Internal Wave Frequency Spectrum in the Amundsen Basin of the Arctic Ocean Inferred from Ice Tethered CTD Instruments Sergey V. Pisarev Introduction Reduction of the extent (area of the ocean with at least 15% of sea ice), average age, and thickness of the drifting sea ice are the widely known manifestations of the natural processes, which have received the title “warming of the Arctic”. Changes in the characteristics of ice are most pronounced in the summer period, but they are also significant in winter. The change in the characteristics of the drifting sea ice in the Arctic, despite a set of other consequences must apparently cause an increase in the energy of internal waves in the Arctic Ocean. The fact is that the existence of the drifting ice is considered among the two main causes explaining the well known low energy of internal waves in the high-latitude Arctic Ocean when compared with the ice-free ocean [1–3]. The current understanding is that internal wave energy is reduced in the ice-covered basins by (among other causes) the dissipation of internal wave energy in the surface boundary layer immediately below the ice [4, 5]. Recent findings demonstrate the sensitivity of the Arctic Ocean circulation to the background deep-ocean mixing. Results using a large-scale coupled ice-ocean model [6] suggest the appropriate model background mixing in the Arctic Ocean is one order of magnitude lower than in the ice-free oceans. Direct measurements of oceanic mixing are dif ficult, but decades of research suggest that deep background mixing is a consequence of the dissipation of internal wave energy. The exact nature of this relationship is an open question, but it makes it possible to infer mixing from relatively simple observations of internal wave energy. Consequently, if the ice cover is reduced, we may see increased internal wave energy, mixing, and heat flux in the deep ocean because less internal wave energy would be lost in the S. V. Pisarev ( ✉ ) Shirshov Institute of Oceanology, Russian Academy of Sciences, Moscow, Russia e-mail: pisarev@ocean.ru © Springer International Publishing AG, part of Springer Nature 2018 M. G. Velarde et al. (eds.), The Ocean in Motion, Springer Oceanography, https://doi.org/10.1007/978-3-319-71934-4_37 581