Watermass transformation processes and vortex
dynamics in the Lofoten Basin of the Norwegian Sea
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The 4-year project ProVolo funded by the basic research programme (FRIPRO) of the Research Council of Norway. The project is a coordinated study to observe, understand, and quantify the fundamental processes that shape the oceanographic structure of the Lofoten Basin.
The Lofoten Basin (LB, right), situated in the northern Norwegian Sea, is emerging as a fundamental player in our climate and fisheries. In this area the warm and salty Atlantic Water is subject to the greatest heat losses anywhere in the Nordic Seas. The warm pool in the Basin is shown on the right as the depth of the specific volume anomaly surface, together with the main AW branches [Søiland and Rossby, 2013].
The Lofoten Basin is energetic: it stands out as a hotspot in the maps of eddy kinetic energy including the slope region associated with eddies shed from the Norwegian slope current, and a maximum at the center of the basin associated with a long-lived, deep and large eddy (Lofoten Basin Eddy, LBE). Maps of EKE derived from (below left) drifters [Koszalka et al., 2011], and (right) altimeter [Raj et al., 2015]. The bottom slope is steep on the Norwegian continental rise east of LB, and the topography is rough over the Mohn Ridge on the western side.
The study addresses the water transformation processes in the three distinct and important regions of the Lofoten Basin: the steep Norwegian continental slope, the basin pooling the warm Atlantic Water, and the frontal region over the rough Mohn Ridge.
The specific objectives of ProVoLo are to:
- conduct dedicated, state-of-the-art observations in the LB, covering processes from mesoscale (50 km) to turbulence (1 cm)
- quantify the contribution of the slope current (on the Norwegian slope) and the front current (over the Mohn Ridge) in the dynamics, tracer and energy variability and mixing in the LB
- describe the generation, propagation and destruction of anticyclones from the slope current and their contribution to the Lofoten Basin Eddy (LBE)
- resolve, track, describe and quantify the features of the LBE and identify its role in watermass transformation
- quantify isopycnal and diapycnal mixing rates across the front over the Mohn Ridge
We hypothesize that
- the slope and the front currents bordering the LB each contribute significantly to the variability of EKE, water properties and their mixing in the basin;
- eddy-induced transport from the instability of the slope current, and sub-mesoscale dynamics are critical for constraining the lateral heat and salt fluxes;
- the LBE is a crucial component of the watermass transformations and mode water formation in the LB;
- the stability and lifetime of the LBE are affected by substantial isopycnal and diapycnal mixing across the rim of the LBE;
- submesoscale processes lead to substantial isopycnal/diapycnal mixing across the front over the Mohn Ridge.
The investigation of these hypotheses is best realized through a combination of Lagrangian and Eulerian measurements, spatial surveys, and high-resolution time series. The main approach is a combination of theory, process modelling and a well-coordinated field experiment with innovative observation techniques using cost-efficient platforms, moored instruments and dedicated cruises covering spatial scales from 1 cm for turbulence to the 50 km scales of mesoscale eddies.
Field experiment plan. Diamonds show the mooring positions (1 to 3). Mooring 3 (black) is co-located with the earlier WHOI mooring. Mooring 2 is co-located with the secondary EKE maximum in Fig 1c. The centre of the LBE is marked together with a 40-km radius range. Tracks marked G are for gliders. G0 (gray) is the idealized track of existing multiple glider missions since 2012, with extended 9 months samplings around the LBE ring. G1 (basin and LBE) and G2 (Mohn Ridge front) are proposed here. After completing the track in approx. 2 month, G1 will sample the LBE ring for one month, and follow the track back east, and repeat the cycle. G2 concentrates at the Mohn Ridge frontal region and repeatedly samples the butterfly pattern. Both summer and winter process cruises will concentrate around LBE and near G2.
The national research team consists of
I. Fer and K.A. Orvik(Geophysical Institute GFI-UoB),
V. Tverberg (Univ. of Nordland, UiN),
H. Søiland (Insitute of Marine Research, IMR),
P.E. Isachsen and J. LaCasce (Univ. of Oslo, UiO),
and a Postdoc and a Ph.D. student (UoB).
The international collaborators include T. Rossby (Univ. Rhodes Island), F. Straeno (WHOI), J. Lilly (North West Res. Assoc.), B Ferron (IFREMER), P. Bouruet-Aubertot and Y. Cuypers (LOCEAN), I. Koszalka (GEOMAR), and T. Belonenko and colleagues (St. Petersburg).
On Thin Ice (NICE)Role of Ocean Heat Flux in Sea Ice Melt
(2014-2017) (to top)
NICE received funding from the joint call issued by the programme Climate Change and Its Impacts in Norway (NORKLIMA), the new large-scale Climate Programme (KLIMAFORSK) and the Polar Research Programme (POLARPROG), primarily to support one PhD study and the associated field work and instrumentation expenses. NICE builds on recently completed US-Norway collaboration projects and the synergy gained from recently funded multidisciplinary, national and international initiatives. The overall objective of NICE is to study the role of diapycnal mixing for the heat and biogeochemical budgets of the Arctic Ocean, the role of ocean heat flux in modulating the ice thickness and area, and the associated feedbacks.
Antarctic Ice Shelves and Ocean Climate
Production, Export, Dynamics and Variability of Bottom Water
in the Southern Weddell Sea
(2011-2014) (to top)
Together with Elin Darelius, my co-PI, we received funding from the NARE programme, through RCN. WEDDELL aims to deliver a more complete and detailed description of the processes that take place in the southern lower limb of the thermohaline circulation in the Atlantic Ocean. We benefit from the unique setting of the southern Weddell Sea which allows us to study processes related to basin-shelf exchange, circulation beneath an ice shelf, ice shelf water (ISW) production, and dense overflow dynamics and mixing, while monitoring ice shelf melting, variability in dense water production, and their contribution to sea level change. Additionnaly we received support from the University, through the Center for Climate Dynamics, for one PhD student. Kjersti L. Daae has filled this position. Recently (2013) Svein Østerhus, together with Elin, received funding from the RCN-NORKLIMA programme to continue with the long-term monitoring at station S2 and Site 5 (see Figure) WEDDELL activities regarding the Site 5 comprise only of planning and design.
The first cruise of the project to the Weddell Sea was onboard RSS Ernest Shackleton in January 2013. The field work included mooring deployments and a survey of ocean hydrography, current, and microstructure. See the details about the field work *here*. The moorings will be recovered in early 2014 from the research icebreaker Polarstern.
The map below shows the study area together with the long-term monitoring stations S2 at the Filchner Sill and Site 5 southwest of Berkner Island. The region identified with the black frame is expanded in the next figure. Areas shaded in light gray are ice shelves; those in dark gray are land. Circulation pattern is after Nicholls et al (2009). Branches of the Filchner overflow downstream of S2 are after Foldvik et al. (2004). The green arrows show the flow of the slope front and coastal currents. Blue and red arrows show the circulation beneath of waters originating from the eastern and western ends of the Ronne Ice Shelf Front, respectively. Black broken arrows indicate the inflow of modified warm deep water.
The BIAC-legacy mooring positions are shown on the right: red, 2009/10; black, 2010/11, recovered 14 February 2011. S2 marks the location of the mooring for monitoring at the sill of the Filchner depression.
Faroe Bank Channel Overflow: Dynamics and Mixing
(2011-2014) (to top)
OVERFLOW project has received funding from RCN through the FRINAT programme. The aim of this 4-year project is to investigate the mixing and entrainment of the dense oceanic overflow from the Faroe Bank Channel. My co-PI is Elin Darelius. Two 2-year post-doctoral researcher positions are filled by Jenny Ullgren (observations) and Chuncheng Guo (modelling), respectively.
The overview map below, where the Greenland-Scotland ridge is identified by the 400 m isobath, shows the location of the Faroe Bank Channel (red rectangle) that is blown up in the panel on the right. The saddle point (cross) and the overflow (arrow) are shown. The study site of the OVERFLOW is marked by the red rectangle.
Existing historical and recent data sets as well as new observations will be exploited together with process-oriented numerical simulations and laboratory experiments. The data will be analyzed to advance our understanding of overflow mixing. New parameterizations will be explored, implemented and tested for better representation of overflows in climate models. The specific objectives are to descrie the dynamics and mixing of the Faroe Bank Channel overflow using detailed observations, utilize gliders to measure entrainment and mixing, describe the formation mechanisms for mesoscale eddies and delineate the role of eddies in modulating the mixing and the descent rate of the plume, investigate the secondary circulation and its effect on entrainment and mixing, and parameterize and implement the entrainment and mixing of overflows.
Early in the project, in collaboration with University Washington, we devised a method to infer ocean mixing from Seagliders (see Beaird et al., 2012). This is an attractive approach as it can remotely map the ocean mixing at a low cost. We used the vertical velocity data from the gliders as an independent measure of mixing and internal waves and compare it to direct measurements of mixing.
In 2012, we have successfully conducted our main “overflow dynamics and mixing experiment” (see the field work details **here**), including a dedicated cruise on board RV Håkon Mosby, and one year-long time series from XX moorings. The project involved use of autonomous underwater gliders, one equipped with turbulence probes, and a moored stationary underwater turbulence buoy system, a set of instruments previously not used by our group. Significant effort was thus put into building expertise and familiarity with the new complex measurement systems. Algot Kristoffer Petersson wrote his Master's dissertation on the methods & results from the deployment of a Teledyne Webb Slocum glider equipped with turbulence probes (picture below).
The figure above, from Fer et al. (2010), shows contours of downchannel velocity and potential density at 0.1 kg m-3 intervals (gray), and dissipation rate for Sections A (near the FBC sill) to C (about 60 km downstream). Dashed curves delineate the plume interface (27.65 kg m-3).
Bipolar Thermohaline Circulation: BIAC
BIAC is an IPY project funded by RCN and co-ordinated by Tor Gammelsrød at
Geophysical Institute, University of Bergen. BIAC’s main objective is to study
the Arctic and Southern Ocean shelf ventilation processes and determine their
impacts on the bipolar Atlantic thermohaline circulation. I am the principal
investigator of working theme (WT) 3 : Downslope processes – pathways, cascading
and mixing. In WT3 field measurements and modelling focusing on the logistically
favorable and accessible sites (Storfjorden, Faroe Bank Channel, and Weddell Sea),
will be conducted to estimate evolution and mixing of shelf-origin dense water
cascades and the associated oxygen and carbon transports. Dedicated advanced
shipboard and moored measurements of fine-scale hydrography and currents, CO2, oxygen, microscale temperature and shear will be made, resolving the temporal
and spatial scales associated with the mixing processes. Mooring locations and
the survey will cover the path of the overflow where the entrainment and mixing
is reported to be enhanced. Modelling activity will comprise idealized cascade
modelling, process-oriented Bergen Ocean Model (BOM) application and regional
ROMS application to overflows. Through BIAC we acquired VMP2000 microstructure
profiler that will allow us to measure dissipation rates as deep as 1500-1700 m,
relevant for Faroe Bank Channel (FBC) overflow and Weddell Sea outflow. FBC
experiment is scheduled in late May 2008 from R.V. Håkon Mosby.
Read the full proposal here [pdf 1940 KB].
Read the BIAC description (by Gammelsrød & Østerhus) appeared in Klima here (in Norwegian, but with descriptive figures).
Ocean Mixing in the Arctic: Case Study at the NPEO
This project is my RCN young-investigator grant and is a product of a
collaborative initiative with Tim Boyd. It aims to investigate ocean mixing
during the drift of the North Pole Environmental Observatory based at
Borneo Ice Camp (approximately 89N), through field observations and
process studies. I benefit from the infrastructure provided by the
North Pole Environmental Observatory (NPEO). The Arctic ice
cover depends on a delicate heat balance in which the magnitude and
distribution of the oceanic vertical heat flux is important. The
amount and spatial distribution of thermal and mechanical forcing,
ocean stratification, internal wave activity and turbulent mixing have
significant impact on this vertical heat flux. With this motivation,
I proposed field work in spring of 2007 and 2008 including time series
of fine scale velocity (using Longranger ADCP) and microstructure
profiles (using MSS90L) from Borneo and vertical profiles of velocity
(using XCPs) and microstructure at stations occupied by a helicopter
along transects across the Lomonosov Ridge. The field work in 2007
is completed and some preliminary results are posted on this link.
Read the full proposal here [pdf 660 KB].
Current Profiling North of Svalbard: CuNoS
CuNoS is funded by RCN and is a US-NO collaboration. I am the co-PI
and together with Peter Haugan (PI), we collaborate with Jamie Morison
of Applied Physics Lab., Univ. of Washington. CuNoS aims to develop XCP
capability (both ship and ice deployments) in Bergen. Through CuNoS,
I received training on XCPs in APL, Washington. Successful on-ice
deployments were made from Borneo Ice Camp in April 2007. In summer 2007,
during a cruise to the Yermak Plateau, we deployed XCPs from R.V.
Håkon Mosby. Preliminary results from this cruise can be read here.
Read the full proposal here [pdf 52 KB].
DAMOCLES (2006-2009) (to top)
DAMOCLES (Developing Arctic Modelling and Observing Capabilities for Long-term Environmental Studies) is an EU-funded (6th frame) project co-ordinated by Jean-Claude Gascard (Université Pierre et Marie Curie, Paris). DAMOCLES is an integrated ice-atmosphere-ocean monitoring and forecasting system designed for observing, understanding and quantifying climate changes in the Arctic. DAMOCLES consortium includes 45 institutions. Here is the descriptive DAMOCLES leaflet (pdf, 1.2 MB) with nice pictures. In DAMOCLES, I am responsible for monitoring of the Storfjorden overflow using bottom-mounted ADCPs on trawl-proof frames (following and improving on the system initiated by the ProClim project.
A sustainable new system for trawl-proof frame is designed and constructed.
The maintenance of the initial trawl-proof system was costly with significant
transport and deployment difficulties. The improvements are a result
of experience gained by maintaining a trawl-proof bottom-mounted ADCP system
at the Storfjorden sill since summer 2003. The new system at the shelf-break
off Sørkapp of Spitsbergen is deployed first in summer 2007.
Reports from the sill-ADCP data are available for year 2004 (detailed report including tidal analysis) and years 2004-2006 (with focus on inter-annual comparison).
Finalized data sets can be accessed here.
Visit the official web-site.
NorClim (2006-2009) (to top)
NorClim is a RCN-funded project co-ordinated by Helge Drange,
Nansen Environmental and Remote Sensing Center (NERSC), Bergen.
The leading research institutes in Bergen, Oslo and Tromsø working
on the physical climate system participate in NorClim. The
goal of the consortium is to actively connect, and by that to optimise, a
major part of the climate research activities in Norway. The project has,
with particular focus on Norway and the Arctic, the following objectives:
- To detect and examine mechanisms for climate variations on time-scales from years to several decades
-To improve the understanding and implementation of processes in the physical climate system that are not well represented in global climate models
-To produce climate scenario projections for time-horizons 2030 and 2100 with quantification of uncertainties
-To provide scientifically based and relevant information on the evolution of the physical climate to governmental bodies, decision and policy makers, researchers, enterprises, NGOs, and the general public
- To unify climate model and analyses tools in Norway to establish a common Earth System Model
- To contribute to long-term capacity and competence building of climate research in Norway
I will contribute to the Ocean Module, led by Bjørn Ådlandsvik, by trying to provide improved parameterization schemes for gravity current entrainment and diapycnal mixing.
Read the full proposal here [pdf 1466 KB].
Polar Ocean Climate Processes: ProClim
ProClim funded by RCN was co-ordinated by Peter M. Haugan at Geophysical Institute, University of Bergen
a number of mesoscale and small scale processes controlling how properties (such as heat, salt, momentum,
nutrients, tracers) are being transferred throughout the air-ice-sea system. Three major regions
: the continental shelf, continental slope and deep basins, are reflected in the first three work
packages, WP1 - WP3. In deep basins, WP1, deep
convection in regions of weak vertical stratification lead to the formation of deep and intermediate
waters which are the main constituents of the Greenland-Iceland-Scotland overflows and ultimately of
the North Atlantic deep water. The focus on shelves mainly concerns brine-enriched water, WP2,
resulting from sea-ice formation in coastal polynyas and along topographically influenced fronts
and ice edges. Interactions between shelves and deep basins are manifested in cross slope exchanges,
WP3, involving slope convection and cascading.
I was involved in WP3, responsible for small-scale processes and turbulence field work and overflow monitoring. Through ProClim, MSS90, a loosely tethered microstructure profiler was acquired.
Visit the web-site .