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OS1.6

This session will focus on variability in the ocean and its role in the wider climate system using both observations and models. Areas to be considered will include both ocean heat uptake and circulation variability as well as exploring the use of sustained ocean observing efforts and models to make progress in understanding the ocean’s role in the climate system. More than 90% of the excess heat in the climate system has been stored in the ocean, which mitigates the rate of surface warming. Better understanding of ocean ventilation mechanisms, as well as the uptake, transport, and storage of oceanic heat are therefore essential for reducing the uncertainties on global warming projections. Circulation variability and connectivity, particularly from the South Atlantic to the North Atlantic and Arctic Ocean, are also of interest as well as how they are driven by local-, large- or global-scale processes or teleconnections. Sustained observations at sea are being made within a wide variety of programmes and are leading to significant advances in our ability to understand and model climate. Thus, this session will also explore ongoing and planned sustained ocean observing efforts and illuminate their roles in improving understanding of the ocean’s role in the climate system. For example, air-sea flux moorings are being maintained at select sites to assess models and air-sea flux fields. Deep temperature and salinity measurements are being made at time series moorings and will be made by deep Argo floats. Significant advances are also being made using Argo floats for biogeochemistry and carbon measurements. Such observations provide the means to develop linkages between sustained ocean observing and climate modelling. In conclusion, the session will consider key aspects of ocean variability and its climate relevance, as well as encouraging the use of observations and models to enhance understanding of these areas.

Public information:
Announcement: We'll host a webinar with speakers from our session next week. May 13., 15:00-18:30 CEST

Agenda for the webinar: http://iacweb.ethz.ch/staff/medhaugi/files/UnofficialEGUOS1p6ZoomMeetingProgramme.pdf.

The webinar will be open to everyone, but please sign up to receive login details: https://forms.gle/6qwNVrBq7aYc7pn78

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Co-organized by CL2
Convener: Simon Josey | Co-conveners: Léon ChafikECSECS, Damien DesbruyeresECSECS, Yavor KostovECSECS, Iselin Medhaug
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| Attendance Fri, 08 May, 08:30–10:15 (CEST)

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Session summary Download all presentations (107MB)

Chat time: Friday, 8 May 2020, 08:30–10:15

D2328 |
EGU2020-5978
| Highlight
Susan Wijffels, Toshio Suga, and Dean Roemmich and the Argo Steering Team

Starting in 2000, Argo reached global coverage in 2007 and has sustained a globally distributed array of ~ 3000 profiling floats for almost two decades. This Argo array delivers ocean temperature and salinity profiles from the sea surface to 2000 dbar roughly 300km apart every 10 days in realtime. Just as the present Argo array originated from an opportunistic mix of developments in both technology and data management, a new step-change in global ocean observing is now possible. Advances in platform and sensor technologies presents a new opportunity to (i) improve Argo’s global reach and value beyond the original design, (ii) extend Argo to span the full ocean depth, (iii) add biogeochemical sensors for improved understanding of oceanic cycles of carbon, nutrients, and ecosystems – all within the context of a comprehensive Argo data system. Each of these enhancements are evolving along a path from experimental deployments to regional pilot arrays to global implementation.The ultimate objective is to implement a fully global, top-to-bottom, dynamically complete, and multidisciplinary Argo Program that will integrate seamlessly with satellite and with other in situ elements of the Global Ocean Observing System. The integrated system will deliver enhanced operational reanalysis and forecasting capability, and assessment of the state and variability of the climate system with respect to physical, biogeochemical, and ecosystems parameters. It will enable basic research of unprecedented breadth and magnitude, and a wealth of ocean-education and outreach opportunities.

How to cite: Wijffels, S., Suga, T., and Roemmich, D. and the Argo Steering Team: Argo Beyond 2020: Towards a global, full-depth multidisciplinary array, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5978, https://doi.org/10.5194/egusphere-egu2020-5978, 2020

D2329 |
EGU2020-12826
Sergey Gulev and Marina Aleksandrova

We consider here the potential of Voluntary Observing Ship (VOS) observations available form the ICOADS for estimating ocean surface heat budget at centennial time scales. VOS provide the longest coverage of the World Ocean by in-situ meteorological observations in time going back to the mid 18th century. We concentrate here on the shortwave and longwave radiative fluxes, largely relying on cloud cover. Visually observed cloud cover reports from Voluntary Observing Ships (VOS) and assimilated in ICOADS are were used to build long-term time series of cloud cover and short-wave radiation characteristics over the ocean for the last century. Cloud cover reports from VOS are subject for a number of inhomogeneities and uncertainties. Considering the centennial perspective, in 1949, WMO changed the practice of reporting cloud cover from tenths to octas. Moreover, some additional uncertainties were inherent in the early 20th century reports. This resulted in a definite break in cloud cover time series which further propagate to the inhomogeneity of the reconstructed time series of shortwave and longwave radiative fluxes. This inhomogeneity was associated with (while not limited to) the biased convertionconversion of tens to octas when developing ICOADS records using IMMA (and earlier generation formats). In this convertionconversion octa values “2” and “6” consolidated values corresponding to 2 and 3 tens and 7 and 8 tens respectively, thus making the fractional cloud cover distribution peaked to 2 and 6 octas. In order to remove correct this bias and to homogenize cloud cover time series we developed a new method based upon a discrete probability distribution for fractional cloud cover. Applying analytical distribution, we provide the correction of cloud cover reports and arrive to homogeneous time series of cloud cover. Further homogenized times series of cloud cover were used for computing radiative fluxes over the global ocean for the period from 1900 onwards.

How to cite: Gulev, S. and Aleksandrova, M.: Homogenizing visually observed cloud cover over global oceans with implications for reconstructions of radiative fluxes at sea surface, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12826, https://doi.org/10.5194/egusphere-egu2020-12826, 2020

D2330 |
EGU2020-13069
| Highlight
Lynne Talley, Kenneth Johnson, Stephen Riser, Jorge Sarmiento, Joellen Russell, Emmanuel Boss, Matthew Mazloff, and Susan Wijffels

The ocean provides critical services to life on the planet, absorbing 93% of the heat from anthropogenic warming and a quarter of human carbon dioxide (CO2) emissions each year. However, rising ocean temperatures and CO2 levels also change the marine environment: pH and oxygen levels fall, ocean currents change, and nutrient fluxes and concentrations are shifting, all with large effects on ecosystems and the cycles of oxygen, nitrogen, and carbon throughout the ocean and atmosphere. Observing these biogeochemical (BGC) processes across remote ocean areas with seasonal to interannual resolution has been impractical due to the prohibitive costs associated with ship observations. Yet such observations are essential to understand the natural and perturbed systems.

Profiling floats, proven in the Argo program, with BGC sensors (oxygen, nitrate, pH, bio-optical) provide a transformative solution to this need.  BGC profiling floats are capable of observing chemical and biological properties from 2000 m depth to the surface every 10 days for many years. Based on various OSSE and sampling approaches, global coverage can be achieved with 1000 BGC floats contributing to the core T/S Argo array of about 4000.

The U.S. Southern Ocean Carbon and Climate Observations and Modeling (SOCCOM) program serves as a major basin-scale pilot for such a global array. Its 141 operating BGC floats, building towards an ultimate 200 floats, demonstrate that the major challenges associated with operating a large-scale, robotic network have been overcome, and that there is a substantial user base for the data. Data have been publicly available in near real-time since the start of SOCCOM. Robust protocols for QC, calibration and validation of BGC float data have been developed, based on GLODAPv2 climatologies and relationships between the observed float variables. Data are being incorporated in BGC state estimation and are being used for comparison/validation of ocean models used for climate. Initial SOCCOM results are already transforming understanding of Southern Ocean biogeochemistry. Annual cycles of air-sea carbon flux are revealing major surprises, including strong outgassing within the Antarctic Circumpolar Current.  Annual net community production in all major regimes of the Southern Ocean has been quantified.  The broad-scale float profiling has validated NASA's satellite algorithms for POC and chlorophyll in the Southern Ocean. As the international community moves forward towards sustained BGC-Argo deployments, SOCCOM can provide its experience in sensors, floats, deployments, calibration, and data management. 

How to cite: Talley, L., Johnson, K., Riser, S., Sarmiento, J., Russell, J., Boss, E., Mazloff, M., and Wijffels, S.: A global Biogeochemical Argo pilot array: Southern Ocean Carbon and Climate Observations and Modeling (SOCCOM) profiling floats and results, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13069, https://doi.org/10.5194/egusphere-egu2020-13069, 2020

D2331 |
EGU2020-5476
Sjoerd Groeskamp

To understand the role of the ocean in the climate system, it is no longer sufficient to study either physics or biogeochemistry. Future efforts need to combine these disciplines to truly understand our future climate. The water mass transformation (WMT) weaves together circulation, thermodynamics, and biogeochemistry into a description of the ocean that complements traditional Eulerian and Lagrangian methods. Here we present a derivation of a WMT framework that offers an analysis that renders novel insights and predictive capabilities for studies of ocean physics and biogeochemistry that determine ocean tracer uptake, circulation and storage. We will discuss application for this framework for biogeochemical studies and its potential for inferring unmeasurable biogeochemical processes from estimates of the measurable physical processes.

How to cite: Groeskamp, S.: The Water Mass Transformation Framework for Ocean Physics and Biogeochemistry, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5476, https://doi.org/10.5194/egusphere-egu2020-5476, 2020

D2332 |
EGU2020-3628
| Highlight
Alice Marzocchi, George Nurser, Louis Clement, and Elaine McDonagh

Changes in regional ocean heat content are not only sensitive to anthropogenic and natural influences, but also substantially impacted by the redistribution of heat, which is in turn driven by changes in ocean circulation and air-sea fluxes. Using a set of numerical simulations with an ocean-sea-ice model of the NEMO framework, we assess where the ocean takes up heat from the atmosphere and how ocean currents transport and redistribute that heat. Here, the strength and patterns of the net uptake of heat by the ocean are treated like a passive tracer, by including simulated sea water vintage dyes, which are released annually between 1958 and 2017. An additional tracer released in year 1800 is also used to investigate longer-term variability. All dye tracers are released from 29 surface patches, representing different water mass production sites, allowing us to identify when and where water masses were last ventilated. The tracers’ distribution and fluxes are shown to capture years of strong and weak convection at deep and mode water formation sites in both hemispheres, when compared to the available observations. Using this approach, which can be applied to any passive tracer in the ocean, we can: (1) assess the relative role of each of the water mass production sites, (2) evaluate the regional and depth distribution of the tracers, and (3) determine their variability on interannual, multidecadal and centennial time scales.

How to cite: Marzocchi, A., Nurser, G., Clement, L., and McDonagh, E.: Pathways and time scales of ocean heat uptake and redistribution in a global ocean-ice model, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3628, https://doi.org/10.5194/egusphere-egu2020-3628, 2020

D2333 |
EGU2020-4696
Till Kuhlbrodt, Aurore Voldoire, Matthew Palmer, Rachel Killick, and Colin Jones

Ocean heat content is arguably one of the most relevant metrics for tracking global climate change and in particular the current global heating. Because of its enormous heat capacity, the global ocean stores about 93 percent of the excess heat in the Earth System. Time series of global ocean heat content (OHC) closely track Earth’s energy imbalance as observed as the net radiative balance at the top of the atmosphere. For these reasons simulated OHC time series are a cornerstone for assessing the scientific performance of Earth System models (ESM) and global climate models. Here we present a detailed analysis of the OHC change in simulations of the historical climate (20th century up to 2014) performed with four of the current, state-of-the art generation of ESMs and climate models. These four models are UKESM1, HadGEM3-GC3.1-LL, CNRM-ESM2-1 and CNRM-CM6-1. All four share the same ocean component, NEMO3.6 in the shaconemo eORCA1 configuration, and they all take part in CMIP6, the current Phase 6 of the Coupled Model Intercomparison Project. Analysing a small number of models gives us the opportunity to analyse OHC change for the global ocean as well as for individual ocean basins. In addition to the ensemble means, we focus on some individual ensemble members for a more detailed process understanding. For the global ocean, the two CNRM models reproduce the observed OHC change since the 1960s closely, especially in the top 700 m of the ocean. The two UK models (UKESM1 and HadGEM3-GC3.1-LL) do not simulate the observed global ocean warming in the 1970s and 1980s, and they warm too fast after 1991. We analyse how this varied performance across the models relates to the simulated radiative forcing of the atmosphere. All four models show a smaller ocean heat uptake since 1971, and a larger transient climate response (TCR), than the CMIP5 ensemble mean. Close analysis of a few individual ensemble members indicates a dominant role of heat uptake and deep-water formation processes in the Southern Ocean for variability and change in global OHC. Evaluating OHC change in individual ocean basins reveals that the lack of warming in the UK models stems from the Pacific and Indian basins, while in the Atlantic the OHC change 1971-2014 is close to the observed value. Resolving the ocean warming in depth and time shows that regional ocean heat uptake in the North Atlantic plays a substantial role in compensating small warming rates elsewhere. An opposite picture emerges from the CNRM models. Here the simulated OHC change is close to observations in the Pacific and Indian basins, while tending to be too small in the Atlantic, indicating a markedly different role for the Atlantic meridional overturning circulation (AMOC) and cross-equatorial heat transport in these models.

How to cite: Kuhlbrodt, T., Voldoire, A., Palmer, M., Killick, R., and Jones, C.: Historical ocean heat uptake in CMIP6 Earth System models: global and regional perspectives, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4696, https://doi.org/10.5194/egusphere-egu2020-4696, 2020

How to cite: Kuhlbrodt, T., Voldoire, A., Palmer, M., Killick, R., and Jones, C.: Historical ocean heat uptake in CMIP6 Earth System models: global and regional perspectives, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4696, https://doi.org/10.5194/egusphere-egu2020-4696, 2020

How to cite: Kuhlbrodt, T., Voldoire, A., Palmer, M., Killick, R., and Jones, C.: Historical ocean heat uptake in CMIP6 Earth System models: global and regional perspectives, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4696, https://doi.org/10.5194/egusphere-egu2020-4696, 2020

D2334 |
EGU2020-3703
Yona Silvy, Eric Guilyardi, Jean-Baptiste Sallée, and Paul Durack

The World Ocean is rapidly changing, with global and regional modification of temperature and salinity evident at the surface and depth. These changes have widespread and irreversible impacts including sea-level rise, changes to the oxygen and carbon contents of the ocean interior, or changing habitats, diversity and resilience of ecosystems. While the most pronounced temperature and salinity changes are located in the upper few hundred metres, changes in water-masses at depth are already observed and will likely strengthen and persist in the future as water-masses form at the surface and propagate in the deep ocean along density surfaces, storing the anthropogenic signal away from the atmosphere for decades to millennia. Here, using 11 climate models, we define when anthropogenic temperature and salinity changes are expected to emerge from natural background variability in the ocean interior. On a basin-scale zonal average, the model simulations predict that in 2020, 20–55% of the Atlantic, Pacific and Indian basins have an emergent anthropogenic signal; reaching 40–65% in 2050, and 55–80% in 2080. The well-ventilated Southern Ocean water-masses emerge very rapidly, as early as the 1980s-1990s, while the Northern Hemisphere emerges in the 2010s to 2030s. Additionally, dedicated idealized simulations of the IPSL coupled climate model are examined to study the role of each separate surface forcing on the time scales associated with the patterns of temperature and salinity change under a global warming scenario, and the influence of excess versus redistributed heat and salt. Our results highlight the importance of maintaining and augmenting an ocean observing system capable of detecting and monitoring anthropogenic changes. 

How to cite: Silvy, Y., Guilyardi, E., Sallée, J.-B., and Durack, P.: Human-induced changes to the global ocean water masses and their time of emergence, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3703, https://doi.org/10.5194/egusphere-egu2020-3703, 2020

D2335 |
EGU2020-18438
| Highlight
Matthew Couldrey and Jonathan Gregory

Thermosteric sea level change, resulting from ocean heat uptake, is a key component of recent and future sea level rise. The various atmosphere-ocean general circulation models (AOGCMs) used to predict future climate produce diverse spatial patterns of future thermosteric sea level rise. Most of this model spread occurs because the representation of ocean circulation and heat transport is different across models. These effects can be analysed through new simulations carried out as part of the Flux Anomaly Forced Intercomparison Project (FAFMIP), in which the exchanges of heat and salt are attributed to specific ocean circulation processes, namely the vertical dianeutral processes (convection, boundary layer mixing, shear instability mixing etc), isopycnal diffusion and residual-mean advection. Here, we present an intercomparison of ocean heat content change in FAFMIP experiments from a water-mass following perspective, to distinguish oceanic heat redistribution and uptake. We find that the redistribution of heat is a key difference across AOGCMs.

How to cite: Couldrey, M. and Gregory, J.: Intercomparison of anthropogenic ocean heat uptake processes in AOGCMs, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18438, https://doi.org/10.5194/egusphere-egu2020-18438, 2020

D2336 |
EGU2020-5575
| Highlight
Laura Jackson, Clotilde Dubois, Gael Forget, Keith Haines, Matt Harrison, Dorotea Iovino, Armin Kohl, Davi Mignac, Ssimona Masina, Drew Peterson, Christopher Piecuch, Chris Roberts, Jon Robson, Andrea Storto, Takahiro Toyoda, Maria Valdivieso, Chris Wilson, Yiguo Wang, and Hao Zuo

The observational network around the North Atlantic has improved significantly over the last few decades with the advent of Argo and satellite observations, and the more recent efforts to monitor the Atlantic Meridional Overturning Circulation (AMOC) using arrays such as RAPID and OSNAP. These have shown decadal timescale changes across the North Atlantic including in heat content, heat transport and the circulation. 

However there are still significant gaps in the observational coverage, and significant uncertainties around some observational products. Ocean reanalyses integrate the observations with a dynamically consistent ocean model and are potentially tools that can be used to understand the observed changes. However the suitability of the reanalyses for the task must also be assessed.
We use an ensemble of global ocean reanalyses in comparison with observations in order to examine the mean state and interannual-decadal variability of the North Atlantic ocean since 1993. We assess how well the reanalyses are able to capture different processes and whether any understanding can be inferred. In particular we look at ocean heat content, transports, the AMOC and gyre strengths, water masses and convection. 

 

How to cite: Jackson, L., Dubois, C., Forget, G., Haines, K., Harrison, M., Iovino, D., Kohl, A., Mignac, D., Masina, S., Peterson, D., Piecuch, C., Roberts, C., Robson, J., Storto, A., Toyoda, T., Valdivieso, M., Wilson, C., Wang, Y., and Zuo, H.: The mean state and variability of the North Atlantic circulation: a perspective from ocean reanalyses, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5575, https://doi.org/10.5194/egusphere-egu2020-5575, 2020

D2337 |
EGU2020-8192
| Highlight
Bogi Hansen, Karin M. H. Larsen, Hjálmar Hátún, and Svein Østerhus

Warm and saline water from the North Atlantic enters the Arctic Mediterranean through three gaps. The strongest of these three flows is the inflow between Iceland and Faroes, which is focused into a narrow boundary current north of the Faroes. This boundary current, the Faroe Current, has been observed with regular CTD cruises since 1988 and with moored ADCPs since 1997, as well as satellite altimetry since 1993. Once calibrated by the long-term ADCP measurements, the satellite altimetry is found to yield high-accuracy determination of the velocity field and volume transport down to fixed depth. Due to geostrophic adjustment, satellite altimetry combined with CTD data also allow fairly accurate determination of the depth of the Atlantic layer. From the combined data set, monthly transport time series have been generated for the period Jan 1993 to April 2019. Over the period, the annually averaged volume transport of Atlantic water in the Faroe Current seems to have increased slightly, while the heat transport relative to an outflow temperature of 0°C increased by 13%, significant at the 95% level. The salinity increased from the mid-1990s to around 2010, after which it has decreased, especially after 2016, leading to the lowest salinities in the whole period since 1988. To stay updated on a possible inflow reduction due to reduced thermohaline ventilation caused by this freshening, the future monitoring system of the Faroe Current is planned to be expanded with moored PIES (Pressure Inverted Echo Sounders). An experiment with two PIES in 2017-2019 has documented that these instruments allow high-accuracy monitoring of the depth of the Atlantic layer on the section, which combined with satellite altimetry and CTD observations should give more accurate transport estimates.

How to cite: Hansen, B., Larsen, K. M. H., Hátún, H., and Østerhus, S.: Long-term observations of the strongest inflow branch of warm water to the Arctic Mediterranean, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8192, https://doi.org/10.5194/egusphere-egu2020-8192, 2020

D2338 |
EGU2020-18974
Virginie Thierry, Tillys Petit, and Herlé Mercier

The Reykjanes Ridge strongly influences the circulation of the North Atlantic Subpolar Gyre as it flows to the Irminger Sea from the Iceland Basin. The circulation is composed of two main along‐ridge currents: the southwestward East Reykjanes Ridge Current (ERRC) in the Iceland Basin and the northeastward Irminger Current (IC) in the Irminger Sea. To study their interconnection through the ridge, as well as their connections with the interior of each basin, velocity and hydrological measurements were carried out along and perpendicular to the crest of the Reykjanes Ridge in June–July 2015 as part of the Reykjanes Ridge Experiment project. This new data set changes our view of the ERRC and IC as it reveals undocumented along‐stream evolutions of their hydrological properties, structures, and transports. These evolutions are due to flows connecting the ERRC and IC branches at specific locations set by the bathymetry of the ridge and to significant connections with the interiors of the basins. Overall, the ERRC transport increases by 3.2 Sv between 63°N and 59.5°N and remains almost constantly southward. In the Irminger Sea, the increase in IC transport of 13.7 Sv between 56°N and 59.5°N, and the evolution of its properties are explained by both cross‐ridge flows and inflows from the Irminger Sea. Further north, bathymetry steers the IC northwestward into the Irminger Sea. At 63°N, the IC water masses are mostly issued from the cross-ridge flow.

How to cite: Thierry, V., Petit, T., and Mercier, H.: New Insight Into the Formation and Evolution of the East Reykjanes Ridge Current and Irminger Current, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18974, https://doi.org/10.5194/egusphere-egu2020-18974, 2020

D2339 |
EGU2020-9280
Joleen Heiderich and Robert E. Todd

The Gulf Stream is the western boundary current in the subtropical North Atlantic and a principal component of the upper limb of the Atlantic Meridional Overturning Circulation. Thus, it plays an important role in poleward heat and volume transport, as well as in the redistribution and modification of various water masses. Despite its importance in the climate system, many details of the Gulf Stream’s increase in volume along the US East Coast and the associated entrainment of various water masses are not well known due to a paucity of sustained subsurface measurements within and near the Gulf Stream. Observations from more than 30 Spray autonomous underwater glider missions comprising over 22,000 profiles and more than 180 distinct cross-Gulf Stream transects collected between 2004 and the present fill a 1,500-km-long gap in sustained subsurface measurements; they provide concurrent measurements of hydrography and velocity in and near the Gulf Stream over more than 15 degrees of latitude between Florida and New England. These observations are used to characterize the along-stream evolution of Gulf Stream volume transport including classification by water properties. Remotely formed intermediate waters (i.e., Antarctic Intermediate Water (AAIW) and upper Labrador Sea Water (uLSW)) are significant components of Gulf Stream transport. AAIW is formed at high southern latitudes and enters the Gulf Stream through the Florida Strait, while uLSW is formed through deep convection in the Labrador Sea and encounters the Gulf Stream at Cape Hatteras as the uppermost layer of the Deep Western Boundary Current. Though it is well known where AAIW and uLSW initially encounter the Gulf Stream, their distribution, advection, and modification within the Gulf Stream remain poorly resolved. The extensive glider observations are used to characterize the evolution and intermittency of AAIW and uLSW pathways within and near the Gulf Stream, including effects of near-bottom mixing and the mechanisms by which uLSW crosses isobaths to arrive over the O(1000)-m-deep Blake Plateau south of Cape Hatteras. This first look at Gulf Stream transport by water class and the three-dimensional pathways followed by intermediate water masses within the Gulf Stream provides a reference for global circulation models to replicate.

How to cite: Heiderich, J. and Todd, R. E.: Along-stream evolution of Gulf Stream volume transport and water properties from underwater glider observations, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9280, https://doi.org/10.5194/egusphere-egu2020-9280, 2020

D2340 |
EGU2020-10226
| Highlight
Herle Mercier and Marie-Jose Messias

The oceans have mitigated global warming by the absorption of 90% of the excess heat resulting from anthropogenic radiative forcing and of 1/3 of the anthropogenic carbon (Cant). There are still major uncertainties concerning their regional rates of uptake (or loss), transport and storage by the oceans, knowledge of which is key to the heat and carbon balances, and essential to reduce the uncertainties in global warming prediction. Here, we used tracers observations (transient and passive CFC-11, CFC-12, SF6, natural C14, the conservative PO4* and NO3*, salinity and temperature) and a maximum entropy inverse method to compute Green’s functions (G), which contain intrinsically information on ocean dynamics and transit times from the source regions. From G, we propagated surface history of temperature and Cant to reconstruct their fields in the ocean for the industrial era and to quantify their source regions. We present reconstructions of Cant and excess heat (taken as the temperature anomaly from 1850) along the 24°N trans-Atlantic section, at the crossroads of the main contributors of the AMOC and an hot spot of heat and carbon storage, from 5 repeats spanning 1992 to 2015. We show that Cant reconstructions, dominated by the strong increase of Cant in the atmosphere, compare well with a previous global historical reconstruction as well as Cant estimates in the water masses at 24°N. The excess heat reconstructions are tempered by the natural variability that can exceed the anthropogenic trend. They show a net invasion and warming of the top 800m from the 1920’s (0.01°C/y). The trend slightly weakens in the late 1970’s followed by an acceleration from the 2000’s (0.02°C/y). For the well–ventilated deeper waters of the DWBC around 1500m, after a notable cooling period, a weak warming departs in the 1950’s with a trend of 0.001°C/y up to the 2000’s and of 0.006°C/y afterwards. The waters below 2000m suggest a continuous warming from the 1930’s, with a more pronounced trend centered at 3000m of 0.001°C/y up to the 2000’s and of 0.003°C/y afterwards. This excess heat evolution in the DWBC contrasts with the Cant evolution which shows continuous increase in Cant content in the upper NADW. Our results highlight the difference of drowning up of Cant ant heat into the deeper ocean, reflecting their different surface histories in the formation regions.

How to cite: Mercier, H. and Messias, M.-J.: Historical Reconstruction of Anthropogenic Carbon and Excess Heat Content in the Subtropical North Atlantic Ocean, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10226, https://doi.org/10.5194/egusphere-egu2020-10226, 2020

D2341 |
EGU2020-6123
Marion Kersalé, Christopher Meinen, Renellys Perez, Matthieu Le Hénaff, Daniel Valla, Tarron Lamont, Olga Sato, Shenfu Dong, Thierry Terre, Mathias van Caspel, Maria Paz Chidichimo, Marcel van den Berg, Sabrina Speich, Alberto Piola, Edmo Campos, Isabelle Ansorge, Denis Volkov, Rick Lumpkin, and Silvia Garzoli

Variations in the Meridional Overturning Circulation (MOC) are known to have important impacts on global scale climate phenomena including precipitation patterns, surface air temperatures, coastal sea level, and extreme weather. The MOC flow structure in the South Atlantic is thought to control the stability of the entire global MOC system. Given this importance, significant resources have been invested on observing the MOC in the South Atlantic over the past decade. Multiple years of full-depth daily observations from moored instruments at 34.5°S are used to calculate the meridional transports near the western and eastern boundaries, as well as the basin-wide interior transports, via geostrophic methods. These transport estimates are combined with Ekman transports derived from satellite wind products to yield daily estimates of the total meridional transports. Analysis of the MOC volume transport using all available moored instruments from 2013 to 2017 allows us to quantify for the first time the daily volume transport of both the upper and abyssal overturning cells at 34.5°S. The structure of these flows is characterized in unprecedented detail; no statistically significant trend is detectable in either cell. Abyssal-cell transport variability is largely independent of the transport variability in the upper-cell. Analysis of this new data set is crucial for improving our understanding of the temporal and spatial scales of variability that governs MOC related flows, and for disentangling their respective roles in modulating its overall variability.

How to cite: Kersalé, M., Meinen, C., Perez, R., Le Hénaff, M., Valla, D., Lamont, T., Sato, O., Dong, S., Terre, T., van Caspel, M., Chidichimo, M. P., van den Berg, M., Speich, S., Piola, A., Campos, E., Ansorge, I., Volkov, D., Lumpkin, R., and Garzoli, S.: Temporal Variability of the Meridional Overturning Cells in the South Atlantic, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6123, https://doi.org/10.5194/egusphere-egu2020-6123, 2020

D2342 |
EGU2020-4202
Atanas Palazov, Snejana Moncheva, Elisaveta Peneva, Ivan Ivanov, Rumen Kishev, Elitca Petrova, Peycho Kaloyanchev, Christo Pirovsky, and Dimitar Stavrev

MASRI – Infrastructure for Sustainable Development of Marine Research Including the Participation of Bulgaria in the European Infrastructure Euro-Argo is a project of the National roadmap for scientific Infrastructure (2017-2023) of Bulgaria. The mission of MASRI is to build and utilize a modern research infrastructure which will provide the basis for highly efficient marine and maritime research to expand our knowledge of the marine environment and to support blue growth and implementation of marine policy and maritime spatial planning in order to achieve UN Sustainable Development Goal 14: Conservation and sustainable use of oceans, seas and marine resources for sustainable development.

MASRI activities include the modernization of existing unique resources and equipment and the establishment of new facilities. The research infrastructure consists of four main modules: Research fleet; National Operational Marine Observing System – NOMOS; Data and information center and Research laboratory complex, each representing a distinct on functional basis part of the scientific infrastructure, and consists of separate components distributed physically in different scientific organizations, in the city of Varna. Thus, MASRI is intended to be a large-scale, interdisciplinary multifunctional (physics, chemistry, biology, geology, aquacultures, medicine, energy, underwater, and offshore technologies) marine research infrastructure of scientific significance and will provide unique facilities (including databases and computer network) which will be widely accessible on national, regional and international level for multidisciplinary researches.

Research vessels are intended to provide access to the investigated medium – the sea and they are providing a working platform for conducting research. NOMOS is a system of systems to measure in situ parameters of the marine environment and the surrounding atmosphere. It is designed to provide information on the state of the marine environment for scientific research, forecasting and marine industry. Data and information center provide a computing environment, communication environment and environment for quality control and reliable storage of data and information within the scientific infrastructure. Research laboratory Complex represents a system of research laboratories for chemical, biological and geological analyzes and for relevant research on marine medicine as well as of laboratories for marine resources and technologies research.

As an important module of MASRI, NOMOS includes several components: BulArgo – a system of profiling floats to measure the profiles of the characteristics of the marine environment in the depth up to 2000m; waves and currents monitoring system; national sea level observing system; moorings network; coast research bases and metrological control laboratory.

MASRI is also intended to support the participation of Bulgaria in European research infrastructure consortia Euro-Argo ERIC. Al least three floats are provided and launched in the Black sea every year in the frame of the BulArgo project. Thus, BulArgo gives an important contribution to the Argo program in particular in the Black sea, providing a significant volume of very important in-situ data both for climatic research, for assimilation into the models and verification of the forecasts.

How to cite: Palazov, A., Moncheva, S., Peneva, E., Ivanov, I., Kishev, R., Petrova, E., Kaloyanchev, P., Pirovsky, C., and Stavrev, D.: Infrastructure for Sustainable Development of Marine Research, Including the Participation of Bulgaria in the European Infrastructure Euro-Argo, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4202, https://doi.org/10.5194/egusphere-egu2020-4202, 2020

D2343 |
EGU2020-9044
Kerstin Jochumsen, Ralf Bachmayer, Burkard Baschek, Angelika Brandt, Jan-Stefan Fritz, Birgit Gaye, Felix Janssen, Johannes Karstensen, Alexandra Kraberg, Pedro Martinez, Annemiek Vink, and Oliver Zielinski

Germany’s national ocean observing activities are carried out by multiple actors including governmental bodies, research institutions, and universities, and miss central coordination and governance. A particular strategic approach to coordinate and facilitate ocean research has formed in Germany under the umbrella of the German Marine Research Consortium (KDM). KDM aims at bringing together the marine science expertise of its member institutions and collectively presents them to policy makers, research funding organizations, and to the general public. Within KDM, several strategic groups (SGs), composed of national experts, have been established in order to strengthen different scientific and technological aspects of German Marine Research. Here we present the SG for sustained open ocean observing and the SG for sustained coastal observing. The coordination effort of the SG’s include (1) Representing German efforts in ocean observations, providing information about past, ongoing and planned activities and forwarding meta-information to data centers (e.g., JCOMMOPS), (2) Facilitating the integration of national observations into European and international observing programs (e.g. GCOS, GOOS, BluePlanet, GEOSS), (3) Supporting innovation in observing techniques and the development of scientific topics on observing strategies, (4) Developing strategies to expand and optimize national observing systems in consideration of the needs of stakeholders and conventions, (5) Contributing to agenda processes and roadmaps in science strategy and funding, and (6) Compiling recommendations for improved data collection and data handling, to better connect to the global data centers adhering to quality standards.

How to cite: Jochumsen, K., Bachmayer, R., Baschek, B., Brandt, A., Fritz, J.-S., Gaye, B., Janssen, F., Karstensen, J., Kraberg, A., Martinez, P., Vink, A., and Zielinski, O.: Coordinating sustained coastal and ocean observing efforts in Germany, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9044, https://doi.org/10.5194/egusphere-egu2020-9044, 2020

D2344 |
EGU2020-11585
Richard Cornes, Elizabeth Kent, David Berry, and John Kennedy

We describe the construction of a new global dataset of Night Marine Air Temperature (NMAT), which provides monthly 5-degree values of NMAT back to 1880 with associated uncertainty estimates. The new dataset (CLASSnmat) builds on the HadNMAT2 dataset, which was released in 2013. CLASSnmat uses the ship-based NMAT values from the International Comprehensive Ocean-Atmosphere Data Set (ICOADS Release 3). However, a new method is used in CLASSnmat to remove duplicated values from the observations, and to infill missing ship identifiers. In addition, a revised method of correcting the warm-bias that occurs in the data during World 2 is applied, which allows the retention of more data than in HadNMAT2. As with its predecessor, the NMAT data in CLASSnmat are not interpolated to grid-cells devoid of observations, but a revised gridding method is used which improves the propagation of uncertainty from the individual measurements through to the gridded values. CLASSnmat is released with NMAT values corrected to 2, 10 and 20m height to allow direct comparison against other measures of temperature, e.g. land-based observations or reanalysis temperature values.

How to cite: Cornes, R., Kent, E., Berry, D., and Kennedy, J.: CLASSnmat: a new dataset of Night Marine Air Temperature back to 1880, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11585, https://doi.org/10.5194/egusphere-egu2020-11585, 2020

D2345 |
EGU2020-20408
| Highlight
Luca Centurioni and Verena Hormann

Accurate estimates and forecasts of physical and biogeochemical processes at the air-sea interface must rely on integrated in-situ and satellite surface observations of essential Ocean/Climate Variables (EOVs /ECVs). Such observations, when sustained over appropriate temporal and spatial scales, are particularly powerful in constraining and improving the skills, impact and value of weather, ocean and climate forecast models. The calibration and validation of satellite ocean products also rely on in-situ observations, thus creating further positive high-impact applications of observing systems designed for global sustained observations of EOV and ECVs.

The Global Drifter Program has operated uninterrupted for several decades and constitutes a particular successful example of a network of multiparametric platforms providing observations of climate, weather and oceanographic relevance (e.g. air-pressure, sea surface temperature, ocean currents). This presentation will review the requirements of sustainability of an observing system such as the GDP (i.e. cost effectiveness, peer-review of the observing methodology and of the technology, free data access and international cooperation), will present some key metrics recently used to quantify the impact of drifter observations, and will discuss two prominent examples of GDP regional observations and the transition to operations of novel platforms, such us wind and directional wave spectra drifters, in sparsely sampled regions of the Arabian Sea and of the North Atlantic Ocean.

How to cite: Centurioni, L. and Hormann, V.: Global In-Situ Observations of Essential Climate and Ocean Variables by the Global Drifter Program. Applications and Impacts, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20408, https://doi.org/10.5194/egusphere-egu2020-20408, 2020

D2346 |
EGU2020-7828
Charles Turner, Kevin Oliver, Peter Brown, and Elaine McDonagh

Whilst anthropogenic activities are significantly altering the climate, both warming the atmosphere and increasing CO2, the ocean is

significantly ameliorating both effects. This effect is so important that the transient climate response to carbon emissions (TCRE), can be

formulated primarily in terms of the ocean. We show that in direct analogy to the TCRE, Anthropogenic Carbon (Canth) and temperature increases in the ocean are

linearly related, both globally and integrated over a range of scales. These ocean responses are typically of order 0.02K/mumol/kg,

(equivalently ~80MJ/mol). This linear relation allows for direct translation between temperature and carbon inventory increases. Furthermore,

we are far better able to decompose DIC changes into Canth increases and that of other carbon pools, than we are decomposing heat

inventory changes into added and redistributed heat. By separating total DIC change into Canth and that of other carbon pools, we can therefore remove the effect

of the transient response relationship between heat and carbon. This allows the production of estimates of added and redistributed heat in the

ocean from remaining DIC changes. Our results suggest that the variability of the transient response is predominately set by heat uptake, not carbon, and that this

variability may be traced to individual water masses. Therefore, it may be necessary to separate this transient response regionally in order

to obtain accurate estimates of added and redistributed heat at a global scale using this technique. The Eulerian transient response is set

predominantly by isotherm heave. The part of the transient response set by climate sensitivity, analogous to a semi-Lagrangian approach, is

set largely by patterns of regional heat uptake.

How to cite: Turner, C., Oliver, K., Brown, P., and McDonagh, E.: Heat and carbon changes in the ocean as a transient response and tool for decomposing heat uptake, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7828, https://doi.org/10.5194/egusphere-egu2020-7828, 2020

D2347 |
EGU2020-20822
Rene Navarro-Labastida and Riccardo Farneti

The aim of the project is to evaluate the response of the global ocean climate to anomalous surface fluxes in terms of ocean heat uptake and circulation changes. All simulations have been performed with the NOAA-GFDL Modular Ocean Model (MOM) version 5. Ocean-only MOM has been integrated toward a near-equilibrium state using as multicentinal initial conditions derivated from a former CORE-I protocol implementation (Griffies et al., 2009). After equilibrium, a restored control simulation has been obtained by a further 70 years of integration while effective total air-sea heat fluxes and freshwater fluxes were stored at daily intervals. A second control simulation has been obtained by the prescription of these storage fluxes. Differences between the restored and prescribed fluxes controls are rather small. Explicit flux sensitivity experiments are proposed by the Flux-Anomaly-Forced Model Intercomparison Project (FAFMIP) in which prescribed surface flux perturbations are applied to the ocean in separated simulations (Gregory et al., 2016). Experiments are 70 years long and branch from piControl conditions. Both wind stress and freshwater anomalies implies nearly-to-zero temperature changes in volume mean temperature. Only the last implies a rather small cooling effect after year 50 of integration. In contrast, anomalous heat flux causes significant volume mean temperature changes. Observed total temperature changes are solely determined by the local addition of heat implying vanishing of the redistribution effect in the entire ocean by inter-basin exchanges and vertical mixing. So far, surface heat anomalies produce the most notable zonal-mean change in ocean temperature. Strong positive temperature change is observed along the top ocean while deepening of temperature anomalies occurs at high latitudes in both hemispheres. Both added and redistributed temperature tracers show maxima in the same area. In most cases, both processes are proportionally inverse. Except for the northern ocean, added temperature tracer is roughly limited to the first 1000 m deep. In contrast, redistributed temperature tracer shows the cooling of subtropical areas and the warming of both the tropical and southern ocean. Maximum at the North Atlantic is possibly due to atmosphere-sea feedbacks, while near-surface tropical and subtropical changes are due to redistribution processes. Heat is mainly taken as a passive tracer in the North Atlantic Ocean and along the entire Southern Ocean. Warming up of mid and low latitudes by redistribution processes is due to the weakening of the Atlantic Meridional Overturning Circulation (AMOC). In turn, changes in AMOC are dominated by surface heat flux changes. The reduction of northward heat transport cools down high latitudes near the surface causing low latitudes to warm up.

 

How to cite: Navarro-Labastida, R. and Farneti, R.: Ocean climate response to anomalous surface buoyancy and momentum fluxes, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20822, https://doi.org/10.5194/egusphere-egu2020-20822, 2020

D2348 |
EGU2020-10120
Peter Shatwell, Arnaud Czaja, and David Ferreira

Over 90% of the excess heat energy due to global warming is taken up by the oceans. Because of this, ocean heat uptake and planetary heat uptake can be considered equivalent. This heat energy is readily taken up by the oceanic mixed-layer on decadal timescales and subsequently transferred to the thermocline and deep ocean below on longer, centennial timescales by different ventilation mechanisms. The ventilation rate is affected by many things including the mixed-layer depth, the strength of the overturning, and mode-water formation. In current two-layer energy-balance models (EBMs), all ventilation mechanisms are reduced and parameterised by a simple linear vertical heat-exchange term that depends on the temperature difference between the upper and lower layers (representing the mixed-layer and deep ocean, respectively). 

Two-layer EBMs have been used successfully to reproduce the global mean surface temperature responses for CMIP5 models in abrupt CO2-quadrupling experiments. Little attention has been paid to the EBM-predicted deep ocean response, however. We perform an abrupt CO2-doubling experiment using an idealised aquaplanet model with a simple geometry that splits the ocean into small, large, and southern ocean basins. By fitting a two-layer EBM regionally to each basin's deep temperature response, we find that it provides a good fit only for the small basin. We suggest this is due to the small basin exhibiting a deep overturning circulation — not seen in the other model basins — which connects the ocean surface to its interior; only this ventilation mechanism can be successfully parameterised by a linear vertical heat-exchange. By considering the wind-driven circulation theory of Rhines and Young, we suggest a new parameterisation for the two-layer EBM deep ocean heat uptake that may be more suitable for basins without deep overturning.

How to cite: Shatwell, P., Czaja, A., and Ferreira, D.: On the suitability of two-layer energy-balance models for representing deep ocean heat uptake, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10120, https://doi.org/10.5194/egusphere-egu2020-10120, 2020

D2349 |
EGU2020-6157
Yanxu Chen, Sabrina Speich, and Laurent Bopp

Mode water formation results from air-sea exchange processes in association with the dynamics and thermodynamics of ocean currents or fronts in every ocean basin. Here, a new algorithm is applied to the Argo global array to define surface mixed layer depths and to detect mode waters with homogeneous properties underneath. Specifically, we revisit the spatial and temporal evolution of South Atlantic subtropical mode water (SASTMW) using this new algorithm and find that our set of criteria is more precise than previous detections of mode water. With satellite altimetry measurements and eddy tracking algorithms (Laxenaire et al., 2018), the colocalization between mesoscale eddies and mode waters can be achieved. We then test how much the profiles indicative of mode water are matched with locations of mesoscale eddies and to what extent these eddies influence mode water variability. In addition, we investigate the relationship between the temporal integral of surface heat flux with the heat stored within the layers of the SASTMWs during the formation periods. Nearly all Argo profiles indicate that mode water formation occurs at the time and within the region where loss of latent heat flux from ocean to the atmosphere is significant. Anticyclonic eddies, specifically, play a crucial role in heat redistribution associated with mode waters advected by the subtropical gyre.

How to cite: Chen, Y., Speich, S., and Bopp, L.: Effect of mesoscale eddies on subtropical mode water formation and ocean heat storage, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6157, https://doi.org/10.5194/egusphere-egu2020-6157, 2020

D2350 |
EGU2020-11409
Frank Nilsen, Eli Anne Ersdal, and Ragnheid Skogseth

The pathway by which Atlantic Water ultimately inflows to the Arctic Ocean via the Yermak Plateau are of great interest for improving the current understanding of the evolving state of the European Arctic. The Arctic branches of the West Spitsbergen Current (WSC), i.e. the Svalbard Branch (SB), the Yermak Pass Branch (YPB) and the Yermak Branch (YB), are the primary routes through which warm AW enters the Arctic Ocean (AO). These branches either flow around (YB) or passes (SB, YPB) over the Yermak Plateau, the Arctic Sill, which is a topographic obstacle for warm water intrusion to the Arctic and possible melting of sea ice. In addition, The Spitsbergen Polar Current (SPC), carrying fresh costal and Arctic type water from the Barents Sea has to cross the Yermak Platea along the northwestern corner of the Spitsbergen coastline. In order to reveal the dynamics across the YP and the roles of the different AW branches in heat flux variability across this arctic sill, a set of in situ ocean data, ocean climatology (UNIS HD), reanalyzed atmospheric data (NORA10) and altimetry data products from Ssalto/Duacs (CMEMS), where synthesized in order to study the seasonal and year-to-year variability in ocean currents across the YP. In situ data from the Remote Sensing of Ocean Circulation and Environmental Mass Changes (REOCIRC) project consist of water time series of temperature, salinity, ocean current and Ocean Bottom Pressure (OBP), which covered the SB and the SPC. Air-ocean interaction mechanisms for controlling volume transport and heat fluxes in the SB and SPC are presented, and further linked to the variability of the other primary AW routes towards the AO. Moreover, surface geostrophic currents from Absolute Dynamic Topography (ADT) are calibrated against the geostrophic bottom current calculated from in situ OBP recorders. Estimates of winter volume- and heat transports across the YP for the time period 1993-2019 are presented, and interannual variability in the SB linked to the WSC and other AW branches are discussed together with consequences for sea ice melting north of Svalbard.

How to cite: Nilsen, F., Ersdal, E. A., and Skogseth, R.: Atlantic- and Arctic Water transport across the Yermak Plateau, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11409, https://doi.org/10.5194/egusphere-egu2020-11409, 2020

D2351 |
EGU2020-17494
Kjersti Kalhagen, Frank Nilsen, Ragnheid Skogseth, Ilker Fer, Zoé Koenig, and Eivind Kolås

On the continental slope north of Svalbard, Atlantic Water is transported eastward as a part of the Arctic Circumpolar Boundary Current. As inflow of Atlantic Water through the Fram Strait is the largest oceanic heat source to the Arctic Ocean, it is important to improve our knowledge about the dynamics and processes that govern the heat exchange between Atlantic Water and water masses of Arctic origin. This includes processes that enable lateral exchange across the shelf break or into the interior of the deep basin. Here, we study the vorticity dynamics on the slope and its contribution to the water mass modifications and heat exchange. Focusing on topographically trapped waves – sub-inertial oscillations trapped to follow the continental slope – we establish their existence and properties on the northern slope of Svalbard using a free baroclinic wave model. Their dependence on background stratification and current properties is explored in sensitivity analysis. Next, we discuss their contribution to lateral exchange from the boundary current on the slope to the continental shelf, troughs, and the deep Nansen Basin in the Arctic Ocean, including exchange associated with instabilities and resulting eddy shedding off the vorticity waves. Hydrographic and current time series from 2018-19 at two mooring arrays crossing the slope north of Svalbard (The Nansen Legacy project) are used to associate the observed physical environment with model-predicted topographic waves. Analysis of the in-situ data will determine which wave mode that can exist over the sloping seafloor and the observed hydrography and flow, and the model will give the corresponding spatial characteristics for the given frequencies and wave numbers. Energetic oscillations present in the observations are analyzed in light of the model results. Of special interest are the seasonal variability in hydrography and current strength and the resulting modification of the wave characteristics. Moreover, the interaction between the vorticity waves and tidal oscillations in the diurnal band is emphasized.

How to cite: Kalhagen, K., Nilsen, F., Skogseth, R., Fer, I., Koenig, Z., and Kolås, E.: Topographically trapped waves along the continental slope north of Svalbard, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17494, https://doi.org/10.5194/egusphere-egu2020-17494, 2020

D2352 |
EGU2020-10620
Frédéric Cyr, Olivia Gibb, David Bélanger, Guoqi Han, Gary Maillet, and Pierre Pepin

Located on a crossroads of some of the main currents associated to the Atlantic meridional overturning circulation (AMOC), Newfoundland and Labrador (NL) shelves are specially affected by changes in large-scale ocean circulation. Such circulation changes impact not only the regional climate, but also the overall water masses composition, with consequences on physical conditions, nutrient availability, oxygen content, pH, etc. Systematic hydrographic observations of this system have been carried out by Canada and other countries since 1948. The observational program was reinforced in 1999 with the creation of the Atlantic Zone Monitoring Program (AZMP), ensuring enhanced seasonal coverage and new biogeochemical observations. In 2014, this monitoring was augmented with the monitoring of ocean acidification parameters. Here we review historical physical-biogeochemical changes on the NL shelves, with an emphasis on low frequency variability and cycles. Results suggest, for example, that the cold intermediate layer (CIL), a cold mid-depth layer that is a key feature of the NL ecosystem, exhibited profound changes during the last 70 years. In the mid 60's, the CIL was anomalously warm compared to the rest of the time series. This warm period was followed by a cold period centered in the early 90's. Historical salinity records also suggest that fresher waters are found during warmer years, and vice-versa. Nitrate/Phosphate ratios suggest recent changes in water masses composition towards less Arctic waters flowing on the shelves. This is concurrent with a reduction in nutrients concentration on the NL shelves since about 2012, together with changes in the strength of the Labrador Current along the shelf.

How to cite: Cyr, F., Gibb, O., Bélanger, D., Han, G., Maillet, G., and Pepin, P.: Decadal physical-biogeochemical changes in the Newfoundland and Labrador ecosystem, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10620, https://doi.org/10.5194/egusphere-egu2020-10620, 2020

D2353 |
EGU2020-22652
Marie-José Messias and Herlé Mercier

Repeated hydrographic surveys have allowed for the monitoring of the 24.5°N trans-Atlantic transect of volume and heat transports  since the middle of the last century. However, identifying the geographic origins and the temporal characteristics of full depth ocean heat content (OHC) anomalies is still at the frontier of  global ocean warming research albeit it is critical to the  understanding of  the current warming of the ocean and its future evolution. To address this gap,  we  combine volume transports at 24.5°N  with an historical reconstruction of  excess heat, which we define as the heat gained across the section since the year 1850 to  present. The  reconstruction is based on  a maximum entropy approach  that links the  location and time of the last entry into the ocean of a series of transient and geochemical tracers to their full depth in situ measurements in the interior. Here, we apply it to tracers measured on the hydrographic sections at  24.5°N since 1992. This methodology is a step forward in exploring the coherence of the OHC distributions at 24.5°N over time with the variability of the SST in  the source regions and the role of the AMOC, all genuinely based on observations. We find that the AMOC ranges from 16 to 19 Sv, heat transport from 0.9 to 1.5 PW and excess heat transport from 19 to 31 TW. The excess heat is transported northward across 24.5°N thus reinforcing the warming of the North Atlantic Ocean.

How to cite: Messias, M.-J. and Mercier, H.: Transport of Excess Heat at 24.5°N, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22652, https://doi.org/10.5194/egusphere-egu2020-22652, 2020

D2354 |
EGU2020-10929
Absolute Brazil Current transport variability at 34.5°S from a long-term moored array
(withdrawn)
Maria Paz Chidichimo, Alberto R. Piola, Christopher S. Meinen, Edmo J. Campos, Renellys Perez, Daniel Valla, Shenfu Dong, Rick Lumpkin, and Silvia L. Garzoli