Sampling at sea
Measurements on board R/V Svea provide important knowledge about the state of the sea – a prerequisite for understanding and managing our marine environments. Photo: Johanna Linders

SMHI – monitoring the marine environment

Page reviewed:  12/11/2025

Every month, all year round, the research vessel Svea leaves port with SMHI on board. These offshore expeditions are a central part of Sweden’s national environmental monitoring – systematic surveys that show how the sea is doing and how it changes over time.

On board, SMHI’s oceanographers measure parameters such as temperature, salinity, oxygen, pH, and nutrients, and collect samples of phytoplankton and zooplankton from the water column. Each dataset is a vital piece of the puzzle that, together, reveals how the marine environment shifts through the seasons and across decades.

At the heart of SMHI’s sampling work is the CTD rosette, which is lowered through the water column to measure physical and chemical properties while taking water samples at different depths. Many of these samples are analyzed directly at sea, in Svea’s accredited laboratories. The vessel is also equipped with a FerryBox system and a Moving Vessel Profiler, which record data continuously while Svea is underway.

From observation to understanding

At several stations, observations have been carried out for many decades. These long time series make it possible to detect trends, distinguish natural variation from human impact, and identify early signs of problems in the marine environment such as oxygen depletion, ocean acidification, and harmful algal blooms.

The data collected during the expeditions form the basis for research, management, and political decision-making. Together, they constitute a cornerstone for understanding the marine environment and the processes that shape it. Through this monitoring, SMHI can track how marine ecosystems respond to climate change, pollution, and eutrophication – and assess whether measures taken are having the intended effect.

SMHI’s expeditions with Svea are carried out in collaboration with the Swedish Agency for Marine and Water Management (HaV).

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