A 2-decade (1988–2009) record of diatom fluxes in the Mauritanian coastal upwelling: impact of low-frequency forcing and a two-step shift in the species composition

Abstract

Abstract. Eastern boundary upwelling ecosystems (EBUEs) are among the most productive marine regions in the world's oceans. Understanding the degree of interannual to decadal variability in the Mauritania upwelling system is crucial for the prediction of future changes of primary productivity and carbon sequestration in the Canary Current EBUE as well as in similar environments. A multiyear sediment trap experiment was conducted at the mooring site CBmeso (“Cape Blanc mesotrophic”, ca. 20∘ N, ca. 20∘40′ W) in the highly productive coastal waters off Mauritania. Here, we present results on fluxes of diatoms and the species-specific composition of the assemblage for the time interval between March 1988 and June 2009. The temporal dynamics of diatom populations allows the proposal of three main intervals: (i) early 1988–late 1996, (ii) 1997–1999, and (iii) early 2002–mid 2009. The Atlantic Multidecadal Oscillation (AMO) appears to be an important driver of the long-term dynamics of diatom population. The long-term AMO-driven trend is interrupted by the occurrence of the strong 1997 El Niño–Southern Oscillation (ENSO). The extraordinary shift in the relative abundance of benthic diatoms in May 2002 suggests the strengthening of offshore advective transport within the uppermost layer of filament waters and in the subsurface and in deeper and bottom-near layers. It is hypothesized that the dominance of benthic diatoms was the response of the diatom community to the intensification of the slope and shelf poleward undercurrents. This dominance followed the intensification of the warm phase of AMO and the associated changes of the Atlantic Meridional Overturning Circulation. Transported valves (siliceous remains) from shallow Mauritanian coastal waters into the bathypelagic should be considered for the calculation and model experiments of bathy- and pelagic nutrients budgets (especially Si), the burial of diatoms, and the paleoenvironmental signal preserved in downcore sediments. Additionally, our 1988–2009 data set contributes to the characterization of the impact of low-frequency climate forcings in the northeastern Atlantic and will be especially helpful for establishing the scientific basis for forecasting and modeling future states of the Canary Current EBUE and its decadal changes.

Seasonal flux patterns and carbon transport from low-oxygen eddies at the Cape Verde Ocean Observatory: lessons learned from a time series sediment trap study (2009–2016)

“…These species are assumed to be transported from the west African coast to CVOO within eddies (Karstensen et al, 2015). The same benthic species have also been found offshore Cap Blanc (Mauritania) at the sediment trap mooring sites CBeu (Romero et al, 2020) and CBmeso (Romero et al, 2021). Their occurrence in the sediment trap samples in the hemipelagic points to lateral transport within the eddy from the inner shelf (<50 m) of the African coast to CVOO.…”

Orbital and Suborbital‐Scale Variations of Productivity and Sea Surface Conditions in the Gulf of Alaska During the Past 54,000 Years: Impact of Iron Fertilization by Icebergs and Meltwater

“…Spores of Chaetoceros and T. nitzschioides var. nitzschioides are common components of the upwelling assemblage in low‐ and high‐latitude coastal areas (Nave et al., 2001; Ren et al., 2014; Romero & Armand, 2010; Romero et al., 2021)…”

“…nitzschioides are common components of the upwelling assemblage in low‐ and high‐latitude coastal areas (Nave et al., 2001; Ren et al., 2014; Romero & Armand, 2010; Romero et al., 2021) Diatoms occurring in pelagic cold waters, which today mainly respond to low‐to‐moderate dissolved silica content in hemi‐to‐pelagial waters of moderate to low SST (Barron et al., 2009; Hasle & Syvertsen, 1996; Ren et al., 2014; Sancetta, 1981). Neodenticula seminae and Thalassiosira nordenskioldii contributed the most to this group at Site U1419 The assemblage typical of pelagic temperate waters was composed of taxa, which today thrive in open‐ocean temperate waters, with low to moderate levels of dissolved silica levels and weak mixing (Crosta et al., 2012; Nave et al., 2001; Ren et al., 2014; Romero et al., 2005, 2021). At Site U1419, this group was dominated by Roperia tesselata and Stephanopyxis spp…”

“…Spores of Chaetoceros and T. nitzschioides var. nitzschioides are common components of the upwelling assemblage in low-and high-latitude coastal areas (Nave et al, 2001;Ren et al, 2014;Romero & Armand, 2010;Romero et al, 2021) 5. Diatoms occurring in pelagic cold waters, which today mainly respond to low-to-moderate dissolved silica content in hemi-to-pelagial waters of moderate to low SST (Barron et al, 2009;Hasle & Syvertsen, 1996;Ren et al, 2014;Sancetta, 1981).…”

“…Neodenticula seminae and Thalassiosira nordenskioldii contributed the most to this group at Site U1419 6. The assemblage typical of pelagic temperate waters was composed of taxa, which today thrive in open-ocean temperate waters, with low to moderate levels of dissolved silica levels and weak mixing (Crosta et al, 2012;Nave et al, 2001;Ren et al, 2014;Romero et al, 2005Romero et al, , 2021. At Site U1419, this group was dominated by Roperia tesselata and Stephanopyxis spp…”