Field studies and some results of numerical modeling of a ring structure on Baikal ice

Abstract

Geological ring structures of various sizes and ori gins are observed on the Earth's surface. In the past decade, ice ring structures on Lake Baikal were regu larly identified by satellites [1]. On April 4, 2009, these structures emerged in the western end of South Baikal and near the Svyatoi Nos Peninsula in Central Baikal [1][2][3] and were destroyed along with the ice at the end of April. The expedition for studying the ice and hydrophysical measurements in the area of the ring structure in South Baikal was organized on April 7. This work presents the results of the field studies and modeling of the currents and variations in the ice thickness.The MODIS satellite data in the visible range with a spatial resolution of 250 m (www.geol.irk.ru) were used for remote study of the ring structure. During the field studies, the ice thickness was measured and the ice cores were drilled along two sections, which transect the center of the ring structure at 51°40′35″ N, 103°52′15″ E (Fig. 1a). The measurement stations were placed in the center of the structure and 1, 2, 3, and 4 km from it along the sections and 7 and 8 km to the west and to the east, respectively, from the center along the EW section. The ice surface in the center of the structure, at its periphery, and in the area of the dark ring was visually similar. No water was visible on the ice surface, and the ice was made up of vertical crys tals. The ice thickness was 74 cm in the center, decreased to 43 cm at the distance of 2 km from the center, and increased up to more than 70 cm beyond the ring.The temperature and electric conductivity of the water column were registered by a SBE 19 profiler. The water in the center was warmer by 0.5°С and less saline (for 2 mg/kg) relative to the periphery (Fig. 1b). In spite of the higher temperature in the center, the ice thickness was similar to that beyond the structure; i.e., the temperature of the water layer was not the major factor responsible for the decrease in the ice thickness. The deepening of the thermocline in the center of the structure (Fig. 1b) indicated the presence of the ring anticyclonic current.According to the tracer movements, the maximum velocities of the water currents (3-4 cm/s) were observed at a distance of 2-3 km from the center of the Abstract-This work presents the results of complex analysis of the field data and of mathematical modeling of the ice ring structure more than 4 km across, which was identified by the space images of South Baikal in April 2009. The measurements revealed that the ice thickness was 74 cm in the center of the structure, decreased to 43 cm at a distance of 2 km, and increased up to 70 cm and more beyond the ring. The ice water in the central part was warmer by 0.5°C and less saline (for 2 mg/kg) relative to the periphery of the structure. According to the tracer movements, the maximum velocities of the ice currents (3-4 cm/s) were observed at a distance of 2-3 km from the center of the structure with minimum ice thickness. The event was modeled using several mathem...

Giant ice rings on lakes Baikal and Hovsgol: Inventory, associated water structure and potential formation mechanism

“…However for the conductivity/salinity this similarity is only partial. Granin et al () found less mineralised water in the center than at the periphery of the ring (this is similar to our observations), but from the depth of 40 m downward their observations show no increase of salinity. This observation apparently led the authors to conclude that this anomalous structure results from upwelling of deep waters (with lower mineralisation and higher temperature) through the thermocline, and is potentially related to the presence of gas hydrates in bottom sediments.…”

“…Our observations for Lake Baikal in 2012 and 2014 show water structure similar to the one found below the ice ring in 2009 (Granin et al ) for temperature (core values 1–1.25°C). However for the conductivity/salinity this similarity is only partial.…”

“…In this respect, satellite imagery is a unique tool providing the means for their identification and monitoring on a large‐spatial scale. Existing publications (“Circles in thin ice.” 2009; Granin ; Hsu ; “Ring‐like structures” 2009; “Strange Circles…” 2009; “Ice rings.” 2013; Granin et al ) refer to a total of 13 rings (Table ) in Lake Baikal based mostly on data from MODIS. To our knowledge, until now no ice rings had been observed outside Lake Baikal.…”

Giant ice rings on lakes and field observations of lens‐like eddies in the Middle Baikal (2016–2017)

“…It is not possible to estimate the driving force of eddy generation without in situ data before the formation of the ice ring in Southern Baikal in 2009 or near Cape Krestovskiy in 2013. However, for the region of the Nizhneye Izgolovye Cape, there are several cases that appear to contradict the hypothesis of upwelling of deep water (Granin et al ) and the results of estimation of period for the formation of the ring structure (Granin et al ).…”

“…Granin et al () have analyzed heat fluxes in the ice cover and in the system water–ice. They calculated variations in the ice thickness inside the ring in Southern Baikal in 2009 in the framework of the Stefan problem using a two‐dimensional axis‐symmetrical model and current speed from a 3D nonhydrostatic model (using the upwelling of deep water hypothesis).…”