Presentation is loading. Please wait.

Presentation is loading. Please wait.

Spatial and temporal coherence between Amazon River discharge, satellite salinity and light absorption by colored organic carbon in Western Tropical Atlantic.

Similar presentations


Presentation on theme: "Spatial and temporal coherence between Amazon River discharge, satellite salinity and light absorption by colored organic carbon in Western Tropical Atlantic."— Presentation transcript:

1 Spatial and temporal coherence between Amazon River discharge, satellite salinity and light absorption by colored organic carbon in Western Tropical Atlantic surface water. Joseph Salisbury 1, Douglas Vandemark 1, Christopher Hunt 1, Janet Campbell 1, Nicolas Reul 2, Bertrand Chapron 2 Dominik Wisser 1 1. University of New Hampshire, Durham, NH, USA 2. Laboratoire d’Oceanographie Spatiale, Institut Francais de Recherche et d’Exploitationde la Mer, Plouzane´, France. Abstract: The temporal evolution and spatial distribution of satellite-derived sea surface salinity and colored detrital matter (cdm) were evaluated in coastal waters adjacent to the Amazon’s discharge. Study objectives were: first, to document the spatial coherence between Amazon discharge, salinity, cdm, and the nature of the salinity-cdm relationship in a region adjacent to the Brazilian Shelf; second, to document the temporal and spatial variability of cdm along the trajectory of the low-salinity Amazon plume, and third, to explore the departure of cdm from conservative mixing behavior along the plume trajectory into the open ocean. Our work clearly demonstrates the value of satellite derived salinity for interpreting biology and biogeochemical data obtained from ocean color sensors.  Figure 2: Seasonal climatologies ( ) of satellite variables: AMSR-E salinity (left) and MODIS acdm 443 (right). The seasons (low flow, ascending, high flow, descending) were determined based on the climatological hydrograph of the Amazon River at Obidos, Brazil. Seasonal climatologies are estimated as the mean of seasonal NASA Aqua satellite data ( ). Salinity is estimated using microwave brightness temperatures from the NASA AMSR-E sensor. Monthly acdm 443 data are derived using monthly MODIS ocean color radiance data to which the QAA algorithm was applied (see text). The axis of the low salinity plume climatology (to ~36psu) is traced on the salinity data (black dash).  Figure 4: Monthly climatologies of salinity and acdm 443 along the low-salinity plume trajectories ( ). Salinity (lt. brown) and acdm 443 (green). For each climatological month, all salinity and acdm 443 data subtended by the low salinity trajectories were binned by distance from the Amazon mouth (50km/bin), averaged, and plotted as a function of distance.  Figure 1: Area of interes. The northwestern Tropical Atlantic. On land, the Amazon River and its major tributaries within our region of interest are shown, as are the Orinoco, Xingu and Tocatins (Toc.) Rivers. The location of the Obidos, Brazil discharge gauge is indicated as a solid circle. In the ocean, major currents are indicated: North Brazil Current (NBC), Northern Equatorial Current (NEC), North Equatorial Counter Current (NECC), Guyana tCurrent and Caribbean Current. The small flow vectors show the mean surface current direction and relative velocity during September. These were created from climatological ARGO float trajectory data.  Figure 3: Time series of monthly salinity, acdm 443 and discharge. Data were retrieved and averaged for locations corresponding to the proximal (mouth to 600km), medial ( km) and distal ( km) sections of the low salinity plume trajectories and then plotted as a function of time. Salinity (lt. brown), modeled Amazon discharge (black solid), modeled discharge for the Rio Negro (black, 4a, second panel only), acdm 443 (green), averaged acdm 443 for the same region as Figure 3, (dashed green). Note the different axis scales for each plot.  Figure 5 : a) Distance (km) versus acdm 443 residual (blue). b) Satellite CbPM data versus acdm 443 residual (blue). Red lines represent the number of values in each bin: (a) binned by 50 km intervals. (b) binned by 50 mgC m -2 d -1 intervals. The dashed lines represent +/- 1 standard deviation of each bin average Conclusions: 1. AMSR-E provides salinity data in time and space that is of sufficient accuracy to study biogeochemical processes in coastal regions. It complementary to ocean color data in these endeavors. 2. Salinity is spatio-temporally coherent with satellite acdm data, but there are spatial and seasonal anomalies in conservative mixing of salinity and acdm. 3. Anomalies below the mixing line tend to be related to distance along the plume trajectory, suggesting time- evolving photo-oxidation of acdm. 4. Anomalies above the mixing are predominately found in high productivity regions, invoking the role of phytoplankton as a source of acdm. 5. At the mouth of the Amazon, there is a lag between mini mum salinity and maximum acdm. We speculate that the discharge of the Rio Negro is partly responsible for this observation. Acknowledgements: We are grateful for the NASA support that funded our efforts: NASA Carbon Grants (NNX08AL8OG and NNX08AE59G), NASA Ocean Salinity Team Grant (NNX09AU69G), and NASA NEWS (NNX09AU89G). We deeply appreciate the technical support and advice from colleagues Tim Moore and Stanley Glidden. Observed discharge data has been provided by the Global Runoff Data Centre (GRDC) in Koblenz, GDR


Download ppt "Spatial and temporal coherence between Amazon River discharge, satellite salinity and light absorption by colored organic carbon in Western Tropical Atlantic."

Similar presentations


Ads by Google