scholarly journals Storm-induced water dynamics and thermohaline structure at the tidewater Flade Isblink Glacier outlet to the Wandel Sea (NE Greenland)

Ocean Science ◽  
2017 ◽  
Vol 13 (6) ◽  
pp. 947-959 ◽  
Author(s):  
Sergei Kirillov ◽  
Igor Dmitrenko ◽  
Søren Rysgaard ◽  
David Babb ◽  
Leif Toudal Pedersen ◽  
...  
Keyword(s):  
Time Series ◽  
Tidal Flow ◽  
Internal Tide ◽  
Acoustic Doppler Current Profiler ◽  
Water Dynamics ◽  
Storm Event ◽  
Thermohaline Structure ◽  
Relaxation Phase ◽  
Ice Cap ◽  
Glacier Terminus

Abstract. In April 2015, an ice-tethered conductivity–temperature–depth (CTD) profiler and a down-looking acoustic Doppler current profiler (ADCP) were deployed from the landfast ice near the tidewater glacier terminus of the Flade Isblink Glacier in the Wandel Sea, NE Greenland. The 3-week time series showed that water dynamics and the thermohaline structure were modified considerably during a storm event on 22–24 April, when northerly winds exceeded 15 m s−1. The storm initiated downwelling-like water dynamics characterized by on-shore water transport in the surface (0–40 m) layer and compensating offshore flow at intermediate depths. After the storm, currents reversed in both layers, and the relaxation phase of downwelling lasted ∼ 4 days. Although current velocities did not exceed 5 cm s−1, the enhanced circulation during the storm caused cold turbid intrusions at 75–95 m depth, which are likely attributable to subglacial water from the Flade Isblink Ice Cap. It was also found that the semidiurnal periodicities in the temperature and salinity time series were associated with the lunar semidiurnal tidal flow. The vertical structure of tidal currents corresponded to the first baroclinic mode of the internal tide with a velocity minimum at ∼ 40 m. The tidal ellipses rotate in opposite directions above and below this depth and cause a divergence of tidal flow, which was observed to induce semidiurnal internal waves of about 3 m height at the front of the glacier terminus. Our findings provide evidence that shelf–basin interaction and tidal forcing can potentially modify coastal Wandel Sea waters even though they are isolated from the atmosphere by landfast sea ice almost year-round. The northerly storms over the continental slope cause an enhanced circulation facilitating a release of cold and turbid subglacial water to the shelf. The tidal flow may contribute to the removal of such water from the glacial terminus.

scholarly journals Storm-induced water dynamics and thermohaline structure at the tidewater Flade Isblink Glacier outlet to the Wandel Sea (NE Greenland)

2017 ◽  
Author(s):  
Sergei Kirillov ◽  
Igor Dmitrenko ◽  
Søren Rysgaard ◽  
David Babb ◽  
Leif Toudal Pedersen ◽  
...  
Keyword(s):  
Tidal Flow ◽  
Internal Tide ◽  
Acoustic Doppler Current Profiler ◽  
Water Dynamics ◽  
Storm Event ◽  
Thermohaline Structure ◽  
Relaxation Phase ◽  
Ice Cap ◽  
Glacier Terminus ◽  
Current Profiler

Abstract. In April 2015, an ice-tethered conductivity-temperature-depth (CTD) profiler and a down-looking Acoustic Doppler Current Profiler (ADCP) were deployed from the landfast ice near the tidewater glacier terminus of the Flade Isblink Glacier in the Wandel Sea, NE Greenland. The three week timeseries showed that water dynamics and the thermohaline structure were modified considerably during a storm event on 22–24 April when northerly winds exceeded 15 m/s. The storm initiated downwelling-like water dynamics characterized by on-shore water transport in the surface (0–40 m) layer and compensating off-shore flow at intermediate depths. After the storm, currents reversed in both layers, and the relaxation phase of downwelling lasted ~4 days. Although current velocities did not exceed 5 cm/s, the enhanced circulation during the storm caused cold turbid intrusions at 75–95 m depth that are likely attributed to sub-glacial water from the Flade Isblink Ice Cap. It was also found that the semidiurnal periodicities in the temperature and salinity time series were associated with the lunar semidiurnal tidal flow. The vertical structure of tidal currents corresponded to the first baroclinic mode of the internal tide with a velocity minimum at ~40 m. The tidal ellipses rotate in opposite directions above and below this depth and cause a divergence of tidal flow which was observed to induce semidiurnal internal waves of about 3 m height at the front of the glacier terminus. Our findings provide evidence that shelf-basin interaction and tidal forcing can potentialy modify coastal Wandel Sea waters even though they are isolated from the atmosphere by landfast sea ice almost year round. The northerly storms over the continental slope cause an enhanced circulation facilitating a release of cold and turbid sub-glacial water to the shelf. The tidal flow may contribute to the removal of such water from the glacial terminus.

scholarly journals Acoustic and optical methods to infer water transparency at Time Series Station Spiekeroog, Wadden Sea

Ocean Science ◽  
2016 ◽  
Vol 12 (6) ◽  
pp. 1155-1163 ◽  
Author(s):  
Anne-Christin Schulz ◽  
Thomas H. Badewien ◽  
Shungudzemwoyo P. Garaba ◽  
Oliver Zielinski
Keyword(s):  
Time Series ◽  
Wadden Sea ◽  
Acoustic Doppler Current Profiler ◽  
Water Transparency ◽  
Optical Observations ◽  
Optical Methods ◽  
Acoustic Measurements ◽  
Data Set ◽  
Backscatter Signal ◽  
Current Profiler

Abstract. Water transparency is a primary indicator of optical water quality that is driven by suspended particulate and dissolved material. A data set from the operational Time Series Station Spiekeroog located at a tidal inlet of the Wadden Sea was used to perform (i) an inter-comparison of observations related to water transparency, (ii) correlation tests among these measured parameters, and (iii) to explore the utility of both acoustic and optical tools in monitoring water transparency. An Acoustic Doppler Current Profiler was used to derive the backscatter signal in the water column. Optical observations were collected using above-water hyperspectral radiometers and a submerged turbidity metre. Bio-fouling on the turbidity sensors optical windows resulted in measurement drift and abnormal values during quality control steps. We observed significant correlations between turbidity collected by the submerged metre and that derived from above-water radiometer observations. Turbidity from these sensors was also associated with the backscatter signal derived from the acoustic measurements. These findings suggest that both optical and acoustic measurements can be reasonable proxies of water transparency with the potential to mitigate gaps and increase data quality in long-time observation of marine environments.

scholarly journals Turbulence and hypoxia contribute to dense biological scattering layers in a Patagonian fjord system

Ocean Science ◽  
2018 ◽  
Vol 14 (5) ◽  
pp. 1185-1206 ◽  
Author(s):  
Iván Pérez-Santos ◽  
Leonardo Castro ◽  
Lauren Ross ◽  
Edwin Niklitschek ◽  
Nicolás Mayorga ◽  
...  
Keyword(s):  
Kinetic Energy ◽  
Water Column ◽  
Turbulent Kinetic Energy ◽  
Tidal Flow ◽  
Vertical Mixing ◽  
Acoustic Doppler Current Profiler ◽  
Marine Species ◽  
Eddy Diffusivity ◽  
Diel Vertical Migrations

Abstract. The aggregation of plankton species along fjords can be linked to physical properties and processes such as stratification, turbulence and oxygen concentration. The goal of this study is to determine how water column properties and turbulent mixing affect the horizontal and vertical distributions of macrozooplankton along the only northern Patagonian fjord known to date, where hypoxic conditions occur in the water column. Acoustic Doppler current profiler moorings, scientific echo-sounder transects and in situ plankton abundance measurements were used to study macrozooplankton assemblages and migration patterns along Puyuhuapi Fjord and Jacaf Channel in Chilean Patagonia. The dissipation of turbulent kinetic energy was quantified through vertical microstructure profiles collected throughout time in areas with high macrozooplankton concentrations. The acoustic records and in situ macrozooplankton data revealed diel vertical migrations (DVM) of siphonophores, chaetognaths and euphausiids. In particular, a dense biological backscattering layer was observed along Puyuhuapi Fjord between the surface and the top of the hypoxic boundary layer (∼100 m), which limited the vertical distribution of most macrozooplankton and their DVM, generating a significant reduction of habitat. Aggregations of macrozooplankton and fishes were most abundant around a submarine sill in Jacaf Channel. In this location macrozooplankton were distributed throughout the water column (0 to ∼200 m), with no evidence of a hypoxic boundary due to the intense mixing near the sill. In particular, turbulence measurements taken near the sill indicated high dissipation rates of turbulent kinetic energy (ε∼10-5 W kg−1) and vertical diapycnal eddy diffusivity (Kρ∼10-3 m2 s−1). The elevated vertical mixing ensures that the water column is well oxygenated (3–6 mL L−1, 60 %–80 % saturation), creating a suitable environment for macrozooplankton and fish aggregations. Turbulence induced by tidal flow over the sill apparently enhances the interchange of nutrients and oxygen concentrations with the surface layer, creating a productive environment for many marine species, where the prey–predator relationship might be favored.

scholarly journals Velocity Structure of Internal Tide Beams Emanating from Kaena Ridge, Hawaii

2012 ◽  
Vol 42 (6) ◽  
pp. 1039-1044 ◽  
Author(s):  
Andy Pickering ◽  
Matthew H. Alford
Keyword(s):  
Numerical Simulations ◽  
Velocity Structure ◽  
Internal Tide ◽  
Acoustic Doppler Current Profiler ◽  
Ocean Model ◽  
Surface Reflection ◽  
Model Predictions ◽  
Current Profiler ◽  
North And South ◽  
Ray Paths

Abstract Observations are reported of the semidiurnal (M2) internal tide across Kaena Ridge, Hawaii. Horizontal velocity in the upper 1000–1500 m was measured during eleven ~240-km-long shipboard acoustic Doppler current profiler (ADCP) transects across the ridge, made over the course of several months. The M2 motions are isolated by means of harmonic analysis and compared to numerical simulations using the Princeton Ocean Model (POM). The depth coverage of the measurements is about 3 times greater than similar past studies, offering a substantially richer view of the internal tide beams. Sloping features are seen extending upward north and south from the ridge and then downward from the surface reflection about ±40 km from the ridge crest, closely matching theoretical M2 ray paths and the model predictions.

scholarly journals Climate reconstruction since the Little Ice Age by modelling Koryto glacier, Kamchatka Peninsula, Russia

2008 ◽  
Vol 54 (184) ◽  
pp. 125-130 ◽  
Author(s):  
Satoru Yamaguchi ◽  
Renji Naruse ◽  
Takayuki Shiraiwa
Keyword(s):  
20Th Century ◽  
Meteorological Data ◽  
Ice Core ◽  
Kamchatka Peninsula ◽  
Winter Precipitation ◽  
Ice Age ◽  
Equilibrium Line Altitude ◽  
Ice Cap ◽  
Glacier Terminus ◽  
Tree Ring Data

AbstractBased on the field data at Koryto glacier, Kamchatka Peninsula, Russia, we constructed a one-dimensional numerical glacier model which fits the behaviour of the glacier. The analysis of meteorological data from the nearby station suggests that the recent rapid retreat of the glacier since the mid-20th century is likely to be due to a decrease in winter precipitation. Using the geographical data of the glacier terminus variations from 1711 to 1930, we reconstructed the fluctuation in the equilibrium-line altitude by means of the glacier model. With summer temperatures inferred from tree-ring data, the model suggests that the winter precipitation from the mid-19th to the early 20th century was about 10% less than that at present. This trend is close to consistent with ice-core results from the nearby ice cap in the central Kamchatka Peninsula.

scholarly journals Dissolved and Particulate Organic Carbon in Icelandic Proglacial Streams: A First Estimate

Water ◽  
2019 ◽  
Vol 11 (4) ◽  
pp. 748 ◽  
Author(s):  
Peter Chifflard ◽  
Christina Fasching ◽  
Martin Reiss ◽  
Lukas Ditzel ◽  
Kyle S. Boodoo
Keyword(s):  
Organic Matter ◽  
Organic Carbon ◽  
Particulate Organic Carbon ◽  
Ice Cap ◽  
Glacier Terminus ◽  
Fluorescence Measurements ◽  
Sampling Locations ◽  
Carbon Release ◽  
Annual Carbon ◽  
Spatio Temporal

Here for the first time, we analyze the concentration of dissolved (DOC) and particulate organic carbon (POC), as well as its optical properties (absorbance and fluorescence) from several proglacial streams across Iceland, the location of Europe’s largest non-polar ice cap. We found high spatial variability of DOC concentrations and dissolved organic matter (DOM) composition during peak melt, sampling 13 proglacial streams draining the 5 main Icelandic glaciers. Although glacial-derived organic matter (OM) was dominated by proteinaceous florescence, organic matter composition was variable among glaciers, often exhibiting relatively higher aromatic content and increased humification (based on absorbance and fluorescence measurements) closer to the glacier terminus, modulated by the presence of glacial lakes. Additional sampling locations the in flow path of the river Hvitá revealed that while POC concentrations decreased downstream, DOC concentrations and the autochthonous fraction of OM increased, suggesting the reworking of the organic carbon by microbial communities, with likely implications for downstream ecosystems as glaciers continue to melt. Based on our measured DOC concentrations ranging from 0.11 mg·L−1 to 0.94 mg·L−1, we estimate a potential annual carbon release of 0.008 ± 0.002 Tg·C·yr−1 from Icelandic glaciers. This non-conservative first estimate serves to highlight the potentially significant contribution of Icelandic pro-glacial streams to the global carbon cycle and the need for the quantification and determination of the spatio-temporal variation of DOC and POC fluxes and their respective drivers, particularly in light of increased rates of melting due to recent trends in climatic warming.

scholarly journals Analyzing Water Dynamics Based on Sentinel-1 Time Series—a Study for Dongting Lake Wetlands in China

2020 ◽  
Vol 12 (11) ◽  
pp. 1761 ◽  
Author(s):  
Juliane Huth ◽  
Ursula Gessner ◽  
Igor Klein ◽  
Hervé Yesou ◽  
Xijun Lai ◽  
...  
Keyword(s):  
Time Series ◽  
Wetland Management ◽  
Dongting Lake ◽  
Water Dynamics ◽  
Minimum Size ◽  
Optical Data ◽  
Small Scale ◽  
Lake Area ◽  
Ramsar Site ◽  
Extreme Flood

In China, freshwater is an increasingly scarce resource and wetlands are under great pressure. This study focuses on China’s second largest freshwater lake in the middle reaches of the Yangtze River—the Dongting Lake—and its surrounding wetlands, which are declared a protected Ramsar site. The Dongting Lake area is also a research region of focus within the Sino-European Dragon Programme, aiming for the international collaboration of Earth Observation researchers. ESA’s Copernicus Programme enables comprehensive monitoring with area-wide coverage, which is especially advantageous for large wetlands that are difficult to access during floods. The first year completely covered by Sentinel-1 SAR satellite data was 2016, which is used here to focus on Dongting Lake’s wetland dynamics. The well-established, threshold-based approach and the high spatio-temporal resolution of Sentinel-1 imagery enabled the generation of monthly surface water maps and the analysis of the inundation frequency at a 10 m resolution. The maximum extent of the Dongting Lake derived from Sentinel-1 occurred in July 2016, at 2465 km2, indicating an extreme flood year. The minimum size of the lake was detected in October, at 1331 km2. Time series analysis reveals detailed inundation patterns and small-scale structures within the lake that were not known from previous studies. Sentinel-1 also proves to be capable of mapping the wetland management practices for Dongting Lake polders and dykes. For validation, the lake extent and inundation duration derived from the Sentinel-1 data were compared with excerpts from the Global WaterPack (frequently derived by the German Aerospace Center, DLR), high-resolution optical data, and in situ water level data, which showed very good agreement for the period studied. The mean monthly extent of the lake in 2016 from Sentinel-1 was 1798 km2, which is consistent with the Global WaterPack, deviating by only 4%. In summary, the presented analysis of the complete annual time series of the Sentinel-1 data provides information on the monthly behavior of water expansion, which is of interest and relevance to local authorities involved in water resource management tasks in the region, as well as to wetland conservationists concerned with the Ramsar site wetlands of Dongting Lake and to local researchers.

scholarly journals Internal tide energy flux over a ridge measured by a co-located ocean glider and moored acoustic Doppler current profiler

Ocean Science ◽  
2019 ◽  
Vol 15 (6) ◽  
pp. 1439-1453 ◽  
Author(s):  
Rob A. Hall ◽  
Barbara Berx ◽  
Gillian M. Damerell
Keyword(s):  
Energy Flux ◽  
Internal Tide ◽  
Acoustic Doppler Current Profiler ◽  
Small Scale ◽  
Negative Bias ◽  
Potential Density ◽  
Shelf Slope ◽  
Current Profiler ◽  
Circle Diameter ◽  
Horizontal Wavelength

Abstract. Internal tide energy flux is an important diagnostic for the study of energy pathways in the ocean, from large-scale input by the surface tide to small-scale dissipation by turbulent mixing. Accurate calculation of energy flux requires repeated full-depth measurements of both potential density (ρ) and horizontal current velocity (u) over at least a tidal cycle and over several weeks to resolve the internal spring–neap cycle. Typically, these observations are made using full-depth oceanographic moorings that are vulnerable to being “fished out” by commercial trawlers when deployed on continental shelves and slopes. Here we test an alternative approach to minimize these risks, with u measured by a low-frequency acoustic Doppler current profiler (ADCP) moored near the seabed and ρ measured by an autonomous ocean glider holding station by the ADCP. The method is used to measure the semidiurnal internal tide radiating from the Wyville Thomson Ridge in the North Atlantic. The observed energy flux (4.2±0.2 kW m−1) compares favourably with historic observations and a previous numerical model study. Error in the energy flux calculation due to imperfect co-location of the glider and ADCP is estimated by subsampling potential density in an idealized internal tide field along pseudorandomly distributed glider paths. The error is considered acceptable (<10 %) if all the glider data are contained within a “watch circle” with a diameter smaller than 1∕8 the mode-1 horizontal wavelength of the internal tide. Energy flux is biased low because the glider samples density with a broad range of phase shifts, resulting in underestimation of vertical isopycnal displacement and available potential energy. The negative bias increases with increasing watch circle diameter. If watch circle diameter is larger than 1∕8 the mode-1 horizontal wavelength, the negative bias is more than 3 % and all realizations within the 95 % confidence interval are underestimates. Over the Wyville Thomson Ridge, where the semidiurnal mode-1 horizontal wavelength is ≈100 km and all the glider dives are within a 5 km diameter watch circle, the observed energy flux is estimated to have a negative bias of only 0.4 % and an error of less than 3 % at the 95 % confidence limit. With typical glider performance, we expect energy flux error due to imperfect co-location to be <10 % in most mid-latitude shelf slope regions.

scholarly journals Temporal variations of zooplankton biomass in the Ligurian Sea inferred from long time series of ADCP data

Ocean Science ◽  
2014 ◽  
Vol 10 (1) ◽  
pp. 93-105 ◽  
Author(s):  
R. Bozzano ◽  
E. Fanelli ◽  
S. Pensieri ◽  
P. Picco ◽  
M. E. Schiano
Keyword(s):  
Time Series ◽  
Acoustic Doppler Current Profiler ◽  
Temporal Variations ◽  
Zooplankton Biomass ◽  
Mesopelagic Fish ◽  
Ligurian Sea ◽  
Time Frequency ◽  
Backscattering Strength ◽  
Current Profiler ◽  
Long Time

Abstract. Three years of 300 kHz acoustic doppler current profiler data collected in the central Ligurian Sea are analysed to investigate the variability of the zooplankton biomass and the diel vertical migration in the upper thermocline. After a pre-processing phase aimed at avoiding the slant range attenuation, hourly volume backscattering strength time series are obtained. Despite the lack of concurrent net samples collection, different migration patterns are identified and their temporal variability examined by means of time–frequency analysis. The effect of changes in the environmental condition is also investigated. The highest zooplankton biomasses are observed in April–May just after the peak of surface primary production in March–April. The main migration pattern found here points to a "nocturnal" migration, with zooplankton organisms occurring deeper in the water column during the day and shallower at night. Also, twilight migration is highlighted during this study. The largest migrations are recorded in November–December, corresponding to lowest backscattering strength values and they are likely attributable to larger and more active organisms (i.e. euphausiids and mesopelagic fish). The results suggest further applications of the available historical acoustic doppler current profiler time series.

scholarly journals Seiche excitation in a highly stratified fjord of southern Chile: the Reloncaví fjord

Ocean Science ◽  
2017 ◽  
Vol 13 (1) ◽  
pp. 145-160 ◽  
Author(s):  
Manuel I. Castillo ◽  
Oscar Pizarro ◽  
Nadin Ramírez ◽  
Mario Cáceres
Keyword(s):  
Time Series ◽  
Sea Level ◽  
Low Frequency ◽  
Phase Speed ◽  
Acoustic Doppler Current Profiler ◽  
Southern Chile ◽  
Density Profiles ◽  
Level Data ◽  
Spectral Peaks ◽  
Current Profiler

Abstract. We describe a seiche process based on current, temperature, and sea-level data obtained from the Reloncaví fjord (41.6° S, 72.5° W) in southern Chile. We combined 4 months of acoustic Doppler current profiler (ADCP) data with sea-level, temperature, and wind time series to analyze the dynamics of low-frequency (periods > 1 day) internal oscillations in the fjord. Additionally, seasonal conductivity, temperature, and depth (CTD) data from 19 along-fjord stations were used to characterize the seasonality of the density field. The density profiles were used to estimate the internal long-wave phase speed (c) using two approximations: (1) a simple reduced gravity model (RGM) and (2) a continuously stratified model (CSM). No major seasonal changes in c were observed using either approximation (e.g., the CSM yielded 0.73 < c < 0.87 m s−1 for mode 1). The natural internal periods (TN) were estimated using Merian's formula for a simple fjord-like basin and the above phase speeds. Estimated values of TN varied between 2.9 and 3.5 days and were highly consistent with spectral peaks observed in the along-fjord currents and temperature time series. We conclude that these oscillations were forced by the wind stress, despite the moderate wind energy. Wind conditions at the end of winter gave us an excellent opportunity to explore the damping process. The observed damping time (Td) was relatively long (Td =  9.1 days).

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