Nutrient intrusions at the entrance to the Gulf of Finland

The nutrient distribution peculiarities below the seasonal thermocline were analysed on the basis of high vertical resolution (2.5 m) data at the entrance area to the Gulf of Finland. Remarkable increase of nutrient concentration and DIN:DIP and a decrease of temperature on the isopycnals in the onshore direction (towards the Finnish coast) were registered. An intrusive finestructure of the temperature and nutrient fields was observed in the warmer side of thermohaline front, which separates the near-shore and open gulf waters. Nutrient-rich intrusions were cold, with a thickness of 5 to 20 m and the largest horizontal scale of about 5 km. The maximum intensities of intrusions, e.g. for phosphorus and silicate were approximately 0.3 µM and 3 µM, respectively. The generation and isopycnic spreading of intrusions is hypothesized as one link in the chain of overall nutrient transport.