At Sea
It’s a bright and beautiful day, blue skies, hazy cumulous clouds and sunshine highlighting the whitecaps as we make our northbound transit of the Drake Passage. Soon we will cross the Antarctic Convergence, that all-but-invisible boundary between the Southern Ocean and the waters of the Atlantic, Pacific and Indian Oceans to the north. It is time to say farewell to all the wonder and beauty of the White Continent and time to reflect on all that we have seen and done there.
Leaving the Southern Ocean behind us is a largely symbolic experience. Though fogbanks and congregations of seabirds occasionally mark the position of the convergence, today there is no visible sign of this transition. But this is the biological boundary of the Antarctic; to the north are warmer waters whose biology and chemistry closely resemble that of the temperate and tropical seas that stretch from here to the equator. To the south is a polar sea that is far different from all the other waters in the world; and it is this sea that underpins and powers all the incredible life of the Antarctic.
The unique physical oceanography, primary productivity and trophic webs of the Southern Ocean form an amazing natural factory of life, and they accomplish this under some the harshest environmental conditions on the planet. The seas here, though bone-chillingly cold, are enormously rich in many basic mineral nutrients like nitrogen and phosphorus. Still, a few, particularly iron, are missing from many areas and these places are relatively poor in marine life. But, in a process that can only be called perfect for the Antarctic seas, melting icebergs fertilize the waters around them with iron-rich dust that they have carried down from terrestrial glaciers.
With this key addition, life takes off. Under the long polar days of the Antarctic summer many species of phytoplankton, one-celled photosynthetic organisms, incorporate the mineral resources of the seas into enormous blooms that form the foundation of the food chain. Next come the krill, the shrimp-like crustaceans that are the keystone species of the marine food web here. They have solved the tricky problem of gathering and feeding on the tiny phytoplankton and consequently have become one of the most common macroscopic organisms anywhere in the world, with a biomass that dwarfs that of all the humans on the planet. On this fabulous bounty of zooplankton feed the whales, the seals, the penguins, the fish and much more, all the wonderful wildlife of the White Continent, which arises in a few short steps from the rich waters of the seas that surround it.
So, as we cross the subtle boundary and leave the waters of the Southern Ocean in our wake, we look back and reflect on our experiences there. We have seen the amazing animals at the top of the web, the rookeries crowded with thousands of chattering penguins, the seals relaxing on sculptural icebergs, the whales blowing and sounding, and even the rainbow communities of corals, sponges and seastars that make their homes deep in this strange sea. Although the mineral riches of the sea, the phytoplankton and the swarms of krill have remained hidden from us, we have learned to appreciate their role in the creation of all that we have enjoyed here. Today this remarkable remote sea faces unprecedented threats from poorly managed fisheries, changing climate and more. But we have become advocates; we are now constituents of the Southern Ocean, bound to it by our experiences here and already thinking of how we can help to ensure its rich and beautiful future.
