Project Details
Projekt
The role of diazotrophic cyanobacterial blooms in the expansion of bottom water hypoxia in the Holocene and late Weichselian Baltic Sea
Subject Area
Palaeontology
Term
from 2014 to 2018
Project identifier
Deutsche Forschungsgemeinschaft (DFG) - Project number 261181348
The present-day Baltic Sea is characterized by massive blooms of N2-fixing heterocystous cyanobacteria, which pose a severe threat for the health of the aquatic ecosystem as their occurrence is considered to promote the spread of hypoxic conditions (dissolved oxygen <2 mg/L). Although there is common consensus that the increased anthropogenic loading of nutrients (in particular phosphorous) to the Baltic Sea has stimulated the intensity and frequency of cyanobacterial blooms in the recent past, only little is known about how environmental factors other than nutrient availability facilitate bloom formation and how the massive accumulation and export of cyanobacterial biomass affects the water chemistry, nutrient cycling and ecosystem health of the Baltic Sea. Subsurface sediments, obtained from the Baltic Sea during IODP Expedition 347: Baltic Sea Paleoenvironment, provide continuous archives of environmental and climate changes and they, for the first time, allow reconstructing the role of cyanobacterial bloom formation on the spread of hypoxic condition and its consequences for the ecosystem of the Baltic Sea from the last glacial maximum to the present-day. Within the first funding period of the project, we have investigated sediment sequences from the Landsort Deep (M0063), Bornholm Basin (M0065) and Little Belt (M0059) that were drilled during IODP Expedition 347 for their bulk-geochemical as well as lipid biomarker inventory and have established high-resolution records of cyanobacterial activity and sea surface temperature change. Results of our analyses demonstrate that cyanobacterial blooms occurred repeatedly in the Baltic at least since the establishment of brackish conditions about 7,000 yrs ago and that the occurrence and intensity of cyanobacterial blooms coincides with periods of increased primary productivity and the spread of bottom-water anoxia. Interestingly, all of the time intervals characterized by abundant and widespread cyanobacterial blooms show TEXL86-reconstructed sea surface temperatures that exceed a threshold of 16°C and temperature variation thus seems to be a major driver for promoting cyanobacterial bloom formation in the Baltic Sea. This is particularly noteworthy as, based on our initial results, the current global warming may result in a severe increase in cyanobacterial activity and consequently the spread of hypoxic conditions in the Baltic Sea in the future. The research conducted within the second phase of the project will specifically address the questions how climate variation controls the abundance, composition and spatiotemporal distribution of cyanobacterial blooms in the Baltic Sea. This determines to which extent cyanobacterial blooms affect the water chemistry and the composition of the aquatic community structure in the Baltic Sea with the ultimate aim to develop models that accurately predict the impact of cyanobacterial blooms on the ecosystem health of the Baltic Sea under future global warming.
DFG Programme
Infrastructure Priority Programmes
International Connection
Netherlands, Sweden
Cooperation Partners
Professor Dr. Bo Gustaffson; Professorin Dr.-Ing. Caroline P. Slomp
