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Author Posting. © The Author(s), 2010. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Deep Sea Research Part II: Topical Studies in Oceanography 58 (2011): 753-763, doi:10.1016/j.dsr2.2010.10.015., The SOLAS air-sea gas exchange experiment (SAGE) was a multiple-objective study investigating gas-transfer processes and the influence of iron fertilisation on biologically driven gas exchange in high-nitrate low-silicic acid low-chlorophyll (HNLSiLC) Sub-Antarctic waters characteristic of the expansive Subpolar Zone of the southern oceans. This paper provides a general introduction and summary of the main experimental findings. The release site was selected from a pre-voyage desktop study of environmental parameters to be in the south-west Bounty Trough (46.5°S 172.5°E) to the south-east of New Zealand and the experiment conducted between mid-March and mid-April 2004. In common with other mesoscale iron addition experiments (FeAX’s), SAGE was designed as a Lagrangian study quantifying key biological and physical drivers influencing the air-sea gas exchange processes of CO2, DMS and other biogenic gases associated with an iron-induced phytoplankton bloom. A dual tracer SF6/3He release enabled quantification of both the lateral evolution of a labelled volume (patch) of ocean and the air-sea tracer exchange at the 10’s of km’s scale, in conjunction with the iron fertilisation. Estimates from the dual-tracer experiment found a quadratic dependency of the gas exchange coefficient on windspeed that is widely applicable and describes air-sea gas exchange in strong wind regimes. Within the patch, local and micrometeorological gas exchange process studies (100 m scale) and physical variables such as near-surface turbulence, temperature microstructure at the interface, wave properties, and wind speed were quantified to further assist the development of gas exchange models for high-wind environments. There was a significant increase in the photosynthetic competence (Fv/Fm) of resident phytoplankton within the first day following iron addition, but in contrast to other FeAX’s, rates of net primary production and column-integrated chlorophyll a concentrations had only doubled r, SAGE was jointly funded through the New Zealand Foundation for Research, Science and Technology (FRST) programs (C01X0204) "Drivers and Mitigation of Global Change" and (C01X0223) "Ocean Ecosystems: Their Contribution to NZ Marine Productivity." Funding was also provided for specific collaborations by the US National Science Foundation from grants OCE-0326814 (Ward), OCE-0327779 (Ho), and OCE 0327188 OCE-0326814 (Minnett) and the UK Natural Environment Research Council NER/B/S/2003/00282 (Archer). The New Zealand International Science and Technology (ISAT) linkages fund provided additional funding (Archer and Ziolkowski), and the many collaborator institutions also provided valuable support.

[EN] Computerized image-analysis of epifluorescence preparations is the most accurate and simple method for the estimation of bacterial size. We present a simple and inexpensive image-analysis system used to measure and count planktonic bacteria and presently in operation in our laboratory. We show that there is a wide range of image exposures (brightness) over which the system performs correctly. Even though the procedure involves some steps that depend upon operator intervention, the results obtained are highly reproducible and we have estimated the among-operator variability at 5%. We then discuss the advantages and disadvantages of different algorithms used for the estimation of volume from two-dimensional images and we identify those that perform better for curved and unusual cells. We finally estimate that 4 to 6 images and 200 - 250 cells are the optimal number of images to be processed and cells to be measured to obtain accurate estimates of population values with the minimum effort. These calibrations should be useful to all those laboratories that are implementing image-analysis systems, [ES] El análisis de imágenes obtenidas a partir de preparaciones de epifluorescencia es el método más sencillo y preciso para medir el tamaño bacteriano. En este trabajo se presenta un sistema de análisis de imágenes sencillo y asequible, actualmente en funcionamiento en nuestro laboratorio, desarrollado para medir y contar bacterias planctónicas. Se demuestra que el sistema funciona correctamente dentro de un rango amplio de brillo de imagen. Aunque algunos pasos del proceso dependen del operador, los resultados obtenidos fueron altamente reproducibles, y se estimó una variabilidad entre operadores del 5%. Se discuten las ventajas de los diferentes algoritmos usados para calcular el biovolumen a partir de imágenes de dos dimensiones, e identificamos el algoritmo que funciona mejor en células curvados o de formas inusuales. Finalmente, se estimó que para obtener medidas precisas del tamaño medio de la población con el mínimo esfuerzo se debían procesar entre 4 y 6 imágenes y contar entre 200 y 250 células. La información presentada en este trabajo puede ser útil para aquellos laboratorios que deseen desarrollar sistemas de análisis de imágenes parecidos

A one year field study of four stations in the Gulf of Bothnia during 1991 showed that the biomass was ca. two times, and primary productivity ca, four times, lower in the north (Bothnian Bay) than in the south (Bothnian Sea) during the summer. Nutrient addition experiments indicated phosphorus limitation of phytoplankton in the Bothnian Bay and the coastal areas in the northern Bothnian Sea, but nitrogen limitation in the open Bothnian Sea. A positive correlation between the phosphate concentration and the production/biomass ratio of phytoplankton was demonstrated, which partly explained the differences in the specific growth rate of the phytoplankton during the summer. Differences in photosynthetic active radiation between the stations also showed a covariation with the primary productivity. The relative importance of nutrient or light limitation for photosynthetic carbon fixation could not, however, be conclusively determined from this study. Marked differences in phytoplankton species composition from north to south were also observed. The number of dominating species was higher in the Bothnian Sea than in the Bothnian Bay. The distribution of some species could be explained as due to nutrient availability (e.g. Nodularia spumigena, Aphanizomenon sp.), while salinity probably limits the distribution of some limnic as well as marine species. The potentially toxic phytoplankton N. spumigena, Dinophysis acuminata and Chrysochromulina spp. were common in the Bothnian Sea but not in the Bothnian Bay. The pico- and nanoplankton biomass during late summer was higher than previously reported due to a revised carbon/volume ratio.