ArticlePDF Available

On the potential causes of the recent Pelagic Sargassum blooms events in the tropical North Atlantic Ocean

Authors:

Abstract

Since 2011, unprecedented and repetitive blooms and large mass strandings of the floating brown macroalgæ, Sargassum natans and Sargassum fluitans have been reported along the West Indies, the Caribbean, the Brazilian and the West Africa coasts. Recent studies have highlighted a new tank of Sargassum: the North Equatorial Recirculation Region of the Atlantic Ocean. This region is located off the northeast of Brazil, approximately between the equator and 10° N and from 50° W to 25° W. The potential causes of these recent blooms and mass strandings are still poorly understood. Observational datasets and modelling outputs involving hydrological parameters and climate events are examined focusing on their potential feedback on the observed blooms and mass strandings. The results show that combined conditions have been in favor of these recent changes. High anomalously unprecedented positive sea surface temperature observed in the tropical Atlantic in 2010–2011 could have induced favorable temperature conditions for Sargassum blooms. These favorable conditions were then fed by additional continental nutrients inputs, principally from the Amazon River. These continental nutrients load are the consequences of deforestation, agroindustrial and urban activities in the Amazonian forest. The results also suggest that subsurface intake of nutrients from the equatorial upwelling could also contribute to the blooms of the Sargassum seaweed in the Atlantic Ocean but further studies are needed to confirm these additional inputs.
On the potential causes of the recent Pelagic Sargassum blooms
events in the tropical North Atlantic Ocean
Sandrine Djakouré1,2,4, Moacyr Araujo2,3, Aubains Hounsou-Gbo2,3 , Carlos Noriega2,3, and
Bernard Bourlès4
1Laboratoire de Physique de l’Atmosphère et de Mécanique des Fluides (LAPA-MF), UFR SSMT, Université Félix
Houphouët-Boigny, 22 BP 582 Abidjan 22, Côte d’Ivoire
2Laboratório de Oceanografia Física Estuarina e Costeira (LOFEC), Departamento de Oceanografia da Universidade Federal
de Pernambuco (DOCEAN/UFPE), Recife, PE, Brazil
3Brazilian Research Network on Global Climate Changes (Rede CLIMA), São José dos Campos, SP, Brazil
4Laboratoire d’Études en Géophysique et Océanographie Spatiales (LEGOS), UMR 5566 CNES/CNRS/IRD/UPS, Plouzané,
France
Correspondence to: Sandrine Djakouré (agre.djakoure@ird.fr)
Abstract. Since 2011, unprecedented and repetitive blooms and large mass strandings of the floating brown macroalgæ, Sar-
gassum natans and Sargassum fluitans have been reported along the West Indies, the Caribbean, the Brazilian and the West
Africa coasts. Recent studies have highlighted a new tank of Sargassum: the North Equatorial Recirculation Region of the At-
lantic Ocean. This region is located off the northeast of Brazil, approximately between the equator and 10N and from 50W
to 25W. The potential causes of these recent blooms and mass strandings are still poorly understood. Observational datasets5
and modelling outputs involving hydrological parameters and climate events are examined focusing on their potential feedback
on the observed blooms and mass strandings. The results show that combined conditions have been in favor of these recent
changes. High anomalously unprecedented positive sea surface temperature observed in the tropical Atlantic in 2010-2011
could have induced favorable temperature conditions for Sargassum blooms. These favorable conditions were then fed by ad-
ditional continental nutrients inputs, principally from the Amazon River. These continental nutrients load are the consequences10
of deforestation, agroindustrial and urban activities in the Amazonian forest. The results also suggest that subsurface intake of
nutrients from the equatorial upwelling could also contribute to the blooms of the Sargassum seaweed in the Atlantic Ocean
but further studies are needed to confirm these additional inputs.
Key words: Pelagic Sargassum, North Equatorial Recirculation Region, Sea Surface Temperature, Amazon River, nutrients15
1 Introduction
The Pelagic Sargassum are brown macroalgæ, which have been firstly documented in the North Atlantic Ocean by Christopher
Columbus, from the Sargasso Sea off the East Coast of the United States. Mainly two species of the genus Sargassum live and
float on the surface of the tropical Atlantic : the Sargassum natans (Linnaeus) Gaillon and the Sargassum fluitans (Børgesen)
Børgesen (Butler et al., 1983; Butler and Stoner, 1984; Lapointe, 1995; Guiry and Guiry, 2011; Szèchy et al., 2012; Smetacek20
1
Biogeosciences Discuss., https://doi.org/10.5194/bg-2017-346
Manuscript under review for journal Biogeosciences
Discussion started: 20 September 2017
c
Author(s) 2017. CC BY 4.0 License.
and Zingone, 2013; Sissini et al., 2017). The Pelagic Sargassum are also found in the northern Gulf of Mexico (Gower et al.,
2006; Gower and King, 2011; Hu et al., 2016), 90 % of Sargassum natans and 10 % of the Sargassum fluitans (Hernandez,
2011).
Since 2011, large mass strandings of the floating Sargassum have been reported along the West Indies and the Caribbean
coasts (Gower et al., 2013; Mazéas, 2014; Wang and Hu, 2017), the Brazilian coasts (Szèchy et al., 2012; Sissini et al., 2017)5
and the West Africa coasts (Smetacek and Zingone, 2013; Johnson et al., 2013; Oyesiku and Egunyomi, 2014; Sankaré et al.,
2016). These massive strandings and their locations in the topical Atlantic are unprecedented, observed almost yearly from
2011 (Wang and Hu, 2016, 2017; Sissini et al., 2017) and have important consequences for the coastal and marine ecosystems,
the water quality, the health of the population and the economic life. Such events indicate Sargassum recent changes in both
spatial and temporal distributions in the tropical North Atlantic.10
Gower et al. (2013) and Wang and Hu (2016) have highlighted a new tank of Sargassum in a region located off the northeast
of Brazil, approximately between the equator and 10N and from 50W to 25W, called the North Equatorial Recirculation
Region of the Atlantic Ocean (NERR, Fig. 1, bottom). During some year periods, the pelagic Sargassum are transported by the
Atlantic currents system from the northern tropical Atlantic to the Caribbean and the West Indies, as well as to West Africa.
Gower et al. (2013) have used remote sensing based on the Medium Resolution Imaging Spectrometer (MERIS) to describe15
the new Sargassum distributions in the Northern Atlantic Ocean, between 2002 and 2011. Large amounts of Sargassum natans
or Sargassum fluitans have been detected in an area off North Brazil, which is centered at about 7N, 45W and extending
from the Caribbean to Africa, from July to September 2011. Wang and Hu (2016) got similar results by using the Moderate
Resolution Imaging Spectroradiometer (MODIS) alternative floating algae index (AFAI), over the Central West Atlantic region
(0N-22N, 63W-38W) and from 2000 to 2015. Since 2011, only the year 2013 showed a minimal Sargassum coverage20
in the Central West Atlantic region. The maximum Sargassum coverage has been detected during 2015.
The causes of these recent blooms and mass strandings of Sargassum are not yet well apprehended. The knowledge about
these changes is limited and several hypotheses have been put forward: anomalous nutrient inputs from the tropical Atlantic
large rivers discharges (Amazon, Orinoco and Congo) but also by equatorial upwelling, African atmospheric dust, climate
changes induced increasing of sea water temperature and/or ocean currents changes (Johnson et al., 2013; Goes et al., 2014;25
Franks et al., 2014; Oxenford et al., 2015; Guimberteau et al., 2016).
Free floating marine plants need the energy of the sun (light) and carbon dioxide and nutrients (nitrate, phosphate, iron)
intakes for their growth (Ang, 2006; King, 2011; Sfriso and Facca, 2013; Xu et al., 2017). Gao and McKGao (1994) indicated
that the most important parameters affecting macroalgæ, such as Sargassum production, are irradiance, temperature, nutrients
and plankton grazing. Gao and Nakahara (1990) have demonstrated that the macroalgæ Sargassum horneri photosynthesis is30
correlated to the temporal changes in nitrate concentration and water temperature. Moreover, rapid water motion results in
higher productivity of macroalgæ. Indeed, increasing current speed facilitates the uptake of nutrients by macroalgæ, even in
seawater with low nutrient concentration (Gellenbeck and Chapman, 1986; Gao, 1991; Carpente et al., 1991; Gao and McKGao,
1994). Lapointe (1986, 1995) have also evinced the increased production of Sargassum natans and Sargassum fluitans by an
extra addition of phosphate and nitrate. The Sargassum productivity was enhanced in the coastal waters by nutrient loads from35
2
Biogeosciences Discuss., https://doi.org/10.5194/bg-2017-346
Manuscript under review for journal Biogeosciences
Discussion started: 20 September 2017
c
Author(s) 2017. CC BY 4.0 License.
land. Nevertheless, Sargassum natans is more nitrate than phosphate limited Lapointe (1995). Smetacek and Zingone (2013)
have also observed that the increase of Sargassum natans and Sargassum fluitans is related to higher nutrients inputs from the
Mississippi River in the Gulf of Mexico.
In addition to nutrients from rivers and equatorial upwelling, African atmospheric dust, the world’s largest dust source
(Prospero et al., 2014), has been also proposed to be a potential cause for the recent Sargassum blooms in the tropical North5
Atlantic (Johnson et al., 2013; Franks et al., 2014; Oxenford et al., 2015). The African dust transport has been found to cause
a significant degradation of soils while the re-sedimentation provides a supply of nutrients (iron, phosphate) to terrestrial
ecosystems and an increase in fertility in the area of dust settlement, as observed for the Amazon forest (Swap et al., 1992;
Scheuvens et al., 2013). Nevertheless, the amount of these nutrients inputs is significantly less than the one provided by
tropical rivers and equatorial upwelling (Prospero et al., 2014; Yu and al., 2015). Furthermore, the African aerosol transport10
has decreased over the past two decades since the peak in the 1980s (Hsu et al., 2012; Chin et al., 2014). Using AVHRR satellite,
Ridley et al. (2014) have observed a decreased of 10 % per decade from 1982 to 2008. Evan et al. (2016) have also found a
significant downward trend in African dust emission and transport related to an increase of the greenhouse gas concentrations
over the twenty-first century. The results of Wang et al. (2012) suggest a possible explanation of this mechanism for the North
Atlantic sea surface temperature (SST). Indeed, a warm (cold) North Atlantic SST produces a wet (dry) condition over Sahel15
which induces a low (high) concentration of dust in the tropical North Atlantic.
The blooms of Sargassum in the tropical Atlantic could also be due to a warmer SST associated with nutrient-enriched
oceans, induced by the continental runoff in addition to urban and agro-industrial sources (Sissini et al., 2017). Nevertheless,
these authors mentioned that alternative hypotheses need to be considered, for example for Sargassum originating from the
Mexican coast, as there is no evidence of drift from north to south. These authors concluded that the Sargassum bloom events20
are still unknown and more information are required. It is therefore important to continue the investigation and to explore new
tracks.
This paper focuses on the analysis of observations, model outputs of hydrological parameters and ocean conditions over the
tropical Atlantic basin, in order to investigate climate variations, trends or events and their potential feedback on the recent
Sargassum blooms and mass strandings. The following section describes the datasets and the methodology used for this study.25
In section 3 the major (main) results of this study are presented, before a discussion and a summary in the last section.
2 Materials and methods
To investigate the potential effects of climate variations and events on the recent occurrence of Sargassum blooms, interannual
variability of oceanic and atmospheric state-variables have been analyzed.
2.1 Sea Surface Temperature and wind stress data30
The monthly SST and wind stress data used herein are provided by the latest update of TropFlux (Air-Sea Fluxes for the
Global Tropical Oceans), products from the ESSO-Indian National Centre for Ocean Information Services. This dataset is
3
Biogeosciences Discuss., https://doi.org/10.5194/bg-2017-346
Manuscript under review for journal Biogeosciences
Discussion started: 20 September 2017
c
Author(s) 2017. CC BY 4.0 License.
made available at http://www.incois.gov.in/tropflux datasets/data. TropFlux dataset is based upon the ECMWF Re-Analysis
interim (ERA-I) and ISCCP (International Satellite Cloud Climatology Project) projects. Daily and monthly high-quality air-
sea fluxes, SST and wind stresses are produced by this project over the global tropical ocean belt (30N-30S) and are
available from 1979 to 2016. These data are gridded at a 1×1resolution (Praveen Kumar et al., 2013).
2.2 Climate indices5
Three climate indices are used : (i) the Atlantic Multi-decadal Oscillation (AMO), which is based on the average anomalies of
SST from the Kaplan SST dataset, in the North Atlantic basin over 0N-80N (Trenberth et al., 2017); (ii) the North Atlantic
Oscillation (NAO) based upon the difference of normalized sea level pressure, between Lisbon (Portugal) and Reykjavik
(Iceland) (Hurrell and for Atmospheric Research Staff , Eds) and (iii) the Atlantic Meridional Mode (AMM) index based
upon the meridional variability of the NCEP SST in the tropical Atlantic (Chiang and Vimont, 2004), obtained from the10
National Oceanic and Atmospheric Administration (NOAA). These data are available from https://www.esrl.noaa.gov/psd/gcos
wgsp/Timeseries/AMO/ for AMO index, from https://www.esrl.noaa.gov/psd/gcos wgsp/Timeseries/NAO/ for NAO index and
from https://www.esrl.noaa.gov/psd/data/timeseries/monthly/AMM/ for AMM SST index.
2.3 River discharges
In order to evaluate rivers discharges and variability and their influence on the Sargassum blooms, the products from the French15
HYBAM ”Geodynamical, hydrological and biogeochemical control of erosion/alteration and material transport in the Amazon,
Orinoco and Congo basins” Environmental Research Observatory are used. South America data are managed by the Brazilian
National Water Agency (ANA). All the dataset (daily and monthly) are freely available at http://www.ore-hybam.org/. The
Amazon River discharge data, available from 1968 to 2016, have been extracted from the Obidos station at 01.92S in latitude
and 55.67W in longitude. For the Orinoco River, we used data extracted at Ciudad Bolivar, located at 08.15N in latitude and20
63.54W in longitude, from 2003 to 2016. The Congo River discharge data have been extracted from the Brazzaville station,
at 4.26S in latitude and 15.25E in longitude, from 1990 to 2016.
2.4 Nutrients load
Due to the lack of sufficient in situ nutrients data, continental nutrients loads were estimated from statistical modelling outputs.
Formulas (1)-(4) are applied for the fluxes of dissolved inorganic nitrogen (DIN) and dissolved inorganic phosphorus (DIP)25
from regression models, which were built using 165 water systems worldwide analysis, DIN and DIP information (Smith et al.,
2003; Araujo et al., 2014). Note that the works of Smith et al. (2003) and Araujo et al. (2014) are an update analysis of the
Meybeck’s DIN and DIP estimates deduced from 30 large rivers (Meybeck, 1982; Meybeck and Ragu, 1997). The regression
models used are based on the surface water systems runoffs and the population density. The interannual surface water systems
4
Biogeosciences Discuss., https://doi.org/10.5194/bg-2017-346
Manuscript under review for journal Biogeosciences
Discussion started: 20 September 2017
c
Author(s) 2017. CC BY 4.0 License.
runoffs are extracted from the ANA and the HYBAM data sets. The population density rates for the rivers basins were extracted
from the five worldwide databases (refer to Smith et al. (2003) and Araujo et al. (2014) for more methodology details).
Log(DI N )=3.99 + 0.35 ×Log(P) + 0.75 ×Log(R)(1)
Log(DI P )=2.72 + 0.36 ×Log(P) + 0.78 ×Log(R)(2)5
where DIN, DIP are the discharged exportation into the coastal region of dissolved inorganic nitrogen (moles km2year1)
and the discharged exportation into the coastal region of dissolved inorganic phosphorus moles (moles km2year1); P is
the population density (hab km2) and R is the surface runoff (m year1). The nitrate (N O
3) and the phosphate (P O3
4)10
concentrations are then calculated using the following formula :
[NO
3] = 62.5×DIN ×P
3600 ×24 ×365 (3)
[P O3
4] = 45 ×DIP ×P
3600 ×24 ×365 (4)
15
where [NO
3] is the nitrate concentration in moles m3and [P O3
4] the phosphate concentration in moles m3and Q the
river discharge in m3s1.
We also used numerical outputs data of nitrate, phosphate, iron and chlorophyll concentrations obtained from the Marine
Copernicus MERCATOR GREEN (http://marine.copernicus.eu/). The model is forced by the biogeochemical model Pelagic20
Interaction Scheme for Carbon and Ecosystem Studies: PISCES) (Aumont and Bopp, 2006), gridded at 1spatial resolution,
and initialized by LEVITUS and the GLobal Ocean Data Analysis Project (GLODAP) climatologies. The rivers discharges are
initialized with the climatological datasets of Dai et al. (2009). The MERCATOR GREEN dataset is available from 1998 to
2014.
All the monthly anomalies have been calculated by removing the climatological seasonal cycle, which is the most dominant25
in the tropical Atlantic (Burls et al., 2011), and calculated over the period 1993-2015, which is the common period of most all
the variables at hand.
5
Biogeosciences Discuss., https://doi.org/10.5194/bg-2017-346
Manuscript under review for journal Biogeosciences
Discussion started: 20 September 2017
c
Author(s) 2017. CC BY 4.0 License.
3 Results
3.1 Sea Surface Temperature and climate indices
Water temperature is one of the most sensitive parameters that influence the Sargassum productivity (Gao and McKGao, 1994).
To check for any trends or events specific to the Sargassum blooms years in the tropical Atlantic, the interannual anomalies of
SSTs are analyzed (Fig. 1). The spatio-temporal variability of the SST anomalies and the surface wind stress (Praveen Kumar5
et al., 2013; Servain et al., 2014) from 2009 to 2015 are depicted for the whole Atlantic basin (Fig. 1, top). This figure presents
anomalously high positive anomalies of SST (with values greater than 1.5C) in the whole Atlantic basin and especially in
the northwest part of the basin, in 2010 and early 2011. These positive anomalies are associated with a very high positive
index of AMO and a strong negative index of the NAO. A cooling trend, especially in the eastern basin, is then observed
from 2012. Figure 1 (bottom) presents the interannual variability of SST anomalies in the NERR. The black stars represent the10
years of Sargassum blooms. A cool period is observed from 1979 to 1995, and from 1996 to 2015 both positive and negative
SST anomalies are portrayed. The abnormally high positive anomalies of 2010 (with values of 0.8C) and the negative SST
anomalies from 2012 to 2015 are also depicted.
In order to investigate climatic events that could be linked to the Sargassum blooms, the climate indices AMO and NAO,
along with the AMM are presented in Fig. 2. From 1950 to 2015, the analysis of the AMO (Fig. 2a) suggests three major15
periods: a warm phase from 1950 to 1963, a cool phase from 1964 to 1994 and a second warm phase from 1995 to 2015. Note
that AMO is a climate cycle at large time scale that affects the SSTs in the North Atlantic (McCarthy et al., 2015). A positive
(respectively negative) phase of AMO is associated with warmer (respectively cooler) SSTs in the North tropical Atlantic. The
anomalously high AMO is obtained in 2010 along with the anomalously high negative phase of the NAO (Fig. 2b) (Lefèvre
et al., 2013; Servain et al., 2014). The NAO is also a climatic index linked to the direction and magnitude of the westerly20
winds that control the location of storms in the North Atlantic basin (Hurrel, 2003). A negative NAO index is observed from
2009 to 2011, associated with weak trade winds and warmer SSTs, whereas a positive phase of NAO is observed from 2012
to 2015, associated with strong trade winds and cooler SSTs. The AMM is the dominant source of coupled ocean-atmosphere
variability in the tropical Atlantic and linked to rainfall in Northeast Brazil and tropical cyclone development in the North
Atlantic (http://www.aoml.noaa.gov/phod/research/tav/tcv/amm/index.php). A positive phase of the AMM is associated with25
a northward shift of the Atlantic Intertropical Convergence Zone (ITCZ), which causes drought in Northeast Brazil, warmer
SSTs and weaker vertical wind shear in the tropical North Atlantic (Foltz et al., 2012). From 2011 to 2012 (respectively 2013
to 2015), a positive phase (respectively a negative phase) of the AMM is observed (Fig. 2c).
3.2 Rivers discharges and nutrients load
The analysis of the Amazon, Orinoco and Congo rivers discharges (the majors rivers off western and eastern tropical Atlantic)30
(Araujo et al., 2014) is essential to better understand the origin of the Sargassum recent blooms because of the nutrients load.
Figure 3 presents the interannual (Fig. 3a), the climatology (Fig. 3b) and the anomalies of seasonal discharges (Fig. 3c) as
inferred from the HYBAM observatory database. The interannual variability of the three discharges (Fig. 3a) shows that the
6
Biogeosciences Discuss., https://doi.org/10.5194/bg-2017-346
Manuscript under review for journal Biogeosciences
Discussion started: 20 September 2017
c
Author(s) 2017. CC BY 4.0 License.
amplitude of the Amazon discharge variability is considerably larger than those of the two other rivers. From 1979 to 2015, the
Amazon River discharge oscillated between the maximum value of 30×104m3s1, obtained in 2006 and the minimum value
of 7×104m3s1, reached between the end of 2010 and early 2011. Note that the first Sargassum blooms have been reported
in 2011. The Orinoco and the Congo rivers discharges do not present a significant year-to-year variability. The climatological
signal (Fig. 3b) indicates that the Sargassum blooms and mass strandings in the tropical Atlantic Ocean, occurred generally5
during the ascending and the high flow of the Amazon River, i.e. from February to August. Furthermore, Sargassum mass
strandings in the West Indies and Carribean mostly occur from February to May (Gower et al., 2013; Wang and Hu, 2016),
when the Orinoco River low flow and the descending phase of the Congo River are observed. The mean seasonal anomalies
of the Amazon River (Fig. 3c) indicate that during the first year of Sargassum blooms in 2011 and Sargassum maximal spatial
coverage amount in 2015 (Wang et al., 2012), the normalized discharge anomalies are not significant, compare to the 50 %10
of the discharge standard deviation. Only the mean values from July 2013 to December 2014 and July to September 2015 are
more than 50 % of the discharge standard deviation.
Sargassum natans and Sargassum fluitans productivity is influenced by nutrients intake, and nitrate and phosphate have been
found to enhance these algae’s production (Lapointe, 1986; Gao and Nakahara, 1990; Lapointe, 1995; Smetacek and Zingone,
2013; Sissini et al., 2017). But these latter are more nitrate limited than phosphate limiting (Lapointe, 1995). Figure 4 exhibits15
the interannual variability of nitrate and phosphate fluxes anomalies for the Amazon (Fig. 4a), and the Congo rivers (Fig. 4b).
In addition to interannual variability, the mean seasonal anomalies of nitrate flux is also shown for the Amazon and the Congo
rivers (Figures 4c-d). These results are obtained from regression models built using 165 water systems worldwide analysis,
and DIN and DIP information (Smith et al., 2003; Araujo et al., 2014). Concerning the Amazon River, a clear upward trend
is noticeable from 1979 to 2015 for nitrate and phosphate. The Congo River nutrients variabilities also present an upward20
trend but not pronounced if compared to the Amazon River’s one. From 2011 to 2015, the difference between nitrate from
Amazon and Congo rivers can reach 20 kg mol d1. The continental nutrient load from the Amazon basin during these years
is unprecedented. Furthermore, the mean seasonal average for the Amazon River from 2011 evinces the anomalously high
values of continental nitrate load during the blooms events. On the contrary, positive anomalies of nitrate fluxes for the Congo
River, from 2011 to 2015, are similar to values observed during previous years (2006 to 2010).25
In addition to continental nutrients flux from the rivers, Fig. 5 exhibits results from the Copernicus-Marine MERCATOR
GREEN products for the mean seasonal anomalies, related to the period 1998-2014: nitrate concentration in the NERR box
(Fig. 5a) and in the equatorial upwelling region [2S-2N; 0-20W] (Fig. 5b); phosphate concentration in the NERR box
(Fig. 5c) and in the equatorial upwelling region (Fig. 5d); iron concentration in the NERR box (Fig. 5e) and chlorophyll con-
centration in the NERR box (Fig. 5f). Due to the deepening of the thermocline in the west and its shoaling in the eastern basin,30
the values have been average from 100 mto the surface for NERR and from 40 mto the surface for the equatorial region. In
the NERR, the nitrate concentration anomalies are negative from 2010 to April-May-June 2012. During the Sargassum blooms
events, only the period from the end of 2012 to 2015 evinces high unprecedented anomalies from 1998 to 2015, with value >
0.4 µmol l1. In contrast to the NERR region, the equatorial upwelling region exhibits high anomalies with values up to 1.35
µmol l1during the 2011 to 2015 year period. Thereby, the limiting nutrient for the Sargassum fluitans and the Sargassum35
7
Biogeosciences Discuss., https://doi.org/10.5194/bg-2017-346
Manuscript under review for journal Biogeosciences
Discussion started: 20 September 2017
c
Author(s) 2017. CC BY 4.0 License.
natans show relative high positive anomaly of nitrate concentration with two sources (in the west and in the east) during the
recent Sargassum blooms. The same patterns are visible for the phosphate concentrations for both the NERR and the equatorial
upwelling region: the years 2011 to 2015 show unprecedented positive anomalies of phosphate in the NERR, with values as
high as 0.13 µmol l1. Note that the variability of phosphate is usually similar to those of nitrate (Smith et al., 2003). An
increase of iron concentration, from the African dust, in the western basin has also been proposed to be a potential cause of the5
recent Sargassum blooms in the tropical Atlantic (Franks et al., 2014; Oxenford et al., 2015). Nonetheless, Fig. 5e indicates a
relative iron decrease from 2011 to 2015. Only the beginning of 2011, the end of 2012 and the beginning of 2013 show positive
anomalies of iron. However, these values are not superior to those of the period 2005-2008 when no Sargassum blooms have
been reported. From 1998 to 2010, the anomalies of chlorophyll concentration in the NERR are generally negative, then they
are positive from July to September 2011 (Fig. 5f). The highest value of 0.034 mg m3is reached in July-August-September10
2014. Thus, the increase of chlorophyll corresponds to the period of the recent blooms of Sargassum in the tropical Atlantic.
In summary, these results mostly indicate that :
anomalously high SSTs were present in the western basin, in the NERR in 2010 and during early 2011, when the blooms
began to be observed;15
the Amazon River discharge is not directly linked to the blooms and mass strandings events of Sargassum, observed in
the tropical Atlantic Ocean since 2011;
on the contrary, highest values of the Amazon River nutrients inputs, are well reached during the years when blooms
were reported from 2011.
4 Discussions and conclusions20
The potential causes of the recent Sargassum blooms events in the tropical Atlantic Ocean are studied by the analysis of climate
or environmental variations that could have generated these unprecedented and repetitive blooms. Indeed, mass strandings of
the Sargassum natans and the Sargassum fluitans have been reported along the West Indies, the Caribbean and the West
Africa coasts since 2011. These strandings have been shown to also come from a new area of Sargassum concentration, the
North Equatorial Recirculation Region of the Atlantic Ocean (NERR) (Gower et al., 2013; Wang and Hu, 2016). Sargassum25
production, is influenced principally by irradiance, temperature and nutrients (Gao and Nakahara, 1990; Gao and McKGao,
1994). Furthermore, Sargassum natans and Sargassum fluitans productivity is increased by an extra addition of nitrate and
phosphate in the coastal waters, by nutrient loads from land (Lapointe, 1986, 1995; Smetacek and Zingone, 2013).
This study presents for the most part, interannual variability of observations and model outputs data of SSTs, climate indices
and nutrients inputs (from rivers and equatorial upwelling region) and their potential effects on the Sargassum blooms.30
The results of the seasonal anomalies of SST, from 2008 to 2015, indicate that very high positive anomalies have been
observed in the whole Atlantic basin in 2010 and especially in the northwest basin and in the NERR region, in 2010 and early
8
Biogeosciences Discuss., https://doi.org/10.5194/bg-2017-346
Manuscript under review for journal Biogeosciences
Discussion started: 20 September 2017
c
Author(s) 2017. CC BY 4.0 License.
2011. The analyses of the climate indices AMO and NAO (Fig. 2) confirm that these high positive anomalies are concurrently
related, with strong high positive AMO and negative NAO indices as proposed by Lefèvre et al. (2013) and Servain et al. (2014).
This warming of the SST could have been in favor of Sargassum blooms by assuming that the optimum growth temperature for
Sargassum natans and Sargassum fluitans has been reached. Note that this optimal Sargassum growth temperature is not well
defined. Furthermore, the effect of temperature on Sargassum growth seems to be related to nutrient conditions. Indeed, it has5
been shown that an increase in temperature, from 23C to 29C has not effect on the palatability of Sargassum filipendula
but increases the rate of consumption (O’Connor, 2009; Endo et al., 2013). The growth rate of the Sargassum patens has also
been found to be increased indirectly by an increase of temperature within the range of 10C to 30C but this effect only
depends on the nutrient availability (Endo et al., 2013). Similar conclusions were made by Talling (2012) for algal growth,
which has been found to be affected by light and nutrient conditions. In contrast to 2010 to 2011, negative anomalies of SSTs10
from 2013 to 2015 were observed in the NERR <0.75C in average (Fig. 1), while the blooms were still observed with a
maximum spatial coverage in 2015. Considering these previous results, further studies in genetic or in biology are needed to
determine the optimal temperature for the Sargassum natans and the Sargassum fluitans maximum productivity in different
nutrient conditions.
The repetitive and unprecedented peaks in the major climate indices (NAO, AMM, AMO) have also been proposed to have15
generated these blooms phenomenon (Franks et al., 2014). Figure 2b shows a NAO positive phase from 2012 to 2015, which
may have been related to more cool waters and strong trade winds, more vertical mixing and more subsurface nutrients. Nev-
ertheless, a NAO positive phase with similar values was also observed from 1989 to 1995, but no blooms were reported during
these years. Moreover, a NAO negative phase is observed from 2010 to 2011 when the blooms occurred. So, major climate
variations in the tropical Atlantic cannot directly explain the recent Sargassum blooms. Note that, the analysis of the ITCZ20
position, from 1979 to 2015 did not reveal any abnormal event (or significant abnormalities compared to the climatological
mean) during the years of Sargassum bloom (not shown).
The study also addresses the relative importance of nutrients for Sargassum natans and Sargassum fluitans growth, principally
nitrate and phosphate as they have been identified as limiting nutrients (Lapointe, 1986, 1995; Smetacek and Zingone, 2013).
Rivers are important sources of nutrients. The Amazon, the Orinoco and the Congo Rivers are the three major rivers of the25
tropical Atlantic. The analysis of the Amazon, Orinoco and Congo Rivers discharges, indicates that the volume of water flowing
is not the dominant control of the changes in the Sargassum natans and the Sargassum fluitans ecosystem. Indeed, the discharge
normalized anomalies are not significant during the first year of Sargassum recent blooms in 2011 and Sargassum maximum
spatial coverage amount in 2015 (Wang et al., 2012). Moreover, there was none bloom that has been reported in 2006, year of
the maximum discharge for the Amazon River, which is the most important river of the world. Nevertheless, it is important to30
notice that the blooms and the mass strandings are generally observed during the ascending and high flow of the Amazon River
(Gower et al., 2013; Wang and Hu, 2016).
One important point to mention from the present study is that a good agreement is found between the continental inputs
of nitrate and phosphate from the Amazon River and the Sargassum blooms. On the contrary, the Congo River nutrients
inputs do not significantly increased during the Sargassum blooms. Thus, our results indicate that the increase of nutrients35
9
Biogeosciences Discuss., https://doi.org/10.5194/bg-2017-346
Manuscript under review for journal Biogeosciences
Discussion started: 20 September 2017
c
Author(s) 2017. CC BY 4.0 License.
may certainly be linked to the deforestation, the increase of sediments and the continental run-off in the Amazon basin ob-
served these last years. Similar conclusions in the NERR region are also suggested by the MERCATOR GREEN outputs
(Fig. 5a,c). The Brazilian government have taken steps to reduce deforestation and its effect (a decelerate trend from 2004
to 2012). But the Amazonian forest deforestation continues and an increase of 29 % in 2015 and 2016 has been reported
by the Brazilian Instituto Nacional de Pesquisas Espaciais (INPE: http://www.inpe.br/noticias/noticia.php?CodNoticia=4344;5
http://www.obt.inpe.br/prodes/index.php). Moreover, note that pollution of groundwater and river water by nitrate and phos-
phate or eutrophication, which is characterized by an excessive development of the seaweed, is a slow process which has a
deferred character. It means that it takes several years for a drop of nitrate to seep into the soil and its way into a river. The
effects of deforestation on the continental nitrate and phosphate inputs can be felt years later (Meyer-Reil and Köster, 2000).
In addition, eutrophication is also made by excessive agroindustrial and urban activities. It is also important to notice that10
Brazil has been found to be the biggest consumer of agrotoxics (fertilizers, pesticides and agricultural fertilizers) in the world,
by the increase of agroindustrial activities (https://alencontre.org/ameriques/amelat/bresil/bresil-oligopolisation-pollution-et-
agriculture.html; refer to Correio da Cidadania dated August 15th 2012). Thereby deforestation, increase of sediments and
increase of agroindustrial activities are in favor of nitrate and phosphate pollution in the Amazon River that may have in-
fluenced the recent Sargassum blooms. Similar conclusions were reached by Sissini et al. (2017). These authors argued that15
a possible explanation for the recent blooms may be linked to warmer SSTs in nutrient-enriched oceans conditions induced
by continental runoff with agroindustrial and urban origin. Thus, positive SST anomalies observed in 2010-2011 could have
induce favorable conditions for Sargassum blooms, then fed by additional nutrients inputs from the Amazon River.
This study also suggests, from very recent numerical results, that the subsurface intake of nutrients in the equatorial up-
welling region could also have contributed in the blooms and the mass strandings of the Sargassum blooms (Fig. 5b) in the20
Atlantic Ocean. However, another datasets need to be analyzed, keeping in mind that there are probably some biases in the
vertical velocity of the MERCATOR GREEN, at the equator that could artificially enhance the potential equatorial upwelling
effect. Finally, Guerreiro et al. (2017) have reported that African dust could have be a fertilizer for marine phytoplankton in
the Atlantic Ocean; further studies are also needed to evaluate the potential impact, even with weaker amount than nutrients,
of the iron and the African dust inputs in the NERR.25
This work highlights and provides new insights about of the effects of the combined warmer SSTs in 2010 and the in-
crease of nitrate and phosphate continental inputs of the Amazon River due to continental run-off generate by deforestation,
agroindustrial and urban source as the one of the main causes of the recent Sargassum blooms in the tropical Atlantic Ocean.
Additional datasets and models outputs have to be analyzed in order to continue this investigation.
Acknowledgements. This study is a part of the physical oceanography component of the French Institut de Recherche pour le Développe-30
ment (IRD/ MEDD) project "Sargasses" and was initiated during a 8 months visit of the 1st author at the Departamento de Oceanografia da
Universidade Federal de Pernambuco (DOCEAN/UFPE) in Recife. It has received funding from the Brazilian National Council for Scientific
and Technological Development (CNPq) and from IRD through the Laboratoire d’Etudes en Géophysique et Océanographie Spatiales (LE-
10
Biogeosciences Discuss., https://doi.org/10.5194/bg-2017-346
Manuscript under review for journal Biogeosciences
Discussion started: 20 September 2017
c
Author(s) 2017. CC BY 4.0 License.
GOS), UMR 5566 CNES/CNRS/IRD/UPS. The first author would like to acknowledge these or-ganizations. M. A., G. H. and C. N. thank the
support of the Brazilian Research Network on Global Climate Change-Rede CLIMA (FINEP grants 01.13.0353-00). Thanks to the authors
of data sets made available in free access. The TropFlux data is produced thanks to a collaboration between Laboratoire d’Océanographie:
Expérimentation et Approches Numériques (LOCEAN) from Institut Pierre Simon Laplace (IPSL, Paris, France) and National Institute of
Oceanography/CSIR (NIO, Goa, India), and supported by the French Institut de Recherche pour le Développement (IRD, France). TropFlux5
relies on data provided by the ECMWF Re-Analysis interim (ERA-I) and ISCCP projects. The authors also acknowledge the Marine Coper-
nicus Service and Dr Fabrice Hernandez for kindly providing the MERCATOR BIOMER data. Thanks are given to Dr Jacques Servain, Dr
Fréderic Ménard and the Mediterranean Institute of Oceanography (MIO) team and also to Dr Pierrick Penven for constructive discussions
during this work. This paper also represents a contribution to Project Pólo de Interação para o Desenvolvimento de Estudos Conjuntos em
Oceanografia do Atlântico Tropical (PILOTE), CNPq-IRD grant 490289/2013-4.10
11
Biogeosciences Discuss., https://doi.org/10.5194/bg-2017-346
Manuscript under review for journal Biogeosciences
Discussion started: 20 September 2017
c
Author(s) 2017. CC BY 4.0 License.
References
Ang, P. O.: Phenology of Sargassum spp. in Tung Ping Chau Marine Park, Hong Kong SAR, China, J. Appl. Phycol., 18, 403–410, 2006.
Araujo, M., Noriega, C., and Lefèvre, N.: Nutrients and carbon fluxes in the estuaries of major rivers flowing into the tropical Atlantic, Front.
Mar. Sci., 1:10, https://doi.org/10.3389/fmars.2014.00010, 2014.
Aumont, O. and Bopp, L.: Globalizing results from Ocean in situ iron fertilization studies, Glob. Biogeochem. Cycles, 20, 2006.5
Burls, N. J., Reason, C. J. C., Penven, P., and Philander, S. G.: Similarities between the tropical Atlantic seasonal cycle and ENSO: An
energetics perspective, J. Geophys. Res., 116, C11010, https://doi.org/10.1029/2011JC007164, 2011.
Butler, J. N. and Stoner, A. W.: Pelagic Sargassum: has its biomass changed in the last 50 years ? , Deep Sea Research, 31, 1259–1264,
https://doi.org/10.1016/0198-0149(84)90061-X, 1984.
Butler, J. N., Morris, B. F., Cadwallader, J., and Stoner, A. W.: Studies of Sargassum and the Sargassum community, 307 pp, Bermuda10
Biological Station Special Publication 22, 1983.
Carpente, R. C., Hackney, J. M., and Adey, W. H.: Measurements of primary productivity and nitrogenase activity of coral reef algae in a
chamber incorporating oscillatory flow, Limnol. Oceanogr., 36, 40–49, 1991.
Chiang, J. C. H. and Vimont, D. J.: Analogous meridional modes of atmosphere-ocean variability in the tropical Pacific and tropical Atlantic,
J. Climate, 17, 4143–4158, 2004.15
Chin, M., Diehl, T., Tan, Q., Prospero, J. M., Kahn, R. A., Remer, L. A., Yu, H., Sayer, A. M., Bian, H., Geogdzhayev, I. V., Holben, B. N.,
Howell, S. G., Huebert, B. J., Hsu, N. C., Kim, D., Kucsera, T. L., Levy, R. C., Mishchenko, M. I., Pan, X., Quinn, P. K., Schuster,
G. L., Streets, D. G., Strode, S. A., Torres, O., and Zhao, X.-P.: Multi-decadal aerosol variations from 1980 to 2009: a perspective from
observations and a global model, Atmos. Chem. Phys, 14, 3657–3690, https://doi.org/10.5194/acp-14-3657-2014, 2014.
Dai, A., Qian, T., Trenberth, K. E., and Milliman, J. D.: Changes in continental freshwater discharge from 1948-2004, J. Climate, 22,20
2773–2791, 2009.
Endo, H., Suehiro, K., Kinoshita, J., Gao, X., and Agatsuma, Y.: Combined Effects of Temperature and Nutrient Availability on Growth and
Phlorotannin Concentration of the Brown Alga Sargassum patens (Fucales; Phaeophyceae), American Journal of Plant Sciences, 4, 14–20,
https://doi.org/10.4236/ajps.2013.412A2002, http://www.scirp.org/journal/ajps, 2013.
Evan, A. T., Flamant, C., Gaetani, M., and Guichard, F.: The past, present and future of African dust, Nature,25
https://doi.org/10.1038/nature17149, 2016.
Foltz, G. R., McPhaden, M. J., and Lumpkin, R.: A strong Atlantic Merional Mode event in 2009: The role of mixed layer dynamics, J.
Climate, 25, 363–380, https://doi.org/10.1175/JCLI-D-11-00150.1, 2012.
Franks, J., Johnson, D., and Ko, D.-S.: Pelagic Sargassum; Retention and growth of pelagic sargassum in the North Equatorial Convergence
Region of the Atlantic Ocean: hypothesis for examining recent mass strandings of sargassum along Caribbean and West Africa coast, in:30
Gulf and Caribbean Fisheries Institute Caribbean Sargassum, 2014.
Gao, G. and McKGao, K. R.: Use of macroalgae for marine biomass production and CO2 remediation: a review, J. Appl. Phycol., 6, 45–60,
1994.
Gao, K.: Effects of seawater current speed on the photosynthetic oxygen evolution of Sargassum thunbergii (Phaeophyta), Jpn. J. Phycol.,
39, 291–293 (Japanese, with English summary)., 1991.35
Gao, K. and Nakahara, H.: Effects of nutrients on the photosynthesis of Sargassum thunbergii, Bot. Mar., 33, 375–383, 1990.
12
Biogeosciences Discuss., https://doi.org/10.5194/bg-2017-346
Manuscript under review for journal Biogeosciences
Discussion started: 20 September 2017
c
Author(s) 2017. CC BY 4.0 License.
Gellenbeck, K. and Chapman, D.: Feasibility of mariculture of the brown seaweed, Sargassum muticum (Phaeo- phyta): Growth and culture
conditions, culture methods, alginic acid content and conversion to methane, In Barclay WR, 1986.
Goes, J. I., Gomes, H. d. R., Chekalyuk, A. M., Carpenter, E. J., Montoya, J. P., Coles, V. J., Yager, P. L., Berelson, W. M., Capone, D. G.,
Foster, R. A., Steinberg, D. K., Subramaniam, A., and Hafez, M. A.: Influence of the Amazon River discharge on the biogeography of
phytoplankton communities in the western tropical north Atlantic, Progress in Oceanography, 120, 29–40, http://www.sciencedirect.com/5
science/article/pii/S0079661113001237, 2014.
Gower, J. and King, S.: Distribution of floating Sargassum in the Gulf of Mexico and the Atlantic Ocean mapped using MERIS, International
Journal of Remote Sensing, 32, 1917–1929, 2011.
Gower, J., Hu, C., Borstad, G., and King, S.: Ocean color satellites show extensive lines of floating Sargassum in the Gulf of Mexico, IEEE
Transactions on Geoscience and Remote Sensing, 44, 3619–3625., 44, 3619–3625, 2006.10
Gower, J., Young, E., and King, S.: Satellite images suggest a new Sargassum source region in 2011, Remote Sens Lett, 4:8, 764–773,
http://dx.doi.org/10.1080/2150704X.2013.796433, 2013.
Guerreiro, C. V., Baumann, K.-H., A, G.-J., Brummer, Fischer, G., Korte, L. F., Merkel, U., Sá, C., de Stigter, H., and Stuut, J.-B. W.:
Coccolithophore fluxes in the open tropical North Atlantic: influence of the Amazon river and of Saharan dust deposition, Biogeosciences
Discuss., https://doi.org/10.5194/bg-2017-216, 2017.15
Guimberteau, M., Ciais, P., Ducharne, A., Boisier, J. P., Aguiar, A. P. D., Biemans, H., De Deurwaerder, H., Galbraith, D., Kruijt, B.,
Langerwisch, F., Poveda, G., Rammig, A., Rodriguez, D. A., Tejada, G., Thonicke, K., Von Randow, C., Von Randow, R. C. S., Zhang,
K., and Verbeeck, H.: Impacts of future deforestation and climate change on the hydrology of the Amazon basin: a multi-model analysis
with a new set of land-cover change scenarios, Hydrol. Earth Syst. Sci. Discuss., in review, https://doi.org/10.5194/hess-2016-430, 2016.
Guiry, M. and Guiry, G.: AlgaeBase: world-wide electronic publication, Galway: National University of Ireland. Electronic Database acces-20
sible at http://www.algaebase.org/ . Searched on 10 April 2012., 2011.
Hernandez, F. J.: Sargassum in the northern Gulf of Mexico, http://www.marine.usf.edu/conferences/fio/NSTC-SOST-PI-2011/documents/
LMR/Hernandez_LMR.pdf, 2011.
Hsu, N. C., Gautam, R., Sayer, A. M.and Bettenhausen, C., Li, C., Jeong, M. J., Tsay, S.-C., and Holben, B. N.: Global and regional trends
of aerosol optical depth over land and ocean using SeaWiFS measurements from 1997 to 2010, Atmos. Chem. Phys., 12, 8037–8053,25
https://doi.org/10.5194/acp-12-8037-2012, 2012.
Hu, C., Hardy, R., and Ruder, E., e. a.: Sargassum coverage in the northeastern Gulf of Mexico during 2010 from Land-
sat and airborne observations: Implications for the Deepwater Horizon oil spill, Marine Pollution Bulletin, 107, 15–21,
https://doi.org/10.1016/j.marpolbul.2016.04.045, 2016.
Hurrel, J. W.: The North Atlantic Oscillation: Climatic Significance and Environmental Impact, American Geophysical Union,30
https://doi.org/ISBN 9780875909943, 2003.
Hurrell, J. and for Atmospheric Research Staff (Eds), N. C.: The Climate Data Guide: Hurrell North Atlantic Oscillation (NAO) Index
(station-based), Retrievedfromhttps://climatedataguide.ucar.edu/climate-data/hurrell-north-atlantic-oscillation-nao-index-station-based,
2017.
Johnson, D. R., Ko, D. S., Franks, J. S., Moreno, P., and Sanchez-Rubio, G.: The Sargassum invasion of the Eastern Caribbean and dynamics35
of the Equatorial North Atlantic, in: Proceedings of the 65th Annual Gulf and Caribbean Fisheries Institute Conference, pp. 102–103,
2013.
13
Biogeosciences Discuss., https://doi.org/10.5194/bg-2017-346
Manuscript under review for journal Biogeosciences
Discussion started: 20 September 2017
c
Author(s) 2017. CC BY 4.0 License.
King, W.: Life is Controlled by the Limiting Nutrient, http://web.colby.edu/colbyatsea/2011/02/01/
life-is-controlled-by-the-limiting-nutrient/, 2011.
Lapointe, B. E.: Phosphorus-limited photosynthesis and growth of Sargassum natans and Sargassum fluitans (Phaeophyceae) in the western
North Atlantic, Deep Sea Res., 33, 391–399, 1986.
Lapointe, B. E.: A comparison of nutrient-limited productivity in Sargassum natans from neritic vs. oceanic waters of the western North5
Atlantic Ocean, Limnology and Oceanography, 40(3), 625–633, 1995.
Lefèvre, N., Caniaux, G., Janicot, S., and Gueye, A. K.: Increased CO2outgassing in February–May 2010 in the tropical Atlantic following
the 2009 Pacific El Niño, J.Geophys. Res., 118, 1–13, https://doi.org/10.1002/jgrc.20107, 2013.
Mazéas, F.: Note Sargasses, http://www.guadeloupe.developpement-durable.gouv.fr/IMG/pdf/Note_DEAL_sur_description_et_
explications_des_echouages_Dec2014-MAJ_13aout2015.pdf, 2014.10
McCarthy, G. D., Haigh, I. D., Hirschi, J. J. M., Grist, J. P., and Smeed, D. A.: Ocean impact on decadal Atlantic climate variability revealed
by sea-level observations, Nature, 521, 508–510, https://doi.org/10.1038/nature14491, 2015.
Meybeck, M.: Carbon, nitrogen and phosphorus transport by world rivers, Am. J. Sci., 282, 401–450, https://doi.org/10.2475/ajs.282.4.401,
1982.
Meybeck, M. and Ragu, A.: Presenting the GEMS-GLORI, a compendium of world river discharge to the oceans, Ass. Hydrol. Sci. Publ.,15
243, 3–14, 1997.
Meyer-Reil, L.-A. and Köster, M.: Eutrophication of Marine Waters: Effects on Benthic Microbial Communities, Marine Poll. Bull., 41,
255–263, 2000.
O’Connor, M. I.: Warming Strengthens an Herbivore- Plant Interaction, vol. 90, Ecology, https://doi.org/10.1890/08-0034.1, 2009.
Oxenford, H. A., Franks, J., and Johnson, D.: Facing the threat of Sargassum seaweed, in: Symposium: Challenges, dialogue & cooperation20
towards Sustainability of the Caribbean Sea, 2015.
Oyesiku, O. O. and Egunyomi, A.: Identification and chemical studies of pelagic masses of Sargassum natans (Linnaeus) Gaillon and S.
fluitans (Borgessen) Borgesen (brown algae), found offshore in Ondo State, Nigeria, African Journal of Biotechnology, 13(10), 2014.
Praveen Kumar, B., Vialard, J., Lengaigne, M., Murty, V. S. N., McPhaden, M. J., Cronin, M. F., Pinsard, F., and Reddy, K. G.: TropFlux:
Air-Sea Fluxes for the Global Tropical Oceans-Description and evaluation, Clim. Dyn., 8, 1521–1543, https://doi.org/0.1007/s00382-011-25
1115-0, 2013.
Prospero, J. M., Collard, F.-X., Molinié, J., and Jeannot, A.: Characterizing the annual cycle of African dust transport to the
Caribbean Basin and South America and its impact on the environment and air quality, Global Biogeochem. Cycles, 29, 757–773,
https://doi.org/10.1002/2013GB004802, 2014.
Ridley, D. A., Heald, C. L., and Prospero, J. M.: What controls the recent changes in African mineral dust aerosol across the Atlantic?,30
Atmos. Chem. Phys., 14, 5735–5747, https://doi.org/10.5194/acp-14-5735-2014, www.atmos-chem-phys.net/14/5735/2014/, 2014.
Sankaré, Y., Komoé, K., Aka, K. S., and Fofié, N’guessan Bra Yvette ad Bamba, A.: Répartition et abondance des sargasses Sargassum
natans et Sargassum fluitans (Sargassaceae, Fucales) dans les eaux marines ivoiriennes (Afrique de l’Ouest), Int. J. Biol. Chem. Sci.,
10(4), 1853–1864, 2016.
Scheuvens, D., Schütz, L., Kandler, K., Ebert, M., and Weinbruch, S.: Bulk composition of northern African dust and its source sediments-35
A compilation, Earth-Science Reviews, 116, 170–194, http://www.sciencedirect.com/science/article/pii/S001282521200102X, 2013.
Servain, J., Caniaux, G., Kouadio, Y. K., McPhaden, M. J., and Araujo, M.: Recent climatic trends in the tropical Atlantic, Clim. Dyn., 43,
3071–3089, https://doi.org/10.1007/s00382-014-2168-7, 2014.
14
Biogeosciences Discuss., https://doi.org/10.5194/bg-2017-346
Manuscript under review for journal Biogeosciences
Discussion started: 20 September 2017
c
Author(s) 2017. CC BY 4.0 License.
Sfriso, A. and Facca, C.: Annual growth and environmental relation- ships of the invasive species Sargassum muticum and Undaria pinnatifida
in the lagoon of Venice, Estuar. Coast. Shelf S, 129, 162–172, 2013.
Sissini, M. N., Barreto, M. B. B. D. B., Szèchy, M. T. M., Lucena, M. B. D., Oliveira, M. C., Gower, J., Bastos, G. L. E. D. O., Milstein, D.,
and al.: The floating Sargassum (Phaeophyceae) of the South Atlantic Ocean- likely scenarios, Phycologia, 56 (3), 321–328, 2017.
Smetacek, V. and Zingone, A.: Green and golden seaweed tides on the rise, Nature, 504(7478), 84–88, 2013.5
Smith, S. V., Swaney, D. P., Talaue-McManus, L., Bartley, J. D., Sandhei, P. T., McLaughlin, C. J., and et al.: Humans, hydrology, and the
distribution of inorganic nutrient loading to the Ocean, Bioscience, 53, 235–245, https://doi.org/10.1641/0006-3568(2003)053, 2003.
Swap, R., Garstang, M., Greco, S., Talbot, R., and Kallberg, P.: Saharan dust in the Amazon Basin, Tellus, 44B, 133–149, 1992.
Szèchy, M. T. M., Guedes, P. M., Baeta-Neves, M. H., and Oliveira, E.: Verification of Sargassum natans (Linnaeus) Gaillon (Heterokonto-
phyta: Phaeophyceae) from the Sargasso Sea off the coast of Brazil, western Atlantic Ocean, Check List, 8(4), 638–641, 2012.10
Talling, J.: Temperature Increase–An Uncertain Stimulant of Algal Growth and Primary Production in Fresh Waters, Freshwater Biological
Association, 5(2), :73–84, https://doi.org/10.1608/FRJ-5.2.471, http://www.bioone.org/doi/full/10.1608/FRJ-5.2.471, 2012.
Trenberth, K., Zhang, R., and for Atmospheric Research Staff (Eds), N. C.: The Climate Data Guide: Atlantic Multi-decadal Oscillation
(AMO), Retrievedfromhttps://climatedataguide.ucar.edu/climate-data/atlantic-multi-decadal-oscillation-amo., 2017.
Wang, C., Dong, S., Evan, A. T., Foltz, G. R., and Lee, S.-K.: Multidecadal Covariability of North Atlantic Sea Surface Temperature, African15
Dust, Sahel Rainfall, and Atlantic Hurricanes, 25, https://doi.org/http://dx.doi.org/10.1175/JCLI-D-11-00413.1, 2012.
Wang, M. and Hu, C.: Mapping and quantifying Sargassum distribution and coverage in the Central West Atlantic using MODIS observations,
Remote Sens. Environ., 183, 350–367, http://www.sciencedirect.com/science/article/pii/S0034425716301833, 2016.
Wang, M. and Hu, C.: Predicting Sargassum blooms in the Caribbean Sea from MODIS observations, Geophys. Res. Lett., 44, 3265–3273,
https://doi.org/10.1002/2017GL072932, 2017.20
Xu, Z., Gao, G., Xu, J., and Wu, H.: Physiological response of a golden tide alga (Sargassum muticum) to the interaction of ocean acidification
and phosphorus enrichment, Biogeosciences, 14, 671–681, 2017.
Yu, H. and al.: The fertilizing role of African dust in the Amazon rainforest: A first multiyear assessment based on data from Cloud-Aerosol
Lidar and Infrared Pathfinder Satellite Observations, Geophys. Res. Lett., 42, https://doi.org/10.1002/2015GL06304, 2015.
15
Biogeosciences Discuss., https://doi.org/10.5194/bg-2017-346
Manuscript under review for journal Biogeosciences
Discussion started: 20 September 2017
c
Author(s) 2017. CC BY 4.0 License.
0.0 2 N .m 2
10° S
10° N
20° N
80° W 55°W 30 °W 5°W 20° E
JFM--20 09
0.0 2 N .m 2
10° S
10° N
20° N
80° W 55°W 30 °W 5°W 20° E
AMJ--2009
0.0 2 N .m 2
10° S
10° N
20° N
80° W 55°W 30 °W 5°W 20° E
JAS--20 09
0.0 2 N .m 2
10° S
10° N
20° N
80° W 55°W 30 °W 5°W 20° E
OND--20 09
2009
0.0 2 N .m 2
10° S
10° N
20° N
80° W 55°W 30 °W 5°W 20° E
JFM--20 10
0.0 2 N .m 2
10° S
10° N
20° N
80° W 55°W 30 °W 5°W 20° E
AMJ--2010
0.0 2 N .m 2
10° S
10° N
20° N
80° W 55°W 30 °W 5°W 20° E
JAS--20 10
0.0 2 N .m 2
10° S
10° N
20° N
80° W 55°W 30 °W 5°W 20° E
OND--20 10
2010
0.0 2 N .m 2
10° S
10° N
20° N
80° W 55°W 30 °W 5°W 20° E
JFM--20 11
0.0 2 N .m 2
10° S
10° N
20° N
80° W 55°W 30 °W 5°W 20° E
AMJ--2011
0.0 2 N .m 2
10° S
10° N
20° N
80° W 55°W 30 °W 5°W 20° E
JAS--20 11
0.0 2 N .m 2
10° S
10° N
20° N
80° W 55°W 30 °W 5°W 20° E
OND--20 11
2011
0.0 2 N .m 2
10° S
10° N
20° N
80° W 55°W 30 °W 5°W 20° E
JFM--20 12
0.0 2 N .m 2
10° S
10° N
20° N
80° W 55°W 30 °W 5°W 20° E
AMJ--2012
0.0 2 N .m 2
10° S
10° N
20° N
80° W 55°W 30 °W 5°W 20° E
JAS--20 12
0.0 2 N .m 2
10° S
10° N
20° N
80° W 55°W 30 °W 5°W 20° E
OND--20 12
2012
0.0 2 N .m 2
10° S
10° N
20° N
80° W 55°W 30 °W 5°W 20° E
JFM--20 13
0.0 2 N .m 2
10° S
10° N
20° N
80° W 55°W 30 °W 5°W 20° E
AMJ--2013
0.0 2 N .m 2
10° S
10° N
20° N
80° W 55°W 30 °W 5°W 20° E
JAS--20 13
0.0 2 N .m 2
10° S
10° N
20° N
80° W 55°W 30 °W 5°W 20° E
OND--20 13
2013
0.0 2 N .m 2
10° S
10° N
20° N
80° W 55°W 30 °W 5°W 20° E
JFM--20 14
0.0 2 N .m 2
10° S
10° N
20° N
80° W 55°W 30 °W 5°W 20° E
AMJ--2014
0.0 2 N .m 2
10° S
10° N
20° N
80° W 55°W 30 °W 5°W 20° E
JAS--20 14
0.0 2 N .m 2
10° S
10° N
20° N
80° W 55°W 30 °W 5°W 20° E
OND--20 14
2014
0.0 2 N .m 2
10° S
10° N
20° N
80° W 55°W 30 °W 5°W 20° E
JFM--20 15
0.0 2 N .m 2
10° S
10° N
20° N
80° W 55°W 30 °W 5°W 20° E
AMJ--2015
0.0 2 N .m 2
10° S
10° N
20° N
80° W 55°W 30 °W 5°W 20° E
JAS--20 15
0.0 2 N .m 2
10° S
10° N
20° N
80° W 55°W 30 °W 5°W 20° E
OND--20 15
2015
19 80
19 82
19 84
19 86
19 88
19 90
19 92
19 94
19 96
19 98
20 00
20 02
20 04
20 06
20 08
20 10
20 12
20 14
2.0
1.6
1.2
0.8
0.4
0.0
0.4
0.8
SST anom aly [ C]
Raw sign al
Low -pass signa l
15° S
15° N
60° W 35°W 1 0°W 15° E
NE RR
Figure 1. Upper panel: Spatial distributions of seasonal SST [C] and wind stress direction anomalies [N m2] from 2009 to 2015. The
anomalies are related to the period 1993-2015 (per three months periods). The zero isotherm is represented in gray line. Lower panel:
Interannual SST anomalies [C], from the TropFlux dataset, related to the period 1993 to 2015, in the box NERR [0-10N; 50-10W]
from 1979 to 2015. The black stars represent the years of Sargassum blooms.
16
Biogeosciences Discuss., https://doi.org/10.5194/bg-2017-346
Manuscript under review for journal Biogeosciences
Discussion started: 20 September 2017
c
Author(s) 2017. CC BY 4.0 License.
1950
1954
1958
1962
1966
1970
1974
1978
1982
1986
1990
1994
1998
2002
2006
2010
2014
5
4
3
2
1
0
1
2
3
4
5
NAO i nde x
1950
1954
1958
1962
1966
1970
1974
1978
1982
1986
1990
1994
1998
2002
2006
2010
2014
0.6
0.4
0.2
0.0
0.2
0.4
0.6
AMO i nd ex
1950
1954
1958
1962
1966
1970
1974
1978
1982
1986
1990
1994
1998
2002
2006
2010
2014
8
6
4
2
0
2
4
6
8
10
AMM ind ex [oC]
(a)
(b)
(c)
Figure 2. Climate indices from 1950 to 2016: AMO index average value from March to May (a) [source:https://www.esrl.noaa.gov], NAO
index average value from December to February (b) [source:https://www.esrl.noaa.gov] and AMM index [source: University Wisconsin using
the NCEP SST] (c).
17
Biogeosciences Discuss., https://doi.org/10.5194/bg-2017-346
Manuscript under review for journal Biogeosciences
Discussion started: 20 September 2017
c
Author(s) 2017. CC BY 4.0 License.
Ja n Fev Mar Ap r Ma y Ju n Ju l A ug Sep Oc t No v Dec
0
10
20
30
40
50
Disc harg e [104m3s1]
Low flo w Asce ndin g Hig h fl ow
Am azon Ri ver
Ori noco Rive r
Cong o Rive r
10° S
10° N
20° N
80° W 55°W 30 °W 5°W 20°E
1980
1982
1984
1986
1988
1990
1992
1994
1996
1998
2000
2002
2004
2006
2008
2010
2012
2014
10
0
10
20
30
40
50
Disc harg e [104m3s1]
Max im u m
Am azon Ri ver
Orin oco Ri ver
Cong o Rive r
1989
1991
1993
1995
1997
1999
2001
2003
2005
2007
2009
2011
2013
2015
5
4
3
2
1
0
1
2
3
4
Nor ma lized disc har ge ano m aly
Raw s igna l
+ /- 0 .5*STD 10° S
10° N
20° N
80° W 60°W 4 0°W
(a)
(b)
(c)
Figure 3. Rivers discharge anomalies [m3s1] for Amazon, Orinoco and Congo rivers: interannual (a), climatology (b) and mean seasonal
value (only for the Amazon River, c). The anomalies are related to the period 1993-2015, from HYBAM dataset. The mean seasonal value
during the Sargassum blooms events are represented in red (c). The dotted grey lines depict 50 % of the standard deviation.
18
Biogeosciences Discuss., https://doi.org/10.5194/bg-2017-346
Manuscript under review for journal Biogeosciences
Discussion started: 20 September 2017
c
Author(s) 2017. CC BY 4.0 License.
1980
1982
1984
1986
1988
1990
1992
1994
1996
1998
2000
2002
2004
2006
2008
2010
2012
2014
160
120
80
40
0
40
80
Nit rate flu x [k gmol d 1]
4
3
2
1
0
1
2
3
4
Phosp hate flu x [kgmol d 1]
Nit rat e Phospha te 10°S
10°N
20°N
80°W 60°W 4 0°W
1992
1994
1996
1998
2000
2002
2004
2006
2008
2010
2012
2014
160
120
80
40
0
40
80
Nit rate flu x [k gmol d 1]
4
3
2
1
0
1
2
3
4
Phosp hate flu x [kgmol d 1]
Nit rat e Phospha te 10°S
10°N
20°N
20°W 0 ° 20° E
19 90
19 92
19 94
19 96
19 98
20 00
20 02
20 04
20 06
20 08
20 10
20 12
20 14
80
60
40
20
0
20
40
60
80
Nit rat e flu x an oma ly [ kgmol d 1]
Raw i gnal
+ /- 0 .5*STD 10°S
10°N
20°N
80°W 60°W 4 0°W
19 90
19 92
19 94
19 96
19 98
20 00
20 02
20 04
20 06
20 08
20 10
20 12
20 14
80
60
40
20
0
20
40
60
80
Nit rat e flu x an oma ly [ kgmol d 1]
Raw si gnal
+ /- 0 .5*STD 10°S
10°N
20°N
20°W 0 ° 20° E
(a) (b)
(c) (d)
Figure 4. Continental nutrients load flux anomalies [kg mol d1], related to the period 1993-2015: nitrate and phosphate from the Amazon
River (a) and the Congo River (b); mean seasonal nitrate for the Amazon (c) and for the Congo (d) rivers. The mean seasonal value during
the Sargassum blooms events are represented in brown (c, d).
19
Biogeosciences Discuss., https://doi.org/10.5194/bg-2017-346
Manuscript under review for journal Biogeosciences
Discussion started: 20 September 2017
c
Author(s) 2017. CC BY 4.0 License.
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
2011
2012
2013
2014
2015
1.2
0.8
0.4
0.0
0.4
0.8
1.2
1.6
Nit rate conc ent rati on a noma ly [ umol L 1]
15° S
15° N
60° W 35°W 10 °W 15 °E
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
2011
2012
2013
2014
2015
0.2
0.1
0.0
0.1
0.2
Phosp hate conc ent rati on an oma l [ umol L 1]
15° S
15° N
60° W 35°W 10 °W 15 °E
NER R
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
2011
2012
2013
2014
2015
0.0 3
0.0 2
0.0 1
0.0 0
0.0 1
0.0 2
0.0 3
0.0 4
Mass Concen ra ion of Ch lorop hyl l [mg m 3]
15° S
15° N
60° W 35°W 10 °W 15 °E
NER R
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
2011
2012
2013
2014
2015
0.1
0.0
0.1
Iron con cent rat ion a nom aly [nm ol L 1]
15° S
15° N
60° W 35°W 10 °W 15 °E
NER R
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
2011
2012
2013
2014
2015
1.2
0.8
0.4
0.0
0.4
0.8
1.2
1.6
Nit rate conc ent rati on a noma ly [ umol L 1]
15° S
15° N
60° W 35°W 10 °W 15 °E
NER R
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
2011
2012
2013
2014
2015
0.2
0.1
0.0
0.1
0.2
Phosp hate conc ent rati on an oma l [ umol L 1]
15° S
15° N
60° W 35°W 10 °W 15 °E
(a) (b)
(c) (d)
(e) (f)
Figure 5. Upper and middle panels: Mean seasonal anomalies of nitrate concentration [µmol l1] in the box NERR [0-10N; 50-10W]
(a) and in equatorial upwelling region [2S-2N; 0-20W] (b). Mean seasonal anomalies of phosphate concentration [µmol l1] in the
box NERR (c) and in equatorial upwelling region (d). The nitrate and the phosphate concentration have been average over 100 m(a,c) and
40 mfor (b,d). Lower panels: Mean seasonal anomalies of iron concentration [ηmol l1] in the box NERR (e) and mean seasonal anomalies
of chlorophyll concentration [mg m3] in the box NERR (f) from the Marine Copernicus MERCATOR GREEN products. The iron and
the chlorophyll concentration have been average over 100 min the box NERR (e,f). The mean seasonal value during the Sargassum blooms
events are represented in chocolate (a,b), in orange (c,d) in red (e) and in green (f). The anomalies are related to the period 1998-2014.
20
Biogeosciences Discuss., https://doi.org/10.5194/bg-2017-346
Manuscript under review for journal Biogeosciences
Discussion started: 20 September 2017
c
Author(s) 2017. CC BY 4.0 License.
... They are particularly difficult to manage because the factors driving this over-proliferation of Sargassum are multiple and respond to marine wind patterns, currents, cloud cover and atmospheric pressure, all of which are dynamic and none of which are limited by national boundaries. Researchers are still very much unsure as to what is causing the blooms (Israel et al. 2010;Dreckmann and Sentíes 2013;Djakouré et al. 2017;Hu et al. 2015), and these uncertainties form part of the world risk society and modern reflexivity (Beck 2009). ...
... Oils spills, such as the Deepwater Horizon event in 2010, may also play a role (Powers et al. 2013). Marine winds and currents then move the resulting Sargassum floating mats until they wash up on coasts (Hinds et al 2016;Djakouré et al. 2017). Satellite monitoring systems can accurately predict their movements and provide early warning of the arrival of Sargassum floating mats (Chavez et al. 2020). ...
... The social reality of the blooms is manifest most clearly on coasts in the form of local and regional economic impacts (Adet et al. 2017;Djakouré et al. 2017;Torres 2019), as well as health impacts from the chemical composition and heavy metal content of this biomass (Chavez et al. 2020). Very limited research has been done on the effects coastal Sargassum accumulation has on economies and human health, emphasizing the need for long-term, multidisciplinary studies. ...
Article
Full-text available
When the COVID-19 pandemic reached the Mexican Caribbean in late March 2020, this world-renown tourist destination had already been struggling with Sargassum influxes for 5 years. The nature and magnitude of these two impacts are not directly comparable, but both have contributed to profoundly transforming the region. As extreme COVID-19 containment measures were implemented nationwide, the tourism industry contracted by 98% as over 23 million visitors failed to arrive in 2020 and 400 daily flights stopped landing at Cancun Airport. Sargassum accumulations on Caribbean beaches, and their collection, containment and removal had been a challenging socioeconomic issue in the Caribbean region years before the COVID-19 pandemic shut down the tourist industry. We explore Beck’s concept of a risk society as an approach to these socioenvironmental impacts. We analyze five premises about risk society, combining them with a mainly ethnography methodology involving 61 informants. We present the results in terms of impacts. Using the concept of trajectory based on pandemic event chronology, we review the main stages of the pandemic during the research period (May to July 2020) and how the studied population worked to prevent virus infection and spread. We employ narratives to analyze risk perception both of the Sargassum influx and the pandemic. The discussion highlights the importance of moving beyond nature/society dichotomies and dualisms. In summary, the profound transformations caused by these impacts provide a unique opportunity for the Mexican Caribbean to reconstitute itself in a way that encompasses the world risk society concept, perhaps in a more socially and environmentally resilient incarnation.
... In late spring, the eastward North Equatorial Counter Current (NECC) develops in the approximate zone 5-10°N in the central tropical North Atlantic. The NBC starts to retroflect joining the NECC to form a very efficient re-circulation system in the so-called North Equatorial Recirculation Region (NERR, 0-10°N, 25-50°W) where the largest sargassum biomass peaks are typically observed (Gower et al. 2013;Wang and Hu 2016;Djakoure et al. 2017). Strong re-circulation in this region may act as a nutrient trap in an area where sargassum naturally accumulates within the ITCZ, therefore driving optimal conditions to initiate and sustain a sargassum bloom. ...
... Earlier studies of post-2010 sargassum blooms in the tropical Atlantic suggested that increases in riverine, atmospheric deposition and upwelling nutrient fluxes, and higher temperatures could be all factors contributing to sargassum proliferation in this region (Djakoure et al. 2017;Sissini et al. 2017;Oviatt et al. 2019). However, Wang et al. (2019) found a negative correlation between SST and sargassum blooming, suggesting that cool upwelled nutrient-rich waters were associated with increased sargassum biomass. ...
... Maximum sargassum abundance was found every year post-2011 in and around the NERR peaking in June, except for the non-bloom year of 2013 when very low concentrations were obtained across the whole region and in all seasons. The very strong ocean re-circulation system developing during late spring and summer comprising westward equatorial currents and the NBC which retroflects and joins the NECC (Fig. 4) may transport and potentially trap nutrients within NERR originating from the Amazon outflow and the equatorial upwelling zone (Gower et al. 2013;Wang and Hu 2016;Djakoure et al. 2017). Close to the Amazon River mouth, the equatorial westward flow that transports upwelled nutrients all along the equatorial upwelling zone joins the Amazon River nutrient-rich outflow suggesting increased nutrient transport feeding the central equatorial and tropical North Atlantic. ...
Article
Full-text available
Since 2011, unprecedented pelagic sargassum seaweed blooms have occurred across the tropical North Atlantic, with severe socioeconomic impacts for coastal populations. To investigate the role of physical drivers in post-2010 sargassum blooms in the Central West Atlantic (CWA), conditions are examined across the wider tropical North Atlantic, using ocean and atmospheric re-analyses and satellite-derived datasets. Of particular consequence for the growth and drift of sargassum are patterns and seasonality of winds and currents. Results suggest that in years of exceptionally large sargassum blooms (2015, 2018), the Intertropical Convergence Zone (ITCZ), an area of maximum wind convergence where sargassum naturally accumulates, shifted southward, towards nutrient-rich waters of the Amazon River plume and the equatorial upwelling zone further stimulating sargassum growth. These changes are associated with modes of natural variability in the tropical Atlantic, notably a negative phase of the Atlantic Meridional Mode (AMM) in 2015 and 2018, and a positive phase of the Atlantic Niño in 2018. Negative AMM in these 2 years is also associated with stronger trade winds and enhanced northwest Africa upwelling, probably resulting in stronger southwestward nutrient transport into the eastern part of CWA. Moreover, in contrast with most years, important secondary winter blooms took place in both 2015 and 2018 in the northern part of CWA, associated with excessive wind-driven equatorial upwelling and anomalously strong northwestward nutrient transport.
... Once washed up on beaches, Sargassum decomposes, producing a gas impacting inhabitants' health, tourism and the coastal environment. Scientific researches are conducted to gain an understanding of the evolution of the Sargassum [3,4]. Remote sensing techniques can provide interesting information regarding standing stock forecasts in terms of spatial location, period of occurrence and abundance [5]. ...
Article
Full-text available
The invasive species of brown algae Sargassum gathers in large aggregations in the Caribbean Sea, and has done so especially over the last decade. These aggregations wash up on shores and decompose, leading to many socio-economic issues for the population and the coastal ecosystem. Satellite ocean color data sensors such as Sentinel-3/OLCI can be used to detect the presence of Sargassum and estimate its fractional coverage and biomass. The derivation of Sargassum presence and abundance from satellite ocean color data first requires atmospheric correction; however, the atmospheric correction procedure that is commonly used for oceanic waters needs to be adapted when dealing with the occurrence of Sargassum because the non-zero water reflectance in the near infrared band induced by Sargassum optical signature could lead to Sargassum being wrongly identified as aerosols. In this study, this difficulty is overcome by interpolating aerosol and sunglint reflectance between nearby Sargassum-free pixels. The proposed method relies on the local homogeneity of the aerosol reflectance between Sargassum and Sargassum-free areas. The performance of the adapted atmospheric correction algorithm over Sargassum areas is evaluated. The proposed method is demonstrated to result in more plausible aerosol and sunglint reflectances. A reduction of between 75% and 88% of pixels showing a negative water reflectance above 600 nm were noticed after the correction of the several images.
... In addition, pelagic sargassum carries along associated species that can be exotic to regional ecosystems, which can compromise the local ecological balance (van Tussenbroek et al., 2017;Rodríguez-Martínez et al., 2019). The main hypothesis for these occurrences pertains to regime change in climatic conditions, such as the warming of the ocean surface, changes in marine current patterns, and the nutrient enrichment of oceans (Djakouré et al., 2017a(Djakouré et al., , 2017b. These changes may favor the population increase of sargassum species, displacing these drifting algae to the coastal areas of the Gulf of Mexico, the Caribbean, West Africa, and northern Brazil (Gower et al., 2006;Brooks et al., 2018;Arencibia-Carballo et al., 2020;Louime et al., 2017;Franks et al., 2016;Sissini et al., 2017;J. ...
Article
Pelagic Sargassum, usually found at the Sargasso Sea and the Western portion of the North Atlantic and Gulf of Mexico, has been detected in many new locations through the tropical Atlantic. The huge biomass found from the African coast to the Caribbean was called the Great Atlantic Sargassum Belt and is responsible for the stranding of tons of algae on coastal regions. Despite the environmental, social, and economic impacts, sargassum is a valuable source for multiple uses at the industry, such as alginates, cosmetics, recycled paper and bioplastics, fertilizers, and as raw material for civil construction. This work presents a systematic literature review on the use of algae at the civil construction sector, with a focus on the valorization of the pelagic Sargassum spp. biomass, by identifying the potential applications related to the use of other algal species. The review considered other genera of marine algae and marine angiosperms, resulting in a total of 31 selected articles. The marine grass Posidonia oceanica was the most used species, found in eight published papers, followed by the red alga Kappaphycus alvarezii with four studies. Two articles were available on the use of pelagic Sargassum spp. (S. fluitans and S.natans) for construction materials (adobe and pavement), with potential good results. The literature presented results from the use of marine algae and sea grasses for particleboards, polymeric and cemented composites, adobe, pavement, facades, and roofs. This article provides a state-of-the-art review of algal application in the civil construction sector and points out the main directions for the potentialities on the insertion of the Sargassum spp. biomass into the production chain of the sector.
... In a recent satellite retrospective (2011)(2012)(2013)(2014)(2015)(2016)(2017)(2018), pelagic Sargassum was annually detected in the tropics, stretching across the Great Atlantic Sargassum Belt from West Africa through the Caribbean to the Gulf of Mexico (Wang et al., 2019). To complicate the narrative, pelagic Sargassum rafts observed in the open tropics during a 2017 field expedition (Thibaut, (Djakouré et al., 2017;Johns et al., 2020). If each morphotype hosts a different faunal community and possibly represents different levels of ecological value (Calder, 1995;Govindarajan et al., 2019;Martin et al., 2021), accurate identification of pelagic Sargassum is essential and can be facilitated by genetic differentiation of morphotypes. ...
Article
Sargassum natans and Sargassum fluitans are uniquely holopelagic macroalgae, providing open ocean nursery and foraging habitat for commercially and ecologically important species. Recent basin‐wide changes in pelagic Sargassum diversity and distribution have manifested in proliferation of a previously rare morphotype, Sargassum natans VIII, to rival biomass levels of historically dominant S. natans I and S. fluitans III. Precise genetic identification of these morphotypes can improve accuracy and interpretation of ecological studies as well as clarify evolutionary history and population connectivity. For 139 field samples collected from the subtropical and tropical North Atlantic, three mitochondrial genes (cox3, nad6, and mt16S rRNA) were used to examine genetic divergence among the three common pelagic Sargassum morphotypes. These gene sequences successfully differentiated among morphotypes regardless of geographic origin, confirming in situ morphology‐based identifications. Sargassum natans I and S. natans VIII exhibited divergence consistent with that between the S. natans‐complex and S. fluitans III. Phylogenetic analysis of these samples also indicated evolutionary divergence between Sargassum morphologies. The genetic divergence among morphotypes, compared with benthic Sargassum species, suggested that taxonomic reclassification of the three most common pelagic morphotypes may be warranted.
... Par ailleurs, à l'échelle des Caraïbes, les échouages massifs de sargasses pélagiques qui pourraient également résulter du changement climatique (Franks et al., 2011 ;Djakouré et al., 2017) ...
Thesis
Les herbiers marins constituent des habitats remarquables et diversifiés des eaux côtières des territoires ultramarins français. Une meilleure compréhension de leur état écologique sous l’influence des perturbations multiples auxquels ils sont soumis est nécessaire pour répondre aux enjeux des politiques publiques environnementales s’appliquant à l’échelle de ces territoires. Divers paramètres représentant la plupart des compartiments biologiques, allant de la physiologie des phanérogames marines à l’écosystème ont été testés in situ dans des conditions environnementales contrastées. Ces expérimentations ont permis d’évaluer les relations pressions-état des herbiers de différents territoires dans les trois océans et de sélectionner les descripteurs les plus pertinents selon les principaux objectifs de gestion. Sur la base des données collectées, une première version d’indicateurs intégrés combinant des indicateurs d'alerte précoce et de diagnostic (nutriments et certains métaux traces) et des paramètres de réponse à long terme (densité des plants et recouvrement) adaptés aux échelles de temps de la gestion ont été développés. Une première classification de l’état des herbiers étudiés est ainsi proposée. Ces outils intégrés devraient permettre de renforcer l’efficacité des mesures de gestion, tout en facilitant une mise en oeuvre mutualisée des différentes politiques publiques. L'évaluation de l'état de santé des herbiers marins et de leur environnement est essentielle afin de déployer des mesures de gestion et de préservation appropriées pour améliorer de manière durable l’état et la résilience de cet écosystème menacé.
... Pelagic Sargassum originates in the Great Atlantic Sargassum Belt, a region of the tropical North Atlantic Ocean (8 • -23 • N and 89 • -58 • W) with aerial coverage of approximately 3000 square kilometres (km) [13,14]. At this growth location, the recent phenomena of mass Sargassum proliferation has been inextricably linked to global anthropogenic changes such as global warming, rising ocean temperatures, eutrophication from the Amazon, Orinoco and Congo rivers, and Sahara African dust emissions [15][16][17]. Annually, large quantities of pelagic Sargassum wash ashore in the Caribbean, Gulf of Mexico and West Africa. Peak deposition to the Caribbean of approximately 10,000 wet tonnes per day (t/d) was reported in 2015 [4,18]. ...
Article
Pelagic Sargassum inundation of coastlines across the North Atlantic is an ongoing challenge but presents new opportunities for value-added resource recovery. This study assessed the techno-economic feasibility and environmental impact of utilising these invasive brown seaweed, and food waste as feedstock for energy production and fertiliser recovery in Barbados. The biorefinery concept evaluated was designed with hydrothermal pretreatment (HTP) and anaerobic digestion (AD) technologies. Financial analyses of four varied feedstock and process scenarios (S1-S4) established a linear relationship between profitability and the sale of products (electricity and fertiliser). In all cases, simple sale of power generated to the national grid resulted in a negative cash flow and required the introduction of fertiliser sales to achieve positive cash flows. Moreover, the net loss in the electricity only scenarios exceeded that of the landfill disposal, the present operation employed on the island for Sargassum management. The addition of the solid digestate to the revenue stream increased the profit margin and financial attractiveness of the process. Maximum income generation could be attained through 100% supply of the digestate to international markets. However, this approach provides zero support to local food security. The preferred option involves the 50/50 split utilisation of the solid digestate in local and international agricultural practice. While HTP is energy-intensive technology, the recirculation of waste heat generated by a combined heat and power unit for HTP reduced the input energy demand. It also lowered the potential environmental impact by more than 10-fold, relative to landfill disposal. Recycling of the liquid digestate also reduced the fresh water demand and its associated costs. Despite the promising results, process scale-up and commercialisation remain a main challenge, primarily due to the seasonality and variability of Sargassum seaweed for continuous bioprocessing.
... This study of motile epifauna assemblages occurs during a time of great change in the biomass, distribution, and diversity of pelagic Sargassum throughout the western and tropical North Atlantic (Schell et al. 2015;Wang et al. 2019;Garcia-Sanchez et al. 2020). Preliminary review suggests the cause of recent and unprecedented blooms across the Great Atlantic Sargassum Belt (Wang et al. 2019) may be attributed to warming and excess nutrients (Djakouré et al. 2017), a sentiment supported by modeling studies (Putnam et al. 2018(Putnam et al. , 2020Berline et al. 2020). A persistent (lingering or ongoing) shift in motile epifauna community composition has also been documented though not mechanistically explained (Stoner and Greening 1984;Huffard et al. 2014;this effort). ...
Article
Full-text available
Pelagic Sargassum macroalgal rafts in the North Atlantic support sessile and motile epifauna that attract ecologically and economically important migratory organisms. Three prevalent pelagic Sargassum morphotypes vary in their degree of branching and foliation, and thus have different structural complexities that can influence their respective value as motile epifauna habitat. Sargassum fluitans III and S. natans I have denser foliation, creating a complex habitat; in contrast, S. natans VIII is more open and architecturally simple. In 2015/2016, 373 dip net samples of algae were collected from the Tropical Atlantic, Greater Caribbean, Gulf of Mexico, Gulf Stream, and Sargasso Sea. 20,975 individual motile epifauna from 32 taxa were recorded. Sargassum fluitans III supported higher densities of individuals and greater numbers of taxa than S. natans VIII or S. natans I, a pattern attributed to its more complex architecture and consistent with communities on benthic and floating macroalgae. Most assemblages comprised a few dominant and many rare motile epifauna; when compared to historical studies , dominant motile epifauna had shifted. These findings suggest important differences in ecological value between pelagic Sargassum morphotypes with implications for coastal and pelagic conservation strategies, which warrant consideration given recent shifts in morphotype distribution and recurring pelagic Sargassum inundation events.
Article
The beaches of the Caribbean Islands are regularly affected by the stranding of plant debris (algae, phanerogams, etc.) at the tide mark line, which becomes mixed with sand at the top of the beach, along with deadwood and other waste of anthropogenic origin. This situation has worsened since 2011 as a result of the stranding of sargassum seaweed, which significantly reduces beach access and produces emanations of harmful gases. This is damaging for the Caribbean islands of the Lesser Antilles, since their economies are heavily dependant on tourism. These deposits also play a complex role in the sedimentary dynamics of beaches by favouring the trapping or, alternatively, the re-mobilization of sands. Does this accumulation of drift reinforce the erosion of beaches or, on the contrary, does it contribute to their growth? What are the impacts of the manual or mechanical collection of these drift materials on the sediment budget and dynamics of beaches? In an attempt to address these questions, an in-situ experimental study was carried out on the beaches of the Anse Caffard (Le Diamant) and the Anse au Bois (Sainte-Anne) on Martinique. The pocket beach of the Anse au Bois was divided into three sectors. In the first sector, the drift was completely removed by collection, while a second sector was treated by spreading the stranded debris and a third sector was left in a natural state, without any collection. Topographic and hydrodynamic measurements were carried out on the three sectors to characterize the sedimentary response of the beach according to these three methods of managing the stranded drift. Measurements were also carried out on the Anse Caffard beach, which was managed by mechanical collection. These experiments reveal morphodynamic trends which need to be taken into account in the framework of the management of sargassum seaweed crises.
Article
Full-text available
Coccolithophores are calcifying phytoplankton and major contributors to both the organic and inorganic oceanic carbon pumps. Their export fluxes, species composition and seasonal patterns were determined in two sediment trap moorings in the open equatorial North Atlantic (M4 at 12ºN 49ºW and M2 at 14ºN 37ºW), which collected settling particles synchronously in successive 16-day intervals from October 2012 to November 2013, at 1200 m water depth. The two trap locations show a similar seasonal pattern in total coccolith export fluxes and a predominantly tropical coccolithophore settling assemblage throughout the monitored year. Species fluxes were yearlong dominated by lower photic zone (LPZ) taxa (Florisphaera profunda, Gladiolithus flabellatus), but also included upper photic zone (UPZ) taxa (Umbellosphaera spp., Rhabdosphaera spp., Umbilicosphaera spp., Helicosphaera spp.). The LPZ flora was most abundant during fall 2012, whereas the UPZ flora was more important during summer. In spite of these similarities, the western part of the study area produced persistently higher fluxes, averaging 241x10 7 coccoliths m-2 d-1 (117x10 7 to 423 x10 7 coccoliths m-2 d-1) at station M4, compared to only 66x10 7 coccoliths m-2 d-1 (25x10 7 to 153x10 7 coccoliths m-2 d-1) at station M2. Higher fluxes at M4 were mainly produced by the LPZ species, although most UPZ species also contributed higher fluxes, reflecting enhanced productivity in the western equatorial North Atlantic. In addition, we found two marked flux peaks of the more opportunistic species Gephyrocapsa muellerae and Emiliania huxleyi indicating a fast response to nutrient-enrichment of the UPZ, probably by wind-forced mixing, whereas increased fluxes of G. oceanica and E. huxleyi in October/November 2013 coincided with the occurrence of Amazon River affected surface waters. Since the spring and fall events of 2013 were also 30 accompanied by two dust flux peaks we propose a scenario where atmospheric dust also provided fertilizing nutrients to this area. Enhanced surface buoyancy associated to the river plume indicates that the Amazon acted not only as a nutrient source, but also as a surface density retainer for nutrients supplied from the atmosphere. Still, lower total coccolith fluxes during these events compared to the maxima recorded in November 2012 and July 2013 indicate that transient productivity by opportunistic species was less important than " background " tropical productivity in the equatorial North Atlantic. This study illustrates how two seemingly similar sites in an open-ocean tropical setting actually differ greatly in ecological and oceanographic terms, and provides valuable insights into the processes governing the ecological dynamics and the downward export of coccolithophores in the tropical North Atlantic.
Article
Full-text available
The evolvement of golden tides would be influenced by global change factors, such as ocean acidification and eutrophication, but the related studies are very scarce. In this study, we cultured a golden tide alga, Sargasssum muticum, at two levels of pCO2 (400, 1000 µatm) and phosphate (0.5 µM, 40 µM) conditions to investigate the interactive effects of elevated pCO2 and phosphate on physiological properties of the thalli. The higher pCO2 level and phosphate (P) level alone increased the relative growth rate by 40.82 % and 47.78 %, net photosynthetic rate by 46.34 % and 55.16 %, soluble carbohydrates by 32.78 % and 61.83 % respectively whilst the combination of these two levels did not promote growth or soluble carbohydrates further. The higher levels of pCO2 and P alone also enhanced the nitrate uptake rate by 68.27 % and 35.89 %, nitrate reductase activity by 89.08 % and 39.31 %, and soluble protein by 19.05 % and 15.13 % respectively. The nitrate uptake rate and soluble protein was further enhanced although the nitrate reductase activity was reduced when the higher levels of pCO2 and P worked together. The higher pCO2 level and higher P level alone did not affect the dark respiration rate of thalli but they together increased it by 32.30 % compared to the condition of the lower pCO2 and lower P. The mute effect of the higher level of pCO2 and higher P on growth, soluble carbohydrates, combined with the promoting effect of it on soluble protein and dark respiration, suggests more energy was drawn from carbon assimilation to nitrogen assimilation at the condition of higher pCO2 and higher P, probably to act against the higher pCO2 caused acid-base perturbation via synthesizing H+ transport-related protein. Our results indicate ocean acidification and eutrophication may not boost the gold tides events synergistically although each of them alone has a promoting effect.
Article
Full-text available
The pelagic seaweed found offshore and negatively impacting fishing activity in Ondo State Nigeria, has been identified to be a mixture of Sargassum natans and Sargassum fluitans which presumably floated from the Sagasso Sea of North Atlantic. In a bid to harness the potential uses of the seaweed biomass, the mixed Sargassum species were analyzed for the proximate composition, some minerals and phytochemical constituents using standard methods. The mixed Sargassum species contained 154 mg/100 g% protein, 86.5 mg/100 g ash content, 25.5 mg/100 g fat, 71.5 mg/100 g fibre and 573 mg/100 g carbohydrate. Thus it could be consumed by humans if cleaned. Owing to the small concentration of Nitrogen (6.3 mg/100 g), phosphorus (96.5 mg/100 g) potassium (28 mg/100 g), the percentage ratio of N-P-K (1-10-3) of Sargassum spp. was recommended as fertilizer. The presence of flavonoids, tannins, terpenoids and saponins show that the species can be harnessed for their medicinal potentials. Keywords: Sargassum natans, Sargassum fluitans , brown algae, proximate analysis, phytochemical, fertilizer, Nigeria African Journal of Biotechnology , Vol. 13(10), pp. 1188-1193, 5 March, 2014
Article
Full-text available
In the summer of 2011, a major ‘Sargassum event’ brought large amounts of seaweed onto the beaches of the islands of the eastern Caribbean with significant effects on local tourism. We present satellite observations showing that the event had its origin north of the mouth of the Amazon in an area not previously associated with Sargassum growth. A significant concentration of Sargassum was detected in April, when it was centred at about 7° N latitude and 45° W longitude. By July it had spread to the coast of Africa in the east and to the Lesser Antilles and the Caribbean in the west. We have previously used images from MERIS (Medium Resolution Imaging Spectrometer) and MODIS (Moderate Resolution Imaging Spectroradiometer) to show the value of satellite observations in tracking patterns of Sargassum. For the years 2003–2010, we were able to determine the seasonal distribution over the range of 20°–40° N latitude and 100°–40° W longitude covering the ‘Sargasso Sea’ region of the North Atlantic and the Gulf of Mexico. In 2011, satellite data showed a large shift in the distribution, whose cause is unclear.
Article
Full-text available
Knowledge of the seasonal variability of river discharge and the concentration of nutrients in the estuary waters of large rivers flowing into the tropical Atlantic contributes to a better understanding of the biogeochemical processes that occur in adjacent coastal and ocean systems. The monthly averaged variations of the physical and biogeochemical contributions of the Orinoco, Amazon, São Francisco, Paraíba do Sul (South America), Volta, Niger and Congo (Africa) Rivers are estimated from models or observations. The results indicate that these rivers deliver approximately 0.1 Pg C yr-1 in its dissolved organic (DOC 0.046 Pg C yr-1) and inorganic (DIC 0.053 Pg C yr-1) forms combined. These values represent 27.3% of the global DOC and 13.2% of the global DIC delivered by rivers into the world’s oceans. Estimations of the air-sea CO2 fluxes indicate a slightly higher atmospheric liberation for the African systems compared with the South American estuaries (+10.67 mmol m-2 day-1 and +5.48 mmol m-2 day-1, respectively). During the high river discharge periods, the fluxes remained positive in all of the analyzed systems (average +128 mmol m-2 day-1), except at the mouth of the Orinoco River, which continued to act as a sink for CO2. During the periods of low river discharges, the mean CO2 efflux decreased to +5.29 mmol m-2 day-1. The updated and detailed review presented here contributes to the accurate quantification of CO2 input into the atmosphere and to ongoing studies on the oceanic modeling of biogeochemical cycles in the tropical Atlantic.
Article
Full-text available
Aerosol variations and trends over different land and ocean regions from 1980 to 2009 are analyzed with the Goddard Chemistry Aerosol Radiation and Transport (GOCART) model and observations from multiple satellite sensors and available ground-based networks. Excluding time periods with large volcanic influence, aerosol optical depth (AOD) and surface concentration over polluted land regions generally vary with anthropogenic emissions, but the magnitude of this association can be dampened by the presence of natural aerosols, especially dust. Over the 30-year period in this study, the largest reduction in aerosol levels occurs over Europe, where AOD has decreased by 40–60% on average and surface sulfate concentrations have declined by a factor of up to 3–4. In contrast, East Asia and South Asia show AOD increases, but the relatively high level of dust aerosols in Asia reduces the correlation between AOD and pollutant emission trends. Over major dust source regions, model analysis indicates that the change of dust emissions over the Sahara and Sahel has been predominantly driven by the change of near-surface wind speed, but over Central Asia it has been largely influenced by the change of the surface wetness. The decreasing dust trend in the North African dust outflow region of the tropical North Atlantic and the receptor sites of Barbados and Miami is closely associated with an increase of the sea surface temperature in the North Atlantic. This temperature increase may drive the decrease of the wind velocity over North Africa, which reduces the dust emission, and the increase of precipitation over the tropical North Atlantic, which enhances dust removal during transport. Despite significant trends over some major continental source regions, the model-calculated global annual average AOD shows little change over land and ocean in the past three decades, because opposite trends in different land regions cancel each other out in the global average, and changes over large open oceans are negligible. This highlights the necessity for regional-scale assessment of aerosols and their climate impacts, as global-scale average values can obscure important regional changes.
Article
Recurrent and significant Sargassum beaching events in the Caribbean Sea (CS) have caused serious environmental and economic problems, calling for a long-term prediction capacity of Sargassum blooms. Here we present predictions based on a hindcast of 2000 – 2016 observations from Moderate Resolution Imaging Spectroradiometer (MODIS), which showed Sargassum abundance in the CS and the Central West Atlantic (CWA), as well as connectivity between the two regions with time lags. This information was used to derive bloom and non-bloom probability matrices for each 1o square in the CS for the months of May – August, predicted from bloom conditions in a hotspot region in the CWA in February. A suite of standard statistical measures were used to gauge the prediction accuracy, among which the user's accuracy and kappa statistics showed high fidelity of the probability maps in predicting both blooms and non-blooms in the eastern CS with several months of lead time, with overall accuracy often exceeding 80%. The bloom probability maps from this hindcast analysis will provide early warnings to better study Sargassum blooms and prepare for beaching events near the study region. This approach may also be extendable to many other regions around the world that face similar challenges and opportunities of macroalgal blooms and beaching events.
Article
Sargassum washing ashore on the beaches of the Caribbean Islands since 2011 has caused problems for the local environments, tourism, and economies. Although preliminary results of Sargassum distributions in the nearby oceans have been obtained using measurements from the Medium Resolution Imaging Spectrometer (MERIS), MERIS stopped functioning in 2012, and detecting and quantifying Sargassum distributions still face technical challenges due to ambiguous pixels from clouds, cloud shadows, cloud adjacency effect, and large-scale image gradient. In this paper, a novel approach is developed to detect Sargassum presence and to quantify Sargassum coverage using the Moderate Resolution Imaging Spectroradiometer (MODIS) alternative floating algae index (AFAI), which examines the red-edge reflectance of floating vegetation. This approach includes three basic steps: 1) classification of Sargassum-containing pixels through correction of large-scale gradient, masking clouds and cloud shadows, and removal of ambiguous pixels; 2) linear unmixing of Sargassum-containing pixels; and, 3) statistics of Sargassum area coverage in pre-defined grids at monthly, seasonal, and annual intervals. In the absence of direct field measurements to validate the results, limited observations from the Hyperspectral Imager for the Coastal Ocean (HICO) measurements and numerous local reports support the conclusion that the elevated AFAI signals are due to the presence of Sargassum instead of other floating materials, and various sensitivity analyses are used to quantify the uncertainties in the derived Sargassum area coverage. The approach was applied to MODIS observations between 2000 and 2015 over the Central West Atlantic (CWA) region (0–22°N, 63–38°W) to derive the spatial and temporal distribution patterns as well as the total area coverage of Sargassum. Results indicate that the first widespread Sargassum distribution event occurred in 2011, consistent with previous MERIS findings. Since 2011, only 2013 showed a minimal Sargassum coverage similar to the period of 2000 to 2010; all other years showed significantly more coverage. More alarmingly, the summer months of 2015 showed mean coverage of > 2000 km2, or about 4 times of the summer 2011 coverage and 20 times of the summer 2000 to 2010 coverage. Analysis of several environmental variables provided some hints on the reasons causing the inter-annual changes after 2010, yet further multi-disciplinary research (including in situ measurements) is required to understand such changes and long-term trends in Sargassum coverage.
Article
Using high-resolution airborne measurements and more synoptic coverage of Landsat measurements, we estimated the total Sargassum coverage in the northeastern Gulf of Mexico (NE GOM) during 2010, with the ultimate purpose to infer how much Sargassum might have been in contact with oil from the Deepwater Horizon oil spill. Mean Sargassum coverage during the four quarters of 2010 for the study region was estimated to range from ~ 3148 ± 2355 km2 during January–March to ~ 7584 ± 2532 km2 during July–September (95% confidence intervals) while estimated Sargassum coverage within the integrated oil footprint ranged from 1296 ± 453 km2 (for areas with > 5% thick oil) to 736 ± 257 km2 (for areas with > 10% thick oil). Similar to previous studies on estimating Sargassum coverage, a direct validation of such estimates is impossible given the heterogeneity and scarcity of Sargassum occurrence. Nonetheless, these estimates provide preliminary information to understand relative Sargassum abundance in the NE GOM.