B. Hansen, K. Larsen, H. Hátún, S. Olsen, A. Gierisch, S. Østerhus, S. Ólafsdóttir
Abstract. The inflow of warm and saline Atlantic water to the Arctic Mediterranean (Nordic Seas and Arctic Ocean) between Iceland and the Faroes (IF inflow) is the strongest Atlantic inflow branch in terms of volume transport and is associated with a large transport of heat towards the Arctic. The IF inflow is monitored in a section east of the Iceland–Faroe Ridge (IFR) by use of sea level anomaly (SLA) data from satellite altimetry, a method that has been calibrated by in situ observations gathered over 2 decades. Monthly averaged surface velocity anomalies calculated from SLA data were strongly correlated with anomalies measured by moored acoustic Doppler current profilers (ADCPs) with consistently higher correlations when using the reprocessed SLA data released in December 2021 rather than the earlier version. In contrast to the earlier version, the reprocessed data also had the correct conversion factor between sea level slope and surface velocity required by geostrophy. Our results show that the IF inflow crosses the IFR in two separate branches. The Icelandic branch is a jet over the Icelandic slope with average surface speed exceeding 20 cm s−1, but it is narrow and shallow with an average volume transport of less than 1 Sv (106 m3 s−1). Most of the Atlantic water crosses the IFR close to its southernmost end in the Faroese branch. Between these two branches, water from the Icelandic branch turns back onto the ridge in a retroflection with a recirculation over the northernmost bank on the IFR. Combining multi-sensor in situ observations with satellite SLA data, monthly mean volume transport of the IF inflow has been determined from January 1993 to December 2021. The IF inflow is part of the Atlantic Meridional Overturning Circulation (AMOC), which is expected to weaken under continued global warming. Our results show no weakening of the IF inflow. Annually averaged volume transport of Atlantic water through the monitoring section had a statistically significant (95 % confidence level) increasing trend of (0.12±0.10) Sv per decade. Combined with increasing temperature, this caused an increase of 13 % in the heat transport, relative to 0 ∘C, towards the Arctic of the IF inflow over the 29 years of monitoring. The near-bottom layer over most of the IFR is dominated by cold water of Arctic origin that may contribute to the overflow across the ridge. Our observations confirm a dynamic link between the overflow and the Atlantic water flow above. The results also provide support for a previously posed hypothesis that this link may explain the difficulties in reproducing observed transport variations in the IF inflow in numerical ocean models, with consequences for its predictability under climate change.
摘要在冰岛和法罗群岛之间，大西洋暖流和咸水流入北极地中海(北欧海和北冰洋)(IF流入)是大西洋流入的最强分支，就体积输送而言，它与向北极输送大量热量有关。利用来自卫星测高的海平面异常(SLA)数据监测冰岛-法罗基(IFR)以东一段的中频流入，该方法已通过20多年来收集的现场观测进行校准。SLAdata计算的月平均地表速度异常与系泊声学多普勒电流剖面仪(ADCPs)测量的异常密切相关，当使用2021年12月发布的重新处理的SLA数据时，相关性始终较高。与早期版本相比，重新处理的数据也具有正确的海平面坡度和地表速度之间的转换因子。我们的结果表明，中频流入在两个独立的分支中穿过IFR。冰岛分支是冰岛斜坡上的射流，平均表面速度超过20 cm s - 1，但它又窄又浅，平均体积输送小于1 Sv(106 m3 s - 1)。大部分的大西洋水穿过ifr靠近其最南端的法罗分支。在这两个分支之间，来自冰岛分支的水在IFR最北岸的再循环中以反射的方式回流到山脊上。结合多传感器现场观测和卫星SLA数据，确定了1993年1月至2021年12月中频入流的月平均体积输送。中频流入是大西洋经向翻转环流(AMOC)的一部分，预计在全球持续变暖的情况下，该环流将减弱。我们的研究结果表明，中频流入没有减弱。通过监测断面的大西洋年平均输水量有统计学上显著的(95%置信水平)增长趋势(0.12±0.10)Sv / 10年。再加上气温升高，在29年的监测中，相对于0°C，中暑流入向北极的热输送增加了13%。IFR大部分上空的近底层主要是来自北极的冷水，这可能会导致横越高压脊的溢流。我们的观测证实了溢流和上面大西洋水流之间的动态联系。这些结果还支持了先前提出的一个假设，即这种联系可以解释在数值海洋模式中重现观测到的中频流入的输送变化的困难，并影响其在气候变化下的可预测性。
{"title":"The Iceland–Faroe warm-water flow towards the Arctic estimated from satellite altimetry and in situ observations","authors":"B. Hansen, K. Larsen, H. Hátún, S. Olsen, A. Gierisch, S. Østerhus, S. Ólafsdóttir","doi":"10.5194/os-19-1225-2023","DOIUrl":"https://doi.org/10.5194/os-19-1225-2023","url":null,"abstract":"Abstract. The inflow of warm and saline Atlantic water to the\u0000Arctic Mediterranean (Nordic Seas and Arctic Ocean) between Iceland and the\u0000Faroes (IF inflow) is the strongest Atlantic inflow branch in terms of\u0000volume transport and is associated with a large transport of heat towards the\u0000Arctic. The IF inflow is monitored in a section east of the Iceland–Faroe\u0000Ridge (IFR) by use of sea level anomaly (SLA) data from satellite altimetry,\u0000a method that has been calibrated by in situ observations gathered over 2\u0000decades. Monthly averaged surface velocity anomalies calculated from SLA\u0000data were strongly correlated with anomalies measured by moored acoustic\u0000Doppler current profilers (ADCPs) with consistently higher correlations when\u0000using the reprocessed SLA data released in December 2021 rather than the\u0000earlier version. In contrast to the earlier version, the reprocessed data\u0000also had the correct conversion factor between sea level slope and surface\u0000velocity required by geostrophy. Our results show that the IF inflow crosses\u0000the IFR in two separate branches. The Icelandic branch is a jet over the\u0000Icelandic slope with average surface speed exceeding 20 cm s−1, but it\u0000is narrow and shallow with an average volume transport of less than 1 Sv\u0000(106 m3 s−1). Most of the Atlantic water crosses the IFR\u0000close to its southernmost end in the Faroese branch. Between these two\u0000branches, water from the Icelandic branch turns back onto the ridge in a\u0000retroflection with a recirculation over the northernmost bank on the IFR.\u0000Combining multi-sensor in situ observations with satellite SLA data, monthly\u0000mean volume transport of the IF inflow has been determined from January 1993\u0000to December 2021. The IF inflow is part of the Atlantic Meridional\u0000Overturning Circulation (AMOC), which is expected to weaken under continued\u0000global warming. Our results show no weakening of the IF inflow. Annually\u0000averaged volume transport of Atlantic water through the monitoring section\u0000had a statistically significant (95 % confidence level) increasing trend\u0000of (0.12±0.10) Sv per decade. Combined with increasing temperature,\u0000this caused an increase of 13 % in the heat transport, relative to 0 ∘C, towards the Arctic of the IF inflow over the 29 years of\u0000monitoring. The near-bottom layer over most of the IFR is dominated by cold\u0000water of Arctic origin that may contribute to the overflow across the ridge.\u0000Our observations confirm a dynamic link between the overflow and the\u0000Atlantic water flow above. The results also provide support for a previously\u0000posed hypothesis that this link may explain the difficulties in reproducing\u0000observed transport variations in the IF inflow in numerical ocean models,\u0000with consequences for its predictability under climate change.\u0000","PeriodicalId":19535,"journal":{"name":"Ocean Science","volume":"5 1","pages":""},"PeriodicalIF":3.2,"publicationDate":"2023-08-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"84603860","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Magdalena Fritz, M. Mayer, L. Haimberger, S. Winkelbauer
Abstract. The transport of heat and freshwater from the Pacific Ocean to the Indian Ocean via the Indonesian seas is commonly referred to as the Indonesian Throughflow (ITF). The interaction between the ITF and large-scale phenomena occurring from intraseasonal to decadal timescales reflects its connection to the global ocean and the climate system, indicating the need for monitoring the ITF region. In situ observations in this region are highly valuable, but they are temporally and spatially insufficient for near-real-time monitoring. Ocean reanalyses have the potential to serve as near-real-time monitoring tools and to extend time series backward in time, yet a comprehensive quality assessment of their realism in this region with challenging bathymetry has been lacking so far. We focus on oceanic transports diagnosed from the Copernicus Marine Service (CMEMS) Global Reanalysis Ensemble Product (GREP) and the higher-resolution product GLORYS12V1, totaling six reanalysis products. They are validated against in situ observations taken from two different monitoring programs, namely International Nusantara Stratification and Transport (INSTANT 2004–2006) and Monitoring the Indonesian Throughflow (MITF 2006–2011 and 2013–2017), resulting in a total time series of about 11.5 years in the major inflow passage of the Makassar Strait and shorter sampled time series in the Lombok Strait, the Ombai Strait, and the Timor Passage. Results show that there is reasonable agreement between reanalysis-based transports and observations in terms of means, seasonal cycles, and variability, although some shortcomings stand out. The lower-resolution products do not represent the spatial structure of the flow accurately. They also tend to underestimate the integrated net flow in the narrower straits of Lombok and Ombai, an aspect that is improved in GLORYS12V1. Reanalyses tend to underestimate the effect of seasonal Kelvin waves on the transports, which leads to errors in the mean seasonal cycle. Interannual variations of reanalyzed transports agree well with observations, but uncertainties are much larger on sub-annual variability. Finally, as an application of physically consistent and observationally constrained fields provided by ocean reanalyses, we study the impact of the vertically varying pressure gradient on the vertical structure of the ITF to better understand an apparent two-layer regime of the flow.
{"title":"Assessment of Indonesian Throughflow transports from ocean reanalyses with mooring-based observations","authors":"Magdalena Fritz, M. Mayer, L. Haimberger, S. Winkelbauer","doi":"10.5194/os-19-1203-2023","DOIUrl":"https://doi.org/10.5194/os-19-1203-2023","url":null,"abstract":"Abstract. The transport of heat and freshwater from the Pacific Ocean to the Indian Ocean via the Indonesian seas is commonly referred to as the Indonesian Throughflow (ITF). The interaction between the ITF and large-scale phenomena occurring from intraseasonal to decadal timescales reflects its connection to the global ocean and the climate system, indicating the need for monitoring the ITF region. In situ observations in this region are highly valuable, but they are temporally and spatially insufficient for near-real-time monitoring. Ocean reanalyses have the potential to serve as near-real-time monitoring tools and to extend time series backward in time, yet a comprehensive quality assessment of their realism in this region with challenging bathymetry has been lacking so far. We focus on oceanic transports diagnosed from the Copernicus Marine Service (CMEMS) Global Reanalysis Ensemble Product (GREP) and the higher-resolution product GLORYS12V1, totaling six reanalysis products. They are validated against in situ observations taken from two different monitoring programs, namely International Nusantara Stratification and Transport (INSTANT 2004–2006) and Monitoring the Indonesian Throughflow (MITF 2006–2011 and 2013–2017), resulting in a total time series of about 11.5 years in the major inflow passage of the Makassar Strait and shorter sampled time series in the Lombok Strait, the Ombai Strait, and the Timor Passage. Results show that there is reasonable agreement between reanalysis-based transports and observations in terms of means, seasonal cycles, and variability, although some shortcomings stand out. The lower-resolution products do not represent the spatial structure of the flow accurately. They also tend to underestimate the integrated net flow in the narrower straits of Lombok and Ombai, an aspect that is improved in GLORYS12V1. Reanalyses tend to underestimate the effect of seasonal Kelvin waves on the transports, which leads to errors in the mean seasonal cycle. Interannual variations of reanalyzed transports agree well with observations, but uncertainties are much larger on sub-annual variability. Finally, as an application of physically consistent and observationally constrained fields provided by ocean reanalyses, we study the impact of the vertically varying pressure gradient on the vertical structure of the ITF to better understand an apparent two-layer regime of the flow.\u0000","PeriodicalId":19535,"journal":{"name":"Ocean Science","volume":"29 1","pages":""},"PeriodicalIF":3.2,"publicationDate":"2023-08-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"76640238","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Abstract. We investigated the connectivity properties of an idealized western boundary current system separating two ocean gyres, where the flow is characterized by a well-defined mean circulation as well as energetic fine-scale features (i.e., mesoscale and submesoscale currents). We used a time-evolving 3D flow field from a high-resolution (HR-3D) ocean model of this system. In order to evaluate the role of the fine scales in connectivity estimates, we computed Lagrangian trajectories in three different ways: using the HR-3D flow, using the same flow but filtered on a coarse-resolution grid (CR-3D), and using the surface layer flow only (HR-SL). We examined connectivity between the two gyres along the western boundary current and across it by using and comparing different metrics, such as minimum and averaged values of transit time between 16 key sites, arrival depths, and probability density functions of transit times. We find that when the fine-scale flow is resolved, the numerical particles connect pairs of sites faster (between 100 to 300 d) than when it is absent. This is particularly true for sites that are along and near the jets separating the two gyres. Moreover, the connectivity is facilitated when 3D instead of surface currents are resolved. Finally, our results emphasize that ocean connectivity is 3D and not 2D and that assessing connectivity properties using climatologies or low-resolution velocity fields yields strongly biased estimates.
{"title":"Sensitivity of gyre-scale marine connectivity estimates to fine-scale circulation","authors":"S. Hariri, S. Speich, B. Blanke, M. Lévy","doi":"10.5194/os-19-1183-2023","DOIUrl":"https://doi.org/10.5194/os-19-1183-2023","url":null,"abstract":"Abstract. We investigated the connectivity properties of an\u0000idealized western boundary current system separating two ocean gyres, where\u0000the flow is characterized by a well-defined mean circulation as well as\u0000energetic fine-scale features (i.e., mesoscale and submesoscale currents).\u0000We used a time-evolving 3D flow field from a high-resolution (HR-3D) ocean\u0000model of this system. In order to evaluate the role of the fine scales in\u0000connectivity estimates, we computed Lagrangian trajectories in three\u0000different ways: using the HR-3D flow, using the same flow but filtered on a\u0000coarse-resolution grid (CR-3D), and using the surface layer flow only\u0000(HR-SL). We examined connectivity between the two gyres along the western\u0000boundary current and across it by using and comparing different metrics, such\u0000as minimum and averaged values of transit time between 16 key sites, arrival\u0000depths, and probability density functions of transit times. We find that\u0000when the fine-scale flow is resolved, the numerical particles connect pairs\u0000of sites faster (between 100 to 300 d) than when it is absent. This\u0000is particularly true for sites that are along and near the jets separating\u0000the two gyres. Moreover, the connectivity is facilitated when 3D instead of\u0000surface currents are resolved. Finally, our results emphasize that ocean\u0000connectivity is 3D and not 2D and that assessing connectivity properties\u0000using climatologies or low-resolution velocity fields yields strongly biased\u0000estimates.\u0000","PeriodicalId":19535,"journal":{"name":"Ocean Science","volume":"66 1","pages":""},"PeriodicalIF":3.2,"publicationDate":"2023-08-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"83851290","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Abstract. Analytical and numerical solutions of the linearized rotating shallow water equations are combined to study the geostrophic adjustment on the midlatitude β plane. The adjustment is examined in zonal periodic channels of width Ly=4Rd (narrow channel, where Rd is the radius of deformation) and Ly=60Rd (wide channel) for the particular initial conditions of a resting fluid with a step-like height distribution, η0. In the one-dimensional case, where η0=η0(y), we find that (i) β affects the geostrophic state (determined from the conservation of the meridional vorticity gradient) only when b=cot(ϕ0)RdR≥0.5 (where ϕ0 is the channel's central latitude, and R is Earth's radius); (ii) the energy conversion ratio varies by less than 10 % when b increases from 0 to 1; (iii) in wide channels, β affects the waves significantly, even for small b (e.g., b=0.005); and (iv) for b=0.005, harmonic waves approximate the waves in narrow channels, and trapped waves approximate the waves in wide channels. In the two-dimensional case, where η0=η0(x), we find that (i) at short times the spatial structure of the steady solution is similar to that on the f plane, while at long times the steady state drifts westward at the speed of Rossby waves (harmonic Rossby waves in narrow channels and trapped Rossby waves in wide channels); (ii) in wide channels, trapped-wave dispersion causes the equatorward segment of the wavefront to move faster than the northern segment; (iii) the energy of Rossby waves on the β plane approaches that of the steady state on the f plane; and (iv) the results outlined in (iii) and (iv) of the one-dimensional case also hold in the two-dimensional case.
{"title":"Geostrophic adjustment on the midlatitude β plane","authors":"Itamar Yacoby, N. Paldor, H. Gildor","doi":"10.5194/os-19-1163-2023","DOIUrl":"https://doi.org/10.5194/os-19-1163-2023","url":null,"abstract":"Abstract. Analytical and numerical solutions of the linearized rotating shallow water equations are combined to study the geostrophic adjustment on the midlatitude β plane. The adjustment is examined in zonal periodic channels of width Ly=4Rd (narrow channel, where Rd is the radius of deformation) and Ly=60Rd (wide channel) for the particular initial conditions of a resting fluid with a step-like height distribution, η0. In the one-dimensional case, where η0=η0(y), we find that (i) β affects the geostrophic state (determined from the conservation of the meridional vorticity gradient) only when b=cot(ϕ0)RdR≥0.5 (where ϕ0 is the channel's central latitude, and R is Earth's radius); (ii) the energy conversion ratio varies by less than 10 % when b increases from 0 to 1; (iii) in wide channels, β affects the waves significantly, even for small b (e.g., b=0.005); and (iv) for b=0.005, harmonic waves approximate the waves in narrow channels, and trapped waves approximate the waves in wide channels. In the two-dimensional case, where η0=η0(x), we find that (i) at short times the spatial structure of the steady solution is similar to that on the f plane, while at long times the steady state drifts westward at the speed of Rossby waves (harmonic Rossby waves in narrow channels and trapped Rossby waves in wide channels); (ii) in wide channels, trapped-wave dispersion causes the equatorward segment of the wavefront to move faster than the northern segment; (iii) the energy of Rossby waves on the β plane approaches that of the steady state on the f plane; and (iv) the results outlined in (iii) and (iv) of the one-dimensional case also hold in the two-dimensional case.\u0000","PeriodicalId":19535,"journal":{"name":"Ocean Science","volume":"16 1","pages":""},"PeriodicalIF":3.2,"publicationDate":"2023-08-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"74680092","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Michael Hemming, M. Roughan, N. Malan, A. Schaeffer
Abstract. Sea surface temperature observations have shown that western boundary currents, such as the East Australian Current (EAC), are warming faster than the global average. However, we know little about coastal temperature trends inshore of these rapidly warming regions, particularly below the surface. In addition to this, warming rates are typically estimated linearly, making it difficult to know how these rates have changed over time. Here we use long-term in situ temperature observations through the water column at five coastal sites between approximately 27.3–42.6∘ S to estimate warming trends between the ocean surface and the bottom. Using an advanced trend detection method, we find accelerating warming trends at multiple depths in the EAC extension region at 34.1 and 42.6∘ S. We see accelerating trends at the surface and bottom at 34.1∘ S but similar trends in the top 20 m at 42.6∘ S. We compare several methods, estimate uncertainty, and place our results in the context of previously reported trends, highlighting that magnitudes are depth-dependent, vary across latitude, and are sensitive to the data time period chosen. The spatial and temporal variability in the long-term temperature trends highlight the important role of regional dynamics against a background of broad-scale ocean warming. Moreover, considering that recent studies of ocean warming typically focus on surface data only, our results show the necessity of subsurface data for the improved understanding of regional climate change impacts.
{"title":"Observed multi-decadal trends in subsurface temperature adjacent to the East Australian Current","authors":"Michael Hemming, M. Roughan, N. Malan, A. Schaeffer","doi":"10.5194/os-19-1145-2023","DOIUrl":"https://doi.org/10.5194/os-19-1145-2023","url":null,"abstract":"Abstract. Sea surface temperature observations have shown that western boundary currents, such as the East Australian Current (EAC), are warming faster than the global average. However, we know little about coastal temperature trends inshore of these rapidly warming regions, particularly below the surface. In addition to this, warming rates are typically estimated linearly, making it difficult to know how these rates have changed over time. Here we use long-term in situ temperature observations through the water column at five coastal sites between approximately 27.3–42.6∘ S to estimate warming trends between the ocean surface and the bottom. Using an advanced trend detection method, we find accelerating warming trends at multiple depths in the EAC extension region at 34.1 and 42.6∘ S. We see accelerating trends at the surface and bottom at 34.1∘ S but similar trends in the top 20 m at 42.6∘ S. We compare several methods, estimate uncertainty, and place our results in the context of previously reported trends, highlighting that magnitudes are depth-dependent, vary across latitude, and are sensitive to the data time period chosen. The spatial and temporal variability in the long-term temperature trends highlight the important role of regional dynamics against a background of broad-scale ocean warming. Moreover, considering that recent studies of ocean warming typically focus on surface data only, our results show the necessity of subsurface data for the improved understanding of regional climate change impacts.\u0000","PeriodicalId":19535,"journal":{"name":"Ocean Science","volume":"71 1","pages":""},"PeriodicalIF":3.2,"publicationDate":"2023-07-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"81602820","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
A. Chaigneau, Stéphane Law-Chune, A. Melet, A. Voldoire, G. Reffray, L. Aouf
Abstract. Wind waves and swells are major drivers of coastal environment changes and coastal hazards such as coastal flooding and erosion. Wave characteristics are sensitive to changes in water depth in shallow and intermediate waters. However, wave models used for historical simulations and projections typically do not account for sea level changes whether from tides, storm surges, or long-term sea level rise. In this study, the sensitivity of projected changes in wave characteristics to the sea level changes is investigated along the Atlantic European coastline. For this purpose, a global wave model is dynamically downscaled over the northeastern Atlantic for the 1970–2100 period under the SSP5–8.5 climate change scenario. Twin experiments are performed with or without the inclusion of hourly sea level variations from regional 3D ocean simulations in the regional wave model. The largest impact of sea level changes on waves is located on the wide continental shelf where shallow-water dynamics prevail, especially in macro-tidal areas. For instance, in the Bay of Mont-Saint-Michel in France, due to an average tidal range of 10 m, extreme historical wave heights were found to be up to 1 m higher (+30 %) when sea level variations are included. At the end of the 21st century, extreme significant wave heights are larger by up to +40 % (+60 cm), mainly due to the effect of tides and mean sea level rise. The estimates provided in this study only partially represent the processes responsible for the sea-level–wave non-linear interactions due to model limitations in terms of resolution and the processes included.
{"title":"Impact of sea level changes on future wave conditions along the coasts of western Europe","authors":"A. Chaigneau, Stéphane Law-Chune, A. Melet, A. Voldoire, G. Reffray, L. Aouf","doi":"10.5194/os-19-1123-2023","DOIUrl":"https://doi.org/10.5194/os-19-1123-2023","url":null,"abstract":"Abstract. Wind waves and swells are major drivers of coastal environment\u0000changes and coastal hazards such as coastal flooding and erosion. Wave\u0000characteristics are sensitive to changes in water depth in shallow and\u0000intermediate waters. However, wave models used for historical simulations\u0000and projections typically do not account for sea level changes whether from\u0000tides, storm surges, or long-term sea level rise. In this study, the\u0000sensitivity of projected changes in wave characteristics to the sea level changes is investigated along the Atlantic\u0000European coastline. For this purpose, a global wave model is dynamically\u0000downscaled over the northeastern Atlantic for the 1970–2100 period under the\u0000SSP5–8.5 climate change scenario. Twin experiments are performed with or\u0000without the inclusion of hourly sea level variations from regional 3D ocean\u0000simulations in the regional wave model. The largest impact of sea level changes on waves is located on the wide continental shelf\u0000where shallow-water dynamics prevail, especially in macro-tidal areas. For\u0000instance, in the Bay of Mont-Saint-Michel in France, due to an average tidal range of\u000010 m, extreme historical wave heights were found to be up to 1 m\u0000higher (+30 %) when sea level variations are included. At the end of\u0000the 21st century, extreme significant wave heights are larger by up to\u0000+40 % (+60 cm), mainly due to the effect of tides and mean sea level\u0000rise. The estimates provided in this study only partially represent the\u0000processes responsible for the sea-level–wave non-linear interactions due to\u0000model limitations in terms of resolution and the processes included.\u0000","PeriodicalId":19535,"journal":{"name":"Ocean Science","volume":"10 1","pages":""},"PeriodicalIF":3.2,"publicationDate":"2023-07-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"83377920","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Abstract. We investigated the variabilities in coastal circulation and dynamics in response to spatiotemporally variable high-resolution atmospheric forcing off the Pearl River estuary during the downwelling wind. Our investigation focused on the dynamics of coastal downwelling circulation in response to variable atmospheric forcing of (1) single-station observation, (2) global reanalysis data, and (3) a high-resolution regional atmospheric model. We found that the high-resolution atmospheric model significantly improved the representations of the near-surface wind and air temperature, and the ocean model driven by the high-resolution and spatially variable atmospheric forcing improved the circulation and associated hydrographic properties in the coastal ocean. Momentum and vorticity analyses further revealed that the cross-isobath water exchange was primarily governed by the along-isobath pressure gradient force (PGF), which was influenced by different components of the atmospheric forcing. The spatial–temporal variability in high-resolution wind forcing determined the strength and structure of coastal circulation and improved estimates of cross-isobath transport and the associated PGF by refining the net stress curl and nonlinear advection of relative vorticity in the simulation. The high-resolution heat forcing can greatly improve the sea surface temperature simulation and adjust the nonlinear advection of relative vorticity, resulting in changes in cross-isobath transport.
{"title":"Variability in coastal downwelling circulation in response to high-resolution regional atmospheric forcing off the Pearl River estuary","authors":"W. Lai, J. Gan","doi":"10.5194/os-19-1107-2023","DOIUrl":"https://doi.org/10.5194/os-19-1107-2023","url":null,"abstract":"Abstract. We investigated the variabilities in coastal circulation\u0000and dynamics in response to spatiotemporally variable high-resolution\u0000atmospheric forcing off the Pearl River estuary during the downwelling wind.\u0000Our investigation focused on the dynamics of coastal downwelling circulation\u0000in response to variable atmospheric forcing of (1) single-station\u0000observation, (2) global reanalysis data, and (3) a high-resolution regional\u0000atmospheric model. We found that the high-resolution atmospheric model\u0000significantly improved the representations of the near-surface wind and air\u0000temperature, and the ocean model driven by the high-resolution and spatially\u0000variable atmospheric forcing improved the circulation and associated\u0000hydrographic properties in the coastal ocean. Momentum and vorticity\u0000analyses further revealed that the cross-isobath water exchange was\u0000primarily governed by the along-isobath pressure gradient force (PGF), which\u0000was influenced by different components of the atmospheric forcing. The\u0000spatial–temporal variability in high-resolution wind forcing determined the\u0000strength and structure of coastal circulation and improved estimates of\u0000cross-isobath transport and the associated PGF by refining the net stress\u0000curl and nonlinear advection of relative vorticity in the simulation. The\u0000high-resolution heat forcing can greatly improve the sea surface temperature\u0000simulation and adjust the nonlinear advection of relative vorticity,\u0000resulting in changes in cross-isobath transport.\u0000","PeriodicalId":19535,"journal":{"name":"Ocean Science","volume":"38 1","pages":""},"PeriodicalIF":3.2,"publicationDate":"2023-07-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"90958838","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
K. Reeve, T. Kanzow, O. Boebel, Myriel Vredenborg, V. Strass, R. Gerdes
Abstract. The Weddell Gyre plays an important role in the global climate system by supplying heat to underneath the ice shelves and in the formation of deep and bottom water masses, which have been subject to widespread warming over past decades. In this study, we investigate the re-distribution of heat throughout the Weddell Gyre by diagnosing the terms of the heat conservation equation for a 1000 m thick layer of water encompassing the core of Warm Deep Water. The spatial distributions of the different advective and diffusive terms in terms of heat tendencies are estimated using gridded climatologies of temperature and velocity, obtained from Argo floats in the Weddell Gyre from 2002 to 2016. While the results are somewhat noisy on the grid scale and the representation of the effects of eddy mixing is highly uncertain due to the need to parameterise them by means of turbulent diffusion, the heat budget (i.e. the sum of all terms) closes (within the uncertainty range) when integrated over the open inflow region in the southern limb, whereas the interior circulation cell remains unbalanced. There is an overall balance in the southern limb between the mean horizontal advection and horizontal turbulent diffusion of heat, whereas the vertical terms contribute comparatively little to the heat budget throughout the Weddell Gyre. Heat convergence due to mean horizontal advection balances with divergence due to horizontal turbulent diffusion in the open southern limb of the Weddell Gyre. In contrast, heat divergence due to mean horizontal advection is much weaker than convergence due to horizontal turbulent diffusion in the interior circulation cell of the Weddell Gyre, due to large values in the latter along the northern boundary due to large meridional temperature gradients. Heat is advected into the Weddell Gyre along the southern limb, some of which is turbulently diffused northwards into the interior circulation cell, while some is likely turbulently diffused southwards towards the shelf seas. This suggests that horizontal turbulent diffusion plays a role in transporting heat both towards the gyre interior where upwelling occurs and towards the ice shelves. Horizontal turbulent diffusion is also a mechanism by which heat can be transported into the Weddell Gyre across the open northern boundary. Temporal deviations from the mean terms are not included due to study limitations. In order to appreciate the role of transient eddying processes, a continued effort to increase the spatial and temporal coverage of observations in the eastern Weddell Sea is required.
{"title":"The Weddell Gyre heat budget associated with the Warm Deep Water circulation derived from Argo floats","authors":"K. Reeve, T. Kanzow, O. Boebel, Myriel Vredenborg, V. Strass, R. Gerdes","doi":"10.5194/os-19-1083-2023","DOIUrl":"https://doi.org/10.5194/os-19-1083-2023","url":null,"abstract":"Abstract. The Weddell Gyre plays an important role in the global climate\u0000system by supplying heat to underneath the ice shelves and in the formation of deep and bottom water masses, which have been subject to widespread\u0000warming over past decades. In this study, we investigate the re-distribution\u0000of heat throughout the Weddell Gyre by diagnosing the terms of the heat\u0000conservation equation for a 1000 m thick layer of water encompassing the\u0000core of Warm Deep Water. The spatial distributions of the different advective\u0000and diffusive terms in terms of heat tendencies are estimated using gridded\u0000climatologies of temperature and velocity, obtained from Argo floats in the\u0000Weddell Gyre from 2002 to 2016. While the results are somewhat noisy on the\u0000grid scale and the representation of the effects of eddy mixing is highly\u0000uncertain due to the need to parameterise them by means of turbulent diffusion,\u0000the heat budget (i.e. the sum of all terms) closes (within the uncertainty\u0000range) when integrated over the open inflow region in the southern limb,\u0000whereas the interior circulation cell remains unbalanced. There is an\u0000overall balance in the southern limb between the mean horizontal advection\u0000and horizontal turbulent diffusion of heat, whereas the vertical terms\u0000contribute comparatively little to the heat budget throughout the Weddell\u0000Gyre. Heat convergence due to mean horizontal advection balances with\u0000divergence due to horizontal turbulent diffusion in the open southern limb\u0000of the Weddell Gyre. In contrast, heat divergence due to mean horizontal\u0000advection is much weaker than convergence due to horizontal turbulent\u0000diffusion in the interior circulation cell of the Weddell Gyre, due to large\u0000values in the latter along the northern boundary due to large meridional\u0000temperature gradients. Heat is advected into the Weddell Gyre along the\u0000southern limb, some of which is turbulently diffused northwards into the\u0000interior circulation cell, while some is likely turbulently diffused\u0000southwards towards the shelf seas. This suggests that horizontal turbulent\u0000diffusion plays a role in transporting heat both towards the gyre interior\u0000where upwelling occurs and towards the ice shelves. Horizontal turbulent diffusion is also a mechanism by which heat can be transported\u0000into the Weddell Gyre across the open northern boundary. Temporal deviations\u0000from the mean terms are not included due to study limitations. In order to\u0000appreciate the role of transient eddying processes, a continued effort to\u0000increase the spatial and temporal coverage of observations in the eastern\u0000Weddell Sea is required.\u0000","PeriodicalId":19535,"journal":{"name":"Ocean Science","volume":"67 1","pages":""},"PeriodicalIF":3.2,"publicationDate":"2023-07-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"90643594","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Abstract. Satellite altimetry provides a unique technique for observing the sea surface height (SSH) signature of internal tides from space. Previous studies have constructed empirical internal tide models for the four largest constituents M2, S2, K1, and O1 by satellite altimetry. Yet no empirical models have been constructed for minor tidal constituents. In this study, we observe mode-1 N2 internal tides (the fifth largest constituent) using about 100 satellite years of SSH data from 1993 to 2019. We employ a recently developed mapping procedure that includes two rounds of plane wave analysis and a two-dimensional bandpass filter in between. The results show that mode-1 N2 internal tides have millimeter-scale SSH amplitudes. Model errors are estimated from background internal tides that are mapped using the same altimetry data but with a tidal period of 12.6074 h (N2 minus 3 min). The global mean error variance is about 25 % that of N2, suggesting that the mode-1 N2 internal tides can overcome model errors in some regions. We find that the N2 and M2 internal tides have similar spatial patterns and that the N2 amplitudes are about 20 % of the M2 amplitudes. Both features are determined by the N2 and M2 barotropic tides. The mode-1 N2 internal tides are observed to propagate hundreds to thousands of kilometers in the open ocean. The globally integrated N2 and M2 internal tide energies are 1.8 and 30.9 PJ, respectively. Their ratio of 5.8 % is larger than the theoretical value of 4 % because the N2 internal tides contain relatively larger model errors. Our mode-1 N2 internal tide model is evaluated using independent satellite altimetry data in 2020 and 2021. The results suggest that the model can make internal tide correction in regions where the model variance is greater than twice the error variance. This work demonstrates that minor internal tidal constituents can be observed using multiyear multi-satellite altimetry data and dedicated mapping techniques.
摘要卫星测高为从空间观测内部潮汐的海面高度特征提供了一种独特的技术。已有研究利用卫星测高技术构建了M2、S2、K1和O1四个最大分量的经验内潮模型。然而，还没有为微小的潮汐成分建立经验模型。在本研究中，我们使用1993年至2019年约100个卫星年的SSH数据观测了1型N2内部潮汐(第五大组成部分)。我们采用最近开发的映射程序，包括两轮平面波分析和二维带通滤波器之间。结果表明，1型N2内潮具有毫米尺度的SSH振幅。模式误差是根据使用相同高程数据绘制的背景内潮来估计的，但潮汐周期为12.6074 h (N2 - 3 min)。全球平均误差方差约为N2的25%，表明1型内潮在部分地区可以克服模式误差。我们发现N2和M2内部潮汐具有相似的空间格局，N2振幅约为M2振幅的20%。这两个特征都是由N2和M2正压潮决定的。据观察，1型N2内部潮汐可在开阔海域传播数百至数千公里。全球积分的N2和M2内潮能分别为1.8和30.9 PJ。它们的5.8%比理论值的4%要大，因为N2内潮包含相对较大的模式误差。我们的模式1 N2内部潮汐模型是使用2020年和2021年的独立卫星测高数据进行评估的。结果表明，在模型方差大于误差方差2倍的区域，模型可以进行内部潮汐校正。这项工作表明，使用多年多卫星测高数据和专用制图技术可以观测到较小的内部潮汐成分。
{"title":"Mode-1 N2 internal tides observed by satellite altimetry","authors":"Zhong‐Kuo Zhao","doi":"10.5194/os-19-1067-2023","DOIUrl":"https://doi.org/10.5194/os-19-1067-2023","url":null,"abstract":"Abstract. Satellite altimetry provides a unique technique for observing the sea surface height (SSH) signature of internal tides from space. Previous studies have constructed empirical internal tide models for the four largest constituents M2, S2, K1, and O1 by satellite altimetry. Yet no empirical models have been constructed for minor tidal constituents. In this study, we observe mode-1 N2 internal tides (the fifth largest constituent) using about 100 satellite years of SSH data from 1993 to 2019. We employ a recently developed mapping procedure that includes two rounds of plane wave analysis and a two-dimensional bandpass filter in between. The results show that mode-1 N2 internal tides have millimeter-scale SSH amplitudes. Model errors are estimated from background internal tides that are mapped using the same altimetry data but with a tidal period of 12.6074 h (N2 minus 3 min). The global mean error variance is about 25 % that of N2, suggesting that the mode-1 N2 internal tides can overcome model errors in some regions. We find that the N2 and M2 internal tides have similar spatial patterns and that the N2 amplitudes are about 20 % of the M2 amplitudes. Both features are determined by the N2 and M2 barotropic tides. The mode-1 N2 internal tides are observed to propagate hundreds to thousands of kilometers in the open ocean. The globally integrated N2 and M2 internal tide energies are 1.8 and 30.9 PJ, respectively. Their ratio of 5.8 % is larger than the theoretical value of 4 % because the N2 internal tides contain relatively larger model errors. Our mode-1 N2 internal tide model is evaluated using independent satellite altimetry data in 2020 and 2021. The results suggest that the model can make internal tide correction in regions where the model variance is greater than twice the error variance. This work demonstrates that minor internal tidal constituents can be observed using multiyear multi-satellite altimetry data and dedicated mapping techniques.\u0000","PeriodicalId":19535,"journal":{"name":"Ocean Science","volume":"32 1","pages":""},"PeriodicalIF":3.2,"publicationDate":"2023-07-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"82972830","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Rasa Idzelytė, Natalja Čerkasova, Jovita Mėžinė, Toma Dabuleviciene, A. Razinkovas-Baziukas, A. Ertürk, G. Umgiesser
Abstract. We analyse the cumulative impacts of climate change in a complex basin–lagoon–sea system continuum, which covers the Nemunas river basin, Curonian Lagoon, and the southeastern part of the Baltic Sea. A unique, state-of-the-art coupled modelling system was developed using hydrological and hydrodynamic models. The results of four regional downscaled models from the Rossby Centre high-resolution regional atmospheric climate model have been bias-corrected using in situ measurements and were used as forcing to assess the changes that the continuum will undergo until the end of this century. Results show that the Curonian Lagoon will be subjected to higher river discharges that in turn increase the outgoing fluxes into the Baltic Sea. Through these higher fluxes, both the water residence time and saltwater intrusion into the lagoon event frequency will decrease. Most of these changes will be more pronounced in the northern part of the lagoon, which is more likely to be influenced by the variations in the Nemunas river discharge. Its delta area may be susceptible to flooding as a result of the elevated discharge during winter. The southern part of the lagoon will experience lesser changes. While water temperatures in the entire lagoon and the southeastern Baltic Sea will steadily increase and salinity will decrease, the foreseen changes in the physical characteristics will not cause significant shifts in the ecosystem functioning but may affect the nutrient retention capacity. However, some ecosystem services such as ice fishing are expected to vanish completely due to the loss of ice cover.
{"title":"Coupled hydrological and hydrodynamic modelling application for climate change impact assessment in the Nemunas river watershed–Curonian Lagoon–southeastern Baltic Sea continuum","authors":"Rasa Idzelytė, Natalja Čerkasova, Jovita Mėžinė, Toma Dabuleviciene, A. Razinkovas-Baziukas, A. Ertürk, G. Umgiesser","doi":"10.5194/os-19-1047-2023","DOIUrl":"https://doi.org/10.5194/os-19-1047-2023","url":null,"abstract":"Abstract. We analyse the cumulative impacts of climate change in a complex basin–lagoon–sea system continuum, which covers the Nemunas river basin, Curonian Lagoon, and the southeastern part of the Baltic Sea. A unique, state-of-the-art coupled modelling system was developed using hydrological and hydrodynamic models. The results of four regional downscaled models from the Rossby Centre high-resolution regional atmospheric climate model have been bias-corrected using in situ measurements and were used as forcing to assess the changes that the continuum will undergo until the end of this century. Results show that the Curonian Lagoon will be subjected to higher river\u0000discharges that in turn increase the outgoing fluxes into the Baltic Sea.\u0000Through these higher fluxes, both the water residence time and saltwater\u0000intrusion into the lagoon event frequency will decrease. Most of these\u0000changes will be more pronounced in the northern part of the lagoon, which is more likely to be influenced by the variations in the Nemunas river\u0000discharge. Its delta area may be susceptible to flooding as a result of the\u0000elevated discharge during winter. The southern part of the lagoon will\u0000experience lesser changes. While water temperatures in the entire lagoon and the southeastern Baltic Sea will steadily increase and salinity will\u0000decrease, the foreseen changes in the physical characteristics will not cause significant shifts in the ecosystem functioning but may affect the nutrient retention capacity. However, some ecosystem services such as ice fishing are expected to vanish completely due to the loss of ice cover.\u0000","PeriodicalId":19535,"journal":{"name":"Ocean Science","volume":"15 1","pages":""},"PeriodicalIF":3.2,"publicationDate":"2023-07-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"81852701","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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