P. Sheehan, G. Damerell, Philip J. Leadbitter, K. Heywood, R. Hall
Abstract. Ocean gliders enable us to collect the high-resolution microstructure observations necessary to calculate the dissipation rate of turbulent kinetic energy, ε, on timescales of weeks to months: far longer than is normally possible using traditional ship-based platforms. Slocum gliders have previously been used to this end; here, we report the first detailed estimates of ε calculated using the Batchelor spectrum method on observations collected by a FP07 fast thermistor mounted on a Seaglider. We use these same fast thermistor observations to calculate ε following the Thorpe scale method and find very good agreement between the two methods. The Thorpe scale method yields larger values of ε, but the average difference, which is less than an order of magnitude, is smaller than reported elsewhere. The spatio-temporal distribution of ε is comparable for both methods. Maximum values of ε (10−7 W kg−1) are observed in the surface mixed layer; values of approximately 10−9 W kg−1 are observed between approximately 200 and 500 m depth. These two layers are separated by a 100 m thick layer of low ε (10−10 W kg−1), which is co-located with a high-salinity layer of Subtropical Underwater and a peak in the strength of stratification. We calculate the turbulent heat and salt fluxes associated with the observed turbulence. Between 200 and 500 m, ε induces downward fluxes of both properties that, if typical of the annual average, would have a very small influence on the heat and salt content of the overlying salinity-maximum layer. We compare these turbulent fluxes with two estimates of double-diffusive fluxes that occur in regions susceptible to salt fingers, such as the western tropical Atlantic. We find that the double-diffusive fluxes of both heat and salt are larger than the corresponding turbulent fluxes.
摘要海洋滑翔机使我们能够收集高分辨率的微观结构观测数据，以便在数周到数月的时间尺度上计算湍流动能ε的耗散率，这比传统的船舶平台要长得多。在此之前，滑翔机已被用于此目的;在这里，我们报告了第一个使用Batchelor谱法对安装在滑翔机上的FP07快速热敏电阻收集的观测数据计算的ε的详细估计。我们使用这些相同的快速热敏电阻观测值，按照索普尺度法计算ε，发现两种方法非常吻合。索普尺度法得到的ε值较大，但平均差值小于一个数量级，比其他文献报道的要小。两种方法得到的ε的时空分布具有可比性。在表面混合层中观测到ε的最大值(10 ~ 7 W kg−1);在大约200到500 m深度之间观测到的值约为10−9 wkg−1。这两层被一个100 m厚的低ε (10 ~ 10 W kg−1)层隔开，该层与副热带水下高盐度层共存，分层强度达到峰值。我们计算了与观测到的湍流相关的湍流热通量和盐通量。在200 ~ 500 m之间，ε引起两种性质的向下通量，如果是典型的年平均通量，则对上覆最大盐度层的热量和盐含量的影响很小。我们将这些湍流通量与发生在易受盐指影响的地区(如西热带大西洋)的双扩散通量的两种估计进行了比较。我们发现，热和盐的双扩散通量都大于相应的湍流通量。
{"title":"Turbulent kinetic energy dissipation rate and associated fluxes in the western tropical Atlantic estimated from ocean glider observations","authors":"P. Sheehan, G. Damerell, Philip J. Leadbitter, K. Heywood, R. Hall","doi":"10.5194/os-19-77-2023","DOIUrl":"https://doi.org/10.5194/os-19-77-2023","url":null,"abstract":"Abstract. Ocean gliders enable us to collect the high-resolution microstructure observations necessary to calculate the dissipation rate of turbulent kinetic energy, ε, on timescales of weeks to months: far longer than is normally possible using traditional ship-based platforms. Slocum gliders have previously been used to this end; here, we report the first detailed estimates of ε calculated using the Batchelor spectrum method on observations collected by a FP07 fast thermistor mounted on a Seaglider. We use these same fast thermistor observations to calculate ε following the Thorpe scale method and find very good agreement between the two methods. The Thorpe scale method yields larger values of ε, but the average difference, which is less than an order of magnitude, is smaller than reported elsewhere. The spatio-temporal distribution of ε is comparable for both methods. Maximum values of ε (10−7 W kg−1) are observed in the surface mixed layer; values of approximately 10−9 W kg−1 are observed between approximately 200 and 500 m depth. These two layers are separated by a 100 m thick layer of low ε (10−10 W kg−1), which is co-located with a high-salinity layer of Subtropical Underwater and a peak in the strength of stratification. We calculate the turbulent heat and salt fluxes associated with the observed turbulence. Between 200 and 500 m, ε induces downward fluxes of both properties that, if typical of the annual average, would have a very small influence on the heat and salt content of the overlying salinity-maximum layer. We compare these turbulent fluxes with two estimates of double-diffusive fluxes that occur in regions susceptible to salt fingers, such as the western tropical Atlantic. We find that the double-diffusive fluxes of both heat and salt are larger than the corresponding turbulent fluxes.\u0000","PeriodicalId":19535,"journal":{"name":"Ocean Science","volume":"2 1","pages":""},"PeriodicalIF":3.2,"publicationDate":"2023-01-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"90884555","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. Identifying the causes for historical sea-level changes in coastal tide-gauge records is important for constraining oceanographic, geologic, and climatic processes. The Río de la Plata estuary in South America features the longest tide-gauge records in the South Atlantic. Despite the relevance of these data for large-scale circulation and climate studies, the mechanisms underlying relative sea-level changes in this region during the past century have not been firmly established. I study annual data from tide gauges in the Río de la Plata and stream gauges along the Río Paraná and Río Uruguay to establish relationships between river streamflow and sea level over 1931–2014. Regression analysis suggests that streamflow explains 59 %±17 % of the total sea-level variance at Buenos Aires, Argentina, and 28 %±21 % at Montevideo, Uruguay (95 % confidence intervals). A long-term streamflow increase effected sea-level trends of 0.71±0.35 mm yr−1 at Buenos Aires and 0.48±0.38 mm yr−1 at Montevideo. More generally, sea level at Buenos Aires and Montevideo respectively rises by (7.3±1.8)×10-6 m and (4.7±2.6)×10-6 m per 1 m3 s−1 streamflow increase. These observational results are consistent with simple theories for the coastal sea-level response to streamflow forcing, suggesting a causal relationship between streamflow and sea level mediated by ocean dynamics. Findings advance understanding of local, regional, and global sea-level changes; clarify sea-level physics; inform future projections of coastal sea level and the interpretation of satellite data and proxy reconstructions; and highlight future research directions. Specifically, local and regional river effects should be accounted for in basin-scale and global mean sea-level budgets as well as reconstructions based on sparse tide-gauge records.
摘要在沿海测潮记录中确定历史海平面变化的原因对于限制海洋学、地质和气候过程是重要的。南美洲的Río de la Plata河口拥有南大西洋最长的潮汐测量记录。尽管这些数据与大尺度环流和气候研究具有相关性，但过去一个世纪以来该地区相对海平面变化的机制尚未得到牢固确立。我研究了Río de la Plata的潮汐计和Río paran和Río乌拉圭沿岸的流量计的年度数据，以建立1931-2014年河流流量和海平面之间的关系。回归分析表明，在阿根廷的布宜诺斯艾利斯和乌拉圭的蒙得维的亚，水流解释了总海平面变化的59%±17%和28%±21%(95%置信区间)。长期流量增加对布宜诺斯艾利斯和蒙得维的亚海平面趋势的影响分别为0.71±0.35 mm yr - 1和0.48±0.38 mm yr - 1。更一般地说，布宜诺斯艾利斯和蒙得维的亚的海平面每增加1 m3 s - 1流速分别上升(7.3±1.8)×10-6 m和(4.7±2.6)×10-6 m。这些观测结果与沿海海平面对径流强迫响应的简单理论相一致，表明在海洋动力的介导下，径流与海平面之间存在因果关系。研究结果促进了对地方、区域和全球海平面变化的理解;澄清海平面物理;为沿海海平面的未来预估以及卫星数据的解释和代理重建提供信息;并突出未来的研究方向。具体来说，应该在流域尺度和全球平均海平面预算以及基于稀疏的测潮记录的重建中考虑当地和区域河流的影响。
{"title":"River effects on sea-level rise in the Río de la Plata estuary during the past century","authors":"C. Piecuch","doi":"10.5194/os-19-57-2023","DOIUrl":"https://doi.org/10.5194/os-19-57-2023","url":null,"abstract":"Abstract. Identifying the causes for historical sea-level changes in coastal tide-gauge records is important for constraining oceanographic, geologic, and climatic processes. The Río de la Plata estuary in South America features the longest tide-gauge records in the South Atlantic. Despite the relevance of these data for large-scale circulation and climate studies, the mechanisms underlying relative sea-level changes in this region during the past century have not been firmly established. I study annual data from tide gauges in the Río de la Plata and stream gauges along the Río Paraná and Río Uruguay to establish relationships between river streamflow and sea level over 1931–2014. Regression analysis suggests that streamflow explains 59 %±17 % of the total sea-level variance at Buenos Aires, Argentina, and 28 %±21 % at Montevideo, Uruguay (95 % confidence intervals). A long-term streamflow increase effected sea-level trends of 0.71±0.35 mm yr−1 at Buenos Aires and 0.48±0.38 mm yr−1 at Montevideo. More generally, sea level at Buenos Aires and Montevideo respectively rises by (7.3±1.8)×10-6 m and (4.7±2.6)×10-6 m per 1 m3 s−1 streamflow increase. These observational results are consistent with simple theories for the coastal sea-level response to streamflow forcing, suggesting a causal relationship between streamflow and sea level mediated by ocean dynamics. Findings advance understanding of local, regional, and global sea-level changes; clarify sea-level physics; inform future projections of coastal sea level and the interpretation of satellite data and proxy reconstructions; and highlight future research directions. Specifically, local and regional river effects should be accounted for in basin-scale and global mean sea-level budgets as well as reconstructions based on sparse tide-gauge records.\u0000","PeriodicalId":19535,"journal":{"name":"Ocean Science","volume":"28 1","pages":""},"PeriodicalIF":3.2,"publicationDate":"2023-01-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"75496131","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. Twenty years of daily MODIS-Aqua ocean color observations (2002–2022) are used to identify periodic variability of near-surface chlorophyll (Chl a) in the Indonesian seas. The frequency spectrum of Chl a is dominated by the mean and low-frequency monsoonal variability; however, a prominent peak around the fortnightly tidal period, MSf, is present. Harmonic analysis is used to quantify and map the fortnightly Chl a signal, which is discovered to be significant along the continental shelves of NW Australia and at several sites associated with narrow passages between the Lesser Sunda Islands, within the Sulu Archipelago, and at a few other sites in the Philippines Archipelago. Fortnightly variability at the shallow coastal sites is attributed to the spring–neap cycle of barotropic ocean currents, while we hypothesize that the variability in deeper water near the island passages is due to the modulation of vertical nutrient fluxes by baroclinic tidal mixing. The results document the significance of tidal mixing and highlight the heterogeneous character of biophysical processes within the Indonesian seas.
{"title":"Fortnightly variability of Chl a in the Indonesian seas","authors":"E. Zaron, T. A. Capuano, A. Koch‐Larrouy","doi":"10.5194/os-19-43-2023","DOIUrl":"https://doi.org/10.5194/os-19-43-2023","url":null,"abstract":"Abstract. Twenty years of daily MODIS-Aqua\u0000ocean color observations (2002–2022) are used to identify periodic variability of near-surface\u0000chlorophyll (Chl a) in the Indonesian seas.\u0000The frequency spectrum of Chl a is dominated by the mean and low-frequency monsoonal variability;\u0000however, a prominent peak around the fortnightly tidal period, MSf, is present.\u0000Harmonic analysis is used to quantify and map the fortnightly Chl a signal,\u0000which is discovered to be significant along the continental shelves of NW Australia\u0000and at several sites associated with narrow passages between the Lesser Sunda Islands,\u0000within the Sulu Archipelago, and at a few other sites in the Philippines Archipelago.\u0000Fortnightly variability at the shallow coastal sites is attributed to the\u0000spring–neap cycle of barotropic ocean currents, while we hypothesize that the variability\u0000in deeper water near the island passages is due to the modulation of vertical\u0000nutrient fluxes by baroclinic tidal mixing.\u0000The results document the significance of tidal mixing\u0000and highlight the heterogeneous character of biophysical processes within the Indonesian seas.\u0000","PeriodicalId":19535,"journal":{"name":"Ocean Science","volume":"1 1","pages":""},"PeriodicalIF":3.2,"publicationDate":"2023-01-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"76081643","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}
C. Camargo, R. Riva, T. Hermans, Eike M. Schütt, M. Marcos, I. Hernández‐Carrasco, A. Slangen
Abstract. Attribution of sea-level change to its different drivers is typically done using a sea-level budget approach. While the global mean sea-level budget is considered closed, closing the budget on a finer spatial scale is more complicated due to, for instance, limitations in our observational system and the spatial processes contributing to regional sea-level change. Consequently, the regional budget has been mainly analysed on a basin-wide scale. Here we investigate the sea-level budget at sub-basin scales, using two machine learning techniques to extract domains of coherent sea-level variability: a neural network approach (self-organizing map, SOM) and a network detection approach (δ-MAPS). The extracted domains provide more spatial detail within the ocean basins and indicate how sea-level variability is connected among different regions. Using these domains we can close, within 1σ uncertainty, the sub-basin regional sea-level budget from 1993–2016 in 100 % and 76 % of the SOM and δ-MAPS regions, respectively. Steric variations dominate the temporal sea-level variability and determine a significant part of the total regional change. Sea-level change due to mass exchange between ocean and land has a relatively homogeneous contribution to all regions. In highly dynamic regions (e.g. the Gulf Stream region) the dynamic mass redistribution is significant. Regions where the budget cannot be closed highlight processes that are affecting sea level but are not well captured by the observations, such as the influence of western boundary currents. The use of the budget approach in combination with machine learning techniques leads to new insights into regional sea-level variability and its drivers.
{"title":"Regionalizing the sea-level budget with machine learning techniques","authors":"C. Camargo, R. Riva, T. Hermans, Eike M. Schütt, M. Marcos, I. Hernández‐Carrasco, A. Slangen","doi":"10.5194/os-19-17-2023","DOIUrl":"https://doi.org/10.5194/os-19-17-2023","url":null,"abstract":"Abstract. Attribution of sea-level change to its different drivers is typically done using a sea-level budget approach. While the global mean sea-level budget is considered closed, closing the budget on a finer spatial scale is more complicated due to, for instance, limitations in our observational system and the spatial processes contributing to regional sea-level change.\u0000Consequently, the regional budget has been mainly analysed on a basin-wide scale.\u0000Here we investigate the sea-level budget at sub-basin scales, using two machine learning techniques to extract domains of coherent sea-level variability: a neural network approach (self-organizing map, SOM) and a network detection approach (δ-MAPS).\u0000The extracted domains provide more spatial detail within the ocean basins and indicate how sea-level variability is connected among different regions.\u0000Using these domains we can close, within 1σ uncertainty, the sub-basin regional sea-level budget from 1993–2016 in 100 % and 76 % of the SOM and δ-MAPS regions, respectively.\u0000Steric variations dominate the temporal sea-level variability and determine a significant part of the total regional change.\u0000Sea-level change due to mass exchange between ocean and land has a relatively homogeneous contribution to all regions. In highly dynamic regions (e.g. the Gulf Stream region) the dynamic mass redistribution is significant.\u0000Regions where the budget cannot be closed highlight processes that are affecting sea level but are not well captured by the observations, such as the influence of western boundary currents.\u0000The use of the budget approach in combination with machine learning techniques leads to new insights into regional sea-level variability and its drivers.\u0000","PeriodicalId":19535,"journal":{"name":"Ocean Science","volume":"18 1","pages":""},"PeriodicalIF":3.2,"publicationDate":"2023-01-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"77506410","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}
Alexia D. Saint-Macary, A. Marriner, Theresa Barthelmeß, Stacy Deppeler, K. Safi, Rafael Costa Santana, M. Harvey, C. Law
Abstract. Elevated dimethyl sulfide (DMS) concentrations in the sea surface microlayer (SML) have been previously related to DMS air–sea flux anomalies in the southwestern Pacific. To further address this, DMS, its precursor dimethylsulfoniopropionate (DMSP), and ancillary variables were sampled in the SML and also subsurface water at 0.5 m depth (SSW) in different water masses east of New Zealand. Despite high phytoplankton biomass at some stations, the SML chlorophyll a enrichment factor (EF) was low (< 1.06), and DMSP was enriched at one station with DMSP EF ranging from 0.81 to 1.25. DMS in the SML was determined using a novel gas-permeable tube technique which measured consistently higher concentrations than with the traditional glass plate technique; however, significant DMS enrichment was present at only one station, with the EF ranging from 0.40 to 1.22. SML DMSP and DMS were influenced by phytoplankton community composition, with correlations with dinoflagellate and Gymnodinium biomass, respectively. DMSP and DMS concentrations were also correlated between the SML and SSW, with the difference in ratio attributable to greater DMS loss to the atmosphere from the SML. In the absence of significant enrichment, DMS in the SML did not influence DMS emissions, with the calculated air–sea DMS flux of 2.28 to 11.0 µmol m−2 d−1 consistent with climatological estimates for the region. These results confirm previous regional observations that DMS is associated with dinoflagellate abundance but indicate that additional factors are required to support significant enrichment in the SML.
摘要海表微层(SML)中二甲基硫化物(DMS)浓度升高与西南太平洋DMS海气通量异常有关。为了进一步解决这个问题，在新西兰东部的SML和0.5 m深度(SSW)的不同水团中采样了DMS，其前体二甲基磺酰丙酸盐(DMSP)和辅助变量。尽管部分站点浮游植物生物量较高，但SML叶绿素a富集因子(EF)较低(< 1.06)，DMSP富集在一个站点，DMSP EF在0.81 ~ 1.25之间。SML中的DMS是用一种新型的透气性管技术测定的，该技术测量的浓度始终高于传统的玻璃板技术;然而，只有一个站点存在显著的DMS富集，EF范围为0.40 ~ 1.22。SML DMSP和DMS受浮游植物群落组成的影响，分别与鞭毛藻和裸子藻生物量相关。DMSP和DMS浓度在SML和SSW之间也存在相关性，其比值差异可归因于SML向大气中损失了更多的DMS。在没有显著富集的情况下，SML中的DMS不影响DMS排放，计算出的空气- seadms通量为2.28至11.0µmol m - 2 d - 1，与该地区的气候估计一致。这些结果证实了先前的区域观察，即DMS与鞭毛藻丰度有关，但表明需要其他因素来支持SML的显着富集。
{"title":"Dimethyl sulfide cycling in the sea surface microlayer in the southwestern Pacific – Part 1: Enrichment potential determined using a novel sampler","authors":"Alexia D. Saint-Macary, A. Marriner, Theresa Barthelmeß, Stacy Deppeler, K. Safi, Rafael Costa Santana, M. Harvey, C. Law","doi":"10.5194/os-19-1-2023","DOIUrl":"https://doi.org/10.5194/os-19-1-2023","url":null,"abstract":"Abstract. Elevated dimethyl sulfide (DMS) concentrations in the sea\u0000surface microlayer (SML) have been previously related to DMS air–sea flux\u0000anomalies in the southwestern Pacific. To further address this, DMS, its\u0000precursor dimethylsulfoniopropionate (DMSP), and ancillary variables were\u0000sampled in the SML and also subsurface water at 0.5 m depth (SSW) in\u0000different water masses east of New Zealand. Despite high phytoplankton\u0000biomass at some stations, the SML chlorophyll a enrichment factor (EF) was low\u0000(< 1.06), and DMSP was enriched at one\u0000station with DMSP EF ranging from 0.81 to 1.25. DMS in the SML was\u0000determined using a novel gas-permeable tube technique which measured\u0000consistently higher concentrations than with the traditional glass plate\u0000technique; however, significant DMS enrichment was present at only one station,\u0000with the EF ranging from 0.40 to 1.22. SML DMSP and DMS were influenced by\u0000phytoplankton community composition, with correlations with dinoflagellate\u0000and Gymnodinium biomass, respectively. DMSP and DMS concentrations were also correlated\u0000between the SML and SSW, with the difference in ratio attributable to\u0000greater DMS loss to the atmosphere from the SML. In the absence of significant enrichment, DMS in the SML did not\u0000influence DMS emissions, with the calculated air–sea\u0000DMS flux of 2.28 to 11.0 µmol m−2 d−1 consistent with\u0000climatological estimates for the region. These results confirm previous\u0000regional observations that DMS is associated with dinoflagellate abundance\u0000but indicate that additional factors are required to support significant enrichment\u0000in the SML.\u0000","PeriodicalId":19535,"journal":{"name":"Ocean Science","volume":"1 1","pages":""},"PeriodicalIF":3.2,"publicationDate":"2023-01-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"90122412","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. The Dutch Wadden Sea is a UN World Heritage Site connected to the North Sea by multiple tidal inlets. Although there are strong tidal currents flowing through these inlets, the magnitude and direction of the residual circulation in the western Dutch Wadden Sea is important for sediment, salinity and nutrient balances. We found that the direction of this residual flow is reversing. This residual circulation has been the subject of various studies since the 1970s, in which substantially different net volume fluxes were presented. Differences in tidal conditions in the main inlets, tidal rectification and meteorology were identified as driving mechanisms. Here we analysed almost 13 years of acoustic Doppler current profiler (ADCP) observations collected on the ferry crossing the Marsdiep tidal inlet in the Dutch Wadden Sea since 2009. The results are combined with earlier investigations covering the period 1998–2009. We find a significant trend in the magnitude of the residual volume flux, with decreasing export to the North Sea and with occasional imports observed in recent years. We hypothesise that this trend is related predominantly to changes in tides in the North Sea, which are caused by increased strength and duration of stratification in response to global warming. With warming projected to continue, we expect the residual flow in the Marsdiep to continue to reverse to full inflow within the current decade, with potential knock-on effects for the sediment budget and ecosystem of the western Wadden Sea.
{"title":"Imminent reversal of the residual flow through the Marsdiep tidal inlet into the Dutch Wadden Sea based on multiyear ferry-borne acoustic Doppler current profiler (ADCP) observations","authors":"J. van der Molen, S. Groeskamp, L. Maas","doi":"10.5194/os-18-1805-2022","DOIUrl":"https://doi.org/10.5194/os-18-1805-2022","url":null,"abstract":"Abstract. The Dutch Wadden Sea is a UN World Heritage Site connected to the\u0000North Sea by multiple tidal inlets. Although there are strong tidal currents\u0000flowing through these inlets, the magnitude and direction of the residual\u0000circulation in the western Dutch Wadden Sea is important for sediment,\u0000salinity and nutrient balances. We found that the direction of this residual\u0000flow is reversing. This residual circulation has been the subject of various studies since the\u00001970s, in which substantially different net volume fluxes were presented. Differences in tidal conditions in the main inlets,\u0000tidal rectification and meteorology were identified as driving mechanisms. Here we analysed\u0000almost 13 years of acoustic Doppler current profiler (ADCP) observations collected on the ferry crossing the\u0000Marsdiep tidal inlet in the Dutch Wadden Sea since 2009. The results are\u0000combined with earlier investigations covering the period 1998–2009. We find\u0000a significant trend in the magnitude of the residual volume flux, with\u0000decreasing export to the North Sea and with occasional imports observed in\u0000recent years. We hypothesise that this trend is related predominantly to\u0000changes in tides in the North Sea, which are caused by increased strength\u0000and duration of stratification in response to global warming. With warming\u0000projected to continue, we expect the residual flow in the Marsdiep to\u0000continue to reverse to full inflow within the current decade, with potential\u0000knock-on effects for the sediment budget and ecosystem of the western Wadden\u0000Sea.\u0000","PeriodicalId":19535,"journal":{"name":"Ocean Science","volume":"1 1","pages":""},"PeriodicalIF":3.2,"publicationDate":"2022-12-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"84035942","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. A coastal sea level reconstruction based on tide gauge observations is developed and applied to the western basin of the Mediterranean sea. The reconstructions are carried out in four frequency bands and are based on an optimal interpolation method in which the correlation between tide gauge data and all coastal points has been determined from the outputs of a numerical model. The reconstructions for frequencies lower than 1 month use monthly observations from the Permanent Service for Mean Sea Level (PSMSL) database and cover the period from 1884 to 2019. For the reconstruction of higher frequencies, hourly observations from the Global Extreme Sea Level Analysis (GESLA-2) dataset are used and cover from 1980 to 2015. Total sea level is retrieved with high accuracy from the merging of the different frequency bands. Results of a cross-validation test show that independent tide gauge series are highly correlated with the reconstructions. Moreover, they correlate significantly better with the reconstructions than with altimetry data in all frequency bands, and therefore the reconstruction represents a valuable contribution to the attempts of recovering coastal sea level. The obtained reconstructions allow us to characterize the coastal sea level variability, estimate coastal sea level trends along the entire coastline, and examine the correlation between western Mediterranean coastal sea level and the main North Atlantic climate indices. The limitations and applicability of the method to other regions are also discussed.
{"title":"Reconstruction of Mediterranean coastal sea level at different timescales based on tide gauge records","authors":"J. Ramos-Alcántara, D. Gomis, G. Jordà","doi":"10.5194/os-18-1781-2022","DOIUrl":"https://doi.org/10.5194/os-18-1781-2022","url":null,"abstract":"Abstract. A coastal sea level reconstruction based on tide gauge\u0000observations is developed and applied to the western basin of the\u0000Mediterranean sea. The reconstructions are carried out in four frequency\u0000bands and are based on an optimal interpolation method in which the\u0000correlation between tide gauge data and all coastal points has been\u0000determined from the outputs of a numerical model. The reconstructions for\u0000frequencies lower than 1 month use monthly observations from the Permanent Service for Mean Sea Level (PSMSL)\u0000database and cover the period from 1884 to 2019. For the reconstruction of\u0000higher frequencies, hourly observations from the Global Extreme Sea Level\u0000Analysis (GESLA-2) dataset are used\u0000and cover from 1980 to 2015. Total sea level is retrieved with high accuracy\u0000from the merging of the different frequency bands. Results of a\u0000cross-validation test show that independent tide gauge series are highly\u0000correlated with the reconstructions. Moreover, they correlate significantly\u0000better with the reconstructions than with altimetry data in all frequency\u0000bands, and therefore the reconstruction represents a valuable contribution\u0000to the attempts of recovering coastal sea level. The obtained\u0000reconstructions allow us to characterize the coastal sea level variability,\u0000estimate coastal sea level trends along the entire coastline, and examine\u0000the correlation between western Mediterranean coastal sea level and the main\u0000North Atlantic climate indices. The limitations and applicability of the\u0000method to other regions are also discussed.","PeriodicalId":19535,"journal":{"name":"Ocean Science","volume":"10 1","pages":""},"PeriodicalIF":3.2,"publicationDate":"2022-12-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"90572431","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}
D. Volkov, C. Schmid, Leah N. Chomiak, C. Germineaud, Shenfu Dong, Marlos Goes
Abstract. The gyre-scale, dynamic sea surface height (SSH) variability signifies the spatial redistribution of heat and freshwater in the ocean, influencing the ocean circulation, weather, climate, sea level, and ecosystems. It is known that the first empirical orthogonal function (EOF) mode of the interannual SSH variability in the North Atlantic exhibits a tripole gyre pattern, with the subtropical gyre varying out of phase with both the subpolar gyre and the tropics, influenced by the low-frequency North Atlantic Oscillation. Here, we show that the first EOF mode explains the majority (60 %–90 %) of the interannual SSH variance in the Labrador and Irminger Sea, whereas the second EOF mode is more influential in the northeastern part of the subpolar North Atlantic (SPNA), explaining up to 60 %–80 % of the regional interannual SSH variability. We find that the two leading modes do not represent physically independent phenomena. On the contrary, they evolve as a quadrature pair associated with a propagation of SSH anomalies from the eastern to the western SPNA. This is confirmed by the complex EOF analysis, which can detect propagating (as opposed to stationary) signals. The analysis shows that it takes about 2 years for sea level signals to propagate from the Iceland Basin to the Labrador Sea, and it takes 7–10 years for the entire cycle of the North Atlantic SSH tripole to complete. The observed westward propagation of SSH anomalies is linked to shifting wind forcing patterns and to the cyclonic pattern of the mean ocean circulation in the SPNA. The analysis of regional surface buoyancy fluxes in combination with the upper-ocean temperature and salinity changes suggests a time-dependent dominance of either air–sea heat fluxes or advection in driving the observed SSH tendencies, while the contribution of surface freshwater fluxes (precipitation and evaporation) is negligible. We demonstrate that the most recent cooling and freshening observed in the SPNA since about 2010 were mostly driven by advection associated with the North Atlantic Current. The results of this study indicate that signal propagation is an important component of the North Atlantic SSH tripole, as it applies to the SPNA.
{"title":"Interannual to decadal sea level variability in the subpolar North Atlantic: the role of propagating signals","authors":"D. Volkov, C. Schmid, Leah N. Chomiak, C. Germineaud, Shenfu Dong, Marlos Goes","doi":"10.5194/os-18-1741-2022","DOIUrl":"https://doi.org/10.5194/os-18-1741-2022","url":null,"abstract":"Abstract. The gyre-scale, dynamic sea surface height (SSH) variability\u0000signifies the spatial redistribution of heat and freshwater in the ocean,\u0000influencing the ocean circulation, weather, climate, sea level, and\u0000ecosystems. It is known that the first empirical orthogonal function (EOF)\u0000mode of the interannual SSH variability in the North Atlantic exhibits a\u0000tripole gyre pattern, with the subtropical gyre varying out of phase with\u0000both the subpolar gyre and the tropics, influenced by the low-frequency\u0000North Atlantic Oscillation. Here, we show that the first EOF mode explains\u0000the majority (60 %–90 %) of the interannual SSH variance in the Labrador and\u0000Irminger Sea, whereas the second EOF mode is more influential in the\u0000northeastern part of the subpolar North Atlantic (SPNA), explaining up to\u000060 %–80 % of the regional interannual SSH variability. We find that the two\u0000leading modes do not represent physically independent phenomena. On the\u0000contrary, they evolve as a quadrature pair associated with a propagation of\u0000SSH anomalies from the eastern to the western SPNA. This is confirmed by the\u0000complex EOF analysis, which can detect propagating (as opposed to\u0000stationary) signals. The analysis shows that it takes about 2 years for sea\u0000level signals to propagate from the Iceland Basin to the Labrador Sea, and\u0000it takes 7–10 years for the entire cycle of the North Atlantic SSH tripole\u0000to complete. The observed westward propagation of SSH anomalies is linked to\u0000shifting wind forcing patterns and to the cyclonic pattern of the mean ocean\u0000circulation in the SPNA. The analysis of regional surface buoyancy fluxes in\u0000combination with the upper-ocean temperature and salinity changes suggests a\u0000time-dependent dominance of either air–sea heat fluxes or advection in\u0000driving the observed SSH tendencies, while the contribution of surface\u0000freshwater fluxes (precipitation and evaporation) is negligible. We\u0000demonstrate that the most recent cooling and freshening observed in the SPNA\u0000since about 2010 were mostly driven by advection associated with the North\u0000Atlantic Current. The results of this study indicate that signal propagation\u0000is an important component of the North Atlantic SSH tripole, as it applies\u0000to the SPNA.\u0000","PeriodicalId":19535,"journal":{"name":"Ocean Science","volume":"36 1","pages":""},"PeriodicalIF":3.2,"publicationDate":"2022-12-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"76678885","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}
Everton Giachini Tosetto, A. Bertrand, S. Neumann-Leitão, A. Costa da Silva, M. Nogueira Júnior
Abstract. In western boundary current systems (WBCSs), strong currents flow coastward carrying oceanic water masses and their associated planktonic fauna. Variation in the intensity of these currents and in the continental runoff may affect the dynamic interplay between oceanic and coastal communities. In addition, changes in the continental runoff and the thermohaline structure modulate the primary production, adding complexity to the dynamics of these oligotrophic systems. These dynamics likely shape the planktonic cnidarian communities. To further understand such relationships, we used a comprehensive dataset encompassing samples collected above the shelf and slope and around oceanic seamounts and islands of the Fernando de Noronha Ridge in the western tropical South Atlantic, in two seasons characterised by distinct thermohaline structure and circulation patterns. Results show that in the tropical South Atlantic and, likely, other western boundary systems with narrow continental shelves, coastward currents spread oceanic waters and their associated cnidarian species over the continental shelf. However, while both coastal and oceanic communities co-occur when the continental runoff is notable, oceanic species dominate almost the entire shelf during the dry season characterised by a stronger boundary current intensity. We also conclude that when the mixed-layer depth and associated nutricline are shallower, the enhanced primary productivity supports larger populations of planktonic cnidarian species through a bottom–up control.
{"title":"Planktonic cnidarian responses to contrasting thermohaline and circulation seasonal scenarios in a tropical western boundary current system","authors":"Everton Giachini Tosetto, A. Bertrand, S. Neumann-Leitão, A. Costa da Silva, M. Nogueira Júnior","doi":"10.5194/os-18-1763-2022","DOIUrl":"https://doi.org/10.5194/os-18-1763-2022","url":null,"abstract":"Abstract. In western boundary current systems (WBCSs), strong\u0000currents flow coastward carrying oceanic water masses and their associated\u0000planktonic fauna. Variation in the intensity of these currents and in the\u0000continental runoff may affect the dynamic interplay between oceanic and\u0000coastal communities. In addition, changes in the continental runoff and the\u0000thermohaline structure modulate the primary production, adding complexity to\u0000the dynamics of these oligotrophic systems. These dynamics likely shape the\u0000planktonic cnidarian communities. To further understand such relationships,\u0000we used a comprehensive dataset encompassing samples collected above the\u0000shelf and slope and around oceanic seamounts and islands of the Fernando de\u0000Noronha Ridge in the western tropical South Atlantic, in two seasons\u0000characterised by distinct thermohaline structure and circulation patterns.\u0000Results show that in the tropical South Atlantic and, likely, other western\u0000boundary systems with narrow continental shelves, coastward currents spread\u0000oceanic waters and their associated cnidarian species over the continental\u0000shelf. However, while both coastal and oceanic communities co-occur when the\u0000continental runoff is notable, oceanic species dominate almost the entire\u0000shelf during the dry season characterised by a stronger boundary current\u0000intensity. We also conclude that when the mixed-layer depth and associated\u0000nutricline are shallower, the enhanced primary productivity supports larger\u0000populations of planktonic cnidarian species through a bottom–up control.\u0000","PeriodicalId":19535,"journal":{"name":"Ocean Science","volume":"7 1","pages":""},"PeriodicalIF":3.2,"publicationDate":"2022-12-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"74414413","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}
Pia Kolb, A. Zorndt, H. Burchard, U. Gräwe, F. Kösters
Abstract. The Weser estuary has been subject to profound changes in topography in the past 100 years through natural variations and river engineering measures, leading to strong changes in hydrodynamics. These changes are also expected to have affected the dynamics of saltwater intrusion. Using numerical modelling, we examined saltwater intrusion in the Weser estuary in four different system states (1966, 1972, 1981, 2012). Models of each system state were set up with the respective topography and boundary values. We calibrated and validated each model individually to account for differences in sediments, bedforms, and the resolution of underlying bathymetric data between historical and recent system states. In simulations of 1 hydrological year, each with realistic forcing (hindcasting study), the influence of topography is overshadowed by the effects of other factors, particularly river discharge. At times of identical discharge, results indicate a landward shift of the salinity front between 1966 and 2012. Subsequent simulations with different topographies but identical boundary conditions (scenario study) confirm that topography changes in the Weser estuary affected saltwater intrusion. Solely through the topography changes, at a discharge of 300 m3 s−1, the position of the tidally averaged and depth-averaged salinity front shifted landwards by about 2.5 km between 1972 and 1981 and by another 1 km between 1981 and 2012. These changes are significant but comparatively small, since due to seasonal variations in run-off, the tidally averaged saltwater intrusion can vary by more than 20 km. An analysis of the salt flux through a characteristic cross section showed that saltwater intrusion in the Weser estuary is primarily driven by tidal pumping and only to a lesser degree due to estuarine circulation. However, results indicate that the contribution of individual processes has changed in response to anthropogenic measures.
{"title":"Modelling the impact of anthropogenic measures on saltwater intrusion in the Weser estuary","authors":"Pia Kolb, A. Zorndt, H. Burchard, U. Gräwe, F. Kösters","doi":"10.5194/os-18-1725-2022","DOIUrl":"https://doi.org/10.5194/os-18-1725-2022","url":null,"abstract":"Abstract. The Weser estuary has been subject to profound changes in\u0000topography in the past 100 years through natural variations and river\u0000engineering measures, leading to strong changes in hydrodynamics. These\u0000changes are also expected to have affected the dynamics of saltwater\u0000intrusion. Using numerical modelling, we examined saltwater intrusion in the\u0000Weser estuary in four different system states (1966, 1972, 1981, 2012).\u0000Models of each system state were set up with the respective topography and\u0000boundary values. We calibrated and validated each model individually to\u0000account for differences in sediments, bedforms, and the resolution of\u0000underlying bathymetric data between historical and recent system states. In\u0000simulations of 1 hydrological year, each with realistic forcing\u0000(hindcasting study), the influence of topography is overshadowed by the\u0000effects of other factors, particularly river discharge. At times of\u0000identical discharge, results indicate a landward shift of the salinity front\u0000between 1966 and 2012. Subsequent simulations with different topographies\u0000but identical boundary conditions (scenario study) confirm that topography\u0000changes in the Weser estuary affected saltwater intrusion. Solely through\u0000the topography changes, at a discharge of 300 m3 s−1,\u0000the position of the tidally averaged and depth-averaged salinity front\u0000shifted landwards by about 2.5 km between 1972 and 1981 and by another 1 km\u0000between 1981 and 2012. These changes are significant but comparatively\u0000small, since due to seasonal variations in run-off, the tidally averaged\u0000saltwater intrusion can vary by more than 20 km. An analysis of the salt\u0000flux through a characteristic cross section showed that saltwater\u0000intrusion in the Weser estuary is primarily driven by tidal pumping and only\u0000to a lesser degree due to estuarine circulation. However, results indicate\u0000that the contribution of individual processes has changed in response to\u0000anthropogenic measures.\u0000","PeriodicalId":19535,"journal":{"name":"Ocean Science","volume":"71 1","pages":""},"PeriodicalIF":3.2,"publicationDate":"2022-12-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"81848240","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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