Present-day Patagonian dust emissions: Mass flux constraints, meteorological triggers and the effect on phytoplankton biomass

NICOLAS COSENTINO; DIEGO GAIERO; LAURA A. RUIZ ETCHEVERRY; FABRICE LAMBERT; GONZALO BIA ; LUCIO SIMONELLA; RENATA COPPO; GABRIELA TORRE; MARTIN SARACENO; VERONICA TUR

Congreso; EGU General Assembly 2021; 2021

Copernicus Meetings

The magnitude of the climatic forcing associated with mineral dust aerosols remains uncertaindue in part to a lack of direct observations on dust source areas. While modeling and satellitestudies provide spatially extensive constraints, these studies must be supported by surfacevalidating,in situ dust monitoring. Our study focuses on Patagonia, the main source of dust to thesouthern oceans (>45ºS), a region of low biological productivity potentially susceptible to increasedmicronutrient fertilization through dust deposition and associated atmosphere‐to‐ocean CO2flux. This mechanism is hypothesized to have contributed significantly to the lastinterglacial‐to‐glacial climatic transition. However, the dust‐phytoplankton biomass connectionremains contentious for the present‐day climate system.We analysed multi-year time series of surface dust-related visibility reduction (DRVR) and dustmass sampling at four downwind coastal monitoring sites, along with key meteorological timeseries at these same sites. We find that local DRVR across Patagonia is partly controlled by longtermwater deficit (i.e., months), while same-day conditions play a smaller role, reflective of waterretention properties of fine-grained dust-emitting soils in low-moisture conditions. This conclusionis supported independently by reanalysis data showing that large-scale dust outbreaks are usuallyassociated with anomalously high long-term water deficit. By combining visibility data with surfacedust sampling we were able to derive emission rates associated with regional patches of dustemittingsurfaces and test the skill of dust emission schemes to simulate dust activity close to thesources. Our results suggest that the inclusion of long-term hydrologic soil balance may improvethe performance of dust emission schemes in climate models.We also analyzed the impact of southernmost Patagonian dust emissions on southwesternAtlantic Ocean continental shelf and proximal open ocean satellite chlorophyll‐a concentration.We used the DRVR and mass flux time series of the southernmost site to model dust emission,transport, and deposition to the ocean. We then performed a dust event‐based analysis ofchlorophyll‐a time series, using a novel approach by which time series are corrected forpost‐depositional particle advection due to ocean currents. Finally, we performed chemicalanalysis of iron in dust samples, a key micronutrient limiting phytoplankton biomass inhigh‐nutrient, low‐chlorophyll oceans such as offshore of the 200‐m isobath off Patagonia. Wefind no compelling evidence for an influence of dust as an enhancer of phytoplankton biomasseither on shelf or proximal open ocean waters of the southwestern Atlantic Ocean. For openocean waters this is consistent with a lack of source‐inherited bioavailable iron in dust samples.Future case studies addressing similar questions should concentrate on dust sources withidentified high contents of bioavailable iron, particularly in the Southern Hemisphere whereatmospheric processing of iron is weak.