Beschreibung: We contend that ocean turbulent fluxes should be included in the list of Essential Ocean Variables (EOVs) created by the Global Ocean Observing System. This list aims to identify variables that are essential to observe to inform policy and maintain a healthy and resilient ocean. Diapycnal turbulent fluxes quantify the rates of exchange of tracers (such as temperature, salinity, density or nutrients, all of which are already EOVs) across a density layer. Measuring them is necessary to close the tracer concentration budgets of these quantities. Measuring turbulent fluxes of buoyancy (Jb), heat (Jq), salinity (JS) or any other tracer requires either synchronous microscale (a few centimeters) measurements of both the vector velocity and the scalar (e.g., temperature) to produce time series of the highly correlated perturbations of the two variables, or microscale measurements of turbulent dissipation rates of kinetic energy (ϵ) and of thermal/salinity/tracer variance (χ), from which fluxes can be derived. Unlike isopycnal turbulent fluxes, which are dominated by the mesoscale (tens of kilometers), microscale diapycnal fluxes cannot be derived as the product of existing EOVs, but rather require observations at the appropriate scales. The instrumentation, standardization of measurement practices, and data coordination of turbulence observations have advanced greatly in the past decade and are becoming increasingly robust. With more routine measurements, we can begin to unravel the relationships between physical mixing processes and ecosystem health. In addition to laying out the scientific relevance of the turbulent diapycnal fluxes, this review also compiles the current developments steering the community toward such routine measurements, strengthening the case for registering the turbulent diapycnal fluxes as an pilot Essential Ocean Variable.

Beschreibung: A 15-year (2004–2018) record of mooring observations from the upper 50 m of the ocean in the eastern Eurasian Basin reveals increased current speeds and vertical shear, associated with an increasing coupling between wind, ice, and the upper ocean over 2004–2018, particularly in summer. Substantial increases in current speeds and shears in the upper 50 m are dominated by a two times amplification of currents in the semidiurnal band, which includes tides and wind-forced near-inertial oscillations. For the first time the strengthened upper ocean currents and shear are observed to coincide with weakening stratification. This coupling links the Atlantic Water heat to the sea ice, a consequence of which would be reducing regional sea ice volume. These results point to a new positive feedback mechanism in which reduced sea ice extent facilitates more energetic inertial oscillations and associated upper-ocean shear, thus leading to enhanced ventilation of the Atlantic Water.

Beschreibung: A 15-yr duration record of mooring observations from the eastern (〉70°E) Eurasian Basin (EB) of the Arctic Ocean is used to show and quantify the recently increased oceanic heat flux from intermediate-depth (~150–900 m) warm Atlantic Water (AW) to the surface mixed layer and sea ice. The upward release of AW heat is regulated by the stability of the overlying halocline, which we show has weakened substantially in recent years. Shoaling of the AW has also contributed, with observations in winter 2017–18 showing AW at only 80 m depth, just below the wintertime surface mixed layer, the shallowest in our mooring records. The weakening of the halocline for several months at this time implies that AW heat was linked to winter convection associated with brine rejection during sea ice formation. This resulted in a substantial increase of upward oceanic heat flux during the winter season, from an average of 3–4 W m−2 in 2007–08 to 〉10 W m−2 in 2016–18. This seasonal AW heat loss in the eastern EB is equivalent to a more than a twofold reduction of winter ice growth. These changes imply a positive feedback as reduced sea ice cover permits increased mixing, augmenting the summer-dominated ice-albedo feedback.

Beschreibung: As a part of the Scientific Committee on Oceanographic Research (SCOR) Working Group #160 “Analyzing ocean turbulence observations to quantify mixing” (ATOMIX), we have developed recommendations on best practices for estimating the rate of dissipation of kinetic energy, ε, from measurements of turbulence shear using shear probes. The recommendations provided here are platform-independent and cover the conceivable range of dissipation rates in the ocean, seas, and other natural waters. They are applicable to commonly deployed platforms that include vertical profilers, fixed and moored instruments, towed profilers, submarines, self-propelled ocean gliders, and other autonomous underwater vehicles. The procedure for preparing the shear data for spectral estimation is discussed in detail, as are the quality control metrics that should accompany each estimate of ε. The methods are illustrated using a high-quality ‘benchmark’ dataset, while potential pitfalls are demonstrated with a second dataset containing common faults.

Beschreibung: Turbulent mixing in the ocean, lakes and reservoirs facilitates the transport of momentum, heat, nutrients, and other passive tracers. Turbulent fluxes are proportional to the rate of turbulent kinetic energy dissipation per unit mass, ε. A common method for ε measurements is using microstructure profilers with shear probes. Such measurements are now widespread, and a non-expert practitioner will benefit from best practice guidelines and benchmark datasets. As a part of the Scientific Committee on Oceanographic Research (SCOR) working group on “Analysing ocean turbulence observations to quantify mixing” (ATOMIX), we compiled a collection of five benchmark data of ε from measurements of turbulence shear using shear probes. The datasets are processed using the ATOMIX recommendations for best practices documented separately. Here, we describe and validate the datasets. The benchmark collection is from different types of instruments and covers a wide range of environmental conditions. These datasets serve to guide the users to test their ε estimation methods and quality-assurance metrics, and to standardize their data for archiving.

Beschreibung: During Polarstern expedition PS131 (ATWAICE: ATlantic WAter pathways to the ICE), a large number of autonomous instruments were installed on three representative ice floes across the marginal ice zone northwest of Svalbard in July 2022. The aim was to investigate sea ice summer melt processes, with a focus on the contribution of the Atlantic water inflow into the region. The attached .zip file includes raw data files obtained from all instruments deployed on the northernmost floe, also referred to as Floe North. Depending on the instrument, the data were transmitted via satellite, collected on internal memory, or both. The instruments were installed on Floe North on 13 July 2022, revisited for maintenance on 20 July 2022, and partially recovered on 30 July 2022. The sensors included 3 ADCPs in different configurations to measure ocean currents, a CTD buoy (SIT) with 6 SBE37IMP and an ECO Triplet fluorometer, a HOBO under-ice conductivity chain, 3 ice mass balance buoys (IMBs) of different types to determine ice surface and bottom melt, a radiation station equipped with 3 TriOS RAMSES radiometers to measure albedo and the under-ice light field, a Campbell Scientific weather station for atmospheric conditions, an OpenMetBuoy (OMB) and IMU logger for wave detection, a handful of GPS drifters to mark instruments, and 4 timelapse cameras to document surface changes. All instruments performed as expected, except one S1000 ADCP that failed due to power issues. All but three instruments (one OpenMetBuoy, one SVP, and one IMB) were recovered before leaving the study area on 30 July. The processed data will be provided and linked to when available.

Beschreibung: During the MOSAiC drift, vertical profiles of turbulence and auxiliary parameters were measured with MSS microstructure profilers manufactured by Sea and Sun Technology, Germany. Here, the raw binary data from one of in total three different probes deployed during the drift is archived, in the instrument-specific .MRD data format. Every profile is stored in one individual binary file.

Beschreibung: Time series data of physical oceanography (seawater conductivity, temperature, pressure, salinity) and ocean current velocities were obtained from mooring M3 on the upper part (750 m isobath) of the continental slope, just east of the Filchner Trough in the southern Weddell Sea in February 2017 - February 2021. The mooring was deployed during the WAPITI expedition on James Clark Ross (JR16004), and recovered during the COSMUS expedition with Polarstern (PS124). The attached archive contains data from 1 RCM7 (21 meters above bottom (mab herafter) and sampling interval (sint hereafter) 2h), 13 SBE56 (22,56,81,106,159,184,6508,260,285,310,335,360,385 mab, sint: 120 s), 4 SBE37 (31, 134, 209, 410 mab, sint: 600 s), 1 RDI ADCP 75 kHz (235 mab, upwardlooking, sint: 2h), 1 SBE39 (435 mab, sint: 900s). Mooring diagrams and information about data processing are provided.

Beschreibung: During the MOSAiC drift, vertical profiles of turbulence and auxiliary parameters were measured with MSS microstructure profilers manufactured by Sea and Sun Technology, Germany. Here, the raw binary data from one of in total three different probes deployed during the drift is archived, in the instrument-specific .MRD data format. Every profile is stored in one individual binary file.