δ¹⁸O and Mg/Ca Thermometry in Planktonic Foraminifera: A Multiproxy Approach Toward Tracing Coastal Upwelling Dynamics

Abstract

Planktonic foraminifera δ18O 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 δ18O 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 δ18O 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 δ18O and Mg/Ca temperature reconstructions. The δ18O‐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 δ18O 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.

Tracking Agulhas leakage in the South Atlantic using modern planktic foraminifera nitrogen isotopes

“…(1.9‰ and 1.8‰ for G. truncatulinoides and G. hirsuta, respectively) is likely explained by their similar depth habitat and a common food source. Likewise, the similar (and larger) FT-δ 15 N offset for G. inflata and G. bulloides (2.9‰ and 3.4‰, respectively) suggests a similar depth habitat (and thus access to similar food sources), as has been observed for these two species in nutrient-rich regions (Mohtadi et al, 2007;Salgueiro et al, 2020;Zarkogiannis et al, 2020). The larger FTδ 15 N offset for these and other shallow-to intermediate-depth dwellers (including G. siphonifera) compared to G. truncatulinoides and G. hirsuta could be linked to their faster isotope turnover times (i.e., shorter lifespans and/or faster metabolisms) and/or their inhabiting a restricted depth range within the eddy (e.g., upper 100 m, Table 1), leading them to incorporate the low-δ 15 N signature of the eddy more quickly.…”

New Insights Into the Surface‐Ocean Dynamics of the Northeastern Atlantic Ocean Across the Marine Isotope Stage 7

“…We used the same ANN configuration as Singh et al (2023). And the networks were trained on the combined MARGO North Atlantic and the Iberian Margin planktic foraminiferal databases to reconstruct the annual SST (Kucera et al, 2005;Salgueiro et al, 2014Salgueiro et al, , 2020Singh et al, 2023). Estimated error of the reconstructed annual SST record is ±1.22°C (for details see Singh et al, 2023).…”

micropaleontología como herramienta de datación e identificación de eventos climáticos en registros sedimentarios marinos

“…Otras técnicas muy usadas para reconstruir la temperatura superficial del agua utilizan indicadores biogeoquímicos que están íntimamente ligados a la temperatura del agua, como la concentración de magnesio respecto a calcio (e.g. Salgueiro et al, 2020) en las conchas de foraminíferos planctónicos, o la concentración de alquenonas en el sedimento, una sustancia producida por algunas algas cocolitoforales (e.g. Martrat et al, 2007;Rodrigues et al, 2017).…”