This doesn’t sound new: Having bad data is worse than having no data! Anyone who had to deal with ‘fishy’ numbers coming out from instrument will agree.
A strong motivation is driving Dalhousie team of scientists to work around the clock on collecting and processing water samples in order to produce QC data for e.g. oxygen sensors on CTD rosette, SeaCycler, a surface-profiling mooring, and other moorings. Only the sensor float of SeaCycler itself is populated with 13 (!) different sensors, which require in situ calibration. While some water samples can be processed straightaway in the chemistry lab onboard, the rest will be sent home and analyzed at Dalhousie University in Halifax, NS, Canada.
So what’s happening in the lab?
GEOMAR and Dalhousie provided two titration systems for the analysis of oxygen samples onboard. Chemistry behind the method was described by Winkler back in 1888 and with certain modifications it remains a gold standard for oxygen measurements for more than a century now. However two systems utilize their own detection method (voltammetry vs. colorimetry), sample volume and concentration of reagents. Despite all the differences, an agreement in oxygen values between two systems is impeccable. The results are truly encouraging for both GEOMAR and Dalhousie teams who rely on their systems in the assessment of instruments’ performance.
Chlorophyll and CDOM (Coloured Dissolved Organic Matter) samples are partly processed onboard and preserved for later analysis. The same concerns nutrients and the carbonate system probes.
Once the chemists have done their job, it’s up to the deployed instruments to show what is hidden in the blue and cold waters of the Labrador Sea. See CERC.OCEAN website for more information about the SeaCycler mooring.
Fig.1: Work routine: Dasha and Kat are running two independent Winkler oxygen systems in parallel.
Fig.2: A filtering station for Chlorophyll, CDOM and nutrients gets ready for the next batch of samples.
The VITALS (Ventilation, Interactions and Transports Across the Labrador Sea) research network is funded to study how the deep ocean exchanges carbon dioxide, oxygen, and heat with the atmosphere through the Labrador Sea. To address this topic, a multi-instrumented, deep-ocean mooring has been deployed to measure and collect oceanographic parameters in the Labrador Sea.
The mooring contains a surface-profiling “SeaCycler” at its top, with 9 x MicroCAT CTD’s and two RDI ADCP’s below it. SeaCycler is ideally suited for VITALS research due to its unique ability to profile the upper ocean making numerous simultaneous measurements near the surface.
The deployment was very successful and early engineering results are encouraging.
At the time of writing, SeaCycler has completed:
12 profiles to the surface from a parking depth of 154m,
Is moored in 3526m of water located mid-way between Greenland and Newfoundland, Canada,
Has sent 72 data files to shore,
and has profiled a total vertical distance of 3.3 km underwater.
Unless new commands are sent, the system is programmed to profile every 20 hours for the next year.
The average water temperature in the upper 150m is currently 3.9 °C.
SeaCycler – A Short Description:
Fig 1, SeaCycler Mooring Components
SeaCycler is a moored, deep-ocean, surface-piercing profiler with two-way satellite communication. This means it’s anchored to the sea floor and cycles (or “profiles”) oceanographic sensors through the upper 150m of the ocean collecting measurements on the way (see Fig 1).
At the top of the profile, it surfaces a satellite telemetry system to transfer data to shore and receive new commands. After communication, it returns its profiling elements to a depth resistant to bio-fouling and safe from surface hazards such as ships and storm waves.
Primary to SeaCycler’s success is its ability to profile a sizable sensor suite (currently 11 sensors) using substantial buoyancy to resist mooring knock-over from ocean currents while conserving battery-stored energy to permit over 500 x 150m profiles throughout year-long deployments.
SeaCycler senses surface conditions and will abort profiles prematurely if wave loading exceeds an adjustable limit. Profiling movement is controlled by a unique drive system which powers an underwater winch that has built-in compliance and no rotating seals or slip-rings to enhance reliability.
Deployment Description:
The weather was good with light winds and 1 to 2m waves. We started early in the day as winds were forecasted to pick up. A quick site survey revealed flat bathymetry and good water depths.
SeaCycler components were deployed in the usual “MechFloat-tow, CommFloat, SensorFloat, MechFloat-slip” fashion (B-L of Fig 2), which worked well.
The buy ativan online A-Frame was used to deploy most mooring components including the MechFloat. The CommFloat was slipped by hand and a slewing crane deployed the anchors.
A capstan winch was used to pay out cable and deck cleats were used to slip mooring loads.
The deployment took less time than expected and resulted in an estimated 3-hour tow to achieve station. It was decided to omit 1 x 5m length of chain and deploy immediately to avoid the long tow. The final mooring location was about 2 nm further from the AR7W line than originally planned.
The ship was maneuvered to follow the mooring’s top floats until they submerged. A nice gentle tow was observed. No mooring beacon hits were received after submergence.
Fig. 3, Mooring top floats being towed by a sinking anchor.
Hydro-acoustic triangulation was not performed at this time and instead, the ship was relocated for K1 deployment. The ship returned to the SeaCycler site later that evening, but triangulation was not performed since a SeaCycler surfacing had already occurred providing a more accurate GPS location fix.
Mooring Position & Anchor Fall-Back:
The 2400kg double-quad steel anchor was slipped in 3526m of water and eventually settled on the bottom 1016m to the South-East. It took 38 minutes for the top of the mooring to submerge after anchor release. This equates to a SeaCycler descent rate of .48 m/s, which is well within acceptable limits.
The final mooring position is determined by averaging CommFloat GPS location fixes shown in Figure 4. The central “Best” point indicates the profile with least amount of “Extra Cable Out”.
Fig 4, CommFloat GPS locations for the first 10 profiles
Acknowledgements:
The entire SeaCycler Team at Dalhousie University and Scripps Institution of Oceanography would like to thank the Maria S. Merian’s Captain Ralf Schmidt for his support and excellent ship handling skills and our Chief Scientist, Dr. Johannes Karstensen from GEOMAR-Kiel for his support and acceptance of our operation into his OSNAP West project. We also acknowledge the support of the VITALS project of the Natural Sciences and Engineering Research Council of Canada (NSERC) and the Canada Excellence Research Chair in Ocean Science and Technology for supporting this deployment.
Many thanks are also given to Christian Begler, Gerd Niehus and Uwe Papenburg for their valuable advice and help on deck and to the many students and ship’s crew for their excellent mooring handling skills and provision of delicious food.
It was a pleasure to meet and work with the entire MSM54 team. We sincerely thank you for your help and assistance and opportunity to sail together.
56°N, 52°W. For days we have been cruising around these coordinates, and no matter whether we are some sea miles further south, north, east or west – the view does not change much. Even so, the ocean looks different every day.
I am on board the Maria S. Merian as a postdoc from GEOMAR and particularly interested in the mooring data from the central Labrador and Irminger Sea. In these regions, the ocean and atmosphere permanently exchange heat, with consequences for both sides. If, for instance, a cold winter storm cools the ocean, the surface water is getting colder and therefore denser, making it sink to the bottom. In reverse, the atmospheric circulation is affected by the sea surface temperature, which can give rise to complex ocean-atmosphere interactions. In my research, I am particularly interested in the uppermost water layer which serves as a bridge between the atmosphere and the deep ocean and thus buy valtrex online forms a connection between our weather and climate.
Photo: Henrike Schmidt
Photo: Henrike Schmidt
Photo: Henrike Schmidt
Photo: Arne Bendinger
In the middle of the Labrador Sea, somewhere near 56°N, 52°W, I watch the waves breaking around the ship. Water and air seem to intermingle and I imagine them carrying the icy winds down into the during a heavy winter storm. At this location, exactly below my feet, the ocean is almost 4 kilometres deep. Water this deep will need a long time to reemerge at the surface. Maybe some centuries. Maybe somewhere near Antarctica. Space and time are intertwining here, just like the days and nights on board the Merian. The depth and vastness of the sea evoke a feeling of timelessness and right in the midst of all this water, I am feeling quite small.
Figure 1: Mooring launch locations (white squares at 53N array, the central Labrador Sea and west Irminger Sea) and CTD stations (small yellow squares). This picture is from Johannes Karstensen (chief scientist of the cruise) with permission.
Another promising year for measuring Atlantic Meridional Overturning Circulation starts with cruise Maria S. Merian 54 (MSM 54), which departed St. John’s, Canada on 12th May and will end on 7th June in Reykjavik, Iceland. During this cruise, we will deploy seven moorings at the exit of the Labrador Sea near 53N, and two deep ones at the entrance near the west Greenland coast (Figure 1, right). These moorings serve to measure the magnitude and variability of the deep western boundary current as well as the connection of deep layer transport between entrance and exit of the Labrador Sea. Besides, direct measurements of the convective activity will be accomplished with mooring deployments in the central Labrador Sea (K1 and SeaCycler) and the central Irminger Sea (CIS). These observations will collectively contribute to our understanding of how the boundary current (both strength and property) varies with time, and the how these buy kamagra online changes are related to the convections.
Along the cruise, we will be conducting 90 CTD casts, crossing the Labrador Sea and west Irminger Sea. We are excited to expect a thick, cold and fresh Labrador Sea Water layer comparable to the ever-observed deepest convection in 1994.
Now we have been at sea for 5 days. The weather was not as good as what I have hoped: it was windy and cold during the first 3 days and got foggy afterwards. Hopefully the weather is getting better so that we can have everything progressed as scheduled.
Just BTW: Food is great on MSM (Figure 2). People are nice (Figure 2). I wish I could speak some German.
At the port of St. Johns, Canada on May 12th before cruise started. by Sijia Zou
With two other students (Christina Schmidt on the left and Patricia Handmann on the right) from GEOMAR (photo credit to Marilena Oltmanns). The flying hair in this photo tells you how important it is to wear a hat on the ship.
One of the great dinners on board (half chicken!!).
After some small highlights like supposed explosives in Mareike’s notebook and an unexpected upgrade to Premium Economy for some of us, we arrived at St. John’s. Thanks to the early flight an the time shift we had enough time to discover the town of St. John’s after the check in in the hotel where we stayed during the first night.
First of all, we said hello at the Merian and went on a small (and quite windy) tour to Signal Hill, from which you have a great view over the harbor and which became popular as Marconi received the first transatlantic radio signal here in 1901. In the evening we went to the city center and enjoyed dinner in a nice Canadian restaurant. The colorful houses and open-minded and witty people make up the great flair of St. John’s.
On Thursday we moved into our cabins at the Merian, which will be our home for the next weeks. After last preparations for the
Wiebke clothed in a survival suit (Photograph by Johannes Karstensen)
cruise and refueling there was the official welcoming by the crew and the security instructions. In the afternoon the Maria S. Merian then left the harbor and after the successfully mastered security exercises during which the most of us entered a rescue boat for the first time, we were introduced to our tasks on the ship. In the evening the first CTD measurement was carried out.
The next day was transit to the next station an actually for most of us this day (Friday) can be summed up in two words: Sea sick or tired due to the anti-sickness pills.
Saturday morning most guys had recovered and after breakfast we spotted the first icebergs, becoming bigger and more the farther we traveled on.
by Johannes Karstensen, chiefscientist MSM54 expedition
The ocean-class German research ships are rarely seen in Germany. They follow a route that is composed by many individual expeditions and converting the ships travel into a long, long journey; for Maria S Merian this journey takes place primarily in the North Atlantic and it transition into the Arctic Ocean. As a consequence – the scientists have to travel to where the ship is and have to bring with them (again by ship, but container ships) the equipment that is needed for the experiments to be performed at sea.
Without equipment brought by the scientists the Maria S Merian is not at all an empty ship – she carries a lot of equipment, required by almost all groups that make use of the ship, such as cranes, work shops, communication devices, instrumentation. However, most important – the ship is manned with a skilled, experienced and simply great crew, providing all support to not only conduct experiments at sea but to find a comfortable atmosphere which makes life at sea easy for us, the non-seamen.
In the last ten years I have been six times to St. Johns, Canada – all times to enter a ship (two times the Maria S Merian) for expeditions to the Labrador Sea. Typically I arrive 3 to 4 days before the cruise starts, just to be here when the ship arrives and to help loading and setting up equipment. The arrival of the ship is always special; for example people often eagerly wait to be back to shore, leaving the steadily moving platform behind – but to discover that the movement continues even on land for the next couple of days. St. Johns is a convenient harbour for us, just 1.5 days transit to one of our main working areas (the “53°N array”) – but it is also a nice little town settled around a large natural harbour bay.
Caption: View from Battery Park on St. Johns harbour. The two research ships (easy to identify by the “A” formed crane mounted at the stern, are the Irish Celtic Explorer (keft) and the German Maria S. Merian (right). credit: J. Karstensen
We, a science crew of 20 people, need for the installations and experiments planned during this trip (called MSM54) an amount of material that came in 7 containers. We fixed 4 containers to the ships deck but the rest of the material is now distributed in the labs.
The science crew is composed of five people from Canada’s Dalhousie University, one person from Duke University in the US, and 14 persons from GEOMAR in Germany. We are a mix of students (9), from PhD to BSc, technicians (7), and full scientists (4). A lot of the work that will be done is very technical – installing quite heavy equipment that ultimately serves us to conduct our experiments at sea generating data that is of use for our scientific investigations. What we are really after is to better understand how our ocean regulates climate – for example by taking up heat and other substances in specific regions, such as the Labrador Sea, where large amounts of near surface water sink to sometime deeper than 2000m depth, and from where it spreads far into the ocean interior.
What regulates the sinking process and how does the water spread in the ocean interior are some of the questions we want to answer. The 53°N-Array has been first installed in 1997, long before I came to Kiel to work in this region. It is a unique time series not only because it is operational since so long, but because it has been well designed from the beginning. Setting up a time series has similarities in buying a house – the only thing that matters is the location!
On this trip we will recovery many instruments that were installed during the last service of the array in 2014. For that cruise we started, guess where? – in St. Johns, correct! but on the French Research Vessel NO Thalassa. Not only the two of us who participated in the Thalassa expedition are now very excited to see how well the instrumentation had worked over the last two years. In 2018 we plan to come to the Labrador Sea again to service the “53°N-Array” – and I hope I can one more time join the long, long journey of the RV Maria S Merian.
Neill Mackay
03:15-03:30 PM
Room 228-230
PO13E-06: Circulation and mixing in the subpolar North Atlantic diagnosed from climatology using a Regional Thermohaline Inverse Method (RTHIM)
The Overturning in the Subpolar North Atlantic Program (OSNAP) aims to quantify the subpolar Atlantic Meridional Overturning Circulation (AMOC), including associated advective and diffusive transport of heat and freshwater. The OSNAP observational array will provide a continuous subpolar record of the AMOC from Labrador-Greenland-Scotland during 2014-2018. To understand the significance of high- and low- frequency changes measured by the array, including changes to AMOC metrics, water mass transformation and transports, Argo observations provide a useful complementary constraint for an inverse method, with the aim of resolving intra-seasonal timescales.
A novel inverse method in thermohaline coordinates has recently been demonstrated as being able to diagnose aspects of the global overturning circulation and mixing from model data. Here we have further developed a Regional Thermohaline Inverse Method, (RTHIM) and have validated it with the NEMO model in the OSNAP region, before applying it to a seasonal Argo climatology.
In an ocean basin there exists a balance between surface heat and freshwater fluxes, advective fluxes at an open boundary and interior diffusive mixing. RTHIM makes use of this balance to determine unknown velocities at the open boundary and diffusive fluxes of heat and salt within http://www.buypropeciaonline.org the domain volume. We identify key transport and mixing regions and events, relevant to the subpolar AMOC, and discuss the robustness of the inverse solutions. RTHIM is also able to identify the particular contributions to AMOC volume transport changes from temperature and salinity components.
Tuesday, 23 February
Susan Lozier
Plenary lecture
10:30–11:30 AM
Great Hall A&B
A Decade after The Day After Tomorrow: Our Current Understanding of the Ocean’s Overturning Circulation
In 1800 Count Rumford ascertained the ocean’s meridional overturning circulation from a single profile of ocean temperature constructed with the use of a rope, a wooden bucket and a rudimentary thermometer. Over two centuries later, data from floats, gliders and moorings deployed across the North Atlantic has transformed our understanding of the temporal and spatial variability of the meridional overturning: the component of the climate system responsible for sequestering heat and anthropogenic carbon dioxide in the deep ocean. In this talk I will review our current understanding of the overturning circulation with a particular focus on what we currently do and don’t understand about the mechanisms controlling its temporal change.
Thursday, February 25, 2016
Ric Williams
08:00-08:15 AM
Rooms 211-213
PC41A-01 Climate sensitivity to ocean sequestration of heat and carbon.
Ocean ventilation is a crucial process leading to heat and anthropogenic carbon being sequestered from the atmosphere. The rate by which the global ocean sequesters heat and carbon has a profound effect on the transient global warming. This climate response is empirically defined in terms of a climate index, the transient climate response to emissions (TCRE). Here, we provide a theoretical framework to understand how the TCRE can be interpreted in terms of a product of three differential terms: the dependence of surface warming on radiative forcing, the fractional radiative forcing contribution from atmospheric CO2 and the dependence of radiative forcing from atmospheric CO2 on cumulative carbon emissions. This framework is used to diagnose two models, an Earth System Model of Intermediate Complexity, configured as an idealised coupled atmosphere and ocean, and an IPCC-class Earth System Model. In both models, the centennial trends in the TCRE are controlled by the response of the ocean, which acts to sequester both heat and carbon; there is a decrease in the dependence of radiative forcing from CO2 on carbon emissions, which is partly compensated by an increase in the dependence of surface warming on radiative forcing. On decadal timescales, there are larger changes in the TCRE due to changes in ocean heat uptake and changes in non-CO2 radiative forcing linked to other greenhouse gases and aerosols. Our framework may be used to interpret the response of different climate models and used to provide traceability between simple and complex climate models.
Helen Johnson
08:45 – 09:00am
Rooms 203-205
PO41A-04 Dynamical Attribution of Recent Variability in Atlantic Overturning
Attributing observed variability of the Atlantic Meridional Overturning Circulation (AMOC) to past changes in surface forcing is challenging but essential for detecting any influence of anthropogenic forcing and reducing uncertainty in future climate predictions. Here we obtain quantitative estimates of wind and buoyancy-driven AMOC variations at 25?N by projecting observed atmospheric anomalies onto model-based dynamical patterns of AMOC sensitivity to surface wind, thermal and freshwater forcing over the preceding 15 years. We show that local wind forcing dominates AMOC variability on short timescales, whereas subpolar heat fluxes dominate on decadal timescales. The reconstructed transport time series successfully reproduces most of the interannual variability observed by the RAPID-MOCHA array. However, the apparent decadal trend in the RAPID-MOCHA time series is not captured, requiring improved model representation of ocean adjustment to subpolar heat fluxes over at least the past two decades, and highlighting the importance of sustained monitoring of the high latitude North Atlantic.
Patricia Handmann et al
09:30 – 09:45 AM
Rooms 203-205
PO41A-07 North Atlantic Deep Western Boundary Current Dynamics as Simulated by the VIKING20 Model Compared with Labrador Sea Observations
The connection of dynamic and hydrographic properties simulated by the VIKING20 model driven by CORE2 atmospheric forcing will be presented and compared to more than decade-long observations at the exit of the Labrador Sea near 53°N. VIKING20 is a high resolution (1/20°) nest, implemented by two-way nesting in a global configuration of the NEMO-LIM2 ocean-sea ice model in the North Atlantic (ORCA25). The exit of the Labrador Sea is the place where water masses from different origins and pathways meet and which are collectively called North Atlantic Deep Water (NADW). The VIKING20 flow field on average reproduces the observed structure as well as the bottom intensification of the western boundary current at 53°N. Here, we investigate the properties of the observed and modeled deep western boundary current by comparing North Atlantic water masses and currents simulated by the high resolution model with moored and hydrographic data from almost 20 year-long observations at 53°N. As comparable density fields in the model in comparison to the observations are found at shallower depths, we will present an evaluation of dynamic and hydrographic changes connected to each other and to atmospheric forcing in the model and observed data. In addition the following key questions will be addressed: How is energy distributed in baroclinic and barotropic components in observations and model in comparison to each other? The seasonal cycle can be found in the shallow Labrador Current in the model and the observations, but how deep is it reaching and causing dynamic and hydrographic changes?
Stuart Cunningham et al
03:00 – 03:15 PM
Rooms 203-205
O43A-05: The Subpolar AMOC: Dynamic Response of the Horizontal and Overturning Circulations due to Ocean Heat Content Changes between 1990 and 2014
Ocean heat content (OHC) in the subpolar region of the North Atlantic varies on interannual to decadal timescales and with spatial variations between its sub-basins as large as the temporal variability. In 2014 the Overturning in the Subpolar North Atlantic Programme (OSNAP) installed a mooring array across the Labrador Sea and from Greenland to Scotland. The objective of the array is to measure volume, heat and fresh-water fluxes. By combining Argo and altimeter data for the period 1990 to 2014 we describe and quantify the anomalous horizontal and overturning circulations and fluxes of heat and fresh-water driven by the long-term OHC changes. We thus provide a longer-term context for the new observations being made as part of OSNAP. Changes to the horizontal circulation involve deceleration of the gyre rim currents, lateral shifts of major open ocean current features and increased exchanges in the eastern intergyre region. These changes impact the Atlantic Meridional Overturning Circulation (AMOC) in density space causing a rich vertical anomalous structure. The net impact over this 24 year period is a reduction in northward heat-flux and decrease in southward fresh-water flux.
Friday, February 26, 2016
Johannes Karstensen et al
03:00 – 03:15 PM
Rooms 203-205
PO53A-05: Observations and causes of hydrographic variability in den deep western boundary current at the exit of the Labrador Sea.
The hydrographic variability of the Deep Western Boundary Current (DWBC) in the Labrador Sea is discussed using observational data from the period 1997 to 2014. This variability of the DWBC occurs on time scales from a few days to multiannual. The hydrographic data is analyzed in terms of signals originating from different “behavioral modes” of the DWBC, including the re-positioning of the core along the sloping topography, the pulsing of the core, and the advection of watermass anomalies within the core. Cross-correlation spectra show that the hydrographic variability on time scales of a few days can be explained by the periodic re-location of the core due to topographic waves. Variability on longer time scales can be interpreted by long-term re-location of the core, potentially related to an adjustment of the core to circulation changes on gyre scale. However, along-flow advection of anomalies is likely another source for this long-term variability. Possible scenarios for the generation of hydrographic variability in the source regions of the DWBC are discussed.
Poster Presentations
Monday, February 22, 2016 04:00 PM – 06:00 PM
Ernest N. Morial Convention Center, Poster Hall
HE14B High Latitude Air-Sea-Ice Interactions in a Changing Climate II Posters
Marilena Oltmanns et al
HE14B-1415: The Role of Local and Regional Atmospheric Forcing for Convection in the Subpolar North Atlantic
https://agu.confex.com/agu/os16/meetingapp.cgi/Paper/92491
Tuesday, February 22, 2016 04:00 PM – 06:00 PM
Ernest N. Morial Convention Center, Poster Hall
PO24B: Mesoscale and Submesoscale Processes: Characterization, Dynamics, and Representation VI Posters
Chris Wilson
PO24B-2949: An Update to the ‘Barrier or Blender’ Model of the Gulf Stream, Based on Lagrangian Analysis of Aviso Altimetry.
Thursday, February 25, 2016 04:00 PM – 06:00 PM
Ernest N. Morial Convention Center, Poster Hall
PO44 Atlantic Meridional Overturning Circulation: Past, Present, and Future III Posters
Chun Zhou PO44A-3118: Subpolar North Atlantic glider observations for OSNAP
Friday, February 26, 2016 04:00 PM – 06:00 PM
Ernest N. Morial Convention Center, Poster Hall
PO54A: Atlantic Meridional Overturning Circulation: Past, Present, and Future V Posters
Amy Bower PO54A-3225: The Charlie-Gibbs Fracture Zone: A Crossroads of the Atlantic Meridional Overturning Circulation
Nicholas Foukal and Susan Lozier PO54A-3229: Variability in Lagrangian-derived througput from the subtropical to the subpolar gyres in the North Atlantic and its impact on inter-gyre heat transport.
Penny Holliday PO54A-3222: The AMOC and subpolar gyre circulation at the OSNAP section in summer 2014.
Ric Williams PO44A-3130: Gyre-specific Ocean Heat Content Changes Controlled by the Meridional Overturning in the North Atlantic
Sijia Zou PO54A-3224: Contradictory Pathways between Labrador Sea Water Advection and Property Propagation.
PO54B: Climate Trends, Hydrographic Variability, Circulation, and Air-Land-Sea Interactions in the Marginal Seas of the North Atlantic III Posters
Femke de Jong & Laura de Steur PO54B-3241: Record deep convection in the Irminger Sea: Observations from the LOCO mooring during winter 2014-2015.
Laura de Steur & Femke de Jong PO54B-3242: Transport variability of the Irminger Current: First year-round results from a mooring array on the Reykjanes Ridge.
Loïc Houpert PO54B-3234: Glider Observations of the Properties, Circulation and Formation of Water Masses on the Rockall Plateau in the North Atlantic.
Virginie Thierry PO54B-3239: Argo float observations of basin-scale deep convection in the Irminger Sea during winter 2011-2012.
‘Go with the flow’: Research on the currents in the subpolar North Atlantic
This past July chief scientist Laura de Steur and the crew of the Pelagia set out to take measurements of the subpolar gyre as part of NACLIM and OSNAP research programs. Research conducted on this cruise, and as part of these programs, is important in understanding the “role of the ocean in our climate and future climate change.” Learn more about their work this summer, and ongoing research, in this film created over the course of the cruise.
by Helen Johnson, Helen Pillar, David Marshall and So Takao
Since 2004, oceanographers from the National Oceanography Centre in Southampton, together with US colleagues, have been using data from ocean moorings on the eastern and western sides of the Atlantic Ocean at 26 N to monitor the strength of the Atlantic meridional overturning circulation (AMOC). This has resulted in a remarkable and unprecedented 10 year timeseries of this key climate index (black line), which is closely related to ocean heat transport in the Atlantic and, as such, of great importance for the climate of western Europe as well as the entire globe. The observations have revealed large amplitude variations in the AMOC on all time-scales, along with an apparent decline over the ten years, and significant wind-driven weakenings in several recent winters. This autumn the team will collect a further 18 months of data from their ocean moorings. But what will this latest batch of data tell us about the strength of the AMOC?
At the University of Oxford, we have been working to reconstruct the time-series of AMOC variability, based on our knowledge of how winds, heat and freshwater fluxes over the Atlantic have changed over the last few decades, combined with our understanding of how sensitive the AMOC is to variations in these quantities. We use an ocean model and its adjoint to determine the sensitivity of the AMOC to surface wind, heat and freshwater forcing over the entire globe and the preceding 15 years. We then project observed forcing anomalies onto these sensitivity patterns; only those forcing anomalies which project strongly in space and time onto the sensitivity fields will generate variability in the AMOC.
Our reconstructed AMOC time series (orange line) successfully reproduces most of the interannual variability in the observed AMOC time series; these short-timescale fluctuations are dominated by wind forcing (including, but not limited to, Ekman transport anomalies). However, the decadal trend in the observed AMOC time series is not well captured by our reconstruction. This longer timescale variability results from the integrated response of the ocean to heat fluxes over the subpolar North Atlantic over at least the last two decades, and as yet ocean models are unable to accurately represent the ocean’s adjustment to forcing anomalies on such timescales.
Since NCEP II reanalysis atmospheric forcing data is available until June 2015, our reconstructed AMOC time series extends 15 months beyond the end of the currently available observed AMOC time-series. We have reasonable confidence in that portion of the variability which is wind-driven (blue line). We therefore “predict” that the RAPID team will discover that the mean AMOC over this period has been roughly equal to that over the previous few years (a small increase of 0.3 ± 0.2 Sv over the 2009-2014 mean). We further predict that the RAPID data won’t reveal any evidence of a large “dip” over the 2014-2015 winter; in contrast we expect to find that the AMOC reached a maximum in November-January.
These predictions will be validated when the RAPID team publish their updated AMOC time-series early in 2016! And as RAPID data continue to accrue, alongside observations from higher latitudes such as those made by the OSNAP programme, we will learn more about the climatically-important longer-term AMOC changes which are currently inaccessible via our reconstruction – watch this space!
