Optics, structure and variability of the offshore Columbia River plume

The Columbia River delivers the greatest amount of freshwater to the coastal ocean along the U.S. Pacific coast. This freshwater forms the Columbia River plume, a mesoscale plume with significant implications on coastal ocean physical, biological, chemical, and geological processes. The plume is transported south and offshore during the upwelling season (The offshore Columbia River plume) in response to the dominant southward upwelling-favorable winds and associated surface circulation. Here a detailed investigation of the optics, structure and variability of the offshore plume is presented. A study of the interannual variability of river plumes off central-southern Chile is also included for comparison with another eastern boundary upwelling system with significant freshwater river outflows.Chapter 2 presents the main optical characterization of the offshore Columbia River plume, combining in situ observations from underwater gliders and MODIS satellite imagery. The cross-shore variability of relevant optical properties are described for the offshore Columbia River plume in comparison with ambient waters in absence of the plume off Newport, central Oregon. The plume thickens in the offshore direction, through a fresh and warm surface layer, which is concordant with the deepening of peaks in optical properties. This pattern has implications for the detection of the plume from ocean color remote sensing as the plume is practically undetectable from MODIS imagery by itself farther than ∼154 km from shore. Empirical algorithms, based on multivariate regression analyses of normalized-water leaving radiance (nLw(λ)) plus sea surface temperature (SST), are presented with more accurate results detecting offshore plume waters than previous studies using single visible bands.Chapter 3 contains a study of the structure and variability of the offshore Columbia River plume, with emphasis on the cross-shore structure off central Oregon, and its variability in response to wind forcing and river discharge. On average, the plume presents marked seasonal variability off central Oregon – early in spring it is located nearshore (inshore of 126◦W) whereas later in the upwelling season (July and August) its offshore extension increases to about 128◦W. On the interannual scale, anomalously fresh plume events occurred during the highest river discharges associated with spring snowmelt (i.e. 2008, 2011, 2012). Additional glider observations from the Ocean Observatories Initiative Endurance array and along-track Aquarius measurements provide new insights about the alongshore plume structure and its response to wind variability. Idealized numerical experiments of a large river plume during coastal upwelling, resembling the offshore Columbia River plume, are also presented with the objective of isolating the effects of differences in the strength of upwelling-favorable winds and discharge rates on the offshore plume.Chapter 4 inspects the interannual variability of freshwater plumes along the Oregon coast, including not only the offshore Columbia River plume but also the small coastal rivers along the entire Oregon coast with high accumulated winter discharges. Empirical Orthogonal Function (EOF) analysis reveals two dominant modes associated with (i) the winter plumes of coastal rivers which are merged along the entire Oregon shelf (EOF1) due to their dominant downstream direction of propagation as coastal-attached buoyancy-driven flows, and (ii) the offshore Columbia River plume occupying most of the coastal ocean off Oregon (EOF2) as it is transported south and offshore during spring-summer upwelling. Major plumes are found to correspond mainly with El Niño Southern Oscillation cycles, but longer time series are needed to better evaluate the influence of Pacific Decadal Oscillation and the North Pacific Gyre Oscillation because of their dominant decadal variability.Finally, Chapter 5 includes a comparative study of the influence of climate variability on the development of anomalous turbid river plumes off central-southern Chile, another eastern boundary upwelling system with significant freshwater input during the winter and spring seasons. Major turbid river plume events occur primarily during warm phases of the El Niño Southern Oscillation and Pacific Decadal Oscillation, and negative phases of the Antarctic Oscillation, when storm tracks are further north off central Chile. Anomalously large turbid plumes extend long distances offshore (∼70-80 km), and individual plumes coalesce into a continuous plume along the coast that covers the entire continental shelf.Keywords: Columbia River plume, coastal ocean, upwellin

Peningkatan Performa Prediksi Daerah Potensi Penangkapan Ikan Dengan Metode Threshold Adaptif

Metode yang digunakan untuk penentuan thermal fronts adalah algoritme Single Image Edge Detection dengan threshold statis 0,5 yang didapatkan dari penelitian terdahulu. Kekurangan dari metode threshold statis adalah tingginya bias akurasi hasil deteksi dikarenakan lebih banyaknya hasil deteksi negatif tervalidasi dibandingkan deteksi front murni yang tervalidasi. Penelitian yang diusulkan bertujuan untuk meningkatkan performa metode deteksi daerah potensi ikan. Peningkatan performa deteksi thermal front dapat dilakukan dengan mencari nilai threshold optimal yang sesuai untuk masing-masing citra. Threshold adaptif didapatkan dari hasil analisis histogram pada setiap citra greyscale yang diproses. Untuk mendapatkan nilai threshold optimal dipilih Algoritme Otsu dengan pertimbangan proses cepat dan ketepatan hasil menengah. Penyesuaian metode dibutuhkan karena sifat dasar data SST yang dikonversi menjadi raster. Modifikasi metode Otsu dilakukan pada perhitungan nilai threshold optimal dengan rentang intensitas greyscale 1-254. Pemurnian front menggunakan pendekatan Geodesic Buffering dengan jarak maksimal 10 kilometer untuk mengatasi pergeseran front akibat noise suppression. Penelitian telah dilakukan dan menghasilkan metode deteksi daerah potensi ikan dengan performa recall yang lebih tinggi 25,42% dibandingkan metode threshold statis. Nilai recall lebih tinggi membuktikan bahwa metode yang diusulkan mampu menghasilkan lebih banyak hasil deteksi front murni yang lokasinya tervalidasi dengan data aktual penangkapan ikan

Atmospheric water supply to the Atacama Desert from newly developed satellite remote sensing techniques and reanalysis

Many facets of atmospheric water supply to the Atacama Desert are poorly understood. However, in-depth knowledge regarding water availability, moisture sources and the underlying mechanisms is required to investigate biological and geological processes and to identify potential mutual relationships. This thesis provides a comprehensive meteorological perspective on the atmospheric water supply to the Atacama Desert within the context of the recent climate. Spatial and temporal variability of moisture as well as their controlling mechanisms depend on the type of water supply, i.e. clouds, water vapor, fog or precipitation. To investigate the influence of the persistent stratocumulus cloud deck above the southeast Pacific on the desert region, a new cloud base height retrieval method is introduced. It allows to estimate the vertical position of these clouds, which can help to identify regions within the coastal desert that are potentially influenced by these clouds. A first application of this new method revealed a strong relation between stratocumulus properties and the isotopic composition of coastal Tillandsia populations. The proximity of the Atacama Desert to main acting zones of the El Niño-Southern Oscillation (ENSO) phenomenon and of the Pacific Decadal Oscillation (PDO) together with results from previous studies suggest that modes of climate variability have strong influence on the moisture supply to this region. As oscillating extreme phases of these climate modes have recurring periods on the order of a few years to decades, a long data record is needed to study their impact. Therefore, spatio-temporal variability of integrated water vapor (IWV) provided by a century-spanning reanalysis data set is studied in relation to ENSO and PDO. It is shown that the reanalysis represents IWV in a suitable manner to study its long-term variability. On a decadal time scale, the PDO revealed a stronger coupling to IWV compared to ENSO. According to a seasonal analysis, identified relationships between ENSO and IWV are in line with findings reported for precipitation in the northeastern Atacama. This suggests that IWV has the potential to serve as a proxy for precipitation. The ENSO signal is opposite for summer and winter season. The negative phase (La Niña) favors wetter summers and drier winters, whereas the positive phase (El Niño) is associated with drier summers and wetter winters. Besides, it is shown that enhanced IWV under La Niña conditions is not constrained to the northeastern part of the Atacama Desert but can reach even offshore regions near the west coast. This effect can be typically observed in the summer season. Thus, the moisture can be supplied to the Atacama Desert from easterly or westerly sources depending on season and ENSO phase with regionally varying impacts. Water vapor is a key variable which controls fog formation. While a few studies demonstrate the impact of fog on the coastal desert based on in-situ measurements as well as spatially and temporally limited satellited-based observations, this thesis introduces a novel satellite-based fog detection method which allows a region-wide assessment. An application of the algorithm for a 3-year period shows the spatial distribution of fog frequencies across the Atacama Desert. Aside from the coastal maximum, high fog frequencies are also revealed for isolated locations farther inland, which often coincide with salt flats within the central valley. The mechanisms driving fog formation within these inland regions remain unclear. The novel fog detection method creates the opportunity to further investigate this issue in future research. Aside from westerly moisture sources associated with the Pacific Ocean and episodic easterly inflow from the continental interior, a third scenario is identified in this thesis. By investigating the role of atmospheric rivers for the Atacama Desert, it is revealed that moisture can be transported from the Amazon Basin across the Andes and the southeast Pacific towards the Atacama Desert. Furthermore, fractional precipitation rates of more than 50 % for various regions within the Atacama Desert demonstrate the importance of atmospheric rivers for this hyperarid environment

In-situ, High-Frequency Assessment of Phytoplankton Functional Groups and Their Ecology in Diverse Marine Areas

Challenges ahead in phytoplankton ecology lie increasingly within the small scales, spatially and temporally, and how the diverse components of the community adapt to biotic and abiotic constraints. Despite advances made possible with new instrumentation, still little is known about the distribution of phytoplankton assemblages at the meso/submesoscale and at the diel scale. The work presented here aims at investigating phytoplankton functional groups at those scales, with a focus on their distribution and traits through time and space in different areas, and on the role of environmental factors in shaping these distribution patterns. For this purpose, a pulse-shape flow cytometer was used in-situ at high-frequency, either on-board vessels or at fixed sites, to sample ocean-to-coast gradients, and coastal areas. Besides estimating concentrations of the different functional groups, a relationship derived from cell scatter helped estimating the biomass represented by each of them, and their average cellular biomass. The total biomass of phytoplankton and the individual biomass of optically-defined groups varied significantly in relation to water masses and their properties. A refined trait-based approach was applied to qualify phytoplankton functional groups from optical features, and the diel variability of these optical features was explored. Traits were significantly correlated with several abiotic factors, mainly temperature and salinity. Multivariate ordination techniques were applied to cope with the amount of data handled and revealed patterns in phytoplankton distribution, significantly tied to hydrological features down to the submesoscale. A Cytometric Diversity Index was calculated per sample and appeared tied to water mass properties, which determined the abundance of each phytoplankton size-classes. Picophytoplankton was found to be most abundant in every location (Eastern North Atlantic, Western Mediterranean Sea, North Adriatic) and drove total phytoplankton abundance (e.g. accounting for 94.2 ± 4% in the Atlantic), while total biomass was driven by nanoeukaryotes (87 ± 6%) and occasionally by microeukaryotes (0% to 58%) and was tied both to environmental conditions and hydrological features

Characteristics and impact of mesoscale eddies in the eastern tropical North Atlantic = Charakteristik und Einfluss mesoscaliger Wirbel im östlichen tropischen Nord Atlantik

A combination of multiple ocean observing system elements is used to assess the mesoscale eddy activity in the tropical Atlantic off northwestern Africa (12-22°N and 15-26°W). Considering just the rotation direction of the surface flow field, eddies are categorized into cyclonic (CEs) and anticyclonic eddies. If vertical stratification is considered additionally, a refinement can be made by distinguishing between anticyclonic (AEs) and anticyclonic modewater eddies (ACMEs). ACMEs are characterized by a subsurface mode of rather homogenous water located between upward and downward displaced isopycnals. Eddies can be identified and classified from space by investigating the sea surface parameters: Sea level anomaly (SLA), sea surface temperature (SST) and sea surface salinity (SSS). AEs/CEs are associated with an elevation/depression of SLA and enhanced/reduced SST and SSS in their cores. However, 20% of all anticyclonic eddies are associated with reduced SST and SSS instead and are identified as ACMEs. In the area of interest, about 146±4 eddies per year with a minimum lifetime of 7 days are identified (52% CEs, 39% AEs, 9% ACMEs). All observed eddies are isolated and serve as transport agents, exporting water from the coast into the open ocean. In CEs and ACMEs low oxygen cores are identified and related to enhanced primary production at the surface and an associated elevated respiration rates within the isolated eddy cores. It could be observed that the phase speed of NIWs and the speed of the mean eddy flow are of similar magnitude. Therefore, critical layer formation is expected and mixing is likely to occur close to the euphotic zone at the eddy periphery. These processes describe one mechanism that support an upward nutrient flux towards the euphotic zone and the coexistence with a highly isolated eddy core. The analysis shows that anomalous environments associated with eddy cores occur more frequently than previously expected

Charakteristik und Einfluss mesoscaliger Wirbel im östlichen tropischen Nord Atlantik

A combination of multiple ocean observing system elements is used to assess the mesoscale eddy activity in the tropical Atlantic off northwestern Africa (12-22°N and 15-26°W). Considering just the rotation direction of the surface flow field, eddies are categorized into cyclonic (CEs) and anticyclonic eddies. If vertical stratification is considered additionally, a refinement can be made by distinguishing between anticyclonic (AEs) and anticyclonic modewater eddies (ACMEs). ACMEs are characterized by a subsurface mode of rather homogenous water located between upward and downward displaced isopycnals. Eddies can be identified and classified from space by investigating the sea surface parameters: Sea level anomaly (SLA), sea surface temperature (SST) and sea surface salinity (SSS). AEs/CEs are associated with an elevation/depression of SLA and enhanced/reduced SST and SSS in their cores. However, 20% of all anticyclonic eddies are associated with reduced SST and SSS instead and are identified as ACMEs. In the area of interest, about 146±4 eddies per year with a minimum lifetime of 7 days are identified (52% CEs, 39% AEs, 9% ACMEs). All observed eddies are isolated and serve as transport agents, exporting water from the coast into the open ocean. In CEs and ACMEs low oxygen cores are identified and related to enhanced primary production at the surface and an associated elevated respiration rates within the isolated eddy cores. It could be observed that the phase speed of NIWs and the speed of the mean eddy flow are of similar magnitude. Therefore, critical layer formation is expected and mixing is likely to occur close to the euphotic zone at the eddy periphery. These processes describe one mechanism that support an upward nutrient flux towards the euphotic zone and the coexistence with a highly isolated eddy core. The analysis shows that anomalous environments associated with eddy cores occur more frequently than previously expected.In dieser Studie wurden die Eigenschaften mesoskaliger Wirbel im tropischen Nordost Atlantik untersucht. Berücksichtigt man ausschließlich die Rotationsrichtungen, lassen sich Wirbel in Zyklone (CEs) und Antizyklone (AEs) unterteilen. Mithilfe der vertikalen Schichtung kann ein dritter Wirbeltyp unterschieden werden, der antizyklonale Modewasser-Wirbel (ACME). Der Kern eines ACME besteht aus einer vergleichsweise homogenen Wassermasse, und wird von nach oben und unten ausgelenkten Dichteflächen eingeschlossen. Alle drei Wirbeltypen konnten via folgenden Satellitenbeobachtung identifiziert werden: Meeresoberflächenauslenkung (SLA), Meeresoberflächentemperatur (SST) und Meeresoberflächensalzgehalt (SSS). AEs/CEs weisen erhöhte/reduzierte SLA, SST und SSS auf. Von allen antizyklonal rotierenden Wirbeln jedoch zeigten etwa 20% reduzierte SST und SSS auf und konnten somit als ACMEs identifiziert werden. Im gesamten Untersuchungsgebiet wurden 146±4 Wirbel pro Jahr mit einer Lebensdauer von mehr als 7 Tagen gezählt (52% CEs, 39% AEs, 9% ACMEs). Alle untersuchten Wirbel waren isoliert und transportierten Wassermassen von der Küste offshore. CEs und ACMEs zeichneten sich mit einer sehr niedrigen Sauerstoffkonzentration in ihren Wirbelkernen, einer verstärkten Primärproduktion an der Oberfläche sowie einem höheren Sauerstoffverbrauch innerhalb des isolierten Wirbelkerns aus. Es wird die Hypothese aufgestellt, dass die Bildung kritischer Schichten und infolgedessen eine intensive vertikale Durchmischung am Wirbelrand auftritt. Hervorgerufen wird diese durch die Wechselwirkung der Rotation des Wirbels mit Wellen, die eine Frequenz nahe der Trägheitsfrequenz aufweisen. Dieser Prozess könnte einen Weg beschreiben, der vertikalen Transport von Nährstoffen in die euphotischen Zone und die zeitgleiche Existenz eines isolierten Kerns möglich macht. Die Analyse zeigt, dass die beobachteten extremen Wassermassenanomalien in den Wirbelkernen häufiger als zuvor erwartet auftreten