Carbonate fluxes by coccolithophore species between NW Africa and the Caribbean: Implications for the biological carbon pump

Abstract

Coccolithophores are among the most important calcifying pelagic organisms. To assess how coccolithophore species with different coccolith-carbonate mass and distinct ecological resilience to ocean warming will influence the "rain ratio" and the "biological carbon pump", 1 yr of species-specific coccolith-carbonate export fluxes were quantified using sediment traps moored at four sites between NW Africa and the Caribbean (i.e., CB-20 N/21 W, at 1214 m; M1-12 N/23 W, at 1150 m; M2-14 N/37 W, at 1235 m; M4-12 N/49 W, at 1130 m). Highest coccolith-CaCO 3 fluxes at the westernmost site M4, where the nutricline is deepest along the tropical North Atlantic, were dominated by deep-dwelling small-sized coccolith species Florisphaera profunda and Gladiolithus flabellatus. Total coccolith-CaCO 3 fluxes of 371 mg m À2 yr À1 at M4 were followed by 165 mg m À2 yr À1 at the north-easternmost CB, 130 mg m À2 yr À1 at M1, and 114 mg m À2 yr À1 at M2 in between. Coccoliths accounted for nearly half of the total carbonate flux at M4 (45%), much higher compared to 23% at M2 and 15% at M1 and CB. At site M4, highest ratios of coccolith-CaCO 3 to particulate organic carbon fluxes and weak correlations between the carbonate of deep-dwelling species and particulate organic carbon suggest that increasing productivity in the lower photic zone in response to ocean warming might enhance the rain ratio and reduce the coccolithballasting efficiency. The resulting weakened biological carbon pump could, however, be counterbalanced by increasing frequency of Saharan dust outbreaks across the tropical Atlantic, providing mineral ballast as well as nutrients to fuel fast-blooming and ballast-efficient coccolithophore species.

Response of coccolithophore communities to oceanographic and atmospheric processes across the North- and Equatorial Atlantic

“…Recent work based on coccolith species fluxes from four sediment-trap time-series across the tropical North Atlantic report evidence supporting the hypothesis of Saharan dust acting as a fertilizer for marine phytoplankton, including opportunistic coccolithophore species (Guerreiro et al, 2017;Guerreiro et al, 2019). A striking flux increase of POC and of coccolith fluxes by fast-blooming surface-dwelling species E. huxleyi and G. oceanica during times of enhanced dust deposition and Amazon water dispersal was seen promoting a more efficient coccolith-ballasting and resulting in lower rain ratios (Korte et al, 2020;Guerreiro et al, 2021). Whether these species have grown by directly consuming nutrients supplied by dust, or indirectly by consuming N 2 released from duststimulated N 2 -fixation, and whether these events mostly reflected an ecological response and/or a higher export efficiency due to dustand coccolith-ballasting (see Pabortsava et al, 2017), remain as open questions.…”

“…Our observations provide a snapshot perception on the importance of coccolithophore productivity in typical gyre conditions, considered as a modern analog for future productivity in the context of an increasingly stratified upper ocean. While this provides good perspectives for their survival in the face of ocean warming, a growing use of mixotrophy in detriment of autotrophy could significantly alter the role of coccolithophore communities in the organic and inorganic carbon pumps, with implications for both O 2 production and atmospheric CO 2 sequestration (e.g., Hutchins, 2011;Guerreiro et al, 2019;Godrijan et al, 2020;Guerreiro et al, 2021).…”

“…According to this study, fluxes produced by these species in this highly stratified region were almost as high as those produced in the mesotrophic region off the coast of Mauritania for the same period. The resulting striking flux increase of POC and coccoliths was seen promoting a more efficient coccolith-ballasting and resulting in lower rain ratios (Korte et al, 2020;Guerreiro et al, 2021).…”

“…Among the main groups of marine phytoplankton, coccolithophores are the main primary producers able to biomineralize calcite platelets (coccoliths) around their cell surface to form an exoskeleton (coccosphere) (Pienaar, 1994;Monteiro et al, 2016) through a biogeochemical process that incorporates carbon in calcite and releases CO 2 into the environment (Rost and Riebesell, 2004). This means that coccolithophores influence the carbon cycle both via photosynthesis (while producing POC -CO 2 sink); via calcification (while producing particulate inorganic carbon, PIC -CO 2 source); and via carbon-burial in oceanic sediments through coccolith-ballasting POC (Rost and Riebesell, 2004;Ziveri et al, 2007;Guerreiro et al, 2021). Hence, coccolithophores contribute crucially to modulate biogenic PIC/POC export from the surface down to the deep ocean (also termed "rain ratio"), which is largely what determines the efficiency of the biological carbon pump in sequestering atmospheric CO 2 (Rost and Riebesell, 2004;Cermeño et al, 2008).…”

Variação sazonal da composição taxonômica e natureza biogênica do fluxo vertical de material particulado na plataforma externa da Região Sudeste do Brasil

“…Cocolitoforídeos são um importante grupo fitoplanctônico, responsáveis por uma intensa produção primária e exportação de CaCO 3 e MOP (Thierstein e Yung, 2013;Guerreiro et al, 2021). A correlação entre os fluxos de CaCO 3 e os fluxos estruturas carbonáticas (dinoflagelados calcários e foraminíferos) não descrevem a variação de CaCO 3 calculada por Tura et al (2021), uma lacuna provavelmente deixada pela ausência de dados sobre o fluxo de cocolitoforídeos.…”