Coccolithophore productivity at the western Iberian Margin during the Middle Pleistocene (310–455 ka) – evidence from coccolith Sr∕Ca data

Abstract

Abstract. Coccolithophores contribute significantly to marine primary productivity and play a unique role in ocean biogeochemistry by using carbon for photosynthesis (soft-tissue pump) and for calcification (carbonate counter pump). Despite the importance of including coccolithophores in Earth system models to allow better predictions of the climate system's responses to planetary change, the reconstruction of coccolithophore productivity mostly relied on proxies dependent on accumulation and sedimentation rates and preservation conditions. In this study we used an independent proxy, based on the coccolith fraction (CF) Sr∕Ca ratio, to reconstruct coccolithophore productivity. We studied the marine sediment core MD03-2699 from the western Iberian margin (IbM), concentrating on glacial–interglacial cycles of Marine Isotopic Stage (MIS) 12 to MIS 9. We found that IbM coccolithophore productivity was controlled by changes in the oceanographic conditions, such as in sea surface temperature (SST) and nutrient availability, and by competition with other phytoplankton groups. Long-term coccolithophore productivity was primarily affected by variations in the dominant surface water mass. Polar and subpolar surface waters during glacial substages were associated with decreased coccolithophore productivity, with the strongest productivity minima concomitant with Heinrich-type events (HtEs). Subtropical, nutrient-poorer waters, increased terrigenous input, and moderate to strong upwelling during the deglaciation and early MIS11 are hypothesized to have attributed a competitive advantage to diatoms to the detriment of coccolithophores, resulting in intermediate coccolithophore productivity levels. During the progression towards full glacial conditions an increasing presence of nutrient-richer waters, related to the growing influence of transitional surface waters and/or intensified upwelling, probably stimulated coccolithophore productivity to maxima following the rapid depletion of silica by diatoms. We present conceptual models of the carbon and carbonate cycle components for the IbM in different time slices that might serve as a basis for further investigation and modelling experiments.

Control Mechanisms of Primary Productivity Revealed by Calcareous Nannoplankton From Marine Isotope Stages 12 to 9 at the Shackleton Site (IODP Site U1385)

“…Ultimately, both interglacial sea-level high stands during the early MIS 11c and MIS 9e (Rohling et al, 2009) exclude any offshore displacement of the coastal upwelling cells through the position of the Site U1385. A recently suggested increased influence of nutrient-poorer subtropical waters during the full interglacial MIS 11 and 9 to the north of our Site (Cavaleiro et al, 2020) is consistent with our observations. As well, similar primary productivity scenario and associated upwelling conditions was described at the IbM during other more recent interglacial periods (i.e., MIS 5; Pailler & Bard, 2002) and the Holocene (Incarbona et al, 2010).…”

“…Strengthened wind-stress together with reduced winter IPC (Figure 3e), promoting the maintained influence of the surface PC, is considered, as well, to result in the prevalent upward advection of deeper and nutrient-richer subsurface ENACWsp fueling the regional upwelling. This observation is in agreement with nutrient-richer surface waters favoring coccolithophore proliferation against diatoms discussed by Cavaleiro et al (2020) at the nearby site MD03-2699. Additionally, the strengthened atmospheric circulation could have resulted in substantial widening of the coastal upwelling (e.g., Pailler & Bard, 2002), benefiting eutrophication at Site U1385 due to greater proximity of the upwelled filaments (or area of influence of the upwelling).…”

“…Overall, productivity reduction and associated hydrological and paleoceanographic conditions observed during these abrupt cold events of different duration for the studied interval impacted nannoplankton assemblages on a regional level, as proven by the consistency of our record with that from core MD03-2699 (Cavaleiro et al, 2020). The mechanism that reduces primary productivity is probably comparable to that proposed during the Heinrich episodes of the last glacial (e.g., Ausín et al, 2020;Incarbona et al, 2010).…”

“…Pailler and Bard (2002) linked this to the enhanced wind-driven upwelling controlled by shifts in the atmospheric circulation patterns over the North Atlantic, that were favored by substantial changes in northern hemisphere ice volume. Further work of Cavaleiro et al (2020) observed similar patterns of coccolithophore productivity in response to G/I and millennial-scale variability, primarily attributed to variations in the dominant surface water masses and their influence (i.e., changes in nutrient content) on the state of competition between phytoplankton groups, but suggested to be connected to wind-driven upwelling. However, in these studies a clear determination of the mechanisms controlling vertical mixing dynamics and fertilization was severely hampered by the absence of direct information about prevailing wind regimes and atmospheric configuration.…”

New Insights Into the Surface‐Ocean Dynamics of the Northeastern Atlantic Ocean Across the Marine Isotope Stage 7

“…Surface hydrography and productivity conditions along the SW Iberian Margin are modulated by various physical parameters such as the surface winds, surface currents, migration of the thermal fronts, nutrients in the sub‐surface waters and the offshore displacement of the coastal upwelling filaments (e.g., Amore et al., 2012; Ausín et al., 2020; Cavaleiro et al., 2020; González‐Lanchas et al., 2021; Incarbona et al., 2010; Pailler & Bard, 2002; Palumbo et al., 2013; Salgueiro et al., 2014; Singh et al., 2023; Voelker et al., 2009). A detailed assessment of these coupled ocean‐atmospheric parameters is essential to better understand the underlying processes driving the surface ocean conditions.…”