They have to drill holes in the ice, dive down into the water -- cold, cold water -- to get hold of the instrument, bring it up, do any repairs and maintenance that they need to do, put it back and get out before the ice melts.
Eles precisam abrir buracos no gelo, mergulhar na água - água muito gelada - para pegar o instrumento, trazer para cima, fazer qualquer reparo e manutenção necessários, colocar de volta e sair antes do gelo derreter.