Coccolithophore fluxes in the open tropical North Atlantic: influence of thermocline depth, Amazon water, and Saharan dust

Abstract

Abstract. Coccolithophores are calcifying phytoplankton and major contributors to both the organic and inorganic oceanic carbon pumps. Their export fluxes, species composition, and seasonal patterns were determined in two sediment trap moorings (M4 at 12 • N, 49 • W and M2 at 14 • N, 37 • W) collecting settling particles synchronously from October 2012 to November 2013 at 1200 m of water depth in the open equatorial North Atlantic.The two trap locations showed a similar seasonal pattern in total coccolith export fluxes and a predominantly tropical coccolithophore settling assemblage. Species fluxes were dominated throughout the year by lower photic zone (LPZ) taxa (Florisphaera profunda, Gladiolithus flabellatus) but also included upper photic zone (UPZ) taxa (Umbellosphaera spp., Rhabdosphaera spp., Umbilicosphaera spp., Helicosphaera spp.). The LPZ flora was most abundant during fall 2012, whereas the UPZ flora was more important during summer. In spite of these similarities, the western part of the study area produced persistently higher fluxes, averaging 241 × 10 7 ± 76 × 10 7 coccoliths m −2 d −1 at station M4 compared to only 66 × 10 7

Flux variability of phyto- and zooplankton communities in the Mauritanian coastal upwelling between 2003 and 2008

“…In this ecosystem, several long-term continuous sediment-trap-based monitoring records are available since the late 1980s. Until now, stud-ies monitoring variability of this seasonally dynamic ecosystem mostly focused on the variability of bulk fluxes (Fischer et al, 1996(Fischer et al, , 2016(Fischer et al, , 2019Bory et al, 2001;Marcello et al, 2011;Skonieczny et al, 2013), particular groups of microorganisms (Lange et al, 1998;Romero et al, 1999Romero et al, , 2002Romero et al, , 2003Köbrich and Baumann, 2008;Romero and Armand, 2010;Zonneveld et al, 2010;Köbrich et al, 2016;Romero and Fischer, 2017;Guerreiro et al, 2019) or seasurface temperature (Müller and Fischer, 2001;Mollenhauer et al, 2015). However, the simultaneous comparison of the seasonal and interannual dynamics of several phyto-and zooplankton communities by means of multiyear sediment trap experiments has not been performed in this region and is rare in other EBUEs or other ocean areas as well (Bringué et al, 2019).…”

Two Production Stages of Coccolithophores in Winter as Revealed by Sediment Traps in the Northern South China Sea

“…During this period, the relative abundance of F. profunda may have been as low as 20% in the western Pacific (Jin et al, ), and the primary productivity may have been as large as 161–237 gC·m −2 year −1 , based on the transfer functions in the equatorial Indian Ocean and SCS (Beaufort et al, ; Zhang et al, ) being approximately 50–120% higher than the oligotrophic modern western Pacific. Such a high phytoplankton productivity required a large quantity of nutrient inventory at the ocean's surface, which may have been fueled by a long‐term enhanced aeolian dust deposition (Guerreiro et al, ), weathering (Rickaby et al, ), terrestrial inputs (Flores et al, ), and a shallowing of the thermocline (mixed layer depth) and nutricline. However, no such evidence was reported to support these ideas from a global perspective or at least in the western Pacific.…”

Effects of dry and wet Saharan dust deposition in the tropical North Atlantic Ocean

“…Bonnet et al (2005) and Blain et al (2004) showed that Saharan dust from the Hoggar regions in southern Algeria is a 25 potential source of bioavailable Fe that stimulates mainly the picophytoplankton (< 2 µm) in the Mediterranean Sea and diatoms in the northeast Atlantic Ocean. Observed under natural conditions, Guerreiro et al (2017) reported a flux increase of opportunistic coccolithophore species during the fall 2013 in the western tropical North Atlantic in combination with a wet dust deposition event, suggesting that calcifying phytoplankton also benefited from Saharan dust-born nutrients in this region.…”

“…Saharan dust deposition has been shown to have a great impact in the biogeochemical cycling of oceanic waters underneath the most prominent dust plumes blown towards the Mediterranean Sea (Bonnet et al, 2005;Romero et al, 2011;Desboeufs et al, 2014;Guieu et al, 2014a;Ridame et al, 2014) and towards the tropical North Atlantic Ocean (Jickells, 1999;Baker et al, 2003;Mills et al, 2004;Bristow et al, 2010). Both fertilization (Jickells et al, 2005;Pabortsava et al, 2017;Guerreiro et al, 2017) and ballasting of marine snow aggregates (Van der Jagt 10 et al, 2018) from dust deposition impact the carbon dioxide content of surface waters. Mesocosm experiments in the Mediterranean Sea revealed that dust predominates the particulate phase that is exported to the base of the mesocosms (Desboeufs et al, 2014) and that up to 50 % of the particulate organic carbon flux (POC) can be associated with lithogenic dust particles (Bressac et al, 2014).…”

“…Ocean is low (Sohm et al, 2011) as strong vertical water stratification reduces the introduction of nutrients from the deep into the upper mixed layer. Furthermore, as the nutricline deepens westward across the tropical North Atlantic (Guerreiro et al, 2017), phytoplankton production in the upper layers of the open ocean may depend on atmospheric dust deposition delivering the necessary nutrients. Based on an inverse correlation between low nitrogen isotopic composition and the POC flux in the North oligotrophic gyre, Pabortsava et al (2017) showed a link between POC fluxes and newly fixed nitrogen by diazotrophs 35 whose activity was interpreted to be stimulated by Saharan dust driven nutrient input.…”