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We’ve reached our southernmost point (67 41’S) and have started (slowly) to make our way north again. We got to within about 14 nautical miles of the coast to the east of the Mertz Glacier before the ice stopped us going any further. The 1400 m deep trough found to the west of the Mertz Glacier apparently does not continue further east, as had been thought, at least not at comparable depths. The deepest water we found was about 650 m deep. If there is a deep trough here, it would have to be a narrow feature between our southernmost point and the coast. We are now doing some east-west lines of CTD stations across a shallow trough as we move north. These will help tell us whether dense water also escapes the shelf in this region. Pretty much everywhere we have been on the shallow waters of the shelf, we have encountered an intense phytoplankton bloom. The sea looks greyish-green to the eye, like coastal waters rather than the intense blue more typical of offshore Southern Ocean waters. In some places, there is so much organic material raining down through the water column that we can see a signal in the fluorometer (an optical instrument that uses light to measure how much chlorophyll is in the water) down to depths of more than 200 m. Usually we only find chlorophyll in the upper 50-75 m. Bronte Tilbrook’s group is measuring some of the lowest carbon dioxide values they have ever measured in the Southern Ocean, indicating that the phytoplankton are growing rapidly, taking up lots of carbon as they photosynthesise, and making this part of the ocean a strong “sink” of atmospheric carbon dioxide. It may be that melt of all the old ice released by the calving of the Mertz Glacier is helping to support the bloom. The wind continues to blow hard (30+ knots for the last 12 hours), but is forecast to ease later today.
REGARDS: Steve, Fred and Penny
Map
A map showing Australia and Antarctica. The map shows the journey of one voyage that has occured in the season, with each route highlighted in a distinct colour.