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Cyanobacteria net community production in the Baltic Sea as inferred from profiling pCO2 measurements
Biogeosciences ( IF 4.9 ) Pub Date : 2021-03-01 , DOI: 10.5194/bg-2021-40
Jens Daniel Müller , Bernd Schneider , Ulf Gräwe , Peer Fietzek , Marcus Bo Wallin , Anna Rutgersson , Norbert Wasmund , Siegfried Krüger , Gregor Rehder

Abstract. Organic matter production by cyanobacteria blooms is a major environmental concern for the Baltic Sea as it promotes thespread of anoxic zones. Partial pressure of carbon dioxide (pCO2) 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 the depth–integrated net community production (NCP) due to their restriction to the sea surface. This study tackles the resulting knowledge gap through (1) providing a best–guess NCP estimatefor an individual cyanobacteria bloom based on repeated profiling measurements of pCO2 and (2) establishing an algorithm to accurately reconstruct depth–integrated NCP from surface pCO2 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 and August 2018 in the Eastern Gotland Sea. For the biogeochemical interpretation, recorded pCO2 profiles were converted to CT*, which is the dissolved inorganic carbon concentration normalised to alkalinity. We found that the investigated Nodularia–dominated bloom event had many biogeochemical characteristics in common with blooms in previous years. In particular, it lasted for about three weeks, caused a CT* drawdown of 80 μmol kg−1, and was accompanied by a sea surface temperature increase of 10 °C. The novel finding of this study is the vertical extension of the CT* drawdown up to 12 m water depth. Integration of the CT* drawdown across this depth and correction for vertical fluxes permit a best–guess NCP estimate of ~1.2 mol–C m−2. Addressing goal (2), we combined modelled hydrographical profiles with surface pCO2 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 a reconstructed NCP estimate that agrees to the best–guess within 10 %. Applying the TPD approach to almost two decades of surface pCO2 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.

中文翻译:

根据p CO 2测量结果推断,波罗的海蓝细菌净群落产量

摘要。蓝藻繁殖产生的有机物是波罗的海关注的主要环境问题,因为它促进了缺氧区域的扩散。自2003年以来,在机会船(SOOP)上进行的二氧化碳分压(p CO 2)测量已被证明是解决时空绽放碳动态的有力工具。然而,由于SOOP测量对海面的限制,因此无法直接限制深度综合的净群落生产(NCP)。这项研究通过以下方法解决了由此产生的知识鸿沟:(1)根据对p CO 2的重复分析测量结果,为单个蓝藻水华提供最佳猜测的NCP估计(2)建立一个算法,结合表面温度曲线,从表面p CO 2观测值中准确重建深度积分的NCP 。目标(1)是通过从小型帆船上部署最先进的传感器技术来实现的。低成本,灵活的平台使观测范围涵盖了东部哥得兰海2018年7月和8月发生的整个开花事件。为了进行生物地球化学解释,将记录的p CO 2曲线转换为C T *,这是归一化为碱度的溶解无机碳浓度。我们发现被调查的结节病–主导的水华事件具有许多生物地球化学特征,与前几年的水华相同。特别地,它持续了大约三周,导致C T *下降了80μmolkg -1,并且伴随着海面温度上升了10°C。这项研究的新颖发现是C T *垂降垂直延伸至水深12 m。跨此深度的C T *降落的积分和垂直通量的校正允许最佳猜测的NCP估计为〜1.2 mol–C m -2。为实现目标(2),我们将模拟的水文剖面与SOOP Finnmaid记录的表面p CO 2观测值相结合在研究区域内。通过引入温度穿透深度(TPD)作为整合SOOP跨深度观测值的新参数,我们获得了重构的NCP估计值,该估计值与10%以内的最佳猜测相符。将TPD方法应用于可用于波罗的海的近二十年的表面p CO 2观测值,具有为蓝藻NCP的控制和长期趋势提供新见识的潜力。这种了解对于有效设计和监控旨在实现波罗的海良好环境状况的养护措施至关重要。
更新日期:2021-03-01
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