Temporal Relationships Between African Dust and Chlorophyll-α in the
Eastern Caribbean Basin
Abstract
Seasonal African Dust (AD) transports soluble iron to oligotrophic
Caribbean waters, and when bioavailable, it could increase marine
primary productivity (PP). Recently, the region has experienced the
proliferation of unusually high quantities of Sargassum, an
iron-absorbing macroalgae inhabiting the air-sea interface, which
possess ecological and economic challenges and whose driving factors are
still uncertain. AD events reach Puerto Rico (PR) mostly during boreal
summer months. This is also the season when chlorophyll-α (CHL)
concentrations are highest, when the algae starts to bloom, and when
sediment plumes from the Orinoco River (ORP), also reach nutrient
discharge maxima. This study seeks to better understand the temporal
relationships between increases in chlorophyll-α (CHL) and the presence
of AD events in the region. Aerosol data collected at the Cabezas de San
Juan Atmospheric Observatory was used to identify AD events between
January 2005 and December 2015. Light scattering coefficients were
measured with a integrating Nephelometer, while light absorption
coefficients were obtained from either the Particle Soot/Absorption
Photometer (PSAP) or the Continuous Light Absorption Photometer (CLAP).
Spectral properties suggesting AD events were cross-referenced with
surface dust concentration image models and source-attributed air masses
corresponding to dusty periods using Hybrid Single-Particle Lagrangian
Integrated Trajectories (HYSPLIT). For all years with spectral data,
modeled monthly wet dust deposition was correlated (R= 0.64) with mean
CHL concentrations from NASA’s Moderate Resolution Imaging
Spectroradiometer (MODIS). Daily dust mass column densities from NASA’s
MERRA-2 model were also correlated (R^2= 0.53) to sea surface iron
concentrations from NASA’s Ocean Biogeochemical Model. We present the
2010 case study, which coincides with the start of the Sargassum bloom
and shows CHL peaks occurring a month before ORPs but during the AD
season, suggesting the AD role in enhancing PP. Other possible
influencing climatic and oceanographic variables could be associated to
these observations. Further efforts include spatially linking the
Floating Algae Index in satellite imagery to AD concentrations, to
better predict harmful algal blooms and inform management.