Eddy correlation measurements of submarine groundwater discharge

Crusius, John; Berg, Peter; Koopmans, Dirk; Erban, Laura

doi:10.1016/j.marchem.2007.12.004

Cited by 26 publications

(32 citation statements)

References 22 publications

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“…The O 2 eddy correlation system consists of an acoustic Doppler Velocimeter (ADV) (Nortek AS, Norway) that has been modified to record measurements made with a high-resolution custom-made pA amplifier (Max Planck Institute for Marine Microbiology, Germany) to which a fast responding (<0.2 s) Clark-type O 2 microsensor is mounted Huettel, 2008, Berg et al, 2009;Hume et al, 2011). The temperature eddy correlation system consists of a standard ADV coupled to a rapid-response (<0.1 s) temperature and conductivity sensor (Fast CT sensor, Precision Measurement Engineering, USA) (Crusius et al, 2008). Damage to the conductivity sensors prevented simultaneous measurement of the salt flux.…”

Section: Eddy Correlation Measurementsmentioning

confidence: 99%

Oxygen exchange and ice melt measured at the ice-water interface by eddy correlation

et al. 2012

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Abstract. This study examined fluxes across the ice-water interface utilizing the eddy correlation technique. Temperature eddy correlation systems were used to determine rates of ice melting and freezing, and O 2 eddy correlation systems were used to examine O 2 exchange rates driven by biological and physical processes. The study was conducted below 0.7 m thick sea-ice in mid-March 2010 in a southwest Greenland fjord and revealed low rates of ice melt at a maximum of 0.80 mm d −1 . The O 2 flux associated with release of O 2 depleted melt water was less than 13 % of the average daily O 2 respiration rate. Ice melt and insufficient vertical turbulent mixing due to low current velocities caused periodic stratification immediately below the ice. This prevented the determination of fluxes 61 % of the deployment time. These time intervals were identified by examining the velocity and the linearity and stability of the cumulative flux. The examination of unstratified conditions through vertical velocity and O 2 spectra and their cospectra revealed characteristic fingerprints of well-developed turbulence. From the measured O 2 fluxes a photosynthesis/irradiance curve was established by least-squares fitting. This relation showed that light limitation of net photosynthesis began at 4.2 µmol photons m −2 s −1 , and that algal communities were well-adapted to low-light conditions as they were light saturated for 75 % of the day during this early spring period. However, the sea-ice associated microbial and algal community was net heterotrophic with a daily gross primary production of 0.69 mmol O 2 m −2 d −1 and a respiration rate of −2.13 mmol O 2 m −2 d −1 leading to a net ecosystem metabolism of −1.45 mmol O 2 m −2 d −1 . This application of the eddy correlation technique produced high temporal resolution O 2 fluxes and ice melt rates that were measured without disturbing the in situ environmental conditions while integrating over an area of approximately 50 m 2 which incorporated the highly variable activity and spatial distributions of sea-ice communities.

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Section: Eddy Correlation Measurementsmentioning

confidence: 99%

Oxygen exchange and ice melt measured at the ice-water interface by eddy correlation

et al. 2012

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“…The earliest studies focused on measurements of heat fluxes under sea ice (McPhee, 1992;Fukuchi et al, 1997;Shirasawa et al, 1997) and salt fluxes in a salt wedge estuary (Partch and Smith, 1978). More recently, concurrent heat and salt fluxes have also been measured over marine permeable sandy sediments as tracers for groundwater seepage (Crusius et al, 2008). Over the last 10 years, the aquatic eddy covariance technique has become a widely accepted approach for measuring oxygen fluxes between benthic ecosystems and the overlying water .…”

Section: Introductionmentioning

confidence: 99%

Technical note: Time lag correction of aquatic eddy covariance data measured in the presence of waves

et al. 2015

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Abstract. Extracting benthic oxygen fluxes from eddy covariance time series measured in the presence of surface gravity waves requires careful consideration of the temporal alignment of the vertical velocity and the oxygen concentration. Using a model based on linear wave theory and measured eddy covariance data, we show that a substantial error in flux can arise if these two variables are not aligned correctly in time. We refer to this error in flux as the time lag bias. In one example, produced with the wave model, we found that an offset of 0.25 s between the oxygen and the velocity data produced a 2-fold overestimation of the flux. In another example, relying on nighttime data measured over a seagrass meadow, a similar offset reversed the flux from an uptake of −50 mmol m −2 d −1 to a release of 40 mmol m −2 d −1 . The bias is most acute for data measured at shallow-water sites with short-period waves and low current velocities. At moderate or higher current velocities (> 5-10 cm s −1 ), the bias is usually insignificant. The widely used traditional time shift correction for data measured in unidirectional flows, where the maximum numerical flux is sought, should not be applied in the presence of waves because it tends to maximize the time lag bias or give unrealistic flux estimates. Based on wave model predictions and measured data, we propose a new time lag correction that minimizes the time lag bias. The correction requires that the time series of both vertical velocity and oxygen concentration contain a clear periodic wave signal. Because wave motions are often evident in eddy covariance data measured at shallow-water sites, we encourage more work on identifying new time lag corrections.

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“…The EC approach combines several significant advantages: (1) because of its noninvasive nature, the EC approach allows continuous measurements to monitor the response of benthic O 2 uptake on changing environmental conditions [ Hume et al ., ]; (2) it is not confined by boundary interface conditions and allows to investigate O 2 sinks and sources at boundaries such as hard bottom substrate [ Glud et al ., ], sea ice [ Long et al ., ] and sandy sediments [ Reimers et al ., ]; (3) it integrates the flux across a large surface area [ Berg et al ., ] and thus integrates small to mesoscale heterogeneity of many benthic environments. These essential advantages initiated many studies on the boundary layer flux of other scalars such as dissolved nitrogen and phosphate [ Holtappels et al ., ], nitrate [ Johnson et al ., ], salinity [ Crusius et al ., ] and density [ Holtappels and Lorke , ]. However, the downside of the EC approach is the complex data processing and interpretation, which requires knowledge in time series analysis and hydrodynamics.…”

Section: Introductionmentioning

confidence: 99%

Effects of transient bottom water currents and oxygen concentrations on benthic exchange rates as assessed by eddy correlation measurements

et al. 2013

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[1] Eddy correlation (EC) measurements in the benthic boundary layer (BBL) allow estimating benthic O 2 uptake from a point distant to the sediment surface. This noninvasive approach has clear advantages as it does not disturb natural hydrodynamic conditions, integrates the flux over a large foot-print area and allows many repetitive flux measurements. A drawback is, however, that the measured flux in the bottom water is not necessarily equal to the flux across the sediment-water interface. A fundamental assumption of the EC technique is that mean current velocities and mean O 2 concentrations in the bottom water are in steady state, which is seldom the case in highly dynamic environments like coastal waters. Therefore, it is of great importance to estimate the error introduced by nonsteady state conditions. We investigated two cases of transient conditions. First, the case of transient O 2 concentrations was examined using the theory of shear flow dispersion.

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Eddy correlation measurements of submarine groundwater discharge

Cited by 26 publications

References 22 publications

Oxygen exchange and ice melt measured at the ice-water interface by eddy correlation

Oxygen exchange and ice melt measured at the ice-water interface by eddy correlation

Technical note: Time lag correction of aquatic eddy covariance data measured in the presence of waves

Effects of transient bottom water currents and oxygen concentrations on benthic exchange rates as assessed by eddy correlation measurements

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