Shag Rocks
This was our second day at sea sailing between the Falkland Archipelago (Islas Malvinas) and South Georgia. South-westerly winds had built up during the night and early morning, as was expected, and this caused some fairly significant beam seas throughout the day. Even so, unless one looked out a window, it was impossible to tell just how rough it really was, because our wonderful stabilizers did their job extremely well and kept the ship from rolling too much. Okay, I’ll admit it was a little tricky standing in line at the lunch buffet without holding onto something, but it really wasn’t nearly as bad as it would have been on a lesser ship.
National Geographic Explorer reached the Antarctic Convergence (otherwise known as the Polar Front) late yesterday, but because of our east-southeast heading, we found ourselves sailing right along within it rather than crossing it quickly. So, it took us the entire morning to actually cross into true Antarctic waters. The Antarctic Convergence circles the globe at high latitudes (between 50ºS and 60ºS) and delineates the relatively warm Subantarctic waters from the frigid Antarctic waters. The temperature difference of the surface waters at the convergence can amount to as much as 9ºC (18ºF) during part of the year, and it also amounts to a bio-geographic boundary between the calcium carbonate-based plankton (foraminiferans), which dominates to the north and the silica-based plankton (diatoms) that dominates to the south. We could certainly tell the ship had entered Antarctic waters this morning, as the air temperature was very much colder than what was experienced yesterday. We continued on with our lecture series and photography break-out sessions during the day in preparation for the coming days at South Georgia. This great island is rather like a giant oasis in the middle of the Southern Ocean, making it extremely important as a breeding ground for many species of seabirds and pinnipeds that live within the Atlantic sector of the Southern Ocean.
By late afternoon, we passed close to Shag Rocks (named for the birds that breed here by the thousands). These small islets, which lie 150 miles west of South Georgia, consist of small, jagged, and steep geological stringers left behind from mountainous South Georgia as it was dragged eastward during the formation of the Scotia Plate. Its original position of formation was between the northern tip of the Antarctic Peninsula and the southern tip of South America (Cape Horn). This all makes sense when you see it presented in diagrams and power point on the large monitors in the ship’s lounge. Although the thick coating of cormorant guano covering most of the exposed rocks made it difficult to discern what these projections are composed of, we know from the previous work of sea-hardy geologists that Shag Rocks are metamorphosed sandstone accretions…the exact same stuff as we expect to see in South Georgia. See Figures A and B for two views of the dramatic Shag Rocks. These rocks sit on a submerged plateau, surrounded by deep waters, which brings forth much upwelling of nutrients…thereby producing a tremendous amount of potential food that supports not only the local South Georgia blue-eyed shags and macaroni penguins that nest here, but also several species of albatrosses, giant petrels, diving petrels, storm-petrels, white-chinned petrels, and prions. And, of course, whales often gather around the rocks for the same reason. We saw one whale blow, but conditions were not conducive to go see what it was. It was great fun spending time out on the aft deck trying to photograph the myriad seabirds that followed along with our vessel in the windy conditions.
