Long-Term Changes of Particle Flux in the Canary Basin Between 1991 and 2009 and Comparison to Sediment Trap Records Off Mauritania

Abstract

Eastern Boundary Upwelling Ecosystems (EBUEs) are associated with high biological productivity, high fish catch and they highly contribute to marine carbon sequestration. Whether coastal upwelling has intensified or weakened under climate change in the past decades is controversially discussed and different approaches (e.g., timeseries of chlorophyll, wind, sea surface temperature, modeling experiments) have been considered. We present a record of almost two decades of particle fluxes (1991-2009) from ca. 600 to 3100 m water depth in the Canary Basin at site ESTOC (European Station for Time series in the Ocean Canary Islands; ca. 29 • N, 15 • 30.W, ca. 3600 m water depth), located in the offshore transition zone of the northern Canary Current-EBUE. We compare these flux records with those measured at a mesotrophic sediment trap site further south off Cape Blanc (Mauritania, ca. 21 • N). The deep ocean fluxes at ESTOC in ca. 3 km recorded the evolution of the coastal Cape Ghir filament (30-32 • N, 10-12 • W) due to lateral advection of particles, whereas the upper water column sediment traps in ca. 1 km reflected the oligotrophic conditions in the overlying waters of ESTOC. We observed an increased emphasis in springtime fluxes since 2005, associated with a change in particle composition, while satellite chlorophyll biomass did not show this pattern. Due to its northern location in the CC-EBUEs, spring biogenic fluxes at ESTOC provide a better relationship to the forcing of the North Atlantic Oscillation than those recorded further south off Cape Blanc. Off Cape Blanc, deep fluxes showed the best overlap with the deep ESTOC fluxes during the spring season before 2005. On the long-term, both chlorophyll and particle fluxes showed an increasing trend at ESTOC which was not observed further south at the mesotrophic Cape Blanc site. This might indicate that, depending on their location along the NW African margin, coastal upwelling systems react differently to global change.

Surface productivity gradients govern changes in abundance and physiological status of deep ocean prokaryotes across the tropical and subtropical Atlantic

“…Based on results obtained during the same cruise, Gómez-Letona et al (submitted) reported intense fluorescence signals of labile, protein-like dissolved organic matter at stations 8, 9, 11 and 12 for the entire water column. These findings suggest a remarkable vertical transport of organic matter from the surface into the dark ocean in the Guinea Dome-Cape Blanc region, in agreement with previous studies with sediment traps reporting high sinking particle fluxes (Fischer et al 2020).…”

“…Besides the vertical variability, latitudinal gradients were observed in the deep ocean, matching surface productivity gradients, as defined by Chl-a concentrations. The tendency to more abundant, more viable and smaller cells in the mesopelagic and bathypelagic layers under highly productive surface waters with potentially important vertical flux of particles (Fischer et al 2020) suggests a remarkable effect of sinking particles in the prokaryotic communities of the dark ocean. In particular, such relationship between surface productivity and prokaryotic viability in deep waters has not been previously reported to the authors’ knowledge.…”

“…Moreover, it presents a strong surface productivity gradient, comprising both oligotrophic waters and areas directly under the influence of the Northwest African upwelling system, where high export rates of sinking particles have been reported (Fischer et al 2020). We determined the abundance and viability of prokaryotic communities, estimated their biomass, and measured leucine incorporation rates, to assess whether these variables were affected by changes in surface productivity, evaluating the degree to which deep prokaryotic communities were linked to epipelagic waters.…”

“…In the present study, we analyse quantitative and qualitative cytometric signatures and heterotrophic activity estimates of prokaryotic communities along a section crossing the tropical and subtropical Atlantic Ocean, both in the epipelagic layer (0-200 m) and in the deep ocean, down to 3500 m. The studied region is complex, with a considerable number of currents (Brandt et al 2008) and water masses (Pérez et al 2001; Álvarez et al 2014). Moreover, it presents a strong surface productivity gradient, comprising both oligotrophic waters and areas directly under the influence of the Northwest African upwelling system, where high export rates of sinking particles have been reported (Fischer et al 2020). We determined the abundance and viability of prokaryotic communities, estimated their biomass, and measured leucine incorporation rates, to assess whether these variables were affected by changes in surface productivity, evaluating the degree to which deep prokaryotic communities were linked to epipelagic waters.…”

Effects of typical artificial reefs on hydrodynamic characteristics and carbon sequestration potential in the offshore of Juehua Island, Bohai Sea

“…The coastal upwelling currents also affect the transport of particulate carbon. Fischer et al (2020) found a similar result, despite significant differences observed in different regions, the particulate carbon flux usually increased in springs since 2005. Phytoplankton under seawater was also found to have carbon sequestration potential, and estimates of the subscale rates of ascidians, ctenophores, ascidians, and pteropods show that their carbon sequestration capacity cannot be ignored and should be included in the carbon sink quantification model (Lebrato et al, 2013).…”