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Ocean Research

2018:  FEB

June 2017 Issue

Future Larsen C Iceberg
Likely to Survive to 10 Years

On the Larsen C Ice Shelf in the Antarctic, a massive iceberg has begun to break off from the rest. The future iceberg will have a total surface area of nearly 6,000 sq. km.

The Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research has succeeded in modeling how Antarctic icebergs drift through the Southern Ocean and in identifying the physical factors behind their movement and their melting.

How far the future Larsen C iceberg will drift depends on whether it remains intact after calving or quickly breaks up into smaller pieces. Further, the iceberg may run aground for a time. Given its massive weight, the Larsen C iceberg will likely survive for eight to 10 years; according to the computer model, that’s the maximum life expectancy for even the largest iceberg drifts.

The potential routes produced by the model were compared with actual data on large icebergs from the Antarctic Iceberg Tracking Database and with GPS data from icebergs in the Weddell Sea.

New Insight into Behavior of
Volcanoes, Earthquakes

Beneath the ocean, massive tectonic plates undergo subduction, which forms volcanic arcs that can be home to explosive volcanic eruptions and mega earthquakes.

Researchers led by the Woods Hole Oceanographic Institution (WHOI) have discovered a previously unknown process involving the melting of intensely mixed metamorphic rocks—mélange rocks—that form through high stress during subduction at the slab-mantle boundary.

The study shows that the prevailing fluid/sediment melt model cannot be correct. The research shows—for the first time—that mélange melting is the main driver of how the slab and mantle interact.

Subduction zones are the main areas where water and carbon dioxide contained within old seafloor are recycled back into the deep Earth, playing critical roles in the control of long-term climate and the evolution of the planet’s heat budget.

These complex processes can generate catastrophic earthquakes and deadly tsunamis.

The study’s findings call for a re-evaluation of previously published data and a revision of concepts relating to subduction zone processes.

Parrotfish React More to
Competition than to Predators

According to new research by UC Santa Barbara marine scientists, Chlorurus spilurus, known as the bullethead or daisy parrotfish, barely reacts to the presence of predators.

Working in the waters off Mo’orea and the Palmyra Atoll, researchers observed almost constant competitive interactions between predators and bullethead parrotfish—the Pacific Ocean’s most abundant parrotfish species—and other herbivorous fishes. They were constantly chasing each other, and this affected their feeding rates.

Predators such as sharks, snappers and groupers frequently swam past the parrotfish without eliciting any reaction. The research indicates that competition among grazers is the real force in structuring both the space use patterns and the feeding patterns of these parrotfish.

Demo Shows How Wind
Can Cause Rogue Waves

A team of scientists from Australia, Belgium, Italy and the U.K. have demonstrated how ocean winds can generate spontaneous rogue waves, the first step to predicting the potentially dangerous phenomena.

These waves might cause severe damage to ships and structures such as oil and gas platforms. The ability to forecast them would be hugely beneficial, but little is currently understood about what generates them.

Researchers from The University of Melbourne (Australia), The Swinburne University of Technology (Australia), The University of Leuven (Belgium) and The University of East Anglia (U.K.) used a special circular wave tank at The University of Turin (Italy) to study the statistical properties of wind-generated waves and the likelihood of rogue wave development.

Unlike previous experiments on rogue waves generated in conventional longitudinal tanks, the wave field they created by blowing wind in the annular wave flume can be thought of as infinitely long. Researchers started with still water in the tank, before turning on fans that replicated a steady wind, similar to conditions that might be seen on the ocean. Wind was blown over the surface for 2 hours, and the surface elevation of the water measured throughout.

As wind starts blowing, an erratic wave field is generated. Rogue waves appear to develop naturally during the growth of the waves, and were detected just before the wave height reaches a stationary condition. The measurements let the research team estimate the probability of finding high, steep waves, showing that this is higher than expected, thus providing crucial information about the mathematical likelihood of these waves occurring.

Phytoplankton Research at Sea
Using New Instruments

A swath of new instruments were debuted during a 25-day expedition across the Pacific exploring a wide variety of oceanic ecosystems.

The focus of chief scientist Dr. Ivona Cetinic, USRA/NASA, and her team was to explore ocean particles, specifically the phytoplankton at the base of the food web. The research will allow the team to learn how plankton and other living things in the ocean contribute to global climate. The team will use the data to ground-truth satellite observation of ocean color (influenced by phytoplankton) and better understand the processes each planktonic community carries out with regard to the carbon and nitrogen cycles. Phytoplankton produce much of the world’s oxygen and remove carbon dioxide from the atmosphere, thereby helping to control climate. The research was conducted on a cruise on Schmidt Ocean Institute’s RV Falkor. It allowed, for the first time, the following of particles all the way from space with NASA satellites through the surface of the ocean to ocean depths. The oceans are changing, and having accurate ocean color satellites will allow scientists to monitor change over a long period of time.

2018:  FEB

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