Life among the frozen
The term “biological hotspot” is not one you expect to connect with Antarctica, the most remote and inhospitable continent on Earth. Antarctica remains the only continent to be surrounded by a single current, the Antarctic circumpolar current, which flows eastward and connects water from all of the other major oceans. Scientists have long studied this frigid landscape and marveled at the whales, seals and penguins that call this land and the surrounding ocean their home. Just below the surface of the ice, however, a hidden ecosystem teems with life. Microscopic, photosynthesizing “plants” called phytoplankton fill these nearshore waters, making the water below the ice look green or brown. These organisms form the base of the Antarctic food chain, and serve as food for the larger organisms up through food chain. How do these phytoplankton live below the ice where water temperature is below freezing? Sufficient light is able to pass through the ice to support photosynthesis, and the cycle of ice formation and melt produces natural turbulence that carries the essential nutrients that these phytoplankton need up to the surface. This upwelling phenomenon occurs most often in the shallow, nearshore waters, such as along the Western Antarctic Peninsula (WAP), or the “tail” of the Antarctic continent. The strong biological activity in the nearshore regions is in stark contrast to the majority of the Southern Ocean, which is largely devoid of phytoplankton. We’ll talk about why that is on the next On the Ocean! This has been On the Ocean, a program made possible by the Department of Oceanography and a production of KAMU-FM on the campus of Texas A&M University in College Station. For more information and links, please go to ocean.tamu.edu and click “On the Ocean”.
Script Author: Laramie Jensen
Krill larvae under the sea ice in Antarctica
Photosynthesis in Southern Ocean
The Southern Ocean surrounding Antarctica is a surprising biological hotspot with an extensive biodiversity. The nearshore waters along the “tail” of Antarctica, known as the Western Antarctic Peninsula (WAP), remain a popular study site due to the high productivity and concentration of large sea animals such as whales, seals, penguins, and other sea birds. However, much of the rest of the Southern Ocean remains devoid of microscopic photosynthetic organisms that sit at the base of the Antarctic food web. Why are there so few photosynthesizing phytoplankton, called phytoplankton, growing offshore in the Southern Ocean? We know there is plenty of light there in the summer, when the ice melts, and vigorous circulation brings a constant supply of macronutrients, such as nitrate and phosphate, to the surface ocean, allowing phytoplankton to grow. In 1990 we discovered that the so-called “high nutrient, low chlorophyll” regions such as the Southern Ocean have such low phytoplankton biomass due to growth limitation by insufficient iron supply. Iron is a crucial micronutrient required for photosynthesis, and the major supply route of iron to the ocean is terrestrial sources such as dust and continental sediments. Without adequate iron, no life will grow. This is especially important in the context of the global carbon cycle and global climate. During photosynthesis, phytoplankton use carbon dioxide (CO2) and light to make their energy. More photosynthesis means more draw down of CO2 from the atmosphere, resulting in massive storage of carbon within the ocean. This carbon can stay in the water column or sink to the ocean floor where it can remain sequestered in the sediments for millions of years. The Southern Ocean accounts for ~25% of this oceanic carbon uptake globally. This has been On the Ocean, a program made possible by the Department of Oceanography and a production of KAMU-FM on the campus of Texas A&M University in College Station. For more information and links, please go to ocean.tamu.edu and click “On the Ocean”.
Script Author: Laramie Jensen
CO2 is being drawn down in Antarctic ocean waters
The importance of Iron
The Fitzsimmons lab in the Department of Oceanography at Texas A&M studies the global iron cycle, and they visited the coast of the Western Antarctic Peninsula in the austral summer of 2016. As we discussed in last week’s show, the waters near the Antarctic continent are filled with iron coming from sediments near shore, yielding a lot of phytoplankton, or microscopic “plant” growth. However, as we moved away from land we expected to find more evidence of iron limitation, as we were moving away from the continental iron source, and thus the phytoplankton should have become iron limited. As expected, by the time we got ~200 km off the shelf, we found “blue” waters devoid of phytoplankton life. We also did experiments where we added iron to these waters to see whether more phytoplankton would grow compared to control experiments that received no extra iron. As expected, these organisms did in fact need iron! Finding evidence of iron limitation in this area is significant because the Southern Ocean accounts for so much of the carbon uptake from the atmosphere for long-term storage in the deep ocean. In light of today’s rising carbon dioxide levels in the atmosphere, studying areas known to be integral in carbon uptake and yet also limited in phytoplankton activity is absolutely crucial. While determining trace metal distribution from the coast to the open ocean was our main goal on this cruise, iron limitation poses a threat to all marine organisms as it targets the base of the marine food web: phytoplankton. Further research needs to be done in this area to elucidate the full effect of iron limitation on carbon cycling and climate in this region. This highlights the importance of maintaining funding for the well-established scientific research stations in these regions, such as the United States Palmer Research Station that helped this Texas A&M team gather their oceanographic data. This has been On the Ocean, a program made possible by the Department of Oceanography and a production of KAMU-FM on the campus of Texas A&M University in College Station. For more information and links, please go to ocean.tamu.edu and click “On the Ocean”.
Script Author: Laramie Jensen
Filters with obvious growth response to an iron dose after incubation of a few days
C’s are control with no iron added, F’s are iron added. The more color, the more growth was seen.
R/V Laurence McKinley Gould
The Research Vessel Laurence McKinley Gould, or LMG for short, is the sister ship to the larger R/V Nathaniel B. Palmer. Both are United States icebreakers, or at least “ice reinforced” in the case of the LMG. This vessel is well equipped for research expeditions in Antarctic waters, but also serves as a supply ship for US stations in Antarctica. Palmer Station sits on Anvers Island, one of the first points of land when traveling south from the tip of South America, across the Southern Ocean toward the West Antarctic Peninsula. If you can survive the infamous Drake Passage, known for some of the roughest seas in the world, you are rewarded with snowy mountains, icebergs and plenty of wildlife. However, life on a ship is not all gorgeous days and whale watching. Texas A&M scientists and students from the Department of Oceanography experienced this in austral summer 2016. In their makeshift lab they often worked on collecting and filtering water for experiments around the clock. The science does not wait for anyone and when they arrived at a new station, they had to be ready at all hours of the day to collect samples, often in very cold and wet conditions. In 2016 they encountered more sea ice coverage than is typical for the summer near Antarctica, which slowed the boat down considerably. This was, of course, a major factor for limiting historical scientific settlements in Antarctica. Ice coverage blocks ship passage, and cold weather makes even flying airplanes to Antarctica nearly impossible. At some Antarctic research stations, new food and supply shipments cease in April and don’t return until October. Even on a ship, supplies are carefully planned out for length of voyage and some emergency stores in case the ship gets stuck in the ice or has to make an unplanned detour. The ice coverage was good news for the Texas A&M scientists’ sleep schedules but bad for science, as they weren’t able to collect as many significant surface ocean samples as they needed because of ice cover. Part of polar research is being prepared for the unexpected and they managed to use their sample time wisely for their experiments investigating the potential for iron limitation of microscopic photosynthetic activity. We stand to gain much in our understanding of the global carbon cycle from these types of studies in critical regions such as the great Southern Ocean. This has been On the Ocean, a program made possible by the Department of Oceanography and a production of KAMU-FM on the campus of Texas A&M University in College Station. For more information and links, please go to ocean.tamu.edu and click “On the Ocean”.
Script Author: Laramie Jensen
Photos of Antarctica as taken from the R/V LMG