An ice mass balance buoy (IMB) allows scientists studying

sea ice Sea ice arises as seawater freezes. Because ice is less density, dense than water, it floats on the ocean's surface (as does fresh water ice). Sea ice covers about 7% of the Earth's surface and about 12% of the world's oceans. Much of the world' ...

to measure its

temperature Temperature is a physical quantity that quantitatively expresses the attribute of hotness or coldness. Temperature is measurement, measured with a thermometer. It reflects the average kinetic energy of the vibrating and colliding atoms making ...

and the evolution of its interfaces remotely. The autonomous mass balance buoys usually consist of a data controller module and a temperature string. Some ice mass balance buoys also include acoustic sounders above and below the ice, measuring the positions of the snow-ice and ice-water interfaces.

Types

The main types of ice mass balance buoys include * The

CRREL The Cold Regions Research and Engineering Laboratory (CRREL) is a United States Army Corps of Engineers, Engineer Research and Development Center research facility headquartered in Hanover, New Hampshire, that provides scientific and engineering ...

- Dartmouth Ice Mass Balance (IMB) Buoy * Snow and Ice Mass Balance Array (SIMBA) from SAMS * Seasonal Ice Mass Balance buoy (SIMB-1,2,3) The CRREL-Dartmouth Ice Mass Balance Buoy (IMB) includes two ice-facing acoustic rangefinders, a vertical temperature string, and air temperature and pressure sensors. These sensors are connected to a non-floating satellite-connected transmission package. Seasonal Ice Mass Balance Buoy (SIMB-1). The SIMB-1,2,3 instruments have the same sensor package as the CRREL-Dartmouth IMB but are enclosed in a spar-type buoy hull to improve their performance during the melt season. The lower-budget Snow and Ice Mass Balance Array (SIMBA) from SAMS includes only a vertical temperature string and a non-floating satellite-connected transmission package.

Characteristics

The main part of IMBs is a vertical chain of

thermistor A thermistor is a semiconductor type of resistor in which the resistance is strongly dependent on temperature. The word ''thermistor'' is a portmanteau of ''thermal'' and ''resistor''. The varying resistance with temperature allows these devices ...

s. The vertical spacing of the thermistors at modern IMBs is usually around 2–4 cm, while older versions had spacing around 10 cm. The accuracy of each sensor is generally within 0.1–0.5°C. Many modern IMBs measure in-situ temperatures and temperatures after a cycle of internal heating. In experimental

fluid dynamics In physics, physical chemistry and engineering, fluid dynamics is a subdiscipline of fluid mechanics that describes the flow of fluids – liquids and gases. It has several subdisciplines, including (the study of air and other gases in motion ...

, such a mode is called a “hot-wire anemometer”. In IMBs, the heat is added by applying an excitation voltage to the

resistor A resistor is a passive two-terminal electronic component that implements electrical resistance as a circuit element. In electronic circuits, resistors are used to reduce current flow, adjust signal levels, to divide voltages, bias active e ...

bonded to the temperature sensor. The temperature response of the sensor during heating depends on the

thermal diffusivity In thermodynamics, thermal diffusivity is the thermal conductivity divided by density and specific heat capacity at constant pressure. It is a measure of the rate of heat transfer inside a material and has SI, SI units of m2/s. It is an intensive ...

of the surrounding medium (for solids like snow or ice) and the flow rate of the medium (for fluids like seawater or air). The heat transfer in fluids depends on the fluid velocity, and the response usually varies over time scales. The measurements of the temperature response to heating may be used to discriminate different layers within the air-snow-ice-ocean system. The thermistor chain is usually installed in a standard hole produced by a 2-inch

auger Auger may refer to: Engineering * Auger bit, a drill bit * Auger conveyor, a device for moving material by means of a rotating helical flighting * Auger (platform), the world's first tension leg oil rig; see ''Big, Bigger, Biggest'' * Earth auger ...

. A weight is attached to the bottom end to keep it straight. The data is typically returned after each sample using the

Iridium Iridium is a chemical element; it has the symbol Ir and atomic number 77. This very hard, brittle, silvery-white transition metal of the platinum group, is considered the second-densest naturally occurring metal (after osmium) with a density ...

SBD system, while some buoys require manual data collection. During the deployment, the manual measurements of snow thickness, ice draft and freeboard, and location of IMB sensors are usually made. The IMB deployment disturbs the system around sea ice. For example, snow may have poor contact with the thermistor chain. Additionally, the 2-inch hole may refreeze very slowly if the air temperatures are high or the snow is deep. In summer, the presence of the chain may lead to additional solar energy absorption, which may influence the rates of snow and ice melt.

Usage in research

IMBs were used in several Arctic and Antarctic expeditions, including the SHEBA expedition in

Beaufort Gyre The Beaufort Gyre is one of the two major ocean currents in the Arctic Ocean. It is roughly located north of the Alaskan and Canadian coast. In the past, Arctic sea-ice would circulate in the Beaufort gyre up to several years, leading to the forma ...

, N-ICE2015 expedition north of

Svalbard Svalbard ( , ), previously known as Spitsbergen or Spitzbergen, is a Norway, Norwegian archipelago that lies at the convergence of the Arctic Ocean with the Atlantic Ocean. North of continental Europe, mainland Europe, it lies about midway be ...

, and the

MOSAiC expedition The Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC, ) expedition was a one-year-long expedition into the Central Arctic (September 2019 - October 2020). For the first time a modern research icebreaker was able to op ...

across Transpolar drift. The usage of IMBs revealed that in the Central Arctic regions with high sea ice concentration, surface and bottom ice melt are comparable. In contrast, in regions with low sea ice concentration, the amount of ice bottom melt is substantially larger. IMBs can also be used to show spatial and temporal variability of sea ice growth and melt, also providing an estimate of ocean heat fluxes. They can also be used for studying pressure ridges for analysis of their winter consolidation rates, for analysis of ridge consolidation during their warming, and to study effects of snow slush contribution to the ridge consolidation. IMBs also allow the study of the temporal evolution of under-ice meltwater layers, conditions of

false bottom A false bottom (or false back) is an internal partition in a container, typically at the bottom of a drawer, suitcase or similar item, enabling the concealment of objects from a cursory examination of the item's contents. A false bottom may be pr ...

formation, and their effect on ice melt rates.

Data availability

The raw temperature and acoustic sounder or heating data is available for CRREL-Dartmouth IMBs, CRREL-Dartmouth SIMB3 buoys, and for SIMBA buoys. The largest processed datasets with estimates of snow and sea ice thickness include 104 CRREL IMBs during 1993–2017, 82 CRREL IMB and SIMB3 buoys during 1997–2024, and 96 SIMBA buoys during 2012–2023. A significant amount of IMBs were deployed during the MOSAiC expedition, including snow and ice thickness estimates from 22 SIMBA buoys and 24 Digital Thermistor Chains.

References

{{Reflist Glaciology Sea ice Buoyage