Tracking climate dynamics across the Middle Pleistocene Transition, in mid-latitudes and subtropics of the North Atlantic CLIMAx

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delta O-18 and Mg/Ca thermometry in planktonic foraminifera: a multiproxy approach toward tracing oastal upwelling dynamics

Publication . 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, Fatima

Planktonic 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.

2020-02Journal article

Restricted access

Rising atmospheric CO2 concentrations: the overlooked factor promoting SW Iberian Forest development across the LGM and the last deglaciation?

Publication . Domingues Gomes, Sandra; Fletcher, William; Stone, Abi; Anica Claro Rodrigues, Teresa Isabel; Rebotim, Andreia; Oliveira, Dulce; Goñi, Maria Sánchez; Abrantes, Fatima; Naughton, Filipa

A cross the last deglaciation, the atmospheric CO2 concentration (CO2) increased substantially from ∼ 180 to ∼ 280 ppm, yet its impact on vegetation dynamics across this major climatic transition remains insufficiently understood. In particular, Iberian pollen records reveal an intriguing feature that can be related to an often-overlooked role of CO2 in shaping vegetation responses during the last deglaciation. These records reveal the near disappearance of forests during the cold Last Glacial Maximum (LGM) and Heinrich Stadial 1 (HS1) phases and an unexpected recovery during the Younger Dryas (YD) cold phase when CO2 increased. Here, we present high-resolution tracers of terrestrial (pollen, C29: C31 organic biomarker) and marine (alkenone-derived Sea Surface Temperature, C37: 4 %, and long-chain n-alkanes ratios) conditions from the southwestern (SW) Iberian margin Integrated Ocean Drilling Program Site U1385 (“Shackleton site”) for the last 22 cal kyr BP. This direct land-sea comparison approach allows us to investigate how the Iberian Peninsula vegetation responded to major global CO2 changes during the last deglaciation. Our results show that cool and moderately humid conditions of the LGM supported a grassland-heathland mosaic ecosystem, but low CO2 likely caused physiological drought and suppressed forest development. HS1, the coldest and most arid period, combined with sustained low CO2 values, almost suppressed forest growth in favour of Mediterranean steppe. In contrast, the warmer Bølling-Allerød, characterised by a temperature optimum and variable but generally wetter conditions, along with the rise of CO2 above 225 ppm at ∼ 15 cal kyr BP, contributed to substantial forest development. During the YD, sufficient moisture combined with increasing CO2 enabled the persistence of a mixed grassland-forest mosaic despite cooler temperatures. Our study suggests that during cool and humid periods (LGM and YD) different pCO2 values led to contrasting SW Iberian vegetation responses. In contrast, during periods of relatively high CO2, temperature and precipitation played the main role in shaping the distribution and composition of the vegetation.

2025-11-07Journal article

Open access