alaska, Fairbanks have and continue to lead long-term monitoring observations along the margins of the Eurasian Arctic. On two separate occasions, Bangor colleagues and I have participated in these cruises to make turbulence measurements to complement the repeat hydrography. Together the data have been used in several joint publications in respected peer-reviewed journals and the collaboration continues through the sharing of data between partners in ongoing efforts to study the effects of shear on double diffusion that has been funded by the US. National Science Foundation. We have also hosted a collaborative visit of our ESR partner Dr Laurie Padman.
Collaborator Contribution They organise the long-term monitoring and carried a large part of the financial burden of the cruise costs (USD $75000 per day on a Russian Icebreaker). My partners have shared cruise and historical data with us and continue to collaborate on Arctic mixing studies.
Impact joint publications include: Dmitrenko, Igor A., Kirillov, Sergey A., Bloshkina, Ekaterina, Lenn, Yueng-Djern (2012). Tide-induced vertical mixing in the Laptev Sea coastal polynya. J. Geophys. Res., 117, C00G14 (id:2044) Igor V. Polyakov, Andrey V. Pnyushkov, Robert Rember, Vladimir V. Ivanov, Y.-D. Lenn, Laurie Padman, Eddy C. Carmack Mooring-Based Observations of Double-Diffusive Staircases over the Laptev Sea Slope. Journal of Physical Oceanography 42 95-109. PDF or website (id:2007) Polyakov, Igor V. , Vladimir A. Alexeev, Igor M. Ashik, Sheldon Bacon, Agnieszka Beszczynska-Möller, Eddy C. Carmack, Igor A. Dmitrenko, Louis Fortier, Jean-Claude Gascard, Edmond Hansen, Jens Hölemann, Vladimir V. Ivanov, Takashi Kikuchi, Sergey Kirillov, Yueng-Djern Lenn, Fiona A. McLaughlin, Jan Piechura, Irina Repina, Leonid A. Timokhov, Waldemar Walczowski, Rebecca Woodgate (2011). Fate of Early 2000s Arctic Warm Water Pulse. Bulletin of the American Meterological Society, 92(5), 561-566. (id:1914) Yueng-Djern Lenn, Tom P. Rippeth, Chris P. Old, Sheldon Bacon, Igor Polyakov, Vladimir Ivanov, Jens Hölemann (2011). Intermittent Intense Turbulent Mixing under Ice in the Laptev Sea Continental Shelf. Journal of Physical Oceanography, 41(3), 531-547 (id:1924) Yueng-Djern Lenn, Wiles, P. J., Torres-Valdes, S., Abrahamsen, E. P., Rippeth, T. P., Simpson, J. H., Bacon, S., Laxon, S. W., Polyakov, I., Ivanov, V., Kirillov, S. (2009) Vertical mixing at intermediate depths in the Arctic boundary current. Geophysical Research Letters, 36 (5). 5, pp. doi:10.1029/2008GL036792 (id:1724)
Start Year 2007
 
Description BBC News interview about climate change in the Arctic Barents Sea. 
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 Public/other audiences
Results and Impact I was invited to participate in a live interview on the BBC News Channel about the impact of the warming and increasing salt content of the Arctic Barents Sea on 5/2/2019. I was interviewed by Reeta Chakrabati on the 8 pm news programme. My father (climate change denier and TV addict) has become much more open to the science about climate change since then.
Year(s) Of Engagement Activity 2019
URL https://www.changing-arctic-ocean.ac.uk/news/2019/01/arctic-climate-change/
 
Description BBC Radio Cymru Science Cafe interview. 
Form Of Engagement Activity A press release, press conference or response to a media enquiry/interview
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Media (as a channel to the public)
Results and Impact I, alongside Changing Arctic Ocean ARISE investigators Claire Mahaffey & Rachel Jeffereies (University of Liverpool), participated in a BBC Radio Wales Science Cafe discussion with interviewer Adam Walton about how our research is documenting change in the Arctic Ocean. This was broadcast across Wales on the 5/2/2019 and is available to listen on the BBC Sounds App. The current interest from the BBC about the Arctic has made us all aware of the need to be ready to respond to media requests and I have signed up for media engagement training to assist me in the event of future requests. Indeed, my PEANUTS co-investigator has just competed and interview off BBC Radio 4 that will be featured in their piece about UK science in the Arctic.
Year(s) Of Engagement Activity 2019
URL https://www.bbc.co.uk/programmes/m0002bzk
 
Description British Council Researcher Links Panel 
Form Of Engagement Activity A formal working group, expert panel or dialogue
Part Of Official Scheme? Yes
Geographic Reach International
Primary Audience Participants in your research and patient groups
Results and Impact We were able to grade the proposals in a collective manner and present our recommendations to the funding body. In this case the British Council.

The impact is rather more indirect as successful workshops will have benefited both UK scientists and their international partners as well as advance the science in a manner so as to directly affect the public in those nations.
Year(s) Of Engagement Activity 2014
 
Description GRL press release 
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 Public/other audiences
Results and Impact Hopefully this will spark discussion. The press release publicises my student's results that are about to be published in the Geophysical Research Letters.

Yet to be determined.
Year(s) Of Engagement Activity 2014
 
Description MSc tutorial teaching 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach Local
Primary Audience Schools
Results and Impact Teaching Masters Students through tutorials

My leadership inspired one of the Masters students to apply for a PhD with me and she was successful in this respect. Jess is now in her third year and has her first peer-reviewed article in press at the Geophysical Research Letters.
Year(s) Of Engagement Activity 2010,2013,2014
 
Description Popular science article in TheConversation 
Form Of Engagement Activity A magazine, newsletter or online publication
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Public/other audiences
Results and Impact This article was written to translate the results of the Barton et al., 2018 paper in JPO for a general audience, and has reached over 5500 readers since 30 August 2018 when it was published. It also inspired a level discussion online with 63 comments generated, including some from climate denialists (probably why the discussion was so lively). The article was retweeted 82 times and shared on Facebook 196 times. Since the publication of this article, I have been approached by The Conversation to consider authoring article on other topics.
Year(s) Of Engagement Activity 2018
URL https://theconversation.com/extreme-weather-in-europe-linked-to-less-sea-ice-and-warming-in-the-bare...
 
Description STEM activities with schools 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach Regional
Primary Audience Schools
Results and Impact Details of events I co-ordinated and lead as Schools Liaison for Bangor's School of Ocean Sciences. Every event features some practical aspect where students can participate in a science activity. Note numbers given are for students who participated only, but we often find that it is the teachers on whom we also make important and lasting impressions.

10/7/2017: Lymm High School careers day. (20+ students, 3 firm acceptance for Bangor U places)
21/7/2017: Culceth High School, year 12 Biology workshop & lecture (64 students)
29/9/2017: Overleigh St Mary's C of E School, Year 2 science (60 children)
7/2/2018: Welsh Government Serene Network event at Venue Cymru (~10 invited students)
8/3/2018: Culceth High School Careers Fair Years 8-11 (1000+ children)
10/4/2018: Christleton International Studio visit to SOS by International Baccalaureate Students (30 students)
17/5/2018: Derby College Year 10 visit (65 students)
19/6/2018: Girls into STEM* (year 9 from Daffyd Hughes School & Denbigh High School, 28 students total)
21/6/2018: Daffyd Hughes School remaining Year 9 triple science students (39 students)
28/6/2018: Holy Cross Sixth Form College (18 students)
3/7/2018: Bangor University Summer School? (15 students)
10/7/2018: Girls into STEM* (30 students)
12/7/2018: National Citizens Service, year 12 students from Chester (140 students)
19/7/2018: BCA college visit, 30 year 8 students.
25/9/2018: Girls into STEM (28 students)
4/12/2018: Girls into STEM (27 students)

As a result of these visits, students typically find themselves more engaged with science and some become convinced to pursue careers in ocean sciences.
Year(s) Of Engagement Activity 2017,2018
 
Description Schools outreach activities 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach Regional
Primary Audience Schools
Results and Impact As the schools liaison officer for the School of Ocean Sciences, I have hosted numerous visits from school children to the School of Ocean Sciences. A typical visit requires me to provide a short introductory lecture to the multi-disciplinary fields of Ocean Sciences followed by a facilities tour and a hands-on laboratory practical activity. I have also visited schools across North Wales and Northwest of England during STEM careers fairs to introduced students to the field of ocean sciences, during which I frequently bring a fluids dynamics experiment as a demonstration of ocean circulation and overturning, or ice-ocean interactions such as found in the polar oceans.
Year(s) Of Engagement Activity 2015,2016,2017,2018
 
Description University Open days 
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 Schools
Results and Impact I have participated in numerous University Open days, both spending time engaging in conversation with prospective students and parents as well as running demonstration practicals. The practicals frequently feature ocean stratification experiments simulation the Arctic Ocean.
Year(s) Of Engagement Activity 2015,2016,2017,2018