『Abstract
In this study, redox-dependent phosphorus (P) recycling and burial
at 6 sites in the Baltic Sea is investigated using a combination
of porewater and sediment analyses and sediment age dating (210Pb
and 137Cs). We focus on sites in the Kattegat, Danish
Straits and Baltic Proper where present-day bottom water redox
conditions range from fully oxygenated and seasonally hypoxic
to almost permanently anoxic and sulfidic. Strong surface enrichments
of Fe-oxide bound P are observed at oxic and seasonally hypoxic
sites but not in the anoxic basins. Reductive dissolution of Fe-oxides
and release of the associated P supports higher sediment-water
exchange of PO4 at hypoxic sites (up to 〜800
μmol P m-2 d-1) than in the anoxic basins.
This confirms that Fe-bound P in surface sediments in the Baltic
acts as a major internal source of P during seasonal hypoxia,
as suggested previously from water column studies. Most burial
of P takes place as organic P. We find no evidence for significant
authigenic Ca-P formation or biogenic Ca-P burial. The lack of
major inorganic P burial sinks makes the Baltic Sea very sensitive
to the feedback loop between increased hypoxia, enhanced regeneration
of P and increased primary productivity. Historical records of
bottom water oxygen at two sites (Bornholm, Morthern Gotland)
show a decline over the past century and are accompanied by a
rise in values for typical sediment proxies for anoxia (total
sulfur, molybdenum and organic C/P ratios). While sediment reactive
P concentrations in anoxic basins are equal to or higher than
at oxic sites, burial rates of P at hypoxic and anoxic sites are
up to 20 times lower because of lower sedimentation rates. Nevertheless,
burial of reactive P in both hypoxic and anoxic areas is significant
because of their large surface area and should be accounted for
in budgets and models for the Baltic Sea.』
1. Introduction
2. Materials and methods
2.1. Study sites
2.2. Bottom water and porewater analyses
2.3. Sediment analyses
3. Results
4. Discussion
4.1. Diagenetic processes in Baltic Sea sediments and their
link with P cycling
4.2. Temporary burial of P and the internal source of P in the
Baltic Sea
4.3. Burial of P in Baltic Sea sediments: P forma and trends
with time
4.4. Regional burial of P in the Baltic Sea
4.5. Redox-dependent P burial
5. Conclusions
Acknowledgments
Appendix A. Supplementary data
References