Bathymetry used to be done by using a heavy weight lowered over the side of the ship The modern method uses sonar to obtain a highly accurate image of the ocean floor
Due to the extreme ice conditions, the floor of the Arctic Ocean has been studied less than that of any other ocean. In the late 1800s, bathymetry measurements -the measurement of depths - were made by lowering a heavy weight attached to many metres of piano wire over the side of the ship. This method was not only tedious, but also inaccurate, because currents caused the weight to descend on an angle. Moreover, it was was slow because each depth measurement required lowering the line. Today, bathymetry is carried out using echo sounding. This involves sending a sound pulse to the ocean floor where it is reflected back to its source. By measuring the time it takes to make this return trip, with information on the speed of sound in water, the depth can be accurately estimated. This technology, while much used in other oceans, has been used less in the Arctic. However, as a result of studies from ice islands, icebreakers and, particularly, submarines, we now have a fairly good indication of water depths. Nonetheless, there are still many areas of the Arctic Ocean where no soundings have ever been made, and its general topography has only been estimated. See the Arctic Ocean Basin section for more information on the bathymetry of the Arctic Ocean.To directly examine the composition of the sediments and rocks on the Arctic Ocean floor, samples of the bottom are obtained through a process known as coring. This process involves dropping a narrow tube down to the ocean floor where it penetrates into the seabed about 3 metres. This tube captures a core of sediment - mineral or organic particles that have settled on the ocean floor from the upper water layers. By examining these sediments, geologists can determine changes in the physical environment, climate and ecosystems through time. These sediments often contain the skeletons of sea life that tell the tale of past Arctic ecosystems. These sediments have revealed that until 5 million years ago, the Arctic was a far warmer place, and was likely free from ice. So far, the oldest sediments that have been collected from the Arctic Ocean floor are eighty million-year-old black muds, and sixty-seven million-year-old silicaceous oozes.