Carbon dioxide dynamics and fluxes in coastal waters influenced by river plumes
| Autor: | C. T. Arthur Chen, Alberto Borges, Wei-Jun Cai |
|---|---|
| Rok vydání: | 2013 |
| Předmět: |
0106 biological sciences
Shore geography geography.geographical_feature_category 010504 meteorology & atmospheric sciences Continental shelf 010604 marine biology & hydrobiology Biosphere Climate change Estuary Wetland 15. Life on land 01 natural sciences Oceanography 13. Climate action 14. Life underwater Oceanic basin Bank Geology 0105 earth and related environmental sciences |
| DOI: | 10.1017/cbo9781139136853.010 |
| Popis: | Globally, estuaries are a source of CO2 to the atmosphere, releasing a significant fraction of CO2 that the terrestrial biosphere absorbed from the atmosphere, and thus significantly reduce riverine terrestrial carbon fluxes to the ocean. Although several recent synthesis papers brought the flux lower from 0.5 to 0.25 Pg C yr−1 (Table 7.1), the flux is still quite significant in consideration of global carbon budget and pathways. Most importantly, the likely uncertainty in estimating air-water CO2 flux in coastal waters and wetlands is so large (±0.2 Pg C yr−1) that it becomes a major obstacle for a precise assessment of the CO2 flux at the air earth interface (be it terrestrial or ocean), thus making the effort for further improving the accuracy of estimating air-earth surface CO2 exchange fluxes less meaningful for climate change research – if such uncertainty in coastal systems is not tackled (Cai 2011). Previous works have largely focused on inner estuaries within coastal shorelines, and river plumes extending outside the shorelines largely are ignored for a number of reasons. Most importantly, river plumes are not limited geographically, and their areas are not defined clearly. They also have CO2 values closer to saturation with respect to the atmosphere. These properties are in stark contrast to inner estuaries, which are geographically limited by river banks or shorelines and virtually in all cases have CO2 values distinctly higher than the atmosphere. Hence river plumes are difficult to quantify and generalize in terms of an annual exchange flux of CO2 with the atmosphere. River plumes also reside directly on the continental shelves and thus often are included as part of shelves in global syntheses. Freshwater plumes of some large rivers (e.g., Amazon, Congo, Niger) often even extend beyond the continental shelf into the continental slope and ocean basin (Bianchi and Allison 2009). Because of the lack of reliable air-water CO2 flux estimates and the absence of global estimates of surface areas, river plumes have not been included in previous syntheses of global coastal water CO2 fluxes (Borges 2005; Borges et al. 2005; Cai et al. 2006; Chen and Borges 2009; Laruelle et al. 2010). This chapter first briefly reviews the state of knowledge of global (inner) estuarine CO2 flux and the existing problems. Then, we describe the distribution features of CO2 parameters in and around large river plumes over continental shelves to discuss factors that control CO2 distribution in areas dominated by river plumes. We also attempt to estimate air-sea CO2 flux in river plumes globally and provide a general view on whether inclusion of river plume in the estuarine CO2 flux assessments would change the currently best known global estuarine CO2 flux values. |
| Databáze: | OpenAIRE |
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