Deglacial 14C reservoir ages of surface waters at the northern boundary of Peruvian coastal upwelling
- 1Geomar Helmholtz Centre for Ocean Research Kiel, Marine Geosystems, Kiel, Germany (nglock@geomar.de)
- 2Institute of Geosciences, University of Kiel, Olshausenstr. 40, 24098 Kiel, Germany
- 3Department of Oceanography, Dalhousie University, Halifax, Nova Scotia, Canada
- 4Alfred-Wegener-Institut Helmholtz-Zentrum für Polar-und Meeresforschung, Department Geosciences/Marine Geochemistry, 27570 Bremerhaven, Germany
To constrain the accurate age of a marine sediment record, the radiocarbon (14C) ages need to be corrected for short-term and small-scale changes in planktic 14C reservoir ages (Rplank). Nevertheless, accurate records of past changes in Rplank are scarce. Here we present a high-resolution record of deglacial 14C ages measured on Globigerina bulloides in sediment core M77/2-59-1 from the northern boundary (~4°S, 997 m) of the Peruvian upwelling zone. The fine structure of jumps and plateau boundaries in the 14C record were tuned to synchronous, thus global structures in the atmospheric 14C record of Lake Suigetsu (Bronk Ramsey et al., 2012) and used as tie points for an age model with semi-millennial resolution, moreover to reconstruct deglacial changes in Rplank from 17 to 11 cal. ka. In our record, Rplank drops from 1250 14C yr prior to 14 cal. ka to ~600 – 450 14C yr until the plateau named Top of Younger Dryas. The drop suggests a major decrease in coastal upwelling, possibly the result of a southward (poleward) expansion of the Intertropical Convergence Zone and related shift in the southeastern trade wind belt during the Bølling-Allerød. Subsequent to 14 cal. ka our Rplank values are roughly similar to values obtained for thermocline waters near the equator from the age difference between 14C ages of wood chunks and 14C of G. ruber (Zhao & Keigwin, 2018). Prior to 14 cal. ka our Rplank are ~800 14C yr higher, which corroborates the presumed latitudinal shift of coastal upwelling. Our 14C ages measured on G. bulloides differ in part from paired 14C ages of Neogloboquadrina dutertrei, indicating their habitat in different water masses prior to 14 cal. ka, in support of the upwelling affinity of G. bulloides. In addition, we used our Rplank values to accurately derive past ventilation ages of intermediate waters near 1000 m depth based on the difference of paired benthic and planktic 14C ages, which is important to constrain centennial to millennial scale changes in circulation influencing the extent of the Peruvian oxygen minimum zone.
References:
Bronk Ramsey, C., et al., Science, 338, 370–374, 2012.
Zhao & Keigwin, Nature communications, 9, 3077, 2018.
How to cite: Glock, N., Sarnthein, M., Doering, K., Mollenhauer, G., and Salvatteci, R.: Deglacial 14C reservoir ages of surface waters at the northern boundary of Peruvian coastal upwelling, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4727, https://doi.org/10.5194/egusphere-egu2020-4727, 2020
