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W. Scott Pegau - One of the best experts on this subject based on the ideXlab platform.
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Simulation of turbulent exchange processes in summertime leads
Journal of Geophysical Research, 2005Co-Authors: Eric D. Skyllingstad, Clayton A. Paulson, W. Scott PegauAbstract:[1] Ice-ocean heat exchange in polar leads was examined using a large-eddy simulation model coupled to a slab ice model. Simulations were performed using an idealized square domain for a range of lead sizes, surface wind stress (0.05–0.1 N m−2), and lead temperature/salinity profiles. Particular emphasis was placed on understanding the role of Fresh water in leads and how stratification controls the heat budget and ice edge melting rate. With uniform initial conditions we found that solar heating was not strong enough to develop lead Freshening via ice edge melting; even weak winds (0.02 N m−2) generated circulations that maintained a well-mixed lead. In the weak wind case, adding a Fresh water flux representative of surface melt runoff provided enough additional stratification so that the lead water became isolated from the rest of the simulated ocean boundary Layer. However, stronger winds (0.1 N m−2) prevented the Fresh water Layer from forming. Experiments initialized with temperature/salinity profiles similar to observed cases (Fresh water Layer capping the lead) demonstrated that lateral melting rates increase with expanding lead size, agreeing with simple heat balance calculations for a square lead without vertical mixing. However, with stronger winds, lateral melting rates decreased because of greater turbulent mixing of cold water from beneath the Fresh Layer. Inspection of the lead circulation indicated that the strongest melting occurred where the ice edge currents were the largest. Overall, melting fluxes for a 24 m2 lead ranged from 200 to 400 W m−2, depending on the wind speed. Without the Fresh Layer, fluxes ranged from 50 to 60 W m−2, suggesting that Fresh water stratification can have a dominate role in controlling ice edge melting.
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Effects of keels on ice bottom turbulence exchange
Journal of Geophysical Research, 2003Co-Authors: Eric D. Skyllingstad, Clayton A. Paulson, W. Scott Pegau, Miles G. Mcphee, Timothy P. StantonAbstract:[1] The effects of ice keels on the upper ocean are examined using a combination of turbulence measurements and output from a large-eddy simulation (LES) model. Two cases are examined, one during the winter when the under-ice boundary Layer is relatively deep (∼20 m) and near the freezing point and a second during the summer when the ice is melting and the boundary Layer consists of a shallow (∼0.5 m), highly stratified Fresh Layer. In the winter case, measurements show that flow disruption by a 10-m-deep keel causes enhanced vertical mixing, increasing the heat flux from a background value of ∼5 W m−2 to values averaging ∼25 W m−2. Simulations using the LES model are in good agreement with the measurements and indicate that the keel generates a turbulent wake region extending hundreds of meters downstream from the keel. Elevated heat fluxes in the wake region are generated by increased entrainment of warmer water from beneath the mixed Layer. Simulations of summer cases demonstrate that shallow keels (∼0.5 m) generate strong turbulence that is able to rapidly mix the Fresh Layer in the lee of keels. However, this effect decreases quickly as the Fresh Layer accelerates to match the ice velocity. Deeper keels (1 m) follow a similar pattern but generate more mixing as the Fresh Layer is forced under the keel. Simulated ice melt heat fluxes are similar to estimates made from ice balance measurements taken during the Surface Heat Budget of the Arctic Ocean summer field program.
Eric D. Skyllingstad - One of the best experts on this subject based on the ideXlab platform.
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Simulation of turbulent exchange processes in summertime leads
Journal of Geophysical Research, 2005Co-Authors: Eric D. Skyllingstad, Clayton A. Paulson, W. Scott PegauAbstract:[1] Ice-ocean heat exchange in polar leads was examined using a large-eddy simulation model coupled to a slab ice model. Simulations were performed using an idealized square domain for a range of lead sizes, surface wind stress (0.05–0.1 N m−2), and lead temperature/salinity profiles. Particular emphasis was placed on understanding the role of Fresh water in leads and how stratification controls the heat budget and ice edge melting rate. With uniform initial conditions we found that solar heating was not strong enough to develop lead Freshening via ice edge melting; even weak winds (0.02 N m−2) generated circulations that maintained a well-mixed lead. In the weak wind case, adding a Fresh water flux representative of surface melt runoff provided enough additional stratification so that the lead water became isolated from the rest of the simulated ocean boundary Layer. However, stronger winds (0.1 N m−2) prevented the Fresh water Layer from forming. Experiments initialized with temperature/salinity profiles similar to observed cases (Fresh water Layer capping the lead) demonstrated that lateral melting rates increase with expanding lead size, agreeing with simple heat balance calculations for a square lead without vertical mixing. However, with stronger winds, lateral melting rates decreased because of greater turbulent mixing of cold water from beneath the Fresh Layer. Inspection of the lead circulation indicated that the strongest melting occurred where the ice edge currents were the largest. Overall, melting fluxes for a 24 m2 lead ranged from 200 to 400 W m−2, depending on the wind speed. Without the Fresh Layer, fluxes ranged from 50 to 60 W m−2, suggesting that Fresh water stratification can have a dominate role in controlling ice edge melting.
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Effects of keels on ice bottom turbulence exchange
Journal of Geophysical Research, 2003Co-Authors: Eric D. Skyllingstad, Clayton A. Paulson, W. Scott Pegau, Miles G. Mcphee, Timothy P. StantonAbstract:[1] The effects of ice keels on the upper ocean are examined using a combination of turbulence measurements and output from a large-eddy simulation (LES) model. Two cases are examined, one during the winter when the under-ice boundary Layer is relatively deep (∼20 m) and near the freezing point and a second during the summer when the ice is melting and the boundary Layer consists of a shallow (∼0.5 m), highly stratified Fresh Layer. In the winter case, measurements show that flow disruption by a 10-m-deep keel causes enhanced vertical mixing, increasing the heat flux from a background value of ∼5 W m−2 to values averaging ∼25 W m−2. Simulations using the LES model are in good agreement with the measurements and indicate that the keel generates a turbulent wake region extending hundreds of meters downstream from the keel. Elevated heat fluxes in the wake region are generated by increased entrainment of warmer water from beneath the mixed Layer. Simulations of summer cases demonstrate that shallow keels (∼0.5 m) generate strong turbulence that is able to rapidly mix the Fresh Layer in the lee of keels. However, this effect decreases quickly as the Fresh Layer accelerates to match the ice velocity. Deeper keels (1 m) follow a similar pattern but generate more mixing as the Fresh Layer is forced under the keel. Simulated ice melt heat fluxes are similar to estimates made from ice balance measurements taken during the Surface Heat Budget of the Arctic Ocean summer field program.
Timothy P. Stanton - One of the best experts on this subject based on the ideXlab platform.
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evolution of a canada basin ice ocean boundary Layer and mixed Layer across a developing thermodynamically forced marginal ice zone
Journal of Geophysical Research, 2016Co-Authors: Shawn G Gallaher, Timothy P. Stanton, William J Shaw, Sylvia T Cole, John M Toole, Jeremy Wilkinson, Ted Maksym, Byongjun HwangAbstract:A comprehensive set of autonomous, ice-ocean measurements were collected across the Canada Basin to study the summer evolution of the ice-ocean boundary Layer (IOBL) and ocean mixed Layer (OML). Evaluation of local heat and Freshwater balances and associated turbulent forcing reveals that melt ponds (MPs) strongly influence the summer IOBL-OML evolution. Areal expansion of MPs in mid-June start the upper ocean evolution resulting in significant increases to ocean absorbed radiative flux (19 W m−2 in this study). Buoyancy provided by MP drainage shoals and Freshens the IOBL resulting in a 39 MJ m−2 increase in heat storage in just 19 days (52% of the summer total). Following MP drainage, a near-surface Fresh Layer deepens through shear-forced mixing to form the summer mixed Layer (sML). In late summer, basal melt increases due to stronger turbulent mixing in the thin sML and the expansion of open water areas due in part to wind-forced divergence of the sea ice. Thermal heterogeneities in the marginal ice zone (MIZ) upper ocean led to large ocean-to-ice heat fluxes (100–200 W m−2) and enhanced basal ice melt (3–6 cm d−1), well away from the ice edge. Calculation of the upper ocean heat budget shows that local radiative heat input accounted for at least 89% of the observed latent heat losses and heat storage (partitioned 0.77/0.23). These results suggest that the extensive area of deteriorating sea ice observed away from the ice edge during the 2014 season, termed the “thermodynamically forced MIZ,” was driven primarily by local shortwave radiative forcing.
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Effects of keels on ice bottom turbulence exchange
Journal of Geophysical Research, 2003Co-Authors: Eric D. Skyllingstad, Clayton A. Paulson, W. Scott Pegau, Miles G. Mcphee, Timothy P. StantonAbstract:[1] The effects of ice keels on the upper ocean are examined using a combination of turbulence measurements and output from a large-eddy simulation (LES) model. Two cases are examined, one during the winter when the under-ice boundary Layer is relatively deep (∼20 m) and near the freezing point and a second during the summer when the ice is melting and the boundary Layer consists of a shallow (∼0.5 m), highly stratified Fresh Layer. In the winter case, measurements show that flow disruption by a 10-m-deep keel causes enhanced vertical mixing, increasing the heat flux from a background value of ∼5 W m−2 to values averaging ∼25 W m−2. Simulations using the LES model are in good agreement with the measurements and indicate that the keel generates a turbulent wake region extending hundreds of meters downstream from the keel. Elevated heat fluxes in the wake region are generated by increased entrainment of warmer water from beneath the mixed Layer. Simulations of summer cases demonstrate that shallow keels (∼0.5 m) generate strong turbulence that is able to rapidly mix the Fresh Layer in the lee of keels. However, this effect decreases quickly as the Fresh Layer accelerates to match the ice velocity. Deeper keels (1 m) follow a similar pattern but generate more mixing as the Fresh Layer is forced under the keel. Simulated ice melt heat fluxes are similar to estimates made from ice balance measurements taken during the Surface Heat Budget of the Arctic Ocean summer field program.
G. Basterretxea - One of the best experts on this subject based on the ideXlab platform.
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An assessment of karstic submarine groundwater and associated nutrient discharge to a Mediterranean coastal area (Balearic Islands, Spain) using radium isotopes
Biogeochemistry, 2010Co-Authors: E. Garcia-solsona, J. Garcia-orellana, P. Masqué, E. Garcés, O. Radakovitch, A. Mayer, S. Estradé, G. BasterretxeaAbstract:Short and long-lived radium isotopes (^223Ra, ^224Ra, ^226Ra, ^228Ra) were used to quantify submarine groundwater discharge (SGD) and its associated input of inorganic nitrogen (NO_3 ^−), phosphorus (PO_4 ^3−) and silica (SiO_4 ^4−) into the karstic Alcalfar Cove, a coastal region of Minorca Island (Western Mediterranean Sea). Cove water, seawater and groundwater (wells and karstic springs) samples were collected in May 2005 and February 2006 for radium isotopes and in November 2007 for dissolved inorganic nutrients. Salinity profiles in cove waters suggested that SGD is derived from shallow brackish springs that formed a buoyant surface Fresh Layer of only 0.3 m depth. A binary mixing model that considers the distribution of radium activities was used to determine the cove water composition. Results showed that cove waters contained 20% brackish groundwater; of which 6% was recirculated seawater and 14% corresponded to Freshwater discharge. Using a radium-derived residence time of 2.4 days, a total SGD flux of 150,000 m^3 year^−1 was calculated, consisting of 45,000 m^3 year^−1 recirculated seawater and 105,000 m^3 year^−1 Fresh groundwater. Fresh SGD fluxes of NO_3 ^−, SiO_4 ^4− and PO_4 ^3− were estimated to be on the order of 18,000, 1,140 and 4 μmol m^−2 day^−1, respectively, and presumably sustain the high phytoplankton biomass observed in the cove during summer. The total amount of NO_3 ^− and SiO_4 ^4− supplied by SGD was higher than the measured inventories in the cove, while the reverse was true for PO_4 ^3−. These discrepancies are likely due to non-conservative biogeochemical processes that occur within the subterranean estuary and Alcalfar Cove waters.
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An assessment of karstic submarine groundwater and associated nutrient discharge to a Mediterranean coastal area (Balearic Islands, Spain) using radium isotopes
Biogeochemistry, 2009Co-Authors: E. Garcia-solsona, J. Garcia-orellana, P. Masqué, E. Garcés, O. Radakovitch, A. Mayer, S. Estradé, G. BasterretxeaAbstract:19 pages, 6 figures, 3 tablesShort and long-lived radium isotopes (223Ra, 224Ra, 226Ra, 228Ra) were used to quantify submarine groundwater discharge (SGD) and its associated input of inorganic nitrogen (NO3 −), phosphorus (PO4 3−) and silica (SiO4 4−) into the karstic Alcalfar Cove, a coastal region of Minorca Island (Western Mediterranean Sea). Cove water, seawater and groundwater (wells and karstic springs) samples were collected in May 2005 and February 2006 for radium isotopes and in November 2007 for dissolved inorganic nutrients. Salinity profiles in cove waters suggested that SGD is derived from shallow brackish springs that formed a buoyant surface Fresh Layer of only 0.3 m depth. A binary mixing model that considers the distribution of radium activities was used to determine the cove water composition. Results showed that cove waters contained 20% brackish groundwater; of which 6% was recirculated seawater and 14% corresponded to Freshwater discharge. Using a radium-derived residence time of 2.4 days, a total SGD flux of 150,000 m3 year−1 was calculated, consisting of 45,000 m3 year−1 recirculated seawater and 105,000 m3 year−1 Fresh groundwater. Fresh SGD fluxes of NO3 −, SiO4 4− and PO4 3− were estimated to be on the order of 18,000, 1,140 and 4 μmol m−2 day−1, respectively, and presumably sustain the high phytoplankton biomass observed in the cove during summer. The total amount of NO3 − and SiO4 4− supplied by SGD was higher than the measured inventories in the cove, while the reverse was true for PO4 3−. These discrepancies are likely due to non-conservative biogeochemical processes that occur within the subterranean estuary and Alcalfar Cove watersThis project has been partially supported by the Institut Menorquí d’Estudis (IME) and the Departament d’Universitats, Recerca i Societat de la Informació of the Generalitat de Catalunya (PICS program no. 2434). Support from the Spanish Government and the Fulbright Commission for a post-doctoral fellowship to J.G.-O. (ref 2007-0516) is gratefully acknowledged. Support for the research of PM was received through the prize “ICREA Academia”, funded by the Generalitat de CatalunyaPeer reviewe
Frieder W. Scheller - One of the best experts on this subject based on the ideXlab platform.
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New principle of direct real-time monitoring of the interaction of cholinesterase and its inhibitors by piezolectric biosensor.
Biosensors & bioelectronics, 2003Co-Authors: Alexander Makower, Jan Halámek, Petr Skládal, Frank Kernchen, Frieder W. SchellerAbstract:This paper describes a new method for the sensitive detection of cholinesterase inhibitors based on real-time monitoring using a piezoelectric biosensor. The cholinesterase inhibitor paraoxon was immobilized on the sensing surface via a chelate complex as the recognition element. At first, the conjugate of N -mercaptoundecanoic acid (MUA) with Na ,Na -bis (carboxymethyl)-L-lysine (NTA-Lys) was chemisorbed to form a self-assembled monoLayer on the surface of the gold electrode of the piezosensor. In the next step, paraoxon � /spacer � /hexahistidine conjugate was linked to the MUA � /Lys-NTA Layer via the chelate complex with Ni 2� . The paraoxon-modified surface thus obtained was applied for the binding of human butyrylcholinesterase (BChE). Regeneration of the sensing surface was achieved by splitting the chelate complex with EDTA and depositing a Fresh Layer of Ni 2� followed by addition of the paraoxon � /spacer � /hexahistidine. In the presence of free inhibitors like diisopropylfluorophosphate (DFP), binding of BChE to the surface-bound paraoxon was decreased. In this way, a competitive affinity assay for organophosphorus compounds was developed. The limit of detection for DFP as a model compound was 10 nmol/l (ca. 2 mg/l). This new concept seems suitable for constructing biosensors for the group-specific detection of cholinesterase-inhibiting substances like insecticides in the field. # 2003 Elsevier Science B.V. All rights reserved.
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New principle for the direct real-time monitoring ofinteraction of cholinesterase and its inhibitors
Biosensors and Bioelectronics, 2003Co-Authors: Alexander Makower, Jan Halámek, Petr Skládal, Franz Kernchenc, Frieder W. SchellerAbstract:A new method for the sensitive detection of cholinesterase inhibitors based on real-time monitoring using a piezoelectric biosensor. The cholinesterase inhibitor paraoxon was immobilized on the sensing surface via a chelate complex as the recognition element. At first, the conjugate of N?mercaptoundecanoic acid (MUA) with Na, Na-bis (carboxymethyl)-L-Lysine (NTA-Lys) was chemisorbed to form a self-assembled monoLayer on the surface of the gold electrode of the piezosensor. In the next step, paraoxon-spacer-hexahistidine conjugate was linked to the MUA-Lys-NTA Layer via the chelate complex with Ni2+. The paraoxon-modified surface thus obtained was applied for the binding of human butyrylcholinesterase. Regeneration of the sensing surface was achieved by splitting the chelate complex with EDTA and depositing a Fresh Layer of Ni2+ followed by addition of the paraoxon-spacer-hexahistidine. In the presence of free inhibitors like diisopropylfluorphosphate (DFP), binding of BChE to the surface-bound paraoxon was decreased. In this way, a competitive affinity assay for organophosphorus compounds was developed. The limit of detection for DFP as a model compound was 10 nmol/l (approx. 2 mg/l). This new concept seems suitable for constructing biosensors for the group-specific detection of cholinesterase-inhibiting substances like insecticides in the field.
