The Salinity Structure of the Amazon River Plume Drives Spatiotemporal Variation of Oceanic Primary Productivity

Abstract

The Amazon river is a major source of terrestrially derived organic carbon to the tropical Atlantic Ocean. Field, satellite and a vertically generalized production model data were used to estimate empirical surface salinity and fit an inverse logit function to investigate the limiting effect of salinity on the productivity in the Amazon river plume. Satellite data included Moderate Resolution Imaging Spectroradiometer, Soil Moisture and Ocean Salinity, and Aquarius missions. Previous empirical surface salinity models have relied on a very narrow range of salinity values and satellite data to estimate the spatial extent of the river plume. The empirical surface salinity model presented here extended the range of salinity values and captures all the main surface mesoscale features, particularly those related to the main path of the low‐salinity water. We also show that it is possible to gain new insights on the spatiotemporal variability of the Amazon river plume by improving the empirical surface salinity and expanding its sampling period with the aid of remote sensing data. The variability of primary productivity is dominated by the subannual (6 month) and annual (12 month) frequency bands. Low‐salinity river water influences surface primary productivity continuously during the year through mechanisms associated with the western tropical Atlantic circulation and vertical mixing.

The Role of the Amazon River Plume on the Intensification of the Hydrological Cycle

“…The NECC is the main export of low‐salinity water to the interior of the subtropical gyre and the NECC jet (Coles et al, ) and is characterized by sharp SSS NECC gradients. The monthly data sets span from July 2002 to August 2017 and the ARB hydrological variables are (i) precipitation data from the Tropical Rainfall Measuring Mission (TRMM) satellite of the TRMM 3B43v7 product with 0.25° spatial resolution available at https://disc.gsfc.nasa.gov/datasets/TRMM_3B43V7/summary (Huffman et al, ; Huffman et al, ); (ii) total water storage (TWS) from the Gravity Recovery and Climate Experiment with 1° spatial resolution RL05 from the German Research Centre for Geoscience available at http://grace.jpl.nasa.gov/data/get-data/ (Dahle et al, ); (iii) river discharge from 16 in situ flow stations, located along the main rivers and representing the runoff of all Amazon sub‐basins (Madeira, Solimões, Xingu, Negro, and Tapajós) (Figure ) obtained from the Hydrogeodynamics of the Amazon Basin Observatory (ORE‐HYBAM) (http://www.ore-hybam.org/); and (iv) monthly average SSS NECC (black box in Figure ) estimated using Moderate Resolution Imaging Spectroradiometer (MODIS) products following Gouveia et al (), see Text S1 in the supporting information for details). We chose the NECC pathway (Figure 1) because it transports up to 70% of the Amazon plume water that is deflected eastward by the North Brazil Current (NBC) retroflection (Grodsky et al, ; Lentz & Limeburner, ).…”

“…The latter is calculated using the regions defined by ENM W, C, and E according to Wang et al (2018). The color gradient in the ocean represents the average SSS (color bar) for September (2002-2017) based on Gouveia et al (2019). year is responsible for about two thirds of the water input to the WTNA (Coe et al, 2016). Based on our results, it is expected that changes in land cover of the western portion of the ARB, which is tightly connected to the ARB water cycle (Aragão, 2012;Spracklen et al, 2012), may cause greater impact on the WTNA water input than changes in other portions of the basin.…”

“…In the following summer (June–July) river discharge starts feeding the North Equatorial Counter Current (NECC) and in September 70% of ARp water is exported eastward by this pathway (Lentz & Limeburner, ). The ARp water also influences a number of important process such as carbon sequestration from primary production (Gouveia et al, ; Medeiros et al, ; Stukel et al, ; Subramaniam et al, ), heat flux (Field , ; Foltz & McPhaden, ), barrier layer formation (Balaguru et al, ; Pailler et al, ), and ocean circulation (Coles et al, ). Variations in the Amazon River discharge is a key driver of ARp changes (Hu et al, ; Muller‐Karger et al, ; Salisbury et al, ; Zeng et al, ).…”

Integrative taxonomy identifies a new stingray species of the genus Hypanus Rafinesque, 1818 (Dasyatidae, Myliobatiformes), from the Tropical Southwestern Atlantic

“…The Amazon River discharge in the Atlantic Ocean provides a salinity decrease to ca . 20 PSU (Gouveia et al ., 2019), which is a value these stingrays may not tolerate, and therefore the distribution discontinuity. Based on this, it is reasonable to assume both allopatric lineages north and south of this barrier, because the habitat is not adequate for them.…”

Amazon River propagation evidenced by a CO2 decrease at 8°N, 38°W in September 2013

“…Although the salinity minimum in September 2013 was not as low as in 2009 or 2011, the fCO 2 variations show that the Amazon plume also arrives at the mooring in 2013, which is confirmed by the Lagrangian experiment. Using satellite data and empirical surface salinity model over the period 2002, Gouveia et al (2019 conclude that the export of the Amazon plume water has intensified in recent years. Their study area is bounded at 40°W and the Amazon plume reaches 40°W each year from 2009 to 2017.…”