Structure and position of the bottom salinity front in the Amazon Estuary

Molinas, Ernesto; Vinzón, Susana B.; Vilela, Carla de Paula Xavier; Gallo, Marcos Esteban

doi:10.1007/s10236-014-0763-0

Cited by 21 publications

(17 citation statements)

References 34 publications

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“…Another factor that can lead to a large underestimation of basin-wide budgets is not including Amazon River water that travels further offshore from Area 2 and along the coastline. For example, the Amazon River can remain unmixed with the ocean as far as 60 km offshore from Area 2 (Molinas et al, 2014). Abril et al (2014) estimated that only 18% of the CO 2 from a point source would be degassed in a stretch of approximately 150 km downstream in the Amazon River taking into account a kvalue of 15 cm h −1 and water current of 150 cm s −1 .…”

Section: Discussionmentioning

confidence: 99%

“…The river continues to widen and channelize between large islands an additional 150 km downstream of Macapá before being entirely disconnected from land and the riparian zone/floodplains (Figure 1-Area 2). The water entering the ocean can remain completely fresh at the surface as much as 60 km offshore from this point (Figure 1-Area 3; Molinas et al, 2014).…”

Section: Study Areamentioning

confidence: 99%

“…We divided the main channel into two zones: (Area 1) our study boundaries from Óbidos to Macapá, which has a surface area of 7,200 km 2 , and (Area 2) the region extending from Macapá to the geographical river mouth, which has an additional surface area of 9,609 km 2 (Figure 1). Although it has never been studied, we assume that Area 2 will have similar geochemical characteristics as the region near Macapá considering there are still inputs from land and the Amazon River water discharged to the ocean still remains completely fresh at the surface up to ∼100 km further offshore (Figure 1-Area 3; Molinas et al, 2014).…”

Section: Annual Co 2 Emissions From the Lower Amazon Rivermentioning

confidence: 99%

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Carbon Dioxide Emissions along the Lower Amazon River

et al. 2017

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A large fraction of the organic carbon derived from land that is transported through inland waters is decomposed along river systems and emitted to the atmosphere as carbon dioxide (CO 2 ). The Amazon River outgasses nearly as much CO 2 as the rainforest sequesters on an annual basis, representing ∼25% of global CO 2 emissions from inland waters. However, current estimates of CO 2 outgassing from the Amazon basin are based on a conservative upscaling of measurements made in the central Amazon, meaning both basin and global scale budgets are likely underestimated. The lower Amazon River, from Óbidos to the river mouth, represents ∼13% of the total drainage basin area, and is not included in current basin-scale estimates. Here, we assessed the concentration and evasion rate of CO 2 along the lower Amazon River corridor and its major tributaries, the Tapajós and Xingu Rivers. Evasive CO 2 fluxes were directly measured using floating chambers and gas transfer coefficients (k 600 ) were calculated for different hydrological seasons. Temporal variations in pCO 2 and CO 2 emissions were similar to previous observations throughout the Amazon (e.g., peak concentrations at high water) and CO 2 outgassing was lower in the clearwater tributaries compared to the mainstem. However, k 600 -values were higher than previously reported upstream likely due to the generally windier conditions, turbulence caused by tidal forces, and an amplification of these factors in the wider channels with a longer fetch. We estimate that the lower Amazon River mainstem emits 0.2 Pg C year −1 within our study boundaries, or as much as 0.48 Pg C year −1 if the entire spatial extent to the geographical mouth is considered. Including these values with updated basin scale estimates and estimates of CO 2 outgassing from small streams we estimate that the Amazon running waters outgasses as much as 1.39 Pg C year −1 , increasing the global emissions from inland waters by 43% for a total of 2.9 Pg C year −1 . These results highlight a large missing gap in basin-scale carbon budgets along the complete continuum of the Amazon River, and likely most other large river systems, that could drastically alter global scale carbon budgets.

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Section: Discussionmentioning

confidence: 99%

Section: Study Areamentioning

confidence: 99%

Section: Annual Co 2 Emissions From the Lower Amazon Rivermentioning

confidence: 99%

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Carbon Dioxide Emissions along the Lower Amazon River

et al. 2017

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“…Incorporating this new basin-wide budget into the global inland water budget results in a 44% increase in the global budget (3.0 Pg C year −1 ). Further, the completely freshwaters of the Amazon River extend an additional 60 km into the Atlantic Ocean prior to mixing (Molinas et al, 2014), and if this region is included it could add an additional 0.8 Pg C year −1 to the Amazon River budget (Sawakuchi et al, in review). However, no observations have been made in this offshore region and it is not included in plume studies (Cooley et al, 2007;Subramaniam et al, 2008), revealing a critical gap in data coverage along the aquatic continuum, not just in the Amazon River, but rivers worldwide.…”

Section: Carbon Fluxes From Inland Watersmentioning

confidence: 99%

Where Carbon Goes When Water Flows: Carbon Cycling across the Aquatic Continuum

et al. 2017

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The purpose of this review is to highlight progress in unraveling carbon cycling dynamics across the continuum of landscapes, inland waters, coastal oceans, and the atmosphere. Earth systems are intimately interconnected, yet most biogeochemical studies focus on specific components in isolation. The movement of water drives the carbon cycle, and, as such, inland waters provide a critical intersection between terrestrial and marine biospheres. Inland, estuarine, and coastal waters are well studied in regions near centers of human population in the Northern hemisphere. However, many of the world's large river systems and their marine receiving waters remain poorly characterized, particularly in the tropics, which contribute to a disproportionately large fraction of the transformation of terrestrial organic matter to carbon dioxide, and the Arctic, where positive feedback mechanisms are likely to amplify global climate change. There are large gaps in current coverage of environmental observations along the aquatic continuum. For example, tidally-influenced reaches of major rivers and near-shore coastal regions around river plumes are often left out of carbon budgets due to a combination of methodological constraints and poor data coverage. We suggest that closing these gaps could potentially alter global estimates of CO 2 outgassing from surface waters to the atmosphere by several-fold. Finally, in order to identify and constrain/embrace uncertainties in global carbon budget estimations it is important that we further adopt statistical and modeling approaches that have become well-established in the fields of oceanography and paleoclimatology, for example.

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“…Biogeochemical measurements in the bottom layer suggest that the off-shore carbon flux in this "Ekman Drain" is a dominant pathway that delivers particulate carbon and other suspended material to deep water. Molinas et al (2014) use a numerical model in combination with observations to examine the variability of the salinity structure of the world's biggest estuary, the Amazon River outflow. They find that in spite of the tremendous magnitude of river outflow, the variability of estuarine structure is more strongly influenced by changes in tidal forcing conditions and winds than the variation of freshwater discharge.…”

mentioning

confidence: 99%