Examples of underwater sounds in the polar oceans

The low frequency calls of Antarctic blue whales belong to the loudest vocalizations produced by any animal. Most likely blue whales use calls to communicate over long distances. PALAOA records different Antarctic blue whale vocalizations. The spectrogram shows the 'Z-call' which is a population-specific song produced by Antarctic blue whales in the Southern Ocean as well as on their lower latitude areas where breeding is thought to take place.  Please note that we increased the frequency of the sound with 2 octaves to make the sound audible to human ears.

Fin whales produce a variety of short low frequency calls, of which the 20 Hz pulse is most prominent (i.e., a downsweep ranging from around 30-15 Hz) and produced by fin whales worldwide.  We record this call most frequently in the vicinity of Elephant Island, off the northern tip of the Antarctic Peninsula, where the 20 Hz pulse also often contains a higher frequency component around 89 Hz.

In the Southern Ocean, three killer whale ecotypes co-exist which are specialized on different prey species and vary slightly in their visual appearance. Killer whales, also called Orcas, produce a variety of vocalizations, for example whistles, pulsed calls and echolocation clicks. In the sound snippet you hear lots of calls and mainly pulsed calls.

The typical whale songs which are known from various popular media, are usually produced by humpback whales. The Southern Hemisphere humpback whales spend the summer in the Southern Ocean to feed as much as possible. Reproduction and breeding mainly take place in tropical waters. At PALAOA, only humpback whale social sounds such as the ones in the spectrograms have been recorded. Humpback whale song has been found present on many of our offshore recorders along the Greenwich meridian. Ongoing research is investigating to which breeding stock these singing whales can be attributed.  

Sperm whales produce a variety of clicking sounds. During foraging dives they use clicks to localize prey by emitting regular clicks and so-called creaks (short series of clicks with fast repetition rate, close to prey encounter). In social context they produce codas which are repeated patterns of clicks. Different groups of sperm whales use different codas (dialects) and within a group codas can vary slightly by individuals. At PALAOA we recorded regular click trains. In the snippet you hear several overlapping regular click trains (which are barely visible in the spectrogram) as well as some faint Weddell seal calls in the background.

The crabeater seal vocalizes mainly during the breeding season between October and December. Although the males do not defend underwater territories, they are thought to guard a single female on the ice until she is ready for mating and conception. The crabeater seal vocal repertoire at PALAOA consists of two call types. The examples are the typical low moan which is emitted most often. At 15s there is a Weddell seal Trill audible as well.

In leopard seals, females are larger than males, which is more common in aquatic animals than it is in terrestrial animal species. During the breeding period PALAOA detects vocalizations of both male and female leopard seals. Due to the fact that leopard seals are solitary animals, they are thought to use their vocalizations mainly to find a mate during the breeding season. At PALAOA, seven distinct leopard seal vocalizations were recorded. 

The Ross seal is the least investigated Antarctic seal species, which is likely due to its pelagic lifestyle. Ross seals live in the poorly accessible pack ice and also in areas of open water. PALAOA provides us with unique recordings of their underwater calls. Five different call types were identified so far: high, middle, and low frequency sirens, as well as a tonal call which is often associated to the “Whoosh” (audible in the first snippet around 10s and around 29s in the second snippet).

The Weddell seal lives in fast ice areas, close to the Antarctic ice shelf edge. At PALAOA we can hear its vocalizations almost year-round (few/no calls in February). Weddell seals have a large vocal repertoire, of which 14 call types were recorded at PALAOA. Their repertoire is known to differ between breeding populations. Some of these sounds are thought to be produced by males to defend underwater territories. The most typical calls are the 'Falling chirp sequence' (well visible in the snippet) and the Trill (a long descending vocalization, part of it visible at the end of the sound file, around 43s). The sound examples also contain distant calls of leopard seals.

From time to time, large pieces of the Antarctic shelf ice break off (calve) and crash into the ocean. This process is called calving. The animals in the water seem not to be disturbed by these sounds, already shortly after these loud noises, pinnipeds are heard again in the recordings.

The underwater soundscape of the Southern Ocean is dominated by the sounds of ice. These sounds are generated when ice floes rub against each other or bend.

The most intense sounds recorded by the PALAOA station originate from the collision of two icebergs.

The Southern Ocean is one of the last pristine areas of the world’s oceans. Only few fishing and research ships venture into the Southern Ocean (with tourist vessels sailing primairly along its northern perimeter along the Antarctic peninsula and adjacent island chain) and commercial exploitatation of Antarctic natural resources is currently (still) prohibited under the Antarctic Treaty.  Hence few anthropogenic acoustic sources exist in this region while the sea ice cover absorps sound more efficiently than the open water surface, reducing ambient sound levels further.

Twice a year, the German research vessel Polarstern visits the Atka bay to deliver supplies to the Neumayer Station. These visits leave clear acoustic traces in the PALAOA recordings.

Many sounds which are recorded by PALAOA, cannot be identified by scientists. Often it is not even possible to tell if the sounds originate from animals or if these are abiotic. The acoustic example displays a mysterious low-pitched sound. Scientists verified that this sound was recorded when no ship was present within a radius of 1000 km.

The process generating this sound is not know to us as of now.