scholarly journals Combining in-situ measurements and altimetry to estimate volume, heat and salt transport variability through the Faroe Shetland Channel

2013 ◽  
Vol 10 (1) ◽  
pp. 153-195 ◽  
Author(s):  
B. Berx ◽  
B. Hansen ◽  
S. Østerhus ◽  
K. M. Larsen ◽  
T. Sherwin ◽  
...  
Keyword(s):  
Satellite Altimetry ◽  
Water Mass ◽  
Volume Transport ◽  
Salt Transport ◽  
The Arctic ◽  
Average Volume ◽  
Large Level ◽  
Height Data ◽  
Temperature Depth

Abstract. From 1994 to 2011, instruments measuring ocean currents (ADCPs) have been moored on a section crossing the Faroe-Shetland Channel. Together with CTD (Conductivity Temperature Depth) measurements from regular research vessel occupations, they describe the flow field and water mass structure in the channel. Here, we use these data to calculate the average volume transport and properties of the flow of warm water through the channel from the Atlantic towards the Arctic, termed the Atlantic inflow. We find the average volume transport of this flow to be 2.7 ± 0.5 Sv (1 Sv = 106 m3 s−1) between the shelf edge on the Faroe side and the 150 m isobath on the Shetland side. The average heat transport (relative to 0 °C) was estimated to be 107 ± 21 TW and the average salt import to be 98 ± 20 × 106 kg s−1. Transport values for individual months, based on the ADCP data, include a large level of variability, but can be used to calibrate sea level height data from satellite altimetry. In this way, a time series of volume transport has been generated back to the beginning of satellite altimetry in December 1992. The Atlantic inflow has a seasonal variation in volume transport that peaks around the turn of the year and has an amplitude of 0.7 Sv. The Atlantic inflow has become warmer and more saline since 1994, but no equivalent trend in volume transport was observed.

scholarly journals Combining in situ measurements and altimetry to estimate volume, heat and salt transport variability through the Faroe–Shetland Channel

Ocean Science ◽  
2013 ◽  
Vol 9 (4) ◽  
pp. 639-654 ◽  
Author(s):  
B. Berx ◽  
B. Hansen ◽  
S. Østerhus ◽  
K. M. Larsen ◽  
T. Sherwin ◽  
...  
Keyword(s):  
Satellite Altimetry ◽  
Volume Transport ◽  
Salt Transport ◽  
The Arctic ◽  
Average Volume ◽  
Large Level ◽  
Acoustic Doppler Current Profilers ◽  
Height Data ◽  
Temperature Depth

Abstract. From 1994 to 2011, instruments measuring ocean currents (Acoustic Doppler Current Profilers; ADCPs) have been moored on a section crossing the Faroe–Shetland Channel. Together with CTD (Conductivity Temperature Depth) measurements from regular research vessel occupations, they describe the flow field and water mass structure in the channel. Here, we use these data to calculate the average volume transport and properties of the flow of warm water through the channel from the Atlantic towards the Arctic, termed the Atlantic inflow. We find the average volume transport of this flow to be 2.7 ± 0.5 Sv (1 Sv = 106 m3 s–1) between the shelf edge on the Faroe side and the 150 m isobath on the Shetland side. The average heat transport (relative to 0 °C) was estimated to be 107 ± 21 TW (1 TW = 1012 W) and the average salt import to be 98 ± 20 × 106 kg s−1. Transport values for individual months, based on the ADCP data, include a large level of variability, but can be used to calibrate sea level height data from satellite altimetry. In this way, a time series of volume transport has been generated back to the beginning of satellite altimetry in December 1992. The Atlantic inflow has a seasonal variation in volume transport that peaks around the turn of the year and has an amplitude of 0.7 Sv. The Atlantic inflow has become warmer and more saline since 1994, but no equivalent trend in volume transport was observed.

scholarly journals Increasing transports of volume, heat, and salt towards the Arctic in the Faroe Current 1993–2013

2015 ◽  
Vol 12 (3) ◽  
pp. 1013-1050 ◽  
Author(s):  
B. Hansen ◽  
K. M. H. Larsen ◽  
H. Hátún ◽  
R. Kristiansen ◽  
E. Mortensen ◽  
...  
Keyword(s):  
Heat Transport ◽  
Thermohaline Circulation ◽  
Saline Water ◽  
Atlantic Water ◽  
Volume Transport ◽  
Salt Transport ◽  
The Arctic ◽  
Volume Heat ◽  
In Situ Observations

Abstract. The flow of warm and saline water from the Atlantic Ocean, across the Greenland–Scotland Ridge, into the Nordic Seas – the Atlantic inflow – is split into three separate branches. The most intensive of these branches is the inflow between Iceland and the Faroe Islands (Faroes), which is focused into the Faroe Current, north of the Faroes. The Atlantic inflow is an integral part of the North Atlantic thermohaline circulation (THC), which is projected to weaken during the 21 century and might conceivably reduce the oceanic heat and salt transports towards the Arctic. Since the mid-1990s, hydrographic properties and current velocities of the Faroe Current have been monitored along a section extending north from the Faroe shelf. From these in situ observations, time series of volume, heat, and salt transport have previously been reported, but the high variability of the transport series has made it difficult to identify trends. Here, we present results from a new analysis of the Faroe Current where the in situ observations have been combined with satellite altimetry. For the period 1993 to 2013, we find the average volume transport of Atlantic water in the Faroe Current to be 3.8 ± 0.5 Sv (1 Sv =106 m3 s−1) with a heat transport relative to 0 °C of 124 ± 15 TW (1 TW =1012 W). Consistent with other results for the Northeast Atlantic component of the THC, we find no indication of weakening. The transports of the Faroe Current, on the contrary, increased. The overall trend over the two decades of observation was 9 ± 8% for volume transport and 18 ± 9% for heat transport (95% confidence intervals). During the same period, the salt transport relative to the salinity of the deep Faroe Bank Channel overflow (34.93) more than doubled, potentially strengthening the feedback on thermohaline intensity. The increased heat and salt transports are partly caused by the increased volume transport and partly by increased temperatures and salinities of the Atlantic inflow, attributed mainly to the weakened subpolar gyre.

scholarly journals Transport of volume, heat, and salt towards the Arctic in the Faroe Current 1993–2013

Ocean Science ◽  
2015 ◽  
Vol 11 (5) ◽  
pp. 743-757 ◽  
Author(s):  
B. Hansen ◽  
K. M. H. Larsen ◽  
H. Hátún ◽  
R. Kristiansen ◽  
E. Mortensen ◽  
...  
Keyword(s):  
Heat Transport ◽  
Thermohaline Circulation ◽  
Saline Water ◽  
Atlantic Water ◽  
Volume Transport ◽  
Salt Transport ◽  
The Arctic ◽  
Volume Heat ◽  
In Situ Observations

Abstract. The flow of warm and saline water from the Atlantic Ocean, across the Greenland–Scotland Ridge, into the Nordic Seas – the Atlantic inflow – is split into three separate branches. The most intense of these branches is the inflow between Iceland and the Faroe Islands (Faroes), which is focused into the Faroe Current, north of the Faroes. The Atlantic inflow is an integral part of the North Atlantic thermohaline circulation (THC), which is projected to weaken during the 21st century and might conceivably reduce the oceanic heat and salt transports towards the Arctic. Since the mid-1990s, hydrographic properties and current velocities of the Faroe Current have been monitored along a section extending north from the Faroe shelf. From these in situ observations, time series of volume, heat, and salt transport have previously been reported, but the high variability of the transport has made it difficult to establish whether there are trends. Here, we present results from a new analysis of the Faroe Current where the in situ observations have been combined with satellite altimetry. For the period 1993 to 2013, we find the average volume transport of Atlantic water in the Faroe Current to be 3.8 ± 0.5 Sv (1 Sv = 106 m3 s−1) with a heat transport relative to 0 °C of 124 ± 15 TW (1 TW = 1012 W). Consistent with other results for the Northeast Atlantic component of the THC, we find no indication of weakening. The transports of the Faroe Current, on the contrary, increased. The overall increase over the 2 decades of observation was 9 ± 8 % for volume transport and 18 ± 9 % for heat transport (95 % confidence intervals). During the same period, the salt transport relative to the salinity of the deep Faroe Bank Channel overflow (34.93) more than doubled, potentially strengthening the feedback on thermohaline intensity. The increased heat and salt transports are partly caused by the increased volume transport and partly by increased temperatures and salinities of the Atlantic inflow, which have been claimed mainly to be caused by the weakened subpolar gyre.

scholarly journals On the meridional ageostrophic transport in the tropical Atlantic

2017 ◽  
Author(s):  
Yao Fu ◽  
Johannes Karstensen ◽  
Peter Brandt
Keyword(s):  
Mixed Layer Depth ◽  
Volume Transport ◽  
Salt Transport ◽  
Salt Flux ◽  
Ekman Transport ◽  
Flux Calculation ◽  
Vertical Scale ◽  
Salinity Data ◽  
The Difference

Abstract. The meridional Ekman volume, heat and salt transport across two trans-Atlantic sections near 14.5° N and 11° S were estimated using wind products, in-situ observations, and model data. A meridional ageostrophic velocity was obtained as the difference between the directly measured total velocity and the geostrophic velocity derived from observations. Wave-like structures exist in the ageostrophic velocity with 60–80 m vertical scale and large horizontal coherence, which are likely associated with near-inertial waves. The meridional Ekman transport estimated by integrating the ageostrophic velocity was 6.2 ± 2.3 Sv northward at 14.5° N and 11.7 ± 2.1 Sv southward at 11° S, which agrees well with the predictions from in-situ wind stress data of 6.7 ± 3.5 Sv at 14.5° N and 13.6 ± 3.3 Sv at 11° S. The top of the pycnocline well represents the penetration depth of the Ekman currents at both sections, which was typically 20 m deeper than the local mixed layer depth. We observed that in the meridional Ekman heat and salt flux calculation, using only the sea surface temperature and salinity data had a negligible impact on the resulting fluxes compared to using temperature and salinity profile data covering the Ekman layer. The errors in the Ekman heat and salt flux calculation were dominated by the uncertainty in the Ekman volume transport estimates.

Long-term observations of the strongest inflow branch of warm water to the Arctic Mediterranean

2020 ◽  
Author(s):  
Bogi Hansen ◽  
Karin M. H. Larsen ◽  
Hjálmar Hátún ◽  
Svein Østerhus
Keyword(s):  
Satellite Altimetry ◽  
Saline Water ◽  
Accurate Determination ◽  
Volume Transport ◽  
High Accuracy ◽  
The Arctic ◽  
Boundary Current ◽  
Data Set

<p>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.</p>

scholarly journals On the meridional ageostrophic transport in the tropical Atlantic

Ocean Science ◽  
2017 ◽  
Vol 13 (4) ◽  
pp. 531-549 ◽  
Author(s):  
Yao Fu ◽  
Johannes Karstensen ◽  
Peter Brandt
Keyword(s):  
Mixed Layer Depth ◽  
Volume Transport ◽  
Salt Transport ◽  
Salt Flux ◽  
Ekman Transport ◽  
Geostrophic Velocity ◽  
Salinity Data ◽  
The Difference ◽  
Total Velocity

Abstract. The meridional Ekman volume, heat, and salt transport across two trans-Atlantic sections near 14.5° N and 11° S were estimated using in situ observations, wind products, and model data. A meridional ageostrophic velocity was obtained as the difference between the directly measured total velocity and the geostrophic velocity derived from observations. Interpreting the section mean ageostrophy to be the result of an Ekman balance, the meridional Ekman transport of 6.2±2.3 Sv northward at 14.5° N and 11.7±2.1 Sv southward at 11° S is estimated. The integration uses the top of the pycnocline as an approximation for the Ekman depth, which is on average about 20 m deeper than the mixed layer depth. The Ekman transport estimated based on the velocity observations agrees well with the predictions from in situ wind stress data of 6.7±3.5 Sv at 14.5° N and 13.6±3.3 Sv at 11° S. The meridional Ekman heat and salt fluxes calculated from sea surface temperature and salinity data or from high-resolution temperature and salinity profile data differ only marginally. The errors in the Ekman heat and salt flux calculation were dominated by the uncertainty of the Ekman volume transport estimates.

In Situ Calibration of Moored CTDs Used for Monitoring Abyssal Water

2008 ◽  
Vol 25 (9) ◽  
pp. 1695-1702 ◽  
Author(s):  
Hiroshi Uchida ◽  
Takeshi Kawano ◽  
Masao Fukasawa
Keyword(s):  
Potential Temperature ◽  
Pressure Sensors ◽  
Heat Content ◽  
Deep Ocean ◽  
Volume Transport ◽  
In Situ Calibration ◽  
Before And After ◽  
Salinity Data ◽  
Temperature Depth

Abstract To monitor changes in heat content and geostrophic volume transport of abyssal water accurately, 50 moored conductivity–temperature–depth (CTD) recorders used for density measurements were calibrated in situ by simultaneous observations with accurate shipboard CTDs. Comparisons of the data from the moored and shipboard CTDs showed pressure sensitivities of 0–3 mK at 6000 dbar for the temperature sensors of the moored CTDs. From the in situ calibrations, the uncertainties of the moored CTD data for the deep ocean (≥3000 dbar) were estimated to be 0.6 dbar, 0.6 mK, and 0.0026 for pressure, temperature, and salinity, respectively, relative to the shipboard CTD reference. Time drifts of the moored CTD data, estimated from the in situ calibrations before and after 17- or 14-month mooring deployments in the deep ocean, were considerably smaller than typical stabilities as specified by the manufacturer. However, time drifts of the pressure sensors tended to be negative and the result suggests that pressure data from most present Argo floats, which use the same type of pressure sensor, may have a systematic negative bias. Time series salinity data calculated from the in situ–calibrated CTDs were slightly biased (mean of +0.0014) with respect to the shipboard CTD salinity data, based on potential temperature–salinity relationships, possibly due to a disequilibrium of the moored CTD conductivity sensors during the in situ calibrations.

scholarly journals Detection of total water mass changes in the Patagonian glaciers area by satellite gravimetry

2021 ◽  
Vol 60 (2) ◽  
pp. 161-174
Author(s):  
Ayelen Pereira ◽  
Cecilia Cornero ◽  
Ana Cristina Oliveira Cancoro de Matos ◽  
Maria Cristina Pacino ◽  
Denizar Blitzkow
Keyword(s):  
Satellite Altimetry ◽  
Water Mass ◽  
Water Storage ◽  
Correlation Coefficients ◽  
Northern Region ◽  
Satellite Mission ◽  
Satellite Gravimetry ◽  
Southern Patagonia ◽  
Patagonian Lakes

Despite present efforts to better understand glacier changes and their trends, the satellite gravimetry is a powerful tool still not applied in depth to study relatively large areas in the Andes of Argentina and Chile. In this work the mass variations of the Patagonian Icefield are analyzed together with the decrease trends of the ice layer in the region. The purpose of this study is to demonstrate the GRACE satellite mission (Gravity Recovery and Climate Experiment) ability to detect the water storage changes over the glaciers area. Furthermore, the variations of the hydrometric level of some Patagonian lakes were monitored by combining satellite altimetry data and in situ measurements with the observed water mass variations. Data from GRACE was used to estimate gravity trends, and high-resolution CSR GRACE RL05 mascon solutions were used to analyze the water storage change of the icefields in the region under study for the 2002-2017 period. Virtual stations from satellite altimetry obtained from a lake database and also hydrometric height data from in situ stations, located at Patagonian lakes in Argentina and Chile, were also used in order to compare the TWS from GRACE to the water level of the specific lakes. Additionally, correlation coefficients were determined at each station.  The results show a significant water storage decrease in the Icefield area, and they also demonstrate that the ice melt in southern Patagonia (of about 6 cm/year) tends to be more pronounced than in the northern region.

STORM ICE OIL WIND WAVE WATCH SYSTEM (SIOWS): WEB GIS APPLICATION FOR MONITORING THE ARCTIC

2017 ◽  
Author(s):  
Alexander Myasoedov ◽  
Alexander Myasoedov ◽  
Sergey Azarov ◽  
Sergey Azarov ◽  
Ekaterina Balashova ◽  
...  
Keyword(s):  
Satellite Data ◽  
Wind Wave ◽  
Arctic Region ◽  
Web Gis ◽  
The Arctic ◽  
Flexible Tool ◽  
In Situ Data ◽  
Current State ◽  
Watch System

Working with satellite data, has long been an issue for users which has often prevented from a wider use of these data because of Volume, Access, Format and Data Combination. The purpose of the Storm Ice Oil Wind Wave Watch System (SIOWS) developed at Satellite Oceanography Laboratory (SOLab) is to solve the main issues encountered with satellite data and to provide users with a fast and flexible tool to select and extract data within massive archives that match exactly its needs or interest improving the efficiency of the monitoring system of geophysical conditions in the Arctic. SIOWS - is a Web GIS, designed to display various satellite, model and in situ data, it uses developed at SOLab storing, processing and visualization technologies for operational and archived data. It allows synergistic analysis of both historical data and monitoring of the current state and dynamics of the "ocean-atmosphere-cryosphere" system in the Arctic region, as well as Arctic system forecasting based on thermodynamic models with satellite data assimilation.

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