Ice Age‐Holocene Similarity of Foraminifera‐Bound Nitrogen Isotope Ratios in the Eastern Equatorial Pacific

Abstract

The eastern tropical Pacific (ETP) is important in climate and biogeochemical cycles. It hosts three upwelling systems: the equatorial upwelling, the coastal upwelling off California in the eastern tropical North Pacific (ETNP), and the Peru-Chile coastal upwelling in the eastern tropical South Pacific (ETSP) (Figure 1). In these regions, cold, nutrient-rich waters upwell to the surface, fueling productivity. In addition, slow circulation through the thermocline in these regions isolates the mid-depths waters from ventilation by the high latitudes. Due to the combination of slow ventilation and the abundance of sinking organic matter, respiration completely consumes the supply of dissolved oxygen (O 2 ), producing O 2 -deficient zones (ODZs),

Coupled Coccolith-Based Temperature and Productivity High-Resolution Reconstructions in the Eastern Equatorial Pacific During the Last Deglaciation and the Holocene

“…Foraminifera bound d 15 N ( 15 N/ 14 N ratio, a proxy for watercolumn denitrification) measured on Neogloboquadrina dutertrei and N. incompta (average values in Figure 10D) at ME0005A-24JC, show higher values up to the BA suddenly dropping during the YD (Studer et al, 2021). This pattern shows similarities with our CAR and NPP-F.profunda reconstructions, which drop at the end of Termination I (Figures 10A, B).…”

“…This pattern shows similarities with our CAR and NPP-F.profunda reconstructions, which drop at the end of Termination I (Figures 10A, B). Studer et al (2021) suggests that planktonic foraminifera d 15 N could be driven by changes in the d 15 N in intermediate water, nitrogen advection and nitrogen utilization by the phytoplankton, on top of the previously inferred d 15 N reduction in water column denitrification during the glacial suggested by Dubois and Kienast (2011) -based on bulk measurements-. The nitrogen utilization by phytoplankton as an explanation for part of the d 15 N variability is supported by our F. profunda-based data, with high steady NPP during Termination I (up to the BA) and a lower values during the Holocene.…”

“…We interpret the higher e f values during LGM and the deglaciation (Figure 11G) as a rise in nutrient supply to the thermocline, as noted by the higher d 15 N in planktonic foraminifera (N. dutertrei and N. incompta) (Studer et al, 2021) (Figure 10D), which resulted in higher NPP and export production (Costa et al, 2017;Jacobel et al, 2020). The lower SST during this interval prevented high remineralization of the organic detritus in the photic zone, leading to a more efficient downward transport of organic detritus and burial in the seafloor (Henson et al, 2012).…”

“…A further 16 were found to be devoid of coccoliths and therefore excluded from the considered dataset. Based on published radiocarbon dating of planktonic forminifera shells from surface sediments of the EEP (e.g., Koutavas and Lynch-Stieglitz, 2003;Mekik, 2014;Studer et al, 2021) (Table S2; Supplementary Material) as well as on available literature focusing on the south-eastern Pacific (SEP) area (e.g., Abrantes et al, 2007;Saavedra-Pellitero et al, 2010;Saavedra-Pellitero et al, 2011;Saavedra-Pellitero et al, 2013) the age of the sediments can be regarded as no older than late Holocene to Recent, as it mostly lies between 0.79 and 3.57 Cal age ka BP.…”

“…Reconstructions of LGM to Holocene EEP productivity also vary between proxies (e.g., Robinson et al, 2009;Schneider et al, 2010;Calvo et al, 2011;Kienast et al, 2013;Patarroyo and Martıńez, 2015;Costa et al, 2017;Diz et al, 2018;Jacobel et al, 2020), with some proxy systems responding to multiple environmental factors (Jacobel et al, 2020;Studer et al, 2021). Sediment cores separated by just a few degrees of latitude, north and south from the Equator, show diverging trends in productivity-related proxies, most likely as a consequence of the strong gradients in nutrient regimes and variable oceanographic features (e.g., Dubois et al, 2010;Dubois and Kienast, 2011;Costa et al, 2017;Studer et al, 2021). Multi-proxy studies thus provide a fuller, and hopefully more accurate, reconstruction of the coupling between stratification and productivity through time, as well as the basis to consider the spatial variation in productivity regimes across the EEP.…”