A full year of turbulence measurements from a drift campaign in the Arctic Ocean 2019-2020

Abstract

Ocean turbulent mixing is a key process in the global climate system, regulating ocean circulation and the uptake and redistribution of heat, carbon, nutrients, oxygen and other tracers. In polar oceans, turbulent heat transport additionally affects the sea ice mass balance. Due to the inaccessibility of polar regions, direct observations of turbulent mixing are sparse in the Arctic Ocean. During the year-long drift expedition "Multidisciplinary drifting Observatory for the Study of Arctic Climate" (MOSAiC) from September 2019 to September 2020, we obtained an unprecedented data set of vertical profiles of turbulent dissipation rate and water column properties, including oxygen concentration and fluorescence. Nearly 1,700 profiles, covering the upper ocean down to approximately 400 m, were collected in sets of 3 or more consecutive profiles every day, and complemented with several intensive sampling periods. This data set allows for the systematic assessment of upper ocean mixing in the Arctic, and the quantification of turbulent heat and nutrient fluxes, and can help to better constrain turbulence parameterizations in ocean circulation models.

Fig. 1

(a) MSS winch and profiler with sensors and protection cage (ⒸLisa Grosfeld), MSS setup during (b), (c) legs 1–3 within heated tent, (d) leg 4 (prior to installation of tent, with adjacent meltpond draining into hydrohole, ⒸMorven Muilwijk) and (e) leg 5.

Fig. 2

(a) Map of the Arctic Ocean, with gray lines denoting isobars with a spacing of 1000 m, and daily averaged sampling positions. Colors refer to the depth-averaged (5–200 m) dissipation rates. Bathymetric data was taken from the IBCAO data set. (b) Time series of the cumulative number of individual profiles, with intensive sampling periods (see Table 3) and interruptions indicated. Colors refer again to the depth-averaged dissipation rates. Figure 2a was produced using the m_map matlab toolbox.

Fig. 3

(a) Distribution of dissipation rate in the upper 20 m (red), 20–50 m (blue) and lower than 50 m (yellow). The vertical dashed line indicates 8 × 10⁻¹⁰ W kg⁻¹ (b) Scatter plot of the dissipation rate estimates from both shear sensors. Dashed lines indicate a deviation of ± 2.

Fig. 4

Daily averaged (a) turbulent dissipation rate (W kg⁻¹), and (b) Brunt-Väisälä frequency (s⁻²) in the upper 140 m. Gray isolines indicate potential density anomaly of σ_θ = 26, 27, 29, 30, 31 kg m⁻³, gray patches indicate the two major interruptions of the drift.