Estimates of future sea level rise vary a lot and scientists need year-round observations to assess and improve climate change models.
Gathering data in summer months was relatively straightforward but getting ships near the area during the winter was impossible because the area is covered in a thick blanket of sea ice.
The only information available is from "moorings" - or strings of measurement devices anchored to the sea floor.
These could collect data from a few fixed locations, but they could not measure near the sea surface at all because the huge icebergs would collide with them.
So the researchers turned to seals; seven southern elephant seals and seven Weddell seals were fitted with devices that could send back information via satellite.
Measurements of the warmth and saltiness of the water were sent by the seals as they moved around the area and dived from the surface of the ocean down through the water to the sea bed in their hunt for food.
Over a period of nine months, throughout the Antarctic winter, the team collected data from more than 10,000 dives over an area of around 150,000 sq km.
The seals continued to send back signals until they moulted and the devices dropped off.
Analysing the findings, published in the journal Geophysical Research Letters, the researchers discovered that not only was the layer of Circumpolar Deep Water thicker in winter, it was also warmer and saltier than during summer months.
This suggested that there was likely to be more melting of the ice sheets during the winter months.
The temperature differences were less marked closer to one of the glaciers, in a region called Pine Island Bay, possibly because ocean currents, called gyres, recirculate the water.
"We knew very little about what to expect from this research, since this is the first time that data has been collected in this way in this area," said Helen Mallett, who led the study.
"We were able to collect much more information from the seals than all the previous ship-based surveys in the area combined and it was clear that, at least during the seasons we observed, there were substantial differences in temperature between the seasons.
"Although more will need to be done to measure these differences over a number of years, it's clear that enlisting seals to collect this kind of ocean data will offer useful insights for climate change modellers who are attempting to predict how fast sea levels will rise."
The data would also be useful to marine biologists as well, as it will provide new understanding of the foraging behaviour of seals in the Amundsen Sea, and how that might be affected by climate change, as well as commercial fisheries.
It wasn't the first time the approach had been tried.
New Zealand and Australian researchers have already used Weddell seals swimming beneath the frozen Ross Sea to collect oceanographic data on depth, water temperature and salinity.
Niwa oceanographer Dr Craig Stevens said using seals – and also submarines – was becoming an increasingly important way to gather critical information about how Antarctica was responding to climate change.
"As we gather more evidence and build on our understanding, it's actually becoming a core pathway for Antarctic science," said Stevens, who wasn't involved in the latest study.
"One neat thing is they can get us data right near the surface – something hard to do from a ship."
