Ocean bottom seismometer sgy-files of refraction seismic profiles from Professor Logachev cruise TTR16/3

Over the last decade pockmarks have proven to be important seabed features that provide information about fluid flow on continental margins. Their formation and dynamics are still poorly constrained due to the lack of proper three dimensional imaging of their internal structure. Numerous fluid escape features provide evidence for an active fluid-flow system on the Norwegian margin, specifically in the Nyegga region. In June-July 2006 a high-resolution seismic experiment using Ocean Bottom Seismometers (OBS) was carried out to investigate the detailed 3D structure of a pockmark named G11 in the region. An array of 14 OBS was deployed across the pockmark with 1 m location accuracy. Shots fired from surface towed mini GI guns were also recorded on a near surface hydrophone streamer. Several reflectors of high amplitude and reverse polarity are observed on the profiles indicating the presence of gas. Gas hydrates were recovered with gravity cores from less than a meter below the seafloor during the cruise. Indications of gas at shallow depths in the hydrate stability field show that methane is able to escape through the water-saturated sediments in the chimney without being entirely converted into gas hydrate. An initial 2D raytraced forward model of some of the P wave data along a line running NE-SW across the G11 pockmark shows, a gradual increase in velocity between the seafloor and a gas charged zone lying at ~300 m depth below the seabed. The traveltime fit is improved if the pockmark is underlain by velocities higher than in the surrounding layer corresponding to a pipe which ascends from the gas zone, to where it terminates in the pockmark as seen in the reflection profiles. This could be due to the presence of hydrates or carbonates within the sediments.

Archive of the PASATA (PASsive Acoustic Tracking of Antarctic marine mammals) field documentation

Recordings from the PerenniAL Acoustic Observatory in the Antarctic ocean (PALAOA) show seasonal acoustic presence of 4 Antarctic ice-breeding seal species (Ross seal, Ommatophoca rossii, Weddell seal, Leptonychotes weddellii, crabeater, Lobodon carcinophaga, and leopard seal, Hydrurga leptonyx). Apart from Weddell seals, inhabiting the fast-ice in Atka Bay, the other three (pack-ice) species however have to date never (Ross and leopard seal) or only very rarely (crabeater seals) been sighted in the Atka Bay region. The aim of the PASATA project is twofold: the large passive acoustic hydrophone array (hereafter referred to as large array) aims to localize calling pack-ice pinniped species to obtain information on their location and hence the ice habitat they occupy. This large array consists of four autonomous passive acoustic recorders with a hydrophone sensor deployed through a drilled hole in the sea ice. The PASATA recordings are time-stamped and can therefore be coupled to the PALAOA recordings so that the hydrophone array spans the bay almost entirely from east to west. The second, smaller hydrophone array (hereafter referred to as small array), also consists of four autonomous passive acoustic recorders with hydrophone sensors deployed through drilled holes in the sea ice. The smaller array was deployed within a Weddell seal breeding colony, located further south in the bay, just off the ice shelf. Male Weddell seals are thought to defend underwater territories around or near tide cracks and breathing holes used by females. Vocal activity increases strongly during the breeding season and vocalizations are thought to be used underwater by males for the purpose of territorial defense and advertisement. With the smaller hydrophone array we aim to investigate underwater behaviour of vocalizing male and female Weddell seals to provide further information on underwater movement patterns in relation to the location of tide cracks and breathing holes. As a pilot project, one on-ice and three underwater camera systems have been deployed near breathing holes to obtain additional visual information on Weddell seal behavioural activity. Upon each visit in the breeding colony, a census of colony composition on the ice (number of animals, sex, presence of dependent pups, presence and severity of injuries-indicative of competition intensity) as well as GPS readings of breathing holes and positions of hauled out Weddell seals are taken.