These jagged bits of volcanic glass are the leftovers of pyroclastic explosions which scientists didn't think could happen two and a half miles deep on the Arctic Ocean seafloor. The water pressure at this depth was thought to inhibit this kind of eruption but the pyroclastic fragments means that an explosive blast of carbon dioxide was released.
Think of the Chaiten Volcano which erupted recently in Chile with that huge plume of gas and rock and put it underwater.
Analysis of some of the shards showed them to be bits of glass known as limu o Pele, or "Pele's seaweed". These are formed when lava is stretched thin around expanding gas bubbles during an explosion. Scientists collected rock and sediment samples and high definition videos showed shards and bits of basalt over the seafloor with some deposits on top of new lavas an indication the debris had fallen rather than been moved as part of a lava flow.
This is the 10 square kilometre area on the Gakkel Ridge, a mostly unexplored region of the Mid-Ocean Ridge where evidence of the explosive eruptions were gathered. Researchers named the small craters Loke, Oden and Thor. They are now looking at whether pyroclastic eruptions instead of the slow flowing Hawaiian lava type eruptions are common in the deep sea or it's because of special conditions along the Gakkel Ridge.
For the climate change deniers, this volcanic activity has nothing to do with the Polar ice melting faster than usual. The stratified waters of the Arctic Ocean can absorb and disperse any heat and gas from an eruption on the seafloor. Cold dense water in the depths are trapped near the bottom with little mixing with warmer surface layers. Almost no heat is transmitted to the underside of the Polar ice from approximately 3,ooo to 4,000 metres below.