Seminar

Deepwater formation in the northern North Atlantic facilitates global ocean circulation, which is responsible for transporting heat, greenhouse gases, and nutrients throughout the global marine environment. Surface buoyancy changes forced by intense meltwater events are conventionally believed to inhibit deepwater formation, slow ocean circulation and potentially result in a cascade of climate changes around the world. While this may be true in the context of modern climate forcing, geochemical evidence suggests that an active overturning circulation was maintained in the Nordic Seas concomitant with extreme freshwater discharge characteristic of the marine isotope stage 11 interglacial, which highlights our incomplete understanding of the surface mechanisms that regulate deepwater formation. Throughout my PhD, I will be using novel advances in stable nitrogen analysis to characterize structural changes in the surface mixed layer during key interglacial periods, marine isotope stages 11 (424 – 374 ka) and 15 (621 – 563 ka). Combining these data with trace element analyses and oxygen isotope records further enhances surface water reconstructions. Results obtained thus far indicate that mixed layer variability was largely controlled by freshwater forcing in the Nordic Seas during marine isotope stage 11. It is further observed that a connection between mixed layer depth and global ocean ventilation was initiated with the peak interglaciatian of stage 11, suggesting that the Nordic Seas became an important source region for deepwater formation at this time.