On research cruise to the Southern Ocean
The research vessel Kronprins Haakon is on its way to the sea areas outside the Fimbulisen in Dronning Maud Land in Antarctica, where most of the research will be carried out. But some research is also happens along the way to Fimbulisen. Researcher Agneta Fransson has written a post about the work that takes place on board the ship.
The Norwegian research vessel Kronprins Haakon is steaming towards the Dronning Maud Land, Antarctica. Along the route, we are a group of chemical and biological oceanographers from Norway and South Africa that continuously collects water samples in the surface water for various analyses. At about 65°S, 41°W, the Jamaica or Rogaland fylke size iceberg B15 detached from the Ross sea shelf in 2000. Since than the iceberg has broken off pieces and the largest remaining piece B15AA was on our route. The meltwater from this iceberg may give interesting information on chemical content and its effect on the local primary production.
Southern Ocean is generally limited with regard to iron, which is known to limit primary production, hence the ocean uptake of atmospheric CO2. Icebergs can act as a source of iron, where the meltwater can affect the water chemistry, biology and ocean CO2 uptake. For this particular iceberg study, we measured the chemical and biological variables such as chlorophyll a, photosynthetic efficiency, phytoplankton community structure, dissolved iron, partial pressure of CO2 (pCO2), pH, alkalinity, dissolved oxygen and isotopic oxygen ratio, to investigate how the iceberg influences the surrounding iron-poor water. For trace-metal clean water, the South African scientists deployed a trace metal clean torpedo fish pump in the surface water at 5 m, for measurements of dissolved iron. For all other variables, we used the ship's water intake at 4 m for water sampling as well as continuous measurements of pCO2, dissolved oxygen, salinity and temperature.
In the water before reaching the iceberg, surface-water pCO2 was higher than atmospheric pCO2 of 405 µatm, and the chlorophyll-fluorescence data was insignificant, which indicates that the biomass was low. Near the iceberg, we expect a decrease in pCO2 and an increase in chlorophyll a due to photosynthesis in iron-rich water.
Preliminary surface water pCO2 data from previous cruise show that the surface water and atmospheric pCO2 are almost the same (about 405 µatm) in the region north of where we are passing now. Lower surface pCO2 could be due to biological CO2 uptake, which means that the ocean acts as a CO2 sink. Some areas have higher surface pCO2 than atmospheric levels, which means that there could be upwelling of CO2-rich sub-surface water, resulting in ocean outgassing of CO2 (ocean CO2 source).