Scientists have discovered an extensive body of freshwater beyond the Canterbury coast of New Zealand and mapped its structure in 3D.
The MARCAN team includes scientists from the University of Malta, GEOMAR, New Mexico Tech, NIWA, and BGR.
The freshwater is in sediments just 20 metres below the seafloor, making it one of the shallowest in the world. It extends up to sixty kilometres from the coastline and may be as large as two hundred cubic kilometres of water, which is equivalent to half the volume of groundwater across Canterbury. The freshwater system exhibits complex variations in shape and salinity across its entire extent, which has made it challenging to map.
The freshwater is derived from rainfall and is partly being replenished at present by groundwater flow from the coastline between Timaru and Ashburton. However, the majority of the freshwater became trapped offshore during the last three Ice Ages, when sea level was more than a hundred metres lower than today.
This discovery was the result of the integration of seismic reflection profiling, electromagnetic surveying and numerical modelling. This novel approach can characterise offshore freshwater systems in exceptional detail and significantly revise estimations of their occurrence and volume if applied globally. This is important in view of the potential use of offshore freshwater systems as a new source of drinking water, the management of coastal aquifers that extend offshore, and the role they play in the chemistry and biology of the ocean.
This study was recently published in the journal Nature Communications. It is an outcome of the MARCAN project and was funded by the European Research Council, New Zealand Ministry for Business Innovation and Employment, US National Science Foundation and German Research Foundation.