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- Ocean kinetic energy and photosynthetic biomass are important drivers of planktonic foraminifera diversity in the Atlantic OceanPublication . Rufino, Marta M.; Salgueiro, Emilia; H L Voelker, Antje; Polito, Paulo S.; Cermeño, Pedro A.; Abrantes, FatimaTo 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.
- A 1-Ma record of sea surface temperature and extreme cooling events in the North Atlantic: A perspective from the Iberian MarginPublication . Rodrigues, Teresa; Alonso-Garcia, Montserrat; Hodell, D. A.; Rufino, MM; Naughton, F.; Grimalt, J. O.; H L Voelker, Antje; Abrantes, FatimaThe Iberian Margin is a sensitive area to track high and low latitude processes, and is a key location to understand major past climatic and oceanographic changes. Here we present new biomarker data from IODP Site U1385 ("Shackleton site") (1017-336 ka) that, when combined with existing data from Cores MD01-2443/4 (last 335 ka), allows us to assess the evolution of sea surface temperature (SST) and meltwater influx over the last 1 Ma at the Iberian Margin. Interglacial periods throughout the last 1 Ma show SST close to 20 degrees C, even during the so-called "luke-warm" interglacials that are marked by relatively low atmospheric CO2 concentrations. During glacial periods, extremely cold stadial events are recognized at the Iberian Margin, and are very likely related to meltwater discharges from the European and British-Irish ice sheets into the NE Atlantic, which were transported southwards by the Portugal Current. We subdivided the record into four intervals on the basis of the timing and the magnitude of these extremely cold stadials: 1) from 1017 to similar to 900 ka, only minor sporadic freshwater input occurred during deglaciations; 2) from 900 to 675 ka extreme cold events occur as terminal stadial events at the beginning of the deglaciations, which results in abrupt deglacial SST shifts; 3) from 675 to 450 ka only a few, very short-lived events are recorded and seldom is there freshwater input at the Iberian Margin; 4) during the last 450 ka the extreme cold events occurred under full glacial conditions, with particularly severe events during MIS 6 and 8. We propose these mid -glacial events are associated with a strong discharges of European ice sheet (EIS). The fact that these extreme cold events do not coincide with deglaciations questions the role of European ice sheet discharges in triggering deglaciations. (C) 2017 Elsevier Ltd. All rights reserved.
- Reply to the comment by Meco et al. on “Range expansion of tropical shallow-water marine molluscs in the NE Atlantic during the last interglacial (MIS 5e): Causes, consequences and utility of ecostratigraphic indicators for the Macaronesian archipelagos”Publication . Melo, Carlos S.; Martín-González, Esther; da Silva, Carlos M.; Galindo, Inés; González-Rodríguez, Alberto; Baptista, Lara; Rebelo, A. Cristina; Madeira, Patrícia; H L Voelker, Antje; Johnson, Markes E.; Arruda, Samuel A.; Ávila, Sérgio P.It was with much interest that we read the comment made by Meco et al. (2022), regarding our work on “Range expansion of tropical shallow-water marine molluscs in the NE Atlantic during the last interglacial (MIS 5e): Causes, consequences and utility of ecostratigraphic indicators for the Macaronesian archipelagos”. We welcome the discussion generated by our paper and appreciate the recognition of its complexity and broad scope. In our opinion, the arguments offered by Meco et al. (2022) do not contradict our conclusions. Nevertheless, we take this opportunity to address their critiques regarding our list of “ecostratigraphic indicators” and parts of our hypothesized range expansions. Meco et al.
- delta O-18 and Mg/Ca thermometry in planktonic foraminifera: a multiproxy approach toward tracing oastal upwelling dynamicsPublication . Salgueiro, Emilia; H L Voelker, Antje; Martin, P. A.; Rodrigues, Teresa; Zuniga, D.; Frojan, M.; de la Granda, F.; Villacieros-Robineau, N.; Alonso-Perez, F.; Alberto, A.; Rebotim, A.; Gonzalez-Alvarez, R.; Castro, C. G.; Abrantes, FatimaPlanktonic foraminifera delta O-18 and Mg/Ca ratios are widely considered as a powerful proxy to reconstruct past seawater-column temperature. Due to the complex interpretation of planktonic foraminifera delta O-18 data in regard to past seawater temperatures, temperature determination based on the foraminifera shell Mg/Ca ratio is believed to be more accurate. Scarce Mg/Ca calibration data exists for coastal upwelling regions, resulting in incoherent results of past seawater reconstructions. The current study along the NW Iberia coastal upwelling system intends to define the best Mg/Ca temperature equation for the most representative species of this region (Neogloboquadrina incompta, Globigerina bulloides, and Globorotalia inflata). Seawater temperature from delta O-18 and Mg/Ca of these three planktonic foraminifera species was compared with the surface sediments alkenone derived SST and with the in situ temperatures measured at the depths where these foraminifera species currently live and calcify. The equations that better reflect each species calcification depth were selected as our regional equations for delta O-18 and Mg/Ca temperature reconstructions. The delta O-18-estimated temperatures for surface sediment specimens were comparable with in situ seawater-column temperature measurements, whereas the Mg/Ca derived temperatures seem to underestimate in situ values, in special for G. bulloides from samples affected by stronger coastal upwelling. The G. bulloides delta O-18 and Mg/Ca estimated temperatures from samples located offshore, further from coastal upwelling influence, are comparable to surface sediment alkenone derived temperatures. Our study shows that in upwelling areas, regional calibration of planktonic foraminifera Mg/Ca temperature equations is necessary for reliable interpretations of high-resolution past temperature variability in these important environments.
- A 12,000-yr pollen record off Cape Hatteras — Pollen sources and mechanisms of pollen dispersionPublication . Naughton, F.; Keigwin, L.; Peteet, D.; Costas, S.; Desprat, S.; Oliveira, Dulce; de Vernal, A.; H L Voelker, Antje; Abrantes, FatimaIntegrating both marine and terrestrial signals from the same sediment core is one of the primary challenges for understanding the role of ocean-atmosphere coupling throughout past climate changes. It is therefore vital to understand how the pollen signal of a given marine record reflects the vegetation changes of the neighboring continent. The comparison between the pollen record of marine core JPC32 (KNR178JPC32) and available terrestrial pollen sequences from eastern North America over the last 12,170 years indicates that the pollen signature off Cape Hatteras gives an integrated image of the regional vegetation encompassing the Pee Dee river, Chesapeake and Delaware hydrographic basins and is reliable in reconstructing the past climate of the adjacent continent. Extremely high quantities of pollen grains included in the marine sediments off Cape Hatteras were transferred from the continent to the sea, at intervals 10,100-8800 cal yr BP, 8300-7500 cal yr BP, 5800-4300 cal yr BP and 2100-730 cal yr BP, during storm events favored by episodes of rapid sea-level rise in the eastern coast of US. In contrast, pollen grains export was reduced during 12,170-10,150 cal yr BP and 4200-2200 cal yr BP, during episodes of intense continental dryness and slow sea level rise episodes or lowstands in the eastern coast of US. The near absence of reworked pollen grains in core JPC32 contrasts with the high quantity of reworked material in nearby but deeper located marine sites, suggesting that the JPC32 record was not affected by the Deep Western Boundary Current (DWBC) since the end of the Younger Dryas and should be considered a key site for studying past climate changes in the western North Atlantic.
- Early Pleistocene calcareous nannofossil assemblages from the Gulf of Cadiz reveal glacial-interglacial and millennial-scale variabilityPublication . Trotta, Samanta; Marino, Maria; H L Voelker, Antje; Rodrigues, Teresa; Maiorano, Patrizia; Flores, José-Abel; Girone, Angela; Addante, Marina; Balestra, BarbaraCoccolithophore high resolution (300 years) quantitative analyses have been carried out on Early Pleistocene sediment samples from Integrated Ocean Drilling Program Site U1387 retrieved in the Gulf of Cadiz. The studied interval is well constrained by the delta 18O chronological frame and covers marine isotope stage (MIS) 48 to MIS 45, from 1465.9 ka to 1389.9 ka. The aim is to investigate paleoenvironmental changes during a poorly known interval of the "41 ky world" and understand how climate dynamics controlled coccolithophore abundance and variation at orbital up to millennial scale. Assemblage composition variation and Principal Component Analysis (PCA) indicate that temperature and nutrient availability are the main factors influencing coccolithophores. Precession forcing combined with hydrological and atmospheric dynamics affect changes in coccolithophore assemblage composition and abundance highlighting glacial-interglacial cycles and a millennial scale variability, which is more evident during glacials than during interglacials. Interglacial MIS 47 onset is more abrupt than MIS 45 inception in relation to a more prominent insolation maximum, which favors the sharp increase and highest abundance of warm water taxa in the early MIS 47. Short-term abundance peaks of C. pelagicus spp. pelagicus during glacials document polar-subpolar melting water influx into the Gulf of Cadiz and southward migration of the subpolar front during episodes of high volume ice-sheet in the north hemisphere and reduced Atlantic Meridional Overturning circulation. In late MIS 48 the lowest coccolithophore productivity, induced by colder and stratified surface waters, a terminal stadial has been inferred. Enhanced short-term glacial productivity is favored by higher mixing and nutrient content in surface water due to the strengthened westerly winds during symbolscript phases. This promotes arid condition and upwelling along the studied site. The interglacial short-term coccolithophore productivity increases are associated with insolation maxima and enhanced nutrients of land origin during more humid periods led by -NAO-like phases, which induce the southward position of the westerlies and higher precipitation in the Mediterranean region and North Africa, in agreement with the contemporary sapropel occurrences in Mediterranean Sea. Our data-set suggests a connection between climate dynamics in the Gulf of Cadiz and east of Gibraltar Strait during the Early Pleistocene as well as a relationship with the north hemisphere ice-sheet dynamics.
- Combination of insolation and ice-sheet forcing drive enhanced humidity in northern subtropical regions during MIS 13Publication . Oliveira, Dulce; Desprat, Stéphanie; Yin, Qiuzhen; Rodrigues, Teresa; Naughton, Filipa; Trigo, Ricardo M.; Su, Qianqian; Grimalt, Joan O.; Alonso-Garcia, Montserrat; H L Voelker, Antje; Abrantes, Fatima; Sánchez Goñi, Maria FernandaMarine Isotope Stage (MIS) 13, similar to 533-478 ka, has received particular attention due to the unexpected enhancement of monsoon systems under a cool climate characterized by lower atmospheric CO2 and larger ice volume than many other interglacials. Key questions remain about its regional expression (intensity, climate variability, length), and underlying forcing factors, in particular at the mid-latitudes. Here we examine the SW Iberian vegetation, terrestrial climate and sea surface temperature (SST) variability during MIS 13 by combining pollen and biomarker data from IODP Site U1385 with climate-model experiments. We show, for the first time, that despite strong precessional forcing, MIS 13 stands out for its large forest expansions with a reduced Mediterranean character alternating with muted forest contractions, indicating that this stage is marked by a cool-temperate climate regime with high levels of humidity. Results of our data-model comparison reveal that MIS 13 orbitally driven SW Iberian climate and vegetation changes are modulated by the relatively strong ice-sheet forcing. We find that the Northern Hemisphere ice-sheets prescribed at the MIS 13 climate optimum reinforce the insolation effect by increasing the tree fraction and both winter and summer precipitation. We propose that the interactions between ice-sheets and major atmospheric circulation systems may have resulted in the persistent influence of the mid-latitude cells over the SW Iberian region, which led to intensified moisture availability and reduced seasonality, and, in turn, to a pronounced expansion of the temperate forest.