Development of a subsurface chlorophyll maximum at the entrance to the Gulf of Finland, Baltic Sea

Author(s): Kononen KJ, S Hallfors, M Kokkonen, H Kuosa, J Laanemets, J Pavelson

Abstract

 

Horizontal, vertical, and temporal variability of chlorophyll a (Chl a), stratification, currents, and pelagial biology (phytoplankton, size‐fractionated primary productivity and Chl a, ciliates, picocyanobacteria, bacterial production) were followed at the entrance to the Gulf of Finland during a 12‐day cast study in July–August 1994. The study was carried out during weak wind conditions when hydrodynamic activity was minimal and when an intense blooming of diazotrophic cyanobacteria Aphanizomenon flos‐aquae (Linné) Ralfs, Anabaena lemmermannii Richter, and Noduluria spumigena Mertens was in its decaying phase. The property conservation equation was used to differentiate the contributions of physical and biological processes to the local Chl a changes in the layer above the thermocline. Subtraction of the Chl a change due to physical processes, mainly advection, gave a biologically induced mean decrease of 0.18 mg Chl a m−3 d−1. Sampling data confirmed the calculated decrease and revealed the basin‐wide character of the phenomenon. The observed plankton dynamics showed that the pelagial system was “top‐down” controlled and that about half the decrease of Chl a was due to a size‐specific grazing of ciliates on the dominating flagellates Chrysochromulina spp. 2–5 µm and Ochromonas spp. 7–8 µm in the upper layer. The grazers were confined to the layer above the thermocline, while the flagellates inhabited both the thermocline and the layer above. This led to the formation of a subsurface Chl a maximum in the thermocline. 

Similar Articles

Wind-driven coastal upwelling along the western boundary of the Bay of Bengal during the southwest monsoon

Author(s): Shetye SR, Shenoi SSC, Gouveia AD, Michael GS, Sundar D, et al.

The Western Boundary Current of the seasonal subtropical gyre in Bay of Bengal

Author(s): Shetye SR, AD Gouveia, SSC Shenoi, DSundar, GSMichael, et al.

Hydrography and circulation in the western Bay of Bengal during the northeast monsoon

Author(s): Shetye SR, Gouveia AD, Shankar D, Shenoi SSC, Vinayachandran PN, et al.

Observation of the western boundary current of the Bay of Bengal Deep-Sea Res 44:135-145

Author(s): Sanilkumar KV, Kuruvilla TV, Jogendranath D, and Rao RR

Eddy-mediated biological productivity in the Bay of Bengal during fall and spring intermonsoons Deep Sea Research II 54: 1619-1640

Author(s): Prasanna Kumar S, Nuncio M, Ramaiah N, Sardesai S, Narvekar, Jayu, Fernandes, Veronica, & Paul, Jane T

Are eddies nature’s trigger to enhance biological productivity in the Bay of Bengal? Geophys Res Lett 31

Author(s): Prasanna Kumar S, Nuncio M, Narvekar J, Kumar A, Sardesai S, et al.

Seasonal cycle of physicalforcing and biological response in the Bay of BengalIndian J Mar Sci 39: 388-405

Author(s): Prasanna Kumar S, Nuncio M, Narvekar J, Ramaiah N, Sardessai S, et al

Influence of basin-scale and mesoscale physical processes onbiological productivity in the Bay of Bengal during the summer monsoon

Author(s): Muraleedharan KR, Jasmine P, Achuthankutty CT, Revichandran C, Dineshkumar PK, et al

ICES zooplankton methodology manual

Author(s): Harris RP, Wiebe PH, Lenz JH, Skjoldal R & Huntley M

Detection of Bay of Bengaleddies from Topex and in situ observations

Author(s): Gopalan AKS, GopalaKrishna VV, Ali MM, Sharma R

Forcing mechanisms of the Bay of Bengal circulation Current SciIndia 71: 753-763

Author(s): Vinayachandran PN, Shetye SR, Sengupta D, Gadgil S

Analysis of Marine Ecosystems

Author(s): Owen RW

Vertical flux of respiratory carbon by oceanic diel migrant biota Deep-Sea Res 37: 685–694

Author(s): Longhurst AR, Bedo A, Harrison WG, Head EJH, Sameoto DD

Zooplankton vertical migration and the active transport of dissolved organic and inorganic carbon in the Sargasso

Author(s): Steinberg DK, Carlson CA, Bates NR, Goldthwait SA, Madin LP, et al.