the explorers journal the global adventure issue - The Explorers Club

seabirds such as Cape Petrels were more abundant around icebergs than in the open waters of the Weddell Sea. The waterfall behind them is meltwater from the iceberg, which nourishes its surrounding waters .Delighted with our findings, I asked colleaguesinterested in icebergs if they would be willing tolaunch a multidisciplinary study of these driftingislands in the Southern Ocean. The scientificreviewers of my grant proposals, however, werenot convinced that icebergs could influence thepelagic ecosystem. Despite my enthusiasm for theresearch project, it failed to generate any significantinterest. Eventually, we succeeded in obtaininga small grant for exploratory research from theNational Science Foundation (NSF) for a modest,month-long research expeditionto the WeddellSea. Our team of sevenconsisted of BruceRobison (Monterey BayAquarium ResearchInstitute), who wouldstudy the communityof organisms undertheice surface; MariaVernet (University ofCalifornia, San Diego),who would study thephytoplankton; RonKaufmann (Universityof San Diego), whowould study the macrozooplanktonandmicronekton; Tim Shaw(University of South Carolina), who would studythe detrital material associated with the icebergs;John Helly (UCSD), who would study icebergstructure and assess iceberg populations fromsatellite imagery; and Robert Wilson (UCSD) andHenry Ruhl (MBARI), who would study seabirds.On November 27, 2005, our group departedfrom Punta Arenas, at the southern tip of Chile,aboard the RV L. M. Gould, a 76-meter researchship with an orange ice-strengthened hull. Onboard were laboratories and expansive deckspace to conduct over-the-side sampling. Theship was outfitted with a large multiple openingclosingtrawl system and a CTD, a device thatcould be lowered into the water to record salinityand temperature with depth, and a variety of watersamplers. A remotely operated underwater vehicle(ROV) was also on board for observing andsampling under the icebergs. Over the course ofa month, we were able to study two free-driftingicebergs in the Weddell Sea.The smaller iceberg was approximately twokilometers long and 41 meters high, with a submergeddepth greater than 300 meters. To documentchanges in flora and fauna associated withthe iceberg, we put the ship on a spiral track thatbegan at 20 meters out from the island of ice. Wethen began circling it, taking samples at ever-increasingdistances from it up to nine kilometers.The second iceberg was some 21 kilometerslong and 30 meters high, with a submerged depthof more than 230 meters. This iceberg was far toolarge for us to embarkon the spiral samplingused on the smallerone, so we put the shipon a course of paralleltransects along eachlength of the iceberg,out to a distance ofnine kilometers.As the icebergsslowly melt, they shediron-rich terrigenousmaterial, likely pickedup as wind-blowndust and from glaciallyground bedrock whenthe ice was forming.Nutrients from thisterrigenous materialincreased phytoplankton growth in the vicinity ofthe iceberg. Elevated concentrations of phytoplankton,being at the base of the pelagic foodchain, in turn nourished the zooplankton (krill)around the iceberg, which were significantly increasedin number compared to more peripheralwaters. The highest level of the food web, the seabirds—dominatedby Cape petrels and Antarcticfulmars—were also substantially higher in numberaround the iceberg, feeding on the abundant krill.Watching the real-time video from the ROV,secured to the ship with a 300-meter electromechanicaltether, we observed something quiteunexpected—extensive “fields” of attached algae(diatoms) growing on small fragments of volcanicrock embedded in the surface of the submergedice. These algae bloomed where down-wellinglight was sufficient for growth to depths as deepas 60 meters. We also saw swarms of krill andother zooplankton associated with crevasses andoutcrops on the undersurface of the ice.the explorers journal