Optical investigations of CDOM-rich coastal waters in Pärnu Bay

Pärnu Bay in the Eastern Baltic Sea was chosen for studying the spatial-temporal variability of water parameters as an optically complex and semi-enclosed coastal area. The water properties of Pärnu Bay are influenced by the town of Pärnu with its 70 000 inhabitants and by the high inflow from the Pärnu River. The in situ database was collected during the ice-free period of 2006–2007 (11 sampling stations, 10 series of field trips). According to the results, the main factor influencing the light attenuation in the water was coloured dissolved organic matter (CDOM) which overshadows the relationships between the radiation characteristics and organic/inorganic particles. In April and May, when the freshwater discharge of the Pärnu River was highest, the values of aCDOM(380) were between 4.6 and 31.8 m–1, while in September they varied only within 2.52–10.2 m–1. The concentrations of chlorophyll a (including its metabolite phaeophytin a) generally ranged from 4 to 12 mg m–3 but during algal blooms they rapidly increased to 31.8 mg m–3. The temporal and spatial irregularity of suspended matter concentrations was caused by the loading of unpacked peat at the Pärnu River mouth as well as by undulation and ship traffic in Pärnu Bay. MODIS level 1 data with 250 m resolution were used for illustrative comparison of spatial and temporal variations in the water properties in Pärnu Bay and the Gulf of Riga. An attempt to perform the quantitative analysis with the purpose of estimating the concentrations of different optically significant substances separately gave statistically incorrect results

Large-Scale Carbonate Platform Development of Cay Sal Bank, Bahamas, and Implications for Associated Reef Geomorphology

The Bahama Archipelago consists of an arcuate chain of carbonate platforms. Average water depths on the platform-tops, such as the Great Bahama Bank (GBB), are typically 10 m or less, with coral reef-rimmed margins, thick sediment accumulations, and the frequent occurrence of islands. There are, however, exceptions. For example, Cay Sal Bank (CSB), a little studied detached Bahamian carbonate platform with depths ranging from 30 to 7 m, is only slightly deeper than the GBB, but devoid of islands, lacks platform-margin coral reefs and holds little sediment on the platform-top; the platform is incipiently drowned. CSB is interesting as it is conspicuously larger (6000 sq. km) than other incipiently drowned platforms in the region, such as Serranilla Bank (1100 sq. km) and the Cat Island platform (1500 sq. km). Field and remote sensing data are assembled to provide insight into the sedimentology and geomorphology of the CSB. The influence of ocean climate, regional hydrodynamics, and Holocene flooding history are investigated to understand why platform-margin coral reef growth on CSB has been unable to keep pace with Holocene sea-level rise. A decade of regional sea-surface temperature data for the Bahamas report CSB to be situated in the same ocean climate regime as GBB. Temperature cannot explain the platform\u27s different morphologies. The Florida Current has been evoked as a possible reason for the immature development of platform-top processes on the CSB, but numeric modeling suggests its influence to be restricted to the deep flanks of the bank. Further, sediment distribution on CSB, including infill patterns of karst depressions, suggest trade winds (easterlies) to drive platform-top hydrodynamics. By assembling a satellite-derived bathymetry map, it can be shown that CSB flooded earlier and at relatively higher rates of Holocene sea-level rise than its neighboring platforms. Flooding history is identified as the most feasible explanation for the atypical morphology of the CSB. By contrasting the present-day morphology of the CSB and the GBB, the work emphasizes how subtle differences in relative sea-level history can influence the growth of platform-margin coral reefs, features that in turn can conspire to set even closely neighboring carbonate platforms on divergent paths with regard to the development of marine landforms. This insight is relevant to interpreting the morphological diversity of carbonate platforms in the modern ocean and in the rock record

Mudelhinnang parandamaks kaugseire kasutamist tsünobakterite tuvastamisel ja kvatitatiivsel seirel

In the present thesis bio-optical and radiative transfer models were used to show the remote sensing capabilities in pure culture conditions in the Baltic Sea area. Remote sensing instruments with sufficient spectral resolution (10 nm or better) and high radiometric sensitivity may be used for recognition and quantitative mapping of cyanobacteria. The absorption by phycocyanin is causing an appearance of a special feature in reflectance spectra that is typical to only cyanobacteria and can be detected with sufficient spectral resolution instruments. Modelled estimation and some in situ data for the typical open Baltic Sea waters show that the concentration of chlorophyll a should be around 8-10 mg/m3 so that the phycocyanin absorption feature would become detectable in reflectance spectra. Satellite sensor MERIS with suitable spectral bands could be a useful tool for detecting waters dominated by cyanobacteria and estimating phytoplankton biomass in blooms. MERIS bands 6 and 7 (620 and 665 nm respectively) allow detecting phycocyanin absorption feature around 620 nm. The vertical distributions of cyanobacteria also have a significant influence on remote sensing. The variability in reflectance spectra due to modelled different vertical distributions of cyanobacteria was significant in both cases of lower and higher concentrations of cyanobacterial biomass. Knowledge about the vertical distribution of cyanobacteria can help developing remote sensing algorithms and methods for quantitative mapping of cyanobacteria. Kuna tsüanobakterite õitsengud on ajas ja ruumis väga varieeruvad, siis võib nende uurimine in situ mõõtmiste abil võtta aastaid või isegi aastakümneid. Sellepärast on käesolevas töös põhiliselt kasutatud mudelarvutusi, mis baseeruvad labori ja in situ mõõtmistel ning võimaldavad simuleerida kaugseire sensoritega mõõdetavat signaali väga erinevates tingimustes. Töö tulemusena leiti, et piisava spektraalse lahutusvõimega (10 nm või vähem) ja kõrge tundlikkusega kaugseire instrumendid võimaldavad tsüanobakterite tuvastamist ainult tsüanobakteritele omase fükobiliproteiini, fükotsüaniini, kaudu. Mudelarvutuste tulemused näitavad, et Läänemere avaosale sarnaste optiliste omadustega vees peaks klorofüll a kontsentratsioon olema vähemalt 8-10 mg/m3, et fükotsüaniini põhjustatud neeldumine oleks vee heleduskoefitsiendi spektris tuvastatav hüperspektraalsete instrumentidega. Multispektraalsete sensoritega satelliitide, nagu ALI, Landsat ja MODIS, abil ei ole võimalik tsüanobaktereid teistest fütoplanktoni liikidest eristada kuna nendel sensoritel puuduvad 630 ja 650 nm piirkonnas spektrikanalid. Satelliitidest on vaid MERIS’el tsüanobakterite avastamiseks sobivad spektrikanalid. Lisaks näitavad käesoleva töö modelleerimistulemused, et kuigi MODIS’e esimene spektrikanal ei ole ette nähtud vee kaugseireks, saab siiski selle abil kaardistada tsüanobakterite õitsengute ulatust ja hinnata biomassi. Erinevalt teistest fütoplanktoni liikidest on tsüanobakterid suutelised reguleerima oma ujuvust. Modelleerimistulemused näitasid, et tsüanobakterite vertikaalsel jaotusel võib olla väga oluline mõju vee heleduskoefitsiendi spektritele ja ka kaugseire abil saadud biomassi hinnangutele. Tsüanobakterite biomassi uurimiseks ja/või kaugseire algoritmide välja töötamiseks tsüanobakterite biomassi hindamisel on oluline teada tsüanobakterite vertikaalset jaotust veesambas ning ei ole õige kasutada ühest sügavusest kogutud või segatud veeproovi

Optimization of variable fluorescence measurements of phytoplankton communities with cyanobacteria

International audienceExcitation-emission fluorescence matrices of phytoplankton communities were simulated from laboratory-grown algae and cyanobacteria cultures, to define the optical configurations of theoretical fluorometers that either minimize or maximize the representation of these phytoplankton groups in community variable fluorescence measurements. Excitation sources that match the photosystem II (PSII) action spectrum of cyanobacteria do not necessarily lead to equal representation of cyanobacteria in community fluorescence. In communities with an equal share of algae and cyanobacteria, inducible PSII fluorescence in algae can be retrieved from community fluorescence under blue excitation (450-470 nm) with high accuracy (R (2) = 1.00). The highest correlation between community and cyanobacterial variable fluorescence is obtained under orange-red excitation in the 590-650 nm range (R (2) = 0.54). Gaussian band decomposition reveals that in the presence of cyanobacteria, the emission detection slit must be narrow (up to 10 nm) and centred on PSII chlorophyll-a emission (similar to 683 nm) to avoid severe dampening of the signal by weakly variable phycobilisomal fluorescence and non-variable photosystem I fluorescence. When these optimizations of the optical configuration of the fluorometer are followed, both cyanobacterial and algal cultures in nutrient replete exponential growth exhibit values of the maximum quantum yield of charge separation in PSII in the range of 0.65-0.7

Satellite imaging coral reef resilience at regional scale. A case-study from Saudi Arabia

► Spatially estimating a proxy for coral reef resilience from remote sensing data. ► Develop indices of coral stress from satellite data and apply using GIS. ► Propose the first-basis for a remote sensed resilience index (RSRI). ► RSRI provides an estimate of expected reef resilience. ► The framework presented is flexible and may be adapted to other reef regions. We propose a framework for spatially estimating a proxy for coral reef resilience using remote sensing. Data spanning large areas of coral reef habitat were obtained using the commercial QuickBird satellite, and freely available imagery (NASA, Google Earth). Principles of coral reef ecology, field observation, and remote observations, were combined to devise mapped indices. These capture important and accessible components of coral reef resilience. Indices are divided between factors known to stress corals, and factors incorporating properties of the reef landscape that resist stress or promote coral growth. The first-basis for a remote sensed resilience index (RSRI), an estimate of expected reef resilience, is proposed. Developed for the Red Sea, the framework of our analysis is flexible and with minimal adaptation, could be extended to other reef regions. We aim to stimulate discussion as to use of remote sensing to do more than simply deliver habitat maps of coral reefs

Satellite Imaging Coral Reef Resilience at Regional Scale. A Case-Study From Saudi Arabia

We propose a framework for spatially estimating a proxy for coral reef resilience using remote sensing. Data spanning large areas of coral reef habitat were obtained using the commercial QuickBird satellite, and freely available imagery (NASA, Google Earth). Principles of coral reef ecology, field observation, and remote observations, were combined to devise mapped indices. These capture important and accessible components of coral reef resilience. Indices are divided between factors known to stress corals, and factors incorporating properties of the reef landscape that resist stress or promote coral growth. The first-basis for a remote sensed resilience index (RSRI), an estimate of expected reef resilience, is proposed. Developed for the Red Sea, the framework of our analysis is flexible and with minimal adaptation, could be extended to other reef regions. We aim to stimulate discussion as to use of remote sensing to do more than simply deliver habitat maps of coral reefs