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Cyanobacteria net community production in the Baltic Sea as inferred from profiling pCO(2) measurements

Mueller, Jens Daniel and Schneider, Bernd and Graewe, Ulf and Fietzek, Peer and Wallin, Marcus and Rutgersson, Anna and Wasmund, Norbert and Krueger, Siegfried and Rehder, Gregor (2021). Cyanobacteria net community production in the Baltic Sea as inferred from profiling pCO(2) measurements. Biogeosciences. 18 , 4889-4917
[Research article]

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Abstract

Organic matter production by cyanobacteria blooms is a major environmental concern for the Baltic Sea, as it promotes the spread of anoxic zones. Partial pressure of carbon dioxide (pCO(2)) measurements carried out on Ships of Opportunity (SOOP) since 2003 have proven to be a powerful tool to resolve the carbon dynamics of the blooms in space and time. However, SOOP measurements lack the possibility to directly constrain depth-integrated net community production (NCP) in moles of carbon per surface area due to their restriction to the sea surface. This study tackles the knowledge gap through (1) providing an NCP best guess for an individual cyanobacteria bloom based on repeated profiling measurements of pCO(2) and (2) establishing an algorithm to accurately reconstruct depth-integrated NCP from surface pCO(2) observations in combination with modelled temperature profiles.Goal (1) was achieved by deploying state-of-the-art sensor technology from a small-scale sailing vessel. The low-cost and flexible platform enabled observations covering an entire bloom event that occurred in July-August 2018 in the Eastern Gotland Sea. For the biogeochemical interpretation, recorded pCO(2) profiles were converted to C-T*, which is the dissolved inorganic carbon concentration normalised to alkalinity. We found that the investigated bloom event was dominated by Nodularia and had many biogeochemical characteristics in common with blooms in previous years. In particular, it lasted for about 3 weeks, caused a C-T* drawdown of 90 mu mol kg(-1), and was accompanied by a sea surface temperature increase of 10 degrees C. The novel finding of this study is the vertical extension of the C-T* drawdown up to the compensation depth located at around 12 m. Integration of the C-T* drawdown across this depth and correction for vertical fluxes leads to an NCP best guess of similar to 1:2 mol m(-2) over the productive period.Addressing goal (2), we combined modelled hydrographical profiles with surface pCO(2) observations recorded by SOOP Finnmaid within the study area. Introducing the temperature penetration depth (TPD) as a new parameter to integrate SOOP observations across depth, we achieve an NCP reconstruction that agrees to the best guess within 10 %, which is considerably better than the reconstruction based on a classical mixed-layer depth constraint.Applying the TPD approach to almost 2 decades of surface pCO(2) observations available for the Baltic Sea bears the potential to provide new insights into the control and long-term trends of cyanobacteria NCP. This understanding is key for an effective design and monitoring of conservation measures aiming at a Good Environmental Status of the Baltic Sea.

Authors/Creators:Mueller, Jens Daniel and Schneider, Bernd and Graewe, Ulf and Fietzek, Peer and Wallin, Marcus and Rutgersson, Anna and Wasmund, Norbert and Krueger, Siegfried and Rehder, Gregor
Title:Cyanobacteria net community production in the Baltic Sea as inferred from profiling pCO(2) measurements
Series Name/Journal:Biogeosciences
Year of publishing :2021
Volume:18
Page range:4889-4917
Number of Pages:29
Publisher:COPERNICUS GESELLSCHAFT MBH
ISSN:1726-4170
Language:English
Publication Type:Research article
Article category:Scientific peer reviewed
Version:Published version
Copyright:Creative Commons: Attribution 4.0
Full Text Status:Public
Subjects:(A) Swedish standard research categories 2011 > 1 Natural sciences > 106 Biological Sciences (Medical to be 3 and Agricultural to be 4) > Ecology
URN:NBN:urn:nbn:se:slu:epsilon-p-113699
Permanent URL:
http://urn.kb.se/resolve?urn=urn:nbn:se:slu:epsilon-p-113699
Additional ID:
Type of IDID
DOI10.5194/bg-18-4889-2021
Web of Science (WoS)000695404000001
ID Code:25499
Faculty:NJ - Fakulteten för naturresurser och jordbruksvetenskap
Department:(NL, NJ) > Dept. of Aquatic Sciences and Assessment
Deposited By: SLUpub Connector
Deposited On:24 Sep 2021 11:25
Metadata Last Modified:24 Sep 2021 11:31

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