Vivian A. Lutz

Hydrography and chlorophyll a in a transect from the coast to the shelf-break in the Argentinian Sea☆

Abstract On the basis of data obtained during eight research cruises from a section of the Buenos Aires province shelf, three systems are characterized: (1) coastal system; (2) subantarctic shelf waters system; and (3) Malvinas system. These domains are frequently separated by two quasipermanent fronts: (1) the coastal front; and (2) the shelf-break front. The patterns of seasonal variation of phytoplankton biomass in these systems are strongly related to changes in vertical stability, that controls the availability of nutrients and light energy. In the coastal system, the mixing produced by winds and tides gives homogenenous waters all year round, having the lowest nitrate concentration and the lowest N:P ratio. The amplitude of the seasonal variation of chlorophyll was relatively small, although the highest concetrations were detected in spring and autumn. The subantarctic shelf waters system is characterized by the typical development and breakdown cycle of the seasonal thermocline. Two well defined chlorophyll a maxima are observed: the main peak during spring and the secondary one during autumn. Geographical differences occur in the timing of the development and breakdown of the thermocline. Another factor of variability is the advection of low salinity waters from the coastal region of the Rio de la Plata during spring. During winter, when nutrient concentration is the highest, an increasing nitrate gradient from the coastal front to the shelf-break region is observed. During summer, surface nitrate concentration is low over the whole continental shelf, and the highest chlorophyll a concentrations are associated with the depth of the pycnocline. However, associated with the surface nitrate maximum, chlorophyll a values higher than 2 mg m −3 are recorded at the shelf-break front. The observed surface maxima are thought to be related to physical processes associated with the slope, where the enhanced mixing results in nutrient renewal and subsequent phytoplankton growth in the shelf-break region.

DIFFERENCES BETWEEN IN VIVO ABSORPTION AND FLUORESCENCE EXCITATION SPECTRA IN NATURAL SAMPLES OF PHYTOPLANKTON

The fluorescence excitation spectrum of live phytoplankton cells represents the portion of light absorbed that has been effectively transferred to chlorophyll a of photosystem II, whereas light absorbed by photoprotective pigments will not lead to fluorescence. Therefore, the in vivo fluorescence excitation spectrum of phytoplankton has been used as a proxy for the action spectrum of phytoplankton in computations of primary production in the ocean. The distribution of chlorophyll a between photosystems, as well as variations in the pathway of energy inside the photosynthetic membrane, can also influence the fluorescence excitation spectrum. In this study, we investigated the contribution of photoprotective pigments to the differences found between in vivo absorption and fluorescence excitation spectra of phytoplankton measured during two cruises: one from Las Islas Canarias to Nova Scotia and another in the Labrador Sea. A comparison of normalized fluorescence excitation and absorption spectra showed high variability in the difference between absorption and fluorescence in the blue region of the spectrum for samples from the two cruises. This difference was not entirely correlated with the concentration of photoprotective carotenoids. In this paper, results are interpreted in terms of differences in pigment composition and known patterns of energy distribution in the photosystems of different algal groups.

The ANTARES observation network

The ANTARES network seeks to understand the variability of the coastal environment on a continental scale and the local, regional, and global factors and processes that effect this change. The focus are coastal zones of South America and the Caribbean Sea. The initial approach includes developing time series of in situ and satellite-based environmental observations in coastal and oceanic regions. The network is constituted by experts that seek to exchange ideas, develop an infrastructure for mutual logistical and knowledge support, and link in situ time series of observations located around the Americas with real-time and historical satellite-derived time series of relevant products. A major objective is to generate information that will be distributed publicly and openly in the service of coastal ocean research, resource management, science-based policy making and education in the Americas. As a first stage, the network has linked oceanographic time series located in Argentina, Brazil, Chile and Venezuela. The group has also developed an online tool to examine satellite data collected with sensors such as NASAs MODIS. Specifically, continental-scale high-resolution (1 km) maps of chlorophyll and of sea surface temperature are generated and served daily over the web according to specifications of users within the ANTARES network. Other satellite-derived variables will be added as support for the network is solidified. ANTARES serves data and offers simple analysis tools that anyone can use with the ultimate goal of improving coastal assessments, management and policies.

Challenges for global ocean observation: the need for increased human capacity

ABSTRACT Sustained global ocean observations are needed to recognise, understand, and manage changes in marine biodiversity, resources and habitats, and to implement wise conservation and sustainable development strategies. To meet this need, the Global Ocean Observing System (GOOS), a network of observing systems distributed around the world and coordinated by the Intergovernmental Oceanographic Commission (IOC) has proposed Essential Ocean Variables (EOVs) that are relevant to both the scientific and the broader community, including resource managers. Building a network that is truly global requires expanding participation beyond scientists from well-resourced countries to a far broader representation of the global community. New approaches are required to provide appropriate training, and resources and technology should follow to enable the application of this training to engage meaningfully in global observing networks and in the use of the data. Investments in technical capacity fulfil international reporting obligations under the UN Sustainable Development Goal 14A. Important opportunities are emerging now for countries to develop research partnerships with the IOC and GOOS to address these obligations. Implementing these partnerships requires new funding models and initiatives that support a sustained research capacity and marine technology transfer.

Analysis of SeaWiFS imagery over the southwestern Atlantic Ocean during the March 2002 R/V IOFFE cruise

SeaWiFS ocean-colour products for the Southwestern Atlantic Ocean are evaluated in comparison with in situ bio-optical data collected during the March 10-12, 2002 cruise from Ushuaia to Uruguay. Radiometric measurements and surface water sampling were carried out at 14 stations. The in situ dataset included HPLC chlorophyll-a concentration (chl-a), aph( λ) spectral absorption coefficients of phytoplankton, suspended particles, and acdom( λ) dissolved organic matter, RRS remote sensing reflectance, AOT and aerosol optical thickness. In general, the SeaWiFS-derived and SIMBAD measured AOT were low, but with a good agreement within SIMBAD uncertainty errors. The SeaWiFS-derived RRS was systematically underestimated, but still with good fits. The a*ph (440) were high indicating the presence of small size cells with a low packaging effect. The HPLC pigment composition did not show strong variations amongst the sampled points, with communities most probably dominated by small cells. The phytoplankton community was more homogeneous in the southern stations, than in the northernmost stations influenced by the mixing of the Brazil and Malvinas Currents and the La Plata River discharge. The analyzes of the in situ acdom (440) characterized the sampling stations as CDOM rich waters. All SeaWiFS chl-a algorithms showed reasonable performances. The empirical algorithms overestimated lower chl-a while underestimated higher concentrations. The GSM01 semi-analytical algorithm underestimated most chl-a values, while CARDER underestimated only the lower concentrations. It is expected that the accuracy of chlorophyll retrievals in coastal areas of the BMC can be improved by a proper tuning of the semi-analytical models with regional inherent optical properties measurements.