Crustal Structure and Moho Geometry beneath the Northern Apennines (Italy)
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We used receiver functions (RFs) from broad‐band seismic stations to investigate the crustal structure of the Northern Apennines, Italy. Additionally, we use data obtained in this study to provide initial constraints for a map of the Moho depth of Italy. Ten stations were deployed along a transect [N75°E] during the 1994 GeoModAp project. RF analysis shows the presence of lateral variations in the crust. We observed patterns of symmetric and anti‐symmetric converted phases from radial and tangential RFs vs. back‐azimuth. These patterns can be explained by the presence of dipping interfaces and/or anisotropy within the crust. We then inverted RFs following the inversion scheme proposed by Sambridge [1999] . The results show the presence of S ‐velocity inversions in the lower crust beneath the Apennines, the upwelling of Moho in the Tyrrhenian area and its progressive deepening from the Tyrrhenian Sea toward the Adriatic coast.Keywords:
Receiver function
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The importance of coastal upwelling systems is widely recognized. However, several aspects of the current and future behaviors of these systems remain uncertain. Fluctuations in temperature because of anthropogenic climate change are hypothesized to affect upwelling-favorable winds and coastal upwelling is expected to intensify across all Eastern Boundary Upwelling Systems. To better understand how upwelling may change in the future, it is necessary to develop a more rigorous method of quantifying this phenomenon. In this paper, we use SST data and wind data in a novel method of detecting upwelling signals and quantifying metrics of upwelling intensity, duration, and frequency at four sites within the Benguela Upwelling System. We found that indicators of upwelling are uniformly detected across five SST products for each of the four sites and that the duration of those signals is longer in SST products with higher spatial resolutions. Moreover, the high-resolution SST products are significantly more likely to display upwelling signals at 25 km away from the coast when signals were also detected at the coast. Our findings promote the viability of using SST and wind time series data to detect upwelling signals within coastal upwelling systems. We highlight the importance of high-resolution data products to improve the reliability of such estimates. This study represents an important step towards the development of an objective method for describing the behavior of coastal upwelling systems.
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The timing of the onset of coastal upwelling in spring and its intensity over the upwelling season are critical factors in the productivity and structure of the California Current ecosystem (CCE). We use an index of coastal upwelling to characterize physical forcing over the latitudinal extent of the CCE, and compare the evolution of the upwelling season in 2005 with previous years. The onset of coastal upwelling in 2005 in the northern California Current was delayed by 2–3 months. Upwelling was stronger than normal in the latter part of the upwelling season, allowing the cumulative upwelling to reach the climatological mean by fall. Although physical conditions were unusual in 2005, they were not unprecedented in the historical record. However, the timing and strength of coastal upwelling is a critical ecological factor, particularly for species whose life histories are closely tuned to the annual cycle. The unusual physical and biological conditions observed in spring 2005 illustrate the sensitivity of the CCE to possible future climate extremes.
Forcing (mathematics)
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Coastal upwelling is one of the most important oceanographic processes relating to ecosystem function at local and global spatial scales. To better understand how changes in upwelling trends may occur in the face of ongoing anthropogenically induced climate change it is important to quantify historical trends in climatic factors responsible for enabling coastal upwelling. However, a paucity of conclusive knowledge relating to patterns concerning changes in upwelling across the world’s oceans over time makes such analyses difficult. In this study I aimed to quantify these patterns by first identifying when upwelling events occur using a novel method for predicting the behaviours of coastal upwelling systems over time. By using remotely sensed SST data of differing resolutions as well as several wind variables I was able to identify and quantify upwelling signals at several distances away from the coastline of various upwelling systems. Using this novel method of determining upwelling, I then compared upwelling patterns within all Eastern Boundary Upwelling Systems (EBUS) over a period of 37 years, with the assumption that climate change was likely to have driven variable wind patterns leading to a more intense upwelling over time. Overall, upwelling patterns and wind variables did not intensify overtime. This method of identifying upwelling may allow for the development of predictive capabilities to investigate upwelling trends in the future.
Marine ecosystem
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Biogeochemistry
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Spatio‐temporal trends in upwelling patterns were studied along the Canary Upwelling System for the period 1967–2006. The northwestern coast of African from lat 20°N to 32°N is observed to be under a permanent upwelling regime characterized by coastal sea surface temperatures (SST) colder than the oceanic ones at the same latitude. The temperature difference is termed the temperature upwelling index (UI SST ). This regime is consistent with the wind‐derived Ekman transport (UI W ), which is observed near the coast and is directed offshore. This index shows the existence of upwelling‐favorable conditions all year but has an annual cycle characterized by more upwelling‐favorable conditions from April to September, with a maximum in July, and less upwelling‐favorable conditions from October to March, with a minimum in December to January. Although both indices can be used to characterize the phenomenon, only UI W values were used to quantify upwelling change during the four decades under review because this index is less sensitive to external factors compared to UI SST . A strong decrease in upwelling intensity has been observed in all seasons. In particular, the summer (winter) decrease is on the order of 45% (20%) of the mean amplitude of the upwelling cycle.
Annual cycle
Ekman transport
Wind Stress
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Global increases in temperature are altering land-sea temperature gradients. Bakun (1990) hypothesized that changes within these gradients will directly affect atmospheric pressure cells associated with the development of winds and will consequently impact upwelling patterns within ecologically important Eastern Boundary Upwelling Systems (EBUS). In this study we used daily time series of NOAA Optimally Interpolated sea surface temperature (SST) and ERA 5 reanalysis wind products to calculate a series novel of metrics related to upwelling dynamics. We then use these to objectively describe upwelling signals in terms of their frequency, intensity and duration throughout the four EBUS during summer months over the last 37 years (1982–2019). We found that a decrease (increase) in SST is associated with an increase (decrease) in the number of upwelling “events,” a decrease (increase) in the intensity of upwelling, and an increase (decrease) in the cumulative intensity of upwelling, with differences between EBUS and regions within EBUS. The Humboldt Current is the only EBUS that shows a consistent response from north to south with a general intensification of upwelling. However, we could not provide clear evidence for associated changes in the wind dynamics hypothesized to drive the upwelling dynamics.
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把地质的调查， stratigraphic 节测量和室内的全面调查基于地， Zanda 盆在 Himalaya 板中的构造地点被查明，并且 Zanda 盆的形成和进化作为六个阶段在到早更新世的上新世期间被分类：(a) 主要指责裂缝的舞台，(b) 快指责裂缝的舞台，(c) 集中的指责裂缝的舞台，(d) 壅滞舞台，(e) 第二等的指责裂缝的舞台，和(f) 第二等的快指责裂缝的舞台。基于 Zanda 盆的这个六阶段的形成进化理论，当下列五上演，到早更新世的从上新世的西方的 Himalaya 山的 upwelling 过程被分类：(a) 慢 upwelling 舞台(5.44.4 妈) ，(b) 中间速度的 upwelling 舞台(4.43.5 妈) ，(c) 快 upwelling 舞台(3.53.2 妈) ，(d)停止 upwelling 阶段(3.22.7 妈) ，和(e) 快 upwelling 舞台(2.7 妈) 。研究从早上新世(4.7 妈) 在持续时间显示出那到上新世(2.67 妈) 的目的，它持续了 203 万年， Himalaya 山高举了在 0.74 mm/a 的速度的 1500 m；这属于中间速度的 upwelling。在在早更新世的早阶段的 131 万年期间， Himalaya 山在 1.15 mm/a 的速度在另一 1500 m 上面升起了；这是相当快的 upwelling。所有这些数据证明了西方的 Himalaya 山的 upwelling 沿着有 multi-stages，多速度，和非天律不变论的特征的一个复杂过程。
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Research on upwelling in the Taiwan Strait, based on hydrographic observations and numerical modeling, has indicated that there are four upwelling regions in the Strait: along the southwestern coast of the Taiwan Strait (SW-upwelling region), along the northwestern coast of the Taiwan Strait (NW-upwelling region), near the Taiwan Bank (TB-upwelling region), and around the Penghu Islands (PH-upwelling region). These upwellings are principally induced by the southwesterly monsoon and the ascending movement of the northward, near-bottom current along the uplifting bottom topography. The SW-upwelling and NW-upwelling occur during the southwesterly monsoon period in summer, and the TB-upwelling and PH-upwelling occur year- round with varying strength and scale.
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Qiongdong upwelling is seasonal coastal upwelling east of Hainan Island.It usually occurs during April-September with the strongest upwelling in June and July in the area of 18o30’ 20oN and west of 111o30’E,where the summer surface water has low temperature,high salinity,low dissolved oxygen and rich nutrients.In this study,the temporal-spatial characteristics and mechanisms of Qiongdong upwelling are reviewed based on the studies since the 1960s.These studies mainly described basic hydrography,interannual variability,and influences of wind and topography on Qiongdong upwelling.Comparing to the latest studies in coastal upwelling,much work needs to be done on Qiongdong upwelling via comprehensive dynamic and ecologic investigations,on issues such as the interannual variability and its mechanisms,and the interaction between Qiongdong upwelling and large-scale circulation.
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