Mediterranean outflow conditions during the early to middle Pleistocene linked to precession forcing

The Mediterranean Outflow Water (MOW) is an important intermediate depth water mass in the North Atlantic. Here we reconstruct changes in the MOW during the early Pleistocene interval from 630 to 1760 ky, encompassing the Mid-Pleistocene Transition (MPT), which marks an important change in orbital climate forcing. Neither MOW ventilation nor MOW flow strength reveal changes related to the MPT, but incorporate variations related to precession (insolation) forcing. The MPT related change to higher glacial benthic δ O values occurs earlier at Site U1387 than in most deep-sea records, i.e. with MIS 26 instead of the MIS 24 to MIS 22 intervalThis study was supported by FCT through projects CCMAR (UID/Multi/04326/2019) and MOWCADYN (PTDC/MAR-PRO/3761/2012)info:eu-repo/semantics/publishedVersio

Planktonic foraminifera evidence for surface-water conditions off Southern Portugal during Mid-Pleistocene marine isotope stages 20 to 24 (790 – 940 ky)

Characterized by a drastic change in the deep thermohaline circulation, the Mid Pleistocene Transition (MPT) was a global climatic event resulted in more intense and longer lasting glacial periods and cooler sea -surface temperatures. The present study's objective is characterized surface -water variations during the MPT interval at the mid -latitude southern Portuguese margin using planktonic foraminifera faunal data from Site U1387. Stratigraphy records reveals dominantly tropical and subtropical species interrupted by incursions of subpolar waters when the North Atlantic's subarctic front moved to southernmost position during the MPT.info:eu-repo/semantics/publishedVersio

Multi-decadal atmospheric and marine climate variability in southern Iberia during the mid- to late-Holocene

To assess the regional multi-decadal to multicentennial climate variability along the southern Iberian Peninsula during the mid- to late-Holocene record of paleoenvironmental indicators from marine sediments were established for two sites in the Alboran Sea (ODP-161-976A) and the Gulf of Cadiz (GeoB5901-2). High-resolution records of organic geochemical properties and planktic foraminiferal assemblages are used to decipher precipitation and vegetation changes as well as hydrological conditions with respect to sea surface temperature (SST) and marine primary productivity (MPP). As a proxy for precipitation change, records of plant-derived n-alkane composition suggest a series of five distinct dry episodes in southern Iberia at 5.4 +/- 0.3 ka cal BP, from 5.1 to 4.9 +/- 0.1 ka cal BP, from 4.8 to 4.7 +/- 0.1 ka cal BP, from 4.4 to 4.3 +/- 0.1 ka cal BP, and at 3.7 +/- 0.1 ka cal BP. During each dry episode the vegetation suffered from reduced water availability. Interestingly, the dry phase from 4.4 to 4.3 +/- 0.1 ka cal BP is followed by a rapid shift towards wetter conditions revealing a more complex pattern in terms of its timing and duration than was described for the 4.2 ka event in other regions. The series of dry episodes as well as closely connected hydrological variability in the Alboran Sea were probably driven by NAO-like (North Atlantic Oscillation) variability. In contrast, surface waters in the Gulf of Cadiz appear to have responded more directly to North Atlantic cooling associated with Bond events. In particular, during Bond events 3 and 4, a pronounced increase in seasonality with summer warming and winter cooling is found.DFG (German Research Foundation) CRC 1266 2901391021 Fundacao para a Ciencia e Tecnologia SFRH/BPD/111433/2015info:eu-repo/semantics/publishedVersio

Diatoms as a paleoproductivity proxy in the NW Iberian coastal upwelling system (NE Atlantic)

The objective of the current work is to improve our understanding of how water column diatom's abundance and assemblage composition is seasonally transferred from the photic zone to seafloor sediments. To address this, we used a dataset derived from water column, sediment trap and surface sediment samples recovered in the NW Iberian coastal upwelling system. Diatom fluxes (2.2 (+/- 5.6) 10(6) valves m(-2) d(-1)) represented the majority of the siliceous microorganisms sinking out from the photic zone during all studied years and showed seasonal variability. Contrasting results between water column and sediment trap diatom abundances were found during downwelling periods, as shown by the unexpectedly high diatom export signals when diatom- derived primary production achieved their minimum levels. They were principally related to surface sediment remobilization and intense Minho and Douro river discharge that constitute an additional source of particulate matter to the inner continental shelf. In fact, contributions of allochthonous particles to the sinking material were confirmed by the significant increase of both benthic and freshwater diatoms in the sediment trap assemblage. In contrast, we found that most of the living diatom species blooming during highly productive upwelling periods were dissolved during sinking, and only those resistant to dissolution and the Chaetoceros and Leptocylindrus spp. resting spores were susceptible to being exported and buried. Fur-thermore, Chaetoceros spp. dominate during spring-early summer, when persistent northerly winds lead to the upwelling of nutrient-rich waters on the shelf, while Leptocylindrus spp. appear associated with late-summer upwelling relaxation, characterized by water column stratification and nutrient depletion. These findings evidence that the contributions of these diatom genera to the sediment's total marine diatom assemblage should allow for the reconstruction of different past upwelling regimes.CAIBEX [CTM2007-66408-C02-01/MAR]; REIMAGE [CTM2011-30155-C03-03]; Spanish Government, EXCAPA project [10MDS402013PR]; Xunta de Galicia; EU FEDER [INTERREG 2009/2011-0313/RAIA/E]; RAIA. co [INTERREG2011/2013-052/RAIA.co/1E]; CALIBERIA project [PTDC/MAR/102045/2008]; Fundacao para a Ciencia e a Tecnologia (FCT-Portugal) [COMPETE/FEDER-FCOMP01-0124-FEDER-010599]; Xunta de Galicia (Spain) [SFRH/BPD/111433/2015]; FCT (Portugal) [SFRH/BPD/111433/2015]; [SFRH/BD/88439/2012

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

Mediterranean Outflow and surface water variability off southern Portugal during the early Pleistocene: A snapshot at Marine Isotope Stages 29 to 34 (1020-1135 ka)

Centennial-to-millennial scale records from IODP Site U1387, drilled during IODP Expedition 339 into the Faro Drift at 558 m water depth, now allow evaluating the climatic history of the upper core of the Mediterranean Outflow (MOW) and of the surface waters in the northern Gulf of Cadiz during the early Pleistocene. This study focuses on the period from Marine Isotope Stages (MIS) 29 to 34, i.e. the interval surrounding extreme interglacial MIS 31. Conditions in the upper MOW reflect obliquity, precession and millennial-scale variations. The benthic delta O-18 signal follows obliquity with the exception of an additional, smaller delta O-18 peak that marks the MIS 32/31 transition. Insolation maxima (precession minima) led to poor ventilation and a sluggish upper MOW core, whereas insolation minima were associated with enhanced ventilation and often also increased bottom current velocity. Millennial-scale periods of colder sea-surface temperatures (SST) were associated with short-term maxima in flow velocity and better ventilation, reminiscent of conditions known from MIS 3.A prominent contourite layer, coinciding with insolation cycle 100, was formed during MIS 31 and represents one of the few contourites developing within an interglacial period. MIS 31 surface water conditions were characterized by an extended period (1065-1091 ka) of warm SST, but SST were not much warmer than during MIS 33. Interglacial to glacial transitions experienced 2 to 3 stadial/interstadial cycles, just like their mid-to-late Pleistocene counterparts. Glacial MIS 30 and 32 recorded periods of extremely cold (<12 degrees C) SST that in their climatic impact were comparable with the Heinrich events of the mid and late Pleistocene. Glacial MIS 34, on the other hand, was a relative warm glacial period off southern Portugal. Overall, surface water and MOW conditions at Site U1387 show a strong congruence with Mediterranean climate, whereas millennial-scale variations are closely linked to North Atlantic circulation changes. (C) 2015 Elsevier B.V. All rights reserved.Fundação para a Ciência e a Tecnologia (FCT; Portugal) through MOWCADYN project [PTDC/MAR-PRO/3761/2012]; FCT [SFRH/BPD/66025/2009]; Deutsche Forschungsgemeinschaft (DFG) [BA 3809/4, RO 1113/6]; MARUM Research Center; Spanish Ministry of Science and Innovation [CTM 2011-24079]; European Union [228344-EUROFLEETS]info: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

Ocean kinetic energy and photosynthetic biomass are important drivers of planktonic foraminifera diversity in the Atlantic Ocean

To assess the anthropogenic effect on biodiversity, it is essential to understand the global diversity distribution of the major groups at the base of the food chain, ideally before global warming initiation (1850 Common Era CE). Since organisms in the plankton are highly interconnected and carbonate synthesizing species have a good preservation state in the Atlantic Ocean, the diversity distribution pattern of planktonic foraminifera from 1741 core-top surface sediment samples (expanded ForCenS database) provides a case study to comprehend centennial to decadal time-averaged diversity patterns at pre-1970 CE times, the tempo of the substantial increase in tropospheric warming. In this work, it is hypothesized and tested for the first time, that the large-scale diversity patterns of foraminifera communities are determined by sea surface temperature (SST, representing energy), Chl-a (a surrogate for photosynthetic biomass), and ocean kinetic energy (as EKE). Alpha diversity was estimated using species richness (S), Shannon Wiener index (H), and Simpson evenness (E), and mapped using geostatistical approaches. The three indices are significantly related to SST, Chl-a, and EKE (71-88% of the deviance in the generalized additive mixed model, including a spatial component). Beta diversity was studied through species turnover using gradient forest analysis (59% of the variation). The primary community thresholds of foraminifera species turnover were associated with 5-10 degrees C and 22-28 degrees C SST, 0.05-0.15 mg m-(3) Chl-a, and 1.2-2.0 cm(2) s-(2) log10 EKE energy, respectively. Six of the most important foraminifera species identified for the environmental thresholds of beta diversity are also fundamental in transfer functions, further reinforcing the approaches used. The geographic location of the transition between the four main biogeographic zones was redefined based on the results of beta diversity analysis and incorporating the new datasets, identifying the major marine latitudinal gradients, the most important upwelling areas (Benguela Current, Canary Current), the Equatorial divergence, and the subtropical fronts (Gulf Stream-North Atlantic Drift path in the north, and the South Atlantic current in the south). In conclusion, we provide statistical proof that energy (SST), food supply (Chl-a), and currents (EKE) are the main environmental drivers shaping planktonic foraminifera diversity in the Atlantic ocean and define the associated thresholds for species change on those variables.info:eu-repo/semantics/publishedVersio

Holocene climate variability of the Western Mediterranean: surface water dynamics inferred from calcareous plankton assemblages

A high-resolution study (centennial scale) has been performed on the calcareous plankton assemblage of the Holocene portion of the Ocean Drilling Program Site 976 (Alboran Sea) with the aim to identify the main changes in the surface water dynamic. The dataset also provided a seasonal foraminiferal sea surface water temperatures (SSTs), estimated using the modern analog technique SIMMAX 28, and it was compared with available geochemical and pollen data at the site. Three main climate shifts were identified as (1) the increase in abundance of Syracosphaera spp. and Turborotalita quinqueloba marks the early Holocene humid phase, during maximum summer insolation and enhanced river runoff. It is concomitant with the expansion of Quercus, supporting high humidity on land. It ends at 8.2 ka, registering a sudden temperature and humidity reduction; (2) the rise in the abundances of Florisphaera profunda and Globorotalia inflata, at ca. 8 ka, indicates the development of the modern geostrophic front, gyre circulation, and of a deep nutricline following the sea-level rise; and (3) the increase of small Gephyrocapsa and Globigerina bulloides at 5.3 ka suggests enhanced nutrient availability in surface waters, related to more persistent wind-induced upwelling conditions. Relatively higher winter SST in the last 3.5 ka favored the increase of Trilobatus sacculifer, likely connected to more stable surface water conditions. Over the main trends, a short-term cyclicity is registered in coccolithophore productivity during the last 8 ka. Short periods of increased productivity are in phase with Atlantic waters inflow, and more arid intervals on land. This cyclicity has been related with periods of positive North Atlantic Oscillation (NAO) circulations. Spectral analysis on coccolithophore productivity confirms the occurrence of millennial-scale cyclicity, suggesting an external (i.e. solar) and an internal (i.e. atmospheric/oceanic) forcing.Geoscience PhD scholarship, Universita degli Studi di BariPotenziamento Strutturale dell'Universita degli Studi di Bari, Laboratorio per lo Sviluppo Integrato delle Scienze e delle Tecnologie dei Materiali Avanzati e per dispositivi innovativi (SISTEMA) [PONa3_00369]Fundacao para a Ciencia e a Tecnologia (FCT)Portuguese Foundation for Science and TechnologyEuropean Commission [SFRH/BPD/111433/2015]info:eu-repo/semantics/submittedVersio