{"title":"El Nino, Sea Surface Temperature Anomaly and Coral Bleaching in the South Atlantic: A Chain of Events Modeled With a Bayesian Approach","authors":"D. S. Lisboa, R. Kikuchi, Z. M. Leão","doi":"10.1002/2017JC012824","DOIUrl":"https://doi.org/10.1002/2017JC012824","url":null,"abstract":"","PeriodicalId":15836,"journal":{"name":"Journal of Geophysical Research","volume":"123 1","pages":"2554-2569"},"PeriodicalIF":0.0,"publicationDate":"2018-04-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1002/2017JC012824","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45865996","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
L. Arteaga, N. Haëntjens, E. Boss, K. Johnson, J. Sarmiento
Carbon export efficiency (e-ratio) is defined as the fraction of organic carbon fixed through net primary production (NPP) that is exported out of the surface productive layer of the ocean. Recent observations for the Southern Ocean suggest a negative e-ratio versus NPP relationship, and a reduced dependency of export efficiency on temperature, different than in the global domain. In this study, we complement information from a passive satellite sensor with novel space-based lidar observations of ocean particulate backscattering to infer NPP over the entire annual cycle, and estimate Southern Ocean export rates from five different empirical models of export efficiency. Inferred Southern Ocean NPP falls within the range of previous studies, with a mean estimate of 15.8 (6 3.9) Pg C yr for the region south of 30!S during the 2005–2016 period. We find that an export efficiency model that accounts for silica(Si)-ballasting, which is constrained by observations with a negative e-ratio versus NPP relationship, shows the best agreement with in situ-based estimates of annual net community production (annual export of 2.7 6 0.6 Pg C yr south of 30!S). By contrast, models based on the analysis of global observations with a positive e-ratio versus NPP relationship predict annually integrated export rates that are " 33% higher than the Si-dependent model. Our results suggest that accounting for Si-induced ballasting is important for the estimation of carbon export in the Southern Ocean. Plain Language Summary The amount of organic carbon that is exported from the surface to the deep ocean exerts an important control on atmospheric carbon dioxide and the transfer of organic material across trophic levels. In this study, we make use of novel satellite information, combined with autonomous profiling floats, to estimate the efficiency and the amount of organic carbon exported in the Southern Ocean by phytoplankton. We find that previous global formulations can overestimate the amount of carbon exported in this region, and that taking into account the oceanic surface silica concentration is necessary to accurately estimate carbon export in the Southern Ocean.
碳输出效率(e-ratio)被定义为通过净初级生产(NPP)从海洋表层生产层输出的固定有机碳的比例。最近对南大洋的观测表明，e比与NPP呈负相关，出口效率对温度的依赖性降低，这与全球范围的观测结果不同。在这项研究中，我们将无源卫星传感器的信息与新型的天基激光雷达海洋颗粒后向散射观测相补充，以推断整个年周期的NPP，并通过五种不同的出口效率经验模型估计南大洋出口率。推断的南大洋NPP落在先前研究的范围内，30°C以南地区的平均估计为15.8 (6 3.9)Pg C /年。在2005年至2016年期间，该公司在美国上市。我们发现，考虑二氧化硅(Si)压载的出口效率模型(受负e比与NPP关系的观测值的约束)与基于现状的年度净社区产量估算(30!S以南的年出口量为2.7 6 0.6 Pg C)最吻合。相比之下，基于全球观测数据分析的模型预测的年综合出口率比依赖si的模型高33%。我们的研究结果表明，考虑硅致压载对于估计南大洋的碳输出是重要的。从表层向深海输出的有机碳量对大气二氧化碳和有机物质在营养水平上的转移起着重要的控制作用。在这项研究中，我们利用新的卫星信息，结合自主剖面浮标，估计了浮游植物在南大洋输出有机碳的效率和数量。我们发现以往的全球公式可能高估了该地区的碳出口量，并且考虑海洋表面二氧化硅浓度是准确估计南大洋碳出口量的必要条件。
{"title":"Assessment of Export Efficiency Equations in the Southern Ocean Applied to Satellite-Based Net Primary Production: e-ratio models in the Southern Ocean","authors":"L. Arteaga, N. Haëntjens, E. Boss, K. Johnson, J. Sarmiento","doi":"10.1002/2018jc013787","DOIUrl":"https://doi.org/10.1002/2018jc013787","url":null,"abstract":"Carbon export efficiency (e-ratio) is defined as the fraction of organic carbon fixed through net primary production (NPP) that is exported out of the surface productive layer of the ocean. Recent observations for the Southern Ocean suggest a negative e-ratio versus NPP relationship, and a reduced dependency of export efficiency on temperature, different than in the global domain. In this study, we complement information from a passive satellite sensor with novel space-based lidar observations of ocean particulate backscattering to infer NPP over the entire annual cycle, and estimate Southern Ocean export rates from five different empirical models of export efficiency. Inferred Southern Ocean NPP falls within the range of previous studies, with a mean estimate of 15.8 (6 3.9) Pg C yr for the region south of 30!S during the 2005–2016 period. We find that an export efficiency model that accounts for silica(Si)-ballasting, which is constrained by observations with a negative e-ratio versus NPP relationship, shows the best agreement with in situ-based estimates of annual net community production (annual export of 2.7 6 0.6 Pg C yr south of 30!S). By contrast, models based on the analysis of global observations with a positive e-ratio versus NPP relationship predict annually integrated export rates that are \" 33% higher than the Si-dependent model. Our results suggest that accounting for Si-induced ballasting is important for the estimation of carbon export in the Southern Ocean. Plain Language Summary The amount of organic carbon that is exported from the surface to the deep ocean exerts an important control on atmospheric carbon dioxide and the transfer of organic material across trophic levels. In this study, we make use of novel satellite information, combined with autonomous profiling floats, to estimate the efficiency and the amount of organic carbon exported in the Southern Ocean by phytoplankton. We find that previous global formulations can overestimate the amount of carbon exported in this region, and that taking into account the oceanic surface silica concentration is necessary to accurately estimate carbon export in the Southern Ocean.","PeriodicalId":15836,"journal":{"name":"Journal of Geophysical Research","volume":"123 1","pages":"2945-2964"},"PeriodicalIF":0.0,"publicationDate":"2018-04-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1002/2018jc013787","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47077036","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
H. Loisel, D. Stramski, D. Dessailly, C. Jamet, Linhai Li, R. Reynolds
{"title":"An Inverse Model for Estimating the Optical Absorption and Backscattering Coefficients of Seawater From Remote-Sensing Reflectance Over a Broad Range of Oceanic and Coastal Marine Environments: INVERSION OF SEAWATER IOPS","authors":"H. Loisel, D. Stramski, D. Dessailly, C. Jamet, Linhai Li, R. Reynolds","doi":"10.1002/2017jc013632","DOIUrl":"https://doi.org/10.1002/2017jc013632","url":null,"abstract":"","PeriodicalId":15836,"journal":{"name":"Journal of Geophysical Research","volume":"123 1","pages":"2141-2171"},"PeriodicalIF":0.0,"publicationDate":"2018-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1002/2017jc013632","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42790588","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Baroclinic instability of lateral density gradients gives way to lateral buoyancy transport, which often results in convergence of buoyancy transport. Along a sloping bottom, the induced convergence can force upward extension of bottom water. Eddy transport induced convergence at the bottom and the consequent suspended layers of bottom properties are investigated using a three-dimensional idealized model. Motivated by the distinct characteristics of intrusions over the Texas-Louisiana shelf, a series of configura-tions are performed with the purpose of identifying parameter impacts on the intensity of eddy transport. This study uses the ‘‘horizontal slope Burger number’’ as the predominant parameter; the parameter is func-tioned with S H 5 SRi 2 1 = 2 5 d = Ri to identify formation of baroclinic instability, where S is the slope Burger number, d is the slope parameter, and Ri is the Richardson number, previously shown to be the parameter that predicts the intensity of baroclinic instability on the shelf. Intrusion spreads into the interior abutting a layer that is characterized by degraded vertical stratification; a thickening in the bottom boundary layer colocates with the intrusion, which usually thins at either edge of the intrusion because of a density barrier in association with concentrated isopycnals. The intensity of convergence degrades and bottom tracer fluxes reduce linearly with increased S H on logarithmic scales, and the characteristics of bottom boundary layer behavior and the reversal in alongshore current tend to vanish.
{"title":"A Study of Baroclinic Instability Induced Convergence Near the Bottom Using Water Age Simulations: NEAR-BOTTOM CONVERGENCE","authors":"Wenxia Zhang, R. Hetland","doi":"10.1002/2017jc013561","DOIUrl":"https://doi.org/10.1002/2017jc013561","url":null,"abstract":"Baroclinic instability of lateral density gradients gives way to lateral buoyancy transport, which often results in convergence of buoyancy transport. Along a sloping bottom, the induced convergence can force upward extension of bottom water. Eddy transport induced convergence at the bottom and the consequent suspended layers of bottom properties are investigated using a three-dimensional idealized model. Motivated by the distinct characteristics of intrusions over the Texas-Louisiana shelf, a series of configura-tions are performed with the purpose of identifying parameter impacts on the intensity of eddy transport. This study uses the ‘‘horizontal slope Burger number’’ as the predominant parameter; the parameter is func-tioned with S H 5 SRi 2 1 = 2 5 d = Ri to identify formation of baroclinic instability, where S is the slope Burger number, d is the slope parameter, and Ri is the Richardson number, previously shown to be the parameter that predicts the intensity of baroclinic instability on the shelf. Intrusion spreads into the interior abutting a layer that is characterized by degraded vertical stratification; a thickening in the bottom boundary layer colocates with the intrusion, which usually thins at either edge of the intrusion because of a density barrier in association with concentrated isopycnals. The intensity of convergence degrades and bottom tracer fluxes reduce linearly with increased S H on logarithmic scales, and the characteristics of bottom boundary layer behavior and the reversal in alongshore current tend to vanish.","PeriodicalId":15836,"journal":{"name":"Journal of Geophysical Research","volume":"123 1","pages":"1962-1977"},"PeriodicalIF":0.0,"publicationDate":"2018-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1002/2017jc013561","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47022231","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Numerical model experiments are used to study the effects of multiple channel bends on estuarine dynamics and, in particular, on secondary flows. These effects are demonstrated by comparing experiments with two different idealized trumpet-shaped estuaries, one straight and another one with a 8 km meandering section in the middle of the estuary. Meanders complicate the flow field by introducing secondary processes. For instance, meanders increase turbulence and associated mixing locally within the water column, as well as outside the meandering portion. Furthermore, meanders transform up to 30% of the along-channel momentum into secondary circulation. Production of turbulence and secondary currents is different at flood and ebb tidal phases. At flood, meanders lead to unstable stratification and increased turbulence. At ebb, the flow develops a helical pattern and adjusts to the channel curvature with minimal decrease in density stability. The secondary circulation asymmetry is caused by an interplay between the across-channel baroclinic pressure gradient force and the centrifugal force. During ebb both forces enhance each other, whereas they oppose during flood. As a consequence of this interaction between baroclinic forcing and curving morphology, ebb flows and horizontal buoyancy fluxes increase relative to flood. The enhanced ebb dominance shifts a density front toward the mouth of the estuary, thus reducing salt intrusion.
{"title":"Secondary Circulation Asymmetry in a Meandering, Partially Stratified Estuary: SECONDARY CIRCULATION ASYMMETRY","authors":"J. Pein, A. Valle‐Levinson, E. Stanev","doi":"10.1002/2016jc012623","DOIUrl":"https://doi.org/10.1002/2016jc012623","url":null,"abstract":"Numerical model experiments are used to study the effects of multiple channel bends on estuarine dynamics and, in particular, on secondary flows. These effects are demonstrated by comparing experiments with two different idealized trumpet-shaped estuaries, one straight and another one with a 8 km meandering section in the middle of the estuary. Meanders complicate the flow field by introducing secondary processes. For instance, meanders increase turbulence and associated mixing locally within the water column, as well as outside the meandering portion. Furthermore, meanders transform up to 30% of the along-channel momentum into secondary circulation. Production of turbulence and secondary currents is different at flood and ebb tidal phases. At flood, meanders lead to unstable stratification and increased turbulence. At ebb, the flow develops a helical pattern and adjusts to the channel curvature with minimal decrease in density stability. The secondary circulation asymmetry is caused by an interplay between the across-channel baroclinic pressure gradient force and the centrifugal force. During ebb both forces enhance each other, whereas they oppose during flood. As a consequence of this interaction between baroclinic forcing and curving morphology, ebb flows and horizontal buoyancy fluxes increase relative to flood. The enhanced ebb dominance shifts a density front toward the mouth of the estuary, thus reducing salt intrusion.","PeriodicalId":15836,"journal":{"name":"Journal of Geophysical Research","volume":"123 1","pages":"1670-1683"},"PeriodicalIF":0.0,"publicationDate":"2018-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1002/2016jc012623","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41731479","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
V. Tamsitt, R. Abernathey, M. Mazloff, Jian Wang, L. Talley
Upwelling of northern deep waters in the Southern Ocean is fundamentally important for the closure of the global meridional overturning circulation and delivers carbon and nutrient-rich deep waters to the sea surface. We quantify water mass transformation along upwelling pathways originating in the Atlantic, Indian, and Pacific and ending at the surface of the Southern Ocean using Lagrangian trajectories in an eddy-permitting ocean state estimate. Recent related work shows that upwelling in the interior below about 400 m depth is localized at hot spots associated with major topographic features in the path of the Antarctic Circumpolar Current, while upwelling through the surface layer is more broadly distributed. In the ocean interior upwelling is largely isopycnal; Atlantic and to a lesser extent Indian Deep Waters cool and freshen while Pacific deep waters are more stable, leading to a homogenization of water mass properties. As upwelling water approaches the mixed layer, there is net strong transformation toward lighter densities due to mixing of freshwater, but there is a divergence in the density distribution as Upper Circumpolar Deep Water tends become lighter and dense Lower Circumpolar Deep Water tends to become denser. The spatial distribution of transformation shows more rapid transformation at eddy hot spots associated with major topography where density gradients are enhanced; however, the majority of cumulative density change along trajectories is achieved by background mixing. We compare the Lagrangian analysis to diagnosed Eulerian water mass transformation to attribute the mechanisms leading to the observed transformation.
{"title":"Transformation of Deep Water Masses Along Lagrangian Upwelling Pathways in the Southern Ocean: SOUTHERN OCEAN UPWELLING TRANSFORMATION","authors":"V. Tamsitt, R. Abernathey, M. Mazloff, Jian Wang, L. Talley","doi":"10.1002/2017jc013409","DOIUrl":"https://doi.org/10.1002/2017jc013409","url":null,"abstract":"Upwelling of northern deep waters in the Southern Ocean is fundamentally important for the closure of the global meridional overturning circulation and delivers carbon and nutrient-rich deep waters to the sea surface. We quantify water mass transformation along upwelling pathways originating in the Atlantic, Indian, and Pacific and ending at the surface of the Southern Ocean using Lagrangian trajectories in an eddy-permitting ocean state estimate. Recent related work shows that upwelling in the interior below about 400 m depth is localized at hot spots associated with major topographic features in the path of the Antarctic Circumpolar Current, while upwelling through the surface layer is more broadly distributed. In the ocean interior upwelling is largely isopycnal; Atlantic and to a lesser extent Indian Deep Waters cool and freshen while Pacific deep waters are more stable, leading to a homogenization of water mass properties. As upwelling water approaches the mixed layer, there is net strong transformation toward lighter densities due to mixing of freshwater, but there is a divergence in the density distribution as Upper Circumpolar Deep Water tends become lighter and dense Lower Circumpolar Deep Water tends to become denser. The spatial distribution of transformation shows more rapid transformation at eddy hot spots associated with major topography where density gradients are enhanced; however, the majority of cumulative density change along trajectories is achieved by background mixing. We compare the Lagrangian analysis to diagnosed Eulerian water mass transformation to attribute the mechanisms leading to the observed transformation.","PeriodicalId":15836,"journal":{"name":"Journal of Geophysical Research","volume":"123 1","pages":"1994-2017"},"PeriodicalIF":0.0,"publicationDate":"2018-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1002/2017jc013409","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48684412","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
G. Pilo, P. Oke, R. Coleman, T. Rykova, K. Ridgway
Vertical motions within eddies play an important role in the exchange of properties and energy between the upper ocean and the ocean interior. Here we analyze alternating upward and downward cells in anticyclonic eddies in the East Australian Current region using a global eddy‐resolving model. The cells explain over 50% of the variance of vertical velocity within these eddies. We show that the upward and downward cells relate to eddy distortion, defined as the change in eddy shape over time. In anticyclonic eddies in the Southern Hemisphere, an inward distortion is associated with upward motion and an outward distortion is associated with downward motion. We discuss two mechanisms that link eddy distortion to vertical velocity. One mechanism relates to changes in stratification and relative vorticity in the eddy interior. The other mechanism relates to divergence of the horizontal flow in different quadrants of the eddy. We show that mesoscale changes in sea level anomaly can be used to infer the vertical motion within eddies.
{"title":"Patterns of Vertical Velocity Induced by Eddy Distortion in an Ocean Model: VERTICAL VELOCITY AND EDDY DISTORTION","authors":"G. Pilo, P. Oke, R. Coleman, T. Rykova, K. Ridgway","doi":"10.1002/2017jc013298","DOIUrl":"https://doi.org/10.1002/2017jc013298","url":null,"abstract":"Vertical motions within eddies play an important role in the exchange of properties and energy between the upper ocean and the ocean interior. Here we analyze alternating upward and downward cells in anticyclonic eddies in the East Australian Current region using a global eddy‐resolving model. The cells explain over 50% of the variance of vertical velocity within these eddies. We show that the upward and downward cells relate to eddy distortion, defined as the change in eddy shape over time. In anticyclonic eddies in the Southern Hemisphere, an inward distortion is associated with upward motion and an outward distortion is associated with downward motion. We discuss two mechanisms that link eddy distortion to vertical velocity. One mechanism relates to changes in stratification and relative vorticity in the eddy interior. The other mechanism relates to divergence of the horizontal flow in different quadrants of the eddy. We show that mesoscale changes in sea level anomaly can be used to infer the vertical motion within eddies.","PeriodicalId":15836,"journal":{"name":"Journal of Geophysical Research","volume":"123 1","pages":"2274-2292"},"PeriodicalIF":0.0,"publicationDate":"2018-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1002/2017jc013298","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46680224","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2018-02-03eCollection Date: 2018-02-01DOI: 10.1161/JAHA.117.004225
[This corrects the article DOI: 10.1161/JAHA.116.003506.].
[此处更正了文章 DOI：10.1161/JAHA.116.003506]。
{"title":"Erratum: Critical Role of Coaptive Strain in Aortic Valve Leaflet Homeostasis: Use of a Novel Flow Culture Bioreactor to Explore Heart Valve Mechanobiology.","authors":"","doi":"10.1161/JAHA.117.004225","DOIUrl":"10.1161/JAHA.117.004225","url":null,"abstract":"<p><p>[This corrects the article DOI: 10.1161/JAHA.116.003506.].</p>","PeriodicalId":15836,"journal":{"name":"Journal of Geophysical Research","volume":"101 1","pages":"e004225"},"PeriodicalIF":0.0,"publicationDate":"2018-02-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5850228/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"79384933","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
K. Hancke, L. Lund-Hansen, M. Lamare, S. H. Pedersen, M. King, Per Andersen, B. Sorrell
Microalgae colonizing the underside of sea ice in spring are a key component of the Arctic foodweb as they drive early primary production and transport of carbon from the atmosphere to the ocean interior. Onset of the spring bloom of ice algae is typically limited by the availability of light, and the current consensus is that a few tens-of-centimeters of snow is enough to prevent sufficient solar radiation to reach underneath the sea ice. We challenge this consensus, and investigated the onset and the light requirement of an ice algae spring bloom, and the importance of snow optical properties for light penetration. Colonization by ice algae began in May under >1 m of first-year sea ice with 1 m thick snow cover on top, in NE Greenland. The initial growth of ice algae began at extremely low irradiance (<0.17 lmol photons m s) and was documented as an increase in Chlorophyll a concentration, an increase in algal cell number, and a viable photosynthetic activity. Snow thickness changed little during May (from 110 to 91 cm), however the snow temperature increased steadily, as observed from automated high-frequency temperature profiles. We propose that changes in snow optical properties, caused by temperature-driven snow metamorphosis, was the primary driver for allowing sufficient light to penetrate through the thick snow and initiate algae growth below the sea ice. This was supported by radiative-transfer modeling of light attenuation. Implications are an earlier productivity by ice algae in Arctic sea ice than recognized previously.
{"title":"Extreme Low Light Requirement for Algae Growth Underneath Sea Ice: A Case Study From Station Nord, NE Greenland: MINIMUM LIGHT REQUIREMENT FOR ICE ALGAE","authors":"K. Hancke, L. Lund-Hansen, M. Lamare, S. H. Pedersen, M. King, Per Andersen, B. Sorrell","doi":"10.1002/2017jc013263","DOIUrl":"https://doi.org/10.1002/2017jc013263","url":null,"abstract":"Microalgae colonizing the underside of sea ice in spring are a key component of the Arctic foodweb as they drive early primary production and transport of carbon from the atmosphere to the ocean interior. Onset of the spring bloom of ice algae is typically limited by the availability of light, and the current consensus is that a few tens-of-centimeters of snow is enough to prevent sufficient solar radiation to reach underneath the sea ice. We challenge this consensus, and investigated the onset and the light requirement of an ice algae spring bloom, and the importance of snow optical properties for light penetration. Colonization by ice algae began in May under >1 m of first-year sea ice with 1 m thick snow cover on top, in NE Greenland. The initial growth of ice algae began at extremely low irradiance (<0.17 lmol photons m s) and was documented as an increase in Chlorophyll a concentration, an increase in algal cell number, and a viable photosynthetic activity. Snow thickness changed little during May (from 110 to 91 cm), however the snow temperature increased steadily, as observed from automated high-frequency temperature profiles. We propose that changes in snow optical properties, caused by temperature-driven snow metamorphosis, was the primary driver for allowing sufficient light to penetrate through the thick snow and initiate algae growth below the sea ice. This was supported by radiative-transfer modeling of light attenuation. Implications are an earlier productivity by ice algae in Arctic sea ice than recognized previously.","PeriodicalId":15836,"journal":{"name":"Journal of Geophysical Research","volume":"123 1","pages":"985-1000"},"PeriodicalIF":0.0,"publicationDate":"2018-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1002/2017jc013263","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47479228","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
J. Zanden, A. DominicA.vander, I. Cáceres, D. Hurther, S. McLelland, J. Ribberink, T. O'Donoghue
Hydrodynamics under regular plunging breaking waves over a fixed breaker bar were studied in a large-scale wave flume. A previous paper reported on the outer flow hydrodynamics; the present paper focuses on the turbulence dynamics near the bed (up to 0.10 m from the bed). Velocities were measured with high spatial and temporal resolution using a two component laser Doppler anemometer. The results show that even at close distance from the bed (1 mm), the turbulent kinetic energy (TKE) increases by a factor five between the shoaling, and breaking regions because of invasion of wave breaking turbulence. The sign and phase behavior of the time-dependent Reynolds shear stresses at elevations up to approximately 0.02 m from the bed (roughly twice the elevation of the boundary layer overshoot) are mainly controlled by local bed-shear-generated turbulence, but at higher elevations Reynolds stresses are controlled by wave breaking turbulence. The measurements are subsequently analyzed to investigate the TKE budget at wave-averaged and intrawave time scales. Horizontal and vertical turbulence advection, production, and dissipation are the major terms. A two-dimensional wave-averaged circulation drives advection of wave breaking turbulence through the near-bed layer, resulting in a net downward influx in the bar trough region, followed by seaward advection along the bar's shoreward slope, and an upward outflux above the bar crest. The strongly nonuniform flow across the bar combined with the presence of anisotropic turbulence enhances turbulent production rates near the bed.
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