ABSTRACT
Submarine-melting of ice at the glacier-ocean interface accounts for a large portion of the ice-loss at tidewater glaciers and produces sound via bubble-release. The sound production is dominant in the sub-surface region near the glacier-ocean interface. This depth-dependence of the sound is studied by melting ice blocks in a glacial bay at various depths up to 20 m and recording their acoustics over a large frequency range. The acoustic energy decreases with depth in line with expectations from the physics of the phenomenon and is fit to an exponentially decaying curve. The estimated variation will be useful for interpreting the sound in marine-terminating glaciers bays in terms of the submarine-melting activity.
ABSTRACT
Arctic glacial bays are among the loudest natural environments in the ocean, owing to heavy submarine melting, calving, freshwater discharge, and ice-wave interactions. Understanding the coherence and vertical directionality of the ambient sound there can provide insights about the mechanisms behind the ice loss in these regions. It can also provide key information for operating technologies such as sonar, communication, and navigation systems. To study the unexplored sound coherence and vertical directionality in glacial bays, a vertical hydrophone array was deployed, and acoustic measurements were made at four glacier termini in Hornsund Fjord, Spitsbergen, in June and July 2019. The measurements show that the sound generated by melting glacier ice is more dominant in the upper portion of the water column near the glacier terminus. The melt water from the submarine melting and the freshwater discharge from the glacier create a glacially modified water duct near the sea surface. This disrupts the inter-sensor vertical coherence in the channel. However, some coherence across the duct is preserved for sound arising from spatially localized events at low frequencies. Overall, the observations in this study can help improve the understanding of the submarine melting phenomenon in glacial bays.
ABSTRACT
The temporal and spatial variability of heavy metal distribution was studied in an Arctic fjord (Hornsund, Spitsbergen). Seawater from 8 sampling stations and 3 sampling depths was collected in 6 successive months and used for measurement of dissolved and particulate heavy metal concentrations. Salinity and temperature profiles were determined prior to sampling and water masses were classified according to their properties. Isotopic lead composition (206Pb/207Pb and 206Pb/208Pb ratios) was studied to find the sources of Pb to the fjord seawater. Hornsund seawater was contaminated with the studied heavy metals (particularly during the summer months). Extremely high contamination with Cd was measured (dissolved up to 488 ng·L-1, while particulate up to 303 ng·L-1), which is most probably connected to high atmospheric deposition. Depending on the season and the region, metal distribution was modified by glacier meltwater and surface run-off discharges, melting of fast ice, direct atmospheric deposition, transport of sea salt, intrusion of Atlantic water, sediment re-suspension, as well as re-mobilization.
Subject(s)
Metals, Heavy , Water Pollutants, Chemical , Arctic Regions , Environmental Monitoring , Estuaries , Metals, Heavy/analysis , Seawater , Svalbard , Water Pollutants, Chemical/analysisABSTRACT
The directionality of ambient noise in an Arctic tidewater glacier bay was measured using two horizontally spaced, broadband hydrophones. Segments of noise were divided into two frequency bands and analyzed for arrival angle. These data show that different classes of source radiate noise in distinct spectral bands and are spatially diverse. A previously unidentified source, the interaction of surface gravity waves with underside of ice ledges at the periphery of icebergs, is described. The generation of noise by ice-wave interaction suggests that surface waves should be measured if ambient noise is to be used to monitor ice dynamics in glacial fjords.
