Seasonal dynamics of air-sea CO₂ fluxes in the inner and outer Loire estuary (NW Europe)

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• 作者：Y. Bozec^a ; ^b ; ^{bozec@sb-roscoff.fr} ; T. Cariou^a ; ^b ; E. Macé ; ^a ; ^b ; P. Morin^a ; ^b ; D. Thuillier^c ; M. Vernet^a ; ^b
• 关键词：estuaries ; plumes ; air&ndash ; sea CO2 exchange ; seasonal Carbon cycle ; coastal ecosystems ; (46.5&ndash ; 48° ; N ; 1.5&ndash ; 5° ; W)
• 刊名：Estuarine ; Coastal and Shelf Science
• 出版年：2012
• 期刊代码：79_02727714
• 类别：env
• 出版时间：20 March, 2012
• 卷：100
• 期：Complete
• 页码：58-71
• 文件大小：1590 K

摘要

We investigated partial pressure of CO₂ (pCO₂) dynamics in the inner and outer Loire estuary (coastal margin of north-western Europe) over an annual cycle (2009-2010) using a comprehensive dataset of pCO₂, dissolved oxygen concentration (DO) and ancillary data collected during four cruises conducted in different seasons. In the inner estuary, pCO₂ exhibited very large spatial and inter-seasonal amplitudes (from 294 to 2744聽渭atm) mainly driven by strong heterotrophic respiration from spring to fall, thermodynamic effects in summer and mixing during winter floods. In the outer estuary, during spring and to a lesser extent during summer, the large extension of the plume resulted in stratification of the water column and autotrophic processes induced pCO₂ below atmospheric equilibrium in the plume鈥檚 surface waters (mean values of聽鈭?5聽渭atm compared to the atmosphere). During fall, mixing with inner estuary waters influenced by heterotrophic processes induced pCO₂ above atmospheric equilibrium (mean values of聽+86聽渭atm) in the very restricted and shallow plume. During winter floods, thermodynamics as well as episodic winter phytoplankton blooms were responsible for pCO₂ values below atmospheric equilibrium in the plume (mean values of聽鈭?2聽渭atm), whereas the adjacent surface waters were at equilibrium with the聽atmosphere. Air-sea CO₂ fluxes in the inner estuary ranged from 41聽卤聽4聽mmol聽m^鈭?聽d^鈭? during spring to 140聽卤聽18聽mmol聽m^鈭?聽d^鈭? during fall, compared to an outer estuary minimum of聽鈭?.0聽卤聽1.0聽mmol聽m^鈭?聽d^鈭? during spring and maximum of 7.7聽卤聽1.1聽mmol聽m^鈭?聽d^鈭? during fall. Integrated over their respective areas,聽annual CO₂ emissions from the inner estuary of 3.2 10⁹聽mol聽C聽yr^鈭? were offset by the annual CO₂ sink聽of聽鈭?7.9 10⁹聽mol聽C聽yr^鈭? from the plume alone. Based on four seasonal cruises, it seems that because of聽its large size during spring and to a lesser extent during winter, the Loire plume significantly impacted聽estimates of air-sea CO₂ fluxes at a regional scale. Comparison with other major estuarine plumes in diverse continental shelf zones seems to indicate a predominance of CO₂ sinks in these systems suggesting that other estuarine plumes might counteract inner estuary CO₂ emissions at seasonal to annual level.