Page 10. MAINE COASTAL NEWS March 2017 Waterfront News News from Woods Hole Oceanographic Intitute


doesn’t freeze, however, so the unfrozen seawater around the ice becomes saltier. The salt makes the water denser, causing it to sink to the ocean bottom. “These waters are thought to be the


(Illustration by Eric Taylor, Woods Hole Oceanographic Institution)


Antarctic Bottom Waters Freshening at Unexpected Rate


In the cold depths along the sea fl oor,


Antarctic Bottom Waters are part of a global circulatory system, supplying oxygen-, car- bon- and nutrient-rich waters to the world’s oceans. Over the last decade, scientists have been monitoring changes in these waters. But a new study from the Woods Hole Oceanographic Institution (WHOI) suggests these changes are themselves shift- ing in unexpected ways, with potentially signifi cant consequences for the ocean and climate. In a paper published January 25 in Science Advances, a team led by WHOI oceanographers Viviane Menezes and Ali- son Macdonald report that Antarctic Bottom Water (AABW) has freshened at a surprising rate between 2007 and 2016—a shift that could alter ocean circulation and ultimately contribute to rising sea levels. “If you change the circulation, you


change everything in the ocean,” said Menezes, a WHOI postdoctoral investigator and the study’s lead author. Ocean circula- tion drives the movement of warm and cold


waters around the world, so it is essential to storing and regulating heat and plays a key role in Earth’s temperature and climate. “But we don’t have the whole story yet. We have some new pieces, but we don’t have the entire puzzle.” The puzzle itself isn’t new: past studies


suggest that AABW has been undergoing signifi cant changes for decades. Since the 1990s, an international program of repeat surveys has periodically sampled certain ocean basins around the world to track the circulation and conditions at these spots over time. Along one string of sites, or “stations,” that stretches from Antarctica to the southern Indian Ocean, researchers have tracked the conditions of AABW—a layer of profound- ly cold water less than 0°C (it stays liquid because of its salt content, or salinity) that moves through the abyssal ocean, mixing with warmer waters as it circulates around the globe in the Southern Ocean and north- ward into all three of the major ocean basins. The AABW forms along the Antarctic


ice shelves, where strong winds cool open areas of water, called polynyas, until some of the water freezes. The salt in the water


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underpinning of the large-scale global ocean circulation,” said Macdonald, a WHOI senior research specialist and the study’s co-author. “Antarctic Bottom Water gets its characteristics from the atmosphere—for example, dissolved carbon and oxygen— and sends them deep into the ocean. Then, as the water moves around the globe, it mixes with the water around it and they start to share each other’s properties. It’s like taking a deep breath and letting it go really slowly, over decades or even centuries.” As a result, the frigid fl ow plays a crit-


ical role in regulating circulation, tempera- ture, and availability of oxygen and nutrients throughout the world’s oceans, and serves as both a barometer for climate change and a factor that can contribute to that change. A past study using the repeat survey


data found that AABW had warmed and freshened (grown less saline) between 1994 and 2007. When Macdonald and Menezes revisited the line of stations, they measured how AABW has changed in the years since. During the austral summer of 2016,


they joined the crew of the research ship R/V Revelle and cruised north from Antarctica to Australia, braving frequent storms to collect samples every 30 nautical miles. In a ship- board lab, they analyzed the samples using data from conductivity-temperature-depth (CTD) sensors, which measure the water’s salinity, temperature and other properties, with support from study co-author Court- ney Schatzman of the Scripps Institution of Oceanography, who processed the raw data. The team found that the previously de-


tected warming trend has continued, though at a somewhat slower pace. The biggest surprise, however, was its lack of saltiness: AABW in this region has grown fresher four times faster in the past decade than it did between 1994 and 2007. “I thought, ‘Oh wow!’ when I saw the


change in salinity,” said Menezes. “You collect the data and sometimes you spend 2 to 3 years to fi nd something, but this time we knew what we had within hours, and we knew it was very unexpected.” Such a shift, were it global, could sig-


nifi cantly disrupt ocean circulation and sea levels.


“The fresher and warmer the water is,


the less dense it will be, and the more it will expand and take up more space – and that leads to rising sea levels,” Macdonald said. “If these waters no longer sink, it could have far reaching aff ects for global ocean circulation patterns.” Questions remain around the cause


of the shift. Menezes and Macdonald hy- pothesize that the freshening could be due to a recent landscape-changing event. In 2010, an iceberg about the size of Rhode


Island collided with Antarctica’s Mertz Glacier Tongue, carving out a more-than- 1,000-square-mile piece and reshaping the icescape of the George V/Adelie Land Coast, where the AABW observed in this study is thought to form. The subsequent melting dramatically freshened the waters there, which may have in turn freshened the AABW as well. Future studies could use chemical analysis to trace the waters back to the site of the collision and calving and confi rm the hypothesis. This research was funded by the Na- tional Science Foundation and the National Oceanic and Atmospheric Administration.


Study Provides Measurement of Nitro- gen Removal by Local Shellfi sh Towns along Cape Cod and the Islands


are looking to shellfi sh not only as tasty culinary treats, but also for help cleaning up waters degraded by excess nitrogen in the region. While nitrogen is essential for all plants


and animals, too much nitrogen in ponds and waterways—often caused by fertilizer run- off and septic tanks—can fuel algae growth, and cause low oxygen levels. Shellfi sh, such as oysters and quahogs,


are effi cient fi lter feeders that help remove excess nitrogen by incorporating it into their shells and tissue as they grow. But exactly how much nitrogen they’re capable of re- moving in local waterways and how those amounts might vary by location or season has been unknown due to lack of region-spe- cifi c data. A new study by Woods Hole Sea Grant,


Cape Cod Cooperative Extension, and the Mashpee Department of Natural Resources provides the fi rst comprehensive measure- ment of nitrogen removed by shellfi sh har- vested from waters off Cape Cod. “We did this project specifi cally as a


service to local municipalities to get them accurate data to utilize, if they’re going to go with the approach of seeding and grow- ing shellfi sh as part of their water quality management plans,” says Woods Hole Sea Grant Extension Agent Joshua Reitsma, lead author of the paper published online Jan. 10, 2017, in the journal Marine Pollution Bulletin. The NOAA-funded Woods Hole Sea Grant program, based at the Woods Hole Oceanographic Institution, supports research, education, and extension projects that encourage environmental stewardship, long-term economic development, and responsible use of the nation’s coastal and ocean resources. During fi eldwork in 2012, the research


team gathered samples of both wild and farmed oysters (Crassostrea virginica) and quahogs (Mercenaria mercenaria) from various water bodies in the Cape Cod region (see accompanying map for sample sites). The samples were then analyzed for nitro-


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her oversized fenders Phil had brought from the store…But there she was!! All alone! Still tied to the dock. Dock was alone as well. A small island in the middle of wreck- age and debris. Lines were still holding. One of the few docks left. She sat there as if the “God of Small Craft” were watching over her…All alone. Staff , all hands on board, extra crews,


eff ectively sorted the situation out. By next morning semblance of a show had “re-tak- en” place. Essentially though, to all intents,


the show was over. Next few days there were some “ho-hum bumper-kickers” but the buyers had gone home. Many proba- bly catching the last plane out. We rocked and we rolled as the memory waves from the storm slid by, helped a few stray souls aboard as they in turn held tight to any solid handhold or me and I wrote off the show to another “boatbuilding episode”. Several years before I did the Lauderdale show again and the show had returned to Bahia Mar where space was limited and we signed on a year in advance.


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