Studies investigating the effect of increasing CO
Increasing emissions of anthropogenic CO
In the Baltic Sea, several studies of CO
Next to nitrogen, phosphorus (P) controls the productivity of phytoplankton
in the ocean (Karl, 2000; Sanudo-Wilhelmy et al., 2001; Tyrrell, 1999)
and is a limiting factor in some regions (Ammerman et al.,
2003). The total phosphorus (TP) pool comprises phosphate (PO
In general, there is little knowledge on how the P cycle is affected by
ocean acidification and how related changes in P availability influence the
response of organisms to CO
The Baltic Sea and the location near the peninsula Hanko in the western Gulf of Finland where the mesocosms were deployed.
The study was conducted in the northwestern Gulf of Finland, in the
proximity of the Tvärminne Zoological Station (TZS; Fig. 1), between
17 June and 4 August 2012, using the KOSMOS mesocosm system (Riebesell
et al., 2013). Nine mesocosms (M1–M9) were moored in the open waters of
the Storfjärden (5951.5
CO
Daily sample collection started 3 days before the first CO
Phosphorus pool parameters and uptake rates were determined every second day, except for dissolved organic phosphorus (DOP) components, which were measured every 4 days. Termination of the measurements varied due to logistical constrains. Thus, total phosphorus (TP) and DOP were sampled only until day 29 whereas other parameters were sampled until day 43.
The collected water was filled in HCl-cleaned polyethylene canisters that had been pre-rinsed with sample water. All containers were stored in the dark. Back on land, subsamples were processed immediately for each P-analysis. The other analyses were carried out within a few hours of sample collection and sample storage in a climate room at in situ temperature.
Measurements in the fjord and in each mesocosm were conducted using a CTD60M
memory probe (Sea and sun technology, Trappenkamp, Germany) lowered from the
surface to a depth of 17 m at about 0.3 m s
The carbonate system is described in detail in Paul et al. (2015b). The pHT (total scale) was determined using a spectrophotometric method (Dickson et al., 2007) on a Cary 100 (Varian) and the dye m-cresol as indicator. Extinction was measured at 578 (E1) and 434 nm (E2) in a 10 cm cuvette. The pH was calculated from the ratio of E1 and E2 (Clayton and Byrne, 1993).
DIC was measured using a coulometric AIRICA system (MARIANDA, Kiel)
measuring the infrared absorption after N
The
Subsamples of 500 mL were filtered onto GF/F-filters. Chl
A segmented continuous-flow analyzer coupled with a liquid-waveguide
capillary flow-cell (LWCC) of 2 m length was used to determine phosphate
(PO
For the determination of DOP, duplicate 40 mL subsamples were filtered
through pre-combusted (6 h, 450
For all analysed components, subsamples were pre-filtered through
pre-combusted (6 h, 450
The method of (Björkman and Karl, 2001) adapted to Baltic Sea
conditions (Unger et al., 2013) was used to determine dissolved adenosine
triphosphate (dATP). An Mg(OH)
The phosphate content of the dissolved phospholipids (PL-P) was analysed
using a modified method of Suzumura and Ingall (2001, 2004).
Briefly, 400 mL subsamples of the filtrate were stored at
Dissolved DNA and RNA (dDNA and dRNA) concentrations were determined
according to Karl and Bailiff (1989) and as described by Unger et al. (2013). For each sample, 200 mL of the filtrate was gently mixed with
the same volume of ethylene-diamine-tetracetic acid (EDTA, 0.1 M, pH 9.3,
Merck, 1.08454) and 4 mL of cetyltrimethyl-ammonium bromide (CTAB,
Sigma-Aldrich, H5882) and stored frozen at
DNA concentrations were measured using a fluorescence-spectrophotometer (Hitachi F 2000), and RNA concentrations using a dual-beam UV/VIS-spectrophotometer U3010 (Hitachi).
Coupled standards (DNA
Particulate phosphorus (PP) was analysed using two methods in parallel. In
the “aqueous method”, 40 mL of unfiltered subsamples were frozen at
Particulate carbon (PC) and nitrogen (PN) were analysed by filtering 500 mL
samples onto pre-combusted (450
PO
[
Rates of bacterial protein production (BPP) were determined by incorporation
of
The Grubbs test, done online (
Spearman Rank correlations were carried out to describe the relationship between the development of the parameters over time in the mesocosms and in the fjord using Statistica 6 software.
Short-term CO
The different mesocosms were characterized based on their averaged
M1 365
M5 368
M7 497
M6 821
M3 1007
M8 1231
M1 and M5 were the untreated mesocosms and served as controls.
Temperature development in the mesocosms closely followed that in the fjord
ranging from 7.82 to 15.86
Salinity (5.69
Minimum, maximum and mean values of hydrographical parameters and
Temperature and salinity averaged over the 17 m surface layer of
the mesocosms and the fjord. The data were obtained from daily CTD casts.
Large symbols represent temperature and the small symbols salinity. Fjord
water is shown as black dots with broken line while blue symbols denote
untreated, grey intermediate and red high
Chlorophyll
We observed a significant relationship between Chl
Chl
Total phosphorus (TP) concentrations in the mesocosms ranged between 0.49
and 0.68
Mesocosms in which the Spearman Rank correlation between P-pools or
uptake rates and other parameters was significant. The relationship of PP
with TP and Chl
Particulate phosphorus (PP) concentrations varied from 0.10 to 0.23
Dissolved organic phosphorus (DOP) concentrations in the mesocosms ranged
between 0.18 and 0.36
Contribution of the individual P-fractions to TP in fjord water
and in the respective mesocosms. The data are averaged for the period when
TP measurements were done (day
PP concentration in the mesocosms during the initial phase from
day 0 to day 2
In phase I, DOP initially increased in parallel with Chl
Contribution of different phosphorus components to DOP in the mesocosms and in the fjord.
Phosphate (PO
Development of DOP in relation to bacterial production (BPP) and
phytoplankton biomass (Chl
Turnover times of PO
Since PO
PO
PO
ATP turnover times of 0.2 to 3.6 days (mean 0.94
Large variations in
Chl
TP concentrations from day
PP concentrations varied from 0.13 to 0.30
Development of DOP compounds in the mesocosms and in the fjord from day 0 to day 27.
DOP substantially contributed (26–45 %) to the TP pool (Fig. 6).
Concentrations ranged between 0.19 and 0.29
PO
An increase in CO
The Finnish coast off the Gulf of Finland is one of the most important
upwelling regions in the Baltic Sea. During our investigation in 2012,
surface temperatures, obtained from the NOAA satellite (Siegel and
Gerth, 2013), showed that upwelling persisted during the whole study period
but with varying intensity. The intensity of upwelling shaped the pattern of
temperature not only in the fjord but also in the mesocosms varying from 7.8
to 15.9
While nutrients were added in previous CO
Against this background, the CO
The effects of CO
While in phases II and III, high CO
Correlations calculated by using the Spearman rank test between P pools or
uptake rates and other parameters for each mesocosm are presented in Table 2. The relationships between PP and TP with Chl
Independent of the CO
Nutrients in upwelled water during our study were depleted in dissolved
inorganic nitrogen and enriched in PO
PP concentrations of 0.13–0.3
DOP concentration of 0.27
Surface water in Storfjärden showed highly variable
We are grateful to the KOSMOS team for their invaluable help with the logistics and maintenance of the mesocosms throughout the experiment. In particular, we sincerely thank Andrea Ludwig for organizing and coordinating the campaign and for the daily CTD measurements. We appreciate the assistance of Jehane Ouriqua in the nutrient analysis and that of many other participants who carried out the samplings. We also appreciate the collegial atmosphere during the work and thank everyone who contributed to it. We would also like to acknowledge the staff of the Tvärminne Zoological Station for their hospitality and support, for allowing us to use the experimental facilities, and for providing CTD data for the summers of 2008–20011. Finally, we thank Jana Woelk for analysing the phosphorus samples in the IOW. This study was funded by the BMBF project BIOACID II (FKZ 03F06550). Edited by: C. P. D. Brussaard