Upwelling events, coastal offshore exchange, links to biogeochemical processes - Highlights from the Baltic Sea Sciences Congress at Rostock University, Germany, 19-22 March 2007

The Baltic Sea Science Congress was held at Rostock University, Germany, from 19 to 22 March 2007. In the session entitled"Upwelling events, coastal offshore exchange, links to biogeochemical processes" 20 presentations were given,including 7 talks and 13 posters related to the theme of the session.This paper summarises new findings of the upwelling-related studies reported in the session. It deals with investigationsbased on the use of in situ and remote sensing measurements as well as numerical modelling tools. The biogeochemicalimplications of upwelling are also discussed.Our knowledge of the fine structure and dynamic considerations of upwelling has increased in recent decades with the advent ofhigh-resolution modern measurement techniques and modelling studies. The forcing and the overall structure, duration and intensity ofupwelling events are understood quite well. However, the quantification of related transports and the contribution to the overall mixingof upwelling requires further research. Furthermore, our knowledge of the links between upwelling and biogeochemical processes is stillincomplete. Numerical modelling has advanced to the extent that horizontal resolutions of c. 0.5 nautical miles can now be applied,which allows the complete spectrum of meso-scale features to be described. Even the development of filaments can be describedrealistically in comparison with high-resolution satellite data.But the effect of upwelling at a basin scale and possible changes under changing climatic conditions remain open questions

Copernicus Marine Service ocean state report, issue 4

This is the final version. Available from Taylor & Francis via the DOI in this record. FCT/MCTE

Monitoring the effect of upwelling on the chlorophyll a distribution in the Gulf of Finland (Baltic Sea) using remote sensing and in situ data

The spatio-temporal variability of chlorophyl a (Chl a) caused by a sequence of upwelling events in the Gulf of Finland in July–August 2006 was studied using remote sensing data and field measurements. Spatial distributions of sea surface temperature (SST) and Chl a concentration were examined using MODIS and MERIS data respectively. The MERIS data were processed with an algorithm developed by the Free University of Berlin (FUB) for case 2 waters. Evaluation of MERIS Chl a versus in situ Chl a showed good correlation (r2 = 0.67), but the concentration was underestimated. The linear regression for a 2 h window was applied to calibrate MERIS Chl a. The spatio-temporal variability exhibited the clear influence of upwelling events and related filaments on Chl a distribution in the western and central Gulf. The lowest Chl a concentrations were recorded in the upwelled water, especially at the upwelling centres, and the highest concentrations (13 mg m−3) were observed about two weeks after the upwelling peak along the northern coast. The areas along the northern coast of upwelled water (4879 km2) on the SST map, and increased Chl a (5526 km2) two weeks later, were roughly coincident. The effect of upwelling events was weak in the eastern part of the Gulf, where Chl a concentration was relatively consistent throughout this period

Copernicus Marine Service Ocean State Report, Issue 5

Demersal species play a fundamental role in fisheries, thus understanding their distribution and abundance through bottom trawl surveys is crucial for stock and fisheries management. Oceanographic (e.g. biogeochemical, physical) and fishing covariates might be considered, in addition to spatio-temporal variables (latitute, longitude, depth, year and month), to better explain trawl survey data. Here, we analyse biomass indices (kg/km2) for European hake, common sole, mantis shrimp, red mullet and common cuttlefish from scientific trawl surveys carried out in the Adriatic Sea and the Western Ionian Sea. We used three different Generalised Additive Model (GAM) approaches (Gaussian, Tweedie and Delta) to fit and predict species biomass distribution. In order to evaluate trade-offs in using different covariates, we compared the results obtained from GAM approaches based only on spatiotemporal variables and GAMs including also oceanographic and fishing effort covariates. The Delta-GAM approach performed better for European hake, mantis shrimp and common cuttlefish, while GAMs based on Gaussian and Tweedie were performing better for the red mullet and common sole, respectively. The results highlighted that adding specific oceanographic and effort covariates to spatiotemporal variables improved the performances of spatial distribution models especially for European hake, mantis shrimp and red mullet. Significant additional explanatory variables were bottom temperature, bottom dissolved oxygen, salinity, particulate organic carbon, and fishing effort for European hake; the same variables and pH for mantis shrimp; chlorophyll-a, pH, sea surface temperature, bottom dissolved oxygen, nitrate and effort for the red mullet; phosphate and salinity for common sole; bottom temperature, bottom dissolved oxygen, and phosphate for the common cuttlefish. The findings highlight that more accurate estimates of spatial distribution of demersal species biomass from trawl survey data can generally be obtained by integrating oceanographic variables and effort in GAMs approaches with potential impacts on stock assessment and essential fish habitats identification