PP41B-2227
Subsurface pCO2, nutrient levels and ventilation in the Norwegian Sea during the past 135 kyr

Thursday, 17 December 2015
Poster Hall (Moscone South)
Mohamed Ezat, University of Tromsø, Tromsø, Norway, Tine Lander Rasmussen, University of Tromsø, CAGE -Centre for Arctic Gas Hydrate, Environment and Climate, Tromsø, Norway, Baerbel Hoenisch, Columbia University, Lamont-Doherty Earth Observatory, Palisades, NY, United States, Jesper Olsen, Aarhus University, Aarhus, Denmark, Jeroen Groeneveld, MARUM - University of Bremen, Bremen, Germany and Luke Cameron Skinner, University of Cambridge, Cambridge, United Kingdom
Abstract:
Deglacial ∆14C anomalies at mid-depth in the northern North Atlantic have been attributed to venting of an abyssal CO2-rich and 14C-depleted reservoir in the Southern Ocean and northward transport via the Antarctic Intermediate Water (Thornalley et al., 2011). However, the southern source of these ∆14C anomalies remains in question (e.g., Sortor and Lund, 2011; Huang et al., 2014). An alternative source could be the Nordic and Arctic basins (Cléroux et al., 2011; Lund et al., 2015). On the basis of d11B, ∆14C, Cd/Ca and d13C, measured in the shells of the planktic foraminiferal species Neogloboquadrina pachyderma (sinistral) and ∆14C measured in benthic foraminifera, we assess the evolution of subsurface seawater carbonate chemistry, ventilation age and nutrients in the southern Norwegian Sea. We find no evidence for an aged outflow from the Norwegian Sea enough to explain the ∆14C anomalies previously found south of Iceland during the early and late Heinrich Stadial (HS) 1. At mid-HS 1 (~16.5 ka), our seawater carbonate chemistry and ventilation age reconstructions suggest a southward export of relatively well-ventilated waters, possibly by brine formation, potentially ventilating the thermocline in the northern North Atlantic. We also document interspecies differences in the benthic radiocarbon ages from a few hundred years to several thousands of years, adding evidence for caution in using ‘mixed benthic species’ for 14C dates.

References

Cléroux, C., deMenocal, P., & Guilderson, T. (2011). Deglacial radiocarbon history of tropical Atlantic thermocline waters: absence of CO2 reservoir purging signal. Quaternary Science Reviews.

Huang, K.-F., Oppo, D. W., & Curry, W. B. (2014). Decreased influence of Antarctic intermediate water in the tropical Atlantic during North Atlantic cold events. Earth and Planetary Science Letters.

Lund, D. C., Tessin, A. C., Hoffman, J. L., & Schmittner, A. (2015). Southwest Atlantic water mass evolution during the last deglaciation. Paleoceanography.

Sortor, R. N., & Lund, D. C. (2011). No evidence for a deglacial intermediate water Δ14C anomaly in the SW Atlantic. Earth and Planetary Science Letters.

Thornalley, D. J. R., Barker, S., Broecker, W. S., Elderfield, H., & McCave, I. N. (2011). The Deglacial Evolution of North Atlantic Deep Convection. Science.

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