Oceanologia No. 49 (2) / 07




Influence of aerosol vertical profile variability on retrievals of aerosol optical thickness from NOAA AVHRR measurements in the Baltic region
Oceanologia 2007, 49(2), 165-184

Anna Rozwadowska
Institute of Oceanology, Polish Academy of Sciences,
Powstańców Warszawy 55, PL-81-712 Sopot, Poland;
e-mail: ania@iopan.gda.pl

Keywords: aerosol optical thickness, aerosol profile bias, AVHRR channels, satellite algorithm, Baltic region

Received 28 February 2007, revised 8 May 2007, accepted 16 May 2007.

This research was carried out as part of the statutory programme of the Institute of Oceanology in Sopot, Poland (No I.1.2).
The expected influence of variability in atmospheric aerosol profiles on retrievals of aerosol optical thickness (AOT) from NOAA AVHRR measurements is analysed. In particular, the bias in the AOT retrieval due to the assumption of a climatological aerosol profile in the retrieval algorithm is studied. The bias is defined as the difference between AOT retrieved with an algorithm using a climatological aerosol profile, and the actual AOT employed in the calculations of radiances at the top of the atmosphere (TOA). The TOA radiances are simulated by means of the MODTRAN code for different aerosol profiles. Atmospheric conditions and solar and satellite angles used in the bias simulations are typical of the Baltic region. In the simulations, the maximum absolute value of the bias amounts to nearly 40% in channel 2 and 14% in channel 1 of AVHRR.
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Synoptic changes in the deep rim current during stagnant hydrographic conditions in the Eastern Gotland Basin, Baltic Sea
Oceanologia 2007, 49(2), 185-208

Eberhard Hagen*, Rainer Feistel
Leibniz Institute for Baltic Sea Research,
Seestrasse 15, D-18119 Rostock-Warnemünde, Germany;
e-mail: eberhard.hagen@io-warnemuende.de
*corresponding author

Keywords: Baltic Sea, Eastern Gotland Basin, hydrography, current measurements, deep water circulation

Received 16 February 2007, revised 24 April 2007, accepted 8 May 2007.
Hydrographic and current measurements are analysed for stagnant deep-water conditions over the south-eastern topographic flank of the Eastern Gotland Basin (EGB) in April 2000. Results suggest a prevailing barotropic motion mode on a synoptic scale of several days. Deep along-slope volume transports derived from subsurface current meter moorings are compared with those of the baroclinic fraction of geostrophic motions crossing the plane of a hydrographic section. This was aligned perpendicular to deep isobaths and was repeated 40 times with a time step of six hours. Changes in regional winds produced a quasi-ten day cycle in the filling level of the Baltic Proper. Associated wave-like fluctuations of the mass field propagated cyclonically with a velocity of about 0.04 m s-1 around the deep basin's rim. It is concluded that associated changes in deep volume transports result mainly from barotropically governed advection processes and that those of the baroclinic component of geostrophic currents provide a qualitatively and quantitatively quite inaccurate description of related transport fluctuations on a daily scale.
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Spatio-temporal variations in hydro-physical and -chemical parameters during a major upwelling event off the southern coast of the Gulf of Finland in summer 2006
Oceanologia 2007, 49(2), 209-228

Ülo Suursaar, Robert Aps
Estonian Marine Institute, University of Tartu,
Mäealuse 10a, EE-12618 Tallinn, Estonia;
e-mail: ulo.suursaar@ut.ee

Keywords: upwelling, RDCP, coastal jets, vertical fluxes, SST, satellite images, Baltic Sea

Received 8 February 2007, revised 22 May 2007, accepted 25 May 2007.

This work was supported by the Estonian Science Foundation through grant No 5929.
The objective of the paper is to document and examine the major upwelling event that occurred along the northern coast of Estonia in August 2006. With a horizontal extension of 360 km, the event was caused by persistent easterlies and was noticed by a large number of holidaymakers, as it turned the temperature of the coastal sea to a chilly 5-10°C for about a month. In situ measurements from an RDCP current profiler revealed an along-wind coastal jet of up to 60 cm s-1 and a weak near-bottom countercurrent. The depths of the pycnocline and nutricline rose. The maximum drop in water temperature was 16°C, that of salinity was 3.6 PSU. Analysis of satellite images confirmed the large extension and the prominence of the event.
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Acoustic seabed classification applied to Baltic benthic habitat studies: a new approach
Oceanologia 2007, 49(2), 229-243

Andrzej Orlowski
Sea Fisheries Institute,
Kołłątaja 1, PL-81-332 Gdynia, Poland;
e-mail: orlov@mir.gdynia.pl

Keywords: acoustic seabed classification, bottom habitat, ecology, Baltic, bathymetry

Received 2 March 2007, revised 21 May 2007, accepted 25 May 2007.
The application of acoustic methods for the classification of bottom habitats is based mostly on the analysis of measured parameters without relating them to the bathymetric structure. Geological complexity and biological patterns are closely related to bathymetry. This paper presents a new approach to the acoustic classification of bottom habitats in that it combines the distribution of a selected acoustic parameter with its bathymetric structure. The hypothetical effective angle of a bottom echo θ'/2, corresponding to its normalised length, was the acoustic parameter applied. This parameter broadly characterises the complex acoustic reflecting and scattering properties of the seabed. Its highest values correspond to a layered bottom consisting of soft sediment. The southern Baltic area was classified by a direct comparison of two factors measured acoustically: the statistical distribution of θ'/2, and the correlated depth structure within selected standard regular geographical areas (15' latitude and 30' longitude) which the total area was divided into. The area size was matched with the density of the measurements collected. The same factors were also estimated for the whole southern Baltic. The study was based on soundings collected on board r/v "Baltica" during regular acoustic surveys in 1995-2003. The classification applied provides a new possibility of complex seabed identification and comparison of seabed structure dynamics, useful in benthic research and in the ecologically based administration of marine areas.
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Tree stumps from the bottom of the Vistula Lagoon as indicators of water level changes in the Southern Baltic during the Late Holocene
Oceanologia 2007, 49(2), 245-257

Leszek Łęczyński1, Grażyna Miotk-Szpiganowicz2, Joanna Zachowicz2, Szymon Uścinowicz2,*, Marek Krąpiec3
1Institute of Oceanography,
University of Gdańsk,
al. Marszałka Piłsudskiego 46, PL-81-378 Gdynia, Poland
2Branch of Marine Geology,
Polish Geological Institute,
Kościerska 5, PL-80-328 Gdańsk, Poland;
e-mail: szymon.uscinowicz@pgi.gov.pl
*corresponding author
3Academy of Mining and Metallurgy,
al. A. Mickiewicza 30, PL-30-059 Kraków, Poland

Keywords: tree stumps, palynological analysis, water level changes, Vistula Lagoon, southern Baltic Sea

Received 28 February 2007, revised 23 April 2007, accepted 27 April 2007.

The research results presented in this study were obtained partly within the framework of the grant "Water level changes in the Vistula Lagoon in the middle and late Holocene" (No 2 P04D 00927), provided by the Polish Ministry of Science and Higher Education.
The Vistula Lagoon is situated along the south-eastern shore of the Gulf of Gdansk and is linked with the gulf through the Strait of Baltiysk. Separated from the open sea by the Vistula Spit, the Vistula Lagoon is a shallow body of water with a mean depth of 3 m; the bottom is covered with a layer of mud several metres thick. This article presents a unique, newly discovered locality of tree stumps occurring in situ at the bottom of the Vistula Lagoon. The radiocarbon age of the alder stumps and the top of the peat in which they are rooted is Subboreal. The alder wood was dated to 4770±35 and 3295±35 years BP. The top layers of peat were dated to 4670±40, 4410±35 and 3690±35 years BP. The considerable scatter of the dates indicates the significance of erosional processes during marine transgressions. Radiocarbon dates and pollen analyses indicate that in the late Atlantic - early Subboreal periods, the water level of the Vistula Lagoon was about 3 m lower than it is today. The -2 m level was passed no earlier than c. 3500 years ago; the -1 m level was reached around 2000 years ago.
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Modelling nitrogen and phosphorus limitation on phytoplankton growth in Narva Bay, south-eastern Gulf of Finland
Oceanologia 2007, 49(2), 259-276

Gennadi Lessin*, Inga Lips, Urmas Raudsepp
Marine Systems Institute, Tallinn University of Technology,
Akadeemia Rd. 21b, EE-12618 Tallinn, Estonia;
e-mail: gennadi@phys.sea.ee
*corresponding author

Keywords: nutrient limitation, numerical modelling, Narva Bay, Gulf of Finland

Received 28 December 2006, revised 12 April 2007, accepted 17 April 2007.

This work was partially supported by Estonian Science Foundation Research Grant No 5596.
The relative roles of nitrogen and phosphorus in the limitation of phytoplankton growth in Narva Bay, south-eastern Gulf of Finland, were studied by combining the results of numerical modelling and nutrient enrichment experiments. Modelled biomass-based intracellular nutrient concentrations (nutrient functions) were used to estimate the limiting nutrient in Narva Bay. Nutrient functions - NF ∈ [0; 1] for nitrogen and PF ∈ [0; 1] for phosphorus - define the dependence of the phytoplankton growth rate on nutrients: NF = PF = 1 corresponds to non-limitation of phytoplankton growth by nutrients, whereas NF = 0 or PF = 0 to zero growth. The biotests indicated the response of phytoplankton growth to an increase in nutrient concentration in the surrounding water. Three locations were selected for detailed analyses of temporal variations in the nutrient functions: the offshore station N12, station N8 at the mouth of the River Narva, and coastal station 38. The biotests were performed at the same stations. NF and PF reached values of 0.9 prior to the spring bloom. With the onset of the spring bloom, NF decreased rapidly and remained below 0.1 in the open part of Narva Bay for the rest of that period. In the coastal zone, NF was in excess of 0.1, with a local maximum in the river mouth area. PF decreased to 0.3-0.4 in the open bay after the spring bloom. In the coastal zone PF remained above 0.4, with a certain increase from the midsummer minimum towards the end of summer. The numerical modelling results clearly show that nitrogen limits phytoplankton growth in Narva Bay. Phosphorus limitation may occur only for a limited period and over a limited area at the Narva River mouth and other coastal locations. In general, the biotests backed up the modelling results, the main exception being in the open bay during summer. The model does not account for nitrogen fixation, however. Since N-fixing cyanobacteria were prevalent in the offshore area, the addition of phosphorus led to enhanced phytoplankton growth at station N12.
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Factors describing the distribution of the zooplankton community in the Gulf of Finland in the context of interactions between native and introduced predatory cladocerans
Oceanologia 2007, 49(2), 277-290

Arno Põllumäe*, Jonne Kotta
Estonian Marine Institute, University of Tartu,
Mäealuse 10a, EE-12618 Tallinn, Estonia;
e-mail: arno@sea.ee
*corresponding author

Keywords: Baltic, mesozooplankton, non-indigenous, food web, predation

Received 11 December 2006, revised 24 April 2007, accepted 27 April 2007.

This study was financed by the Estonian Target Financing Programmes Nos 0182578s03 and the Estonian Science Foundation Grants Nos 6015 and 6016. Funding was also obtained through a U.S. Government Grant (SEN100-02-GR069). The opinions, findings and conclusions or recommendations expressed herein are those of the authors and do not necessarily reflect those of the U.S. Government.
Mesozooplankton communities were studied monthly at six sites in the Gulf of Finland during six ice-free seasons. The abundances of different zooplankton taxa were related to temperature, salinity, eutrophication level (total nitrogen and phosphorus), phytoplankton Chl a and density of predatory cladocerans, including the non-indigenous Cercopagis pengoi and the native Leptodora kindtii. The results indicated that variability in the zooplankton communities was correlated not only with predation by mesozooplankton but also with bottom-up effects. Predation by the non-indigenous C. pengoi may significantly affect the dynamics of Cladocera and Rotatoria in the Gulf of Finland during the summer season.
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