Calibrating stable carbon isotopes in planktonic foraminifera off the NW Iberian margin: nutrient approach
42th CIESM Congress, Cascais, 7-11 October 2019The interpretation of the carbon isotopic (δ C) si... more 42th CIESM Congress, Cascais, 7-11 October 2019The interpretation of the carbon isotopic (δ C) signal of planktonic foraminifera in sediment records to reconstruct past nutrient availability is complex and poorly understood, especially in coastal upwelling areas, because the isotopic fractions of carbon incorporated into the shells may be derived from different sources and affected by different processes. To minimize the existing uncertainties, we measured δ C from various species of planktonic foraminifera from core-top sediments and plankton net samples collected off the NW Iberian Margin and compared the results directly with water column nutrient content for the purpose of calibrationPeer reviewe
We present a coupled global climate model (CGCM) simulation, integrated for 1500 years to quasi-e... more We present a coupled global climate model (CGCM) simulation, integrated for 1500 years to quasi-equilibrium, of a stadial (cold period) within Marine Isotope Stage 3 (MIS 3). The simulated Greenland stadial 12 (GS12; ∼44 ka BP) annual global mean surface temperature (T s ) is 5.5 • C higher than in the simulated recent past (RP) climate and 1.3 • C lower than in the simulated Last Glacial Maximum (LGM; 21 ka BP) climate. The simulated GS12 climate is evaluated against proxy data of sea surface temperature (SST). Simulated SSTs fall within the uncertainty range of the proxy SSTs for 30-50% of the sites depending on season. Proxy SSTs are higher than simulated SSTs in the Central North Atlantic, in contrast to earlier simulations of MIS 3 stadial climate in which proxy SSTs were found to be lower than simulated SST. The annual global mean T s only changes by 0.10 • C from model years 500-599 to the last century of the simula-CPD
This multi-proxy study of IODP Site U1387 (Faro Drift) aims to reconstruct the history of the sur... more This multi-proxy study of IODP Site U1387 (Faro Drift) aims to reconstruct the history of the surface water and the Mediterranean Outflow Water (MOW) during the interval from 630 to 1100ka, i.e. the Mid-Pleistocene Transition. Surface and MOW experienced orbital-and millennial-scale variations. MOW related proxies show a tight coupling to insolation with poor ventilation during insolation maxima and contourite layers being formed by a faster flowing MOW during insolation minima.
In order to better understand interglacial climate variability within the 41 kyr world, we produc... more In order to better understand interglacial climate variability within the 41 kyr world, we produced high-resolution climate records for interglacial Marine Isotope Stage (MIS) 47 (1424-1452 ka) at IODP Site U1387 (36 • 48 N, 7 • 43 W) on the southern Portuguese margin. Using benthic and planktonic foraminifera stable isotope records, U k' 37 sea-surface temperature (SST), and plankton assemblage data we investigated Mediterranean Outflow Water (MOW) and surface water conditions. The MOW-level records indicate a poorly ventilated and sluggish bottom current during the MIS 48/MIS 47 transition in association with the insolation maximum, whereas a well-ventilated MOW formed a contourite layer during the second insolation maximum. The benthic δ 18 O record shows a fairly abrupt change during the deglaciation of MIS 48, while the surface waters experienced a terminal stadial event that was associated with initial cooling and freshening followed by stepwise warming until interglacial SST was reached at 1450 ka. Interglacial conditions with SST of 24 • C or higher persisted until 1427 ka, although warm SST prevailed into MIS 46. The persistent and prolonged warmth is attributed to a northward expansion of the subtropical gyre during MIS 47 as reflected by the dominance of subtropical-tropical planktonic foraminifera species and the presence of warm water coccolithophores taxa.
Paleoceanography and paleoclimatology, May 1, 2020
Sea surface temperature (SST) are used to infer past changes in the state of the climate system. ... more Sea surface temperature (SST) are used to infer past changes in the state of the climate system. Here we use a combination of newly generated and published organic paleothermometer records, together with novel high-resolution benthic foraminiferal δ 18 O stratigraphy, from four sites in the mid-latitude North Atlantic (41-58 °N) to reconstruct the long-term evolution of the latitudinal SST gradient during the Pliocene and early Pleistocene (4.0 to 2.4 Myr), the last time atmospheric CO2 reached concentrations above 400 ppmv. We demonstrate that the latitudinal SST gradient in the North Atlantic nearly collapsed twice during this period. We conclude that the latitudinal SST gradient in the mid-latitude North Atlantic has two end-members; a maximum as existing at present and a minimum that existed during certain periods of the (late) Pliocene. Our results suggest that the 400 ppmv Pliocene world was much more dynamic than currently thought.
An underground record of past deglaciations Understanding more exactly how the timing of deglacia... more An underground record of past deglaciations Understanding more exactly how the timing of deglaciations depends on changes in insolation, or the energy received by Earth from the Sun, requires precise and independent records of both environmental change and solar energy input. Bajo et al . strengthened the weak link of that two-member chain, the environmental record, by developing a precise, radiometrically dated chronology of the 11 deglaciations of the past million years derived from speleothems. This allowed them to show more clearly how the initiation and duration of glacial terminations over that period depended on solar obliquity and precession. Science , this issue p. 1235
During Integrated Ocean Drilling Program Expedition 339, the shipboard micropaleontological studi... more During Integrated Ocean Drilling Program Expedition 339, the shipboard micropaleontological studies of Site U1387 core catcher samples revealed the preservation of diatoms and radiolarians in specific depths from early Pleistocene age (900-1000 ka). To evaluate the ecological significance of those diatoms, we analyzed 98 samples from the intervals of 244 to 274 m along the corrected splice, corresponding to marine isotope Stage (MIS) 25 to MIS 29, for the abundance of diatoms and silicoflagellates. In 6 samples, the composition of the diatom assemblage was determined as well. Although most samples were barren of siliceous microfossils, the downcore record revealed two intervals, 249-252 corrected meters composite depth (cmcd) and 263-265 cmcd, where diatoms and silicoflagellates reach their maximum values. These maxima occurred from the MIS 26/25 transition to interglacial MIS 25, and again during early MIS 27. The diatom assemblage includes 27 identified taxa with Chaetoceros (Hyalochaete) resting spores being dominant and Thalassionema nitzschioides and Paralia sulcata significant. The Chaetoceros spores clearly indicate strong influence of seasonal upwelling and associated high primary productivity. Special to the diatom record is, however, the occurrence of the large-diameter (>125 µm) centric diatoms Coscinodiscus asteromphalus, Coscinodiscus apiculatus, and Coscinodiscus cf. gigas that imply incursions of low-nutrient, open-ocean water into the southern Portuguese coast during MIS 25.
To assess the anthropogenic effect on biodiversity, it is essential to understand the global dive... more 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 estim...
north, and the South Atlantic current in the south). In conclusion, we provide statistical proof ... more 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.
The Late Pliocene marks the intensification of Northern Hemisphere glaciation (iNHG), offering a ... more The Late Pliocene marks the intensification of Northern Hemisphere glaciation (iNHG), offering a unique opportunity to study climate evolution and ice-sheet-related feedback mechanisms. In this study, we present highresolution Mg / Ca-based sea surface temperatures (SSTs) and subsurface temperatures (SubTs) derived from the foraminiferal species Globigerinoides ruber and Globorotalia hirsuta, respectively, at the Integrated Ocean Drilling Program (IODP) Expedition 306 Site U1313 in the midlatitudinal North Atlantic during the early Late Pliocene, 3.65-3.37 million years ago (Ma). We find distinct differences between our new G. ruber Mg / Ca-based SST record and previously published alkenone-based SST records from the same location. These discrepancies in both absolute values and variations highlight distinctly different seasonal influences on the proxies. The G. ruber Mg / Ca-based SST data were primarily influenced by local summer insolation, showing a dominant precession cycle. Conversely, the variations in alkenone-based SST, dominated by the obliquity and lacking the precession cycle, are found to be more indicative of cold-season changes, despite previous interpretations of these records as reflecting annual mean temperatures. A simultaneous decline in Mg / Ca-based SST and SubT records from 3.65 to 3.5 Ma suggests a diminished poleward oceanic heat transport, implying a weakening of the North Atlantic Current (NAC). A comparison with Early Pleistocene G. ruber Mg / Ca-based SST records shows a shift in the dominant climatic cycle from precession to obliquity, alongside a marked increase in amplitude, indicating an enhanced influence of obliquity cycles correlated with the expansion of Northern Hemisphere ice sheets.
Centennial-millennial scale ocean-climate variability in the northeastern Atlantic across the last three terminations
Global and Planetary Change, 2023
Changes in Earth's orbital parameters pace the Pleistocene glacial-interglacial cycles, although ... more Changes in Earth's orbital parameters pace the Pleistocene glacial-interglacial cycles, although considerable ambiguity still remains over the interaction of the internal climatic variables, such as ice-sheet instability and ocean circulation that allow transitions into and out of an interglacial. Here, we analyse high-resolution planktic foraminiferal proxies including sea-surface temperature (SST) based on an Artificial Neural Network (ANN) across the last three terminations (TI, TII and TIII) and the subsequent interglacials (Holocene, Marine Isotope Stages (MIS) 5e and 7e) from IODP Site U1385, SW Iberian Margin. To demarcate the stadials and interstadials, we combined the faunal and SST records with existing data at Site U1385 including log (Ca/Ti) and benthic and planktic δ18O. The composite records reveal details of the last three terminations in terms of abrupt climatic events occurring during these terminations. Termination I included three well-known climatic events: Heinrich stadial (HS)1, Bølling/Allerød (B/A) complex & Younger Dryas (YD). Termination II was interrupted by only HS11. Termination III included HS8.2 and HS8.1 which show more resemblance to HS2 (a stadial prior to TI) and HS1, suggesting the YD is a unique feature of the last deglaciation. Additionally, TI and TII reveal similar durations (∼6 kyr) with rates of SST change (∼1.5 °C/kyr to ∼2.1 °C/kyr), whereas TIII represents a longer process (∼10 kyr) with a relatively slow rate of SST change (∼0.8 °C/kyr). The anatomy of stadials (HS1, HS2, HS11 & HS8.1) reveals a complex history (‘W' shaped anatomy) with two or three cold phases sandwiching (a) brief warm event(s). The European ice-sheet melting possibly initiated the stadial cooling at the Iberian Margin followed by the mid-latitude summertime warming and the intermediate-depth water mass warming that probably induced the Laurentide ice-sheet melting resulting in the complex stadial pattern. Our records further reveal a major reorganization of the surface current system, oceanographic fronts and productivity conditions across these terminations. We also document broad similarities in the climatic evolution of Holocene, MIS 5e and 7e interglacials in terms of SST, surface productivity and current system. The long-term interglacial trends were superimposed by multiple brief cold events interrupting the Holocene (∼11.3, 9.9, 8.2, 7.1, 5.5, 2.5 ka), MIS 5e (C28, C27, C27’, C27a, C27b, C26, C26’, C25), and MIS 7e (∼238, 234, 231, 230 ka) interglacials. Integration of our records with benthic foraminiferal δ13C records from the Iberian Margin and central North Atlantic suggest fluctuations in the deep water convection process (which in turn were influenced by the conditions in subpolar gyre) possibly resulted in the brief cold events interrupting the interglacials at the Iberian Margin.
We present a comprehensive multi-proxy analysis spanning 550,000 years from the outer Labrador Se... more We present a comprehensive multi-proxy analysis spanning 550,000 years from the outer Labrador Sea region at the Integrated Ocean Drilling Program (IODP) Sites U1302/1303. We combine new benthic foraminiferal stable oxygen (δ 18 O) and carbon (δ 13 C) isotope records, with sediment elemental composition and authigenic neodymium isotope measurements, to provide insights into deep-water mass sourcing and changes of the Deep Western Boundary Current (DWBC), which exports North Atlantic Deep Water (NADW) into the wider North Atlantic as part of the lower limb of the Atlantic Meridional Overturning Circulation. We find that a prominent DWBC likely remained a persistent feature within the Labrador Sea region throughout the past 550 kyr. However, glacial peaks of marine isotope stage (MIS) 14 to MIS 2 were consistently characterized by a weaker or shallower DWBC, while all interglacial periods of MIS 13a to MIS 1, with the exception of MIS 7e, were marked by enhanced DWBC. Additionally, the dominant deep-water masses feeding into the DWBC during these glacial-interglacial periods varied from regional (K-rich sediment, unradiogenic εNd) to more distal sources from the Nordic Seas (Ti-rich sediment, radiogenic εNd). Yet, these changes in deep-water provenance did not consistently correlate with DWBC strength, suggesting that additional factors may have played a significant role in shaping the DWBC strength or core depth throughout the geological past.
Species assemblage composition of marine microfossils offers the possibility to investigate ecolo... more Species assemblage composition of marine microfossils offers the possibility to investigate ecological and climatological change on time scales inaccessible using conventional observations. Planktonic foraminifera-calcareous zooplankton-have an excellent fossil record and are used extensively in palaeoecology and palaeoceanography. During the Last Glacial Maximum (LGM; 19,000-23,000 years ago), the climate was in a radically different state. This period is therefore a key target to investigate climate and biodiversity under different conditions than today. Studying LGM climate and ecosystems indeed has a long history, yet the most recent global synthesis of planktonic foraminifera assemblage composition is now nearly two decades old. Here we present the ForCenS-LGM dataset with 2,365 species assemblage samples collected using standardised methods and with harmonised taxonomy. the data originate from marine sediments from 664 sites and present a more than 50% increase in coverage compared to previous work. the taxonomy is compatible with the most recent global core top dataset, enabling direct investigation of temporal changes in foraminifera biogeography and facilitating seawater temperature reconstructions.
We present the first version of the Ocean Circulation and Carbon Cycling (OC3) working group data... more We present the first version of the Ocean Circulation and Carbon Cycling (OC3) working group database, of oxygen and carbon stable isotope ratios from benthic foraminifera in deep ocean sediment cores from the Last Glacial Maximum (LGM, 23-19 ky) to the Holocene (<10 ky) with a particular focus on the early last deglaciation (19-15 ky BP). It includes 287 globally distributed coring sites, with metadata, isotopic and chronostratigraphic information, and age models. A quality check was performed for all data and age models, and sites with at least millennial resolution were preferred. Deep water mass structure as well as differences between the early deglaciation and LGM are captured by the data, even though its coverage is still sparse in many regions. We find high correlations among time series calculated with different age models at sites that allow such analysis. The database provides a useful dynamical approach to map physical and biogeochemical changes of the ocean throughout the last deglaciation.
Untangling the origin of the newcomer Phorcus sauciatus (Mollusca: Gastropoda) in a remote Atlantic archipelago
Marine Biology, 2021
The marine topshell Phorcus sauciatus is currently found along the temperate–subtropical shores o... more The marine topshell Phorcus sauciatus is currently found along the temperate–subtropical shores of the Northeast Atlantic Ocean. Although present in the Iberian Peninsula, Madeira, and Canaries for centuries, P. sauciatus has only recently reached another oceanic volcanic archipelago in the region. In 2013, a small population was recorded for the first time in Santa Maria Island (Azores), widening its distribution around the entire island and to the neighbouring island of São Miguel in a short period of time. The success of such colonization of the remote archipelago by P. sauciatus still awaits an explanation. To better understand the populational dynamics of the species in the NE Atlantic Ocean, we used a molecular approach to evaluate the genetic structure of P. sauciatus aiming at the determination of a potential origin for the first individuals that reached the Azores. On the foundations of detailed oceanographic, palaeontological, and ecological data, we discuss the impact of climate change as a trigger for colonization of remote oceanic islands and suggest a mechanism that might explain the long-distance dispersal of the non-planktotrophic gastropod P. sauciatus across important biogeographical barriers in the NE Atlantic.
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