The nature of opal burial in the equatorial atlantic during the deglaciation

Relatively high opal concentrations are measured in equatorial Atlantic sediments from the most recent deglaciation. To shed light on their causes, seven cores were analyzed for their content of siliceous (diatom, silicoflagellates, radiolarians, phytoliths, and sponge spicules) and calcareous (coccolithophores) microfossils. An early deglacial signal is detected at the time of rising boreal summer insolation ca. 18 ka by the coccolithophores. The surface freshening is likely due to the rain belt associated with the intertropical convergence zone (ITCZ), implying its southward shift relatively to its present-day average positioning. The diatom assemblages corresponding to the following increase in diatom abundances ca. 15.5 ka suggest the formation of a cold tongue of upwelled water associated with tropical instability waves propagating westward. Such conditions occur at present during boreal summer, when southerly trade winds are intensified, and the ITCZ shifts northward. The presence of the diatom Ethmodiscus rex (Wallich) Hendey and the coccolithophore Florisphera profunda indicates a deep thermocline and nutrient enrichment of the lower photic zone, revealing that Si-rich southern sourced water (SSW) likely contributed to enhanced primary productivity during this time interval. The discrepancies between the maximum opal concentrations and siliceous marine microfossils records evidence the contribution of freshwater diatoms and phytoliths, indicative of other processes. The definition of the nature of the opal record suggests successive productivity conditions associated with specific atmospheric settings determining the latitudinal ITCZ positioning and the development of oceanic processes; and major oceanic circulation changes permitting the contribution of SSW to marine productivity at this latitude.LA/P/0101/2020info:eu-repo/semantics/publishedVersio

Data report: IODP Site U1387: the revised splice between Sections U1387B-18X-3 and U1387C-8R-3 (>171.6 mcd)

The Expedition 339 shipboard splice of Integrated Ocean Drilling Program (IODP) Site U1387 deeper than ~155 meters composite depth (mcd) is based on a composite of the magnetic susceptibility and natural gamma radiation data. When generating high-resolution paleoceanographic reconstructions for the Mid-Pleistocene Transition and early Pleistocene sections of Site U1387, it quickly became obvious that proxy data misfits existed at several splice transitions. Thus, a revised splice was generated for Site U1387 below Core 339-U1387B-18X based on X-ray fluorescence– derived element records (e.g., ln[Fe/Ca]) and the stable isotope records obtained for planktonic and benthic foraminifers. Corrections were needed at most of the splice transitions below Core 339-U1387A-19X, with adjustments ranging from a few centimeters to several meters. In addition, Core 339-U1387A-33X and sections of Core 36X were integrated into the revised splice to replace Core 339-U1387C-2R and sections of Core 5R, respectively. The replacement of Core 339-U1387C-2R with Core 339-U1387A33X is an option for the intended paleoceanographic research and not essential for lower resolution studies. The splice tie point table, therefore, also includes an option for a splice that retains Core 339-U1387C-2R. The extensive revision of the shipboard splice reveals that making a splice for sediment sequences rich in contourite layers and coring disturbances (biscuiting in the extended core barrel cores) can be tricky and that data misfits at splice transitions are not necessarily a data problem but could indicate a splice problem.SFRH/BPD/111433/2015info:eu-repo/semantics/publishedVersio

16S rRNA gene metabarcoding and TEM reveals different ecological strategies within the genus Neogloboquadrina (planktonic foraminifer)

CB was supported on a Daphne Jackson Fellowship sponsored by Natural Environmental Research Council (www.nerc.ac.uk) and the University of Edinburgh via the Daphne Jackson Trust. Field collections were supported by the National Science Foundation (www.nsf.gov) grant number OCE-1261519 to ADR and JSF.Uncovering the complexities of trophic and metabolic interactions among microorganisms is essential for the understanding of marine biogeochemical cycling and modelling climate-driven ecosystem shifts. High-throughput DNA sequencing methods provide valuable tools for examining these complex interactions, although this remains challenging, as many microorganisms are difficult to isolate, identify and culture. We use two species of planktonic foraminifera from the climatically susceptible, palaeoceanographically important genus Neogloboquadrina, as ideal test microorganisms for the application of 16S rRNA gene metabarcoding. Neogloboquadrina dutertrei and Neogloboquadrina incompta were collected from the California Current and subjected to either 16S rRNA gene metabarcoding, fluorescence microscopy, or transmission electron microscopy (TEM) to investigate their species-specific trophic interactions and potential symbiotic associations. 53–99% of 16S rRNA gene sequences recovered from two specimens of N. dutertrei were assigned to a single operational taxonomic unit (OTU) from a chloroplast of the phylum Stramenopile. TEM observations confirmed the presence of numerous intact coccoid algae within the host cell, consistent with algal symbionts. Based on sequence data and observed ultrastructure, we taxonomically assign the putative algal symbionts to Pelagophyceae and not Chrysophyceae, as previously reported in this species. In addition, our data shows that N. dutertrei feeds on protists within particulate organic matter (POM), but not on bacteria as a major food source. In total contrast, of OTUs recovered from three N. incompta specimens, 83–95% were assigned to bacterial classes Alteromonadales and Vibrionales of the order Gammaproteobacteria. TEM demonstrates that these bacteria are a food source, not putative symbionts. Contrary to the current view that non-spinose foraminifera are predominantly herbivorous, neither N. dutertrei nor N. incompta contained significant numbers of phytoplankton OTUs. We present an alternative view of their trophic interactions and discuss these results within the context of modelling global planktonic foraminiferal abundances in response to high-latitude climate change.Publisher PDFPeer reviewe

Last Glacial Maximum and Holocene oceanographic conditions at the Portuguese margin - a reconstruction using planktonic foraminifera

14th International Conference on Paleoceanography, 29 August - 2 September 2022, BergenPaleodata of environmental responses to climate change from the Last Glacial Maximum (LGM) and the Holocene provide a useful performance test for climate models' sensitivity, contributing to better forecasts. Temporal high resolution data for both periods is important to reduce the uncertainties of models regionally.The Portuguese margin, one of the most productive marine regions of the world and having high sedimentation rates, is considered a key area to reconstruct past climate. This high temporal resolution study contributes with planktonic foraminifera (PF) data (fauna and stable isotopes), temperature and export productivity (Pexp) at two sites under different oceanographic conditions: MD03-2699 – off Estremadura spur and Shak-03-6K - off Sines. Preliminary results show that during the LGM, the average SSTs at the Estremadura was lower than Sines (12.3 °C vs. 19.4 °C) while the Pexp was higher (86.2 gC/m2/yr vs. 60.8 gC/m2/yr). In contrast, during the Mid Holocene (MH), at both sites, the average SSTs were warmer and the Pexp was lower than during the LGM (Estremadura - 18.9 °C, 76.1 gC/m2/yr; Sines - 21.2 °C, 55.2 gC/m2/yr). Subtropical and transitional PF species are abundant during the LGM reflecting warm, stable SSTs at both locations relative to the high mid-latitudinal North Atlantic (NA) sites, whereas higher Pexp was possibly caused by stronger westerly winds that enhanced the upwelling. SSTs at both sites during the MH were interrupted by a cold event (starting at 5.2 ky) coincident with a decrease in Pexp at both sites. This cold event could be related to the freshwater input from the melting Laurentide ice sheet, already observed in the NA. Pexp at the Estremadura was relatively higher than off Sines (~20 gC/m2/yr difference), probably because like today this site is under a stronger influence of upwelling events and riverine nutrient input from the Tagus RiverPeer reviewe