A global assessment of carbon flux in the world ocean is one of the major undertakings of the Joint Global Ocean Flux Study (JGOFS). This has to be undertaken using historical in situ data of primary productivity. As required by the temporal and spatial scales involved in a global study, it can be conveniently done by combining, through appropriate models, remotely sensed information (chlorophyll a, temperature) with basic information about the parameters related to the carbon uptake by phytoplanktonic algae. This requires a better understanding as well as a more extended knowledge of these parameters which govern the radiative energy absorption and utilization by algae in photosynthesis. The measurement of the photosynthetic response of algae [the photosynthesis (P) versus in-adiance (£) curves], besides being less shiptime consuming than in situ primary production experiments, allows the needed parameters to be derived and systematically studied as a function of the physical, chemical and ecological conditions. The aim of the present paper is to review the significance of these parameters, especially in view of their introduction into models, to analyze the causes of their variations in the light of physiological considerations, and finally to provide methodological recommendations for meaningful determinations, and interpretation, of the data resulting from /"versus £ determinations. Of main concern are the available and usable irradiance, the chlorophyll a-specific absorption capabilities of the algae, the maximum light utilization coefficient (a), the maximum quantum yield (4>m), the maximum photosynthetic rate (Pm) and the light saturation index (£k). The potential of other, non-intrusive, approaches, such as the stimulated variable fluorescence, or the sun-induced natural fluorescence techniques is also examined.

Parameters of photosynthesis: definitions, theroy and interpretation of results

Analytical approximate wave form for asymmetric waves

[1] A one-dimensional model solving the Reynolds-averaged Navier-Stokes and advection-diffusion equations in conjunction with a k − e model for turbulence closure is used to systematically explore net sediment transport rates beneath skewed asymmetric waves under sheet flow conditions The model, which reproduces net rates obtained in U tube experiments under purely skewed and asymmetric oscillatory flow well, is forced with an analytical expression of free stream oscillatory flow in which we varied the degree of skewness versus asymmetry, the magnitude of the total wave nonlinearity, the oscillatory flow amplitude, and the wave period We find that for a wide range of conditions sediment entrained into the flow during a particular wave half-cycle has not completely settled before flow reversal and tends to be transported during the next half-cycle Consistent with earlier work, these phase-lag effects reduce transport rates under oscillatory flow dominated by velocity skewness, while they enhance net transport rates under oscillatory flow dominated by velocity asymmetry Phase-lag effects are particularly important in fine-medium sands (<≈250 μm) For a given grain size phase-lag effects become more pronounced with an increase in wave nonlinearity and in velocity amplitude, and with a decrease (increase) in wave period under skewed (asymmetric) oscillatory flow When phase-lag effects are negligible, transport rates are largest under skewed oscillatory flow containing some asymmetry; otherwise, they are largest under asymmetric flow Our work implies that nearshore sediment transport equations based on the instantaneous bed shear stress may be restricted in applicability to situations when the grain size exceeds ≈250 μm

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2009JC005416

Modeling sediment transport beneath skewed asymmetric waves above a plane bed

Projecting future distribution of the seagrass Zostera noltii under global warming and sea level rise

Evaluation of a CMIP5 derived dynamical global wind wave climate model ensemble

Local sea level change scenarios for the end of the 21st century and potential physical impacts in the lower Ria de Aveiro (Portugal)

/pdf/global-marine-heatwave-events-using-the-new-cmip6-multi-hxc1ej0glu.pdf

Global marine heatwave events using the new CMIP6 multi-model ensemble: from shortcomings in present climate to future projections

This work investigates the recent morphological changes at the inlet of a complex coastal system (Ria de Aveiro lagoon, Portugal). This study was carried out using bathymetric data analysis and numerical simulations obtained with the 2DH morphodynamic modelling system MORSYS2D. The present simulations considered only tidal forcing, and a sensitivity analysis was performed by tuning the formula used to compute the sediment transports. A non-uniform sediment grain size distribution for the Ria de Aveiro inlet is considered in the numerical simulations, based on surveys performed in this area. The model results are analysed to assess if they resemble the observed trends of erosion and deposition, as calculated from bathymetric data. A quantitative analysis of the differences between the bathymetric changes obtained through surveys and the numerical results over a period of 3 years considering different sediment transport formulations shows that the formulations of Ackers and White (1973) and Engelund and Hansen (1967) are the ones that best describe the morphodynamic changes driven by tides in the Ria de Aveiro inlet.

Sensitivity analysis of a morphodynamic modelling system applied to a coastal lagoon inlet

Modeling SST and chlorophyll patterns in a coupled estuary-coastal system of Portugal: The Tagus case study

Tidal estuaries are regarded as highly important ecosystems, mostly due to their high primary productivity and associated role as carbon sinks. In these ecosystems, primary productivity is mainly due to the photosynthetic carbon fixation by phytoplankton and microphytobenthos. The productivity of the two communities has been mostly studied separately, and directly comparable estimates of their carbon fixation rates in the same estuary are relatively scarce. The present study aimed to characterize the spatio-temporal variability of the productivity of phytoplankton and microphytobenthos in a tidal estuary, the Ria de Aveiro (Portugal), and to estimate the annual ecosystem-level budget for carbon fixation by the two communities. Productivity rates were determined based on synoptic in situ measurements of absolute rates of electron transport rate of photosystem II, using PAM fluorometry. Chlorophyll fluorescence indices were accompanied by measurements of salinity, temperature, water turbidity, solar irradiance, and planktonic and benthic microalgal biomass. Measurements were carried out hourly, along four spring-neap tidal cycles distributed along one year, on three sites of the estuary. The most pronounced trends in the spatio-temporal variability of the photophysiology and productivity of the two communities were the following: (i) maximum biomass and productivity were reached later for microphytobenthos (summer-autumn) than for phytoplankton (spring-summer); (ii) the absorption cross-section of PSII was generally higher for phytoplankton; (iii) the two groups showed a similar photoacclimation state, but microphytobenthos appeared as high light-acclimated when compared to phytoplankton. Biomass-specific productivity was on average higher for phytoplankton than for microphytobenthos, averaging 68.0 and 19.1 mg C mg Chl a-1 d-1, respectively. However, areal depth-integrated production rates were generally higher for the microphytobenthos than for the phytoplankton, averaging 264.5 and 140.0 mg C m-2 d-1, respectively. On an annual basis, phytoplankton productivity averaged 49.9 g C m-2 yr-1 while the productivity of microphytobenthos averaged 105.2 g C m-2 yr-1. When upscaling to the whole estuary, annual primary production rates of phytoplankton and microphytobenthos reached 4894.3 and 7534.0 t C yr-1, respectively, representing 39.4% and 60.6% of the combined total of 12428.3 t C yr-1 determined for the two communities in the Ria de Aveiro.

/pdf/synoptic-spatio-temporal-variability-of-the-photosynthetic-321jb1zd1n.pdf

Sandra Plecha

Papers

Local sea level change scenarios for the end of the 21st century and potential physical impacts in the lower Ria de Aveiro (Portugal)

Global marine heatwave events using the new CMIP6 multi-model ensemble: from shortcomings in present climate to future projections

Sensitivity analysis of a morphodynamic modelling system applied to a coastal lagoon inlet

Modeling SST and chlorophyll patterns in a coupled estuary-coastal system of Portugal: The Tagus case study

Synoptic Spatio-Temporal Variability of the Photosynthetic Productivity of Microphytobenthos and Phytoplankton in a Tidal Estuary