Sea carbon: Hypothesis is rich in iron

Oceanographers Jim Bishop and Todd Wood of Lawrence Berkeley National Laboratory, the Department of Energy investigated 'fate' of carbon particles derived from planktonic plankton in the southern seas, use data from carbon exploration buoys globally for more than a year. Their research shows that most of the carbon from large plankton clusters cannot descend deep into the sea floor.

This surprising finding goes against the Iron Hypothesis. Proponents of this hypothesis believe that by providing iron to plankton in rare iron areas, rich in other nutrients such as nitrogen, silicon, and phosphorus can slow or even reverse the phenomenon. global warming. The South Sea is one such area.

Bishop, a member of Bekerley Laboratory's Earth Science Unit and carbon professor, said: 'Adding iron to the sea has never been proven to be a good plan for carbon storage. It is important whether carbon falls deep into the seabed, and a large amount of carbon in the plankton seems to be sinking fast enough and not deep enough. '

The cause for this phenomenon is very complicated, mainly due to the seasonal behavior of plankton, the impact of Antarctic winter on the development of plants and animals, and the mixing of floors. surface water and deep water due to winter storms. Phytoplankton thrive in the spring is a sign that most zooplankton, necessary for carbon deposition, are starved in the winter.

Carbon exploration buoys involved in the study began in January 2002, part of the Southern Ocean Iron Experiment Program (SOFeX), a collaboration program between scientists at the Moss Marine Laboratory. Landing and Monterey Bay Marine Research Institute. SOFeX is done to test the Iron Hypothesis in the waters between New Zealand and Antarctica during the Antarctic summer. The Berkeley Lab carbon exploration buoys were originally intended to control carbon enrichment experiments for 60 days, but these devices continue to report through the Antarctic fall and winter the following year.

Bishop said: 'We have not been able to make these amazing observations if the carbon probe does not record data 24 hours a day, 7 days a week, at depths above 800 meters, in more than 1 years after the initial experiment has ended '.

He explained that 'predictions of biological vibrations - carbon circulation of marine life - mainly based on estimates and observations from research vessels, with the interval between two studies very far apart. Costs, not to mention the environment, make observations from research ships impossible. Fortunately, carbon exploration buoys take only about a day of research ship use. '

Iron hypothesis, science and prediction

In the 1980s, oceanographer John Martin of the Moss Landing Marine Laboratory, who died in 1993, hypothesized that adding iron to the rare but nutrient-rich marine areas (called low-nutrient-rich areas) Chlorophyl, or HNLC) can stimulate the growth of phytoplankton - an unproven scientific hypothesis.

Martin then suggested that iron enrichment in the sea could change climate. He told 1988: 'Give me half an iron tanker and I'll give you' ice age '.

When testing the Iron Hypothesis, SOFeX researchers found that the problem was not so simple, and the question was not whether the development of plankton could be stimulated, but is whether the carbon they retain is pushed down to deep water?

The SOFeX research vessel enriched iron in two sea areas, one at 55 degrees south and one at 66 degrees south. Carbon exploration equipment was deployed in both areas, a third carbon exploration device operated in an area outside the iron enrichment area. Scientists at the Berkeley Laboratory Todd Wood, Christopher Guay, and Phoebe Lam were members of the research team at the time, while Bishop controlled and contacted carbon probes from Berkeley through a connected computer. with satellite.

One question is whether rare silicate seawater at latitude 55 allows zooplankton, known as diatoms, to form silicon bones. If large diatoms cannot grow in this HNLC area, SOFeX researchers think that carbon deposition will not happen. Partly for this reason, most of the research vessel's efforts focused on latitude 66, where silicon is not a limiting factor.

Contrary to expectations, the sea area at latitude 55 appears large populations of plankton. This populations of carbon exploration, known as the North Patch, during the Antarctic summer, measured carbon particles, including zooplankton waste and other aggregates, sank below populations and carried follow 10 to 20% of carbon from the surface layer - at least less than 100 meters in depth. The initial results of the SOFeX experiment, published in Science in April 2004, seem to support the Iron Hypothesis.

The development of zooplankton and the mixing of water layers due to winter storms are the main factors that lead to carbon biological vibrations.Zooplankton range from microorganisms to jellyfish, including shrimp-like mollusks.(Photo: Lawrence Berkeley National Laboratory).

However, carbon exploration buoys did not stop after 60 days. Two carbon exploration buoys operated for more than 14 months, dive, record, and emerge to report data in the world's most stormy sea area, moving closer to South America before decommissioning. The carbon probe deployed at latitude 66 also operated for 18 months, using its first season to record data at a depth of 800 meters and emerge weekly to report. The collected data is still waiting for analysis.

Return to the South Sea

In 2007, Bishop and Lam (currently at Woods Hole Oceanographic Academy) published the results of measurements from the research ship equipment used in SOFeX, showing the optimistic picture of plankton populations. bringing the carbon deep into the sea is not as simple as the original thought. Deep down carbon depends in part on the size and mass of the element; and more importantly, there seems to be less particle matter down to the depth where biomass is the largest.

Bishop said: 'This article is criticized that based on limited observations from research ships. So Todd Wood and I turned to relentless observations of carbon exploration equipment. '

Carbon Explorers records in Antarctic summer colors and autumn colors 2002 as well as in the winter and spring 2003 (this time is much longer in the case of an exploratory buoy at latitude 66) not only confirms observations from the research ship in a very detailed way, but also opens up a complex picture of the life of the southern marine life.

The carbon probe at latitude 66 records data that has never been observed or reported. During the SOFeX experiment, this probe has recorded the transformation of plankton populations. The concentration of carbon particles decreases significantly when the shadow lasts continuously and the sea ice forms, then increases insignificantly as the light returns and the sea ice melts. Strong sediment deposition - the deposition of large amounts of carbon particles into deep seawater - has not been observed.

Data from operating buoys moving northward at latitude 55 give a surprising panorama. The detector was deployed in the carbon-enriched area, called 55A, showing the emergence of plankton populations as soon as iron was enriched, with sediment deposition at a depth of 100 meters. In particular, there is a similar population in this area the following spring - long after the iron has disappeared - with similar sedimentation to a depth of 100 meters. While the probe in the non-iron-rich area, known as 55C, did not detect any populations forming, it was surprisingly surprising: a 'rain' of carbon particles organic at a depth of 800 meters. The 55C carbon probe has found that sediment deposition in areas with no plankton populations is much larger than that of the 55A.

Explaining this contradictory result, the researchers considered some ideas. It is possible that strong currents have separated planktonic populations from sediment deposition; or there are larger organic carbon particles not recognized by the carbon buoy; or the difference in the mixing of surface water and deep water in winter storms brings isolated iron back to the surface. The first two hypotheses were excluded, and the third hypothesis, if true, also showed that stimulated plankton populations still led to a reduction in sediment deposition at kilometer depths.

The fourth hypothesis, considering light conditions promotes or restricts the development of the most compelling, extremely small plants. The latitude of 55 degrees south is far enough north to allow light to reach the water surface around it (although in winter the light is much reduced). But mixing between surface water and deep water can bring plankton too deep to be able to grow - no light, below depth when growing enough to meet the energy needs of the community. copper plant and animal. The latitude at which the buoy operates is particularly stormy, and the dynamic color of the mixed seawater can reach a depth of 400 or 500 meters.

To survive the winter, zooplankton must be located deep, too dark places for phytoplankton to survive. Storm and deep water mixing ensure the noise of zooplankton. Bishop said: 'Mixing the water layer is a car carrying food deep down. The question is whether this food truck is full or nothing. '

When mixing the aquifer below a certain level, phytoplankton due to no light and cannot grow, food trucks are empty and plankton are starved. When this mixture stops in the spring, phytoplankton begin to return, but there are not enough phytoplankton remaining to continue to develop and form populations, and thus the amount of carbon particles deposition is also less.

The continuous mixing of aquifers can cause zooplankton to be 'hungry', but if this process is interrupted, more phytoplankton grow in the winter to provide zooplankton in the season. east. The winter in the area of ​​the 55C probe, intermittent storms and the mixing of the aquifer occur below 400 meters. When phytoplankton begin to grow in the spring, zooplankton are ready to 'graze', with the increase in carbon deposits.

Bishop said these observations lead to an important lesson: 'Iron is not the only determinant of phytoplankton growth in HNLC areas. Light, the mixing of aquifers, and 'starved' zooplankton are equally important factors. "

Iron hypothesis is not wrong, but more impractical than initial thoughts. Achieving the desirable carbon sedimentation requires the right 'ironing' of iron and other nutrients to properly develop phytoplankton. Bishop said: 'You can grow a lot of Brussels prices, but children don't eat. The same thing happens in the case of plants and zooplankton. The zooplankton community determines carbon deposition '.

The new study presents another important lesson: two carbon probes that operate under similar conditions have little difference in sea conditions leading to completely separate biological reactions. Using carbon probes can provide the necessary data on marine biological vibrations at a much lower cost than using research vessels, and can answer previous questions? there is an answer - for example, the amount of human carbon that the sea can absorb, how long we can still rely on the sea to solve our 'excess product' - and most importantly, the reaction. of biological fluctuations in changing sea conditions.

Refer:
James KB Bishop and Todd J. Wood.Year-round observations of biomass and flux variability in the Southern Ocean.Global Biogeochemical Cycles, DOI: 10.1029 / 2008GB003206