Abstract:the Intertropical Convergence Zone during winter. Between 3.2 and 2.9 Ma, ODP Site 959 Ti/Ca ratios exhibit three maxima corresponding to eccentricity maxima similarly to other dust records of northern Africa. This suggests continent-wide aridity or larger climate variability during that interval. Eccentricity forcing (405 and 100 kyr) and precession frequencies are found in the entire studied interval. The variations of Ti/Al ratio suggest stronger seasonality between 5.8 and 5.5 Ma and after 3.2 Ma.
“…Upper Pliocene sediments were 10.1029/2019PA003804 initially identified based on nannofossil biostratigraphy (Shin, 1998) and comprise nannofossil/foraminifer ooze. Recently, Vallé et al (2017) generated a spliced composite record of the upper~100 m of Holes A, B, and C based on X-Ray Fluorescence scan data. They tuned Fe intensity from their new composite record to orbitally induced variations in insolation (sum of eccentricity, precession and tilt), derived from the La2004 astronomical solution (Laskar et al, 2004), constraining the late Pliocene interval with four cyclostratigraphic tie points.…”
Section: Site Descriptions and Age Modelsmentioning
Late Pliocene deep Atlantic δ 13 C data have been interpreted as evidence for enhanced Atlantic Meridional Overturning Circulation (AMOC) compared to the present, but this hypothesis is not supported by the Pliocene Model Intercomparison Project (PlioMIP). Here, we adopt a new approach to assess variability in deep ocean circulation based on paired stable carbon (δ 13 C) and oxygen isotopes (δ 18 O) of benthic foraminifera, both (semi)conservative water mass tracers. Assuming that deep Atlantic benthic δ 13 C-δ 18 O variability is predominantly driven by mixing, we extrapolate the δ 13 C-δ 18 O data outside the sampled range to identify the end-members. At least three end-members are needed to explain the spatial δ 13 C-δ 18 O variability in the deep North Atlantic Ocean: two Northern Component Water (NCW) and one Southern Component Water (SCW) water masses. We use a ternary mixing model to quantify the mixing proportions between SCW and NCW in the deep Atlantic Ocean. Our analysis includes new data from Ocean Drilling Program Sites 959 and 662 in the eastern equatorial Atlantic and suggests that the AMOC cell was deeper during the M2 glacial than during late Pliocene interglacials. Moreover, we identify a new cold and well-ventilated water mass that was geographically restricted to the southeast Atlantic Ocean between 3.6 and 2.7 Ma and did not contribute significantly to the δ 13 C-δ 18 O variability of the rest of the basin. This high-δ 13 C high-δ 18 O water mass has led to the misconception of a reduced latitudinal δ 13 C gradient. Our analyses show that the late Pliocene δ 13 C gradient between NCW and SCW was similar to the present-day value of 1.1‰.
“…Upper Pliocene sediments were 10.1029/2019PA003804 initially identified based on nannofossil biostratigraphy (Shin, 1998) and comprise nannofossil/foraminifer ooze. Recently, Vallé et al (2017) generated a spliced composite record of the upper~100 m of Holes A, B, and C based on X-Ray Fluorescence scan data. They tuned Fe intensity from their new composite record to orbitally induced variations in insolation (sum of eccentricity, precession and tilt), derived from the La2004 astronomical solution (Laskar et al, 2004), constraining the late Pliocene interval with four cyclostratigraphic tie points.…”
Section: Site Descriptions and Age Modelsmentioning
Late Pliocene deep Atlantic δ 13 C data have been interpreted as evidence for enhanced Atlantic Meridional Overturning Circulation (AMOC) compared to the present, but this hypothesis is not supported by the Pliocene Model Intercomparison Project (PlioMIP). Here, we adopt a new approach to assess variability in deep ocean circulation based on paired stable carbon (δ 13 C) and oxygen isotopes (δ 18 O) of benthic foraminifera, both (semi)conservative water mass tracers. Assuming that deep Atlantic benthic δ 13 C-δ 18 O variability is predominantly driven by mixing, we extrapolate the δ 13 C-δ 18 O data outside the sampled range to identify the end-members. At least three end-members are needed to explain the spatial δ 13 C-δ 18 O variability in the deep North Atlantic Ocean: two Northern Component Water (NCW) and one Southern Component Water (SCW) water masses. We use a ternary mixing model to quantify the mixing proportions between SCW and NCW in the deep Atlantic Ocean. Our analysis includes new data from Ocean Drilling Program Sites 959 and 662 in the eastern equatorial Atlantic and suggests that the AMOC cell was deeper during the M2 glacial than during late Pliocene interglacials. Moreover, we identify a new cold and well-ventilated water mass that was geographically restricted to the southeast Atlantic Ocean between 3.6 and 2.7 Ma and did not contribute significantly to the δ 13 C-δ 18 O variability of the rest of the basin. This high-δ 13 C high-δ 18 O water mass has led to the misconception of a reduced latitudinal δ 13 C gradient. Our analyses show that the late Pliocene δ 13 C gradient between NCW and SCW was similar to the present-day value of 1.1‰.
“…Samples were taken at 5-20 cm intervals from cores 959C-5H and 959C-6H between 35.77 and 48.73 revised Meters Composite Depth (rMCD) following the splice of (Vallé et al, 2016). We combine our new records with previously published early Pliocene data from Norris, (1998) from the 55.32 to 97.17 rMCD interval in cores 959C-7H to 959C-10H.…”
Section: Stable Isotope Analysismentioning
confidence: 99%
“…The Pliocene interval at Site 959 was initially dated using foraminifera and nannofossil biostratigraphy (Norris, 1998;Shin et al, 1998) and more recently updated with astronomical tuning of X-Ray Fluorescence (XRF) scan data, notably Fe records to an eccentricity, tilt and precession (ETP) curve (Vallé et al, 2016; 1.9-6.2 Ma) and tuning of benthic δ 18 O to the LR04 stack (van der Weijst et al, in review (2020); 2.8-3.5 Ma). We use the van der Weijst et al (in review, 2020) age model for the late Pliocene and the Vallé et al (2016) age model for the early Pliocene and latest Miocene interval (3.8-5.7 Ma).…”
Section: Age Modelmentioning
confidence: 99%
“…It is possible that this apparent temporal offset is an artefact of age model inaccuracies at both sites. The early Pliocene age model of Site 959 is based on low-resolution tuning between Fe intensities and the Eccentricity Tilt Precession target curve (Vallé et al, 2016). In contrast, Site 1000 was dated with highresolution tuning of benthic δ 18 O to the δ 18 O records at Site 925/926 (Steph et al, 2006a).…”
Abstract. The tropical thermocline may have played a crucial role in maintaining weaker sea surface temperature gradients during the early Pliocene and in the onset of late Pliocene northern hemisphere glaciation. Whereas the Pliocene Pacific thermocline evolution is well documented, complete records of Pliocene tropical Atlantic thermocline depths are limited to the Caribbean region. Here, we use the oxygen isotope gradient between surface to subsurface dwelling planktic foraminifera from Ocean Drilling Program Site 959 in the eastern equatorial Atlantic to track vertical changes in thermocline depth over the course of the Pliocene. This record shows that eastern equatorial Atlantic thermocline depth varied substantially during the early Pliocene, before finally deepening abruptly around 4.5 Ma to remain relatively stable until at least 2.8 Ma. Eastern equatorial Atlantic and Caribbean records are almost identical, suggesting a common control on the sudden step-wise thermocline deepening across the basin, in contrast to previous assumptions. The Pliocene evolution of the tropical Atlantic thermocline differs is remarkably from the Pacific, which is characterized by gradual basin-wide shoaling. It remains unclear what mechanisms were involved in the dichotomous thermocline evolutions. Whereas Central American Seaway closure may have shoaled the Pacific thermocline, it is not yet understood if and how this process may have deepened the Atlantic thermocline. A divergent evolution of temperatures of the source regions may explain the opposite thermocline developments observed, possibly amplified by a positive feedback loop involving tropical cyclone intensity.
“…The presence and extent of mangrove stands in Africa are directly related to humidity, rainfall, and coastal relief and are known to have undergone extensive expansions and contractions in both range and abundance over time (Saenger & Bellan, 1995 ). Indeed, the study of mangrove cover is a primary source of information for modelling impacts of climate change (Alongi, 2015 ), as well as for palaeoclimatic reconstructions based on historical data from mangrove pollens (Bonefille et al, 1982 ; Leroy & Dupont, 1994 ; Scourse et al, 2005 ; Durogbo et al, 2010 ; Adeonipekun et al, 2016 ; Vallé et al, 2017 ). Fig.…”
Available ecological information, an extensive distributional range, conflicting osteological data, and a proposed early Miocene origin provide the impetus for the present study which investigates genetic structuring, biogeographic, and phylogenetic relationships within the Aplocheilichthys spilauchen lineage. Through the analysis of the mitochondrial gene COI, species delimitation methods (ABGD, GB, GMYC, bPTP) were applied, recognizing 6-7 OTUs with absolute pairwise genetic distances ranging between 8 and 22%. The onset of diversification is estimated to be within the middle Miocene and both dispersal and vicariance-shaped A. spilauchen diversity and distribution, as suggested by time-calibrated and ancestral range reconstruction (S-DIVA) analyses. We report for the first time, a pattern of diversification within a lineage of brackish water fish that is concordant with the historical distribution of coastal mangroves forests, shaped by a series of historical events that likely affected forest cover since the middle Miocene (e.g. major climate shifts and sealevel fluctuations, onset of the modern Congo River outlet, increased volcanism in the Cameroon Volcanic Line).
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