Effect of elevated CO2 on organic matter pools and fluxes in a summer Baltic Sea plankton community

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Paul , A J , Bach , L T , Schulz , K -G , Boxhammer , T , Czerny , J , Achterberg , E P , Hellemann , D , Trense , Y , Nausch , M , Sswat , M & Riebesell , U 2015 , ' Effect of elevated CO2 on organic matter pools and fluxes in a summer Baltic Sea plankton community ' , Biogeosciences , vol. 12 , no. 20 , pp. 6181-6203 . https://doi.org/10.5194/bg-12-6181-2015

Title: Effect of elevated CO2 on organic matter pools and fluxes in a summer Baltic Sea plankton community
Author: Paul, A. J.; Bach, L. T.; Schulz, K. -G.; Boxhammer, T.; Czerny, J.; Achterberg, E. P.; Hellemann, D.; Trense, Y.; Nausch, M.; Sswat, M.; Riebesell, U.
Contributor: University of Helsinki, Environmental Sciences
Date: 2015
Language: eng
Number of pages: 23
Belongs to series: Biogeosciences
ISSN: 1726-4170
URI: http://hdl.handle.net/10138/161802
Abstract: Ocean acidification is expected to influence plankton community structure and biogeochemical element cycles. To date, the response of plankton communities to elevated CO2 has been studied primarily during nutrient-stimulated blooms. In this CO2 manipulation study, we used large-volume (similar to 55 m(3)) pelagic in situ mesocosms to enclose a natural summer, post-spring-bloom plankton assemblage in the Baltic Sea to investigate the response of organic matter pools to ocean acidification. The carbonate system in the six mesocosms was manipulated to yield average fCO(2) ranging between 365 and similar to 1230 mu atm with no adjustment of naturally available nutrient concentrations. Plankton community development and key biogeochemical element pools' were subsequently followed in this nitrogen-limited ecosystem over a period of 7 weeks. We observed higher sustained chlorophyll a and particulate matter concentrations (similar to 25% higher) and lower inorganic phosphate concentrations in the water column in the highest fCO(2) treatment (1231 mu atm) during the final 2 weeks of the study period (Phase III), when there was low net change in particulate and dissolved matter pools. Size-fractionated phytoplankton pigment analyses indicated that these differences were driven by picophytoplankton (<2 mu m) and were already established early in the experiment during an initial warm and more productive period with overall elevated chlorophyll a and particulate matter concentrations. However, the influence of picophyto-plankton on bulk organic matter pools was masked by high biomass of larger plankton until Phase III, when the contribution of the small size fraction (<2 mu m) increased to up to 90% of chlorophyll a. In this phase, a CO2-driven increase in water column particulate carbon did not lead to enhanced sinking material flux but was instead reflected in increased dissolved organic carbon concentrations. Hence ocean acidification may induce changes in organic matter partitioning in the upper water column during the low-nitrogen summer period in the Baltic Sea.
Subject: OCEAN ACIDIFICATION
INORGANIC CARBON
NANOMOLAR CONCENTRATIONS
COASTAL PHYTOPLANKTON
MICROCOSM EXPERIMENTS
NATURAL-WATERS
TECHNICAL NOTE
SEAWATER
BLOOM
NITROGEN
1171 Geosciences
1172 Environmental sciences
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