Iron: Studies on the speciation and bioavailavility in the Baltic Sea
Final Report Abstract
A survey to determine the distribution and speciation of iron in the Baltic Sea has been carried out in light of the fact that ferrous iron (Fe(ll)) in surface waters may be responsible for the fertilization and increase of summer diazotrophic cyanobacterial blooms. Levels of total dissolvable iron (II) (Fe(ll)), total dissolved iron (Fediss) and iron associated with suspended particulate material (FeSPM) were measured in surface waters from all areas of the Baltic. Additionally, depth profiles were made at three characteristic stations for vertical process studies. The highest surface values of Fe(ll) (≈39 nmolL-1), coinciding with maximum Fediss concentrations (≈600 nmolkg-1) and maximum FeSPM values (≈250 nmolL-1), were found in the Bothnian Bay, the region of the Baltic Sea with the lowest salinity. Fe(ll) concentrations in the Baltic Proper ranged from between 0.6 and 4 nmolL-1 with the minimum values in the transition area between the Baltic and the North Sea. In the depth profiles, we found Fe(ll) maxima in anoxic layers (≈30 nmolL-1 at 160 m in the Gotland Basin), which coincided with maximum Fediss (≈1200 nmolkg-1 at 160 m) and decreasing concentrations of FeSPM, revealing a pool of possibly bioavailable Fe(ll) in deep waters. Net diffusion fluxes of 10,1 μmol m-2 day-1 for Fediss and 0.28 μmol m-2 day-1 for Fe(ll) through the redoxcline were calculated. For Fe(ll) a half-time of 162 h was calculated for the oxygen minimum zone, while a half-time of 2 min was calculated for the ≈70 m depth horizon, where oxygen is already present. This result indicated that the Fe(ll) pool in the Gotland Basin deep waters can be neglected as a major Fe(ll) source for the surface waters of the Baltic Proper. To our knowledge, this is the first comprehensive investigation of Fe speciation in oxic and anoxic Baltic Sea waters.
Publications
- (2007). A luminescent whole-cell cyanobacterial bioreporter for measuring Fe availability in diverse marine environments. Appl. Environ. Microbiol., 73/3, 1019-1024
Boyanapalli, R., Bullerjahn, G. S., Pohl, C., Croot, P. L., Boyd, P. W., McKay, R. M. L.
- (2008). Iron in the Baltic Sea. A possible key parameter for cyanobacteria blooms? 10th International Estuarine Biogeochemistry Symposium", State Key Laboratory of Marine Environmental Science, 18.5. - 22.5. 2008, Xiamen, China
Pohl, C , McKay, M., Schoor, A., Staubwasser, M
- (2010). An estimate of the efficiency of the iron- and manganese-driven dissolved inorganic phosphorus trap at an oxic/euxinic water-column redoxcline. Global Biogeochemical Cycles, Vol. 24, GB4025
Turnewitsch, R., Pohl, C.
(See online at https://doi.org/10.1029/2010GB003820) - (2010). Iron distribution and speciation in the Baltic Sea. 30.9.2010 at East China Normal University, Shanghai, China
Pohl, C.; Fernandez-Otero, E.
- (2011). Iron in the Baltic Sea. Sampling, Distribution and Speciation. 25.5.2011 at Bowling Green State University, Bowling Green, Ohio, USA
Pohl, C, Hennings, U., Fernandez-Otero, E., Schoor, A., McKay, R.M.
- (2011). The distribution and speciation of Iron along an entire Baltic Sea transect. 11th International Estuarine Biogeochemistry Symposium, 15.5.-19.5.2011, Atlantic Beach, North Carolina, USA
Pohl, C., Hennings, U., Fernandez-Otero, E., Schulz-Bull, E.D.
