Oceanological and Hydrobiological Studies International Journal of Oceanography and Hydrobiology

Volume 40, Issue 2

ISSN 1730-413X (108–111) eISSN 1897-3191 2011

DOI: 10.2478/s13545-011-0021-8 Received: February 17, 2011 Short communication Accepted: April 04, 2011

Puck Bay is a subregion of the Gulf of Gdańsk in Upwelling intrusion into shallow Puck the southern Baltic Sea (Fig. 1). Puck Bay and the Gulf of Gdańsk are separated from each other by the Lagoon, a part of Puck Bay Hel Peninsula and are connected only in the south. (the Baltic Sea) The bay is divided into two parts: a deeper section with an average depth of 20.5, called Outer Puck Bay, and a markedly shallower part with an average Maciej Matciak1, Jacek Nowacki2, Włodzimierz depth of 3.1 m, called Puck Lagoon. The water Krzymiński3 bodies are separated by Rybitwia Shallow running from the Rewa Cape to the Hel Peninsula. During the year some parts of the shallow can protrude 1 Institute of Oceanography, University of Gdańsk above the water. A passage is situated at each end of al. Marszałka Piłsudskiego 46, 81-378, Gdynia, Poland Rybitwia Shallow: Głębinka Narrows at the 2 Maritime Institute in Gdańsk southwestern end and Kuźnica Passage at the ul. Długi Targ 41/42, 80-830 Gdańsk, Poland northeastern end. Water exchange between these two 3 Institute of Meteorology and Water Management sections of Puck Bay mainly occurs through these ul. Waszyngtona 42, 81-342 Gdynia, Poland passages, especially through Głębinka Narrows (Nowacki 1993a).

Key words: Puck Bay, field measurements, water physical properties, upwelling

Abstract

In this short communication we present the results of field measurements which show the incidence of waters originating from the deeper layers of Puck Bay in shallow Puck Lagoon. The reason for such a situation is the occurrence of a small-scale upwelling. This phenomenon may play a significant role in shaping the ecosystem conditions of Puck Lagoon, which is unique in terms of its natural values.

Fig. 1. Study area ( • - measurement stations; AB, BC - vertical transect lines).

1 corresponding author: [email protected]

Upwelling intrusion into shallow Puck Lagoon, a part of Puck Bay (the Baltic Sea) | 109

Nowacki et al. (2009) analysed the occurrence of of Oceanography, University of Gdańsk). upwelling events in Puck Bay based on several days’ Additionally, the underwater visibility range, in a observations carried out in July 1999. Coastal vertical direction, of a white disk with the diameter of upwelling usually involves wind-driven offshore 0.3 m (Secchi disk depth) was determined at each surface water transport and the compensatory rising station. Northeast and north winds prevailed during of water from deeper sea layers towards the surface data collection and northeast winds prevailed during (e.g. Lehmann and Myrberg 2008). Consequently, an the day prior to data collection, as recorded in the area characterized by hydrological features ship’s log. On June 27 wind speed was ca. 11 m s-1 contrasting with the properties of surrounding waters whereas on the 28th it was considerably lower and did can be observed at the sea surface. The occurrence of not exceed 6 m s-1. such areas usually enables one to detect upwelling The surface waters (0 – 4 m) in Outer Puck Bay events. At some locations offshore winds pushing were characterised by relatively low salinity, from away the surface waters are the direct reason for the about 6.4 to 7 PSU, and poor transparency (Fig. 2a, creation of deeper inflows towards the coast (e.g. 2b). The Secchi disk depth ranged from 2 to 2.5 m. Svansson 1975, Lund-Hansen and Vang 2003). Such In deeper layers the salinity was higher and the water a subsurface current can be further forced upward by transparency was considerably better, which was the bottom topography in shallow areas. proved by high values of the light beam transmission. Morphometric features of Outer Puck Bay create At the Głębinka Passage station and at Puck Lagoon favorable conditions for upwelling induced by station A Secchi disk depths of 5 and 4.5 m were offshore winds as it is surrounded on two sides by noted, respectively, and the salinity in the whole land, and an underwater barrier, Rybitwia Shallow, water column was above 7.2 PSU. Spatial which is located in the north. Generally, based on distributions of salinity and light-beam transmission hydrodynamic simulations, it seems that upwellings along a NW-SE vertical transect indicated that the at the coast of Puck Bay can occur when the surface water advected by a current in the deeper layer of waters flow out the bay through its open border with Outer Puck Bay was moved upwards after reaching the Gulf of Gdańsk while underneath, water flows the bottom slope between Puck Lagoon and Outer into the bay. Such a situation can develop in the case Puck Bay. Then it entered Puck Lagoon through of sufficiently strong winds from the north (NW, N, Głębinka Passage (Fig. 2a, 2b) and rose to the NE) (Nowacki et al. 2009). With opposite wind surface, replacing waters characterized by low direction, from the south, water is pushed into the salinity, which flowed south. Unlike most coastal bay in the surface layer, which causes an outflow at upwellings, where the surface waters decrease in greater depths. temperature, the water temperature in Puck Lagoon It is quite probable that a subsurface was high, slightly above 17°C (Fig. 2c). The high compensation current can get into the Puck Lagoon temperature was a consequence of the waters’ fast through the Głębinka Passage as a consequence of heating in the shallow area. Moreover, the waters upwelling circulation (Nowacki et al. 2009). Water probably upwelled from a depth of ca. 10 m and their flow measurements in the Głębinka Passage temperature did not differ significantly from surface indicated the occurrence of near bottom weak waters. A local upwelling affecting the surface waters currents entering into the Puck Lagoon (Nowacki in the vicinity of the southern entrance to the 1993b). Their presence still cannot prove the Głębinka Passage and south of the Rewa Cape (Fig. upwelling, because that would require studies 1) is also present in the Outer Puck Bay study area. performed at a larger spatial scale. An opportunity to The results of other observations performed by the observe the hydrological manifestation of such a authors indicate that in such a case the upwelling circulation happened during field research on the 28th front rises along the West-east direction (unpublished of June, 2009, on board the Litoral. The vertical data). On the 28th of June 2010 such a situation did profiles of salinity, temperature, and light beam not occur (Fig. 3). transmission were measured at 14 sampling stations. Based on archival data it can be maintained that Temperature was measured using a CTD Ocean the upwelling event described above can significantly Seven 304 probe. Light beam transmission, expressed influence Puck Lagoon waters. Water salinity and in relative units, was measured in the yellow-green transparency are often higher in this area than in the part of the visible spectrum with a central value of surface waters of Outer Puck Bay (Krężel 1993, 560 nm (transmissometer constructed at the Institute Nowacki 1993c). These observations are unusual for

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110 | Maciej Matciak, Jacek Nowacki, Włodzimierz Krzymiński

Fig. 2. Spatial distributions of water properties along Fig. 3. Spatial distributions of water properties along the vertical transects connecting the sampling stations the vertical transects connecting the sampling stations located in Puck Lagoon (A) and Outer Puck Bay (B). located in Outer Puck Bay (B, C).

Upwelling intrusion into shallow Puck Lagoon, a part of Puck Bay (the Baltic Sea) | 111 a shallow, coastal and semi-enclosed reservoir with fresh water inflow from small rivers (the largest of them are the Reda and Płutnica rivers). Puck Lagoon is unique among Polish coastal waters in terms of biodiversity and the occurrence of underwater meadows (Opioła and Kruk-Dowgiałło 2009). For this reason it is subject to protection as the Nadmorski Lanscape Park and is incorporated into the HELCOM network of Baltic Sea Protected Areas and the European Ecological Network Natura 2000. Therefore it is worth considering whether Puck Lagoon biological conditions depend on the lagoon’s water exchange with the deeper layers of Outer Puck Bay.

ACKNOWLEDGEMENTS

These results are published with the approval of „INVESTGAS” S.A. and were obtained as part of the project “Complex pre-investment studies and measurements performed near Mechelinki for the Puck Bay water quality monitoring connected with the discharge of brine from PMG KOSAKOWO building site”.

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