11 research outputs found
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
Coherent current oscillations and water exchange in the straits of the Gulf of Riga
The water exchange processes through the Irbe and Virtsu (Suur) Straits were
investigated in 1993â1997 within the framework of a five-year study programme
â the Gulf of Riga Project. Simultaneous current measurement data from autonomous
mooring stations in both straits were available for the analysis in two
periods. In addition to the dominant signals â inertial oscillations in the Virtsu
Strait and diurnal oscillations in the Irbe Strait â low-frequency oscillations were
found in both straits.
During the experiment in JulyâAugust 1994, 12â14-day oscillations were
observed in both straits: the maximum phase lag in the Virtsu Strait was 1 day.
The other important low-frequency periodic component in both straits was 88
hours. In this case, the phase lag in the Virtsu Strait was about 20 hours.
In the 1995 experiment in the Irbe Strait, 42-hour oscillations were observed
with a phase lag of 10â12 hours. The amplitude was about 30 cm sâ1 in both straits. As in Lilover et al. (1998), where the flow regime in the Irbe Strait was
observed, we can interpret these oscillations as being wind-generated. The present
work shows the existence of these disturbances also in the Virtsu Strait.
The 88-hour oscillations observed in JulyâAugust 1994 can be interpreted as
the first mode of the basinâs eigenoscillations according to the concept of Otsmann
et al. (1997) of a basin with two separate outlets. The lowest frequency oscillation
with the period of 12â14 days seemed to propagate to the Gulf of Riga from the
Baltic Proper, but the generating force could not be established because there was
no noticeable variability between depressions and anticyclones during that period.
Based on the current measurements, two types of water exchange through the
Irbe strait were established: the outflow over the whole cross-section of the strait,
and a bidirectional flow with an inflow near the southern shore and increasing
inflow in the near-bottom layers and an outflow in the northern part of the strait