Question: Doggerland was submerged by a tsunami formed in what ocean?
Context: The National Tsunami Warning Center (NTWC) is one of two tsunami warning centers that are operated by the National Oceanic and Atmospheric Administration (NOAA) in the United States.  It was called the West Coast and Alaska Tsunami Warning Center (WC/ATWC) until October 1, 2013.  The name was changed to reflect its geographical zone of responsibility.  Headquartered in Palmer, Alaska, the NTWC is part of an international tsunami warning system (TWS) program and serves as the operational center for TWS of all coastal regions of Canada and the United States, except Hawaii, the Caribbean, and the Gulf of Mexico.  The other tsunami warning center is the Pacific Tsunami Warning Center (PTWC) in Ford Island, Hawaii, serving participating members and other nations in the Pacific Ocean area of responsibility. Bryony Coles is a prehistoric archaeologist.  Coles is best known for her work studying Doggerland, an area of land now submerged beneath the North Sea. Doggerland was an area now beneath the southern North Sea that connected Great Britain to continental Europe during and after the last glacial period.  It was flooded by rising sea levels around 6,500–6,200 BCE.  Geological surveys have suggested that it stretched from Britain's east coast to the Netherlands and the western coasts of Germany and the peninsula of Jutland.  It was probably a rich habitat with human habitation in the Mesolithic period, although rising sea levels gradually reduced it to low-lying islands before its final submergence, possibly following a tsunami caused by the Storegga Slide. A tsunami warning system (TWS) is used to detect tsunamis in advance and issue warnings to prevent loss of life and damage.  It is made up of two equally important components: a network of sensors to detect tsunamis and a communications infrastructure to issue timely alarms to permit evacuation of the coastal areas.  There are two distinct types of tsunami warning systems: international and regional.  When operating, seismic alerts are used to instigate the watches and warnings; then, data from observed sea level height (either shore-based tide gauges or DART buoys) are used to verify the existence of a tsunami.  Other systems have been proposed to augment the warning procedures; for example, it has been suggested that the duration and frequency content of t-wave energy (which is earthquake energy trapped in the ocean SOFAR channel) is indicative of an earthquake's tsunami potential. A teletsunami (also called an ocean-wide tsunami, distant tsunami, distant-source tsunami, far-field tsunami, or trans-ocean tsunami) is a tsunami that originates from a distant source, defined as more than 1,000 km away or three hours' travel from the area of interest, sometimes travelling across an ocean.  All teletsunamis have been generated by major earthquakes such as the 1755 Lisbon earthquake, 1960 Valdivia earthquake, 1964 Alaska earthquake, and 2004 Indian Ocean earthquake. The three Storegga Slides are considered to be amongst the largest known landslides.  They occurred under water, at the edge of Norway's continental shelf in the Norwegian Sea, approximately 6225–6170 BCE.  The collapse involved an estimated 290 km length of coastal shelf, with a total volume of 3500 km3 of debris, which caused a very large tsunami in the North Atlantic Ocean. Miki Endo (Japanese:遠藤未希 ) (1986, Japan - 2011, Minamisanriku, Japan), was the voice warning and alarm agent of the town of Minamisanriku during the 2011 Tōhoku earthquake and tsunami.  She was employed by the town's Crisis Management Department to broadcast disaster advisories and warnings, and was hailed in the Japanese news media as a heroine for sacrificing her life by continuing to broadcast warnings and alerts over the community loudspeaker system as the tsunami overwhelmed the town.  She was credited with saving many lives.  The three-story headquarters of the department remained standing but was completely gutted, with only a red-colored steel skeleton remaining.  Photos show the roof of the building completely submerged at the height of the inundation, with some people clinging to the rooftop antenna. A submerged forest is the in place ("in situ") remains of trees (especially tree stumps) that lie submerged beneath a bay, sea, ocean, lake, or other body of water.  A forest can become submerged as the result of a lake or sea level rise that results in a lacustrine or marine transgression and in place drowning of the forest.  A submerged forest that lies beneath a lake can also be formed by the blockage of a river valley by either a landslide or manmade dam.  Examples can be found at low tide on the fringes of the submerged landmass known as Doggerland, around the coast of England and Wales, the Channel Islands, north-west France and Denmark.  These remains have usually been buried in mud, peat or sand for several thousand years before being uncovered by sea level change and erosion.  In some places, such as Blackpool Sands, Dartmouth, the remains are normally covered by sand and only rarely exposed.  During the storms of 1974 ("see" Penparcau) and the Winter storms of 2013–14 in the United Kingdom extensive remains of submerged forests were revealed in a number places around the coast of Britain. Helike ( ; Greek: , pronounced ] , modern ] ) was an ancient Greek city that was submerged by a tsunami in the winter of 373 BC.  It was located in Achaea, northern Peloponnesos, two kilometres (12 stadia) from the Corinthian Gulf and near the city of Boura, which, like Helike, was a member of the Achaean League.  Modern research attributes the catastrophe to an earthquake and accompanying tsunami which destroyed and submerged the city.  In an effort to protect the site from destruction, the World Monuments Fund included Helike in its 2004 and 2006 "List of 100 Most Endangered Sites". The Pacific Tsunami Warning Center (PTWC) is one of two tsunami warning centers that are operated by NOAA in the United States.  Headquartered on Ford Island, HI, the PTWC is part of an international tsunami warning system (TWS) program and serves as the operational center for TWS of the Pacific issuing bulletins and warnings to participating members and other nations in the Pacific Ocean area of responsibility.  It is also the regional (local) warning center for the State of Hawaii.  The other tsunami warning center is the National Tsunami Warning Center (NTWC) in Palmer, Alaska, serving all coastal regions of Canada and the United States except Hawaii, the Caribbean Sea and the Gulf of Mexico.
Answer: North Atlantic Ocean