Dinoflagellate cyst population evolution throughout past interglacials: Key features along the Iberian margin and insights from the new IODP Site U1385 (Exp 339)

Abstract

International audienceIODP 339 Site U1385 ("Shackleton site", e.g. Hodell et al., 2013a), from the SW Iberianmargin, offers the opportunity to study marine microfossil population dynamics bycomparing several past interglacials and to test natural shifts of species that occurred acrossthese warm periods, in a subtropical context. Here, more specifically, we present resultsobtained for the dinoflagellate cyst (dinocyst) population integrated at a regional scalethanks to the addition of data from proximal sites from southern Iberian margin. Whenpossible, observations made using the dinocyst bio-indicator are compared to additionalproxies from the same records in order to test the synchronicity of the marine biotaresponse. Pollen data available for some of the compiled marine sequences also offer theopportunity to directly compare marine biota with terrestrial ecosystem responses. Thisspatio-temporal compilation reveals that, over the last 800 ka, surface waters around Iberiawere tightly coupled to (rapid) climate changes and were characterised by coherent dinocystassemblage patterns, highlighting a permanent connection between Atlantic andMediterranean waters as evidenced through a continuous exchange of dinocyst populations.Some index species well illustrate the evolution of the regional hydrographic context alongtime, as for instance Spiniferites and Impagidinium species, together with Lingulodiniummachaerophorum, Bitectatodinium tepikiense and heterotrophic brown cysts. Theyconstitute key bio-indicators in context of natural environmental shifts at long and shorttimescales

Comparison of qualitative and quantitative dinoflagellate cyst approaches in reconstructing glacial-interglacial climate variability at West Iberian Margin IODP ‘Shackleton’ Site U1385

“…were higher during the glacial stage than during the Holocene (Figs. 4 and 5H), as previously observed at sites along the WIM (Zippi, 1992;Boessenkool et al, 2001;Penaud et al, 2011b;Eynaud et al, 2016). The low abundances of S-cysts (heterotrophs) in the Holocene may be partially related to increased oxygen-mediated degradation, as indicated by relatively high kt values from~8 ka (Fig.…”

“…5A-C). The SST dino index at sites SO75-6KL and SU81-18 for the same interval is also highly variable Eynaud et al, 2016, Fig. 7D), while foraminiferal δ 18 O from sites U1385, MD01-2444and MD95-2042(e.g.…”

“…Strikingly, the occurrence of this species has not been consistently reported along the WIM, either in studies dealing with modern dinocyst assemblages (Sprangers et al, 2004, transects along the WIM; Ribeiro and Amorim, 2008, Lisbon Bay) or the last glacial transition , Site SO75-6KL). However, other authors have found P. dalei in sediments of Sites SU81-18 and MD95-2042 for the entire last glacial cycle (MIS1-6; Turon et al, 2003;Eynaud, 1999, Eynaud et al, 2000Sanchez Goñi et al, 1999, 2000a, 2000bPenaud et al, 2011a) and at Site U1385 for MIS11 and MIS19 (Eynaud et al, 2016). The cyst of P. dalei might have been overlooked in some previous dinocyst studies, possibly due to the small size (19-36 μm; cf.…”

“…We assess relative variations in surface water parameters based on selected dinocyst taxa (Table 1) following previous work done in the area Ribeiro and Amorim, 2008;Eynaud et al, 2016 and references therein) and the global geographic distribution of modern dinocysts in surface sediments (Zonneveld et al, 2013 and references therein). The SST dino index is defined as: SST dino = n w /(n w + n c ), where n w = number of 'warm' taxa cysts and n c = number of 'cold' taxa cysts counted (see Table 1 for composition of these groups).…”

Millennial‐Scale Climate Variability and Dinoflagellate‐Cyst‐Based Seasonality Changes Over the Last ~150 kyrs at “Shackleton Site” U1385

“…SST dominantly drives the SST dino index, although a small part of the variation might be related to SSS (Datema et al, ). The SST dino index calculated on the dinocyst data set published in Eynaud et al (), which covers large parts of our 152‐kyr interval, shows very similar results (not shown) indicating the good reproducibility of our approach.…”